The addition of fillers or additives to improve the mechanical properties of degradable plastics such as sago starch has gained the interest of researchers, scientists, and academicians. This research aims to investigate the addition of calcium silicate as an additive filler on the properties of a sago starch-based degradable plastic. The calcium silicate fillers used were 2, 4, 6, and 8% by weight starch, and the gelatinization process temperature used was 70, 80, and 90 ℃. The properties of these plastics were analyzed in terms of their strength, chemical composition, thermal stability, water absorption, and degradation rate. The optimum mechanical characteristics included a tensile strength of 28.04 MPa, 32.55 MPa of elongation at the break, and 70.02% of Young's modulus obtained with the addition of 8% calcium silicate and a gelatinization temperature of 90 ℃. Fourier Transform Infrared (FTIR) showed that there were O-H, C-H, and C = O groups that existed at wave numbers of 3795.91 cm^-1, 2927.94 cm^-1, and 1433.11–1616.35 cm^-1; moreover, these groups are hydrophilic, which bind water, so they can be degraded by the microbial activity in the soil. Differential Scanning Calorimetry (DSC) showed that the degradable plastic had a thermogram peak at 271.38 ℃; additionally an endothermic peak occurred at 309.30 ℃. The maximum swelling value was 64.05% at 2% calcium silicate and a gelatinization temperature of 70 ℃. The addition of calcium silicate made the plastic more water-resistant. The degradation rate of the degradable plastic ranged from 12–15 days and conformed to the American Standard Testing and Materials (ASTM) D-20.96 (maximum 180 days of decomposition for degradable plastic).

Sago starch and cellulose fiber can be used as a raw material for making degradable plastics to replace commercial plastics. This research used corn cob fiber and sugarcane bagasse fiber as filler to improve the properties of degradable plastic. The research method consists of several stages, cellulose fiber preparation, degradable plastic synthesis and plastic characterization. The result showed tensile strength of plastic with corn cob and sugarcane bagasse filler was 6.37–11.5 MPa and 9.70–16.47 MPa, respectively. The compound composition test through Fourier Transformation Infra-Red (FTIR) exhibited hydrophilic behavior, hence plastic easily degraded by soil. Differential Scanning Calorimetry (DSC) shows that degradable plastic with corn cob fiber filler denoted a melting point of 163.84 ℃, while sugarcane bagasse fiber filler at 163.47 ℃. Thermogravimetric Analysis (TGA) analysis indicated degradable plastic had a good thermal stability. Scanning Electron Microscopy (SEM) exhibited few white lumps and indentations on the surface, indicating that the solubility was not homogeny and could be due to the influence of stirring process. In term of ability to absorb water, both plastic with fiber filler had a small water absorption with a range of 5–6%. Melt Flow Rate (MFR) analysis of degradable plastics with corn cob fiber and sugarcane bagasse pointed the value that was suitable for injection molding processing technique. The degradation of both plastics ranged about 50–85 days to completely decomposed naturally in soil, as supported by FTIR analysis.