Effect of alkaline-treated spent coffee grounds and compatibilizer on the mechanical properties of bio-composite based on polypropylene matrix

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In this study, the effect of alkaline-treated spent coffee grounds and compatibilizer on the mechanical properties of bio-composite based on polypropylene (PP) matrix was investigated. After alkaline treatment, the surface of spent coffee grounds became rougher; hence the PP matrix could better adsorb and encapsulate the treated coffee grounds compared with that of untreated ones. T

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Nội dung Text: Effect of alkaline-treated spent coffee grounds and compatibilizer on the mechanical properties of bio-composite based on polypropylene matrix

Cite this paper: Vietnam J. Chem., 2023, 61(S3), 148-153 Research Article DOI: 10.1002/vjch.202300064 Effect of alkaline-treated spent coffee grounds and compatibilizer on the mechanical properties of bio-composite based on polypropylene matrix Nguyen Ngoc Thanh1,*, Vu Minh Tan1, Dang Huu Trung1, Pham Thi Mai Huong1, Le Thi Hong Nhung1, Nguyen Manh Ha1, Ngo Thuy Van1, Nguyen Thanh Tung2, Nguyen Thi Thu Thuy3 1 Faculty of Chemical Technology, Hanoi University of Industry, Bac Tu Liem District, Hanoi 10000, Viet Nam 2 Institute of Chemistry, Vietnam Academy of Science and Technology, Cau Giay, Hanoi 10072, Viet Nam 3 Phenikaa University Nano Institute (PHENA), Phenikaa University, Hanoi 12116, Viet Nam Submitted February 18, 2023; Revised June 28, 2023; Accepted August 6, 2023 Abstract In this study, the effect of alkaline-treated spent coffee grounds and compatibilizer on the mechanical properties of bio-composite based on polypropylene (PP) matrix was investigated. After alkaline treatment, the surface of spent coffee grounds became rougher; hence the PP matrix could better adsorb and encapsulate the treated coffee grounds compared with that of untreated ones. The TGA analysis shows that the alkaline treated spent coffee grounds had better thermal properties than the untreated ones. When increasing the weight percentage of spent coffee grounds from 10 to 20, the tensile strength and flexural strength of PP-based composite decreased. These mechanical properties of PP-based composite containing treated coffee grounds were enhanced compared with that containing untreated coffee grounds due to the better dispersion of treated coffee grounds into the PP matrix. The presence of polypropylene-graft-maleic anhydride (PP-g-MA) compatibilizer at the content of 1, 3, and 5 wt% led to a significant increase the mechanical properties of PP-based bio-composites, reaching the highest tensile strength of 22.7 MPa and flexural strength of 17.3 MPa. Therefore, the alkaline-treated spent coffee ground is a potential additive for producing bio-composite with the advantages of being light and easy to naturally decompose. Keywords. Polypropylene, mechanical properties, spent coffee grounds, biocomposite. INTRODUCTION compatibilizer on the mechanical properties of a PP- based matrix reinforced by spent coffee grounds. In Plastic wastes are a serious threat to human and another study, P. Tapangnoi et al.[8] used spent coffee animal health because of their long decomposition grounds as a reinforcement material for natural period. Around 9 wt% of plastic wastes are recycled, rubber. Spent coffee grounds were alkaline treated in meanwhile, another large amount is accumulating in order to eliminate lignin and other polysaccharide landfills or in the natural environment. To partially impurities before being introduced into rubber. At 5, solve the problems caused by plastic pollution, 10, 15, and 20 wt% of spent coffee grounds added to biodegradable compounds have been added to the reinforce the rubber, the composites showed synthetic polymer matrix to improve their increased stiffness but decreased elongation at break. decomposition rate.[1-5] It was reported that 4 wt% of short loofah fibers N. Prasad et al.[6] used banana fibers to reinforce combined with 10 wt% of ground loofah fiber gave low-density polyethylene at weight percentages of the best mechanical properties of the prepared 10, 15, 20, and 25 % to produce eco-friendly bio- composite.[9] M. A. Paglicawan et al.[10] used a composites. The results showed that the best polyester resin reinforced with loofah fiber in the biodegradable property of the bio-composite was form of sheets and used methyl ketone peroxide as a achieved at 15 by weight of banana fiber. Besides, curing agent to fabricate an eco-friendly composite the treatment of the banana fiber surface and the material by a hand lay up method. addition of a compatibilizer into bio-composites In Vietnam, every year large amount of coffee provided better mechanical properties. N. J. Jaya grounds is discarded after industrial processing and Chitra et al.[7] investigated the effects of a there is a need to find a way to exploit this waste 148 Wiley Online Library © 2023 Vietnam Academy of Science and Technology, Hanoi & Wiley-VCH GmbH
25728288, 2023, S3, Downloaded from https://onlinelibrary.wiley.com/doi/10.1002/vjch.202300064 by Readcube (Labtiva Inc.), Wiley Online Library on [01/05/2024]. See the Terms and Conditions (https://onlinelibrary.wiley.com/terms-and-conditions) on Wiley Online Library for rules of use; OA articles are governed by the applicable Creative Commons License Vietnam Journal of Chemistry Nguyen Ngoc Thanh et al. material because of economic and environmental The destructive surface morphology of PP-based benefits. Chemically treated spent coffee grounds composites reinforced with spent coffee grounds was have become a potential biodegradable material for observed by using a scanning electron microscope partial replacement of synthetic PP resin to produce (SEM, JEOL 6490, Japan) at the Institute for bio-composite materials. Tropical Technology, Vietnam Academy of Science and Technology. All samples were coated with a thin 2. MATERIALS AND METHODS layer of Pt to avoid electrostatic charge before SEM observation. 2.1. Materials and equipment Table 1: The composition of fabricated PP-based Commercial PP granules (J700 Korea) with a density composites reinforced with spent coffee grounds of 0.90 g/cm3 and a melt flow index of 12 g per 10 Spent coffee PP, PP-g-MA, minutes at 230 oC/2.16 kg were used. Commercial Samples grounds, wt% wt% wt% PP-g-MA with a melt flow index of 6g per 10 PP 0 100 0 minutes at 230 oC/2.16 kg and maleic anhydride content of about 8-10 wt% was purchased from PP-10 10 90 0 China. Anhydrous sodium hydroxide (purity ≥ 98%) PP-15 15 85 0 was supplied by Sigma-Aldrich. Spent coffee PP-20 20 80 0 grounds were collected at Hancoffee company in Van PP-20-1 20 79 1 Giang, Hung Yen, Vietnam. A mixer (Brabender® GmbH & Co. KG, model PP-20-3 20 77 3 815655, Germany) and a hot press (GoTech, Taiwan) PP-20-5 20 75 5 were used to produce bio-composites. 2.5. Thermogravimetric analysis (TGA) 2.2. Alkaline treatment of spent coffee grounds TGA was determined on a TGA209F1 (Netzsch, Wet spent coffee grounds were rinsed with water to Germany) at the Institute for Tropical Technology, remove impurities and then dried at 60oC for 12 Vietnam Academy of Science and Technology. hours. Spent coffee grounds were soaked in 8 wt% Samples were placed in a platinum crucible and NaOH solution for 24 hours at room temperature. heated at a rate of 10oC per minute in air from room After that, the treated coffee grounds were filtered temperature to 600oC. and washed several times with distilled water until the solution was neutral. Then treated coffee grounds 2.6. Mechanical properties were dried at 60oC for 12 hours and passed through a 0.03 mm sieve to obtain homogeneous coffee The tensile and flexural strength were determined grounds. according to ASTM D638 standard and D790-03 standard, respectively, on the universal mechanical 2.3. Fabrication of PP-based composites testing machine (Shimadzu AGX-50kNVD, Japan) at reinforced with spent coffee grounds the Institute for Tropical Technology, Vietnam Academy of Science and Technology. PP-based composites reinforced with different contents of spent coffee grounds and PP-g-MA were 3. RESULTS AND DISCUSSION fabricated by a Brabender mixer. PP-g-MA was used as a compatibilizer in order to increase the mixing 3.1. Effects of alkaline treatment on morphology ability between coffee grounds and the PP matrix. and thermal property of spent coffee grounds Samples were fabricated at a temperature of 190oC for 7 minutes at a screw speed of 50 rpm. After The morphology of spent coffee grounds before and that, the samples were pressed into sheets on a after alkaline treatment is shown in Figure 1. It can Gotech pressing system at 190oC with a pressure of be observed that the surface structure of untreated 100 kg/cm2 for 5 minutes. The composition of PP- coffee grounds (Figure 1 a) was dense and not based composites reinforced with spent coffee uniform, whereas that of treated coffee grounds grounds is listed in table 1. (Figure 1 b) appeared rougher but homogeneous with the presence of many holes. The change in 2.4. Morphology of PP-based composites morphology of spent coffee grounds after alkaline reinforced with spent coffee grounds treatment can be attributed to the dissolution of © 2023 Vietnam Academy of Science and Technology, Hanoi & Wiley-VCH GmbH www.vjc.wiley-vch.de 149
25728288, 2023, S3, Downloaded from https://onlinelibrary.wiley.com/doi/10.1002/vjch.202300064 by Readcube (Labtiva Inc.), Wiley Online Library on [01/05/2024]. See the Terms and Conditions (https://onlinelibrary.wiley.com/terms-and-conditions) on Wiley Online Library for rules of use; OA articles are governed by the applicable Creative Commons License Vietnam Journal of Chemistry Effect of alkaline-treated spent coffee grounds… unstable impurities such as hemicellulose, lignin, the low degradation temperature of hemicellulose, pectin, waxes, and lipids[11] presenting in coffee lignin, and pectin,[8] the TGA curve of untreated grounds, leading to the form a rough surface and spent coffee grounds achieved slightly lower more holes. temperatures in the second degradation step (210oC) and the maximum degradation (302oC). This (a) decomposition stage corresponded to the degradation of the amorphous region of cellulose (cleavage of the glycosidic bond), hemicellulose, and lignin. The third degradation step appeared at a temperature range of 275-400oC, when the crystalline region of cellulose was decomposed. 3.2. Effect of spent coffee grounds content on mechanical properties of PP-based composites The tensile strength of PP-based composites (b) reinforced with alkaline untreated and treated spent coffee grounds at different weight percentages of 0, 10, 15, and 20 were exhibited in figure 3. When alkaline untreated and treated spent coffee grounds were added into the PP matrix, the tensile strength of the obtained composites decreased. It can be seen that the higher the coffee grounds content was added; the greater decrease in tensile strength occurred. 30 Untreated Tensile strength (MPa) 25 27.6 Treated Figure 1: Morphology of spent coffee grounds 20 before (a) and after (b) alkaline treatment 19.2 20.5 15 18.1 16.8 16.4 The thermal property of spent coffee grounds 14.5 10 before and after alkaline treatment was determined by TGA as shown in figure 2. 5 0 PP PP10 PP15 PP20 Figure 3: Effect of spent coffee grounds content on tensile strength of PP-based composites Mass loss (%) However, when using alkaline-treated spent coffee grounds, the tensile strength of PP-based composites was better than that of PP-based composites containing untreated spent coffee grounds. This result can be explained by the rougher Figure 2: TGA curves of spent coffee grounds surface of treated coffee grounds, leading to before (dot line CG) and after (solid line CGA8) enhancement in adhesion between PP resin with alkaline treatment coffee grounds. Figure 4 showed the flexural strength of PP- The results in Figure 2 show that the mass loss based composites containing alkaline-untreated and occurred at temperatures between 80 and 150oC due treated spent coffee grounds at different weight to the evaporation of water present in the spent coffee percentages of 0, 10, 15, and 20. Similar to the tensile grounds. The TGA curve of treated spent coffee strength result, the flexural strength of PP-based grounds started the second degradation step at 210oC composites containing alkaline untreated and treated and the maximum degradation at 302oC. Because of spent coffee grounds decreased. Due to the change in © 2023 Vietnam Academy of Science and Technology, Hanoi & Wiley-VCH GmbH www.vjc.wiley-vch.de 150
25728288, 2023, S3, Downloaded from https://onlinelibrary.wiley.com/doi/10.1002/vjch.202300064 by Readcube (Labtiva Inc.), Wiley Online Library on [01/05/2024]. See the Terms and Conditions (https://onlinelibrary.wiley.com/terms-and-conditions) on Wiley Online Library for rules of use; OA articles are governed by the applicable Creative Commons License Vietnam Journal of Chemistry Nguyen Ngoc Thanh et al. morphology of spent coffee grounds treated with grounds were better absorbed and encapsulated by alkaline, the reduction of the flexural strength of PP- the PP matrix. As the result, the PP-based composites based composites containing treated coffee grounds had a smooth fracture surface and no longer as was lower than that of PP-based composites discrete as the PP-based composites containing containing untreated coffee grounds. For example, untreated coffee grounds. This explains why the when using 10 wt% of untreated coffee grounds, the mechanical properties of the PP-based composites flexural strength of this composite decreased from containing the treated coffee grounds were higher 38.3 to 24.6 MPa. Whereas, this value of composite than those containing the untreated ones. containing 10 wt% of treated coffee grounds reached 27.8 MPa. 45 The morphology of fracture surface of PP-based 40 Untreated composites containing alkaline untreated and treated 35 38.3 Flexural strength (MPa) spent coffee grounds at weight percentage of 10, 15, 30 Treated and 20 was observed by SEM images in figure 5. The 25 fracture surface of PP-based composites containing 27.8 20 24.6 alkaline untreated spent coffee grounds was cracked due to the phase separation between coffee grounds 15 18.7 20 and the polymer matrix. When the content of coffee 10 10.7 12.1 grounds increased, the homogeneous dispersion of 5 coffee grounds into the polymer matrix became more 0 difficult, resulting in clearer phase separation. PP PP10 PP15 PP20 Interestingly, the alkaline treated spent coffee grounds showed more homogeneous dispersion into Figure 4: Effect of spent coffee grounds content on the PP matrix without aggregation. The treated coffee flexural strength of PP-based composites (a) (a’) (b) (b’) (c) (c’) Figure 5: Morphology of fracture surface of PP-based composites containing alkaline untreated (a, b, c) and treated (a’, b’, c’) spent coffee grounds at weight percentage of 10 (a, a’), 15 (b, b’), and 20 (c, c’) © 2023 Vietnam Academy of Science and Technology, Hanoi & Wiley-VCH GmbH www.vjc.wiley-vch.de 151
25728288, 2023, S3, Downloaded from https://onlinelibrary.wiley.com/doi/10.1002/vjch.202300064 by Readcube (Labtiva Inc.), Wiley Online Library on [01/05/2024]. See the Terms and Conditions (https://onlinelibrary.wiley.com/terms-and-conditions) on Wiley Online Library for rules of use; OA articles are governed by the applicable Creative Commons License Vietnam Journal of Chemistry Effect of alkaline-treated spent coffee grounds… 3.3. Effects of compatibilizer content on coffee grounds and PP resin, thereby significantly mechanical properties of PP-based composites enhancing the mechanical properties of PP-based composites. PP-based composites containing spent Figure 6 showed the tensile strength of PP-based coffee grounds are a potential material to replace composites containing PP-g-MA compatibilizer at synthetic plastic with the advantages of being lighter different weight percentages of 1, 3, and 5. The and easier to naturally decompose. compatibilizer displayed a strong effect on tensile strength; specifically, this value increased from 16.4 20 to 20.5, 22.1, and 22.7 MPa when the compatibilizer Flexural strength (MPa) was added by weight of 1, 3, and 5 wt%, respectively. 16 17.3 This is because the PP-g-MA compatibilizer had the 16.6 15 role of increasing the dispersion of coffee grounds in 12 the PP matrix, thereby increasing the adhesion 12.1 between coffee grounds and PP resin. 8 25 4 Tensile strength (MPa) 20 22.1 22.7 0 20.5 PP20 PP20-1 PP20-3 PP20-5 15 16.4 10 Figure 7: Effect of PP-g-MA compatibilizer content on flexural strength of PP-based composites 5 0 Conflict of Interest statement. The authors have no PP20 PP20-1 PP20-3 PP20-5 competing interests or personal relationships that could have appeared to influence the work reported Figure 6: Effect of PP-g-MA compatibilizer content in this paper. on tensile strength of PP-based composites REFERENCES The flexural strength of PP-based composites containing PP-g-MA compatibilizer at different 1. T. P. Nguyen, H. G. Mohamed, O. Kazuya, C. Bui, F. Toru. Enhancement of mechanical properties of weight percentages of 1, 3, and 5 is shown in figure carbon fabric/epoxy composites using micro/nano- 7. The flexural strength of PP-based composites was sized bamboo fibril, Mater. Des., 2013, 47, 624-632. enhanced by increasing compatibilizer content, 2. H. P. S A. Khalil, A. H. Bhat, A. F. I. Yusra. Green reaching the maximum value of 17.3 MPa at 5 wt% composites from sustainable cellulose nanofibrils: A of compatibilizer. The tensile and flexural strengths review, Carbohydr. Polym., 2012, 87, 963-979. of composites using PP-g-MA as a compatibilizer 3. J. S. Sohn, Y. Ryu, C.S Yun, K. Zhu, S. W. Cha. were significantly improved. Therefore, the use of Extrusion compounding process for the development PP-g-MA was an effective way to enhance the of eco-friendly SCG/PP composite pellets, mechanical properties of PP-based composites Sustainability, 2019, 11, 1720. containing spent coffee grounds. 4. T. A. Nguyen. Biocomposites developed with litchi peel based on epoxy resin: mechanical properties and flame retardant, Vietnam J. Chem., 2021, 2021, 4. CONCLUSION 3287733. 5. M. Alhijazi, B. Safaei, Q. Zeeshan, M. Asmael, A. In this study, bio-composites have been made based Eyvazian, Z. Qin. Recent developments in Luffa on the PP matrix containing alkaline untreated and natural fiber composites: Review, Sustainability, treated spent coffee grounds at the content of 0, 10, 2020, 12, 7683. 15, and 20 wt%. The results showed that bio- 6. N. Prasad, V. K. Agarwal, S. Sinha. Banana fiber composites containing treated coffee grounds had reinforced low-density polyethylene composites: better mechanical properties than untreated coffee Effect of chemical treatment and compatibilizer grounds. The use of PP-g-MA as a compatibilizer addition, Iran. Polym. J., 2016, 25, 229-241. 7. N. J. Chitra, R. Vasanthakumari, S. Amanulla. played an important role in evenly dispersing coffee Preliminary studies of the effect of coupling agent on grounds into the PP matrix. The presence of PP-g- the properties of spent coffee grounds polypropylene MA prevented the agglomeration of spent coffee bio-composites, Int. J. Eng. Res. Technol., 2014, 7, 9- grounds and increased the adhesion between spent 16. © 2023 Vietnam Academy of Science and Technology, Hanoi & Wiley-VCH GmbH www.vjc.wiley-vch.de 152
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