Effects of Modified Starch and Different Molecular Weight Polyvinyl Alcohols on Biodegradable Characteristics of Polyvinyl Alcohol/Starch Blends

The common biodegradable properties of polymer make them an excellent pair for blending, and the water solubility of polyvinyl alcohol (PVA) makes it easy to mix evenly with the starch. In this study, PVAs with different molecular weights were blended with various compositions of cross-linked starch (CLS) to explore the effects of molecular weight of PVA on the biodegradable characteristics of the PVA/starch blends. Comparing the biodegradability of all the various PVA/starch blends, a PVA was singled out from the PVA/starch blends of higher biodegradability. Further, the chosen PVA was then blended with the acid-modified starch (AMS) to systematically investigate the effects of the modified processing of starch on the biodegradable characteristics of the PVA/starch blends. Differential scanning calorimetry (DSC) analysis of PVA and PVA/starch specimens reveal that the T _m values of PVA/starch specimens reduce gradually as their CLS or AMS contents increase. After the CLS is blended in PVAs of different molecular weights, the tensile strength (σ _f) and elongation at break (ε _f) values of (P ₁₀₀S ₀)G ₂₀M ₁ specimen increase and simultaneously reduce, respectively, as their molecular weights of PVA increase from about 80,000 (PVA _BF-17) to 120,000 (PVA _BF-26). The σ _f and ε _f values of the PVA/modified-starch blends decrease with an increase in the modified starch contents. The σ _f values of the PVA/AMS specimens decrease with an increase in the concentrations of hydrochloric acid. Comparing the σ _f values of the PVA/CLS specimens with those of the PVA/AMS specimens, the σ _f values of the PVA/CLS specimens are better than those of the PVA/AMS specimens. On the contrary, the ε _f values of the PVA/AMS specimens are better than those of the PVA/CLS specimens. According to the biodegradability of all the PVA/starch blends, PVA with higher molecular weights displays higher biodegradability. The biodegradability of the PVA/modified-starch blends increase as the modified starch contents of the PVA/modified-starch blends increase. As evidenced by the results of the biodegradability test, the biodegradability of the PVA/modified-starch blends, therein PVA is blended with 1N AMS, shows better biodegradability. The result of bio-reaction kinetics experiment can evaluate the decomposition tendency of the PVA/starch blends up to any biodegradable rate under ambient environment. Using the kinetic model of the first order reaction, it is estimated that 16. 20 years and 12. 47 years will be needed for the PVA _BF-17/starch blends, containing 20 and 40% of CLS respectively, to be degraded up to 70% under ambient environment. In addition, it is 1. 68 years for the PVA _BF-26 blends with the 40% 2N AMS under decomposition environment while it is 1. 94 years for the 40% 1N AMS. Overall, the decomposition potential of PVA/AMS specimens is better than PVA/CLS specimens. Furthermore, the 1N(26P ₆₀AS ₄₀) ₁₀₀G ₂₀M ₁ specimen is coincidence the biodegradable material criteria of Environmental Protection Administration (EPA) of Taiwan.