Effect of Gas-Grafting Pretreatment of Cellulose on Properties of Cellulose-Polypropylene Composites

Effect of Gas-Grafting Pretreatment of Cellulose on Properties of Cellulose-Polypropylene Composites | 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 Effect of Gas-Grafting Pretreatment of Cellulose on Properties of Cellulose-Polypropylene Composites Kyu Hwan Noh, Cheol Woo Lee, Kyoung-Hwa Choi, Kwang-Seob Lee, and 2 more This is a preprint; it has not been peer reviewed by a journal. https://doi.org/ 10.21203/rs.3.rs-4340356/v1 This work is licensed under a CC BY 4.0 License Status: Posted Version 1 posted You are reading this latest preprint version Abstract This study investigated a method to modify cellulose for enhanced hydrophobicity through gas-phase grafting with palmitoyl chloride, facilitating easier blending of fibers and polypropylene. In addition, cellulose sheets were produced by substituting water in the cellulose fiber stock with ethanol during sheet molding to prevent the matting of macrofibrils on the cellulose surface, thereby improving the hydrophobization efficiency achieved by gas grafting. The results revealed that alcohol-molded sheets, which expanded in volume, exhibited more than twice the amount of reacted fatty acids compared to conventional water-based cellulose sheets after gas grafting. Composite films composed of the pretreated fibers exhibited superior tensile strength relative to those made from non-grafted fibers. In particular, the addition of maleic-anhydride-grafted polypropylene (MAPP) improved the dispersibility of the cellulose fibers within the composite film, indicating the positive contribution of gas grafting and MAPP treatment. Bio-based plastic Cellulose-polypropylene composite Fiber dispersion Free hydroxyl group Gas-phase grafting Figures Figure 1 Figure 2 Figure 3 Figure 4 Figure 5 Figure 6 Figure 7 Figure 8 Figure 9 Figure 10 Figure 11 Figure 12 Figure 13 Figure 14 Figure 15 Figure 16 Introduction With the recent increase in plastic usage contributing to environmental pollution, countries worldwide are making efforts to reduce plastic consumption. Global plastic production has risen steadily, increasing approximately seven-fold from 50 million tons in 1976 to 367 million tons in 2020, with projections suggesting it will quadruple by 2050 compared to that in 2020 (Plastics Europe 2021). As regulations aimed at reducing plastic production strengthen, there have been calls to replace common plastic interior materials in vehicles with eco-friendly alternatives based on natural materials (You 2015). Bio-based plastic composites, derived from natural materials, are eco-friendly alternatives that are either biodegradable or can replace existing plastics using plant-derived resources. Cellulose, a prominent plant-derived natural material known for its excellent mechanical properties, low density, and biodegradability, consists of linear chains linked by β-1, 4 glycosidic bonds and contains hydroxyl groups at carbons 2, 3, and 6 within the glucose unit, making it polar (Bezerra et al. 2015 ; Ma et al. 2016 ; Roy et al. 2009 ). However, in polymer composite manufacturing, cellulose fibers struggle to mix well with nonpolar polymer resins due to fiber flocculation caused by the polar surface of cellulose. To address this issue and enhance the strength of bioplastic composites, the primary approach involves improving the compatibility of cellulose with hydrophobic polymers using compatibilizers (Coutinho et al. 1997 ). A common method to enhance the compatibility of polypropylene (PP), a nonpolar polymer, is by improving interfacial adhesion through the addition of PP modified to maleic anhydride (maleic anhydride-grafted polypropylene (MAPP)) (Kim et al. 2007 ; Mohanty et al. 2004 ; Qiu et al. 2005 ). The reaction mechanism of MAPP is illustrated in Fig. 1 . However, there are concerns that while MAPP improves adhesion at the interface, it may not effectively promote mixing between nonpolar polymer resins and fibers, potentially preventing an increase in the melt viscosity of composite resins owing to the introduction of fibers. The hydroxyl groups of cellulose can undergo chemical surface modification through processes such as etherification, esterification, crosslinking, and graft copolymerization (Hwang et al. 2005 ; Roy et al. 2009 ). In France, Samain ( 2002 ) developed a technique to hydrophobize the surface of hydrophilic cellulose with hydroxyl groups using gas grafting with fatty acid chlorides. Chromatogenic technology forms ester bonds by reacting gaseous fatty acid chlorides with hydroxyl groups, which can be used to modify the surface of cellulose (Choi et al. 2019 ). Previous methods for forming ester bonds between fatty acids and cellulose have primarily involved liquid-phase reactions using organic solvents (Freire et al. 2006 ; Uschanov et al. 2011 ; Vaca-Garcia et al. 1998 ). However, Berlioz et al. ( 2008 ) reported that a vapor-phase grafting reaction using fatty acid chlorides could form ester bonds with the hydroxyl groups of cellulose. Choi et al. ( 2020 ) compared the gas-grafting efficiency of fatty acid chlorides with different alkyl chain lengths and observed that longer alkyl chains resulted in higher hydrophobization efficiency. Fibers hydrophobized by reacting with the hydroxyl groups on the cellulose surface using gaseous fatty acid chlorides can be uniformly dispersed in plastics. Lee et al. ( 2021 ) reported that the flexural strength of bioplastics improved with increasing reaction time and temperature during the gas grafting of cellulose fibers for plastic composite manufacturing. Hydrophobization of cellulose fibers through the gas grafting of chlorinated fatty acids is feasible for fluffy fibers made from cellulose pulp. However, in this case, the large volume of fluffed cellulose fibers poses transportation challenges and necessitates the construction of separate equipment capable of processing substantial amounts of raw materials for the gas-grafting hydrophobization treatment of fluffed fibers. To overcome these challenges, the hydrophobization of cellulose fibers can be achieved using equipment developed for the gas grafting of paper using the existing reel-to-reel method. Cellulose fibers are molded into paper, hydrophobized, and then fluffed to produce fluffy fibers, effectively addressing the aforementioned challenges. During the paper-forming process, hydrogen bonds are formed between fibers through dewatering and drying (Giertz 1964 ; Giertz and Rødland 1979 ; Lindstrom et al. 2005 ; Lobben 1975 ; Retulainen 1997 ; Vainio and Paulapuro 2007 ). However, a disadvantage of this method is that many hydroxyl groups participate in the formation of hydrogen bonds between the fibers constituting the sheet, thereby reducing the number of hydroxyl groups available to react with fatty acid chlorides. Additionally, during paper sheet formation, the availability of hydroxyl groups for the reaction decreases as surface fibrils align with the fiber surface through the drying process. It was expected that the use of alcohol with low surface tension during paper manufacturing would prevent surface fibrils from matting together on the surface even after drying, thereby facilitating the production of bulky sheets. Consequently, increasing the substitution of hydroxyl groups with alkyl chains is expected to increase the hydrophobization efficiency. Hence, we attempted to improve the hydrophobization efficiency of cellulose fibers through gas grafting by increasing the specific surface area of the fibers. This involved manufacturing paper by replacing the water in the cellulose fiber stock with ethanol during sheet molding to prevent the macrofibrils from matting on the fiber surface. In addition, during the addition of a compatibilizer for plastic composite manufacturing, we investigated the degree of fiber dispersion within the composite and assessed changes in the composite strength based on the hydroxyl group content. Materials and methods Materials In this study, bleached hardwood kraft pulp (Moorim P&P, Korea) was provided in a dried lap form and used as the raw material for cellulose sheets. PP (Adstif HA5029, Lyondell Basell, USA) was used to manufacture the composite material, and its physical properties are listed in Table 1 . MAPP (IRUBOND100, Iruchem, Korea) was used to investigate the effect of compatibilizers on the interfacial adhesion between the cellulose fiber and PP. Table 1 Characteristics of polypropylene Item Unit Value Melt flow index (230 ℃/ 2.16 kg) g/10 min 65 Density g/cm³ 0.90 Deflection temperature under load (0.46 N/mm²) ℃ 140 In contrast to the process for conventional handsheet molding, ethyl alcohol (Daejeong Chemicals & Metals, Korea) was used for papermaking instead of water. Palmitoyl chloride (ACROS, Italy) served as the fatty acid chloride for gas grafting. Petroleum ether (Daejeong Chemical Metals, Korea) was used as the diluting solvent for palmitoyl chloride during grafting. The physical properties of palmitoyl chloride are listed in Table 2 . Acetone (Daejeong Chemicals & Metals, Korea) was utilized as the washing solvent to remove the excess fatty acids from the sheet after gas grafting. Table 2 Characteristics of palmitoyl chloride Item Unit Value Melting point ℃ 11–13 Boiling point ℃ 88–90 Molecular weight g/mol 247.87 Beating and sheet forming using water and alcohol The cellulose fibers were beaten to 500 mL CSF (Canadian standard freeness) using a laboratory valley beater and then used to make paper. The freeness was measured according to TAPPI Standard T227 om-99. During handsheet manufacturing, there was a concern about potential differences in the physical properties of the paper owing to the varying fines retention between the alcohol-forming and water-forming processes. To prevent these differences in physical properties due to fines between the handsheets molded with water and alcohol, the fines in the stock were removed by hyperwashing. After hyperwashing the beaten fibers, the fiber suspension was dispersed in ethyl alcohol for alcohol-based sheet formation and in water for water-based sheet formation at a consistency of 0.3%. Handsheets with a target basis weight of 100 ± 1 g/m² were manufactured using a square handsheet former (30×30 cm²) with each stock as a raw material. Gas grafting The handsheets were immersed in a solution of palmitoyl chloride diluted in petroleum ether to a concentration of 1%. After dipping, the handsheets were removed and the petroleum ether was allowed to evaporate. Subsequently, the handsheets were pressed using a hot press at 200°C for the upper plate and 100°C for the lower plate, with a pressing pressure of 400 g f /cm² for a grafting time of 6 s. Following gas grafting by hot pressing, acetone washing was performed to remove any unreacted palmitoyl chloride and free palmitic acid remaining on the sheets. The washed sheets were then subjected to ultrasonic cleaning for 15 min using an ultrasonic cleaner (JAC Ultrasonic 4020; Jinwoo, Korea). Finally, the washed sheets were impregnated with acetone and stirred for 2 min using a shaker further to remove any unreacted palmitoyl chloride and palmitic acid. Cellulose-PP composite manufacturing and sample preparation To manufacture the cellulose-PP composite material, the handsheets were fluffed and mixed with PP using a twin-screw compounding extruder (Bautek, Korea). The cellulose content in the composite was fixed at 30 wt%, and MAPP was added at 0 wt% and 3 wt% under each condition to determine the effect of the compatibilizer. During the production of composite pellets, the zone temperatures of the twin-screw extruder were set to 180/170/170/170/170/170°C, and the screw speed was maintained at 300 rpm. The raw material mixing ratios of the composite materials are listed in Table 3 . To prepare specimens for strength measurements, the manufactured pellets were made into a film with a thickness of 0.2 mm using a hot press. Figure 2 shows a schematic of the film production using a hot press. Table 3 Formulation of the composites Item Handsheet type Cellulose (wt%) PP (wt%) Gas grafting MAPP (wt%) W1 Water 30 70 X 0 W2 3 W3 O 0 W4 3 A1 Alcohol X 0 A2 3 A3 O 0 A4 3 Physical property analysis Water retention value of handsheet To compare the exposure of the number of hydroxyl groups in water and alcohol sheets, both sheets were immersed in water and then dewatered using centrifugal force at 900 G for 30 min. The dewatered wet sheet was subsequently dried in a dryer at 105°C for 24 h, and the water retention value (WRV) was measured. Quantitative analysis of free and grafted palmitic acid in the sheets Gas chromatography (GC, 8890 GC system, Agilent Technologies, USA) was employed to analyze the contents of the reacted palmitic acid and free palmitic acid in the gas-grafted handsheets of each item. Unreacted palmitic acids in the sample, as well as palmitic acids derived from palmitoyl chloride that reacted with the hydroxyl groups of cellulose fibers, were extracted and separated through Soxhlet extraction and saponification. Subsequently, GC analysis was performed (Choi et al. 2019 ). Melt flow index measurement The melt flow index (MFI) of the manufactured cellulose-PP pellets was measured using a melt flow indexer (Hanatek, UK) according to ASTM D1238 (200°C, load 2.16 kg) standards. Tensile strength measurement of composite films The tensile strengths of the cellulose-PP composite films were measured using a universal testing machine (WL2100C, Withlab, Korea) following ASTM D882 standards. Analysis of morphological characteristics of composite materials Scanning electron microscopy (SEM) was employed to observe the fiber dispersion characteristics within the cellulose-PP composite pellets. Platinum was used as the coating material for capturing the fracture surface and surface images of the pellets. SEM (CX-200TM, COXEM, Korea) imaging was performed at an acceleration voltage of 20 kV. To indirectly measure the dispersion of cellulose fibers in the composite film, fiber dispersion images were captured using a transmission microscope (AST-ICS305B, Alphasystec, Korea). In addition, to quantify the degree of fiber dispersion, the captured images were printed on overhead projector (OHP) film, and the formation index of the dispersed fibers was measured using an Optest Formation Tester (Optest Equipment, Canada). Figure 3 shows the overall experimental method and schematic for measuring the degree of fiber dispersion in the film. Results and discussion Comparison of grafting efficiency by handsheet type Morphological characteristics of handsheet The WRV was measured to indirectly compare the exposed hydroxy groups of conventional water-formed and alcohol-formed handsheets. When using the existing WRV measurement method to assess dissociated paper stock, evaluation of the exposed hydroxyl content in the handsheet form is complicated due to the formation of extra fibrils on the fiber surface. To address this, the handsheets were immersed in water and then dewatered using a centrifuge. The WRV measurements are shown in Fig. 4 . The alcohol-formed handsheet exhibited a higher WRV compared to the regular water-formed handsheet. This difference is attributed to the higher number of exposed hydroxyl groups in the alcohol-formed handsheet. During sheet formation, the external fibrils of beaten fibers tend to mat down through dewatering and drying. Using alcohol instead of water for sheet molding prevents fibril matting by disrupting hydrogen bonding, thereby increasing the surface area. Consequently, the alcohol-formed handsheet exhibited an enhanced WRV, indicative of improved hydrophobization efficiency following the gas-grafting reaction. GC analysis of free and grafted palmitic acid in sheets Figure 5 shows the quantities of reacted palmitic acid and unreacted free palmitic acid after the gas grafting of the handsheet. Significantly, the amount of palmitic acid that reacted in the alcohol-formed handsheet was more than twice that in the water-formed handsheet. During the gas-grafting reaction, the unreacted palmitoyl chloride from the applied palmitoyl chloride dissipated into the air. In contrast, in the case of the alcohol-formed handsheet, the gas grafting of palmitoyl chloride proceeded effectively, allowing the palmitoyl chloride to react without dissipating, resulting in more than double the amount of reacted palmitic acid compared to that in the water-formed handsheet. Despite similar amounts of unreacted palmitic acid in the water and alcohol handsheets, the grafting reaction proceeded normally. These results are believed to be attributed to the increased accessibility of the hydroxyl group in the alcohol-formed handsheet. Changes in physical properties of composite due to hydrophobization pretreatment of fibers Melt flow index of composite To evaluate the impact of cellulose hydrophobization on the melt flow of the cellulose-PP composite, the MFI was measured, and the results are shown in Fig. 6 and Fig. 7 . The analysis revealed a significant increase in the MFI when the composite was manufactured using fibers hydrophobized through a vapor-phase graft reaction. This process involved hydrophobizing cellulose fibers through gas grafting and ensuring uniform mixing with PP to improve fluidity during the production of plastic composites. In the un-grafted case, the MFI of the alcohol sheet-based composite was lower than that of the water sheet due to the presence of more fibrils on the alcohol sheet surface, which facilitated fiber aggregation. Conversely, in the grafted case, the MFI of the alcohol sheet-based composite was higher than that of the water sheet, as the surface fibrils of the alcohol sheet promoted hydrophobization. The addition of a compatibilizer increased the viscosity of the composite, resulting in a reduction in the MFI. This effect is attributed to the increased viscosity caused by the combination of MAPP with cellulose fibers, forming longer molecular chains. Tensile strength of composite film The tensile strength was measured to assess the strength characteristics of the cellulose-PP composite based on cellulose fiber hydrophobization and the addition of MAPP. Owing to significant variations in the specimen weight when cut to a specific size, the tensile strength was normalized into a tensile index (Fig. 8 and Fig. 9 ). The experimental results indicated that the tensile strength of the composite with hydrophobized fibers was superior to that of the composite with untreated fibers without gas grafting. It is believed that the improved fiber dispersibility through gas grafting contributed to the enhanced strength of the composite. When bulky handsheets made with alcohol were subjected to gas-grafting hydrophobization, the amount of reacted palmitic acid was twice that in the regular water handsheet. Hence, it was predicted that the number of residual hydroxyl groups available to react with the compatibilizer would decrease. However, contrary to these predictions, the tensile strength of the alcohol handsheet-based composite was superior to that of the regular water handsheet, even with the addition of the compatibilizer. In the case of the composite made of alcohol sheets, the strength improvement due to grafting was greater than that of the water sheets. Considering the WRV, it was found that unlike general water handsheets, during the production of alcohol handsheets, the fibrils on the surface of the fibers did not decrease but instead dispersed, increasing the specific surface area of the fibers. Therefore, even though the amount of reacted palmitic acid increased, the number of hydroxyl groups available for reacting with the compatibilizer did not decrease. This suggests that the strength-improvement effect of the compatibilizer in the alcohol handsheet-based composite was superior to that of the water handsheet. For the composites based on grafted fibers, the strength-improvement effect of the compatibilizer was weaker compared to that for the ungrafted composite. Morphological results of cellulose-PP composite SEM results of cellulose-PP composite The fracture surface and surface images of the pellets obtained using SEM are shown in Figs. 10 – 13 . The surface of the composite pellet without gas-grafted fibers appears rough, whereas that of the pellet with gas-grafted fibers appears smooth. The gas-grafted cellulose fibers were uniformly dispersed in the PP matrix without agglomeration, contributing to the smooth surface appearance. By observing the fracture surface after adding MAPP, it was confirmed that MAPP enhanced interfacial adhesion, resulting in more uniform fiber bonding. Thus, gas grafting of the fiber sheets significantly improved fiber dispersion and the MFI of the composite material, while also enhancing interfacial adhesion with the compatibilizer. Transmission microscopy analysis of composite films After manufacturing the plastic composite film, transmission microscopy images were captured to confirm the degree of cellulose fiber dispersion (Figs. 14 and 15 ). Each image was analyzed using a formation tester typically used for assessing paper formation, and the degree of fiber dispersion was quantified, as shown in Fig. 16 . Upon observing the transmission microscope images, it was confirmed that gas grafting had a significant effect on the uniformity of the cellulose-PP film fiber distribution. The formation index increased, indicating improved dispersion of the gas-grafted fibers. Furthermore, the formation index was found to increase with the addition of MAPP. This phenomenon is attributed to the increased viscosity of the composite material upon the addition of MAPP, which reduces fiber agglomeration. Conclusion Hydrophilic cellulose and hydrophobic PP do not blend well during the manufacturing of bio-based plastic composites. Previous efforts have focused on enhancing the interfacial adhesion between cellulose and plastics by adding compatibilizers such as MAPP. However, it remains uncertain whether improving the compatibility would reduce the MFI of fiber-blended PP and promote extrusion. In this study, a method was explored to modify cellulose fibers to render them hydrophobic, facilitating easier blending with PP. Gas grafting of palmitoyl chloride onto paper was attempted using a laboratory-scale hot press. One disadvantage of this method is that the number of hydroxyl groups available for reacting with fatty acid chlorides decreases due to hydrogen bond formation between the fibers during paper molding. However, hydrophobizing the molded paper presents an advantage, in that the hydroxyl groups on the surface of the inter-fiber bond, where the gas-grafting reaction did not occur, can later react with the compatibilizer. Pretreated fibers can achieve more uniform dispersion in plastic by forming ester bonds via the reaction of the hydroxyl groups on the cellulose surface with gaseous palmitoyl chlorides. To improve the efficiency of cellulose hydrophobization through gas grafting, we aimed to increase the specific surface area of the fibers. For this purpose, paper was manufactured by replacing the water in the cellulose fiber stock with ethanol during sheet molding to prevent macrofibrils from matting on the fiber surface. The resulting alcohol-molded sheets, which had a higher volume, contained more than twice the amount of reacted palmitic acid compared to ordinary water-based paper after gas-grafting treatment. Measurements revealed that the cellulose-PP composite film composed of pretreated fibers exhibited superior tensile strength compared to the film composed of non-grafted fibers. In other hand, the addition of MAPP, improved the fiber dispersibility, likely due to the increased viscosity of the composite; reduced fiber agglomeration; and increased the formation index. The improved dispersibility resulting from gas grafting correlated with increased composite strength. However, in the case of the grafted-fiber-based composites, the strength-improvement effect of the compatibilizer was weaker than for the ungrafted composite. A larger surface area facilitated a more efficient grafting process and increased the MFI. Unlike with MAPP addition, gas grafting of the fibers improved the composite strength by enhancing the fiber dispersibility without reducing the MFI. Declarations Conflict of interest The authors declare no competing financial interest. Consent for publication All authors approved the final version of the manuscript. Ethnical approval All authors have consented to participate on the manuscript. Acknowledgements This work was supported by the Technology Innovation Program (No.20010431) of Korea Evaluation Institute of Industrial Technology (KEIT) funded by the Ministry of trade, Industry & Energy (MOTIE). References Berlioz S, Stinga C, Condoret J et al (2008) SFGP 2007-investigation of a novel principle of chemical grafting for modification of cellulose fibers. International Journal of Chemical Reactor Engineering 6(1): 1-14. https://doi.org/10.2202/1542-6580.1672 Bezerra RDS, Teixeira PRS, Teixeira ASNM et al (2015) Chemical functionalization of cellulose materials: Main reaction and application in the contaminants of removal of aqueous medium. 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05:26:54","currentVersionCode":1,"declarations":"","doi":"10.21203/rs.3.rs-4340356/v1","doiUrl":"https://doi.org/10.21203/rs.3.rs-4340356/v1","draftVersion":[],"editorialEvents":[],"editorialNote":"","failedWorkflow":false,"files":[{"id":56178027,"identity":"c3986b08-cd3f-4ab1-9ec6-20bc3ce60833","added_by":"auto","created_at":"2024-05-09 13:32:50","extension":"png","order_by":1,"title":"Figure 1","display":"","copyAsset":false,"role":"figure","size":1145996,"visible":true,"origin":"","legend":"\u003cp\u003eFunctions of MAPP compatibilizer in cellulose-PP composites.\u003c/p\u003e","description":"","filename":"Figure1.png","url":"https://assets-eu.researchsquare.com/files/rs-4340356/v1/8afeada51cdcb1c25472d2ce.png"},{"id":56177400,"identity":"8f4a28cd-b4b6-4570-8824-270a25665735","added_by":"auto","created_at":"2024-05-09 13:24:49","extension":"png","order_by":2,"title":"Figure 2","display":"","copyAsset":false,"role":"figure","size":26230,"visible":true,"origin":"","legend":"\u003cp\u003eSchematic of film production using a hot press with pellets.\u003c/p\u003e","description":"","filename":"Figure2.png","url":"https://assets-eu.researchsquare.com/files/rs-4340356/v1/48bc0f8c4f93194feadf9694.png"},{"id":56178034,"identity":"6dfae90d-6341-45ef-a3f1-47329c8bb856","added_by":"auto","created_at":"2024-05-09 13:32:51","extension":"png","order_by":3,"title":"Figure 3","display":"","copyAsset":false,"role":"figure","size":41130,"visible":true,"origin":"","legend":"\u003cp\u003eSchematic illustrating the overall experimental method and procedures for film formation testing.\u003c/p\u003e","description":"","filename":"Figure3.png","url":"https://assets-eu.researchsquare.com/files/rs-4340356/v1/885ee4d0f76db1cce9f733b1.png"},{"id":56178539,"identity":"d0a1ca50-77b8-40a6-b5d2-027ae23828a2","added_by":"auto","created_at":"2024-05-09 13:40:51","extension":"png","order_by":4,"title":"Figure 4","display":"","copyAsset":false,"role":"figure","size":39250,"visible":true,"origin":"","legend":"\u003cp\u003eChange in water retention value with different types of handsheets.\u003c/p\u003e","description":"","filename":"Figure4.png","url":"https://assets-eu.researchsquare.com/files/rs-4340356/v1/601cc317792726b79bea96ac.png"},{"id":56177403,"identity":"251c1b6a-73f0-4f1f-8657-e43af35be078","added_by":"auto","created_at":"2024-05-09 13:24:50","extension":"png","order_by":5,"title":"Figure 5","display":"","copyAsset":false,"role":"figure","size":45207,"visible":true,"origin":"","legend":"\u003cp\u003eChanges in reacted/free fatty acid content in different types of grafted handsheets.\u003c/p\u003e","description":"","filename":"Figure5.png","url":"https://assets-eu.researchsquare.com/files/rs-4340356/v1/13129a5aec4d5ec483a227e3.png"},{"id":56178029,"identity":"cb3431f1-0b5c-4264-9eb3-d0f85b4acfde","added_by":"auto","created_at":"2024-05-09 13:32:50","extension":"png","order_by":6,"title":"Figure 6","display":"","copyAsset":false,"role":"figure","size":47183,"visible":true,"origin":"","legend":"\u003cp\u003eMFI change in cellulose-PP composite based on gas-grafting pretreatment of cellulose fibers without the addition of MAPP.\u003c/p\u003e","description":"","filename":"Figure6.png","url":"https://assets-eu.researchsquare.com/files/rs-4340356/v1/9d0a14d48d7fa1a8fd611614.png"},{"id":56177407,"identity":"2de9811c-8ef0-4b83-b325-df7a1bf935ac","added_by":"auto","created_at":"2024-05-09 13:24:51","extension":"png","order_by":7,"title":"Figure 7","display":"","copyAsset":false,"role":"figure","size":47095,"visible":true,"origin":"","legend":"\u003cp\u003eMFI change in cellulose-PP composite with 3% MAPP addition based on gas-grafting pretreatment of cellulose fibers.\u003c/p\u003e","description":"","filename":"Figure7.png","url":"https://assets-eu.researchsquare.com/files/rs-4340356/v1/e748b73bcf392c22a153fb00.png"},{"id":56179037,"identity":"9e9b07de-acc9-4ea8-8ec2-92d131bf0c76","added_by":"auto","created_at":"2024-05-09 13:48:54","extension":"png","order_by":8,"title":"Figure 8","display":"","copyAsset":false,"role":"figure","size":52477,"visible":true,"origin":"","legend":"\u003cp\u003eTensile index change in ungrafted handsheet mixed cellulose-PP composite with the addition of 3% MAPP.\u003c/p\u003e","description":"","filename":"Figure8.png","url":"https://assets-eu.researchsquare.com/files/rs-4340356/v1/a3fbde87957b189fd3b82ff6.png"},{"id":56178040,"identity":"a8c774c5-d282-41c5-a4a4-65ad49145407","added_by":"auto","created_at":"2024-05-09 13:32:52","extension":"png","order_by":9,"title":"Figure 9","display":"","copyAsset":false,"role":"figure","size":49352,"visible":true,"origin":"","legend":"\u003cp\u003eTensile index change in grafted handsheet mixed cellulose-PP composite with the addition of 3% MAPP.\u003c/p\u003e","description":"","filename":"Figure9.png","url":"https://assets-eu.researchsquare.com/files/rs-4340356/v1/21156c5b3f29dc591c41cec7.png"},{"id":56178548,"identity":"6385b271-235d-46e3-8f04-0badb7e69075","added_by":"auto","created_at":"2024-05-09 13:40:53","extension":"png","order_by":10,"title":"Figure 10","display":"","copyAsset":false,"role":"figure","size":5769129,"visible":true,"origin":"","legend":"\u003cp\u003eSEM images of un-grafted cellulose-PP composite without MAPP (a, b, c) and un-grafted cellulose-PP composite with MAPP (d, e, f) at magnifications of 100× (a, d), 400× (b, e), and 200× (surface image, c, f).\u003c/p\u003e","description":"","filename":"Figure10.png","url":"https://assets-eu.researchsquare.com/files/rs-4340356/v1/39c5d699b52fa247e0553b17.png"},{"id":56177415,"identity":"5c8e3267-4597-4188-a66e-0f6b91a9d19f","added_by":"auto","created_at":"2024-05-09 13:24:54","extension":"png","order_by":11,"title":"Figure 11","display":"","copyAsset":false,"role":"figure","size":5856856,"visible":true,"origin":"","legend":"\u003cp\u003eSEM images of grafted cellulose-PP composite without MAPP (a, b, c) and grafted cellulose-PP composite with MAPP (d, e, f) at magnifications of 100× (a, d), 400× (b, e), and 200× (surface image, c, f).\u003c/p\u003e","description":"","filename":"Figure11.png","url":"https://assets-eu.researchsquare.com/files/rs-4340356/v1/b77937cc4c84d24354b4d748.png"},{"id":56178542,"identity":"1809b5ab-f136-4ace-a5d4-7743d052378b","added_by":"auto","created_at":"2024-05-09 13:40:52","extension":"png","order_by":12,"title":"Figure 12","display":"","copyAsset":false,"role":"figure","size":5774897,"visible":true,"origin":"","legend":"\u003cp\u003eSEM images of un-grafted alcohol sheet cellulose-PP composite without MAPP (a, b, c) and un-grafted alcohol sheet cellulose-PP composite with MAPP (d, e, f) at magnifications of 100× (a, d), 400× (b, e), and 200× (surface image, c, f).\u003c/p\u003e","description":"","filename":"Figure12.png","url":"https://assets-eu.researchsquare.com/files/rs-4340356/v1/2dd5c41c0fd6292cccd0d4fc.png"},{"id":56179035,"identity":"f7cc8cc5-3ccc-43f8-b381-5815bae47675","added_by":"auto","created_at":"2024-05-09 13:48:52","extension":"png","order_by":13,"title":"Figure 13","display":"","copyAsset":false,"role":"figure","size":5743688,"visible":true,"origin":"","legend":"\u003cp\u003eSEM images of grafted alcohol sheet cellulose-PP composite without MAPP (a, b, c) and grafted alcohol sheet cellulose-PP composite with MAPP (d, e, f) at magnifications of 100× (a, d), 400× (b, e), and 200× (surface image, c, f).\u003c/p\u003e","description":"","filename":"Figure13.png","url":"https://assets-eu.researchsquare.com/files/rs-4340356/v1/cb5044e8b269dc3a8597dbf5.png"},{"id":56179404,"identity":"3607a292-fce1-469f-b593-9a950cbd74ba","added_by":"auto","created_at":"2024-05-09 13:56:52","extension":"png","order_by":14,"title":"Figure 14","display":"","copyAsset":false,"role":"figure","size":7038952,"visible":true,"origin":"","legend":"\u003cp\u003eMicroscopic images of water handsheet-based composite films at 50× magnification.\u003c/p\u003e","description":"","filename":"Figure14.png","url":"https://assets-eu.researchsquare.com/files/rs-4340356/v1/41096207817bd1f4fd92b604.png"},{"id":56179032,"identity":"0facc3d5-601b-4439-af43-5cccc0dc5050","added_by":"auto","created_at":"2024-05-09 13:48:51","extension":"png","order_by":15,"title":"Figure 15","display":"","copyAsset":false,"role":"figure","size":7088491,"visible":true,"origin":"","legend":"\u003cp\u003eMicroscopic images of alcohol handsheet-based composite films at 50× magnification.\u003c/p\u003e","description":"","filename":"Figure15.png","url":"https://assets-eu.researchsquare.com/files/rs-4340356/v1/394d61390ea73b1f03d41248.png"},{"id":56177413,"identity":"ffb01ff1-364e-412e-a5e2-9652b65e592d","added_by":"auto","created_at":"2024-05-09 13:24:53","extension":"png","order_by":16,"title":"Figure 16","display":"","copyAsset":false,"role":"figure","size":32456,"visible":true,"origin":"","legend":"\u003cp\u003eFormation index of cellulose-PP composites.\u003c/p\u003e","description":"","filename":"Figure16.png","url":"https://assets-eu.researchsquare.com/files/rs-4340356/v1/096d1c7b09226326a03874bd.png"},{"id":56318225,"identity":"d24cefe2-9d3e-4102-970e-1e2ccaefc493","added_by":"auto","created_at":"2024-05-12 01:02:00","extension":"pdf","order_by":0,"title":"","display":"","copyAsset":false,"role":"manuscript-pdf","size":49346375,"visible":true,"origin":"","legend":"","description":"","filename":"manuscript.pdf","url":"https://assets-eu.researchsquare.com/files/rs-4340356/v1/c732b037-0aeb-4766-b585-928072147bf9.pdf"}],"financialInterests":"No competing interests reported.","formattedTitle":"Effect of Gas-Grafting Pretreatment of Cellulose on Properties of Cellulose-Polypropylene Composites","fulltext":[{"header":"Introduction","content":"\u003cp\u003eWith the recent increase in plastic usage contributing to environmental pollution, countries worldwide are making efforts to reduce plastic consumption. Global plastic production has risen steadily, increasing approximately seven-fold from 50\u0026nbsp;million tons in 1976 to 367\u0026nbsp;million tons in 2020, with projections suggesting it will quadruple by 2050 compared to that in 2020 (Plastics Europe 2021). As regulations aimed at reducing plastic production strengthen, there have been calls to replace common plastic interior materials in vehicles with eco-friendly alternatives based on natural materials (You 2015). Bio-based plastic composites, derived from natural materials, are eco-friendly alternatives that are either biodegradable or can replace existing plastics using plant-derived resources.\u003c/p\u003e \u003cp\u003eCellulose, a prominent plant-derived natural material known for its excellent mechanical properties, low density, and biodegradability, consists of linear chains linked by β-1, 4 glycosidic bonds and contains hydroxyl groups at carbons 2, 3, and 6 within the glucose unit, making it polar (Bezerra et al. \u003cspan citationid=\"CR2\" class=\"CitationRef\"\u003e2015\u003c/span\u003e; Ma et al. \u003cspan citationid=\"CR17\" class=\"CitationRef\"\u003e2016\u003c/span\u003e; Roy et al. \u003cspan citationid=\"CR22\" class=\"CitationRef\"\u003e2009\u003c/span\u003e). However, in polymer composite manufacturing, cellulose fibers struggle to mix well with nonpolar polymer resins due to fiber flocculation caused by the polar surface of cellulose. To address this issue and enhance the strength of bioplastic composites, the primary approach involves improving the compatibility of cellulose with hydrophobic polymers using compatibilizers (Coutinho et al. \u003cspan citationid=\"CR5\" class=\"CitationRef\"\u003e1997\u003c/span\u003e). A common method to enhance the compatibility of polypropylene (PP), a nonpolar polymer, is by improving interfacial adhesion through the addition of PP modified to maleic anhydride (maleic anhydride-grafted polypropylene (MAPP)) (Kim et al. \u003cspan citationid=\"CR11\" class=\"CitationRef\"\u003e2007\u003c/span\u003e; Mohanty et al. \u003cspan citationid=\"CR18\" class=\"CitationRef\"\u003e2004\u003c/span\u003e; Qiu et al. \u003cspan citationid=\"CR20\" class=\"CitationRef\"\u003e2005\u003c/span\u003e). The reaction mechanism of MAPP is illustrated in Fig.\u0026nbsp;\u003cspan refid=\"Fig1\" class=\"InternalRef\"\u003e1\u003c/span\u003e. However, there are concerns that while MAPP improves adhesion at the interface, it may not effectively promote mixing between nonpolar polymer resins and fibers, potentially preventing an increase in the melt viscosity of composite resins owing to the introduction of fibers.\u003c/p\u003e \u003cp\u003e \u003c/p\u003e \u003cp\u003eThe hydroxyl groups of cellulose can undergo chemical surface modification through processes such as etherification, esterification, crosslinking, and graft copolymerization (Hwang et al. \u003cspan citationid=\"CR10\" class=\"CitationRef\"\u003e2005\u003c/span\u003e; Roy et al. \u003cspan citationid=\"CR22\" class=\"CitationRef\"\u003e2009\u003c/span\u003e). In France, Samain (\u003cspan citationid=\"CR24\" class=\"CitationRef\"\u003e2002\u003c/span\u003e) developed a technique to hydrophobize the surface of hydrophilic cellulose with hydroxyl groups using gas grafting with fatty acid chlorides. Chromatogenic technology forms ester bonds by reacting gaseous fatty acid chlorides with hydroxyl groups, which can be used to modify the surface of cellulose (Choi et al. \u003cspan citationid=\"CR3\" class=\"CitationRef\"\u003e2019\u003c/span\u003e).\u003c/p\u003e \u003cp\u003ePrevious methods for forming ester bonds between fatty acids and cellulose have primarily involved liquid-phase reactions using organic solvents (Freire et al. \u003cspan citationid=\"CR7\" class=\"CitationRef\"\u003e2006\u003c/span\u003e; Uschanov et al. \u003cspan citationid=\"CR25\" class=\"CitationRef\"\u003e2011\u003c/span\u003e; Vaca-Garcia et al. \u003cspan citationid=\"CR26\" class=\"CitationRef\"\u003e1998\u003c/span\u003e). However, Berlioz et al. (\u003cspan citationid=\"CR1\" class=\"CitationRef\"\u003e2008\u003c/span\u003e) reported that a vapor-phase grafting reaction using fatty acid chlorides could form ester bonds with the hydroxyl groups of cellulose. Choi et al. (\u003cspan citationid=\"CR4\" class=\"CitationRef\"\u003e2020\u003c/span\u003e) compared the gas-grafting efficiency of fatty acid chlorides with different alkyl chain lengths and observed that longer alkyl chains resulted in higher hydrophobization efficiency. Fibers hydrophobized by reacting with the hydroxyl groups on the cellulose surface using gaseous fatty acid chlorides can be uniformly dispersed in plastics. Lee et al. (\u003cspan citationid=\"CR13\" class=\"CitationRef\"\u003e2021\u003c/span\u003e) reported that the flexural strength of bioplastics improved with increasing reaction time and temperature during the gas grafting of cellulose fibers for plastic composite manufacturing. Hydrophobization of cellulose fibers through the gas grafting of chlorinated fatty acids is feasible for fluffy fibers made from cellulose pulp. However, in this case, the large volume of fluffed cellulose fibers poses transportation challenges and necessitates the construction of separate equipment capable of processing substantial amounts of raw materials for the gas-grafting hydrophobization treatment of fluffed fibers. To overcome these challenges, the hydrophobization of cellulose fibers can be achieved using equipment developed for the gas grafting of paper using the existing reel-to-reel method. Cellulose fibers are molded into paper, hydrophobized, and then fluffed to produce fluffy fibers, effectively addressing the aforementioned challenges.\u003c/p\u003e \u003cp\u003eDuring the paper-forming process, hydrogen bonds are formed between fibers through dewatering and drying (Giertz \u003cspan citationid=\"CR8\" class=\"CitationRef\"\u003e1964\u003c/span\u003e; Giertz and R\u0026oslash;dland \u003cspan citationid=\"CR9\" class=\"CitationRef\"\u003e1979\u003c/span\u003e; Lindstrom et al. \u003cspan citationid=\"CR14\" class=\"CitationRef\"\u003e2005\u003c/span\u003e; Lobben \u003cspan citationid=\"CR16\" class=\"CitationRef\"\u003e1975\u003c/span\u003e; Retulainen \u003cspan citationid=\"CR21\" class=\"CitationRef\"\u003e1997\u003c/span\u003e; Vainio and Paulapuro \u003cspan citationid=\"CR27\" class=\"CitationRef\"\u003e2007\u003c/span\u003e). However, a disadvantage of this method is that many hydroxyl groups participate in the formation of hydrogen bonds between the fibers constituting the sheet, thereby reducing the number of hydroxyl groups available to react with fatty acid chlorides. Additionally, during paper sheet formation, the availability of hydroxyl groups for the reaction decreases as surface fibrils align with the fiber surface through the drying process. It was expected that the use of alcohol with low surface tension during paper manufacturing would prevent surface fibrils from matting together on the surface even after drying, thereby facilitating the production of bulky sheets. Consequently, increasing the substitution of hydroxyl groups with alkyl chains is expected to increase the hydrophobization efficiency. Hence, we attempted to improve the hydrophobization efficiency of cellulose fibers through gas grafting by increasing the specific surface area of the fibers. This involved manufacturing paper by replacing the water in the cellulose fiber stock with ethanol during sheet molding to prevent the macrofibrils from matting on the fiber surface. In addition, during the addition of a compatibilizer for plastic composite manufacturing, we investigated the degree of fiber dispersion within the composite and assessed changes in the composite strength based on the hydroxyl group content.\u003c/p\u003e"},{"header":"Materials and methods","content":"\u003cdiv id=\"Sec3\" class=\"Section2\"\u003e \u003ch2\u003eMaterials\u003c/h2\u003e \u003cp\u003eIn this study, bleached hardwood kraft pulp (Moorim P\u0026amp;P, Korea) was provided in a dried lap form and used as the raw material for cellulose sheets. PP (Adstif HA5029, Lyondell Basell, USA) was used to manufacture the composite material, and its physical properties are listed in Table\u0026nbsp;\u003cspan refid=\"Tab1\" class=\"InternalRef\"\u003e1\u003c/span\u003e. MAPP (IRUBOND100, Iruchem, Korea) was used to investigate the effect of compatibilizers on the interfacial adhesion between the cellulose fiber and PP.\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\u003eCharacteristics of polypropylene\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=\"left\" class=\"colspec\" colname=\"c3\" colnum=\"3\"\u003e\u003c/div\u003e \u003cthead\u003e \u003ctr\u003e \u003cth align=\"left\" colname=\"c1\"\u003e \u003cp\u003eItem\u003c/p\u003e \u003c/th\u003e \u003cth align=\"left\" colname=\"c2\"\u003e \u003cp\u003eUnit\u003c/p\u003e \u003c/th\u003e \u003cth align=\"left\" colname=\"c3\"\u003e \u003cp\u003eValue\u003c/p\u003e \u003c/th\u003e \u003c/tr\u003e \u003c/thead\u003e \u003ctbody\u003e \u003ctr\u003e \u003ctd align=\"left\" colname=\"c1\"\u003e \u003cp\u003eMelt flow index (230 ℃/ 2.16 kg)\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c2\"\u003e \u003cp\u003eg/10 min\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c3\"\u003e \u003cp\u003e65\u003c/p\u003e \u003c/td\u003e \u003c/tr\u003e \u003ctr\u003e \u003ctd align=\"left\" colname=\"c1\"\u003e \u003cp\u003eDensity\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c2\"\u003e \u003cp\u003eg/cm\u0026sup3;\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c3\"\u003e \u003cp\u003e0.90\u003c/p\u003e \u003c/td\u003e \u003c/tr\u003e \u003ctr\u003e \u003ctd align=\"left\" colname=\"c1\"\u003e \u003cp\u003eDeflection temperature under load (0.46 N/mm\u0026sup2;)\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c2\"\u003e \u003cp\u003e℃\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c3\"\u003e \u003cp\u003e140\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\u003eIn contrast to the process for conventional handsheet molding, ethyl alcohol (Daejeong Chemicals \u0026amp; Metals, Korea) was used for papermaking instead of water. Palmitoyl chloride (ACROS, Italy) served as the fatty acid chloride for gas grafting. Petroleum ether (Daejeong Chemical Metals, Korea) was used as the diluting solvent for palmitoyl chloride during grafting. The physical properties of palmitoyl chloride are listed in Table\u0026nbsp;\u003cspan refid=\"Tab2\" class=\"InternalRef\"\u003e2\u003c/span\u003e. Acetone (Daejeong Chemicals \u0026amp; Metals, Korea) was utilized as the washing solvent to remove the excess fatty acids from the sheet after gas grafting.\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\u003eCharacteristics of palmitoyl chloride\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=\"left\" class=\"colspec\" colname=\"c3\" colnum=\"3\"\u003e\u003c/div\u003e \u003cthead\u003e \u003ctr\u003e \u003cth align=\"left\" colname=\"c1\"\u003e \u003cp\u003eItem\u003c/p\u003e \u003c/th\u003e \u003cth align=\"left\" colname=\"c2\"\u003e \u003cp\u003eUnit\u003c/p\u003e \u003c/th\u003e \u003cth align=\"left\" colname=\"c3\"\u003e \u003cp\u003eValue\u003c/p\u003e \u003c/th\u003e \u003c/tr\u003e \u003c/thead\u003e \u003ctbody\u003e \u003ctr\u003e \u003ctd align=\"left\" colname=\"c1\"\u003e \u003cp\u003eMelting point\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c2\"\u003e \u003cp\u003e℃\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c3\"\u003e \u003cp\u003e11\u0026ndash;13\u003c/p\u003e \u003c/td\u003e \u003c/tr\u003e \u003ctr\u003e \u003ctd align=\"left\" colname=\"c1\"\u003e \u003cp\u003eBoiling point\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c2\"\u003e \u003cp\u003e℃\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c3\"\u003e \u003cp\u003e88\u0026ndash;90\u003c/p\u003e \u003c/td\u003e \u003c/tr\u003e \u003ctr\u003e \u003ctd align=\"left\" colname=\"c1\"\u003e \u003cp\u003eMolecular weight\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c2\"\u003e \u003cp\u003eg/mol\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c3\"\u003e \u003cp\u003e247.87\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=\"Sec4\" class=\"Section2\"\u003e \u003ch2\u003eBeating and sheet forming using water and alcohol\u003c/h2\u003e \u003cp\u003eThe cellulose fibers were beaten to 500 mL CSF (Canadian standard freeness) using a laboratory valley beater and then used to make paper. The freeness was measured according to TAPPI Standard T227 om-99. During handsheet manufacturing, there was a concern about potential differences in the physical properties of the paper owing to the varying fines retention between the alcohol-forming and water-forming processes. To prevent these differences in physical properties due to fines between the handsheets molded with water and alcohol, the fines in the stock were removed by hyperwashing. After hyperwashing the beaten fibers, the fiber suspension was dispersed in ethyl alcohol for alcohol-based sheet formation and in water for water-based sheet formation at a consistency of 0.3%. Handsheets with a target basis weight of 100\u0026thinsp;\u0026plusmn;\u0026thinsp;1 g/m\u0026sup2; were manufactured using a square handsheet former (30\u0026times;30 cm\u0026sup2;) with each stock as a raw material.\u003c/p\u003e \u003c/div\u003e \u003cdiv id=\"Sec5\" class=\"Section2\"\u003e \u003ch2\u003eGas grafting\u003c/h2\u003e \u003cp\u003eThe handsheets were immersed in a solution of palmitoyl chloride diluted in petroleum ether to a concentration of 1%. After dipping, the handsheets were removed and the petroleum ether was allowed to evaporate. Subsequently, the handsheets were pressed using a hot press at 200\u0026deg;C for the upper plate and 100\u0026deg;C for the lower plate, with a pressing pressure of 400 g\u003csub\u003ef\u003c/sub\u003e/cm\u0026sup2; for a grafting time of 6 s. Following gas grafting by hot pressing, acetone washing was performed to remove any unreacted palmitoyl chloride and free palmitic acid remaining on the sheets. The washed sheets were then subjected to ultrasonic cleaning for 15 min using an ultrasonic cleaner (JAC Ultrasonic 4020; Jinwoo, Korea). Finally, the washed sheets were impregnated with acetone and stirred for 2 min using a shaker further to remove any unreacted palmitoyl chloride and palmitic acid.\u003c/p\u003e \u003c/div\u003e \u003cdiv id=\"Sec6\" class=\"Section2\"\u003e \u003ch2\u003eCellulose-PP composite manufacturing and sample preparation\u003c/h2\u003e \u003cp\u003eTo manufacture the cellulose-PP composite material, the handsheets were fluffed and mixed with PP using a twin-screw compounding extruder (Bautek, Korea). The cellulose content in the composite was fixed at 30 wt%, and MAPP was added at 0 wt% and 3 wt% under each condition to determine the effect of the compatibilizer. During the production of composite pellets, the zone temperatures of the twin-screw extruder were set to 180/170/170/170/170/170\u0026deg;C, and the screw speed was maintained at 300 rpm. The raw material mixing ratios of the composite materials are listed in Table\u0026nbsp;\u003cspan refid=\"Tab3\" class=\"InternalRef\"\u003e3\u003c/span\u003e. To prepare specimens for strength measurements, the manufactured pellets were made into a film with a thickness of 0.2 mm using a hot press. Figure\u0026nbsp;\u003cspan refid=\"Fig2\" class=\"InternalRef\"\u003e2\u003c/span\u003e shows a schematic of the film production using a hot press.\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\u003eFormulation of the composites\u003c/p\u003e \u003c/div\u003e \u003c/caption\u003e \u003ccolgroup cols=\"6\"\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=\"char\" char=\".\" class=\"colspec\" colname=\"c6\" colnum=\"6\"\u003e\u003c/div\u003e \u003cthead\u003e \u003ctr\u003e \u003cth align=\"left\" colname=\"c1\"\u003e \u003cp\u003eItem\u003c/p\u003e \u003c/th\u003e \u003cth align=\"left\" colname=\"c2\"\u003e \u003cp\u003eHandsheet type\u003c/p\u003e \u003c/th\u003e \u003cth align=\"left\" colname=\"c3\"\u003e \u003cp\u003eCellulose\u003c/p\u003e \u003cp\u003e(wt%)\u003c/p\u003e \u003c/th\u003e \u003cth align=\"left\" colname=\"c4\"\u003e \u003cp\u003ePP\u003c/p\u003e \u003cp\u003e(wt%)\u003c/p\u003e \u003c/th\u003e \u003cth align=\"left\" colname=\"c5\"\u003e \u003cp\u003eGas grafting\u003c/p\u003e \u003c/th\u003e \u003cth align=\"left\" colname=\"c6\"\u003e \u003cp\u003eMAPP\u003c/p\u003e \u003cp\u003e(wt%)\u003c/p\u003e \u003c/th\u003e \u003c/tr\u003e \u003c/thead\u003e \u003ctbody\u003e \u003ctr\u003e \u003ctd align=\"left\" colname=\"c1\"\u003e \u003cp\u003eW1\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c2\" morerows=\"3\" rowspan=\"4\"\u003e \u003cp\u003eWater\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c3\" morerows=\"7\" rowspan=\"8\"\u003e \u003cp\u003e30\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c4\" morerows=\"7\" rowspan=\"8\"\u003e \u003cp\u003e70\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c5\" morerows=\"1\" rowspan=\"2\"\u003e \u003cp\u003eX\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c6\"\u003e \u003cp\u003e0\u003c/p\u003e \u003c/td\u003e \u003c/tr\u003e \u003ctr\u003e \u003ctd align=\"left\" colname=\"c1\"\u003e \u003cp\u003eW2\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c6\"\u003e \u003cp\u003e3\u003c/p\u003e \u003c/td\u003e \u003c/tr\u003e \u003ctr\u003e \u003ctd align=\"left\" colname=\"c1\"\u003e \u003cp\u003eW3\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c5\" morerows=\"1\" rowspan=\"2\"\u003e \u003cp\u003eO\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c6\"\u003e \u003cp\u003e0\u003c/p\u003e \u003c/td\u003e \u003c/tr\u003e \u003ctr\u003e \u003ctd align=\"left\" colname=\"c1\"\u003e \u003cp\u003eW4\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c6\"\u003e \u003cp\u003e3\u003c/p\u003e \u003c/td\u003e \u003c/tr\u003e \u003ctr\u003e \u003ctd align=\"left\" colname=\"c1\"\u003e \u003cp\u003eA1\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c2\" morerows=\"3\" rowspan=\"4\"\u003e \u003cp\u003eAlcohol\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c5\" morerows=\"1\" rowspan=\"2\"\u003e \u003cp\u003eX\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c6\"\u003e \u003cp\u003e0\u003c/p\u003e \u003c/td\u003e \u003c/tr\u003e \u003ctr\u003e \u003ctd align=\"left\" colname=\"c1\"\u003e \u003cp\u003eA2\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c6\"\u003e \u003cp\u003e3\u003c/p\u003e \u003c/td\u003e \u003c/tr\u003e \u003ctr\u003e \u003ctd align=\"left\" colname=\"c1\"\u003e \u003cp\u003eA3\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c5\" morerows=\"1\" rowspan=\"2\"\u003e \u003cp\u003eO\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c6\"\u003e \u003cp\u003e0\u003c/p\u003e \u003c/td\u003e \u003c/tr\u003e \u003ctr\u003e \u003ctd align=\"left\" colname=\"c1\"\u003e \u003cp\u003eA4\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c6\"\u003e \u003cp\u003e3\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 \u003c/p\u003e \u003c/div\u003e \u003cdiv id=\"Sec7\" class=\"Section2\"\u003e \u003ch2\u003ePhysical property analysis\u003c/h2\u003e \u003cdiv id=\"Sec8\" class=\"Section3\"\u003e \u003ch2\u003eWater retention value of handsheet\u003c/h2\u003e \u003cp\u003eTo compare the exposure of the number of hydroxyl groups in water and alcohol sheets, both sheets were immersed in water and then dewatered using centrifugal force at 900 G for 30 min. The dewatered wet sheet was subsequently dried in a dryer at 105\u0026deg;C for 24 h, and the water retention value (WRV) was measured.\u003c/p\u003e \u003c/div\u003e \u003c/div\u003e \u003cdiv id=\"Sec9\" class=\"Section2\"\u003e \u003ch2\u003eQuantitative analysis of free and grafted palmitic acid in the sheets\u003c/h2\u003e \u003cp\u003eGas chromatography (GC, 8890 GC system, Agilent Technologies, USA) was employed to analyze the contents of the reacted palmitic acid and free palmitic acid in the gas-grafted handsheets of each item. Unreacted palmitic acids in the sample, as well as palmitic acids derived from palmitoyl chloride that reacted with the hydroxyl groups of cellulose fibers, were extracted and separated through Soxhlet extraction and saponification. Subsequently, GC analysis was performed (Choi et al. \u003cspan citationid=\"CR3\" class=\"CitationRef\"\u003e2019\u003c/span\u003e).\u003c/p\u003e \u003c/div\u003e \u003cdiv id=\"Sec10\" class=\"Section2\"\u003e \u003ch2\u003eMelt flow index measurement\u003c/h2\u003e \u003cp\u003eThe melt flow index (MFI) of the manufactured cellulose-PP pellets was measured using a melt flow indexer (Hanatek, UK) according to ASTM D1238 (200\u0026deg;C, load 2.16 kg) standards.\u003c/p\u003e \u003c/div\u003e \u003cdiv id=\"Sec11\" class=\"Section2\"\u003e \u003ch2\u003eTensile strength measurement of composite films\u003c/h2\u003e \u003cp\u003eThe tensile strengths of the cellulose-PP composite films were measured using a universal testing machine (WL2100C, Withlab, Korea) following ASTM D882 standards.\u003c/p\u003e \u003c/div\u003e \u003cdiv id=\"Sec12\" class=\"Section2\"\u003e \u003ch2\u003eAnalysis of morphological characteristics of composite materials\u003c/h2\u003e \u003cp\u003eScanning electron microscopy (SEM) was employed to observe the fiber dispersion characteristics within the cellulose-PP composite pellets. Platinum was used as the coating material for capturing the fracture surface and surface images of the pellets. SEM (CX-200TM, COXEM, Korea) imaging was performed at an acceleration voltage of 20 kV.\u003c/p\u003e \u003cp\u003eTo indirectly measure the dispersion of cellulose fibers in the composite film, fiber dispersion images were captured using a transmission microscope (AST-ICS305B, Alphasystec, Korea). In addition, to quantify the degree of fiber dispersion, the captured images were printed on overhead projector (OHP) film, and the formation index of the dispersed fibers was measured using an Optest Formation Tester (Optest Equipment, Canada). Figure\u0026nbsp;\u003cspan refid=\"Fig3\" class=\"InternalRef\"\u003e3\u003c/span\u003e shows the overall experimental method and schematic for measuring the degree of fiber dispersion in the film.\u003c/p\u003e \u003cp\u003e \u003c/p\u003e \u003c/div\u003e"},{"header":"Results and discussion","content":"\u003cdiv id=\"Sec14\" class=\"Section2\"\u003e \u003ch2\u003eComparison of grafting efficiency by handsheet type\u003c/h2\u003e \u003cdiv id=\"Sec15\" class=\"Section3\"\u003e \u003ch2\u003eMorphological characteristics of handsheet\u003c/h2\u003e \u003cp\u003eThe WRV was measured to indirectly compare the exposed hydroxy groups of conventional water-formed and alcohol-formed handsheets. When using the existing WRV measurement method to assess dissociated paper stock, evaluation of the exposed hydroxyl content in the handsheet form is complicated due to the formation of extra fibrils on the fiber surface. To address this, the handsheets were immersed in water and then dewatered using a centrifuge. The WRV measurements are shown in Fig.\u0026nbsp;\u003cspan refid=\"Fig4\" class=\"InternalRef\"\u003e4\u003c/span\u003e. The alcohol-formed handsheet exhibited a higher WRV compared to the regular water-formed handsheet. This difference is attributed to the higher number of exposed hydroxyl groups in the alcohol-formed handsheet. During sheet formation, the external fibrils of beaten fibers tend to mat down through dewatering and drying. Using alcohol instead of water for sheet molding prevents fibril matting by disrupting hydrogen bonding, thereby increasing the surface area. Consequently, the alcohol-formed handsheet exhibited an enhanced WRV, indicative of improved hydrophobization efficiency following the gas-grafting reaction.\u003c/p\u003e \u003cp\u003e \u003c/p\u003e \u003c/div\u003e \u003c/div\u003e \u003cdiv id=\"Sec16\" class=\"Section2\"\u003e \u003ch2\u003eGC analysis of free and grafted palmitic acid in sheets\u003c/h2\u003e \u003cp\u003eFigure\u0026nbsp;\u003cspan refid=\"Fig5\" class=\"InternalRef\"\u003e5\u003c/span\u003e shows the quantities of reacted palmitic acid and unreacted free palmitic acid after the gas grafting of the handsheet. Significantly, the amount of palmitic acid that reacted in the alcohol-formed handsheet was more than twice that in the water-formed handsheet. During the gas-grafting reaction, the unreacted palmitoyl chloride from the applied palmitoyl chloride dissipated into the air. In contrast, in the case of the alcohol-formed handsheet, the gas grafting of palmitoyl chloride proceeded effectively, allowing the palmitoyl chloride to react without dissipating, resulting in more than double the amount of reacted palmitic acid compared to that in the water-formed handsheet. Despite similar amounts of unreacted palmitic acid in the water and alcohol handsheets, the grafting reaction proceeded normally. These results are believed to be attributed to the increased accessibility of the hydroxyl group in the alcohol-formed handsheet.\u003c/p\u003e \u003cp\u003e \u003c/p\u003e \u003c/div\u003e \u003cdiv id=\"Sec17\" class=\"Section2\"\u003e \u003ch2\u003eChanges in physical properties of composite due to hydrophobization pretreatment of fibers\u003c/h2\u003e \u003cdiv id=\"Sec18\" class=\"Section3\"\u003e \u003ch2\u003eMelt flow index of composite\u003c/h2\u003e \u003cp\u003eTo evaluate the impact of cellulose hydrophobization on the melt flow of the cellulose-PP composite, the MFI was measured, and the results are shown in Fig.\u0026nbsp;\u003cspan refid=\"Fig6\" class=\"InternalRef\"\u003e6\u003c/span\u003e and Fig.\u0026nbsp;\u003cspan refid=\"Fig7\" class=\"InternalRef\"\u003e7\u003c/span\u003e. The analysis revealed a significant increase in the MFI when the composite was manufactured using fibers hydrophobized through a vapor-phase graft reaction. This process involved hydrophobizing cellulose fibers through gas grafting and ensuring uniform mixing with PP to improve fluidity during the production of plastic composites. In the un-grafted case, the MFI of the alcohol sheet-based composite was lower than that of the water sheet due to the presence of more fibrils on the alcohol sheet surface, which facilitated fiber aggregation. Conversely, in the grafted case, the MFI of the alcohol sheet-based composite was higher than that of the water sheet, as the surface fibrils of the alcohol sheet promoted hydrophobization. The addition of a compatibilizer increased the viscosity of the composite, resulting in a reduction in the MFI. This effect is attributed to the increased viscosity caused by the combination of MAPP with cellulose fibers, forming longer molecular chains.\u003c/p\u003e \u003cp\u003e \u003c/p\u003e \u003cp\u003e \u003c/p\u003e \u003c/div\u003e \u003c/div\u003e \u003cdiv id=\"Sec19\" class=\"Section2\"\u003e \u003ch2\u003eTensile strength of composite film\u003c/h2\u003e \u003cp\u003eThe tensile strength was measured to assess the strength characteristics of the cellulose-PP composite based on cellulose fiber hydrophobization and the addition of MAPP. Owing to significant variations in the specimen weight when cut to a specific size, the tensile strength was normalized into a tensile index (Fig.\u0026nbsp;\u003cspan refid=\"Fig8\" class=\"InternalRef\"\u003e8\u003c/span\u003e and Fig.\u0026nbsp;\u003cspan refid=\"Fig9\" class=\"InternalRef\"\u003e9\u003c/span\u003e). The experimental results indicated that the tensile strength of the composite with hydrophobized fibers was superior to that of the composite with untreated fibers without gas grafting. It is believed that the improved fiber dispersibility through gas grafting contributed to the enhanced strength of the composite.\u003c/p\u003e \u003cp\u003eWhen bulky handsheets made with alcohol were subjected to gas-grafting hydrophobization, the amount of reacted palmitic acid was twice that in the regular water handsheet. Hence, it was predicted that the number of residual hydroxyl groups available to react with the compatibilizer would decrease. However, contrary to these predictions, the tensile strength of the alcohol handsheet-based composite was superior to that of the regular water handsheet, even with the addition of the compatibilizer. In the case of the composite made of alcohol sheets, the strength improvement due to grafting was greater than that of the water sheets. Considering the WRV, it was found that unlike general water handsheets, during the production of alcohol handsheets, the fibrils on the surface of the fibers did not decrease but instead dispersed, increasing the specific surface area of the fibers. Therefore, even though the amount of reacted palmitic acid increased, the number of hydroxyl groups available for reacting with the compatibilizer did not decrease. This suggests that the strength-improvement effect of the compatibilizer in the alcohol handsheet-based composite was superior to that of the water handsheet. For the composites based on grafted fibers, the strength-improvement effect of the compatibilizer was weaker compared to that for the ungrafted composite.\u003c/p\u003e \u003cp\u003e \u003c/p\u003e \u003cp\u003e \u003c/p\u003e \u003c/div\u003e \u003cdiv id=\"Sec20\" class=\"Section2\"\u003e \u003ch2\u003eMorphological results of cellulose-PP composite\u003c/h2\u003e \u003cdiv id=\"Sec21\" class=\"Section3\"\u003e \u003ch2\u003eSEM results of cellulose-PP composite\u003c/h2\u003e \u003cp\u003eThe fracture surface and surface images of the pellets obtained using SEM are shown in Figs.\u0026nbsp;\u003cspan refid=\"Fig10\" class=\"InternalRef\"\u003e10\u003c/span\u003e\u0026ndash;\u003cspan refid=\"Fig13\" class=\"InternalRef\"\u003e13\u003c/span\u003e. The surface of the composite pellet without gas-grafted fibers appears rough, whereas that of the pellet with gas-grafted fibers appears smooth. The gas-grafted cellulose fibers were uniformly dispersed in the PP matrix without agglomeration, contributing to the smooth surface appearance. By observing the fracture surface after adding MAPP, it was confirmed that MAPP enhanced interfacial adhesion, resulting in more uniform fiber bonding. Thus, gas grafting of the fiber sheets significantly improved fiber dispersion and the MFI of the composite material, while also enhancing interfacial adhesion with the compatibilizer.\u003c/p\u003e \u003cp\u003e \u003c/p\u003e \u003cp\u003e \u003c/p\u003e \u003cp\u003e \u003c/p\u003e \u003cp\u003e \u003c/p\u003e \u003c/div\u003e \u003c/div\u003e \u003cdiv id=\"Sec22\" class=\"Section2\"\u003e \u003ch2\u003eTransmission microscopy analysis of composite films\u003c/h2\u003e \u003cp\u003eAfter manufacturing the plastic composite film, transmission microscopy images were captured to confirm the degree of cellulose fiber dispersion (Figs.\u0026nbsp;\u003cspan refid=\"Fig14\" class=\"InternalRef\"\u003e14\u003c/span\u003e and \u003cspan refid=\"Fig15\" class=\"InternalRef\"\u003e15\u003c/span\u003e). Each image was analyzed using a formation tester typically used for assessing paper formation, and the degree of fiber dispersion was quantified, as shown in Fig.\u0026nbsp;\u003cspan refid=\"Fig16\" class=\"InternalRef\"\u003e16\u003c/span\u003e. Upon observing the transmission microscope images, it was confirmed that gas grafting had a significant effect on the uniformity of the cellulose-PP film fiber distribution. The formation index increased, indicating improved dispersion of the gas-grafted fibers. Furthermore, the formation index was found to increase with the addition of MAPP. This phenomenon is attributed to the increased viscosity of the composite material upon the addition of MAPP, which reduces fiber agglomeration.\u003c/p\u003e \u003cp\u003e \u003c/p\u003e \u003cp\u003e \u003c/p\u003e \u003cp\u003e \u003c/p\u003e \u003c/div\u003e"},{"header":"Conclusion","content":"\u003cp\u003eHydrophilic cellulose and hydrophobic PP do not blend well during the manufacturing of bio-based plastic composites. Previous efforts have focused on enhancing the interfacial adhesion between cellulose and plastics by adding compatibilizers such as MAPP. However, it remains uncertain whether improving the compatibility would reduce the MFI of fiber-blended PP and promote extrusion.\u003c/p\u003e \u003cp\u003eIn this study, a method was explored to modify cellulose fibers to render them hydrophobic, facilitating easier blending with PP. Gas grafting of palmitoyl chloride onto paper was attempted using a laboratory-scale hot press. One disadvantage of this method is that the number of hydroxyl groups available for reacting with fatty acid chlorides decreases due to hydrogen bond formation between the fibers during paper molding. However, hydrophobizing the molded paper presents an advantage, in that the hydroxyl groups on the surface of the inter-fiber bond, where the gas-grafting reaction did not occur, can later react with the compatibilizer. Pretreated fibers can achieve more uniform dispersion in plastic by forming ester bonds via the reaction of the hydroxyl groups on the cellulose surface with gaseous palmitoyl chlorides.\u003c/p\u003e \u003cp\u003eTo improve the efficiency of cellulose hydrophobization through gas grafting, we aimed to increase the specific surface area of the fibers. For this purpose, paper was manufactured by replacing the water in the cellulose fiber stock with ethanol during sheet molding to prevent macrofibrils from matting on the fiber surface. The resulting alcohol-molded sheets, which had a higher volume, contained more than twice the amount of reacted palmitic acid compared to ordinary water-based paper after gas-grafting treatment. Measurements revealed that the cellulose-PP composite film composed of pretreated fibers exhibited superior tensile strength compared to the film composed of non-grafted fibers. In other hand, the addition of MAPP, improved the fiber dispersibility, likely due to the increased viscosity of the composite; reduced fiber agglomeration; and increased the formation index. The improved dispersibility resulting from gas grafting correlated with increased composite strength. However, in the case of the grafted-fiber-based composites, the strength-improvement effect of the compatibilizer was weaker than for the ungrafted composite. A larger surface area facilitated a more efficient grafting process and increased the MFI. Unlike with MAPP addition, gas grafting of the fibers improved the composite strength by enhancing the fiber dispersibility without reducing the MFI.\u003c/p\u003e"},{"header":"Declarations","content":"\u003cp\u003e\u003cstrong\u003eConflict of interest\u003c/strong\u003e\u003c/p\u003e\n\u003cp\u003eThe authors declare no competing financial interest.\u003c/p\u003e\n\u003cp\u003e\u003cstrong\u003eConsent for publication\u003c/strong\u003e\u0026nbsp;\u003c/p\u003e\n\u003cp\u003eAll authors approved the final version of the manuscript.\u003c/p\u003e\n\u003cp\u003e\u003cstrong\u003eEthnical approval\u003c/strong\u003e\u0026nbsp;\u003c/p\u003e\n\u003cp\u003eAll authors have consented to participate on the manuscript.\u003c/p\u003e\n\u003cp\u003e\u003cstrong\u003e\u0026nbsp;\u003c/strong\u003e\u003cstrong\u003eAcknowledgements\u003c/strong\u003e\u003c/p\u003e\n\u003cp\u003eThis work was supported by the Technology Innovation Program (No.20010431) of Korea Evaluation Institute of Industrial Technology (KEIT) funded by the Ministry of trade, Industry \u0026amp; Energy (MOTIE).\u003c/p\u003e"},{"header":"References","content":"\u003col\u003e\n\u003cli\u003eBerlioz S, Stinga C, Condoret J et al (2008) SFGP 2007-investigation of a novel principle of chemical grafting for modification of cellulose fibers. 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Commercialization and Market of Bio-Plastics, Clean Technology 21(3): 141-152. https://doi.org/10.7464/ksct.2015.21.3.141\u003c/li\u003e\n\u003c/ol\u003e"}],"fulltextSource":"","fullText":"","funders":[],"hasAdminPriorityOnWorkflow":false,"hasManuscriptDocX":true,"hasOptedInToPreprint":true,"hasPassedJournalQc":"","hasAnyPriority":false,"hideJournal":true,"highlight":"","institution":"","isAcceptedByJournal":false,"isAuthorSuppliedPdf":false,"isDeskRejected":"","isHiddenFromSearch":false,"isInQc":false,"isInWorkflow":false,"isPdf":false,"isPdfUpToDate":true,"isWithdrawnOrRetracted":false,"journal":{"display":true,"email":"[email protected]","identity":"researchsquare","isNatureJournal":false,"hasQc":true,"allowDirectSubmit":true,"externalIdentity":"","sideBox":"","snPcode":"","submissionUrl":"/submission","title":"Research Square","twitterHandle":"researchsquare","acdcEnabled":true,"dfaEnabled":false,"editorialSystem":"","reportingPortfolio":"","inReviewEnabled":false,"inReviewRevisionsEnabled":true},"keywords":"Bio-based plastic, Cellulose-polypropylene composite, Fiber dispersion, Free hydroxyl group, Gas-phase grafting","lastPublishedDoi":"10.21203/rs.3.rs-4340356/v1","lastPublishedDoiUrl":"https://doi.org/10.21203/rs.3.rs-4340356/v1","license":{"name":"CC BY 4.0","url":"https://creativecommons.org/licenses/by/4.0/"},"manuscriptAbstract":"\u003cp\u003eThis study investigated a method to modify cellulose for enhanced hydrophobicity through gas-phase grafting with palmitoyl chloride, facilitating easier blending of fibers and polypropylene. In addition, cellulose sheets were produced by substituting water in the cellulose fiber stock with ethanol during sheet molding to prevent the matting of macrofibrils on the cellulose surface, thereby improving the hydrophobization efficiency achieved by gas grafting. The results revealed that alcohol-molded sheets, which expanded in volume, exhibited more than twice the amount of reacted fatty acids compared to conventional water-based cellulose sheets after gas grafting. Composite films composed of the pretreated fibers exhibited superior tensile strength relative to those made from non-grafted fibers. In particular, the addition of maleic-anhydride-grafted polypropylene (MAPP) improved the dispersibility of the cellulose fibers within the composite film, indicating the positive contribution of gas grafting and MAPP treatment.\u003c/p\u003e","manuscriptTitle":"Effect of Gas-Grafting Pretreatment of Cellulose on Properties of Cellulose-Polypropylene Composites","msid":"","msnumber":"","nonDraftVersions":[{"code":1,"date":"2024-05-09 13:24:13","doi":"10.21203/rs.3.rs-4340356/v1","editorialEvents":[{"type":"communityComments","content":0}],"status":"published","journal":{"display":true,"email":"[email protected]","identity":"researchsquare","isNatureJournal":false,"hasQc":true,"allowDirectSubmit":true,"externalIdentity":"","sideBox":"","snPcode":"","submissionUrl":"/submission","title":"Research Square","twitterHandle":"researchsquare","acdcEnabled":true,"dfaEnabled":false,"editorialSystem":"","reportingPortfolio":"","inReviewEnabled":false,"inReviewRevisionsEnabled":true}}],"origin":"","ownerIdentity":"39a093c9-6021-48a7-901e-bdd82cbcf348","owner":[],"postedDate":"May 9th, 2024","published":true,"recentEditorialEvents":[],"rejectedJournal":[],"revision":"","amendment":"","status":"posted","subjectAreas":[],"tags":[],"updatedAt":"2024-05-12T00:53:30+00:00","versionOfRecord":[],"versionCreatedAt":"2024-05-09 13:24:13","video":"","vorDoi":"","vorDoiUrl":"","workflowStages":[]},"version":"v1","identity":"rs-4340356","journalConfig":"researchsquare"},"__N_SSP":true},"page":"/article/[identity]/[[...version]]","query":{"redirect":"/article/rs-4340356","identity":"rs-4340356","version":["v1"]},"buildId":"qtupq5eGEP_6zYnWcrvyt","isFallback":false,"isExperimentalCompile":false,"dynamicIds":[84888],"gssp":true,"scriptLoader":[]}