The Heat Resistant Capabilities of Bioplastic Composites on Sago Hampas Starch-Al 2 O 3

Sago hampas are a waste with high starch content. The starch from sago hampas can be used as a raw material for bioplastics. However, because bioplastics have a lower heat resistance than conventional plastics, additives are required to increase heat resistance. Aluminum oxide can be used as a metal compound that acts as an additive to increase heat resistance. Bioplastics were created using a weight percentage of 0, 1, 3, and 5% Al 2 O 3 . Analysis was carried out with DTA to determine the melting point of bioplastics. Furthermore, bioplastics tested the mechanical properties, density, and water resistance. The best results were identified using FTIR and SEM. The results showed that adding Al 2 O 3 at 1, 3, and 5% increased the heat resistance of bioplastics with melting points of 270, 274, and 280 o C. Bioplastic obtained the best results except for mechanical properties with a melting point of 280 o C, tensile strength of 3.41 Mpa, elongation of 38.66%, density of 5.52 g cm -3 , and 80.28% water resistance for bioplastic with 5% Al 2 O 3 that suitable on Indonesian National Standard 7188.7:2016. The FTIR analysis revealed that bioplastic containing Al 2 O 3 experienced physical interactions. Morphological analysis revealed that Al 2 O 3 was evenly distributed on the bioplastic's surface.


Introduction
Bioplastics are made from biomass, which microorganisms can decompose in the environment. Natural polymers such as lignin, protein, natural rubber, starch, cellulose, and chitin can be used to make bioplastics (Kabasci, 2014). Because of its abundance, starch is widely used as a material for the production of bioplastics. Starch can be obtained from tubers, seeds, nuts, and the trunks of sago trees. Several studies have used cassava starch, sago starch, a mixture of durian seed starch and sago starch, jackfruit seed starch, and other starch sources as the main ingredients for bioplastics (Wahyuningtyas and Suryanto, 2017;Amni et al., 2019).
Indonesia has 5.4 million ha of sago (Metroxylon sp.) land, with Papua accounting for 95% (Kementan, 2020). In 2007, a modern sago mill was established to aid sago management. As a result, more waste is produced. Waste from sago processing includes bark and hampas. The extracted sago hampas account for approximately 14% of the total wet weight of sago stalks (Flach, 1997). Sago hampas is currently used in animal feed, biosorbent, compost, and fermentation ( Husin et al., 2019). Despite the abundance of sago hampas, it still has a reasonably high starch content of 52.98%. As a result, sago hampas can be recycled to produce starch.
Several studies have addressed these shortcomings by adding additives such as ZnO, which can improve the mechanical and antimicrobial properties of cassava starch bioplastics because starch-based bioplastics have several shortcomings, including low physical properties, brittleness, and low water resistance (Hidayat et al., 2019). TiO2 is used as reinforcement and heat resistance in corn starch bioplastic (Amin et al., 2019), and rice husk nanosilica as reinforcement and reduces water vapor transmissibility. Aside from these characteristics, the heat resistance of bioplastics derived from natural polymers varies depending on the source of starch and other supporting materials. According to Abdullah et al. (2019), increasing the ratio of cassava starch and glycerol can improve mechanical properties and melting point.
According to Amin et al. (2019), TiO2 can improve the mechanical properties and heat resistance of bioplastics made from corn starch, glycerol, and acetic acid, resulting in a melting point of 291 o C without TiO2 and 303 o C with TiO2.
Furthermore, Chueangchayaphan et al. (2019), discovered a melting point of 280 o C in a thermoplastic cassava starch-TiO2-Al2O3 and glycerol using variations in particle size of Al2O3. Al2O3 is a chemical that is widely used in industry. Because of its high heat capacity, this compound is used as a high-temperature insulator because it is a good electrical insulator. Al2O3 has a high melting point of 2050 o C (Selvam et al., 2021).
Starch, such as cassava starch and cornstarch, is still required as an ingredient in daily consumption so that its use as a bioplastic material is limited. The high starch content of sago hampas can be reused as a raw material for bioplastics to reduce industrial waste. The amount of starch and glycerol used in bioplastics can affect their heat resistance properties . On the other hand, adding additives can increase heat resistance (Amin et al., 2019). The utilization of Al2O3 as additives in bioplastic is still less. This study aimed to investigate the effect of Al2O3 on increasing the heat resistance of sago starch-based bioplastics.

Starch Separation
The method for separating starch from sago hampas was that sago hampas were mixed with water in a container. The sago hampas were squeezed three times. The juice was left for 24 hours to allow starch deposits to form. Following that, the starch precipitate was sundried. The dried precipitate was ground and sieved through a sieve with 60 mesh.

Preparation of Bioplastic
A total of 10 g of sago hampas starch was combined with Al2O3 at 0, 1, 3, and 5% by weight of sago hampas starch and filled into a beaker glass, respectively. 100 mL of distilled water, 10 mL of acetic acid, and 3 mL of glycerol mixed into sago hampas starch and Al2O3. The mixture was heated to 90 ºC using a hot plate magnetic stirrer and stirred at 800 rpm. After the mixture was homogeneous, the sample was poured into a glass mold and dried at room temperature for 24 hours.

Analysis and Characterization of Bioplastic
The melting point of bioplastics was performed using a differential thermal analysis (DTA Hitachi STA7300). A sample of bioplastic was placed in an alumina pan holder. The sample was then vacuumed to a pressure of 1 bar. The nitrogen gas was then introduced at 100 mL/min rate. Thermal testing of bioplastics was performed at temperatures as high as 1000 o C. The DTA test results were evaluated in the form of an endothermic or exothermic peak.
Bioplastics were tested using a universal testing machine (Zwickroel) for tensile strength and elongation. Each bioplastic sample was cut to a specific length and clamped on both sides. The test of tensile strength and elongation according to ASTM D882.
A density test was performed using a pycnometer to determine the density of bioplastics. A density test was performed using a pycnometer to determine the density of bioplastics by using Equation 1.
Remark: ds (g cm -3 ) : density mp (g) : mass of pycnometer mps (g) : mass of pycnometer and sample mpl (g) : mass of pycnometer and water mpls (g) : mass of pycnometer + water + sample d1 (g/mL) : water density da (g/mL) : air density The water resistance test was used to determine the amount of water that was not absorbed by the bioplastic. The test was carried out by cutting each bioplastic sheet and weighing the sample. The sample was then placed in a container containing distilled water at room temperature and allowed to stand for 24 hours. After settling, the sample was cleaned with a dry cloth and weighed. Equations calculated the test results: Remark: WA (%) : water absorption W (g) : wet weight W0 (g) : conditioned weight WR (%) : water resistance Functional groups analysis was carried out using fourier transform infrared spectroscopy (FTIR Perkin Elmer Spectrum 2). Bioplastic was prepared with KBr and then pressed with a hydraulic jack and measured using FTIR. The test results, which included the wavenumber and percent transmittance, were then interpreted to determine the functional group.
Morphology analysis wa carried out using scanning electron microscopy (SEM JEOL JSM-6510LA). The bioplastic sample was placed in a set holder with two adhesive strips. Following that, it is vacuum-coated with gold metal and inserted into the sample holder of the SEM. SEM magnified the sample and morphological images were taken.

Bioplastic
The gelatinization process occurs during heating treatment, resulting in a thick and chewy solution (Adawiyah et al., 2021). The bioplastics properties obtained have a smooth and transparent texture, as shown in Figure 1. The addition of glycerol results in smooth properties, caused reduces the rough texture of the bioplastics (Lusiana et al., 2019). The transparency is due to colorless materials. Al2O3 is a white solid, the more Al2O3 added, the whiter the color of the bioplastic and the lower transparency.

Melting Point
The DTA results shown in Figure 2 revealed that bioplastics with 0, 1, 3, and 5% Al2O3 added had melting points of 266, 270, 274, and 280 o C, respectively. The melting point of sago starch bioplastic without Al2O3 is higher than that of cassava starch bioplastic at 120 o C by Abdullah et al. (2019). Because sago starch contains less amylopectin than cassava starch, its amylose content is higher. Amylose has a higher melting point than amylopectin (Delcour and Hoseney, 2010). As a result, sago starch bioplastics have a higher melting point than cassava starch bioplastics. The addition of Al2O3 raises the melting point from 4 to 14 o C. The raises are due to its high density (Alaerts et al., 2018). In this study, the highest yield was bioplastic with 5% Al2O3 addition with a melting point of 280 o C. The melting point of bioplastics differs only slightly between variations because the amount of Al2O3 differs slightly. The resulting melting point represents starch decomposition (Chueangchayaphan et al., 2019). Bioplastics with Al2O3 added can be used as a wrap/cover for heat materials.

Tensile Strength and Elongation
The tensile strengths of bioplastics with 0, 1, 3, and 5% Al2O3 were 2.98, 3.45, 3.09, and 3.41 MPa, respectively (Figure 3a). The low tensile strength for all bioplastics is due to the addition of glycerol. The addition of glycerol reduces in the strength of the intermolecular forces so that the mobility between the molecular chains increases (Hamzah et al., 2021). However, these findings suggest that adding Al2O3 to bioplastics can increase their tensile strength. Bioplastics containing 1, 3, and 5% Al2O3 produced varying tensile strength values. The elongation values of bioplastics with 0, 1, 3, and 5% Al2O3 addition were 46.39, 50.06, 37.10, and 38.66%, respectively ( Figure 3b). However, the elongation value of bioplastics decreased with the addition of 3 and 5% Al2O3. The uneven thickness of the bioplastic causes fluctuating tensile strength and elongation results. Bioplastic containing 1% Al2O3 increased elongation value compared to bioplastic without Al2O3. The more Al2O3 is added, the stronger its physical properties will be. Because Al2O3 is a crystalline compound with a stable structure, it forms a strong nature. In this study, the highest yield obtained by bioplastic containing 1% Al2O3 can increase tensile strength from 2.98 to 3.45 MPa and elongation from 46.39 to 50.06%. Tensile strength has a standard of 24.7-302 MPa and elongation of 21-220% according to SNI 7188.7:2016 plastics, so the mechanical properties of bioplastics do not meet the standards.  Figure 4 showed the density of bioplastics with 0, 1, 3, and 5% Al2O3 were 2.86, 3.70, 4,89, and 5.52 g cm -3 , respectively. Due to the hollow space in the bioplastic inserted by Al2O3, the addition of Al2O3 can increase the density. Density value can raise the melting point of bioplastics. However, the density did not differ significantly with the addition of Al2O3. The difference because the amount of Al2O3 added varies slightly. In this study, bioplastic with 5% Al2O3 produced the highest yield. Overall, the density of bioplastics without and with Al2O3 conforms to SNI 7188.7:2016 with a plastic density of 0.95 g cm -3 . Figure 4. Effect of bioplastic with Al2O3 addition to density. Figure 5 showed the water resistance values for bioplastics with 0, 1, 3, and 5% Al2O3 were 67.32, 77.86, 78.49, and 80.28%, respectively. The addition of Al2O3 increases the value of water resistance. Due to hydrophilic, starch is one of the factors that can reduce water resistance (Seligra et al., 2015). Starch binding to water can be reduced by the higher embedding of Al2O3 in bioplastics. High density also contributes to increase water resistance. Bioplastics with Al2O3 additions of 1, 3, and 5% only differ slightly in water resistance because the Al2O3 addition is slightly different. As a result, the water resistance was not significantly different with the addition of Al2O3. In this study, the highest yield is obtained by bioplastic containing 5% Al2O3, which has a water resistance value of 80.28%. According to Indonesian National Standard 7188.7:2016, plastic's maximum water absorption capacity is 21.5% or water resistance of at least 78.5%, indicating that bioplastics with Al2O3 3 and 5% have met Indonesian National Standard. As a result, bioplastics with the addition of Al2O3 can be used as water-resistant wrapping/covering materials. Figure 6 shows the FTIR spectrum of bioplastics with 0 and 5% Al2O3 addition. Table  1 showed that bioplastics containing 0% Al2O3 have an absorption band with a wavenumber of 3272 cm -1 and a broad peak corresponding to the -OH group. The absorption of wavenumber 2927 cm -1 represents the C-H group. The C-O-C (glycoside) group of starch exhibits strong absorption at wavenumber 1003 cm -1 . The FTIR spectra of bioplastics containing 5% Al2O3 revealed the presence of a -OH group at 3273 cm -1 absorption with a broad peak and lower transmittance due to the strong hydrogen bonding effect (Coates, 2006).

Functional Grup
The absorption wavenumber of 2925 cm -1 indicates the presence of a C-H group with a slight shift. The C-O-C (glycoside) group exhibits a sharp absorption at a wavenumber of 1003 cm -1 , with no shift in wavenumber, indicating that Al2O3 does not affect the breaking of glycosidic bonds in starch. In bioplastics containing 5% Al2O3, there is an absorption group with a wavenumber of 665 cm -1 and a very small peak identified as the Al-O group of Al2O3 (Tong et al., 2015). The fact that the wavenumber shift does not change significantly indicates that the interaction is physical.

Morphology
SEM analysis of bioplastic without Al2O3 revealed a smooth surface, indicating a homogeneous mixture of bioplastics ( Figure  7a). There are small grains with an uneven surface in bioplastic with 5% Al2O3 addition (Figure 7b). The granules are thought to be Al2O3 incorporated into the bioplastic. On the surface of the bioplastic, Al2O3 is evenly distributed. According to Chueangchayaphan et al. (2019), Al2O3 is homogeneously dispersed evenly in the composite.

Conclusion
Adding Al2O3 to bioplastics can improve heat resistance and increase melting point value than bioplastics that do not contain Al2O3. Due to the uneven thickness, the mechanical properties of bioplastics with Al2O3 addition of 0, 1, 3, and 5% do not meet the standards. The addition of Al2O3 to bioplastics can increase density and water resistance. The density of bioplastics with Al2O3 addition of 0, 1, 3, and 5% have met the standard, according to Indonesian National Standard 7188.7:2016. However, the water resistance of bioplastics containing 3 and 5% Al2O3 only meets the standard. The interaction in bioplastics with the addition of Al2O3 is a physical interaction and Al2O3 can be evenly distributed on the bioplastic's surface.