Continuous reuse of polyamide 12 in Powder Bed Fusion

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Antończak This is a preprint; it has not been peer reviewed by a journal. https://doi.org/ 10.21203/rs.3.rs-6672836/v1 This work is licensed under a CC BY 4.0 License Status: Published Journal Publication published 26 Jul, 2025 Read the published version in Scientific Reports → Version 1 posted 12 You are reading this latest preprint version Abstract The thermal degradation of polymers in powder bed fusion (PBF, additive manufacturing) is one of the major issues preventing wider adoption of this technology at the production scale. Although standard PBF allows for elastic production of complex parts in a single-step manufacturing process, it is materially inefficient – only approximately 10% of the material is used, with the majority of semicrystalline polyamide 12 (PA12) remaining in the form of free-flowing powder. Because the rest of the material remains below the melting point for a long time, it cannot be directly reused in subsequent processes. In this work, we present a novel way to process PA12 at room temperature without exposure to a thermal agent. Dual beam laser sintering (DBLS) uses a double laser system that effectively compensates for the temperature in the melting zone and prevents material shrinkage. To demonstrate the effectiveness of the DBLS method, the material was kept in a closed loop. Specimens from each iteration of the process ( n = 4) were analyzed. No significant changes were observed in the chemical properties (molecular weight and melt viscosity, assessed via gel permeation chromatography (GPC) and melt flow index (MFI) analysis) or technological properties (flowability) of the powder samples or in the mechanical properties of the built specimens compared with the initial values. Physical sciences/Engineering/Electrical and electronic engineering Physical sciences/Engineering/Mechanical engineering Physical sciences/Engineering Physical sciences/Materials science additive manufacturing laser-based powder bed fusion of polymers dual beam laser sintering polyamide 12 powder reuse polymer degradation Figures Figure 1 Figure 2 Figure 3 Figure 4 Figure 5 Figure 6 Figure 7 Figure 8 1 Introduction Laser beam powder bed fusion of polymers (PBF-LB/P) is an additive manufacturing process that enables flexible, layer-by-layer fabrication of parts with complex geometries. A sequence of steps, including powder application, heating, melting, and lowering the build platform, is repeated to transform a digital model into a functional part. Parts are most commonly made from polyamide 12 (PA12), which has a dominant market share. Achieving bonding between layers requires the use of additional heat energy, which is provided by a laser. The material is applied via a roller or a recoater each time after the build platform is lowered. Reducing the temperature gradient between the scanned area and the rest of the powder bed eliminates curling of the melted cross-sections; for this purpose, an additional heating system is used to keep the material below the melting point. Unfortunately, maintaining the material at elevated temperatures for some time, usually in the order of hours, results in degradation of the unmelted material. Moreover, only 10–25% of the material is used to build parts [ 1 , 2 ]. The remaining, unmelted material supports the parts during fabrication but becomes waste at the end of the process. Continuous processing (without the addition of virgin material) is possible in PBF-LB/P [ 3 – 5 ], but the degree of material degradation due to chemical (dominant role) and physical (secondary role) mechanisms increases with each subsequent cycle [ 6 ]. Chemical degradation mechanisms such as thermal oxidation, solidstate postcondensation, peak merging due to the Brill transition, and hydrolysis involve molecular chain scission, molecular cross-linking, chain branching, chain lengthening, and thermal property changes [ 1 , 7 – 9 ]. Physical degradation mechanisms include relaxation of orientation, agglomeration, postcrystallization effects, concentration changes, particle aggregation, spherulite growth/structure, increased crystallization degree, and increased lamellar thickness [ 10 , 11 ]. These changes in material properties affect various aspects of PBF-LB, resulting in increased porosity, reduced mechanical properties, dimensional instability, and surface roughness. Many material-driven approaches can be applied to enable reuse of this material in the PBF-LB/P process, including mixing postprocess powder with virgin powder [ 2 ], material doping [ 12 ], powder hydration [ 13 ], and recycling [ 14 ], but such methods eliminate only the effect and not the cause. Additionally, upcycling of the material [ 15 – 18 ] is only a partial solution. The only way to improve the material efficiency of the PBF-LB/P process is to limit or eliminate the aging mechanisms caused by prolonged thermal exposure. Maintaining the build chamber temperature well below the processing window temperature requires compensation measures, either through the use of support structures or an increase in energy density in the scanning zone. For PA12, support structures have been used to build chamber temperatures of 150°C [ 19 ], 130°C [ 20 ], 80°C [ 21 ] and room temperature [ 22 – 24 ], but each time, the resulting properties were well below typical values. In turn, Schlicht et al . [ 25 ] reported that a stable process at 75°C could be achieved by increasing the energy density using a fractal exposure sequence derived from the Peano curve. Based on a similar assumption, in [ 26 ], we proved that it is possible to process PA12 at room temperature by using dual beam laser sintering (DBLS) [ 27 ]. Additionally, we demonstrated our method on poly (lactic acid) and poly (lactic acid)/hydroxyapatite microspheres, focusing on the correlation of process parameters with the mechanical properties and internal structure of the manufactured parts [ 28 , 29 ]. In these studies, the DBLS method was used to reduce degradation in the context of widely used biomedical engineering materials. Moreover, for each material used, the optimal parameters (i.e., those resulting in mechanical and chemical properties as good as/better than those of standard selective laser sintering (SLS)) were determined. Heating the polymer using a second laser instead of using heaters that permanently maintain the polymer at an elevated process temperature has several significant benefits. A heating beam has a much larger diameter (experimentally assumed value of 8 mm) than a sintering beam (usually on the order of hundreds of µm). The heating beam is positioned coaxially with the sintering beam, regardless of the scanning direction on the surface of a given layer and always reaches every point to be sintered first. Owing to the very high speed of laser heating (on the order of 10 6 K/s or more), the temperature required for sintering with the main sintering beam (whose small diameter ensures the necessary working resolution) can be reached in given point. During scanning of a given layer, a small volume of powder is heated, proportional to the diameter of the heating beam and the depth of heat penetration (thermal diffusion path). This, in turn, minimizes the exposure of the material in the working chamber in terms of both time and volume, which directly minimizes or eliminates postprocess powder degradation (uncontrolled changes in molecular weight). The elimination of heater units in the DBLS method provides a number of potential advantages compared with standard PBF-LB/P: simplified material management, reduced process time due to eliminating the warm-up and cool-down phases, stable powder feeding conditions, and online process control in the melting zone. This work is based on an original DBLS approach developed to limit the thermal degradation of the polymers described in detail in our previous work on the sintering of polylactide [ 27 ] and the most popular PBF-LB/P material, PA12 [ 26 ]. To demonstrate the advantages of this method over other methods, the degree of material degradation and the mechanical properties of samples manufactured at room temperature in a continuous reuse scheme were verified for the first time. 2 Materials and methods 2.1 Dual-beam laser sintering device DBLS is an original modification of the standard PBF-LB/P process, in which the polymer preheating step in the process chamber (typically based on the use of heaters) is replaced by irradiation with a second laser beam with a suitably larger diameter to heat only a small area (volume) of the working field in the vicinity of the sintering point. The DBLS method has been described in detail in our previous works [ 26 , 27 ]. Rapid heating of the material with a second laser beam only during sintering and in the vicinity of the sintering point minimizes the exposure (in terms of time and space) of the polymer to elevated temperature. This, in turn, limits the thermal degradation of the material. Due to the developmental nature of the setup used in the DBLS experiment, two identical, independently controlled CO 2 lasers (Synrad, Inc. USA, series 48 − 2 with a wavelength of 10.6 µm and output power of up to 25 W) were used. The main sintering beam was focused with a 2.5” focal length lens, resulting in a diameter of 210 µm on the material surface. The heating beam, which was enlarged with a BEX-10.6-2Z1i beam expander (Ronar-Smith®, Wavelength Opto-Electronic Ltd., Singapore), achieved a diameter of 8 mm in the working field and was aligned coaxially with the sintering beam. Both beams simultaneously scanned the material surface at a given speed (V). This change in polymer heating approach requires a new way of defining process parameters. In the DBLS method, two main parameters are used to control the process: process temperature (T P ) and sintering laser power (P S ). The heating laser power (P H ) is set automatically (via a control algorithm) to achieve the set T P , which is controlled layer by layer by an infrared sensor (CTlaser P7, Optris GmbH, Germany). 2.2 Methodology and study overview This study investigated the degradation of PA12 powder and the mechanical properties of specimens in a continuous reuse scheme based on DBLS. Virgin PA12 powder (PA2201, EOS, Krailling, Germany) was initially loaded into the feed bin. After each iteration of the build process, the used powder (P n ) was weighed, sieved, homogenized, and characterized. The postprocess material was then reloaded into the feed bin, and the build process, along with the subsequent steps (weighing, sieving, homogenization), was repeated. A total of four iterations of build processes and subsequent tasks were completed (Table 1 and Figure. 1), where virgin powder was loaded in the first iteration (denoted as I1), while in the following iterations (I2-I4), used powder (P1-P3) from the previous iteration was loaded. Table 1 Designations and symbols used in this work. Symbol Meaning Additional information I iteration set of build processes and routines; loading is performed using powder with the same thermal history N current iteration number values range from 1 to 4, where virgin powder is loaded in I1 I n iteration n iteration in which all processes are loaded with powder used n -1 times without regeneration P n postprocess powder resulting after n repeated process cycles powder used n times; e.g. I3 is loaded with P2, and P0 is virgin powder S n dog-bone specimen in the n -th iteration specimen built with powder P( n -1) The build process was consistent for each manufacturing cycle, in which two dog-bone shaped specimens were oriented horizontally (XYZ according to ISO 17295:2023) in the center position, 6 mm apart. To ensure 19% nesting density, additional models were added between, above and below the specimens (Figure. 2). The geometry and dimensions of the specimens were determined in accordance with ISO 527-2-5B. The experiment was carried under the optimal process parameters determined in previous work (see Table 3 in [ 26 ]), which produced samples with the maximum ultimate tensile strength and elongation at break while maintaining the stability of the DBLS process. The following process parameters were used: sintering power P S = 3.0 W, process temperature T P = 180°C, surface scanning speed V = 710 mm/s and process resolution h = 25.4 µm (distance between successive laser pulses in the X and Y planes). Bidirectional scanning was performed along the X-axis, covering only the fill and excluding the contour. The remaining elements of the DBLS system, including the powder dosing method, were implemented in typical layer-by-layer fashion, as in the standard PBF-LB/P approach. The DBLS process chamber was 55 mm in diameter, and the mass of input powder for each build process was approximately 3 g. To account for nesting density, random build process issues, caking and the characteristics of the used powder, a total of approximately 190 g of virgin PA12 was processed in I1. This iteration comprised 50 build processes (yielding 100 specimens) and 152.5 g of P1. The sieved powder was subjected to postprocessing, and the remainder was used as feedstock for I2 (Table 2 ). The scheme was repeated for 2 additional iterations until all powder was used. After each iteration, 5 specimens were selected at random and used for mechanical tests. Additionally, approximately 30 g of used powder from iterations I1-I3 (after postprocessing) was used for powder characterization. In the final iteration (I4), only three build processes were completed, producing six specimens, but the used powder (P4) was not characterized due to the limited amount remaining (approximately 1 g). Table 2 Material weights and number of processes. Iteration Number of processes in iteration [a.u.] Postprocess powder amount [g] I1 50 152.5 I2 38 82.5 I3 17 35.3 I4 3 - Table 3 Selected particle size distributions and flowability parameters of the PA12 virgin and postprocessed powders. Powder First avalanche [°] Cumulative hysteresis of cohesion index [a.u.] D10 [µm] D50 [µm] D90 [µm] < 10 µm [%] Filler-to-powder index [%] P0 (ref.) 34.36 ± 1.98 10.85 36.00 59.36 85.78 1.03 3.85 P1 37.00 ± 2.02 13.55 38.38 61.43 89.27 1.21 2.44 P2 40.67 ± 1.85 23.78 38.82 61.18 88.36 0.99 1.84 P3 44.98 ± 1.28 9.79 39.35 62.70 90.80 1.47 0.57 2.3 Particle size distribution The particle size distribution (PSD) was determined using a laser diffraction spectroscope Sympatec, HELOS/BR 4470 C (Clausthal-Zellerfeld, Germany) with the dry dispersion method using a RODOS/T4, R4 system (Clausthal-Zellerfeld, Germany). Measurements were carried out in accordance with ISO 13220-1. The powder sample was fed by a vibration feeder. The gap was set at 3.0 mm with maximum vibration (feed rate 100%). Powder was then dispersed at a pressure of 2 bar. 2.4 Scanning electron microscopy Scanning electron microscopy (SEM) was employed to determine the morphology of the powder particles. Before observation, the powder samples were coated with gold via plasma sputtering with a Q150R ES coater (Quorum, Laughton, United Kingdom). The gold-coated samples were observed under vacuum using an EVO MA25 microscope (Zeiss, Oberkochen, Germany) with a backscattered electron detector with an acceleration voltage of 20.0 kV and a current of 1.5 nA. Additionally, energy dispersive spectroscopy (EDS) was used to identify the filler type. 2.5 Microscope image processing The filler was identified and quantified via binarization of SEM images. SEM images of PA12 powder samples were thoroughly visually investigated; the filler was identified and quantified by examining the upper range of grayscale values (white or near-white pixels), while the powder particles were visible in the middle range of grayscale values (dark gray or light gray). Binarization was performed with OpenCV (version 4.11.0.86) for Python. Each SEM image corresponded to an area of 1.5 mm × 1.2 mm. The images were classified into two distinct categories: images with binarized filler and images with binarized powder particles. The pixel coverage of the target feature was calculated for both types of binarized images to determine the area coverage of filler relative to that of powder particles; an example process is presented in Fig. 3 . 2.6 Revolution powder analysis Dynamic flowability was measured using revolution powder analysis, in which a rotating drum is coupled with image processing to evaluate powder subjected to varying conditions. Measurement was carried out in two modes: first avalanche and speed hysteresis. The first avalanche angle was measured by image analysis at a low drum speed (0.5 rpm), while in hysteresis mode, the cohesion index was measured at variable speeds while either increasing or decreasing the rotation speed (1, 2, 5, 10, 15, 20, 30, 40, 50, and 60 rpm). For both measurements, the drum was filled with 55 ml of powder sample. At each speed, 25 images were taken at an interval of 1.0 s. The average position of the powder/air interface and fluctuations around this value were tracked from the recorded images using GranuDrum software 9.23.8.29 (GranuTools, Awans, Belgium). The postprocess powder (P n ) from iterations I1-I3 was tested under the same humidity and temperature conditions (40% relative humidity and 20°C). 2.7 Melt flow index Melt flow index (MFI) was determined using an Mflow capillary rheometer (Zwick Roell, Ulm, Germany). Before testing, each powder sample weighing 4.5 g was dried in a 50/1.X2.IC.A weighing dryer (Radwag, Radom, Poland). The drying profile of the PA12 powders was determined according to VDI 3405. The sample was heated to 105°C and maintained at this temperature for 10 min; then, the temperature was increased from 105°C to 140°C for 5 min; in the last step, the sample was kept at 140°C for an additional 2 min. The MFI test was performed in volumetric mode using method B described in ISO 1133 to determine the melt volume ratio (MVR). Before testing, each sample was preheated in the cylinder for 300 s at 235°C. The test temperature was set at 235°C. A load of 2.16 kg was applied both during preheating and during the measurement cycle. Each powder sample was assessed three times, with five 3 mm measuring sections for each test. 2.8 Gel permeation chromatography The average molecular weight and molecular weight distribution (MWD) were determined by gel permeation chromatography (GPC) using a Max VE2001 chromatograph (Viscotek Corp, Malvern, United Kingdom) equipped with a degasser, an eluent flow and pressure monitoring system, a thermostat with two Shodex columns (HFIP 803 E211533 and HFIP 805 E211525) connected in series and an RI detector (Viscotek VE3580). The analysis was carried out in accordance with ISO 16014 and ASTM D 5296-11. The PA12 powder samples were dissolved in hexafluoro-isopropanol (HFIP + 0.02 M sodium trifluoroacetate) for 24 h at room temperature. After each sample was dissolved, the 10 mg/ml solution was filtered through a 0.20 µm PTFE filter and analyzed using a chromatographic system with an eluent flow rate of 1 ml/min and an injection volume of 100 µl. Two injections were performed for each solution. The chromatographic system was calibrated using certified monodisperse poly (methyl methacrylate) (PMMA) standards with molecular weights in the range of 860–1,020,000. The measured molecular weights of the tested samples were expressed as the relative molecular weights (relative to PMMA). The data was processed using OmniSEC 5.0 software. This approach enabled the determination of molecular weights and their distribution in a sample. The evaluated parameters included the number-average molecular weight M n , weight-average molecular weight M w , “zeto”-average molecular weight M z , molecular weight corresponding to the peak value M p and polydispersity index M w /M n . 2.9 Tensile testing The static tensile test was carried out on a Multitest-I testing machine (Mecmesin Ltd., West Sussex, United Kingdom). A 1 kN load cell (Mecmesin Ltd., West Sussex, United Kingdom) was used with vise grips with a maximum load of 10 kN. During the tests, the specimens were preloaded with 2 N, and measurements were collected at a speed of 10 mm/min. The dependence of the tensile force on the increase in displacement between the grips was recorded. The criterion for the end of the test was the first drop in registered force of at least 80%, which corresponded to the fracture of the specimen. The recorded data were used to determine the ultimate tensile strength (UTS), Young's modulus (E) and relative elongation at break (εb). For each series, five dog-bone shaped specimens were subjected to the tensile test. 2.10 Statistical analysis Significant differences were determined via one-way analysis of variance (one-way ANOVA) with Tukey's post hoc test (OriginPro, OriginLab Corporation, Northampton, MA, USA). The means were then classified into groups (labeled with uppercase letters – A, B), and the results within a group were considered not to be significantly different at ρ < 0.05. The results of the tensile tests are presented as the mean values with standard deviations. 3 Results and discussion 3.1 Powder characterization: powder particle morphology and flowability The powder particle morphology was determined using SEM (Figure. 4a-d). Regardless of the sample, the powder particles exhibited a globular shape, which is attributable to the precipitation-based production method [ 30 ]. Furthermore, smaller particles, predominantly irregular in shape, were discernible at higher magnification (Figure. 4e). Due to the greater brightness of the filler particles, additional EDS measurements were conducted. The resulting EDS spectral data are presented in Figure. 4f. In addition to the common peaks observed for all reference points (Figure. 4e), namely, at 0.277 keV (carbon), 0.525 keV (oxygen), and 2.120 keV (gold from the conductive coating), the measurement of filler particles (cf. points 1 and 3 in Figure. 4e) also revealed a peak at 1.739 keV, which may be correlated with silica. Silica compounds, most often SiO 2 , are utilized as fillers to enhance the flowability of polymer powders [ 31 , 32 ]. The presence of SiO 2 in PA12 powders was also reported by Leung et al . [ 33 ]. The quantity of large aggregates formed on the surface of the particles decreased; consequently, image processing was utilized. The binarization results are presented as powder-to-filler area index values in Table 3 . Image analysis confirmed that there was a demonstrable decrease in filler material in subsequent iterations of the powder application process. This phenomenon can be attributed to the loss of filler particles resulting from repeated application in the powder bed, sieving, and mixing between iterations. Although no significant changes in morphology were observed, the continuous reuse of PA12 influenced the quasistatic and dynamic flowability. The quasistatic flowability is represented by the first avalanche angle, which increased after the first and second iterations. The reduced flowability may be due to mechanical wear of the SiO 2 filler, especially as PA2200/PA2201 are low-additive powders [ 32 ]. Similar observations were made in the case of dynamic flowability. The best characteristics were presented by the virgin powder, especially when comparing the hysteresis of the curves. The cumulative hysteresis of the cohesion index of the postprocess samples increased compared with that of the reference sample (Table 3 ). This effect can be explained by the fact that this powder is prone to agglomeration, phase segregation or static charge accumulation. Nevertheless, all the samples tested had a cohesion index below 25 (Figure. 6), which is considered an acceptable level for achieving successful powder layer deposition [ 34 ]. The observed minor differences should not disrupt the PBF process. Notably, in a typical use cycle, print-ready powder used to fabricate parts would need to be supplemented (due to the amount of consumed powder), which could compensate for the reduction in flowability. If this approach is not sufficient, the addition of a flow agent may be needed. 3.2 Powder characterization: thermal behavior The melt viscosity results, represented by the MVR index, are presented in Table 4 . All samples, both virgin and postprocess, had a similar viscosity. The observed differences between mean values are within the error of the measurement method used [ 35 ]. Typically, after PBF with a consistently high chamber temperature, an increase in viscosity is expected [ 36 ]. Moreover, Gruber et al. [ 26 ] reported that the same polymer (PA2201) processed with the standard PBF-LB/P approach had a mean MVR of 10.5 cm 3 /10 min. The melt viscosity measurements suggest that no thermal degradation occurs during subsequent reuse of PA12 powder via the DBLS process. Table 4 MVR index of virgin and postprocess PA12 powder samples. Powder P0 (ref.) P1 P2 P3 MVR [cm 3 /10 min] 29.64 ± 2.10 32.09 ± 2.66 31.51 ± 1.56 31.04 ± 4.13 3.3 Powder characterization: molecular weight distribution The differential molecular weight distribution (MWD) curves for the analyzed powders are shown in Figure. 7. The M n , M w , M z , M p and M w /M n values are summarized in Table 5 . Table 5 Average values of M n , M w , M z , M p and Mw/Mn expressed with respect to PMMA for virgin and postprocess PA12 powder samples. Powder M n M w M z M p M w /M n Name Meas'. [Da] [%]* [Da] [%]* [Da] [%]* [Da] [%]* [-] [%]* P0 (ref.) I 8248 - 18680 - 35740 - 14828 - 2.265 - II 8248 18703 38148 14407 2.268 P1 I 8200 -1.1 18660 -1.1 37423 -0.9 14490 -1.5 2.275 -0.1 II 8119 18298 35791 14293 2.254 P2 I 7859 -4.8 18338 -1.8 36642 -1.9 14830 0.9 2.333 3.1 II 7840 18365 35841 14658 2.342 P3 I 7875 -0.4 18172 -2.4 36120 -3.2 14574 -1.2 2.307 -1.9 II 8556 18324 35371 14323 2.142 * – relative % change in the average value of two measurements relative to the average value of the reference powder The maximum changes in corresponding molecular weights do not exceed one percent. This result is one to two orders of magnitude better than that of the standard PBF-LB/P method, for which an increase from over 50% for M n to almost 100% for M w and M z was noted [ 26 ]. The above analysis confirms that the DBLS method produces negligible changes in postprocess powder. 3.4 DBLS sample characterization: mechanical behavior The tensile testing results for samples produced by DBLS from virgin P0 and postprocess (P1-P3) powders are presented in Table 6 and Figure. 8. The results revealed no statistically significant differences in the mechanical behavior of the samples that were manufactured from powder subjected to subsequent processing. The observed differences between iterations may be caused by variations in flowability and hardware limitations of the current DBLS setup. The most important factor is the scanning speed, which does not compensate for the thermal dissipation of heat. By upgrading the DBLS setup with galvanometric scanners, the negative effect of heat dissipation on some of the assessed properties could be compensated for. Table 6 Mechanical properties of PA12 tensile specimens. Sample UTS [MPa] ε b [%] E [MPa] S1 49.50 ± 2.20 32.73 ± 3.04 1102.32 ± 95.60 S2 48.40 ± 1.51 36.81 ± 6.62 1165.42 ± 59.96 S3 48.52 ± 1.23 36.37 ± 4.89 1147.53 ± 68.35 S4 46.65 ± 0.75 42.95 ± 6.67 1109.40 ± 22.93 The only significant differences were observed for specimens S1 and S4. The utilization of virgin powder in I1 yielded samples with the highest mean UTS and the lowest ε b . Moreover, the last specimen series (S4) demonstrated highest ε b and the lowest UTS. The mechanical properties of each series of samples meet the required standards. It is hypothesized that the elevated standard deviation of the determined parameters, particularly with respect to ε b , is attributable to DLBS hardware limitations. Moreover, it can be hypothesized that the higher elongation at break of S4 is attributable to the significantly smaller amount of filler in P3 than in the previous postprocess powders. 4 Conclusions This paper analyses the application of a new DBLS method for processing PA12 powder in a continuous reuse scheme at room temperature. The use of only laser radiation for preheating the polymer (i.e., a heating laser beam instead of a heater) significantly reduced the thermal degradation of the input material while simultaneously enabling a stable and repeatable process. As a result, the postprocess powder can be directly reused in a closed loop without the need for refreshment or replenishment. GPC showed that the MWD curves of powders after successive iterations had almost the same distribution, and the maximum changes in the corresponding molecular weights did not exceed a single percentage point. These findings are also supported by the melt viscosity measurements, which indicated that the observed differences are within the error range of the measurement method. Desirable results were also observed for the sintered specimens. Tensile testing showed very small changes in the mechanical properties of the produced samples in successive iterations. The only statistically significant changes in UTS and εb occurred between the samples fabricated from the virgin powder and from powder that was reused twice. However, even in the last iteration (I4), the samples exhibited satisfactory mechanical properties. The particle morphology and size distribution differed slightly; the most significant differences were observed in the dynamic flow properties. These differences are likely due to minor changes in the postprocess powder (especially the SiO 2 filler content), as confirmed by additional analyses using EDS and SEM. Overall, despite some changes in particle size distribution and flowability, the mechanical properties and postprocess quality remained consistent across reuse cycles. Proper management of material circulation in the PBF-LB/P process is crucial to minimize financial losses and environmental impacts. The ASTM F3456-22 standard specifies two main powder reuse schemes: one scheme without refreshing with virgin powder and one with refreshing. The second, more common approach involves mixing used powder with virgin powder at a predetermined ratio for subsequent build cycles ( continuous refreshing with virgin powder ) or adding virgin powder to the used powder accumulated from one batch ( continuous reuse while replenishing with virgin powder ). This process is repeated until the powder is depleted or fails to meet the reuse criteria. In this approach, every subsequent process differs (assuming the classical PBF-LB/P approach) in terms of the mechanical specimens and postprocess properties. This variation, in turn, leads to inconsistency and further problems. On the other hand, the DBLS approach has been shown to be feasible without the need for refreshing with virgin powder. In this scenario, the nondegradable powder can be used in a closed loop until exhausted ( continuous reuse ). This greatly simplifies material preparation and management. Notably, in a typical use cycle, the print-ready powder used to fabricate parts would need to be replenished, which may compensate for the reduction in flowability. If this approach is not sufficient, the addition of a flow agent may be needed. Further studies on DBLS application in a system based on galvanometric scanning will be carried out in the near future. Theoretical analysis of the problem indicates that this approach will realize a further reduction in material degradation while improving the performance of the method. Declarations Funding This research was supported by a pro-quality subsidy granted by the Faculty of Mechanical Engineering at the Wroclaw University of Science and Technology (Poland) with funding from the “ Excellence Initiative – Research University ” program for 2024, the task “R educing thermal degradation of polyamide 12 using dual beam laser sintering process ” and the Opus project “ Laser modification of bioresorbable polymeric materials in thermal processes of additive manufacturing ” financed by the National Centre of Science (UMO-2017/27/B/ST8/01780). Competing interests The authors declare that they have no known competing financial interests or personal relationships that could have appeared to influence the work reported in this manuscript. Data availability Data will be made available on request. Point of contact: corresponding author Arkadiusz Antończak – Tel.: +48 71 320 46 98, E-mail address: [email protected] Code availability Code will be available on request. Authors’ contribution Conceptualization: Arkadiusz Antończak, Michał Olejarczyk; Data curation: Piotr Gruber, Arkadiusz Antończak; Formal analysis: Piotr Gruber, Michał Olejarczyk; Funding acquisition: Michał Olejarczyk, Arkadiusz Antończak; Investigation: Michał Olejarczyk, Piotr Gruber; Arkadiusz Antończak; Methodology: Aleksander Kubeczek, Piotr Gruber; Project administration: Arkadiusz Antończak; Resources: Aleksander Kubeczek, Michał Olejarczyk, Piotr Gruber, Arkadiusz Antończak; Software: Aleksander Kubeczek, Piotr Gruber; Supervision: Arkadiusz Antończak; Validation: Aleksander Kubeczek, Piotr Gruber, Arkadiusz Antończak; Visualization: Piotr Gruber; Writing – original draft, review & editing: Aleksander Kubeczek, Michał Olejarczyk, Piotr Gruber, Arkadiusz Antończak. References Dadbakhsh, S. et al. 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Sci. 63 (1), 126–138. https://doi.org/10.1002/pen.26191 (2023). Yang, F., Zobeiry, N., Mamidala, R. & Chen, X. A review of aging, degradation, and reusability of PA12 powders in selective laser sintering additive manufacturing. Mater. Today Commun. 34 , 105279. https://doi.org/10.1016/j.mtcomm.2022.105279 (2023). Paolucci, F., van Mook, M. J. H., Govaert, L. E. & Peters, G. W. M. Influence of post-condensation on the crystallization kinetics of PA12: From virgin to reused powder. Polymer 175 , 161–170. https://doi.org/10.1016/j.polymer.2019.05.009 (2019). Chen, P. et al. Systematical mechanism of Polyamide-12 aging and its micro-structural evolution during laser sintering. Polym. Test. 67 , 370–379. https://doi.org/10.1016/j.polymertesting.2018.03.035 (2018). Yang, F. & Chen, X. A combined theoretical and experimental approach to model polyamide 12 degradation in selective laser sintering additive manufacturing. J. Manuf. Process. 70 , 271–289. https://doi.org/10.1016/j.jmapro.2021.08.051 (2021). Wudy, K., Drummer, D., Kühnlein, F. & Drexler, M. Influence of degradation behavior of polyamide 12 powders in laser sintering process on produced parts. AIP Conference Proceedings, 1593 (1), 691–695. (2014). https://doi.org/10.1063/1.4873873 Wörz, A., Wudy, K., Drummer, D., Wegner, A. & Witt, G. Comparison of long-term properties of laser sintered and injection molded polyamide 12 parts. J. Polym. Eng. 38 (6), 573–582. https://doi.org/10.1515/polyeng-2017-0227 (2017). Weinmann, S. & Bonten, C. Recycling of PA12 powder for selective laser sintering. AIP Conference Proceedings, 2289 (1), 020056. (2020). https://doi.org/10.1063/5.0029945 Chen, Y. et al. Dynamic polyamide networks via amide-imide exchange. Macromolecules 54 (20), 9703–9711. https://doi.org/10.1021/acs.macromol.1c01389 (2021). Olejarczyk, M. et al. New powder reuse schema in laser-based powder bed fusion of polymers. Waste Manage. 187 , 11–21. https://doi.org/10.1016/j.wasman.2024.06.030 (2024). Wang, L., Kiziltas, A., Mielewski, D. F., Lee, E. C. & Gardner, D. J. Closed-loop recycling of polyamide12 powder from selective laser sintering into sustainable composites. J. Clean. Prod. 195 , 765–772. https://doi.org/10.1016/j.jclepro.2018.05.235 (2018). Uddin, M., Williams, D. & Blencowe, A. Recycling of selective laser sintering waste nylon powders into fused filament fabrication parts reinforced with Mg particles. Polymers, 13 (13), 2046. (2021). https://doi.org/10.3390/polym13132046 Feng, L., Wang, Y. & Wei, Q. PA12 powder recycled from SLS for FDM. Polymers 11 (4), 727. https://doi.org/10.3390/polym11040727 (2019). Napolitano, F., Papa, I., Cimino, F., Lopresto, V. & Russo, P. Thermomechanical assessment of recovered PA12 powders with basalt filler for automotive components. Polymers 16 (19), 2682. https://doi.org/10.3390/polym16192682 (2024). Yang, L., Gu, H. & Bashir, Z. A new processing method for laser sintering polymer powders at low bed temperatures. Polymers 16 (23), 3301. https://doi.org/10.3390/polym16233301 (2024). Kigure, T., Yamauchi, Y. & Niino, T. Relationship between powder bed temperature and microstructure of laser sintered PA12 parts. In Proceedings of the 30th annual international solid freeform fabrication symposium . (pp. 827–834). University of Texas at Austin. (2019). Menge, D. & Schmid, H. J. Low temperature laser sintering on a standard system: First attempts and results with PA12. In Proceedings of the solid freeform fabrication 2021. (pp. 636–644). University of Texas at Austin. (2021). Niino, T., Haraguchi, H., Itagaki, Y., Iguchi, S. & Hagiwara, M. Feasibility study on plastic laser sintering without powder bed preheating. In Proceedings of the 2011 JSPE autumn conference. (pp. 17–29). Kanazawa, Japan. (2011). Niino, T., Haraguchi, H., Itagaki, Y., Hara, K. & Morita Susumu, Microstructural observation and mechanical property evaluation of plastic parts obtained by preheat free laser sintering. In Proceedings of the solid freeform fabrication symposium 2012 (pp. 2992–2997). University of Texas at Austin. (2012). Yamauchi, Y., Kigure, T. & Niino, T. Penetration depth optimization for proper interlayer adhesion using near-infrared laser in a low-temperature process of PBF-LB/P. J. Manuf. Process. 98 , 126–137. https://doi.org/10.1016/j.jmapro.2023.05.006 (2023). Schlicht, S., Greiner, S. & Drummer, D. Low temperature powder bed fusion of polymers by means of fractal quasi-simultaneous exposure strategies. Polymers 14 (7), 1428. https://doi.org/10.3390/polym14071428 (2022). Gruber, P., Kubeczek, A., Olejarczyk, M., Ziółkowski, G. & Antończak, A. J. Laser sintering of polyamide 12 with limited thermal degradation. J. Manuf. Process. 124 , 834–842. https://doi.org/10.1016/j.jmapro.2024.06.056 (2024). Antończak, A. J. et al. First, do not degrade – Dual Beam Laser Sintering of polymers. Additive Manuf. 53 , 102715. https://doi.org/10.1016/j.addma.2022.102715 (2022). Gruber, P. et al. High porosity composite structures produced from poly(lactic acid)/hydroxyapatite microspheres using novel dual beam laser sintering method: Analysis of structural, mechanical and thermal properties. J. Manuf. Process. 84 , 1284–1297. https://doi.org/10.1016/j.jmapro.2022.11.010 (2022). Kryszak, B. et al. Mechanical properties and degradation of laser sintered structures of PLA microspheres obtained by dual beam laser sintering method. Int. J. Adv. Manuf. Technol. 120 (11–12), 7855–7872. https://doi.org/10.1007/s00170-022-09253-6 (2022). Schmid, M. Laser sintering with plastics . Hanser. (2018). Schmidt, J. & Peukert, W. Dry powder coating in additive manufacturing. Front. Chem. Eng. 4 , 995221. https://doi.org/10.3389/fceng.2022.995221 (2022). Marschall, M., Heintges, C. & Schmidt, M. Influence of flow aid additives on optical properties of polyamide for Laser-Based Powder Bed Fusion. Procedia CIRP . 111 , 51–54. https://doi.org/10.1016/j.procir.2022.08.114 (2022). Leung, C. L. A. et al. Unravel melt pool and bubble dynamics during laser powder bed fusion of polyamides using synchrotron X-ray imaging and process simulation. Virtual Phys. Prototyp. 20 (1), e2465905. https://doi.org/10.1080/17452759.2025.2465905 (2025). Baesso, I. et al. Characterization of powder flow behavior for additive manufacturing. Additive Manuf. 47 , 102250. https://doi.org/10.1016/j.addma.2021.102250 (2021). Rides, M., Allen, C., Omloo, H., Nakayama, K. & Cancelli, G. Interlaboratory comparison of melt flow rate testing of moisture sensitive plastics. Polym. Test. 28 (6), 572–591. https://doi.org/10.1016/j.polymertesting.2009.03.013 (2009). Hesse, N. et al. From trash to treasure in additive manufacturing: Recycling of polymer powders by acid catalyzed hydrolysis. Additive Manuf. 71 , 103591. https://doi.org/10.1016/j.addma.2023.103591 (2023). Additional Declarations No competing interests reported. Cite Share Download PDF Status: Published Journal Publication published 26 Jul, 2025 Read the published version in Scientific Reports → Version 1 posted Editorial decision: Revision requested 05 Jul, 2025 Reviews received at journal 26 Jun, 2025 Reviews received at journal 26 Jun, 2025 Reviews received at journal 16 Jun, 2025 Reviewers agreed at journal 16 Jun, 2025 Reviewers agreed at journal 11 Jun, 2025 Reviewers agreed at journal 11 Jun, 2025 Reviewers invited by journal 29 May, 2025 Editor assigned by journal 29 May, 2025 Editor invited by journal 29 May, 2025 Submission checks completed at journal 28 May, 2025 First submitted to journal 15 May, 2025 You are reading this latest preprint version Research Square lets you share your work early, gain feedback from the community, and start making changes to your manuscript prior to peer review in a journal. As a division of Research Square Company, we’re committed to making research communication faster, fairer, and more useful. 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Also discoverable on Platform About Our Team In Review Editorial Policies Advisory Board Help Center Resources Author Services Accessibility API Access RSS feed Manage Cookie Preferences © Research Square 2026 | ISSN 2693-5015 (online) Privacy Policy Terms of Service Do Not Sell My Personal Information {"props":{"pageProps":{"initialData":{"identity":"rs-6672836","acceptedTermsAndConditions":true,"allowDirectSubmit":false,"archivedVersions":[],"articleType":"Article","associatedPublications":[],"authors":[{"id":464697297,"identity":"69e57b24-e281-4773-acf4-987c315d09b2","order_by":0,"name":"Aleksander Kubeczek","email":"","orcid":"","institution":"Wrocław University of Science and Technology","correspondingAuthor":false,"prefix":"","firstName":"Aleksander","middleName":"","lastName":"Kubeczek","suffix":""},{"id":464697298,"identity":"9df55ea6-08f2-4959-b86f-392e464af997","order_by":1,"name":"Michał Olejarczyk","email":"","orcid":"","institution":"Wrocław University of Science and Technology","correspondingAuthor":false,"prefix":"","firstName":"Michał","middleName":"","lastName":"Olejarczyk","suffix":""},{"id":464697299,"identity":"a5c1c757-a8df-4999-b507-33e3e4acabd9","order_by":2,"name":"Piotr Gruber","email":"","orcid":"","institution":"Wrocław University of Science and Technology","correspondingAuthor":false,"prefix":"","firstName":"Piotr","middleName":"","lastName":"Gruber","suffix":""},{"id":464697300,"identity":"4446a877-adc4-4c4a-9438-39ce9627fb9c","order_by":3,"name":"Arkadiusz J. Antończak","email":"data:image/png;base64,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","orcid":"","institution":"Wrocław University of Science and Technology","correspondingAuthor":true,"prefix":"","firstName":"Arkadiusz","middleName":"J.","lastName":"Antończak","suffix":""}],"badges":[],"createdAt":"2025-05-15 12:53:24","currentVersionCode":1,"declarations":"","doi":"10.21203/rs.3.rs-6672836/v1","doiUrl":"https://doi.org/10.21203/rs.3.rs-6672836/v1","draftVersion":[],"editorialEvents":[{"content":"https://doi.org/10.1038/s41598-025-12573-8","type":"published","date":"2025-07-26T15:58:28+00:00"}],"editorialNote":"","failedWorkflow":false,"files":[{"id":83765947,"identity":"f34f621d-4e37-494d-8fb4-ec1936738197","added_by":"auto","created_at":"2025-06-02 11:07:16","extension":"png","order_by":1,"title":"Figure 1","display":"","copyAsset":false,"role":"figure","size":21190,"visible":true,"origin":"","legend":"\u003cp\u003ePowder reuse and characterization scheme\u003c/p\u003e","description":"","filename":"Figure1.png","url":"https://assets-eu.researchsquare.com/files/rs-6672836/v1/26ff768ae3f8f1b76b0bc7e4.png"},{"id":83765948,"identity":"f9719cbb-081f-4829-81ba-e0f04cd6b1bc","added_by":"auto","created_at":"2025-06-02 11:07:16","extension":"png","order_by":2,"title":"Figure 2","display":"","copyAsset":false,"role":"figure","size":1299311,"visible":true,"origin":"","legend":"\u003cp\u003eManufacturing process: a) drawing of the build orientation with machine coordinates and b) image taken after the complete build process\u003c/p\u003e","description":"","filename":"Figure2.png","url":"https://assets-eu.researchsquare.com/files/rs-6672836/v1/f299d6cd147508a4a89ab9cc.png"},{"id":83766594,"identity":"3bf8886e-ff82-4f46-a366-b0b86612cbad","added_by":"auto","created_at":"2025-06-02 11:15:16","extension":"png","order_by":3,"title":"Figure 3","display":"","copyAsset":false,"role":"figure","size":807237,"visible":true,"origin":"","legend":"\u003cp\u003eExample of the image processing method using the P0 sample: a) original image, b) image with binarized powder particles (yellow), c) image with binarized powder particles and filler (blue)\u003c/p\u003e","description":"","filename":"Figure3.png","url":"https://assets-eu.researchsquare.com/files/rs-6672836/v1/89bf6ec4f95d54b265d1dbde.png"},{"id":83765955,"identity":"bbc62014-fe20-461b-ad76-aeeb738cd1ed","added_by":"auto","created_at":"2025-06-02 11:07:16","extension":"png","order_by":4,"title":"Figure 4","display":"","copyAsset":false,"role":"figure","size":2370387,"visible":true,"origin":"","legend":"\u003cp\u003eSEM images of postprocess PA12 powder samples: P0 a), P1 b), P2 c), P3 d) and a single powder particle of P0 with filler particles e), which was used to identify the filler type by EDS, with EDS spectra of the indicated reference points f)\u003c/p\u003e","description":"","filename":"Figure4.png","url":"https://assets-eu.researchsquare.com/files/rs-6672836/v1/ecaeb6047440d9797f3ce42c.png"},{"id":83766593,"identity":"38f2b284-9ba9-474f-8585-803d6870eeb2","added_by":"auto","created_at":"2025-06-02 11:15:16","extension":"png","order_by":5,"title":"Figure 5","display":"","copyAsset":false,"role":"figure","size":84311,"visible":true,"origin":"","legend":"\u003cp\u003eParticle size cumulative distribution (CD) and density distribution (DD) curves of virgin and postprocess PA12 powder samples\u003c/p\u003e","description":"","filename":"Figure5.png","url":"https://assets-eu.researchsquare.com/files/rs-6672836/v1/3805aa8b95643bdb379a00d8.png"},{"id":83765951,"identity":"8f33557a-5bc6-4ba7-8373-3e7d0151c6b3","added_by":"auto","created_at":"2025-06-02 11:07:16","extension":"png","order_by":6,"title":"Figure 6","display":"","copyAsset":false,"role":"figure","size":75965,"visible":true,"origin":"","legend":"\u003cp\u003eCohesion index curves of virgin and postprocess PA12 powder samples collected while increasing (↑) and decreasing (↓) the rotation speed\u003c/p\u003e","description":"","filename":"Figure6.png","url":"https://assets-eu.researchsquare.com/files/rs-6672836/v1/5e78f53ef2da998e2dbaf5ae.png"},{"id":83765953,"identity":"3d6d68b6-aa01-4e2b-9e0c-a315b66ebe94","added_by":"auto","created_at":"2025-06-02 11:07:16","extension":"png","order_by":7,"title":"Figure 7","display":"","copyAsset":false,"role":"figure","size":38549,"visible":true,"origin":"","legend":"\u003cp\u003eDifferential curves of the function of molecular weight distribution (MWD) for virgin and postprocess PA12 powder samples\u003c/p\u003e","description":"","filename":"Figure7.png","url":"https://assets-eu.researchsquare.com/files/rs-6672836/v1/e76589fb9280f20b2349aced.png"},{"id":83765957,"identity":"999a73b3-5ef3-49a3-8ab4-b73153fc9933","added_by":"auto","created_at":"2025-06-02 11:07:16","extension":"png","order_by":8,"title":"Figure 8","display":"","copyAsset":false,"role":"figure","size":432100,"visible":true,"origin":"","legend":"\u003cp\u003eMechanical properties of PA12 tensile specimens\u003c/p\u003e","description":"","filename":"Figure8.png","url":"https://assets-eu.researchsquare.com/files/rs-6672836/v1/d28aa7f7b60302e06f5e5630.png"},{"id":87756789,"identity":"60c166e0-daaa-47a7-956d-03530034fa93","added_by":"auto","created_at":"2025-07-28 16:09:19","extension":"pdf","order_by":0,"title":"","display":"","copyAsset":false,"role":"manuscript-pdf","size":6908301,"visible":true,"origin":"","legend":"","description":"","filename":"manuscript.pdf","url":"https://assets-eu.researchsquare.com/files/rs-6672836/v1/30143777-d0a1-4200-8573-ad99d86a0be1.pdf"}],"financialInterests":"No competing interests reported.","formattedTitle":"Continuous reuse of polyamide 12 in Powder Bed Fusion","fulltext":[{"header":"1 Introduction","content":"\u003cp\u003eLaser beam powder bed fusion of polymers (PBF-LB/P) is an additive manufacturing process that enables flexible, layer-by-layer fabrication of parts with complex geometries. A sequence of steps, including powder application, heating, melting, and lowering the build platform, is repeated to transform a digital model into a functional part. Parts are most commonly made from polyamide 12 (PA12), which has a dominant market share. Achieving bonding between layers requires the use of additional heat energy, which is provided by a laser. The material is applied via a roller or a recoater each time after the build platform is lowered. Reducing the temperature gradient between the scanned area and the rest of the powder bed eliminates curling of the melted cross-sections; for this purpose, an additional heating system is used to keep the material below the melting point. Unfortunately, maintaining the material at elevated temperatures for some time, usually in the order of hours, results in degradation of the unmelted material. Moreover, only 10\u0026ndash;25% of the material is used to build parts [\u003cspan citationid=\"CR1\" class=\"CitationRef\"\u003e1\u003c/span\u003e, \u003cspan citationid=\"CR2\" class=\"CitationRef\"\u003e2\u003c/span\u003e]. The remaining, unmelted material supports the parts during fabrication but becomes waste at the end of the process.\u003c/p\u003e \u003cp\u003eContinuous processing (without the addition of virgin material) is possible in PBF-LB/P [\u003cspan additionalcitationids=\"CR4\" citationid=\"CR3\" class=\"CitationRef\"\u003e3\u003c/span\u003e\u0026ndash;\u003cspan citationid=\"CR5\" class=\"CitationRef\"\u003e5\u003c/span\u003e], but the degree of material degradation due to chemical (dominant role) and physical (secondary role) mechanisms increases with each subsequent cycle [\u003cspan citationid=\"CR6\" class=\"CitationRef\"\u003e6\u003c/span\u003e]. Chemical degradation mechanisms such as thermal oxidation, solidstate postcondensation, peak merging due to the Brill transition, and hydrolysis involve molecular chain scission, molecular cross-linking, chain branching, chain lengthening, and thermal property changes [\u003cspan citationid=\"CR1\" class=\"CitationRef\"\u003e1\u003c/span\u003e, \u003cspan additionalcitationids=\"CR8\" citationid=\"CR7\" class=\"CitationRef\"\u003e7\u003c/span\u003e\u0026ndash;\u003cspan citationid=\"CR9\" class=\"CitationRef\"\u003e9\u003c/span\u003e]. Physical degradation mechanisms include relaxation of orientation, agglomeration, postcrystallization effects, concentration changes, particle aggregation, spherulite growth/structure, increased crystallization degree, and increased lamellar thickness [\u003cspan citationid=\"CR10\" class=\"CitationRef\"\u003e10\u003c/span\u003e, \u003cspan citationid=\"CR11\" class=\"CitationRef\"\u003e11\u003c/span\u003e]. These changes in material properties affect various aspects of PBF-LB, resulting in increased porosity, reduced mechanical properties, dimensional instability, and surface roughness. Many material-driven approaches can be applied to enable reuse of this material in the PBF-LB/P process, including mixing postprocess powder with virgin powder [\u003cspan citationid=\"CR2\" class=\"CitationRef\"\u003e2\u003c/span\u003e], material doping [\u003cspan citationid=\"CR12\" class=\"CitationRef\"\u003e12\u003c/span\u003e], powder hydration [\u003cspan citationid=\"CR13\" class=\"CitationRef\"\u003e13\u003c/span\u003e], and recycling [\u003cspan citationid=\"CR14\" class=\"CitationRef\"\u003e14\u003c/span\u003e], but such methods eliminate only the effect and not the cause. Additionally, upcycling of the material [\u003cspan additionalcitationids=\"CR16 CR17\" citationid=\"CR15\" class=\"CitationRef\"\u003e15\u003c/span\u003e\u0026ndash;\u003cspan citationid=\"CR18\" class=\"CitationRef\"\u003e18\u003c/span\u003e] is only a partial solution.\u003c/p\u003e \u003cp\u003eThe only way to improve the material efficiency of the PBF-LB/P process is to limit or eliminate the aging mechanisms caused by prolonged thermal exposure. Maintaining the build chamber temperature well below the processing window temperature requires compensation measures, either through the use of support structures or an increase in energy density in the scanning zone. For PA12, support structures have been used to build chamber temperatures of 150\u0026deg;C [\u003cspan citationid=\"CR19\" class=\"CitationRef\"\u003e19\u003c/span\u003e], 130\u0026deg;C [\u003cspan citationid=\"CR20\" class=\"CitationRef\"\u003e20\u003c/span\u003e], 80\u0026deg;C [\u003cspan citationid=\"CR21\" class=\"CitationRef\"\u003e21\u003c/span\u003e] and room temperature [\u003cspan additionalcitationids=\"CR23\" citationid=\"CR22\" class=\"CitationRef\"\u003e22\u003c/span\u003e\u0026ndash;\u003cspan citationid=\"CR24\" class=\"CitationRef\"\u003e24\u003c/span\u003e], but each time, the resulting properties were well below typical values. In turn, Schlicht \u003cem\u003eet al\u003c/em\u003e. [\u003cspan citationid=\"CR25\" class=\"CitationRef\"\u003e25\u003c/span\u003e] reported that a stable process at 75\u0026deg;C could be achieved by increasing the energy density using a fractal exposure sequence derived from the Peano curve. Based on a similar assumption, in [\u003cspan citationid=\"CR26\" class=\"CitationRef\"\u003e26\u003c/span\u003e], we proved that it is possible to process PA12 at room temperature by using dual beam laser sintering (DBLS) [\u003cspan citationid=\"CR27\" class=\"CitationRef\"\u003e27\u003c/span\u003e]. Additionally, we demonstrated our method on poly (lactic acid) and poly (lactic acid)/hydroxyapatite microspheres, focusing on the correlation of process parameters with the mechanical properties and internal structure of the manufactured parts [\u003cspan citationid=\"CR28\" class=\"CitationRef\"\u003e28\u003c/span\u003e, \u003cspan citationid=\"CR29\" class=\"CitationRef\"\u003e29\u003c/span\u003e]. In these studies, the DBLS method was used to reduce degradation in the context of widely used biomedical engineering materials. Moreover, for each material used, the optimal parameters (i.e., those resulting in mechanical and chemical properties as good as/better than those of standard selective laser sintering (SLS)) were determined.\u003c/p\u003e \u003cp\u003eHeating the polymer using a second laser instead of using heaters that permanently maintain the polymer at an elevated process temperature has several significant benefits. A heating beam has a much larger diameter (experimentally assumed value of 8 mm) than a sintering beam (usually on the order of hundreds of \u0026micro;m). The heating beam is positioned coaxially with the sintering beam, regardless of the scanning direction on the surface of a given layer and always reaches every point to be sintered first. Owing to the very high speed of laser heating (on the order of 10\u003csup\u003e6\u003c/sup\u003e K/s or more), the temperature required for sintering with the main sintering beam (whose small diameter ensures the necessary working resolution) can be reached in given point. During scanning of a given layer, a small volume of powder is heated, proportional to the diameter of the heating beam and the depth of heat penetration (thermal diffusion path). This, in turn, minimizes the exposure of the material in the working chamber in terms of both time and volume, which directly minimizes or eliminates postprocess powder degradation (uncontrolled changes in molecular weight).\u003c/p\u003e \u003cp\u003eThe elimination of heater units in the DBLS method provides a number of potential advantages compared with standard PBF-LB/P: simplified material management, reduced process time due to eliminating the warm-up and cool-down phases, stable powder feeding conditions, and online process control in the melting zone.\u003c/p\u003e \u003cp\u003eThis work is based on an original DBLS approach developed to limit the thermal degradation of the polymers described in detail in our previous work on the sintering of polylactide [\u003cspan citationid=\"CR27\" class=\"CitationRef\"\u003e27\u003c/span\u003e] and the most popular PBF-LB/P material, PA12 [\u003cspan citationid=\"CR26\" class=\"CitationRef\"\u003e26\u003c/span\u003e]. To demonstrate the advantages of this method over other methods, the degree of material degradation and the mechanical properties of samples manufactured at room temperature in a continuous reuse scheme were verified for the first time.\u003c/p\u003e"},{"header":"2 Materials and methods","content":"\u003cdiv id=\"Sec3\" class=\"Section2\"\u003e\n \u003ch2\u003e2.1 Dual-beam laser sintering device\u003c/h2\u003e\n \u003cp\u003eDBLS is an original modification of the standard PBF-LB/P process, in which the polymer preheating step in the process chamber (typically based on the use of heaters) is replaced by irradiation with a second laser beam with a suitably larger diameter to heat only a small area (volume) of the working field in the vicinity of the sintering point. The DBLS method has been described in detail in our previous works [\u003cspan class=\"CitationRef\"\u003e26\u003c/span\u003e, \u003cspan class=\"CitationRef\"\u003e27\u003c/span\u003e].\u003c/p\u003e\n \u003cp\u003eRapid heating of the material with a second laser beam only during sintering and in the vicinity of the sintering point minimizes the exposure (in terms of time and space) of the polymer to elevated temperature. This, in turn, limits the thermal degradation of the material. Due to the developmental nature of the setup used in the DBLS experiment, two identical, independently controlled CO\u003csub\u003e2\u003c/sub\u003e lasers (Synrad, Inc. USA, series 48\u0026thinsp;\u0026minus;\u0026thinsp;2 with a wavelength of 10.6 \u0026micro;m and output power of up to 25 W) were used. The main sintering beam was focused with a 2.5\u0026rdquo; focal length lens, resulting in a diameter of 210 \u0026micro;m on the material surface. The heating beam, which was enlarged with a BEX-10.6-2Z1i beam expander (Ronar-Smith\u0026reg;, Wavelength Opto-Electronic Ltd., Singapore), achieved a diameter of 8 mm in the working field and was aligned coaxially with the sintering beam. Both beams simultaneously scanned the material surface at a given speed (V). This change in polymer heating approach requires a new way of defining process parameters. In the DBLS method, two main parameters are used to control the process: process temperature (T\u003csub\u003eP\u003c/sub\u003e) and sintering laser power (P\u003csub\u003eS\u003c/sub\u003e). The heating laser power (P\u003csub\u003eH\u003c/sub\u003e) is set automatically (via a control algorithm) to achieve the set T\u003csub\u003eP\u003c/sub\u003e, which is controlled layer by layer by an infrared sensor (CTlaser P7, Optris GmbH, Germany).\u003c/p\u003e\n \u003cp\u003e\u003cbr\u003e\u003c/p\u003e\n\u003c/div\u003e\n\u003cdiv id=\"Sec4\" class=\"Section2\"\u003e\n \u003ch2\u003e2.2 Methodology and study overview\u003c/h2\u003e\n \u003cp\u003eThis study investigated the degradation of PA12 powder and the mechanical properties of specimens in a continuous reuse scheme based on DBLS. Virgin PA12 powder (PA2201, EOS, Krailling, Germany) was initially loaded into the feed bin. After each iteration of the build process, the used powder (P\u003cem\u003en\u003c/em\u003e) was weighed, sieved, homogenized, and characterized. The postprocess material was then reloaded into the feed bin, and the build process, along with the subsequent steps (weighing, sieving, homogenization), was repeated. A total of four iterations of build processes and subsequent tasks were completed (Table\u0026nbsp;\u003cspan class=\"InternalRef\"\u003e1\u003c/span\u003e and Figure. 1), where virgin powder was loaded in the first iteration (denoted as I1), while in the following iterations (I2-I4), used powder (P1-P3) from the previous iteration was loaded.\u003c/p\u003e\n \u003cdiv class=\"gridtable\"\u003e\u0026nbsp;\u003ctable id=\"Tab1\" border=\"1\"\u003e\n \u003ccaption language=\"En\"\u003e\n \u003cdiv class=\"CaptionNumber\"\u003eTable 1\u003c/div\u003e\n \u003cdiv class=\"CaptionContent\"\u003e\n \u003cp\u003eDesignations and symbols used in this work.\u003c/p\u003e\n \u003c/div\u003e\n \u003c/caption\u003e\n \u003ccolgroup cols=\"3\"\u003e\u003c/colgroup\u003e\n \u003cthead\u003e\n \u003ctr\u003e\n \u003cth align=\"left\"\u003e\n \u003cp\u003eSymbol\u003c/p\u003e\n \u003c/th\u003e\n \u003cth align=\"left\"\u003e\n \u003cp\u003eMeaning\u003c/p\u003e\n \u003c/th\u003e\n \u003cth align=\"left\"\u003e\n \u003cp\u003eAdditional information\u003c/p\u003e\n \u003c/th\u003e\n \u003c/tr\u003e\n \u003c/thead\u003e\n \u003ctbody\u003e\n \u003ctr\u003e\n \u003ctd align=\"left\"\u003e\n \u003cp\u003eI\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"left\"\u003e\n \u003cp\u003eiteration\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"left\"\u003e\n \u003cp\u003eset of build processes and routines; loading is performed using powder with the same thermal history\u003c/p\u003e\n \u003c/td\u003e\n \u003c/tr\u003e\n \u003ctr\u003e\n \u003ctd align=\"left\"\u003e\n \u003cp\u003e\u003cem\u003eN\u003c/em\u003e\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"left\"\u003e\n \u003cp\u003ecurrent iteration number\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"left\"\u003e\n \u003cp\u003evalues range from 1 to 4, where virgin powder is loaded in I1\u003c/p\u003e\n \u003c/td\u003e\n \u003c/tr\u003e\n \u003ctr\u003e\n \u003ctd align=\"left\"\u003e\n \u003cp\u003eI\u003cem\u003en\u003c/em\u003e\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"left\"\u003e\n \u003cp\u003eiteration \u003cem\u003en\u003c/em\u003e\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"left\"\u003e\n \u003cp\u003eiteration in which all processes are loaded with powder used \u003cem\u003en\u003c/em\u003e-1 times without regeneration\u003c/p\u003e\n \u003c/td\u003e\n \u003c/tr\u003e\n \u003ctr\u003e\n \u003ctd align=\"left\"\u003e\n \u003cp\u003eP\u003cem\u003en\u003c/em\u003e\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"left\"\u003e\n \u003cp\u003epostprocess powder resulting after \u003cem\u003en\u003c/em\u003e repeated process cycles\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"left\"\u003e\n \u003cp\u003epowder used \u003cem\u003en\u003c/em\u003e times; e.g. I3 is loaded with P2,\u003c/p\u003e\n \u003cp\u003eand P0 is virgin powder\u003c/p\u003e\n \u003c/td\u003e\n \u003c/tr\u003e\n \u003ctr\u003e\n \u003ctd align=\"left\"\u003e\n \u003cp\u003eS\u003cem\u003en\u003c/em\u003e\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"left\"\u003e\n \u003cp\u003edog-bone specimen in the \u003cem\u003en\u003c/em\u003e-th iteration\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"left\"\u003e\n \u003cp\u003especimen built with powder P(\u003cem\u003en\u003c/em\u003e-1)\u003c/p\u003e\n \u003c/td\u003e\n \u003c/tr\u003e\n \u003c/tbody\u003e\n \u003c/table\u003e\n \u003c/div\u003e\n \u003cp\u003e\u003cbr\u003e\u003c/p\u003e\n \u003cp\u003eThe build process was consistent for each manufacturing cycle, in which two dog-bone shaped specimens were oriented horizontally (XYZ according to ISO 17295:2023) in the center position, 6 mm apart. To ensure 19% nesting density, additional models were added between, above and below the specimens (Figure. 2). The geometry and dimensions of the specimens were determined in accordance with ISO 527-2-5B.\u003c/p\u003e\n \u003cp\u003eThe experiment was carried under the optimal process parameters determined in previous work (see Table \u003cspan class=\"InternalRef\"\u003e3\u003c/span\u003e in [\u003cspan class=\"CitationRef\"\u003e26\u003c/span\u003e]), which produced samples with the maximum ultimate tensile strength and elongation at break while maintaining the stability of the DBLS process. The following process parameters were used: sintering power P\u003csub\u003eS\u003c/sub\u003e = 3.0 W, process temperature T\u003csub\u003eP\u003c/sub\u003e = 180\u0026deg;C, surface scanning speed V\u0026thinsp;=\u0026thinsp;710 mm/s and process resolution h\u0026thinsp;=\u0026thinsp;25.4 \u0026micro;m (distance between successive laser pulses in the X and Y planes). Bidirectional scanning was performed along the X-axis, covering only the fill and excluding the contour. The remaining elements of the DBLS system, including the powder dosing method, were implemented in typical layer-by-layer fashion, as in the standard PBF-LB/P approach.\u003c/p\u003e\n \u003cp\u003eThe DBLS process chamber was 55 mm in diameter, and the mass of input powder for each build process was approximately 3 g. To account for nesting density, random build process issues, caking and the characteristics of the used powder, a total of approximately 190 g of virgin PA12 was processed in I1. This iteration comprised 50 build processes (yielding 100 specimens) and 152.5 g of P1. The sieved powder was subjected to postprocessing, and the remainder was used as feedstock for I2 (Table \u003cspan class=\"InternalRef\"\u003e2\u003c/span\u003e). The scheme was repeated for 2 additional iterations until all powder was used. After each iteration, 5 specimens were selected at random and used for mechanical tests. Additionally, approximately 30 g of used powder from iterations I1-I3 (after postprocessing) was used for powder characterization. In the final iteration (I4), only three build processes were completed, producing six specimens, but the used powder (P4) was not characterized due to the limited amount remaining (approximately 1 g).\u003c/p\u003e\n \u003cdiv class=\"gridtable\"\u003e\n \u003cdiv align=\"left\" class=\"colspec\"\u003e\u003cbr\u003e\u003c/div\u003e\u0026nbsp;\u003ctable id=\"Tab3\" border=\"1\"\u003e\n \u003ccaption language=\"En\"\u003e\n \u003cdiv class=\"CaptionNumber\"\u003eTable 2\u003c/div\u003e\n \u003cdiv class=\"CaptionContent\"\u003e\n \u003cp\u003eMaterial weights and number of processes.\u003c/p\u003e\n \u003c/div\u003e\n \u003c/caption\u003e\n \u003ccolgroup cols=\"3\"\u003e\u003c/colgroup\u003e\n \u003cthead\u003e\n \u003ctr\u003e\n \u003cth align=\"left\"\u003e\n \u003cp\u003eIteration\u003c/p\u003e\n \u003c/th\u003e\n \u003cth align=\"left\"\u003e\n \u003cp\u003eNumber of processes in iteration [a.u.]\u003c/p\u003e\n \u003c/th\u003e\n \u003cth align=\"left\"\u003e\n \u003cp\u003ePostprocess powder amount [g]\u003c/p\u003e\n \u003c/th\u003e\n \u003c/tr\u003e\n \u003c/thead\u003e\n \u003ctbody\u003e\n \u003ctr\u003e\n \u003ctd align=\"left\"\u003e\n \u003cp\u003eI1\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"char\"\u003e\n \u003cp\u003e50\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"left\"\u003e\n \u003cp\u003e152.5\u003c/p\u003e\n \u003c/td\u003e\n \u003c/tr\u003e\n \u003ctr\u003e\n \u003ctd align=\"left\"\u003e\n \u003cp\u003eI2\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"char\"\u003e\n \u003cp\u003e38\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"left\"\u003e\n \u003cp\u003e82.5\u003c/p\u003e\n \u003c/td\u003e\n \u003c/tr\u003e\n \u003ctr\u003e\n \u003ctd align=\"left\"\u003e\n \u003cp\u003eI3\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"char\"\u003e\n \u003cp\u003e17\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"left\"\u003e\n \u003cp\u003e35.3\u003c/p\u003e\n \u003c/td\u003e\n \u003c/tr\u003e\n \u003ctr\u003e\n \u003ctd align=\"left\"\u003e\n \u003cp\u003eI4\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"char\"\u003e\n \u003cp\u003e3\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"left\"\u003e\n \u003cp\u003e-\u003c/p\u003e\n \u003c/td\u003e\n \u003c/tr\u003e\n \u003c/tbody\u003e\n \u003c/table\u003e\n \u003c/div\u003e\u0026nbsp;\u003ctable border=\"1\"\u003e\n \u003ccaption language=\"En\"\u003e\n \u003cdiv\u003eTable 3\u003c/div\u003e\n \u003cdiv\u003e\n \u003cp\u003eSelected particle size distributions and flowability parameters of the PA12 virgin and postprocessed powders.\u003c/p\u003e\n \u003c/div\u003e\n \u003c/caption\u003e\n \u003cthead\u003e\n \u003ctr\u003e\n \u003cth align=\"left\"\u003e\n \u003cp\u003ePowder\u003c/p\u003e\n \u003c/th\u003e\n \u003cth align=\"left\"\u003e\n \u003cp\u003eFirst avalanche [\u0026deg;]\u003c/p\u003e\n \u003c/th\u003e\n \u003cth align=\"left\"\u003e\n \u003cp\u003eCumulative hysteresis of cohesion index\u003c/p\u003e\n \u003cp\u003e[a.u.]\u003c/p\u003e\n \u003c/th\u003e\n \u003cth align=\"left\"\u003e\n \u003cp\u003eD10 [\u0026micro;m]\u003c/p\u003e\n \u003c/th\u003e\n \u003cth align=\"left\"\u003e\n \u003cp\u003eD50 [\u0026micro;m]\u003c/p\u003e\n \u003c/th\u003e\n \u003cth align=\"left\"\u003e\n \u003cp\u003eD90 [\u0026micro;m]\u003c/p\u003e\n \u003c/th\u003e\n \u003cth align=\"left\"\u003e\n \u003cp\u003e\u0026lt;\u0026thinsp;10 \u0026micro;m [%]\u003c/p\u003e\n \u003c/th\u003e\n \u003cth align=\"left\"\u003e\n \u003cp\u003eFiller-to-powder index\u003c/p\u003e\n \u003cp\u003e[%]\u003c/p\u003e\n \u003c/th\u003e\n \u003c/tr\u003e\n \u003c/thead\u003e\n \u003ctbody\u003e\n \u003ctr\u003e\n \u003ctd align=\"left\"\u003e\n \u003cp\u003eP0 (ref.)\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"char\"\u003e\n \u003cp\u003e34.36\u0026thinsp;\u0026plusmn;\u0026thinsp;1.98\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"char\"\u003e\n \u003cp\u003e10.85\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"char\"\u003e\n \u003cp\u003e36.00\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"char\"\u003e\n \u003cp\u003e59.36\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"char\"\u003e\n \u003cp\u003e85.78\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"char\"\u003e\n \u003cp\u003e1.03\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"char\"\u003e\n \u003cp\u003e3.85\u003c/p\u003e\n \u003c/td\u003e\n \u003c/tr\u003e\n \u003ctr\u003e\n \u003ctd align=\"left\"\u003e\n \u003cp\u003eP1\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"char\"\u003e\n \u003cp\u003e37.00\u0026thinsp;\u0026plusmn;\u0026thinsp;2.02\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"char\"\u003e\n \u003cp\u003e13.55\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"char\"\u003e\n \u003cp\u003e38.38\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"char\"\u003e\n \u003cp\u003e61.43\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"char\"\u003e\n \u003cp\u003e89.27\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"char\"\u003e\n \u003cp\u003e1.21\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"char\"\u003e\n \u003cp\u003e2.44\u003c/p\u003e\n \u003c/td\u003e\n \u003c/tr\u003e\n \u003ctr\u003e\n \u003ctd align=\"left\"\u003e\n \u003cp\u003eP2\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"char\"\u003e\n \u003cp\u003e40.67\u0026thinsp;\u0026plusmn;\u0026thinsp;1.85\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"char\"\u003e\n \u003cp\u003e23.78\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"char\"\u003e\n \u003cp\u003e38.82\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"char\"\u003e\n \u003cp\u003e61.18\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"char\"\u003e\n \u003cp\u003e88.36\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"char\"\u003e\n \u003cp\u003e0.99\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"char\"\u003e\n \u003cp\u003e1.84\u003c/p\u003e\n \u003c/td\u003e\n \u003c/tr\u003e\n \u003ctr\u003e\n \u003ctd align=\"left\"\u003e\n \u003cp\u003eP3\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"char\"\u003e\n \u003cp\u003e44.98\u0026thinsp;\u0026plusmn;\u0026thinsp;1.28\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"char\"\u003e\n \u003cp\u003e9.79\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"char\"\u003e\n \u003cp\u003e39.35\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"char\"\u003e\n \u003cp\u003e62.70\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"char\"\u003e\n \u003cp\u003e90.80\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"char\"\u003e\n \u003cp\u003e1.47\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"char\"\u003e\n \u003cp\u003e0.57\u003c/p\u003e\n \u003c/td\u003e\n \u003c/tr\u003e\n \u003c/tbody\u003e\n \u003c/table\u003e\n \u003cp\u003e\u003cbr\u003e\u003c/p\u003e\n\u003c/div\u003e\n\u003cdiv id=\"Sec5\" class=\"Section2\"\u003e\n \u003ch2\u003e2.3 Particle size distribution\u003c/h2\u003e\n \u003cp\u003eThe particle size distribution (PSD) was determined using a laser diffraction spectroscope Sympatec, HELOS/BR 4470 C (Clausthal-Zellerfeld, Germany) with the dry dispersion method using a RODOS/T4, R4 system (Clausthal-Zellerfeld, Germany). Measurements were carried out in accordance with ISO 13220-1. The powder sample was fed by a vibration feeder. The gap was set at 3.0 mm with maximum vibration (feed rate 100%). Powder was then dispersed at a pressure of 2 bar.\u003c/p\u003e\n\u003c/div\u003e\n\u003cdiv id=\"Sec6\" class=\"Section2\"\u003e\n \u003ch2\u003e2.4 Scanning electron microscopy\u003c/h2\u003e\n \u003cp\u003eScanning electron microscopy (SEM) was employed to determine the morphology of the powder particles. Before observation, the powder samples were coated with gold via plasma sputtering with a Q150R ES coater (Quorum, Laughton, United Kingdom). The gold-coated samples were observed under vacuum using an EVO MA25 microscope (Zeiss, Oberkochen, Germany) with a backscattered electron detector with an acceleration voltage of 20.0 kV and a current of 1.5 nA. Additionally, energy dispersive spectroscopy (EDS) was used to identify the filler type.\u003c/p\u003e\n\u003c/div\u003e\n\u003cdiv id=\"Sec7\" class=\"Section2\"\u003e\n \u003ch2\u003e2.5 Microscope image processing\u003c/h2\u003e\n \u003cp\u003eThe filler was identified and quantified via binarization of SEM images. SEM images of PA12 powder samples were thoroughly visually investigated; the filler was identified and quantified by examining the upper range of grayscale values (white or near-white pixels), while the powder particles were visible in the middle range of grayscale values (dark gray or light gray). Binarization was performed with OpenCV (version 4.11.0.86) for Python. Each SEM image corresponded to an area of 1.5 mm \u0026times; 1.2 mm. The images were classified into two distinct categories: images with binarized filler and images with binarized powder particles. The pixel coverage of the target feature was calculated for both types of binarized images to determine the area coverage of filler relative to that of powder particles; an example process is presented in Fig. \u003cspan class=\"InternalRef\"\u003e3\u003c/span\u003e.\u003c/p\u003e\n\u003c/div\u003e\n\u003cdiv id=\"Sec8\" class=\"Section2\"\u003e\n \u003ch2\u003e2.6 Revolution powder analysis\u003c/h2\u003e\n \u003cp\u003eDynamic flowability was measured using revolution powder analysis, in which a rotating drum is coupled with image processing to evaluate powder subjected to varying conditions. Measurement was carried out in two modes: first avalanche and speed hysteresis. The first avalanche angle was measured by image analysis at a low drum speed (0.5 rpm), while in hysteresis mode, the cohesion index was measured at variable speeds while either increasing or decreasing the rotation speed (1, 2, 5, 10, 15, 20, 30, 40, 50, and 60 rpm). For both measurements, the drum was filled with 55 ml of powder sample. At each speed, 25 images were taken at an interval of 1.0 s. The average position of the powder/air interface and fluctuations around this value were tracked from the recorded images using GranuDrum software 9.23.8.29 (GranuTools, Awans, Belgium). The postprocess powder (P\u003cem\u003en\u003c/em\u003e) from iterations I1-I3 was tested under the same humidity and temperature conditions (40% relative humidity and 20\u0026deg;C).\u003c/p\u003e\n \u003cp\u003e\u003cbr\u003e\u003c/p\u003e\n\u003c/div\u003e\n\u003cdiv id=\"Sec9\" class=\"Section2\"\u003e\n \u003ch2\u003e2.7 Melt flow index\u003c/h2\u003e\n \u003cp\u003eMelt flow index (MFI) was determined using an Mflow capillary rheometer (Zwick Roell, Ulm, Germany). Before testing, each powder sample weighing 4.5 g was dried in a 50/1.X2.IC.A weighing dryer (Radwag, Radom, Poland). The drying profile of the PA12 powders was determined according to VDI 3405. The sample was heated to 105\u0026deg;C and maintained at this temperature for 10 min; then, the temperature was increased from 105\u0026deg;C to 140\u0026deg;C for 5 min; in the last step, the sample was kept at 140\u0026deg;C for an additional 2 min. The MFI test was performed in volumetric mode using method B described in ISO 1133 to determine the melt volume ratio (MVR). Before testing, each sample was preheated in the cylinder for 300 s at 235\u0026deg;C. The test temperature was set at 235\u0026deg;C. A load of 2.16 kg was applied both during preheating and during the measurement cycle. Each powder sample was assessed three times, with five 3 mm measuring sections for each test.\u003c/p\u003e\n\u003c/div\u003e\n\u003cdiv id=\"Sec10\" class=\"Section2\"\u003e\n \u003ch2\u003e2.8 Gel permeation chromatography\u003c/h2\u003e\n \u003cp\u003eThe average molecular weight and molecular weight distribution (MWD) were determined by gel permeation chromatography (GPC) using a Max VE2001 chromatograph (Viscotek Corp, Malvern, United Kingdom) equipped with a degasser, an eluent flow and pressure monitoring system, a thermostat with two Shodex columns (HFIP 803 E211533 and HFIP 805 E211525) connected in series and an RI detector (Viscotek VE3580). The analysis was carried out in accordance with ISO 16014 and ASTM D 5296-11. The PA12 powder samples were dissolved in hexafluoro-isopropanol (HFIP\u0026thinsp;+\u0026thinsp;0.02 M sodium trifluoroacetate) for 24 h at room temperature. After each sample was dissolved, the 10 mg/ml solution was filtered through a 0.20 \u0026micro;m PTFE filter and analyzed using a chromatographic system with an eluent flow rate of 1 ml/min and an injection volume of 100 \u0026micro;l. Two injections were performed for each solution. The chromatographic system was calibrated using certified monodisperse poly (methyl methacrylate) (PMMA) standards with molecular weights in the range of 860\u0026ndash;1,020,000. The measured molecular weights of the tested samples were expressed as the relative molecular weights (relative to PMMA). The data was processed using OmniSEC 5.0 software. This approach enabled the determination of molecular weights and their distribution in a sample. The evaluated parameters included the number-average molecular weight M\u003csub\u003en\u003c/sub\u003e, weight-average molecular weight M\u003csub\u003ew\u003c/sub\u003e, \u0026ldquo;zeto\u0026rdquo;-average molecular weight M\u003csub\u003ez\u003c/sub\u003e, molecular weight corresponding to the peak value M\u003csub\u003ep\u003c/sub\u003e and polydispersity index M\u003csub\u003ew\u003c/sub\u003e/M\u003csub\u003en\u003c/sub\u003e.\u003c/p\u003e\n\u003c/div\u003e\n\u003cdiv id=\"Sec11\" class=\"Section2\"\u003e\n \u003ch2\u003e2.9 Tensile testing\u003c/h2\u003e\n \u003cp\u003eThe static tensile test was carried out on a Multitest-I testing machine (Mecmesin Ltd., West Sussex, United Kingdom). A 1 kN load cell (Mecmesin Ltd., West Sussex, United Kingdom) was used with vise grips with a maximum load of 10 kN. During the tests, the specimens were preloaded with 2 N, and measurements were collected at a speed of 10 mm/min. The dependence of the tensile force on the increase in displacement between the grips was recorded. The criterion for the end of the test was the first drop in registered force of at least 80%, which corresponded to the fracture of the specimen. The recorded data were used to determine the ultimate tensile strength (UTS), Young\u0026apos;s modulus (E) and relative elongation at break (\u0026epsilon;b). For each series, five dog-bone shaped specimens were subjected to the tensile test.\u003c/p\u003e\n\u003c/div\u003e\n\u003cdiv id=\"Sec12\" class=\"Section2\"\u003e\n \u003ch2\u003e2.10 Statistical analysis\u003c/h2\u003e\n \u003cp\u003eSignificant differences were determined via one-way analysis of variance (one-way ANOVA) with Tukey\u0026apos;s post hoc test (OriginPro, OriginLab Corporation, Northampton, MA, USA). The means were then classified into groups (labeled with uppercase letters \u0026ndash; A, B), and the results within a group were considered not to be significantly different at \u0026rho;\u0026thinsp;\u0026lt;\u0026thinsp;0.05. The results of the tensile tests are presented as the mean values with standard deviations.\u003c/p\u003e\n\u003c/div\u003e"},{"header":"3 Results and discussion","content":"\u003cdiv id=\"Sec14\" class=\"Section2\"\u003e \u003ch2\u003e3.1 Powder characterization: powder particle morphology and flowability\u003c/h2\u003e \u003cp\u003eThe powder particle morphology was determined using SEM (Figure. 4a-d). Regardless of the sample, the powder particles exhibited a globular shape, which is attributable to the precipitation-based production method [\u003cspan citationid=\"CR30\" class=\"CitationRef\"\u003e30\u003c/span\u003e]. Furthermore, smaller particles, predominantly irregular in shape, were discernible at higher magnification (Figure. 4e). Due to the greater brightness of the filler particles, additional EDS measurements were conducted. The resulting EDS spectral data are presented in Figure. 4f. In addition to the common peaks observed for all reference points (Figure. 4e), namely, at 0.277 keV (carbon), 0.525 keV (oxygen), and 2.120 keV (gold from the conductive coating), the measurement of filler particles (cf. points 1 and 3 in Figure. 4e) also revealed a peak at 1.739 keV, which may be correlated with silica. Silica compounds, most often SiO\u003csub\u003e2\u003c/sub\u003e, are utilized as fillers to enhance the flowability of polymer powders [\u003cspan citationid=\"CR31\" class=\"CitationRef\"\u003e31\u003c/span\u003e, \u003cspan citationid=\"CR32\" class=\"CitationRef\"\u003e32\u003c/span\u003e]. The presence of SiO\u003csub\u003e2\u003c/sub\u003e in PA12 powders was also reported by Leung \u003cem\u003eet al\u003c/em\u003e. [\u003cspan citationid=\"CR33\" class=\"CitationRef\"\u003e33\u003c/span\u003e]. The quantity of large aggregates formed on the surface of the particles decreased; consequently, image processing was utilized. The binarization results are presented as powder-to-filler area index values in Table\u0026nbsp;\u003cspan refid=\"Tab2\" class=\"InternalRef\"\u003e3\u003c/span\u003e. Image analysis confirmed that there was a demonstrable decrease in filler material in subsequent iterations of the powder application process. This phenomenon can be attributed to the loss of filler particles resulting from repeated application in the powder bed, sieving, and mixing between iterations.\u003c/p\u003e \u003cp\u003e \u003c/p\u003e \u003cp\u003e \u003c/p\u003e \u003cp\u003e \u003c/p\u003e \u003cp\u003eAlthough no significant changes in morphology were observed, the continuous reuse of PA12 influenced the quasistatic and dynamic flowability. The quasistatic flowability is represented by the first avalanche angle, which increased after the first and second iterations. The reduced flowability may be due to mechanical wear of the SiO\u003csub\u003e2\u003c/sub\u003e filler, especially as PA2200/PA2201 are low-additive powders [\u003cspan citationid=\"CR32\" class=\"CitationRef\"\u003e32\u003c/span\u003e].\u003c/p\u003e \u003cp\u003eSimilar observations were made in the case of dynamic flowability. The best characteristics were presented by the virgin powder, especially when comparing the hysteresis of the curves. The cumulative hysteresis of the cohesion index of the postprocess samples increased compared with that of the reference sample (Table\u0026nbsp;\u003cspan refid=\"Tab2\" class=\"InternalRef\"\u003e3\u003c/span\u003e). This effect can be explained by the fact that this powder is prone to agglomeration, phase segregation or static charge accumulation. Nevertheless, all the samples tested had a cohesion index below 25 (Figure. 6), which is considered an acceptable level for achieving successful powder layer deposition [\u003cspan citationid=\"CR34\" class=\"CitationRef\"\u003e34\u003c/span\u003e]. The observed minor differences should not disrupt the PBF process. Notably, in a typical use cycle, print-ready powder used to fabricate parts would need to be supplemented (due to the amount of consumed powder), which could compensate for the reduction in flowability. If this approach is not sufficient, the addition of a flow agent may be needed.\u003c/p\u003e \u003cp\u003e \u003c/p\u003e \u003c/div\u003e \u003cdiv id=\"Sec15\" class=\"Section2\"\u003e \u003ch2\u003e3.2 Powder characterization: thermal behavior\u003c/h2\u003e \u003cp\u003eThe melt viscosity results, represented by the MVR index, are presented in Table\u0026nbsp;\u003cspan refid=\"Tab4\" class=\"InternalRef\"\u003e4\u003c/span\u003e. All samples, both virgin and postprocess, had a similar viscosity. The observed differences between mean values are within the error of the measurement method used [\u003cspan citationid=\"CR35\" class=\"CitationRef\"\u003e35\u003c/span\u003e]. Typically, after PBF with a consistently high chamber temperature, an increase in viscosity is expected [\u003cspan citationid=\"CR36\" class=\"CitationRef\"\u003e36\u003c/span\u003e]. Moreover, Gruber \u003cem\u003eet al.\u003c/em\u003e [\u003cspan citationid=\"CR26\" class=\"CitationRef\"\u003e26\u003c/span\u003e] reported that the same polymer (PA2201) processed with the standard PBF-LB/P approach had a mean MVR of 10.5 cm\u003csup\u003e3\u003c/sup\u003e/10 min. The melt viscosity measurements suggest that no thermal degradation occurs during subsequent reuse of PA12 powder via the DBLS process.\u003c/p\u003e \u003cp\u003e \u003cdiv class=\"gridtable\"\u003e\u003ctable float=\"Yes\" id=\"Tab4\" border=\"1\"\u003e \u003ccaption language=\"En\"\u003e \u003cdiv class=\"CaptionNumber\"\u003eTable 4\u003c/div\u003e \u003cdiv class=\"CaptionContent\"\u003e \u003cp\u003eMVR index of virgin and postprocess PA12 powder samples.\u003c/p\u003e \u003c/div\u003e \u003c/caption\u003e \u003ccolgroup cols=\"5\"\u003e \u003cdiv align=\"left\" class=\"colspec\" colname=\"c1\" colnum=\"1\"\u003e\u003c/div\u003e \u003cdiv align=\"left\" class=\"colspec\" colname=\"c2\" colnum=\"2\"\u003e\u003c/div\u003e \u003cdiv align=\"left\" class=\"colspec\" colname=\"c3\" colnum=\"3\"\u003e\u003c/div\u003e \u003cdiv align=\"left\" class=\"colspec\" colname=\"c4\" colnum=\"4\"\u003e\u003c/div\u003e \u003cdiv align=\"left\" class=\"colspec\" colname=\"c5\" colnum=\"5\"\u003e\u003c/div\u003e \u003cthead\u003e \u003ctr\u003e \u003cth align=\"left\" colname=\"c1\"\u003e \u003cp\u003ePowder\u003c/p\u003e \u003c/th\u003e \u003cth align=\"left\" colname=\"c2\"\u003e \u003cp\u003eP0 (ref.)\u003c/p\u003e \u003c/th\u003e \u003cth align=\"left\" colname=\"c3\"\u003e \u003cp\u003eP1\u003c/p\u003e \u003c/th\u003e \u003cth align=\"left\" colname=\"c4\"\u003e \u003cp\u003eP2\u003c/p\u003e \u003c/th\u003e \u003cth align=\"left\" colname=\"c5\"\u003e \u003cp\u003eP3\u003c/p\u003e \u003c/th\u003e \u003c/tr\u003e \u003c/thead\u003e \u003ctbody\u003e \u003ctr\u003e \u003ctd align=\"left\" colname=\"c1\"\u003e \u003cp\u003eMVR [cm\u003csup\u003e3\u003c/sup\u003e/10 min]\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c2\"\u003e \u003cp\u003e29.64\u0026thinsp;\u0026plusmn;\u0026thinsp;2.10\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c3\"\u003e \u003cp\u003e32.09\u0026thinsp;\u0026plusmn;\u0026thinsp;2.66\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c4\"\u003e \u003cp\u003e31.51\u0026thinsp;\u0026plusmn;\u0026thinsp;1.56\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c5\"\u003e \u003cp\u003e31.04\u0026thinsp;\u0026plusmn;\u0026thinsp;4.13\u003c/p\u003e \u003c/td\u003e \u003c/tr\u003e \u003c/tbody\u003e \u003c/colgroup\u003e \u003c/table\u003e\u003c/div\u003e \u003c/p\u003e \u003c/div\u003e \u003cdiv id=\"Sec16\" class=\"Section2\"\u003e \u003ch2\u003e3.3 Powder characterization: molecular weight distribution\u003c/h2\u003e \u003cp\u003eThe differential molecular weight distribution (MWD) curves for the analyzed powders are shown in Figure. 7. The M\u003csub\u003en\u003c/sub\u003e, M\u003csub\u003ew\u003c/sub\u003e, M\u003csub\u003ez\u003c/sub\u003e, M\u003csub\u003ep\u003c/sub\u003e and M\u003csub\u003ew\u003c/sub\u003e/M\u003csub\u003en\u003c/sub\u003e values are summarized in Table\u0026nbsp;\u003cspan refid=\"Tab5\" class=\"InternalRef\"\u003e5\u003c/span\u003e.\u003c/p\u003e \u003cp\u003e \u003cdiv class=\"gridtable\"\u003e\u003ctable float=\"Yes\" id=\"Tab5\" border=\"1\"\u003e \u003ccaption language=\"En\"\u003e \u003cdiv class=\"CaptionNumber\"\u003eTable 5\u003c/div\u003e \u003cdiv class=\"CaptionContent\"\u003e \u003cp\u003eAverage values of M\u003csub\u003en\u003c/sub\u003e, M\u003csub\u003ew\u003c/sub\u003e, M\u003csub\u003ez\u003c/sub\u003e, M\u003csub\u003ep\u003c/sub\u003e and Mw/Mn expressed with respect to PMMA for virgin and postprocess PA12 powder samples.\u003c/p\u003e \u003c/div\u003e \u003c/caption\u003e \u003ccolgroup cols=\"12\"\u003e \u003cdiv align=\"left\" class=\"colspec\" colname=\"c1\" colnum=\"1\"\u003e\u003c/div\u003e \u003cdiv align=\"left\" class=\"colspec\" colname=\"c2\" colnum=\"2\"\u003e\u003c/div\u003e \u003cdiv align=\"left\" class=\"colspec\" colname=\"c3\" colnum=\"3\"\u003e\u003c/div\u003e \u003cdiv align=\"left\" class=\"colspec\" colname=\"c4\" colnum=\"4\"\u003e\u003c/div\u003e \u003cdiv align=\"left\" class=\"colspec\" colname=\"c5\" colnum=\"5\"\u003e\u003c/div\u003e \u003cdiv align=\"left\" class=\"colspec\" colname=\"c6\" colnum=\"6\"\u003e\u003c/div\u003e \u003cdiv align=\"left\" class=\"colspec\" colname=\"c7\" colnum=\"7\"\u003e\u003c/div\u003e \u003cdiv align=\"left\" class=\"colspec\" colname=\"c8\" colnum=\"8\"\u003e\u003c/div\u003e \u003cdiv align=\"left\" class=\"colspec\" colname=\"c9\" colnum=\"9\"\u003e\u003c/div\u003e \u003cdiv align=\"left\" class=\"colspec\" colname=\"c10\" colnum=\"10\"\u003e\u003c/div\u003e \u003cdiv align=\"left\" class=\"colspec\" colname=\"c11\" colnum=\"11\"\u003e\u003c/div\u003e \u003cdiv align=\"left\" class=\"colspec\" colname=\"c12\" colnum=\"12\"\u003e\u003c/div\u003e \u003cthead\u003e \u003ctr\u003e \u003cth align=\"left\" colspan=\"2\" nameend=\"c2\" namest=\"c1\"\u003e \u003cp\u003ePowder\u003c/p\u003e \u003c/th\u003e \u003cth align=\"left\" colspan=\"2\" nameend=\"c4\" namest=\"c3\"\u003e \u003cp\u003eM\u003csub\u003en\u003c/sub\u003e\u003c/p\u003e \u003c/th\u003e \u003cth align=\"left\" colspan=\"2\" nameend=\"c6\" namest=\"c5\"\u003e \u003cp\u003eM\u003csub\u003ew\u003c/sub\u003e\u003c/p\u003e \u003c/th\u003e \u003cth align=\"left\" colspan=\"2\" nameend=\"c8\" namest=\"c7\"\u003e \u003cp\u003eM\u003csub\u003ez\u003c/sub\u003e\u003c/p\u003e \u003c/th\u003e \u003cth align=\"left\" colspan=\"2\" nameend=\"c10\" namest=\"c9\"\u003e \u003cp\u003eM\u003csub\u003ep\u003c/sub\u003e\u003c/p\u003e \u003c/th\u003e \u003cth align=\"left\" colspan=\"2\" nameend=\"c12\" namest=\"c11\"\u003e \u003cp\u003eM\u003csub\u003ew\u003c/sub\u003e/M\u003csub\u003en\u003c/sub\u003e\u003c/p\u003e \u003c/th\u003e \u003c/tr\u003e \u003c/thead\u003e \u003ctbody\u003e \u003ctr\u003e \u003ctd align=\"left\" colname=\"c1\"\u003e \u003cp\u003eName\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c2\"\u003e \u003cp\u003eMeas'.\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c3\"\u003e \u003cp\u003e[Da]\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c4\"\u003e \u003cp\u003e[%]*\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c5\"\u003e \u003cp\u003e[Da]\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c6\"\u003e \u003cp\u003e[%]*\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c7\"\u003e \u003cp\u003e[Da]\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c8\"\u003e \u003cp\u003e[%]*\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c9\"\u003e \u003cp\u003e[Da]\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c10\"\u003e \u003cp\u003e[%]*\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c11\"\u003e \u003cp\u003e[-]\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c12\"\u003e \u003cp\u003e[%]*\u003c/p\u003e \u003c/td\u003e \u003c/tr\u003e \u003ctr\u003e \u003ctd align=\"left\" colname=\"c1\" morerows=\"1\" rowspan=\"2\"\u003e \u003cp\u003eP0\u003c/p\u003e \u003cp\u003e(ref.)\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c2\"\u003e \u003cp\u003eI\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c3\"\u003e \u003cp\u003e8248\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c4\" morerows=\"1\" rowspan=\"2\"\u003e \u003cp\u003e-\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c5\"\u003e \u003cp\u003e18680\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c6\" morerows=\"1\" rowspan=\"2\"\u003e \u003cp\u003e-\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c7\"\u003e \u003cp\u003e35740\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c8\" morerows=\"1\" rowspan=\"2\"\u003e \u003cp\u003e-\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c9\"\u003e \u003cp\u003e14828\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c10\" morerows=\"1\" rowspan=\"2\"\u003e \u003cp\u003e-\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c11\"\u003e \u003cp\u003e2.265\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c12\" morerows=\"1\" rowspan=\"2\"\u003e \u003cp\u003e-\u003c/p\u003e \u003c/td\u003e \u003c/tr\u003e \u003ctr\u003e \u003ctd align=\"left\" colname=\"c2\"\u003e \u003cp\u003eII\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c3\"\u003e \u003cp\u003e8248\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c5\"\u003e \u003cp\u003e18703\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c7\"\u003e \u003cp\u003e38148\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c9\"\u003e \u003cp\u003e14407\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c11\"\u003e \u003cp\u003e2.268\u003c/p\u003e \u003c/td\u003e \u003c/tr\u003e \u003ctr\u003e \u003ctd align=\"left\" colname=\"c1\" morerows=\"1\" rowspan=\"2\"\u003e \u003cp\u003eP1\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c2\"\u003e \u003cp\u003eI\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c3\"\u003e \u003cp\u003e8200\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c4\" morerows=\"1\" rowspan=\"2\"\u003e \u003cp\u003e-1.1\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c5\"\u003e \u003cp\u003e18660\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c6\" morerows=\"1\" rowspan=\"2\"\u003e \u003cp\u003e-1.1\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c7\"\u003e \u003cp\u003e37423\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c8\" morerows=\"1\" rowspan=\"2\"\u003e \u003cp\u003e-0.9\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c9\"\u003e \u003cp\u003e14490\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c10\" morerows=\"1\" rowspan=\"2\"\u003e \u003cp\u003e-1.5\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c11\"\u003e \u003cp\u003e2.275\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c12\" morerows=\"1\" rowspan=\"2\"\u003e \u003cp\u003e-0.1\u003c/p\u003e \u003c/td\u003e \u003c/tr\u003e \u003ctr\u003e \u003ctd align=\"left\" colname=\"c2\"\u003e \u003cp\u003eII\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c3\"\u003e \u003cp\u003e8119\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c5\"\u003e \u003cp\u003e18298\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c7\"\u003e \u003cp\u003e35791\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c9\"\u003e \u003cp\u003e14293\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c11\"\u003e \u003cp\u003e2.254\u003c/p\u003e \u003c/td\u003e \u003c/tr\u003e \u003ctr\u003e \u003ctd align=\"left\" colname=\"c1\" morerows=\"1\" rowspan=\"2\"\u003e \u003cp\u003eP2\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c2\"\u003e \u003cp\u003eI\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c3\"\u003e \u003cp\u003e7859\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c4\" morerows=\"1\" rowspan=\"2\"\u003e \u003cp\u003e-4.8\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c5\"\u003e \u003cp\u003e18338\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c6\" morerows=\"1\" rowspan=\"2\"\u003e \u003cp\u003e-1.8\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c7\"\u003e \u003cp\u003e36642\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c8\" morerows=\"1\" rowspan=\"2\"\u003e \u003cp\u003e-1.9\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c9\"\u003e \u003cp\u003e14830\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c10\" morerows=\"1\" rowspan=\"2\"\u003e \u003cp\u003e0.9\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c11\"\u003e \u003cp\u003e2.333\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c12\" morerows=\"1\" rowspan=\"2\"\u003e \u003cp\u003e3.1\u003c/p\u003e \u003c/td\u003e \u003c/tr\u003e \u003ctr\u003e \u003ctd align=\"left\" colname=\"c2\"\u003e \u003cp\u003eII\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c3\"\u003e \u003cp\u003e7840\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c5\"\u003e \u003cp\u003e18365\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c7\"\u003e \u003cp\u003e35841\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c9\"\u003e \u003cp\u003e14658\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c11\"\u003e \u003cp\u003e2.342\u003c/p\u003e \u003c/td\u003e \u003c/tr\u003e \u003ctr\u003e \u003ctd align=\"left\" colname=\"c1\" morerows=\"1\" rowspan=\"2\"\u003e \u003cp\u003eP3\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c2\"\u003e \u003cp\u003eI\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c3\"\u003e \u003cp\u003e7875\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c4\" morerows=\"1\" rowspan=\"2\"\u003e \u003cp\u003e-0.4\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c5\"\u003e \u003cp\u003e18172\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c6\" morerows=\"1\" rowspan=\"2\"\u003e \u003cp\u003e-2.4\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c7\"\u003e \u003cp\u003e36120\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c8\" morerows=\"1\" rowspan=\"2\"\u003e \u003cp\u003e-3.2\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c9\"\u003e \u003cp\u003e14574\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c10\" morerows=\"1\" rowspan=\"2\"\u003e \u003cp\u003e-1.2\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c11\"\u003e \u003cp\u003e2.307\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c12\" morerows=\"1\" rowspan=\"2\"\u003e \u003cp\u003e-1.9\u003c/p\u003e \u003c/td\u003e \u003c/tr\u003e \u003ctr\u003e \u003ctd align=\"left\" colname=\"c2\"\u003e \u003cp\u003eII\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c3\"\u003e \u003cp\u003e8556\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c5\"\u003e \u003cp\u003e18324\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c7\"\u003e \u003cp\u003e35371\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c9\"\u003e \u003cp\u003e14323\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c11\"\u003e \u003cp\u003e2.142\u003c/p\u003e \u003c/td\u003e \u003c/tr\u003e \u003c/tbody\u003e \u003c/colgroup\u003e \u003ctfoot\u003e \u003ctr\u003e\u003ctd colspan=\"12\"\u003e* \u0026ndash; relative % change in the average value of two measurements relative to the average value of the reference powder\u003c/td\u003e\u003c/tr\u003e \u003c/tfoot\u003e \u003c/table\u003e\u003c/div\u003e \u003c/p\u003e \u003cp\u003e \u003c/p\u003e \u003cp\u003e \u003c/p\u003e \u003cp\u003e \u003c/p\u003e \u003cp\u003eThe maximum changes in corresponding molecular weights do not exceed one percent. This result is one to two orders of magnitude better than that of the standard PBF-LB/P method, for which an increase from over 50% for M\u003csub\u003en\u003c/sub\u003e to almost 100% for M\u003csub\u003ew\u003c/sub\u003e and M\u003csub\u003ez\u003c/sub\u003e was noted [\u003cspan citationid=\"CR26\" class=\"CitationRef\"\u003e26\u003c/span\u003e]. The above analysis confirms that the DBLS method produces negligible changes in postprocess powder.\u003c/p\u003e \u003c/div\u003e \u003cdiv id=\"Sec17\" class=\"Section2\"\u003e \u003ch2\u003e3.4 DBLS sample characterization: mechanical behavior\u003c/h2\u003e \u003cp\u003eThe tensile testing results for samples produced by DBLS from virgin P0 and postprocess (P1-P3) powders are presented in Table\u0026nbsp;\u003cspan refid=\"Tab6\" class=\"InternalRef\"\u003e6\u003c/span\u003e and Figure. 8. The results revealed no statistically significant differences in the mechanical behavior of the samples that were manufactured from powder subjected to subsequent processing. The observed differences between iterations may be caused by variations in flowability and hardware limitations of the current DBLS setup. The most important factor is the scanning speed, which does not compensate for the thermal dissipation of heat. By upgrading the DBLS setup with galvanometric scanners, the negative effect of heat dissipation on some of the assessed properties could be compensated for.\u003c/p\u003e \u003cp\u003e \u003cdiv class=\"gridtable\"\u003e\u003ctable float=\"Yes\" id=\"Tab6\" border=\"1\"\u003e \u003ccaption language=\"En\"\u003e \u003cdiv class=\"CaptionNumber\"\u003eTable 6\u003c/div\u003e \u003cdiv class=\"CaptionContent\"\u003e \u003cp\u003eMechanical properties of PA12 tensile specimens.\u003c/p\u003e \u003c/div\u003e \u003c/caption\u003e \u003ccolgroup cols=\"4\"\u003e \u003cdiv align=\"left\" class=\"colspec\" colname=\"c1\" colnum=\"1\"\u003e\u003c/div\u003e \u003cdiv align=\"char\" char=\"\u0026plusmn;\" class=\"colspec\" colname=\"c2\" colnum=\"2\"\u003e\u003c/div\u003e \u003cdiv align=\"char\" char=\"\u0026plusmn;\" class=\"colspec\" colname=\"c3\" colnum=\"3\"\u003e\u003c/div\u003e \u003cdiv align=\"char\" char=\"\u0026plusmn;\" class=\"colspec\" colname=\"c4\" colnum=\"4\"\u003e\u003c/div\u003e \u003cthead\u003e \u003ctr\u003e \u003cth align=\"left\" colname=\"c1\"\u003e \u003cp\u003eSample\u003c/p\u003e \u003c/th\u003e \u003cth align=\"left\" colname=\"c2\"\u003e \u003cp\u003eUTS [MPa]\u003c/p\u003e \u003c/th\u003e \u003cth align=\"left\" colname=\"c3\"\u003e \u003cp\u003eε\u003csub\u003eb\u003c/sub\u003e [%]\u003c/p\u003e \u003c/th\u003e \u003cth align=\"left\" colname=\"c4\"\u003e \u003cp\u003eE [MPa]\u003c/p\u003e \u003c/th\u003e \u003c/tr\u003e \u003c/thead\u003e \u003ctbody\u003e \u003ctr\u003e \u003ctd align=\"left\" colname=\"c1\"\u003e \u003cp\u003eS1\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\"\u0026plusmn;\" colname=\"c2\"\u003e \u003cp\u003e49.50\u0026thinsp;\u0026plusmn;\u0026thinsp;2.20\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\"\u0026plusmn;\" colname=\"c3\"\u003e \u003cp\u003e32.73\u0026thinsp;\u0026plusmn;\u0026thinsp;3.04\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\"\u0026plusmn;\" colname=\"c4\"\u003e \u003cp\u003e1102.32\u0026thinsp;\u0026plusmn;\u0026thinsp;95.60\u003c/p\u003e \u003c/td\u003e \u003c/tr\u003e \u003ctr\u003e \u003ctd align=\"left\" colname=\"c1\"\u003e \u003cp\u003eS2\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\"\u0026plusmn;\" colname=\"c2\"\u003e \u003cp\u003e48.40\u0026thinsp;\u0026plusmn;\u0026thinsp;1.51\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\"\u0026plusmn;\" colname=\"c3\"\u003e \u003cp\u003e36.81\u0026thinsp;\u0026plusmn;\u0026thinsp;6.62\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\"\u0026plusmn;\" colname=\"c4\"\u003e \u003cp\u003e1165.42\u0026thinsp;\u0026plusmn;\u0026thinsp;59.96\u003c/p\u003e \u003c/td\u003e \u003c/tr\u003e \u003ctr\u003e \u003ctd align=\"left\" colname=\"c1\"\u003e \u003cp\u003eS3\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\"\u0026plusmn;\" colname=\"c2\"\u003e \u003cp\u003e48.52\u0026thinsp;\u0026plusmn;\u0026thinsp;1.23\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\"\u0026plusmn;\" colname=\"c3\"\u003e \u003cp\u003e36.37\u0026thinsp;\u0026plusmn;\u0026thinsp;4.89\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\"\u0026plusmn;\" colname=\"c4\"\u003e \u003cp\u003e1147.53\u0026thinsp;\u0026plusmn;\u0026thinsp;68.35\u003c/p\u003e \u003c/td\u003e \u003c/tr\u003e \u003ctr\u003e \u003ctd align=\"left\" colname=\"c1\"\u003e \u003cp\u003eS4\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\"\u0026plusmn;\" colname=\"c2\"\u003e \u003cp\u003e46.65\u0026thinsp;\u0026plusmn;\u0026thinsp;0.75\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\"\u0026plusmn;\" colname=\"c3\"\u003e \u003cp\u003e42.95\u0026thinsp;\u0026plusmn;\u0026thinsp;6.67\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\"\u0026plusmn;\" colname=\"c4\"\u003e \u003cp\u003e1109.40\u0026thinsp;\u0026plusmn;\u0026thinsp;22.93\u003c/p\u003e \u003c/td\u003e \u003c/tr\u003e \u003c/tbody\u003e \u003c/colgroup\u003e \u003c/table\u003e\u003c/div\u003e \u003c/p\u003e \u003cp\u003eThe only significant differences were observed for specimens S1 and S4. The utilization of virgin powder in I1 yielded samples with the highest mean UTS and the lowest ε\u003csub\u003eb\u003c/sub\u003e. Moreover, the last specimen series (S4) demonstrated highest ε\u003csub\u003eb\u003c/sub\u003e and the lowest UTS. The mechanical properties of each series of samples meet the required standards. It is hypothesized that the elevated standard deviation of the determined parameters, particularly with respect to ε\u003csub\u003eb\u003c/sub\u003e, is attributable to DLBS hardware limitations. Moreover, it can be hypothesized that the higher elongation at break of S4 is attributable to the significantly smaller amount of filler in P3 than in the previous postprocess powders.\u003c/p\u003e \u003c/div\u003e"},{"header":"4 Conclusions","content":"\u003cp\u003eThis paper analyses the application of a new DBLS method for processing PA12 powder in a continuous reuse scheme at room temperature. The use of only laser radiation for preheating the polymer (i.e., a heating laser beam instead of a heater) significantly reduced the thermal degradation of the input material while simultaneously enabling a stable and repeatable process. As a result, the postprocess powder can be directly reused in a closed loop without the need for refreshment or replenishment. GPC showed that the MWD curves of powders after successive iterations had almost the same distribution, and the maximum changes in the corresponding molecular weights did not exceed a single percentage point. These findings are also supported by the melt viscosity measurements, which indicated that the observed differences are within the error range of the measurement method.\u003c/p\u003e \u003cp\u003eDesirable results were also observed for the sintered specimens. Tensile testing showed very small changes in the mechanical properties of the produced samples in successive iterations. The only statistically significant changes in UTS and εb occurred between the samples fabricated from the virgin powder and from powder that was reused twice. However, even in the last iteration (I4), the samples exhibited satisfactory mechanical properties. The particle morphology and size distribution differed slightly; the most significant differences were observed in the dynamic flow properties. These differences are likely due to minor changes in the postprocess powder (especially the SiO\u003csub\u003e2\u003c/sub\u003e filler content), as confirmed by additional analyses using EDS and SEM. Overall, despite some changes in particle size distribution and flowability, the mechanical properties and postprocess quality remained consistent across reuse cycles.\u003c/p\u003e \u003cp\u003eProper management of material circulation in the PBF-LB/P process is crucial to minimize financial losses and environmental impacts. The ASTM F3456-22 standard specifies two main powder reuse schemes: one scheme without refreshing with virgin powder and one with refreshing. The second, more common approach involves mixing used powder with virgin powder at a predetermined ratio for subsequent build cycles (\u003cem\u003econtinuous refreshing with virgin powder\u003c/em\u003e) or adding virgin powder to the used powder accumulated from one batch (\u003cem\u003econtinuous reuse while replenishing with virgin powder\u003c/em\u003e). This process is repeated until the powder is depleted or fails to meet the reuse criteria. In this approach, every subsequent process differs (assuming the classical PBF-LB/P approach) in terms of the mechanical specimens and postprocess properties. This variation, in turn, leads to inconsistency and further problems.\u003c/p\u003e \u003cp\u003eOn the other hand, the DBLS approach has been shown to be feasible without the need for refreshing with virgin powder. In this scenario, the nondegradable powder can be used in a closed loop until exhausted (\u003cem\u003econtinuous reuse\u003c/em\u003e). This greatly simplifies material preparation and management. Notably, in a typical use cycle, the print-ready powder used to fabricate parts would need to be replenished, which may compensate for the reduction in flowability. If this approach is not sufficient, the addition of a flow agent may be needed.\u003c/p\u003e \u003cp\u003eFurther studies on DBLS application in a system based on galvanometric scanning will be carried out in the near future. Theoretical analysis of the problem indicates that this approach will realize a further reduction in material degradation while improving the performance of the method.\u003c/p\u003e"},{"header":"Declarations","content":"\u003ch2\u003eFunding\u003c/h2\u003e\n\u003cp\u003eThis research was supported by a pro-quality subsidy granted by the Faculty of Mechanical Engineering at\u0026nbsp;the Wroclaw University of Science and Technology (Poland) with funding from the “\u003cem\u003eExcellence Initiative – Research University\u003c/em\u003e” program for 2024, the task “R\u003cem\u003eeducing thermal degradation of polyamide 12 using dual beam laser sintering process\u003c/em\u003e” and the Opus project “\u003cem\u003eLaser modification of bioresorbable polymeric materials in thermal processes of additive manufacturing\u003c/em\u003e” financed by the National Centre of Science (UMO-2017/27/B/ST8/01780).\u003c/p\u003e\n\u003ch2\u003eCompeting interests\u003c/h2\u003e\n\u003cp\u003eThe authors declare that they have no known competing financial interests or personal relationships that could have appeared to influence the work reported in this manuscript.\u003c/p\u003e\n\u003ch2\u003eData availability\u003c/h2\u003e\n\u003cp\u003eData will be made available on request.\u003c/p\u003e\n\u003cp\u003ePoint of contact: corresponding author Arkadiusz Antończak – Tel.: +48 71 320 46 98, E-mail address: [email protected]\u003c/p\u003e\n\u003ch2\u003eCode availability\u003c/h2\u003e\n\u003cp\u003eCode will be available on request.\u003c/p\u003e\n\u003ch2\u003eAuthors’ contribution\u003c/h2\u003e\n\u003cp\u003eConceptualization: Arkadiusz Antończak, Michał Olejarczyk;\u003c/p\u003e\n\u003cp\u003eData curation: Piotr Gruber, Arkadiusz Antończak;\u003c/p\u003e\n\u003cp\u003eFormal analysis: Piotr Gruber, Michał Olejarczyk;\u003c/p\u003e\n\u003cp\u003eFunding acquisition: Michał Olejarczyk, Arkadiusz Antończak;\u003c/p\u003e\n\u003cp\u003eInvestigation: Michał Olejarczyk, Piotr Gruber; Arkadiusz Antończak;\u003c/p\u003e\n\u003cp\u003eMethodology: Aleksander Kubeczek, Piotr Gruber;\u003c/p\u003e\n\u003cp\u003eProject administration: Arkadiusz Antończak;\u003c/p\u003e\n\u003cp\u003eResources: Aleksander Kubeczek, Michał Olejarczyk, Piotr Gruber, Arkadiusz Antończak;\u003c/p\u003e\n\u003cp\u003eSoftware: Aleksander Kubeczek, Piotr Gruber;\u003c/p\u003e\n\u003cp\u003eSupervision: Arkadiusz Antończak;\u003c/p\u003e\n\u003cp\u003eValidation: Aleksander Kubeczek, Piotr Gruber, Arkadiusz Antończak;\u003c/p\u003e\n\u003cp\u003eVisualization: Piotr Gruber;\u003c/p\u003e\n\u003cp\u003eWriting – original draft, review \u0026amp; editing: Aleksander Kubeczek, Michał Olejarczyk, Piotr Gruber, Arkadiusz Antończak.\u003c/p\u003e"},{"header":"References","content":"\u003col\u003e\u003cli\u003e\u003cspan\u003eDadbakhsh, S. et al. 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From trash to treasure in additive manufacturing: Recycling of polymer powders by acid catalyzed hydrolysis. \u003cem\u003eAdditive Manuf.\u003c/em\u003e \u003cb\u003e71\u003c/b\u003e, 103591. \u003cspan class=\"ExternalRef\"\u003e\u003cspan class=\"RefSource\"\u003ehttps://doi.org/10.1016/j.addma.2023.103591\u003c/span\u003e\u003cspan address=\"10.1016/j.addma.2023.103591\" targettype=\"DOI\" class=\"RefTarget\"\u003e\u003c/span\u003e\u003c/span\u003e (2023).\u003c/span\u003e\u003c/li\u003e\u003c/ol\u003e"}],"fulltextSource":"","fullText":"","funders":[],"hasAdminPriorityOnWorkflow":false,"hasManuscriptDocX":true,"hasOptedInToPreprint":true,"hasPassedJournalQc":"","hasAnyPriority":false,"hideJournal":false,"highlight":"","institution":"","isAcceptedByJournal":true,"isAuthorSuppliedPdf":false,"isDeskRejected":"","isHiddenFromSearch":false,"isInQc":false,"isInWorkflow":false,"isPdf":false,"isPdfUpToDate":true,"isWithdrawnOrRetracted":false,"journal":{"display":true,"email":"[email protected]","identity":"scientific-reports","isNatureJournal":false,"hasQc":true,"allowDirectSubmit":false,"externalIdentity":"scirep","sideBox":"Learn more about [Scientific Reports](http://www.nature.com/srep/)","snPcode":"","submissionUrl":"","title":"Scientific Reports","twitterHandle":"","acdcEnabled":true,"dfaEnabled":true,"editorialSystem":"stoa","reportingPortfolio":"Scientific Reports","inReviewEnabled":true,"inReviewRevisionsEnabled":true},"keywords":"additive manufacturing, laser-based powder bed fusion of polymers, dual beam laser sintering, polyamide 12, powder reuse, polymer degradation","lastPublishedDoi":"10.21203/rs.3.rs-6672836/v1","lastPublishedDoiUrl":"https://doi.org/10.21203/rs.3.rs-6672836/v1","license":{"name":"CC BY 4.0","url":"https://creativecommons.org/licenses/by/4.0/"},"manuscriptAbstract":"\u003cp\u003eThe thermal degradation of polymers in powder bed fusion (PBF, additive manufacturing) is one of the major issues preventing wider adoption of this technology at the production scale. Although standard PBF allows for elastic production of complex parts in a single-step manufacturing process, it is materially inefficient \u0026ndash; only approximately 10% of the material is used, with the majority of semicrystalline polyamide 12 (PA12) remaining in the form of free-flowing powder. Because the rest of the material remains below the melting point for a long time, it cannot be directly reused in subsequent processes. In this work, we present a novel way to process PA12 at room temperature without exposure to a thermal agent. Dual beam laser sintering (DBLS) uses a double laser system that effectively compensates for the temperature in the melting zone and prevents material shrinkage. To demonstrate the effectiveness of the DBLS method, the material was kept in a closed loop. Specimens from each iteration of the process (\u003cem\u003en\u003c/em\u003e\u0026thinsp;=\u0026thinsp;4) were analyzed. No significant changes were observed in the chemical properties (molecular weight and melt viscosity, assessed via gel permeation chromatography (GPC) and melt flow index (MFI) analysis) or technological properties (flowability) of the powder samples or in the mechanical properties of the built specimens compared with the initial values.\u003c/p\u003e","manuscriptTitle":"Continuous reuse of polyamide 12 in Powder Bed Fusion","msid":"","msnumber":"","nonDraftVersions":[{"code":1,"date":"2025-06-02 11:07:11","doi":"10.21203/rs.3.rs-6672836/v1","editorialEvents":[{"type":"communityComments","content":0},{"type":"decision","content":"Revision requested","date":"2025-07-05T17:04:46+00:00","index":"","fulltext":""},{"type":"editorInvitedReview","content":"","date":"2025-06-26T15:25:37+00:00","index":"hide","fulltext":""},{"type":"editorInvitedReview","content":"","date":"2025-06-26T14:05:45+00:00","index":"hide","fulltext":""},{"type":"editorInvitedReview","content":"","date":"2025-06-16T14:06:24+00:00","index":"hide","fulltext":""},{"type":"reviewerAgreed","content":"123708033269561280785055446824646876239","date":"2025-06-16T07:07:37+00:00","index":"hide","fulltext":""},{"type":"reviewerAgreed","content":"272423396659136613273759686618302706264","date":"2025-06-11T20:13:23+00:00","index":"hide","fulltext":""},{"type":"reviewerAgreed","content":"184204903842799766537942177365461440658","date":"2025-06-11T08:08:12+00:00","index":"hide","fulltext":""},{"type":"reviewersInvited","content":"","date":"2025-05-29T23:03:42+00:00","index":"","fulltext":""},{"type":"editorAssigned","content":"","date":"2025-05-29T23:00:29+00:00","index":"","fulltext":""},{"type":"editorInvited","content":"","date":"2025-05-29T20:46:11+00:00","index":"","fulltext":""},{"type":"checksComplete","content":"","date":"2025-05-28T11:07:02+00:00","index":"","fulltext":""},{"type":"submitted","content":"Scientific Reports","date":"2025-05-15T12:51:43+00:00","index":"","fulltext":""}],"status":"published","journal":{"display":true,"email":"[email protected]","identity":"scientific-reports","isNatureJournal":false,"hasQc":true,"allowDirectSubmit":false,"externalIdentity":"scirep","sideBox":"Learn more about [Scientific Reports](http://www.nature.com/srep/)","snPcode":"","submissionUrl":"","title":"Scientific Reports","twitterHandle":"","acdcEnabled":true,"dfaEnabled":true,"editorialSystem":"stoa","reportingPortfolio":"Scientific Reports","inReviewEnabled":true,"inReviewRevisionsEnabled":true}}],"origin":"","ownerIdentity":"2b8ab1dc-91df-4782-9be7-d8aca2eaeded","owner":[],"postedDate":"June 2nd, 2025","published":true,"recentEditorialEvents":[],"rejectedJournal":[],"revision":"","amendment":"","status":"published-in-journal","subjectAreas":[{"id":49337727,"name":"Physical sciences/Engineering/Electrical and electronic engineering"},{"id":49337728,"name":"Physical sciences/Engineering/Mechanical engineering"},{"id":49337729,"name":"Physical sciences/Engineering"},{"id":49337730,"name":"Physical sciences/Materials science"}],"tags":[],"updatedAt":"2025-07-28T16:05:04+00:00","versionOfRecord":{"articleIdentity":"rs-6672836","link":"https://doi.org/10.1038/s41598-025-12573-8","journal":{"identity":"scientific-reports","isVorOnly":false,"title":"Scientific Reports"},"publishedOn":"2025-07-26 15:58:28","publishedOnDateReadable":"July 26th, 2025"},"versionCreatedAt":"2025-06-02 11:07:11","video":"","vorDoi":"10.1038/s41598-025-12573-8","vorDoiUrl":"https://doi.org/10.1038/s41598-025-12573-8","workflowStages":[]},"version":"v1","identity":"rs-6672836","journalConfig":"researchsquare"},"__N_SSP":true},"page":"/article/[identity]/[[...version]]","query":{"redirect":"/article/rs-6672836","identity":"rs-6672836","version":["v1"]},"buildId":"XKTyCvWXoU3ODBz1xrDgd","isFallback":false,"isExperimentalCompile":false,"dynamicIds":[84888],"gssp":true,"scriptLoader":[]}