The objective of this work was to investigate blend ratio and storage time effects on the morphological, mechanical, and thermal properties of thermoplastic starch/poly(butylene adipate- co -terephthalate) (TPS/PBAT) films. TPS was prepared from plasticized cassava starch using a twin-screw extruder. TPS was subsequently melt-blended with PBAT with varied weight ratios (i.e., 20/80, 40/60 and 60/40) and blown to form TPS/PBAT films. It was found that increasing the TPS/PBAT ratio to 40/60 led to improved distributions of polymeric components and increased PBAT crystallization temperatures while reducing TPS melting transitions and tensile properties of TPS/PBAT films. After three months of storage at 30 °C, the tensile strength and secant modulus at 2% strain of TPS/PBAT films increased due to recrystallization of both TPS and PBAT. Blend ratios were the primary determinant for changes in TPS/PBAT film elongation at break with this storage time. Elongation at break decreased at low TPS:PBAT ratios (i.e., 20/80) and increased at high blend ratios (i.e., 60/40). The recrystallization of both TPS and PBAT components were observed from XRD and DSC analyses. Results obtained from both techniques confirmed the formation of additional crystalline structures of individual components during storage. The recrystallization phenomena also affected thermal transition temperatures of blend components. The crystallization temperature of PBAT-rich phase increased as starch could act as nucleating sites for PBAT. Using DMA, the tan δ curve of TPS/PBAT film exhibited two sharp individual peaks corresponding to the glass transitions of PBAT-rich and starch-rich phases. The tan δ of TPS-rich phase shifted to higher temperature due to recrystallization of TPS-rich phase.

The effect of storage environment on the overall crystallinity and compressive load of commercially sold starch based biodegradable cup was determined. Using FTIR and DSC, the components of the cup was identified as starch, polypropylene (PP) and organic acid as compatibilizer. Using TGA, the weight percentage of starch and PP components were 13 and 58%, respectively. The samples were stored 20°C, 80% RH and 40°C, 40% RH for 4 months. Using DSC, the overall crystallinity was evaluated based on the heat of fusion (Hf ). Using XRD, the crystalline structure was evaluated based on peaks and full width at maximum height (FWMH). After 4 months, DSC results showed only one endothermic peak with melting point of ≈165°C at both conditions. The Hf was remained ≈50 J/g. Based on XRD results, there were no development of new crystalline peaks and the peak FHWM remained unchanged. Initially, the percentage samples below the set limit of compressive load was ≈20%. The percentage below the set limit was ≈40% for samples stored at 20°C, 80% RH, whereas ≈20% for samples stored at 40°C, 40% RH. The 80% RH at 20°C increased the moisture content from 2% to 3.1%. The overall crystallinity remained unchanged after storage. Water became a plasticizer for the starch component. The increase in moisture content could have decreased the compressive load during storage.