Biodegradability testing methods being used nowadays have many disadvantages; they are time-consuming, inefficient medium used, and too much sample needed to do the test. This work aimed to study the biodegradability of starch-based bioplastics by modified ASTM G21-70 method using Salt Agar (SA) medium, dip-hanging method using sterile water, and Soil Burial Test (SBT) method. Bioplastics were prepared by mixing cassava starch and glycerol with a ratio of 3:1 (%, w/w) through a series of processes: (1) blending of starch and glycerol for 3 min, (2) extruding of the starch-glycerol mixture by using a single screw extruder at 80-130°C, and (3) compression molding at temperature and pressure of 150°C and 50 kgf/cm2, respectively. Aspergillus niger was used as bioplastic-degrading fungi for the modified ASTM G21-70 and dip-hanging methods, while compost-soil was used as a source of bioplastic-degrading microbes in SBT method. Bioplastics of 2x2 cm in size were applied to the tests for 10 days. The growth of fungi on the surface of bioplastics was observed visually at two days intervals. A. niger grew well on the surface of bioplastic sample in modified ASTM G21-70 method, indicated that the bioplastic could be degraded by the fungi. On the other hand, the growth of A. niger was poor in the dip-hanging method, even though weight loss of 11.5% occurred. Physical properties changing were indicated in the SBT method. On the 10th day, cracks were observed on the surface of the bioplastic sample, the color of the sample became darker even the bioplastic became fragile, and the weight loss reached 29.89%.

In this study, to make a good bioplastic composite, starch-based bioplastic is produced by adding polylactic acid (PLA) to improve its properties. PLA was added into starch-based bioplastic with various concentrations of 0, 3, and 10 wt.%. The extrusion was performed at 90-150 °C and compression moulding process was conducted at 150 °C and pressured at 50 kgf/cm2. Bioplastic composites have been characterized to know its properties. FTIR analysis indicated shifting and increasing spectra of interaction between PLA and starch-based bioplastic. Contact angle and solubility analysis revealed that adding PLA can increase the stability of hydrophobic characteristic and insoluble properties. The combination of PLA and starch-based bioplastic can improve the mechanical properties. In addition, thermal properties of bioplastic composites have a better thermal stability and produce a lower melting point thus the energy needed to melt for bioplastic composites becomes milt as raising PLA composition. The density of bioplastics was in the range of 1.2 - 1.3 g/cm3 that would be good for light bioplastic. The results of this study showed that the combination of starch-based bioplastics and PLA at low concentration (10wt.%) potentially could enhance the properties of bioplastic composites for food packaging.

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