Enzyme catalysed degradation of polyester fibres – A comparative study between poly(ethylene terephthalate) and poly(butylene adipate-co-terephthalate)

Enzyme catalysed degradation of polyester fibres – A comparative study between poly(ethylene terephthalate) and poly(butylene adipate-co-terephthalate) | Research Square window.SnipcartSettings = { analytics: { enabled: false } }; (function() { var accessVector = localStorage.getItem('access_vector') || ''; window.dataLayer = window.dataLayer || []; if (accessVector) { window.dataLayer.push({ user: { profile: { profileInfo: { snid: accessVector } } } }); } })(); (function(w,d,s,l,i){w[l]=w[l]||[];w[l].push({'gtm.start':new Date().getTime(),event:'gtm.js'});var f=d.getElementsByTagName(s)[0],j=d.createElement(s),dl=l!='dataLayer'?'&l='+l:'';j.async=true;j.src='https://www.googletagmanager.com/gtm.js?id='+i+dl;f.parentNode.insertBefore(j,f);})(window,document,'script','dataLayer','GTM-K279D39R'); Browse Preprints In Review Journals COVID-19 Preprints AJE Video Bytes Research Tools Research Promotion AJE Professional Editing AJE Rubriq About Preprint Platform In Review Editorial Policies Our Team Advisory Board Help Center Sign In Submit a Preprint Cite Share Download PDF Research Article Enzyme catalysed degradation of polyester fibres – A comparative study between poly(ethylene terephthalate) and poly(butylene adipate- co -terephthalate) Huong Lan Nguyen, Sandra Eberle, Thomas Bechtold, Simone Weinberger, and 4 more This is a preprint; it has not been peer reviewed by a journal. https://doi.org/ 10.21203/rs.3.rs-6502055/v1 This work is licensed under a CC BY 4.0 License Status: Published Journal Publication published 18 Aug, 2025 Read the published version in Monatshefte für Chemie - Chemical Monthly → Version 1 posted 4 You are reading this latest preprint version Abstract Enzyme catalysed hydrolysis provides an environmentally friendly route for controlled decomposition of polyester fibres. In this work, the hydrolysis of polyethylene terephthalate (PET) and polybutylene adipate terephthalate (PBAT) by using a cutinase from Humicola insolens (HiC) was compared with the aim, to better understand the relationship between the polymer structure and the enzyme catalysed degradation. PBAT exhibited much higher sensitivity to hydrolysis most likely due to the presence of the longer carbon chain diol and of aliphatic adipic acid in addition to terephthalic acid. In addition, the higher degree of crystallinity of PET restricts the attack of the enzyme and preserves the high order the fibres during the hydrolysis. The results provide further basis for the optimisation of enzyme catalysed hydrolysis and polymer degradation processes of polyester fibres. Enzymatic hydrolysis Fibre Poly(ethylene terephthalate) Poly(butylene adipate-co-terephthalate) Biocatalysed polymer degradation Figures Figure 1 Figure 2 Figure 3 Figure 4 Figure 5 Introduction Within the textile industry, polyester fibre takes the major share of around 55% of the global fibre volume due to its economically viable production and excellent durability [ 1 ]. With a volume of around 70 million metric tons, poly(ethylene terephthalate) (PET) fibre however is considered as one of the sources of plastic pollution to the environment. As an estimation, the total sum of synthetic polymer waste up to 26 million tons reach the oceans per year [ 2 ]. Consequently, biodegradable polymers are attractive materials because they will disappear in nature due to decomposition by extracellular enzymes from bacteria and fungi followed by cell-uptake and biodegradation. Finally, the polymers are transformed into water, carbon dioxide, biomass and inorganic salts [ 3 ]. Therefore, the industry is more and more interested in the use of biodegradable polymers, partly because different governments put some pressure to induce a change to biodegradable polymers. Currently, the world production of polymers is around 400 million tons per year with a meagre 2% that is constituted by biodegradable polymers [ 4 ]. More than 80% of the global production of biodegradable polymers can be attributed to the production of starch blends, poly(lactic acid) (PLA) and poly(butylene adipate- co -terephthalate) (PBAT). Being a copolymer, PBAT shows the most distinct difference compared to the widely used PET with regard to their use as fibres in textile application. While PET fibre is regarded as high strength and durable, PBAT fibre exhibits higher softness and elasticity. The utilisation of enzymes for treating textile fibres and fabrics has been explored since decades due to the sustainable aspect of white biotechnology approaches over conventional chemical treatment techniques [ 5 ]. Recently, the use of enzyme to depolymerise PET is receiving increased attention [ 6 – 9 ]. Several studies have demonstrated the hydrolytic capacities of hydrolases, including esterases, lipases, and cutinases towards polyester [ 10 , 11 ]. Among these enzymes, cutinases are of particular interest since they are efficient biocatalysts for carrying out the hydrolytic processing of various aliphatic and aromatic polyesters [ 12 , 13 ]. With regards to PBAT, some recent studies on the enzymatic hydrolysis with Fusarium solani cutinase, Candida antarctica lipase B and Stenotrophomonas sp.YCJ1 using PBAT films indicated fast degradation [ 14 – 16 ]. In this work we investigated the influence of the polymer structure (aromatic polyester versus aromatic-aliphatic copolyester) on the enzymatic hydrolysis using a cutinase from Humicola insolens (HiC). By combining different characterisation techniques, the structural changes of the fibres as a result of the enzyme catalysed hydrolysis are investigated and discussed. The gained new insight into the selective hydrolysis of the fibres helps to better understand the mechanism and thus, to achieve the controlled enzymatic decomposition of different polyester fibres. Results and Discussion Monomer release and fibre morphology The conditions for the enzymatic hydrolysis of polyester fibres were evaluated in experiments based on the data previously reported [ 13 ]. In the first series with a small sample quantity of 10 mg fibres, the incubation time was chosen between 24 and 168 h. Due to enzymatic scission of the ester bonds, terephthalic acid (TA) was released. While the trend for PBAT is clear, i.e., increased TA release by increasing incubation time (Fig. 1 ), enzymatic hydrolysis for PET is neglectable as no detectable TA release was observed even after 168 h of reaction (0,008 mM TA value). Under identical conditions, no measurable TA release of the blank samples was observed for the control of both PBAT and PET. Considering the hypothesis of enzyme action modes as postulated in [ 17 ] that the hydrolysis starts with an endo-type (independent of the initial polymer microstructure), followed by an exo-type chain scission in the mobile amorphous fraction (MAF) and release of hydrolysis products, the mechanism can be taken to well explain the hydrolysis behaviour of PBAT (low crystallinity, i.e. high MAF proportion, see DSC results). In case of PET fibre with higher crystallinity, where neighbouring ester bonds in crystalline PET and in rigid amorphous fraction (RAF) are often not accessible to the enzyme, the explanation according to the hypothesis in [ 17 ] would be that in a first phase hydrolysis of the accessible mobile amorphous fraction MAF of PET by a combination of endo- and exo-type chain scissions would take place. Subsequently, the enzyme further catalysed only endo-type chain scissions in the less hydrolysis-susceptible RAF or crystalline microstructures of PET, but at a much lower rate. Considering the results obtained for PET i.e., no observable hydrolysis products at the set reaction conditions, the assumption can be made that no exo-type chain scission (or only very little) took place in PET fibres. With regard to fibre morphology, progress of the enzymatic hydrolysis was visualised through SEM imaging of the fibres after different incubation times for both PBAT (Fig. 2 ) and PET (Fig. 3 ). The blank PBAT and PET fibres still exhibited a rather smooth surface after incubation for 168 hours in buffer solution without enzyme (blanks). In the presence of the enzyme, already after 24 h hydrolysis, the PBAT fibre structure was completely destroyed and only few residues in form of stripes (no fibre) could be collected on the filter (Fig. 2 ). This is well in line with the release of TA from PBAT discussed above. In case of PET fibres, the fibre shape almost remains and no change in fibre diameter was observed (Fig. 3 ). The small deformation of some PET fibres could be due to mechanical agitation (at 65°C) during the incubation as well as fibre inhomogeneity. This observation also fits well to the non-detectable TA release of PET fibre after 168 h hydrolysis. In the first series with 10 mg samples, we observed that PET remained unchanged after 168 h of incubation while PBAT almost disappeared after 24 h hydrolysis. Thus, a second series with higher fibre amount of 500 mg was carried out. For PET fibre, the incubation time was extended up to 552 h and for PBAT fibre, shorter incubation time between 2 and 6 h was chosen. Table 1 Table 1 Monomer release as results of enzymatic hydrolysis of PBAT and PET fibres with the fibre/solution ratio 500 mg : 100 mL. Incubation time / h (PBAT) TA release / mM (PET) TA release / mM 2 not detectable 4 0.010 ± 0.001 6 0.506 ± 0.023 216 0.011 ± 0.001 384 0.015 ± 0.001 552 0.036 ± 0.001 It can be observed that a concentration of ca. 0.5 mM TA was released after 6 h of PBAT hydrolysis, which is comparable to between 96 and 168 h hydrolysis at smaller scale (10 mg : 1 mL fibre/solution ratio, Fig. 1 ). The difference can be explained by the different mass transfer occurring in the two reaction set-ups. Furthermore, while for the small-scale reaction 10 mg of fibres per mL (ratio 10:1) of solution was used, the ratio of 5:1 for the large-scale reaction led to higher enzyme density, i.e., 2-fold higher amount of active enzyme molecules over the fibre surface area unit at the bigger scale experiments. Combining with the orbital shaking of the reaction flasks, large-scale hydrolysis seemed to be more efficient. In case of PET fibre, the extended incubation time up to 552 h in large-scale setup also led to higher TA release up to 0.036 mM. However, TA release of PET fibre is still much lower by an order of magnitude when compared to PBAT fibre. The higher fibre amount was also intended for later analysis by ATR and DSC. ATR-FTIR investigation FTIR microscopy was applied in ATR mode to investigate possible changes in chemical structure of the fibre after hydrolysis. In this measurement technique, the ATR diamond is positioned directly on the surface of a single fibre, enabling a lateral resolution of 3–5 µm of the measurement, which is far lower than conventional transmission FTIR techniques would allow [ 18 ]. In Fig. 4 the IR spectra of enzymatically hydrolysed fibres and blanks are shown. For PET fibres (Fig. 4 a ) , it can be observed that all spectra are almost identical and show typical absorption peaks at 2970 cm − 1 (CH stretching), 1715 cm − 1 (C = O stretching) 1245 cm − 1 (C-C-O stretching) and 1097 cm − 1 (O-C-C stretching of aromatic ester). Depending on the thermal and mechanical history, e.g., quenching, annealing and subsequently drawn, differences are observed due to configuration of the ethylene glycol group and also phenylene carbonyl bonds (cis/trans conformers). Many of these absorption bands are split being associated with differences in the force field between amorphous and crystalline regions and also with the chain conformation around the glycol ester configuration [ 19 ]. Theoretically, as result of the polymer hydrolysis, shorter polyester chains are formed and thus, the number of end groups (-COOH and -OH) was expected to increase. However, unlike to the results reported in the literature for PET annealing [ 19 ] or alkali hydrolysis [ 20 ], we did not record any observable changes, either in the 1715 cm − 1 (C = O stretching) region nor in the 2970 cm − 1 (CH stretching) region. This observation, however, fits well to the results reported on the enzymatically hydrolysed PET fibres with different draw ratio in our earlier study [ 13 ]. For PBAT fibres, the situation looks different (Fig. 4 b, Table 2 ) with an increase of the peak intensity at 2961 cm − 1 (CH stretching) and decrease of the peak intensity at 1712 cm − 1 (C = O stretching). The results fit well with the study on alkaline hydrolysis of PET in KOH at 90°C [ 20 ] as well as with the results of the enzymatic hydrolysis of PBAT film reported in [ 14 , 16 ]. Furthermore, increases of peak intensity at 1341 cm − 1 could be observed which is associated with -CH 2 wagging and at 1471 cm − 1 , attributed to the bending mode of the trans rotational isomer. A similar trend was reported for an annealing study of PET, indicating higher crystallinity [ 19 ]. Table 2 Relative peak intensity of different vibration bands of PBAT fibres after enzymatic hydrolysis and blank (min-max normalised spectra). Incubation / h 2961 cm − 1 / a.u 1712 cm − 1 / a.u 1471 cm − 1 / a.u 1341 cm − 1 / a.u blank 0.26 ± 0.03 2.00 ± 0.01 0.27 ± 0.03 0.24 ± 0.02 2 0.27 ± 0.04 1.93 ± 0.11 0.19 ± 0.01 0.22 ± 0.03 4 0.23 ± 0.02 1.91 ± 0.02 0.18 ± 0.01 0.19 ± 0.02 6 1.26 ± 0.02 1.21 ± 0.12 0.55 ± 0.03 0.38 ± 0.03 It is worth noticing that the increases and decreases reported above are best observed when comparing PBAT fibres after 6 h of enzymatic hydrolysis with blank samples. The very fast hydrolysis (TA release between no detectable after 2 h and 0.5 mM) could be the reason for the variation of the results between samples after 2 and 4 h hydrolysis. Furthermore, blank PBAT fibre also underwent 6 h incubation without enzyme at 65°C and therefore, some annealing effect could also be the reason for the difference compared to samples after 2 and 4 h hydrolysis. Comparing the FTIR results between PET and PBAT, we can conclude that PBAT fibres are much more susceptible to enzymatic hydrolysis than PET, most likely due to the lower crystallinity of PBAT apart from the different chemical structure. This observation is further supported by the XRD investigation on enzymatic hydrolysed PBAT [ 14 , 16 ]. DSC thermal analysis To further investigate the hypothesis that hydrolysis preferably takes place at the amorphous part of the polymer fibres, thermal analysis investigation of the PET fibres was carried out using differential scanning calorimetry measurements (DSC). While the first heating run provides information on the original state of the fibre residue after hydrolysis, considering the fibre structure, the cooling run describes the crystallisation behaviour of the polymer from the melted state. Thus, data are collected for first heating and cooling runs (Fig. 5 , Tables 3 and 4 ). Table 3 Melting enthalpy ΔH m and crystallisation enthalpy ΔH c of enzymatic hydrolysed PET fibres and blank. Incubation / h ΔH m / Jg − 1 ΔH c / Jg − 1 blank 52.22 ± 1.74 43.18 ± 0.57 216 55.17 ± 2.49 47.88 ± 2.29 384 57.34 ± 2.59 52.58 ± 1.51 552 56.19 ± 6.61 52.39 ± 4.74 Table 4 Melting enthalpy ΔH m and crystallisation enthalpy ΔH c of enzymatic hydrolysed PBAT fibres and blank. Incubation / h ΔH m / Jg − 1 ΔH c / Jg − 1 blank 9.27 ± 0.26 18.94 ± 0.95 2 10.74 ± 0.49 20.81 ± 1.11 4 14.51 ± 0.93 19.93 ± 0.65 6 20.72 ± 2.03 20.83 ± 3.11 With increased incubation time, the melting enthalpy and crystallisation enthalpy of the both PET and PBAT increases (Tables 3 and 4 ). The biggest differences are observed between samples with the longest incubation time (552 h for PET and 6h for PBAT, respectively) to the blanks. While the enthalpy ΔH m of the first heating increased only slightly for PET after 552 h incubation (56.19 versus 52.22 Jg − 1 ), significant higher melting enthalpy was observed for residue of PBAT fibre after 6h hydrolysis compared to it blank (20.72 versus 9.27 Jg − 1 ). The big change in melting enthalpy of the fibre residue is well in line with the observed changes in IR peak intensities for PBAT reported above. With regards to PET, we observed in an earlier study that there was no significant changes in melting and crystallisation enthalpy for PET fibre after 168 h incubation, along with very low level of TA release of 0.1 mM [ 13 ]. This indicated that an extended incubation to 552 h caused stronger hydrolysis of PET fibre under the same condition. On the crystallisation (cooling run), the situation is different. The DSC results on PBAT fibres only suggest a slight increase in polymer crystallinity (crystallisation enthalpy ΔH c of 20.83 vs. 18.94 Jg − 1 ), while ΔH c for PET was increased from 43.18 Jg − 1 (blank) to 52.39 Jg − 1 (552 h incubation). It seemed that the first heating eliminated district thermal history of PET fibre, including fibre orientation and possible annealing effect during incubation. Another possible explanation is that the layer-by-layer enzymatic hydrolysis and monomer release as reported in [ 21 , 22 ] would cause a stronger changes at the fibre outer region, in particular in case of PBAT where stronger hydrolysis took place. Considering an ATR unit equipped with a Ge crystal as used in this study, a depth of penetration of 0.65 µm at the wavenumber 1040 cm − 1 was calculated [ 23 ]. Thus, this special ATR technique would rather give information on the fibre outer layer, while DSC investigation covers both surface and bulk parts of the fibre. Conclusion Enzyme catalysed hydrolysis provides an environmentally friendly route for controlled decomposition of polyester fibres. In this work we investigated the influence of the polymer structure (aromatic homopolymer versus aromatic-aliphatic copolymer) on the enzymatic hydrolysis using a cutinase from Humicola insolens (HiC). By combining different characterisation techniques, the structural changes of the fibres as a result of the enzyme catalysed hydrolysis are investigated and discussed. The comparison suggests that PBAT is much more susceptible to enzymatic hydrolysis than PET, most likely due to the lower crystallinity of PBAT together with the different chemical structure. This led to much faster hydrolysis of PBAT fibre and higher monomer release already after 6 h incubation at 65°C. In contrary, very long incubation time was needed (up to 552 h) to observe little monomer release from PET hydrolysis, likely due to its higher crystallinity degree of PET that inhibits the attack of the enzyme and preserves the high order the fibres during the hydrolysis. As a result of the very fast hydrolysis, PBAT fibres dissolved and deformed almost completely already after 24 h, while PET fibres retained their sharp and size at much longer incubation time, e.g. after168 h. By prolongation the enzymatic hydrolysis to 552 h (23 days), some monomer release could be observed, which is however, still in a much lower extend compared to the enzymatic hydrolysis of PBAT. Experimental Materials and enzymes Poly(ethylene terephthalate) fibre (1.7 dtex) and poly(butylene adipate- co -terephthalate) fibre (3.1 dtex) are kindly provided by IFG Asota GmbH, Linz, Austria. Prior to enzymatic modification, the fibres were cleaned in a mixture of 5 gL − 1 non-ionic surfactant (fatty alcohol ethoxylate, Marlipal O 13/69, Sasol Germany GmbH, Hamburg, Germany) and 5 gL − 1 Na 2 CO 3 (Merck Darmstadt, Germany) with a liquor ratio of 1:100 using Erlenmeyer flask in water bath at the temperature of 60°C, shaking speed of 140 rpm for 30 min. The fibres were then rinsed 3 times with hot deionised water (60°C) and 1 time with deionised water (25°C) followed by overnight air drying and oven drying at 60°C for approximately 3 h until constant mass was obtained. The cutinase from Humicola insolens (HiC) was purchased from STREAM chemicals (code: 06-3135) and used as received without further purification (esterase activity on p-NPB: 888 U mL − 1 , protein concentration: 6.94 mg mL − 1 ). The purity of the HiC batches purchased was routinely confirmed by SDS-PAGE analysis conducted as previously described [ 6 ]. All the other chemicals, solvents and reagents were purchased from Sigma-Aldrich at reagent grade and used without further purification if not otherwise specified. Enzymatic hydrolysis of fibres In the first series, 10 ± 0.2 mg of washed fibres was weighed out in 2 mL Eppendorf tubes and incubated for 24, 48, 72, 96 and 168 h with 1 mL of 5 µM HiC in 1 M potassium phosphate buffer pH 8. Incubation was carried out at a temperature of 65°C at 150 rpm using an orbital shaker. To better follow up the hydrolysis and collect enough fibre materials for later analytic, a second series of modification with higher fibre amount and justified times was carried out. Here, 500 ± 0.2 mg of fibres was weighed out in 200 mL Pyrex bottles and incubated with 100 mL of 5 µM HiC in 1 M potassium phosphate buffer pH 8. Incubation was carried out at a temperature of 65°C at 150 rpm using an orbital shaker. For PET fibre, the incubation time was extended to 216, 384 and 552 h. For PBAT fibre, shorter incubation time of 2, 4 and 6 h was chosen. Quantification of soluble release products using HPLC-DAD Hydrolysates were precipitated following the ice-cold methanol protocol (1:1 volumetric ratio). Samples were then centrifuged (Centrifuge 5427 R, Eppendorf AG, Hamburg, Germany) at 12700 rpm at 4°C for 15 min and filtered through 0.20 µm PTFE filters (GVS, Indianapolis, USA). The analytes were separated by high performance liquid chromatography HPLC, (Agilent Technologies, 1260 Infinity, Palo Alto, CA, United States) using a reversed phase column C18 (Poroshell 120 EC-C18 2.7 µm 3.0 × 150 mm) equipped with a photodiode array detector (Agilent Technologies, 1290 Infinity II, Vienna, Austria) set at the wavelength of 260 nm to detect the released products. Analyses were run using methanol (MeOH, phase A) and formic acid (HCOOH, phase B) gradient. The flow rate was set to 0.35 ml min − 1 at a constant temperature of 40°C. The injection volume was 10 µL. A terephthalate acid (TA) calibration curve up to 100 mM was used for the quantitative determination of the released TA from the fibres. Scanning Electron Microscopy (SEM) The fibre morphology was assessed through scanning electron microscopy (SEM). All SEM images were acquired by collecting secondary electrons on a Hitachi 3030TM (Japan) with the acceleration voltage of 15 kV. Samples were coated with a 4 nm platinum layer using a sputter coater. Attenuated Total Reflectance Infrared Microscopy (ATR-FTIR) The attenuated total reflectance (ATR) spectra of hydrolysed fibres and blanks was recorded on the surface of single fibres in the spectral range of 4000 to 600 cm − 1 using a FTIR microscope (Bruker Lumos FTIR Microscope, Bruker Optik GmbH, Ettlingen, Germany) with a resolution of 2 cm − 1 and 64 scans per measurement. The ATR stage was equipped with a Ge crystal and a MCT (HgCdTe) detector cooled with LN 2 . The Ge crystal can be positioned directly on different positions of a single fibre for ATR measurement. The setting accuracy of the microscope is 0.1 µm. The spectra are normalised by min-max values over the spectral range from 4000 to 600 cm − 1 . A total of 3 measurements were performed per sample. Differential Scanning Calorimetry (DSC) Thermal analysis of modified fibres and control blanks was performed on a differential scanning calorimeter (DSC3, Mettler Toledo, USA) on about 5 mg specimen encased in 100 µL aluminium crucibles with a pierced lid, under 50 mL min − 1 nitrogen flow in the temperature range between − 50°C and 300°C, at heating and cooling rate of 10 K min − 1 . A total of 3 measurements were performed per sample, and the results were analysed with the on-board evaluation software (Mettler STARe, Version 16.00). Declarations Acknowledgements We are grateful to the State Government of Vorarlberg for the financial support (Project Nr. IIb-17.04-96). 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Polym Degrad Stab 234:111225. https://doi.org/10.1016/j.polymdegradstab.2025.111225 Cite Share Download PDF Status: Published Journal Publication published 18 Aug, 2025 Read the published version in Monatshefte für Chemie - Chemical Monthly → Version 1 posted Reviewers agreed at journal 16 May, 2025 Reviewers invited by journal 30 Apr, 2025 Editor assigned by journal 25 Apr, 2025 First submitted to journal 22 Apr, 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. We do this by developing innovative software and high quality services for the global research community. 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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-6502055","acceptedTermsAndConditions":true,"allowDirectSubmit":false,"archivedVersions":[],"articleType":"Research Article","associatedPublications":[],"authors":[{"id":450077736,"identity":"9ed6e437-8a6c-4dc1-8519-355eb8c6511b","order_by":0,"name":"Huong Lan Nguyen","email":"","orcid":"","institution":"Universitat Innsbruck","correspondingAuthor":false,"prefix":"","firstName":"Huong","middleName":"Lan","lastName":"Nguyen","suffix":""},{"id":450077737,"identity":"c298d4ea-0497-4411-a761-41e395dc81d3","order_by":1,"name":"Sandra Eberle","email":"","orcid":"","institution":"Universitat Innsbruck","correspondingAuthor":false,"prefix":"","firstName":"Sandra","middleName":"","lastName":"Eberle","suffix":""},{"id":450077738,"identity":"7b076fd4-1fb9-497d-8f13-2eaeb365944c","order_by":2,"name":"Thomas Bechtold","email":"","orcid":"","institution":"Universitat Innsbruck","correspondingAuthor":false,"prefix":"","firstName":"Thomas","middleName":"","lastName":"Bechtold","suffix":""},{"id":450077739,"identity":"3101e9ff-818b-47b7-bfd1-3642533c01bc","order_by":3,"name":"Simone Weinberger","email":"","orcid":"","institution":"BOKU: Universitat fur Bodenkultur Wien","correspondingAuthor":false,"prefix":"","firstName":"Simone","middleName":"","lastName":"Weinberger","suffix":""},{"id":450077740,"identity":"d0572089-1bf8-4418-b4c0-155e3326cfe7","order_by":4,"name":"Filippo Fabbri","email":"","orcid":"","institution":"BOKU: Universitat fur Bodenkultur Wien","correspondingAuthor":false,"prefix":"","firstName":"Filippo","middleName":"","lastName":"Fabbri","suffix":""},{"id":450077741,"identity":"e6b5d810-cdca-4b0a-befc-4e7236287418","order_by":5,"name":"Alessandro Pellis","email":"","orcid":"","institution":"Universita degli Studi di Genova","correspondingAuthor":false,"prefix":"","firstName":"Alessandro","middleName":"","lastName":"Pellis","suffix":""},{"id":450077742,"identity":"bc5f5e47-2fde-45db-8000-35719a575a51","order_by":6,"name":"Georg M. Guebitz","email":"","orcid":"","institution":"BOKU: Universitat fur Bodenkultur Wien","correspondingAuthor":false,"prefix":"","firstName":"Georg","middleName":"M.","lastName":"Guebitz","suffix":""},{"id":450077743,"identity":"77dff851-7df7-4f96-aeb7-a73d38d92c83","order_by":7,"name":"Tung Pham","email":"data:image/png;base64,iVBORw0KGgoAAAANSUhEUgAAAZAAAAAyAQMAAABI0h/eAAAABlBMVEX///8AAABVwtN+AAAACXBIWXMAAA7EAAAOxAGVKw4bAAAA3klEQVRIie3RsQrCMBCA4QuFdgm4ZusTCC2COCh9FUuhU5X6Bp3s6BrfoiAEx8KBLnmAig6d1MGh4gsYHXRLOwrmX276uIMDMJl+txLAyQBfszX6IbT8EJJ1I2wKVicSsBleyfbk9tc3H1MJbi+zLrV2C5vHIyLPvjgmHvIKfF7avv4wlgw9skTyJrQBUgB0I4E4yDcJCnDubWRQKxKKiipSQVgAbdkib0MIJUZCxilyySKOdMF1xMmTQXPf4kTscfNId+PJKs+LRkdUNgu/hzBQ32nNavSvM5lMpr/vCc3nUkkg1840AAAAAElFTkSuQmCC","orcid":"https://orcid.org/0000-0001-9957-0553","institution":"Universitat Innsbruck","correspondingAuthor":true,"prefix":"","firstName":"Tung","middleName":"","lastName":"Pham","suffix":""}],"badges":[],"createdAt":"2025-04-22 08:28:57","currentVersionCode":1,"declarations":"","doi":"10.21203/rs.3.rs-6502055/v1","doiUrl":"https://doi.org/10.21203/rs.3.rs-6502055/v1","draftVersion":[],"editorialEvents":[{"content":"https://doi.org/10.1007/s00706-025-03368-8","type":"published","date":"2025-08-18T16:29:31+00:00"}],"editorialNote":"","failedWorkflow":false,"files":[{"id":82272231,"identity":"1f333fa1-15ae-4a47-940f-1bd3018cff76","added_by":"auto","created_at":"2025-05-08 14:23:10","extension":"png","order_by":1,"title":"Figure 1","display":"","copyAsset":false,"role":"figure","size":63765,"visible":true,"origin":"","legend":"\u003cp\u003eMonomer release as a function of incubation time of PBAT (Note that no detectable TA release was observed for PET after 168 h). Bar chart shows average values ± standard deviation.\u003c/p\u003e","description":"","filename":"1.png","url":"https://assets-eu.researchsquare.com/files/rs-6502055/v1/8d4af7abcb84a8fe9b3f13d3.png"},{"id":82272238,"identity":"bd234ca0-77c4-41be-ab4a-29c33ccd3df2","added_by":"auto","created_at":"2025-05-08 14:23:10","extension":"png","order_by":2,"title":"Figure 2","display":"","copyAsset":false,"role":"figure","size":393776,"visible":true,"origin":"","legend":"\u003cp\u003eRepresentative SEM images of PBAT fibres after hydrolysis of up to 168 h and blank (60 × magnification).\u003c/p\u003e","description":"","filename":"floatimage2.png","url":"https://assets-eu.researchsquare.com/files/rs-6502055/v1/253cf0f58b81872fd6ab03c6.png"},{"id":82272245,"identity":"733729ea-d25c-491c-992e-a376b55ee8de","added_by":"auto","created_at":"2025-05-08 14:23:10","extension":"png","order_by":3,"title":"Figure 3","display":"","copyAsset":false,"role":"figure","size":286802,"visible":true,"origin":"","legend":"\u003cp\u003eRepresentative SEM images of PET fibres after hydrolysis up to 168 h and blank (500 × magnification).\u003c/p\u003e","description":"","filename":"floatimage3.png","url":"https://assets-eu.researchsquare.com/files/rs-6502055/v1/9b6bee424619e74403006a82.png"},{"id":82272229,"identity":"1f417051-8bbd-4815-b5b8-7a98237c0fe0","added_by":"auto","created_at":"2025-05-08 14:23:10","extension":"png","order_by":4,"title":"Figure 4","display":"","copyAsset":false,"role":"figure","size":1850590,"visible":true,"origin":"","legend":"\u003cp\u003eRepresentative IR spectra of PET fibres after extended hydrolysis up to 552 h (a) and PBAT fibres after hydrolysis up to 6 h (b) (min-max normalised).\u003c/p\u003e","description":"","filename":"floatimage4.png","url":"https://assets-eu.researchsquare.com/files/rs-6502055/v1/df45dcdbf695f6db4a2f71e8.png"},{"id":82273861,"identity":"0232998d-de7a-47d7-ba70-66510ef05f8d","added_by":"auto","created_at":"2025-05-08 14:31:10","extension":"png","order_by":5,"title":"Figure 5","display":"","copyAsset":false,"role":"figure","size":1365140,"visible":true,"origin":"","legend":"\u003cp\u003eRepresentative DSC curves for PET (a) and PBAT (b). Red: heating run, blue: cooling run.\u003c/p\u003e","description":"","filename":"floatimage5.png","url":"https://assets-eu.researchsquare.com/files/rs-6502055/v1/1f052afb10dd9f6c20a91e5f.png"},{"id":89847310,"identity":"0afb0ace-037b-4b6d-9ef4-8b38bda35365","added_by":"auto","created_at":"2025-08-25 16:43:06","extension":"pdf","order_by":0,"title":"","display":"","copyAsset":false,"role":"manuscript-pdf","size":4634041,"visible":true,"origin":"","legend":"","description":"","filename":"manuscript.pdf","url":"https://assets-eu.researchsquare.com/files/rs-6502055/v1/3b7bf88f-c278-4910-bf56-c357124f5387.pdf"}],"financialInterests":"","formattedTitle":"\u003cp\u003eEnzyme catalysed degradation of polyester fibres – A comparative study between poly(ethylene terephthalate) and poly(butylene adipate-\u003cem\u003eco\u003c/em\u003e-terephthalate)\u003c/p\u003e","fulltext":[{"header":"Introduction","content":"\u003cp\u003eWithin the textile industry, polyester fibre takes the major share of around 55% of the global fibre volume due to its economically viable production and excellent durability [\u003cspan citationid=\"CR1\" class=\"CitationRef\"\u003e1\u003c/span\u003e]. With a volume of around 70\u0026nbsp;million metric tons, poly(ethylene terephthalate) (PET) fibre however is considered as one of the sources of plastic pollution to the environment. As an estimation, the total sum of synthetic polymer waste up to 26\u0026nbsp;million tons reach the oceans per year [\u003cspan citationid=\"CR2\" class=\"CitationRef\"\u003e2\u003c/span\u003e]. Consequently, biodegradable polymers are attractive materials because they will disappear in nature due to decomposition by extracellular enzymes from bacteria and fungi followed by cell-uptake and biodegradation. Finally, the polymers are transformed into water, carbon dioxide, biomass and inorganic salts [\u003cspan citationid=\"CR3\" class=\"CitationRef\"\u003e3\u003c/span\u003e]. Therefore, the industry is more and more interested in the use of biodegradable polymers, partly because different governments put some pressure to induce a change to biodegradable polymers. Currently, the world production of polymers is around 400\u0026nbsp;million tons per year with a meagre 2% that is constituted by biodegradable polymers [\u003cspan citationid=\"CR4\" class=\"CitationRef\"\u003e4\u003c/span\u003e]. More than 80% of the global production of biodegradable polymers can be attributed to the production of starch blends, poly(lactic acid) (PLA) and poly(butylene adipate-\u003cem\u003eco\u003c/em\u003e-terephthalate) (PBAT).\u003c/p\u003e \u003cp\u003eBeing a copolymer, PBAT shows the most distinct difference compared to the widely used PET with regard to their use as fibres in textile application. While PET fibre is regarded as high strength and durable, PBAT fibre exhibits higher softness and elasticity.\u003c/p\u003e \u003cp\u003eThe utilisation of enzymes for treating textile fibres and fabrics has been explored since decades due to the sustainable aspect of white biotechnology approaches over conventional chemical treatment techniques [\u003cspan citationid=\"CR5\" class=\"CitationRef\"\u003e5\u003c/span\u003e]. Recently, the use of enzyme to depolymerise PET is receiving increased attention [\u003cspan additionalcitationids=\"CR7 CR8\" citationid=\"CR6\" class=\"CitationRef\"\u003e6\u003c/span\u003e\u0026ndash;\u003cspan citationid=\"CR9\" class=\"CitationRef\"\u003e9\u003c/span\u003e]. Several studies have demonstrated the hydrolytic capacities of hydrolases, including esterases, lipases, and cutinases towards polyester [\u003cspan citationid=\"CR10\" class=\"CitationRef\"\u003e10\u003c/span\u003e, \u003cspan citationid=\"CR11\" class=\"CitationRef\"\u003e11\u003c/span\u003e]. Among these enzymes, cutinases are of particular interest since they are efficient biocatalysts for carrying out the hydrolytic processing of various aliphatic and aromatic polyesters [\u003cspan citationid=\"CR12\" class=\"CitationRef\"\u003e12\u003c/span\u003e, \u003cspan citationid=\"CR13\" class=\"CitationRef\"\u003e13\u003c/span\u003e]. With regards to PBAT, some recent studies on the enzymatic hydrolysis with \u003cem\u003eFusarium solani\u003c/em\u003e cutinase, \u003cem\u003eCandida antarctica\u003c/em\u003e lipase B and \u003cem\u003eStenotrophomonas\u003c/em\u003e sp.YCJ1 using PBAT films indicated fast degradation [\u003cspan additionalcitationids=\"CR15\" citationid=\"CR14\" class=\"CitationRef\"\u003e14\u003c/span\u003e\u0026ndash;\u003cspan citationid=\"CR16\" class=\"CitationRef\"\u003e16\u003c/span\u003e].\u003c/p\u003e \u003cp\u003eIn this work we investigated the influence of the polymer structure (aromatic polyester versus aromatic-aliphatic copolyester) on the enzymatic hydrolysis using a cutinase from \u003cem\u003eHumicola insolens\u003c/em\u003e (HiC). By combining different characterisation techniques, the structural changes of the fibres as a result of the enzyme catalysed hydrolysis are investigated and discussed. The gained new insight into the selective hydrolysis of the fibres helps to better understand the mechanism and thus, to achieve the controlled enzymatic decomposition of different polyester fibres.\u003c/p\u003e"},{"header":"Results and Discussion","content":"\u003cdiv id=\"Sec3\" class=\"Section2\"\u003e \u003ch2\u003eMonomer release and fibre morphology\u003c/h2\u003e \u003cp\u003eThe conditions for the enzymatic hydrolysis of polyester fibres were evaluated in experiments based on the data previously reported [\u003cspan citationid=\"CR13\" class=\"CitationRef\"\u003e13\u003c/span\u003e]. In the first series with a small sample quantity of 10 mg fibres, the incubation time was chosen between 24 and 168 h.\u003c/p\u003e \u003cp\u003eDue to enzymatic scission of the ester bonds, terephthalic acid (TA) was released. While the trend for PBAT is clear, i.e., increased TA release by increasing incubation time (Fig.\u0026nbsp;\u003cspan refid=\"Fig2\" class=\"InternalRef\"\u003e1\u003c/span\u003e), enzymatic hydrolysis for PET is neglectable as no detectable TA release was observed even after 168 h of reaction (0,008 mM TA value). Under identical conditions, no measurable TA release of the blank samples was observed for the control of both PBAT and PET.\u003c/p\u003e \u003cp\u003e \u003c/p\u003e \u003cp\u003eConsidering the hypothesis of enzyme action modes as postulated in [\u003cspan citationid=\"CR17\" class=\"CitationRef\"\u003e17\u003c/span\u003e] that the hydrolysis starts with an endo-type (independent of the initial polymer microstructure), followed by an exo-type chain scission in the mobile amorphous fraction (MAF) and release of hydrolysis products, the mechanism can be taken to well explain the hydrolysis behaviour of PBAT (low crystallinity, i.e. high MAF proportion, see DSC results).\u003c/p\u003e \u003cp\u003e \u003c/p\u003e \u003cp\u003eIn case of PET fibre with higher crystallinity, where neighbouring ester bonds in crystalline PET and in rigid amorphous fraction (RAF) are often not accessible to the enzyme, the explanation according to the hypothesis in [\u003cspan citationid=\"CR17\" class=\"CitationRef\"\u003e17\u003c/span\u003e] would be that in a first phase hydrolysis of the accessible mobile amorphous fraction MAF of PET by a combination of endo- and exo-type chain scissions would take place. Subsequently, the enzyme further catalysed only endo-type chain scissions in the less hydrolysis-susceptible RAF or crystalline microstructures of PET, but at a much lower rate. Considering the results obtained for PET i.e., no observable hydrolysis products at the set reaction conditions, the assumption can be made that no exo-type chain scission (or only very little) took place in PET fibres.\u003c/p\u003e \u003cp\u003e \u003c/p\u003e \u003cp\u003e \u003c/p\u003e \u003cp\u003eWith regard to fibre morphology, progress of the enzymatic hydrolysis was visualised through SEM imaging of the fibres after different incubation times for both PBAT (Fig.\u0026nbsp;\u003cspan refid=\"Fig5\" class=\"InternalRef\"\u003e2\u003c/span\u003e) and PET (Fig.\u0026nbsp;\u003cspan refid=\"Fig4\" class=\"InternalRef\"\u003e3\u003c/span\u003e). The blank PBAT and PET fibres still exhibited a rather smooth surface after incubation for 168 hours in buffer solution without enzyme (blanks). In the presence of the enzyme, already after 24 h hydrolysis, the PBAT fibre structure was completely destroyed and only few residues in form of stripes (no fibre) could be collected on the filter (Fig.\u0026nbsp;\u003cspan refid=\"Fig5\" class=\"InternalRef\"\u003e2\u003c/span\u003e). This is well in line with the release of TA from PBAT discussed above. In case of PET fibres, the fibre shape almost remains and no change in fibre diameter was observed (Fig.\u0026nbsp;\u003cspan refid=\"Fig4\" class=\"InternalRef\"\u003e3\u003c/span\u003e). The small deformation of some PET fibres could be due to mechanical agitation (at 65\u0026deg;C) during the incubation as well as fibre inhomogeneity. This observation also fits well to the non-detectable TA release of PET fibre after 168 h hydrolysis.\u003c/p\u003e \u003cp\u003e \u003c/p\u003e \u003cp\u003eIn the first series with 10 mg samples, we observed that PET remained unchanged after 168 h of incubation while PBAT almost disappeared after 24 h hydrolysis. Thus, a second series with higher fibre amount of 500 mg was carried out. For PET fibre, the incubation time was extended up to 552 h and for PBAT fibre, shorter incubation time between 2 and 6 h was chosen. Table\u0026nbsp;\u003cspan refid=\"Tab1\" class=\"InternalRef\"\u003e1\u003c/span\u003e\u003c/p\u003e \u003cp\u003e \u003cdiv class=\"gridtable\"\u003e\u003ctable float=\"Yes\" id=\"Tab1\" border=\"1\"\u003e \u003ccaption language=\"En\"\u003e \u003cdiv class=\"CaptionNumber\"\u003eTable 1\u003c/div\u003e \u003cdiv class=\"CaptionContent\"\u003e \u003cp\u003eMonomer release as results of enzymatic hydrolysis of PBAT and PET fibres with the fibre/solution ratio 500 mg : 100 mL.\u003c/p\u003e \u003c/div\u003e \u003c/caption\u003e \u003ccolgroup cols=\"3\"\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=\"char\" char=\"\u0026plusmn;\" class=\"colspec\" colname=\"c3\" colnum=\"3\"\u003e\u003c/div\u003e \u003cthead\u003e \u003ctr\u003e \u003cth align=\"left\" colname=\"c1\"\u003e \u003cp\u003eIncubation time\u003c/p\u003e \u003cp\u003e/ h\u003c/p\u003e \u003c/th\u003e \u003cth align=\"left\" colname=\"c2\"\u003e \u003cp\u003e(PBAT) TA release\u003c/p\u003e \u003cp\u003e/ mM\u003c/p\u003e \u003c/th\u003e \u003cth align=\"left\" colname=\"c3\"\u003e \u003cp\u003e(PET) TA release\u003c/p\u003e \u003cp\u003e/ mM\u003c/p\u003e \u003c/th\u003e \u003c/tr\u003e \u003c/thead\u003e \u003ctbody\u003e \u003ctr\u003e \u003ctd align=\"left\" colname=\"c1\"\u003e \u003cp\u003e2\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c2\"\u003e \u003cp\u003enot detectable\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c3\"\u003e\u0026nbsp;\u003c/td\u003e \u003c/tr\u003e \u003ctr\u003e \u003ctd align=\"left\" colname=\"c1\"\u003e \u003cp\u003e4\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c2\"\u003e \u003cp\u003e0.010\u0026thinsp;\u0026plusmn;\u0026thinsp;0.001\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c3\"\u003e\u0026nbsp;\u003c/td\u003e \u003c/tr\u003e \u003ctr\u003e \u003ctd align=\"left\" colname=\"c1\"\u003e \u003cp\u003e6\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c2\"\u003e \u003cp\u003e0.506\u0026thinsp;\u0026plusmn;\u0026thinsp;0.023\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c3\"\u003e\u0026nbsp;\u003c/td\u003e \u003c/tr\u003e \u003ctr\u003e \u003ctd align=\"left\" colname=\"c1\"\u003e \u003cp\u003e216\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c2\"\u003e\u0026nbsp;\u003c/td\u003e \u003ctd align=\"char\" char=\"\u0026plusmn;\" colname=\"c3\"\u003e \u003cp\u003e0.011\u0026thinsp;\u0026plusmn;\u0026thinsp;0.001\u003c/p\u003e \u003c/td\u003e \u003c/tr\u003e \u003ctr\u003e \u003ctd align=\"left\" colname=\"c1\"\u003e \u003cp\u003e384\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c2\"\u003e\u0026nbsp;\u003c/td\u003e \u003ctd align=\"char\" char=\"\u0026plusmn;\" colname=\"c3\"\u003e \u003cp\u003e0.015\u0026thinsp;\u0026plusmn;\u0026thinsp;0.001\u003c/p\u003e \u003c/td\u003e \u003c/tr\u003e \u003ctr\u003e \u003ctd align=\"left\" colname=\"c1\"\u003e \u003cp\u003e552\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c2\"\u003e\u0026nbsp;\u003c/td\u003e \u003ctd align=\"char\" char=\"\u0026plusmn;\" colname=\"c3\"\u003e \u003cp\u003e0.036\u0026thinsp;\u0026plusmn;\u0026thinsp;0.001\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\u003eIt can be observed that a concentration of ca. 0.5 mM TA was released after 6 h of PBAT hydrolysis, which is comparable to between 96 and 168 h hydrolysis at smaller scale (10 mg : 1 mL fibre/solution ratio, Fig.\u0026nbsp;\u003cspan refid=\"Fig2\" class=\"InternalRef\"\u003e1\u003c/span\u003e). The difference can be explained by the different mass transfer occurring in the two reaction set-ups. Furthermore, while for the small-scale reaction 10 mg of fibres per mL (ratio 10:1) of solution was used, the ratio of 5:1 for the large-scale reaction led to higher enzyme density, i.e., 2-fold higher amount of active enzyme molecules over the fibre surface area unit at the bigger scale experiments. Combining with the orbital shaking of the reaction flasks, large-scale hydrolysis seemed to be more efficient. In case of PET fibre, the extended incubation time up to 552 h in large-scale setup also led to higher TA release up to 0.036 mM. However, TA release of PET fibre is still much lower by an order of magnitude when compared to PBAT fibre.\u003c/p\u003e \u003cp\u003eThe higher fibre amount was also intended for later analysis by ATR and DSC.\u003c/p\u003e \u003c/div\u003e\n\u003ch3\u003eATR-FTIR investigation\u003c/h3\u003e\n\u003cp\u003eFTIR microscopy was applied in ATR mode to investigate possible changes in chemical structure of the fibre after hydrolysis. In this measurement technique, the ATR diamond is positioned directly on the surface of a single fibre, enabling a lateral resolution of 3\u0026ndash;5 \u0026micro;m of the measurement, which is far lower than conventional transmission FTIR techniques would allow [\u003cspan citationid=\"CR18\" class=\"CitationRef\"\u003e18\u003c/span\u003e].\u003c/p\u003e \u003cp\u003e \u003c/p\u003e \u003cp\u003eIn Fig.\u0026nbsp;\u003cspan refid=\"Fig6\" class=\"InternalRef\"\u003e4\u003c/span\u003e the IR spectra of enzymatically hydrolysed fibres and blanks are shown. For PET fibres (Fig.\u0026nbsp;\u003cspan refid=\"Fig6\" class=\"InternalRef\"\u003e4\u003c/span\u003ea\u003cb\u003e)\u003c/b\u003e, it can be observed that all spectra are almost identical and show typical absorption peaks at 2970 cm\u003csup\u003e\u0026minus;\u0026thinsp;1\u003c/sup\u003e (CH stretching), 1715 cm\u003csup\u003e\u0026minus;\u0026thinsp;1\u003c/sup\u003e (C\u0026thinsp;=\u0026thinsp;O stretching) 1245 cm\u003csup\u003e\u0026minus;\u0026thinsp;1\u003c/sup\u003e (C-C-O stretching) and 1097 cm\u003csup\u003e\u0026minus;\u0026thinsp;1\u003c/sup\u003e (O-C-C stretching of aromatic ester). Depending on the thermal and mechanical history, e.g., quenching, annealing and subsequently drawn, differences are observed due to configuration of the ethylene glycol group and also phenylene carbonyl bonds (cis/trans conformers). Many of these absorption bands are split being associated with differences in the force field between amorphous and crystalline regions and also with the chain conformation around the glycol ester configuration [\u003cspan citationid=\"CR19\" class=\"CitationRef\"\u003e19\u003c/span\u003e]. Theoretically, as result of the polymer hydrolysis, shorter polyester chains are formed and thus, the number of end groups (-COOH and -OH) was expected to increase. However, unlike to the results reported in the literature for PET annealing [\u003cspan citationid=\"CR19\" class=\"CitationRef\"\u003e19\u003c/span\u003e] or alkali hydrolysis [\u003cspan citationid=\"CR20\" class=\"CitationRef\"\u003e20\u003c/span\u003e], we did not record any observable changes, either in the 1715 cm\u003csup\u003e\u0026minus;\u0026thinsp;1\u003c/sup\u003e (C\u0026thinsp;=\u0026thinsp;O stretching) region nor in the 2970 cm\u003csup\u003e\u0026minus;\u0026thinsp;1\u003c/sup\u003e (CH stretching) region. This observation, however, fits well to the results reported on the enzymatically hydrolysed PET fibres with different draw ratio in our earlier study [\u003cspan citationid=\"CR13\" class=\"CitationRef\"\u003e13\u003c/span\u003e].\u003c/p\u003e \u003cp\u003eFor PBAT fibres, the situation looks different (Fig.\u0026nbsp;\u003cspan refid=\"Fig6\" class=\"InternalRef\"\u003e4\u003c/span\u003eb, Table\u0026nbsp;\u003cspan refid=\"Tab2\" class=\"InternalRef\"\u003e2\u003c/span\u003e) with an increase of the peak intensity at 2961 cm\u003csup\u003e\u0026minus;\u0026thinsp;1\u003c/sup\u003e (CH stretching) and decrease of the peak intensity at 1712 cm\u003csup\u003e\u0026minus;\u0026thinsp;1\u003c/sup\u003e (C\u0026thinsp;=\u0026thinsp;O stretching). The results fit well with the study on alkaline hydrolysis of PET in KOH at 90\u0026deg;C [\u003cspan citationid=\"CR20\" class=\"CitationRef\"\u003e20\u003c/span\u003e] as well as with the results of the enzymatic hydrolysis of PBAT film reported in [\u003cspan citationid=\"CR14\" class=\"CitationRef\"\u003e14\u003c/span\u003e, \u003cspan citationid=\"CR16\" class=\"CitationRef\"\u003e16\u003c/span\u003e].\u003c/p\u003e \u003cp\u003eFurthermore, increases of peak intensity at 1341 cm\u003csup\u003e\u0026minus;\u0026thinsp;1\u003c/sup\u003e could be observed which is associated with -CH\u003csub\u003e2\u003c/sub\u003e wagging and at 1471 cm\u003csup\u003e\u0026minus;\u0026thinsp;1\u003c/sup\u003e, attributed to the bending mode of the trans rotational isomer. A similar trend was reported for an annealing study of PET, indicating higher crystallinity [\u003cspan citationid=\"CR19\" class=\"CitationRef\"\u003e19\u003c/span\u003e].\u003c/p\u003e \u003cp\u003e \u003cdiv class=\"gridtable\"\u003e\u003ctable float=\"Yes\" id=\"Tab2\" border=\"1\"\u003e \u003ccaption language=\"En\"\u003e \u003cdiv class=\"CaptionNumber\"\u003eTable 2\u003c/div\u003e \u003cdiv class=\"CaptionContent\"\u003e \u003cp\u003eRelative peak intensity of different vibration bands of PBAT fibres after enzymatic hydrolysis and blank (min-max normalised spectra).\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=\"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 \u003cdiv align=\"char\" char=\"\u0026plusmn;\" class=\"colspec\" colname=\"c5\" colnum=\"5\"\u003e\u003c/div\u003e \u003cthead\u003e \u003ctr\u003e \u003cth align=\"left\" colname=\"c1\"\u003e \u003cp\u003eIncubation\u003c/p\u003e \u003cp\u003e/ h\u003c/p\u003e \u003c/th\u003e \u003cth align=\"left\" colname=\"c2\"\u003e \u003cp\u003e2961 cm\u003csup\u003e\u0026minus;\u0026thinsp;1\u003c/sup\u003e\u003c/p\u003e \u003cp\u003e/ a.u\u003c/p\u003e \u003c/th\u003e \u003cth align=\"left\" colname=\"c3\"\u003e \u003cp\u003e1712 cm\u003csup\u003e\u0026minus;\u0026thinsp;1\u003c/sup\u003e\u003c/p\u003e \u003cp\u003e/ a.u\u003c/p\u003e \u003c/th\u003e \u003cth align=\"left\" colname=\"c4\"\u003e \u003cp\u003e1471 cm\u003csup\u003e\u0026minus;\u0026thinsp;1\u003c/sup\u003e\u003c/p\u003e \u003cp\u003e/ a.u\u003c/p\u003e \u003c/th\u003e \u003cth align=\"left\" colname=\"c5\"\u003e \u003cp\u003e1341 cm\u003csup\u003e\u0026minus;\u0026thinsp;1\u003c/sup\u003e\u003c/p\u003e \u003cp\u003e/ a.u\u003c/p\u003e \u003c/th\u003e \u003c/tr\u003e \u003c/thead\u003e \u003ctbody\u003e \u003ctr\u003e \u003ctd align=\"left\" colname=\"c1\"\u003e \u003cp\u003eblank\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\"\u0026plusmn;\" colname=\"c2\"\u003e \u003cp\u003e0.26\u0026thinsp;\u0026plusmn;\u0026thinsp;0.03\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\"\u0026plusmn;\" colname=\"c3\"\u003e \u003cp\u003e2.00\u0026thinsp;\u0026plusmn;\u0026thinsp;0.01\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\"\u0026plusmn;\" colname=\"c4\"\u003e \u003cp\u003e0.27\u0026thinsp;\u0026plusmn;\u0026thinsp;0.03\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\"\u0026plusmn;\" colname=\"c5\"\u003e \u003cp\u003e0.24\u0026thinsp;\u0026plusmn;\u0026thinsp;0.02\u003c/p\u003e \u003c/td\u003e \u003c/tr\u003e \u003ctr\u003e \u003ctd align=\"left\" colname=\"c1\"\u003e \u003cp\u003e2\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\"\u0026plusmn;\" colname=\"c2\"\u003e \u003cp\u003e0.27\u0026thinsp;\u0026plusmn;\u0026thinsp;0.04\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\"\u0026plusmn;\" colname=\"c3\"\u003e \u003cp\u003e1.93\u0026thinsp;\u0026plusmn;\u0026thinsp;0.11\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\"\u0026plusmn;\" colname=\"c4\"\u003e \u003cp\u003e0.19\u0026thinsp;\u0026plusmn;\u0026thinsp;0.01\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\"\u0026plusmn;\" colname=\"c5\"\u003e \u003cp\u003e0.22\u0026thinsp;\u0026plusmn;\u0026thinsp;0.03\u003c/p\u003e \u003c/td\u003e \u003c/tr\u003e \u003ctr\u003e \u003ctd align=\"left\" colname=\"c1\"\u003e \u003cp\u003e4\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\"\u0026plusmn;\" colname=\"c2\"\u003e \u003cp\u003e0.23\u0026thinsp;\u0026plusmn;\u0026thinsp;0.02\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\"\u0026plusmn;\" colname=\"c3\"\u003e \u003cp\u003e1.91\u0026thinsp;\u0026plusmn;\u0026thinsp;0.02\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\"\u0026plusmn;\" colname=\"c4\"\u003e \u003cp\u003e0.18\u0026thinsp;\u0026plusmn;\u0026thinsp;0.01\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\"\u0026plusmn;\" colname=\"c5\"\u003e \u003cp\u003e0.19\u0026thinsp;\u0026plusmn;\u0026thinsp;0.02\u003c/p\u003e \u003c/td\u003e \u003c/tr\u003e \u003ctr\u003e \u003ctd align=\"left\" colname=\"c1\"\u003e \u003cp\u003e6\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\"\u0026plusmn;\" colname=\"c2\"\u003e \u003cp\u003e1.26\u0026thinsp;\u0026plusmn;\u0026thinsp;0.02\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\"\u0026plusmn;\" colname=\"c3\"\u003e \u003cp\u003e1.21\u0026thinsp;\u0026plusmn;\u0026thinsp;0.12\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\"\u0026plusmn;\" colname=\"c4\"\u003e \u003cp\u003e0.55\u0026thinsp;\u0026plusmn;\u0026thinsp;0.03\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\"\u0026plusmn;\" colname=\"c5\"\u003e \u003cp\u003e0.38\u0026thinsp;\u0026plusmn;\u0026thinsp;0.03\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\u003eIt is worth noticing that the increases and decreases reported above are best observed when comparing PBAT fibres after 6 h of enzymatic hydrolysis with blank samples. The very fast hydrolysis (TA release between no detectable after 2 h and 0.5 mM) could be the reason for the variation of the results between samples after 2 and 4 h hydrolysis. Furthermore, blank PBAT fibre also underwent 6 h incubation without enzyme at 65\u0026deg;C and therefore, some annealing effect could also be the reason for the difference compared to samples after 2 and 4 h hydrolysis.\u003c/p\u003e \u003cp\u003eComparing the FTIR results between PET and PBAT, we can conclude that PBAT fibres are much more susceptible to enzymatic hydrolysis than PET, most likely due to the lower crystallinity of PBAT apart from the different chemical structure. This observation is further supported by the XRD investigation on enzymatic hydrolysed PBAT [\u003cspan citationid=\"CR14\" class=\"CitationRef\"\u003e14\u003c/span\u003e, \u003cspan citationid=\"CR16\" class=\"CitationRef\"\u003e16\u003c/span\u003e].\u003c/p\u003e\n\u003ch3\u003eDSC thermal analysis\u003c/h3\u003e\n\u003cp\u003eTo further investigate the hypothesis that hydrolysis preferably takes place at the amorphous part of the polymer fibres, thermal analysis investigation of the PET fibres was carried out using differential scanning calorimetry measurements (DSC). While the first heating run provides information on the original state of the fibre residue after hydrolysis, considering the fibre structure, the cooling run describes the crystallisation behaviour of the polymer from the melted state. Thus, data are collected for first heating and cooling runs (Fig.\u0026nbsp;\u003cspan refid=\"Fig7\" class=\"InternalRef\"\u003e5\u003c/span\u003e, Tables\u0026nbsp;\u003cspan refid=\"Tab3\" class=\"InternalRef\"\u003e3\u003c/span\u003e and \u003cspan refid=\"Tab4\" class=\"InternalRef\"\u003e4\u003c/span\u003e).\u003c/p\u003e \u003cp\u003e \u003c/p\u003e \u003cp\u003e \u003cdiv class=\"gridtable\"\u003e\u003ctable float=\"Yes\" id=\"Tab3\" border=\"1\"\u003e \u003ccaption language=\"En\"\u003e \u003cdiv class=\"CaptionNumber\"\u003eTable 3\u003c/div\u003e \u003cdiv class=\"CaptionContent\"\u003e \u003cp\u003eMelting enthalpy \u003cem\u003eΔH\u003c/em\u003e\u003csub\u003e\u003cem\u003em\u003c/em\u003e\u003c/sub\u003e and crystallisation enthalpy \u003cem\u003eΔH\u003c/em\u003e\u003csub\u003e\u003cem\u003ec\u003c/em\u003e\u003c/sub\u003e of enzymatic hydrolysed PET fibres and blank.\u003c/p\u003e \u003c/div\u003e \u003c/caption\u003e \u003ccolgroup cols=\"3\"\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 \u003cthead\u003e \u003ctr\u003e \u003cth align=\"left\" colname=\"c1\"\u003e \u003cp\u003eIncubation\u003c/p\u003e \u003cp\u003e/ h\u003c/p\u003e \u003c/th\u003e \u003cth align=\"left\" colname=\"c2\"\u003e \u003cp\u003e\u003cem\u003eΔH\u003c/em\u003e\u003csub\u003e\u003cem\u003em\u003c/em\u003e\u003c/sub\u003e\u003c/p\u003e \u003cp\u003e/ Jg\u003csup\u003e\u0026minus;\u0026thinsp;1\u003c/sup\u003e\u003c/p\u003e\u003c/th\u003e \u003cth align=\"left\" colname=\"c3\"\u003e \u003cp\u003e\u003cem\u003eΔH\u003c/em\u003e\u003csub\u003e\u003cem\u003ec\u003c/em\u003e\u003c/sub\u003e\u003c/p\u003e \u003cp\u003e/ Jg\u003csup\u003e\u0026minus;\u0026thinsp;1\u003c/sup\u003e\u003c/p\u003e\u003c/th\u003e \u003c/tr\u003e \u003c/thead\u003e \u003ctbody\u003e \u003ctr\u003e \u003ctd align=\"left\" colname=\"c1\"\u003e \u003cp\u003eblank\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\"\u0026plusmn;\" colname=\"c2\"\u003e \u003cp\u003e52.22\u0026thinsp;\u0026plusmn;\u0026thinsp;1.74\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\"\u0026plusmn;\" colname=\"c3\"\u003e \u003cp\u003e43.18\u0026thinsp;\u0026plusmn;\u0026thinsp;0.57\u003c/p\u003e \u003c/td\u003e \u003c/tr\u003e \u003ctr\u003e \u003ctd align=\"left\" colname=\"c1\"\u003e \u003cp\u003e216\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\"\u0026plusmn;\" colname=\"c2\"\u003e \u003cp\u003e55.17\u0026thinsp;\u0026plusmn;\u0026thinsp;2.49\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\"\u0026plusmn;\" colname=\"c3\"\u003e \u003cp\u003e47.88\u0026thinsp;\u0026plusmn;\u0026thinsp;2.29\u003c/p\u003e \u003c/td\u003e \u003c/tr\u003e \u003ctr\u003e \u003ctd align=\"left\" colname=\"c1\"\u003e \u003cp\u003e384\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\"\u0026plusmn;\" colname=\"c2\"\u003e \u003cp\u003e57.34\u0026thinsp;\u0026plusmn;\u0026thinsp;2.59\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\"\u0026plusmn;\" colname=\"c3\"\u003e \u003cp\u003e52.58\u0026thinsp;\u0026plusmn;\u0026thinsp;1.51\u003c/p\u003e \u003c/td\u003e \u003c/tr\u003e \u003ctr\u003e \u003ctd align=\"left\" colname=\"c1\"\u003e \u003cp\u003e552\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\"\u0026plusmn;\" colname=\"c2\"\u003e \u003cp\u003e56.19\u0026thinsp;\u0026plusmn;\u0026thinsp;6.61\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\"\u0026plusmn;\" colname=\"c3\"\u003e \u003cp\u003e52.39\u0026thinsp;\u0026plusmn;\u0026thinsp;4.74\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\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\u003eMelting enthalpy \u003cem\u003eΔH\u003c/em\u003e\u003csub\u003e\u003cem\u003em\u003c/em\u003e\u003c/sub\u003e and crystallisation enthalpy \u003cem\u003eΔH\u003c/em\u003e\u003csub\u003e\u003cem\u003ec\u003c/em\u003e\u003c/sub\u003e of enzymatic hydrolysed PBAT fibres and blank.\u003c/p\u003e \u003c/div\u003e \u003c/caption\u003e \u003ccolgroup cols=\"3\"\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 \u003cthead\u003e \u003ctr\u003e \u003cth align=\"left\" colname=\"c1\"\u003e \u003cp\u003eIncubation\u003c/p\u003e \u003cp\u003e/ h\u003c/p\u003e \u003c/th\u003e \u003cth align=\"left\" colname=\"c2\"\u003e \u003cp\u003e\u003cem\u003eΔH\u003c/em\u003e\u003csub\u003e\u003cem\u003em\u003c/em\u003e\u003c/sub\u003e\u003c/p\u003e \u003cp\u003e/ Jg\u003csup\u003e\u0026minus;\u0026thinsp;1\u003c/sup\u003e\u003c/p\u003e\u003c/th\u003e \u003cth align=\"left\" colname=\"c3\"\u003e \u003cp\u003e\u003cem\u003eΔH\u003c/em\u003e\u003csub\u003e\u003cem\u003ec\u003c/em\u003e\u003c/sub\u003e\u003c/p\u003e \u003cp\u003e/ Jg\u003csup\u003e\u0026minus;\u0026thinsp;1\u003c/sup\u003e\u003c/p\u003e\u003c/th\u003e \u003c/tr\u003e \u003c/thead\u003e \u003ctbody\u003e \u003ctr\u003e \u003ctd align=\"left\" colname=\"c1\"\u003e \u003cp\u003eblank\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\"\u0026plusmn;\" colname=\"c2\"\u003e \u003cp\u003e9.27\u0026thinsp;\u0026plusmn;\u0026thinsp;0.26\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\"\u0026plusmn;\" colname=\"c3\"\u003e \u003cp\u003e18.94\u0026thinsp;\u0026plusmn;\u0026thinsp;0.95\u003c/p\u003e \u003c/td\u003e \u003c/tr\u003e \u003ctr\u003e \u003ctd align=\"left\" colname=\"c1\"\u003e \u003cp\u003e2\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\"\u0026plusmn;\" colname=\"c2\"\u003e \u003cp\u003e10.74\u0026thinsp;\u0026plusmn;\u0026thinsp;0.49\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\"\u0026plusmn;\" colname=\"c3\"\u003e \u003cp\u003e20.81\u0026thinsp;\u0026plusmn;\u0026thinsp;1.11\u003c/p\u003e \u003c/td\u003e \u003c/tr\u003e \u003ctr\u003e \u003ctd align=\"left\" colname=\"c1\"\u003e \u003cp\u003e4\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\"\u0026plusmn;\" colname=\"c2\"\u003e \u003cp\u003e14.51\u0026thinsp;\u0026plusmn;\u0026thinsp;0.93\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\"\u0026plusmn;\" colname=\"c3\"\u003e \u003cp\u003e19.93\u0026thinsp;\u0026plusmn;\u0026thinsp;0.65\u003c/p\u003e \u003c/td\u003e \u003c/tr\u003e \u003ctr\u003e \u003ctd align=\"left\" colname=\"c1\"\u003e \u003cp\u003e6\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\"\u0026plusmn;\" colname=\"c2\"\u003e \u003cp\u003e20.72\u0026thinsp;\u0026plusmn;\u0026thinsp;2.03\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\"\u0026plusmn;\" colname=\"c3\"\u003e \u003cp\u003e20.83\u0026thinsp;\u0026plusmn;\u0026thinsp;3.11\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\u003eWith increased incubation time, the melting enthalpy and crystallisation enthalpy of the both PET and PBAT increases (Tables\u0026nbsp;\u003cspan refid=\"Tab3\" class=\"InternalRef\"\u003e3\u003c/span\u003e and \u003cspan refid=\"Tab4\" class=\"InternalRef\"\u003e4\u003c/span\u003e). The biggest differences are observed between samples with the longest incubation time (552 h for PET and 6h for PBAT, respectively) to the blanks. While the enthalpy \u003cem\u003eΔH\u003c/em\u003e\u003csub\u003e\u003cem\u003em\u003c/em\u003e\u003c/sub\u003e of the first heating increased only slightly for PET after 552 h incubation (56.19 versus 52.22 Jg\u003csup\u003e\u0026minus;\u0026thinsp;1\u003c/sup\u003e), significant higher melting enthalpy was observed for residue of PBAT fibre after 6h hydrolysis compared to it blank (20.72 versus 9.27 Jg\u003csup\u003e\u0026minus;\u0026thinsp;1\u003c/sup\u003e). The big change in melting enthalpy of the fibre residue is well in line with the observed changes in IR peak intensities for PBAT reported above. With regards to PET, we observed in an earlier study that there was no significant changes in melting and crystallisation enthalpy for PET fibre after 168 h incubation, along with very low level of TA release of 0.1 mM [\u003cspan citationid=\"CR13\" class=\"CitationRef\"\u003e13\u003c/span\u003e]. This indicated that an extended incubation to 552 h caused stronger hydrolysis of PET fibre under the same condition. On the crystallisation (cooling run), the situation is different. The DSC results on PBAT fibres only suggest a slight increase in polymer crystallinity (crystallisation enthalpy \u003cem\u003eΔH\u003c/em\u003e\u003csub\u003e\u003cem\u003ec\u003c/em\u003e\u003c/sub\u003e of 20.83 vs. 18.94 Jg\u003csup\u003e\u0026minus;\u0026thinsp;1\u003c/sup\u003e), while \u003cem\u003eΔH\u003c/em\u003e\u003csub\u003e\u003cem\u003ec\u003c/em\u003e\u003c/sub\u003e for PET was increased from 43.18 Jg\u003csup\u003e\u0026minus;\u0026thinsp;1\u003c/sup\u003e (blank) to 52.39 Jg\u003csup\u003e\u0026minus;\u0026thinsp;1\u003c/sup\u003e (552 h incubation). It seemed that the first heating eliminated district thermal history of PET fibre, including fibre orientation and possible annealing effect during incubation. Another possible explanation is that the layer-by-layer enzymatic hydrolysis and monomer release as reported in [\u003cspan citationid=\"CR21\" class=\"CitationRef\"\u003e21\u003c/span\u003e, \u003cspan citationid=\"CR22\" class=\"CitationRef\"\u003e22\u003c/span\u003e] would cause a stronger changes at the fibre outer region, in particular in case of PBAT where stronger hydrolysis took place. Considering an ATR unit equipped with a Ge crystal as used in this study, a depth of penetration of 0.65 \u0026micro;m at the wavenumber 1040 cm\u003csup\u003e\u0026minus;\u0026thinsp;1\u003c/sup\u003e was calculated [\u003cspan citationid=\"CR23\" class=\"CitationRef\"\u003e23\u003c/span\u003e]. Thus, this special ATR technique would rather give information on the fibre outer layer, while DSC investigation covers both surface and bulk parts of the fibre.\u003c/p\u003e"},{"header":"Conclusion","content":"\u003cp\u003eEnzyme catalysed hydrolysis provides an environmentally friendly route for controlled decomposition of polyester fibres. In this work we investigated the influence of the polymer structure (aromatic homopolymer versus aromatic-aliphatic copolymer) on the enzymatic hydrolysis using a cutinase from \u003cem\u003eHumicola insolens\u003c/em\u003e (HiC). By combining different characterisation techniques, the structural changes of the fibres as a result of the enzyme catalysed hydrolysis are investigated and discussed. The comparison suggests that PBAT is much more susceptible to enzymatic hydrolysis than PET, most likely due to the lower crystallinity of PBAT together with the different chemical structure. This led to much faster hydrolysis of PBAT fibre and higher monomer release already after 6 h incubation at 65\u0026deg;C. In contrary, very long incubation time was needed (up to 552 h) to observe little monomer release from PET hydrolysis, likely due to its higher crystallinity degree of PET that inhibits the attack of the enzyme and preserves the high order the fibres during the hydrolysis. As a result of the very fast hydrolysis, PBAT fibres dissolved and deformed almost completely already after 24 h, while PET fibres retained their sharp and size at much longer incubation time, e.g. after168 h. By prolongation the enzymatic hydrolysis to 552 h (23 days), some monomer release could be observed, which is however, still in a much lower extend compared to the enzymatic hydrolysis of PBAT.\u003c/p\u003e"},{"header":"Experimental","content":"\u003cdiv id=\"Sec8\" class=\"Section2\"\u003e \u003ch2\u003eMaterials and enzymes\u003c/h2\u003e \u003cp\u003ePoly(ethylene terephthalate) fibre (1.7 dtex) and poly(butylene adipate-\u003cem\u003eco\u003c/em\u003e-terephthalate) fibre (3.1 dtex) are kindly provided by IFG Asota GmbH, Linz, Austria. Prior to enzymatic modification, the fibres were cleaned in a mixture of 5 gL\u003csup\u003e\u0026minus;\u0026thinsp;1\u003c/sup\u003e non-ionic surfactant (fatty alcohol ethoxylate, Marlipal O 13/69, Sasol Germany GmbH, Hamburg, Germany) and 5 gL\u003csup\u003e\u0026minus;\u0026thinsp;1\u003c/sup\u003e Na\u003csub\u003e2\u003c/sub\u003eCO\u003csub\u003e3\u003c/sub\u003e (Merck Darmstadt, Germany) with a liquor ratio of 1:100 using Erlenmeyer flask in water bath at the temperature of 60\u0026deg;C, shaking speed of 140 rpm for 30 min. The fibres were then rinsed 3 times with hot deionised water (60\u0026deg;C) and 1 time with deionised water (25\u0026deg;C) followed by overnight air drying and oven drying at 60\u0026deg;C for approximately 3 h until constant mass was obtained.\u003c/p\u003e \u003cp\u003eThe cutinase from \u003cem\u003eHumicola insolens\u003c/em\u003e (HiC) was purchased from STREAM chemicals (code: 06-3135) and used as received without further purification (esterase activity on p-NPB: 888 U mL\u003csup\u003e\u0026minus;\u0026thinsp;1\u003c/sup\u003e, protein concentration: 6.94 mg mL\u003csup\u003e\u0026minus;\u0026thinsp;1\u003c/sup\u003e). The purity of the HiC batches purchased was routinely confirmed by SDS-PAGE analysis conducted as previously described [\u003cspan citationid=\"CR6\" class=\"CitationRef\"\u003e6\u003c/span\u003e]. All the other chemicals, solvents and reagents were purchased from Sigma-Aldrich at reagent grade and used without further purification if not otherwise specified.\u003c/p\u003e \u003c/div\u003e\n\u003ch3\u003eEnzymatic hydrolysis of fibres\u003c/h3\u003e\n\u003cp\u003eIn the first series, 10\u0026thinsp;\u0026plusmn;\u0026thinsp;0.2 mg of washed fibres was weighed out in 2 mL Eppendorf tubes and incubated for 24, 48, 72, 96 and 168 h with 1 mL of 5 \u0026micro;M HiC in 1 M potassium phosphate buffer pH 8. Incubation was carried out at a temperature of 65\u0026deg;C at 150 rpm using an orbital shaker.\u003c/p\u003e \u003cp\u003eTo better follow up the hydrolysis and collect enough fibre materials for later analytic, a second series of modification with higher fibre amount and justified times was carried out. Here, 500\u0026thinsp;\u0026plusmn;\u0026thinsp;0.2 mg of fibres was weighed out in 200 mL Pyrex bottles and incubated with 100 mL of 5 \u0026micro;M HiC in 1 M potassium phosphate buffer pH 8. Incubation was carried out at a temperature of 65\u0026deg;C at 150 rpm using an orbital shaker. For PET fibre, the incubation time was extended to 216, 384 and 552 h. For PBAT fibre, shorter incubation time of 2, 4 and 6 h was chosen.\u003c/p\u003e\n\u003ch3\u003eQuantification of soluble release products using HPLC-DAD\u003c/h3\u003e\n\u003cp\u003eHydrolysates were precipitated following the ice-cold methanol protocol (1:1 volumetric ratio). Samples were then centrifuged (Centrifuge 5427 R, Eppendorf AG, Hamburg, Germany) at 12700 rpm at 4\u0026deg;C for 15 min and filtered through 0.20 \u0026micro;m PTFE filters (GVS, Indianapolis, USA). The analytes were separated by high performance liquid chromatography HPLC, (Agilent Technologies, 1260 Infinity, Palo Alto, CA, United States) using a reversed phase column C18 (Poroshell 120 EC-C18 2.7 \u0026micro;m 3.0 \u0026times; 150 mm) equipped with a photodiode array detector (Agilent Technologies, 1290 Infinity II, Vienna, Austria) set at the wavelength of 260 nm to detect the released products. Analyses were run using methanol (MeOH, phase A) and formic acid (HCOOH, phase B) gradient. The flow rate was set to 0.35 ml min\u003csup\u003e\u0026minus;\u0026thinsp;1\u003c/sup\u003e at a constant temperature of 40\u0026deg;C. The injection volume was 10 \u0026micro;L. A terephthalate acid (TA) calibration curve up to 100 mM was used for the quantitative determination of the released TA from the fibres.\u003c/p\u003e \u003cdiv id=\"Sec11\" class=\"Section2\"\u003e \u003ch2\u003eScanning Electron Microscopy (SEM)\u003c/h2\u003e \u003cp\u003eThe fibre morphology was assessed through scanning electron microscopy (SEM). All SEM images were acquired by collecting secondary electrons on a Hitachi 3030TM (Japan) with the acceleration voltage of 15 kV. Samples were coated with a 4 nm platinum layer using a sputter coater.\u003c/p\u003e \u003c/div\u003e \u003cdiv id=\"Sec12\" class=\"Section2\"\u003e \u003ch2\u003eAttenuated Total Reflectance Infrared Microscopy (ATR-FTIR)\u003c/h2\u003e \u003cp\u003eThe attenuated total reflectance (ATR) spectra of hydrolysed fibres and blanks was recorded on the surface of single fibres in the spectral range of 4000 to 600 cm\u003csup\u003e\u0026minus;\u0026thinsp;1\u003c/sup\u003e using a FTIR microscope (Bruker Lumos FTIR Microscope, Bruker Optik GmbH, Ettlingen, Germany) with a resolution of 2 cm\u003csup\u003e\u0026minus;\u0026thinsp;1\u003c/sup\u003e and 64 scans per measurement. The ATR stage was equipped with a Ge crystal and a MCT (HgCdTe) detector cooled with LN\u003csub\u003e2\u003c/sub\u003e. The Ge crystal can be positioned directly on different positions of a single fibre for ATR measurement. The setting accuracy of the microscope is 0.1 \u0026micro;m. The spectra are normalised by min-max values over the spectral range from 4000 to 600 cm\u003csup\u003e\u0026minus;\u0026thinsp;1\u003c/sup\u003e. A total of 3 measurements were performed per sample.\u003c/p\u003e \u003c/div\u003e \u003cdiv id=\"Sec13\" class=\"Section2\"\u003e \u003ch2\u003eDifferential Scanning Calorimetry (DSC)\u003c/h2\u003e \u003cp\u003eThermal analysis of modified fibres and control blanks was performed on a differential scanning calorimeter (DSC3, Mettler Toledo, USA) on about 5 mg specimen encased in 100 \u0026micro;L aluminium crucibles with a pierced lid, under 50 mL min\u003csup\u003e\u0026minus;\u0026thinsp;1\u003c/sup\u003e nitrogen flow in the temperature range between \u0026minus;\u0026thinsp;50\u0026deg;C and 300\u0026deg;C, at heating and cooling rate of 10 K min\u003csup\u003e\u0026minus;\u0026thinsp;1\u003c/sup\u003e. A total of 3 measurements were performed per sample, and the results were analysed with the on-board evaluation software (Mettler STARe, Version 16.00).\u003c/p\u003e \u003c/div\u003e"},{"header":"Declarations","content":"\u003cp\u003e\u003cstrong\u003eAcknowledgements\u003c/strong\u003e We are grateful to the State Government of Vorarlberg for the financial support (Project Nr. IIb-17.04-96).\u0026nbsp;\u003c/p\u003e\n\u003cp\u003e\u003cstrong\u003eConflicts of interest\u0026nbsp;\u003c/strong\u003eThe authors have no conflicts of interest to declare that are relevant to the content of this article.\u003c/p\u003e"},{"header":"References","content":"\u003col\u003e\n\u003cli\u003eTextile_Exchange (2024) Materials Market Report 2024. In: 26.09.2024. https://textileexchange.org/knowledge-center/reports/materials-market-report-2024/\u003c/li\u003e\n\u003cli\u003eVannela R (2012) Are We \u0026ldquo;Digging Our Own Grave\u0026rdquo; Under the Oceans. Environ Sci Technol 46:7932\u0026ndash;7933. https://doi.org/10.1021/es302584e\u003c/li\u003e\n\u003cli\u003eBastioli C (2020) Handbook of Biodegradable Polymers. De Gruyter\u003c/li\u003e\n\u003cli\u003eEuropean_Bioplastics Bioplastic market development update 2023. In: 12.2023. https://www.european-bioplastics.org/bioplastics-market-development-update-2023-2/\u003c/li\u003e\n\u003cli\u003eMadhu A, Chakraborty JN (2017) Developments in application of enzymes for textile processing. J Clean Prod 145:114\u0026ndash;133. https://doi.org/10.1016/j.jclepro.2017.01.013\u003c/li\u003e\n\u003cli\u003eQuartinello F, Vajnhandl S, Volmajer Valh J, Farmer TJ, Vončina B, Lobnik A, Herrero Acero E, Pellis A, Guebitz GM (2017) Synergistic chemo‐enzymatic hydrolysis of poly(ethylene terephthalate) from textile waste. Microb Biotechnol 10:1376\u0026ndash;1383. https://doi.org/10.1111/1751-7915.12734\u003c/li\u003e\n\u003cli\u003ePellis A, Guebitz GM, Ribitsch D (2023) Bio-upcycling of multilayer materials and blends: closing the plastics loop. Curr Opin Biotechnol 81:102938. https://doi.org/10.1016/j.copbio.2023.102938\u003c/li\u003e\n\u003cli\u003eKaabel S, Therien JPD, Desch\u0026ecirc;nes CE, Duncan D, Fri\u0026scaron;čić T, Auclair K (2021) Enzymatic depolymerization of highly crystalline polyethylene terephthalate enabled in moist-solid reaction mixtures. Proc Natl Acad Sci 118:. https://doi.org/10.1073/pnas.2026452118\u003c/li\u003e\n\u003cli\u003eTarazona NA, Wei R, Brott S, Pfaff L, Bornscheuer UT, Lendlein A, Machatschek R (2022) Rapid depolymerization of poly(ethylene terephthalate) thin films by a dual-enzyme system and its impact on material properties. 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Adv Sci 6:. https://doi.org/10.1002/advs.201900491\u003c/li\u003e\n\u003cli\u003eAlmond J, Sugumaar P, Wenzel MN, Hill G, Wallis C (2020) Determination of the carbonyl index of polyethylene and polypropylene using specified area under band methodology with ATR-FTIR spectroscopy. e-Polymers 20:369\u0026ndash;381. https://doi.org/10.1515/epoly-2020-0041\u003c/li\u003e\n\u003cli\u003eChen Z, Hay JN, Jenkins MJ (2012) FTIR spectroscopic analysis of poly(ethylene terephthalate) on crystallization. Eur Polym J 48:1586\u0026ndash;1610. https://doi.org/10.1016/j.eurpolymj.2012.06.006\u003c/li\u003e\n\u003cli\u003eSammon C, Yarwood J, Everall N (2000) An FT\u0026ndash;IR study of the effect of hydrolytic degradation on the structure of thin PET films. Polym Degrad Stab 67:149\u0026ndash;158. https://doi.org/10.1016/S0141-3910(99)00104-4\u003c/li\u003e\n\u003cli\u003eDonelli I, Freddi G, Nierstrasz VA, Taddei P (2010) Surface structure and properties of poly-(ethylene terephthalate) hydrolyzed by alkali and cutinase. Polym Degrad Stab 95:1542\u0026ndash;1550. https://doi.org/10.1016/j.polymdegradstab.2010.06.011\u003c/li\u003e\n\u003cli\u003eVertommen MAME, Nierstrasz VA, Veer M van der, Warmoeskerken MMCG (2005) Enzymatic surface modification of poly(ethylene terephthalate). J Biotechnol 120:376\u0026ndash;386. https://doi.org/10.1016/j.jbiotec.2005.06.015\u003c/li\u003e\n\u003cli\u003eBuchacher-Kr\u0026ouml;ll M, Bechtold T, Pham T (2025) In-depth analysis of potassium peroxysulfate based oxidation of wool fibre by advanced infrared spectroscopy. Polym Degrad Stab 234:111225. https://doi.org/10.1016/j.polymdegradstab.2025.111225\u003c/li\u003e\n\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":"monatshefte-fur-chemie-chemical-monthly","isNatureJournal":false,"hasQc":true,"allowDirectSubmit":false,"externalIdentity":"mccm","sideBox":"Learn more about [Monatshefte für Chemie - Chemical Monthly](https://www.springer.com/journal/706)","snPcode":"706","submissionUrl":"https://www.editorialmanager.com/mccm/","title":"Monatshefte für Chemie - Chemical Monthly","twitterHandle":"","acdcEnabled":true,"dfaEnabled":true,"editorialSystem":"em","reportingPortfolio":"Springer Hybrid","inReviewEnabled":true,"inReviewRevisionsEnabled":false},"keywords":"Enzymatic hydrolysis, Fibre, Poly(ethylene terephthalate), Poly(butylene adipate-co-terephthalate), Biocatalysed polymer degradation","lastPublishedDoi":"10.21203/rs.3.rs-6502055/v1","lastPublishedDoiUrl":"https://doi.org/10.21203/rs.3.rs-6502055/v1","license":{"name":"CC BY 4.0","url":"https://creativecommons.org/licenses/by/4.0/"},"manuscriptAbstract":"\u003cp\u003eEnzyme catalysed hydrolysis provides an environmentally friendly route for controlled decomposition of polyester fibres. In this work, the hydrolysis of polyethylene terephthalate (PET) and polybutylene adipate terephthalate (PBAT) by using a cutinase from \u003cem\u003eHumicola insolens\u003c/em\u003e (HiC) was compared with the aim, to better understand the relationship between the polymer structure and the enzyme catalysed degradation. PBAT exhibited much higher sensitivity to hydrolysis most likely due to the presence of the longer carbon chain diol and of aliphatic adipic acid in addition to terephthalic acid. In addition, the higher degree of crystallinity of PET restricts the attack of the enzyme and preserves the high order the fibres during the hydrolysis. The results provide further basis for the optimisation of enzyme catalysed hydrolysis and polymer degradation processes of polyester fibres.\u003c/p\u003e","manuscriptTitle":"Enzyme catalysed degradation of polyester fibres – A comparative study between poly(ethylene terephthalate) and poly(butylene adipate-co-terephthalate)","msid":"","msnumber":"","nonDraftVersions":[{"code":1,"date":"2025-05-08 14:23:05","doi":"10.21203/rs.3.rs-6502055/v1","editorialEvents":[{"type":"communityComments","content":0},{"type":"reviewerAgreed","content":"","date":"2025-05-16T15:30:37+00:00","index":0,"fulltext":""},{"type":"reviewersInvited","content":"","date":"2025-04-30T08:20:23+00:00","index":"","fulltext":""},{"type":"editorAssigned","content":"","date":"2025-04-25T04:39:01+00:00","index":"","fulltext":""},{"type":"submitted","content":"Monatshefte für Chemie - Chemical Monthly","date":"2025-04-23T03:25:58+00:00","index":"","fulltext":""}],"status":"published","journal":{"display":true,"email":"[email protected]","identity":"monatshefte-fur-chemie-chemical-monthly","isNatureJournal":false,"hasQc":true,"allowDirectSubmit":false,"externalIdentity":"mccm","sideBox":"Learn more about [Monatshefte für Chemie - Chemical Monthly](https://www.springer.com/journal/706)","snPcode":"706","submissionUrl":"https://www.editorialmanager.com/mccm/","title":"Monatshefte für Chemie - Chemical Monthly","twitterHandle":"","acdcEnabled":true,"dfaEnabled":true,"editorialSystem":"em","reportingPortfolio":"Springer Hybrid","inReviewEnabled":true,"inReviewRevisionsEnabled":false}}],"origin":"","ownerIdentity":"89e4065f-1046-4e23-baea-170052674f89","owner":[],"postedDate":"May 8th, 2025","published":true,"recentEditorialEvents":[],"rejectedJournal":[],"revision":"","amendment":"","status":"published-in-journal","subjectAreas":[],"tags":[],"updatedAt":"2025-08-25T16:36:03+00:00","versionOfRecord":{"articleIdentity":"rs-6502055","link":"https://doi.org/10.1007/s00706-025-03368-8","journal":{"identity":"monatshefte-fur-chemie-chemical-monthly","isVorOnly":false,"title":"Monatshefte für Chemie - Chemical Monthly"},"publishedOn":"2025-08-18 16:29:31","publishedOnDateReadable":"August 18th, 2025"},"versionCreatedAt":"2025-05-08 14:23:05","video":"","vorDoi":"10.1007/s00706-025-03368-8","vorDoiUrl":"https://doi.org/10.1007/s00706-025-03368-8","workflowStages":[]},"version":"v1","identity":"rs-6502055","journalConfig":"researchsquare"},"__N_SSP":true},"page":"/article/[identity]/[[...version]]","query":{"redirect":"/article/rs-6502055","identity":"rs-6502055","version":["v1"]},"buildId":"8U1c8b4HqxoKbykW_rLl7","isFallback":false,"isExperimentalCompile":false,"dynamicIds":[84888],"gssp":true,"scriptLoader":[]}