CET-vol95 DOI: 10.3303/CET2295038 Paper Received: 10 March 2022; Revised: 10 May 2022; Accepted: 3 June 2022 Please cite this article as: Ratnawati R., Aisa A., Aryanti N., Kumoro A.C., 2022, Glycerol and Temperature Effects on Mechanical Properties of Biodegradable Plastic from Rice Four with Rice Husk Filler, Chemical Engineering Transactions, 95, 223-228 DOI:10.3303/CET2295038 CHEMICAL ENGINEERING TRANSACTIONS VOL. 95, 2022 A publication of The Italian Association of Chemical Engineering Online at www.cetjournal.it Guest Editors: Selena Sironi, Laura Capelli Copyright © 2022, AIDIC Servizi S.r.l. ISBN 978-88-95608-94-5; ISSN 2283-9216 Glycerol and Temperature Effects on Mechanical Properties of Biodegradable Plastic from Rice Four with Rice Husk Filler Ratnawati Ratnawati*, Ariana Aisa, Nita Aryanti, Andri Cahyo Kumoro Department of Chemical Engineering, Universitas Diponegoro, Jl. Prof Soedarto, SH, Tembalang, Semarang 50275, Indonesia ratnawati@che.undip.ac.id Biodegradable plastics were fabricated from rice flour by the extrusion method using glycerol and rice husk powder as the plasticizer and filler, respectively. The independent variables were temperature (100−120C), glycerol (25−45%), and rice husk powder (0−20%). The independent variables were varied at three levels following the Box-Behnken experimental design. Three response surface models describing the effect of the independent variables on the tensile strength, elongation at break, and stiffness of the plastics were proposed. The tensile strength and the elongation at the break of the plastics were significantly affected by glycerol and rice husk, while the stiffness of the plastic was only significantly influenced by glycerol. The response optimizer was applied to estimate the optimum conditions for preparing the plastics, i.e., 100C for temperature, 25.81% for glycerol, and 0% for rice husk. The tensile strength, elongation at break, and stiffness of the plastic estimated by the optimum conditions were 7.27 MPa, 12.45%, and 10630 N/m, respectively. The biodegradable plastics prepared with the optimum conditions had a tensile strength of 7.13 MPa, elongation at break of 13.05%, and stiffness of 10400 N/m. These values are closely similar to the predicted values. 1. Introduction Petroleum-based polymers or plastics are extensively utilized for packaging, medical supplies, and other applications due to their superior properties, such as lightweight, durability, hydrophobicity, and formability (Dey et al., 2021). In 2019, the global plastics production reached 370 million tons where about 50% of them were used for single-use purposes, and only 15-18% were recycled. Therefore, most plastic waste ends up in landfills and numerous water bodies, especially oceans, rivers, lakes, and ponds. Because plastic requires several centuries to decompose, it will continuously accumulate and induce environmental issues (Putra et al., 2022). From an environmental point of view, biodegradable plastic is a better alternative to petroleum-based plastics. Renewable materials such as polysaccharides are the potential raw material for biodegradable films (Retnowati et al., 2015). Being an edible and low-price material, starch is the most preferred raw material for biodegradable plastic manufacturing (Woggum et al., 2015). It comprises two natural carbohydrate polymers, which are amylose and amylopectin. Amylose is a linear polymer of anhydroglucose unit, while amylopectin is a branched polymer. Amylose contributes more to plastic strength than amylopectin (Woggum et al., 2015). Because rice flour contains 18-33% of amylose (Chaiwanichsiri et al., 2014), it can be a potential candidate for biodegradable plastic raw material. Another advantage of rice flour is its low price if it is made from brewer’s rice as a by- product of rice processing (Ma'As et al., 2020). Unfortunately, biodegradable plastic derived from rice flour alone has poor mechanical properties (Hasan et al., 2020). Blending rice flour with glycerol and rice husk can be expected to enhance plastic's mechanical properties. Glycerol acts as a plasticizer which increases plastic's processability and flexibility (Wang et al., 2018). Retnowati et al. (2015) used glycerol as much as 30-40% of the total solid weight in preparing biodegradable plastic from durian and jackfruit flours. Ratnawati et al. (2022) prepared biodegradable film from PVA, cassava starch, and lignin by adding glycerol to as much as 25-65% of the total solid weight. They found that the tensile strength of the plastics decreased, while the elongation at break increased as the amount of glycerol increased. Therefore, fillers, such as cellulose can be added to plastics as a reinforcement to improve their tensile strength. 223 Commonly, an appropriate combination of plasticizer with filler can increase the mechanical properties of biodegradable plastics. The filler’s ability to strengthen the composite depends on its dispersibility as well as its interaction with the matrix materials (Majeed et al., 2017). Rice husk, which is renewable, biodegradable, lightweight, and tough is a sustainable source of cellulose. Rice husk contains cellulose (32.67%), hemicellulose (31.68%), lignin (18.81%), and ash (11.88%) (Ma’ruf et al., 2017). The rice husk ash comprises silica up to 94%, which can give a higher stiffness to the plastic (Premalal et al., 2002). Premalal et al. (2002) added rice husk powder as much as 0-60% w/w to the polypropylene composite. Kargarzadeh et al. (2017) used 0-10% of rice husk powder in preparing cassava starch-based plastic. This work applied the extrusion technique for the fabrication of biodegradable plastics. The objective of this work was to study the effect of both glycerol and rice husk percentages as well as the extrusion temperature on the mechanical properties of biodegradable plastics. The Box-Behnken experimental design was utilized to set up the necessary experiments. Finally, an optimum condition for plastic preparation with the best mechanical properties was estimated using the Response Surface Methodology (RSM). 2. Materials and method 2.1 Materials Materials used in this work were rice flour, rice husk, glycerol, distilled water, and a reusable plastic plate. The rice flour was obtained from a local producer, PT. Budi Makmur Perkasa, while rice husk was obtained from a local rice mill. The glycerol was purchased from PT. Hepilab Sukses Bersama. The distilled water was prepared in the laboratory. The plastic plate was purchased from a local market in Semarang (Indonesia). 2.2 Composition analysis of rice flour The proximate analysis of the rice flour was determined according to AOAC International (1990). Carbohydrate was calculated by differences. Amylose was analyzed using a spectrophotometer according to Juliano (1971). The rice husk moisture content was determined using the gravimetric method. Each measurement was conducted in duplicate. 2.3 Experimental design The independent variables used in this work were temperature (T), glycerol (G), and rice husk (H). The independent variables were varied at three levels according to the Box-Behnken design (BBD), i.e., 100, 110, and 120C for T, 25, 35, and 45% (g/100g of solid) for G, and 0, 10, and 20% (g/100g of rice flour) for H. The independent variables were arranged in 15 runs as tabulated in Table 1. RSM was employed to evaluate the effect of the independent variables on the tensile strength (TS), elongation at break (EB), and stiffness (ST). The response (Y), representing TS, EB, and ST, is correlated to the independent variables (Xi) according to: 𝑌 = 𝑏0 + ∑ 𝑏𝑖𝑋𝑖 𝑖 + ∑ 𝑏𝑖𝑖𝑋𝑖 2 𝑖 + ∑ ∑ 𝑏𝑖𝑗𝑋𝑖𝑋𝑗 𝑗𝑖 + 𝜀 (1) where b0 is the intercept of Y, bi is the linear effect coefficient, bii is the square effect coefficient, bij is the interaction coefficient of two independent variables, and ε is a random error (Ratnawati et al., 2022). Statistical analysis was conducted using Minitab version 19 software. 2.4 Preparation of biodegradable plastic Initially, rice husk was washed and dried under the sun for two days to dryness, ground and sieved into 60−80 mesh, and stored in a closed container for further use. The plastic was prepared by mixing 100 g of rice flour, distilled water (75% w/w of total solid), glycerol, and rice husk. The compositions of the mixture followed the experimental design presented in Table 1. The mixture was homogenized using a mixer and kept overnight in a closed container at room temperature. The mixture was extruded at 100-120C (higher than the rice flour gelatinization temperature) to form a plastic slab. The plastic slab was then dried at 50C using an electric oven for 24 hours and stored in a closed container for further analysis. 2.5 Characterization of biodegradable plastic and reusable plastic plate The TS, EB, and ST of the plastics were determined using Lloyd Instruments/Ametek TA Plus Texture Analyzer. The plastic slabs were cut into 5 mm  150 mm slices for the analysis. All the analysis was done in triplicate 3. Results and Discussion The proximate composition (wet basis) of the rice flour was moisture 11.14  0.16%, ash 0.24  0.00%, crude lipid 1.59  0.09%, protein 6.66  0.27%, and total carbohydrate 80.37  0.33%. The amylose content was 26.36 224  0.38% (wet basis) or 30.14  0.39% (dry basis). The moisture content of the rice husk was 9.16  0.18%. The TS, EB, and ST of the plastic plate are 10.27 MPa, 33.07%, and 4702 N/m, respectively. The mechanical properties of the biodegradable plastics are presented in Table 1. Table 1: Experimental design and the mechanical properties of the biodegradable plastic Run Independent variable Experimental value Predicted value T (C) G (%) H (%) TS (MPa) EB (%) ST (N/m) TS (MPa) EB (%) ST (N/m) 1 100 25 10 4.62 3.11 9312 5.32 3.82 9503 2 120 25 10 5.61 6.99 6536 6.44 5.03 7763 3 100 45 10 2.73 12.93 1631 2.20 14.64 283 4 120 45 10 2.45 13.98 1193 2.05 13.01 879 5 100 35 0 3.11 27.76 2780 3.79 24.47 3341 6 120 35 0 4.03 22.05 2248 4.62 21.42 1749 7 100 35 20 2.71 9.54 1591 2.42 9.92 1969 8 120 35 20 2.95 9.51 3101 2.57 12.55 2417 9 110 25 0 9.61 6.58 11391 8.67 8.93 10487 10 110 45 0 1.77 22.25 796 2.04 23.31 1411 11 110 25 20 4.05 3.52 9848 4.08 2.20 9111 12 110 45 20 1.96 9.22 1302 3.20 6.62 2083 13 110 35 10 3.24 17.23 1866 3.11 13.69 2023 14 110 35 10 3.11 13.54 2498 3.11 13.69 2023 15 110 35 10 2.52 10.69 1887 3.11 13.69 2023 3.1 Statistical analysis The effect of T, G, and H on the TS, EB, and ST was analyzed using the Box-Behnken Analysis of Variance (ANOVA). The mathematical models obtained for the TS, EB, and ST are as follows: 𝑇𝑆 = −3.6 + 0.43𝑇 − 0.697𝐺 − 0.476𝐻 − 0.00126𝑇2 + 0.01022𝐺2 + 0.00369𝐻2 − 0.00318𝑇𝐺 − 0.00170𝑇𝐻 + 0.01438𝐺𝐻 (2) 𝐸𝐵 = 53 − 2.39𝑇 + 5.49𝐺 − 1.73𝐻 + 0.0113𝑇2 − 0.0570𝐺2 + 0.02271𝐻2 − 0.0071𝑇𝐺 + 0.0142𝑇𝐻 − 0.0249𝐺𝐻 (3) 𝑆𝑇 = 37145 + 618𝑇 − 3192𝐺 − 909𝐻 − 4.1𝑇2 + 29.94𝐺2 + 7.56𝐻2 + 5.84𝑇𝐺 + 5.10𝑇𝐻 + 5.12𝐺𝐻 (4) The p-values of the models and all the components are presented in Table 2 along with their contribution percentages. The coefficient of determination (R2) of the equations for TS, EB, and ST were 90.15%, 90.82%, and 95.83%, respectively. It indicated that the models could explain 90.15%, 90.82%, and 95.83% of the variations of the TS, EB, and ST, respectively, as a result of the variation of T, G, and H. The p-values of all components of the three models along with their respective contribution percentages are listed in Table 2. The contribution percentage was calculated based on the adjusted sum of squares (Ratnawati et al., 2022). Table 2 exhibits that the p-values of TS, EB, and ST models are 0.044, 0.031, and 0.053, respectively. Based on the obtained p-values (less than 0.05), the models are statistically significant. The models are used to predict the TS, EB, and ST of 15 runs as tabulated in Table 1. The models were also used to describe the simultaneous effect of T, G, and H on the TS, EB, and ST as response surface plots as depicted in Figures 1−3. 3.2 Effect of T, G, and H on the mechanical properties of the biodegradable plastic Table 2 demonstrates that the G gives a significant effect on the mechanical properties of biodegradable plastic. It contributes 53.18, 26.02, and 73.20% to the TS, EB, and ST, respectively. As shown in Figures 1a, 2a, and 3a, the effect of G is not linear. It can be explained by the contribution of G2 to the TS, EB, and ST, i.e., as much as 7.31, 17.10, and 18,74%, respectively. Figures 1a and 3a also show that an increase in G leads to a reduction of both TS and ST, while Figure 2a shows that the EB of the plastic increases as G increases. A similar effect of G on TS and EB was reported by other researchers (Ratnawati et al., 2022; Retnowati et al., 2015). 225 Table 2: Analysis of variance for TS, EB, and ST Source DF p-value Contribution (%) TS EB ST TS EB ST Model 9 0.044 0.038 0.006 T 1 0.545 0.940 0.539 0.83 0.01 0.35 G 1 0.003 0.013 0.000 53.18 26.02 73.20 H 1 0.063 0.006 0.702 11.12 39.18 0.13 T2 1 0.822 0.575 0.540 0.11 0.67 0.35 G2 1 0.112 0.029 0.005 7.31 17.10 18.74 H2 1 0.517 0.282 0.280 0.95 2.71 1.20 TG 1 0.560 0.711 0.375 0.76 0.29 0.77 TH 1 0.752 0.467 0.433 0.22 1.15 0.59 GH 1 0.037 0.226 0.432 15.67 3.55 0.59 Error 5 9.84 9.32 4.07 Total 14 100.00 100.00 100.00 As a small molecule, glycerol can easily fill the spaces between the amylose and amylopectin molecules. In addition, its hydroxyl groups allow more intensive interactions with both amylose and amylopectin molecules through hydrogen bonding and thus reduce the interactions between the amylose and amylopectin molecules. As a result, the mobility of the amylose and amylopectin increases, and hence the TS and ST are lower. Another effect is the enhancement of both flexibility and EB of the plastic (Ratnawati et al., 2022; Retnowati et al., 2015). Figure 1: Effect of (a) G and T and (b) H and T on the TS of the biodegradable plastic. Figure 2: Effect of (a) G and T and (b) H and T on the EB of the biodegradable plastic. (a) (b) (a) (b) 226 Figure 3: Effect of (a) G and T and (b) H and T on the ST of the biodegradable plastic. Rice husk (H) provides a significant effect on the TS and EB with 11.12 and 39.18% contributions, respectively. The effect of H on the TS and EB of the biodegradable plastic is shown in Figures 1b and 2b. The TS and EB decrease with the increase of H. A similar effect of H on TS and EB was reported by other researchers (Premalal et al., 2002; Kargarzadeh et al., 2017). The negative effect of H on TS could be related to poor interfacial adhesion between the rice husk and the matrix. As the rice husk powder increases, it tends to agglomerate, which may induce mixture inhomogeneity (Premalal et al., 2002). Consequently, the discontinuity of the composite increases which leads to reducing both TS and EB. The effect of H on ST is not significant. The contribution of both H and H2 to ST is only 0.13 and 1.20%, respectively. Table 2 indicates that temperature (as both T and T2) does not have any significant effect on the TS, EB, and ST of the biodegradable plastic. The objective of extrusion and heating is to mix the blend and gelatinize the rice flour. The gelatinization of rice flour with moisture content from 100 to 300% (w/w of dry flour) ranges from 65.4 to 74.4C (Saif et al., 2003). Therefore, at the temperature of the extrusion (100−120C), the rice flour with a moisture content of 75% (w/w of dry flour) must have been gelatinized. Furthermore, 120C is well below the degradation temperature of starch (Zhang et al., 2002). Therefore, there is no significant difference in mechanical properties of the biodegradable plastics prepared at 100, 110, and 120C. 3.5 Optimization The optimum conditions for the making of biodegradable plastics were predicted using the response optimizer. The optimum conditions were 100C for the temperature, 25.81% for the glycerol, and 0% for the rice husk. It shows that the plastic without rice husk powder is better than that with the addition of rice husk. Similar results were reported for polypropylene-based plastic (Premalal et al., 2002) and cassava starch-based plastic (Kargarzadeh et al., 2017). It indicates poor adhesion between the filler and the matrix. It could be related to the chemical composition of the rice husk. The rice husk used in this work was native without any chemical treatment. It contained cellulose and hemicellulose (hydrophilic), as well as lignin (relatively hydrophobic). The hydrophobic part might cause poor interaction between the rice husk and the matrix (Boonsuk et al., 2021). Furthermore, without any chemical treatment, the surface of the rice husk powder was relatively smooth, which also led to poor adhesion between the rice husk and the matrix (Bihst et al., 2020). The predicted TS, EB, and ST were 7.27 MPa, 12.45%, and 10630 N/m, respectively. A validation experiment was conducted to verify the accuracy of the model equations. A biodegradable plastic was prepared using the optimum conditions. The TS, EB, and ST of the plastic were 7.13 MPa, 13.05%, and 10400 N/m, respectively. The TS and ST are below the predicted values while the EB is above the predicted value. However, they are still within a 95% confidence interval. Therefore, the models can predict the responses with 95% confidence. The TS and EB of the biodegradable plastic are lower than those of the reusable plastic plate, while the ST is higher. 4. Conclusions Biodegradable plastics have been successfully prepared from rice flour with glycerol as a plasticizer and rice husk powder as a filler by using an extrusion method. The independent variables in the plastic making were temperature (100−120C), glycerol (25−45%), and rice husk (0−20%). Three models describing the effect of the input variables on the TS, EB, and ST were developed. Among all input variables, glycerol was the only variable having a significant effect on TS, EB, and ST. Rice husk powder has a significant effect on the TS and EB, while T does not have any significant effect on all the mechanical properties. The optimum conditions for preparing the plastic are 100C, 25.81%, and 0% for the T, G, and H, respectively. The predicted TS, EB, and ST of the (a) (b) 227 plastic calculated with the optimum conditions are 7.266 MPa, 12.45%, and 10630 N/m, respectively. The mechanical properties of the plastic prepared with the optimum conditions have TS of 7.13 MPa, EB of 13.05%, and ST of 10400 N/m, which are still within the 95% confidence interval of the models. The TS and EB of the biodegradable plastic are less and the ST is higher than those of the reusable plastic plate. Acknowledgments The authors acknowledge the financial support from the Faculty of Engineering Universitas Diponegoro, Semarang, Indonesia through the Strategic Research Project under contract No. 3178/S/kimia/13/UN7.5.3.2/PP/2021. References AOAC International, 1990, Official Methods of Analysis of AOAC International, 16th edition, Arlington, Va: AOAC International. Bisht N., Gope P.C., Rani N., 2020, Rice husk as a fibre in composites: A review, Journal of the Mechanical Behavior of Materials, 29, 147–162. Boonsuk P., Sukolrat A., Bourkaew S., Kaewtatip K., Chantarak S., Kelarakis A., Chaibundit C., 2021, Structure- properties relationships in alkaline treated rice husk reinforced thermoplastic cassava starch biocomposites, International Journal of Biological Macromolecules, 167, 130–140. Chaiwanichsiri S., Thumrongchote D., Suzuki T., Takahashi M., Laohasongkram K., 2014, Properties of Non- glutinous Thai Rice Flour: Effect of rice variety, Research Journal of Pharmaceutical, Biological and Chemical Sciences, 3(1), 150–164. Dey A., Dhumal C.V., Sengupta P., Kumar A., Pramanik N.K., Alam T., 2021, Challenges and possible solutions to mitigate the problems of single-use plastics used for packaging food items: a review, Journal of Food Science and Technology, 58(9), 3251–3269. Hasan M., Gopakumar D.A., Olaiya N.G., Zarlaida F., Alfian A., Aprinasari C., Alfatah T., Rizal S., Abdul Khalil A.P.S., 2020, Evaluation of the thermomechanical properties and biodegradation of brown rice starch-based chitosan biodegradable composite films, International Journal of Biological Macromolecules, 156, 896–905. Juliano B.O., 1971, A simplified assay for milled-rice amylose, Cereal Science Today, 1971, 16(10), 334–340. Kargarzadeh H., Johar N., Ahmad I., 2017, Starch biocomposite film reinforced by multiscale rice husk fiber, Composites Science and Technology, 151, 147–155. Ma’As M.F., Ghazali H.M., Chieng S., 2020, Bioethanol production from brewer’s rice by Saccharomyces cerevisiae and Zymomonas mobilis: evaluation of process kinetics and performance, Energy Sources, Part A: Recovery, Utilization, and Environmental Effects, published online 23 September 2020. Majeed K., Arjmandi R., Al-Maadeed M.A., Hassan A., Ali Z., Khan A.U., Khurram M.S., Inuwa I.M., Khanam P.N., 2017, Structural properties of rice husk and its polymer matrix composites: An overview. In: Jawaid M, Tahir P.M., Saba N. (Eds), Woodhead Publishing - Elsevier, Cambridge, 473–490, 2017. Ma’ruf A., Pramudono B., Aryanti N., 2017, Lignin isolation process from rice husk by alkaline hydrogen peroxide: Lignin and silica extracted, AIP Conference Proceedings 1823, 020013. Premalal H.G.B., Ismail H., Baharin A., 2002, Comparison of the mechanical properties of rice husk powder filled polypropylene composites with talc filled polypropylene composites, Polymer Testing 21, 833–839. Putra P.H.M., Rozali S., Patah M.F.A., Idris A., 2022, A review of microwave pyrolysis as a sustainable plastic waste management technique, Journal of Environmental Management, 303, 114240. Ratnawati R., Wulandari R., Kumoro A.C., Hadiyanto H., 2022, Response surface methodology for formulating PVA/starch/lignin biodegradable plastic, Emerging Science Journal, 6(2), 238–255. Retnowati D.S., Ratnawati R., Purbasari A., 2015, A biodegradable film from jackfruit (Artocarpus heterophyllus) and durian (durio zibethinus) seed flours, Scientific Study & Research: Chemistry & Chemical Engineering, Biotechnology, Food Industry, 16(4), 395–404. Saif S.M.H., Lan Y., Sweat V.E., 2003, Gelatinization properties of rice flour, International Journal of Food Properties, 6(3), 531–542. Wang W., Zhang H., Jia R., Dai Y., Dong H., Hou H., Guo Q., 2018, High performance extrusion blown starch/polyvinyl alcohol/clay nanocomposite films, Food Hydrocolloids, 79, 534–543. Woggum T., Sirivongpaisal P., Wittaya T., 2015, Characteristics and properties of hydroxypropylated rice starch- based biodegradable films, Food Hydrocolloids, 50, 54–64. Zhang X., Golding J., Burgar I., 2002, Thermal decomposition chemistry of starch studied by 13C high-resolution solid-state NMR spectroscopy, Polymer, 43, 5791–5796. 228 123Ratnawati.pdf Glycerol and Temperature Effects on Mechanical Properties of Biodegradable Plastic from Rice Four with Rice Husk Filler