Morphology and mechanical properties of poly(vinyl alcohol) and starch blends prepared by gelation/crystallization from solutions

摘要

In an attempt to produce biodegradation materials, poly(vinyl alcohol) (PV A)-starch (ST) blends were prepared by gelation/crystalli- zation from semidilute solutions in dimethyl sulfoxide (Me_2S0) and water mixtures and elongated up to 8 times. The content of mixed sol- vent represented as Me_2S0/H_2O (volume percent) was set to be 60/ 40 assuring the greatest drawability of PV A homopolymer films. The PV A/ST compositions chosen were 1/1, 1/3, and 1/5. The elongation up to 8 times could be done for the 1/1 blend but any elongation was im- possible for blends whose ST con- tent was beyond 50%. When the blends were immersed in water at 20 or 83degC, the solubility became considerable for an undrawn blend with 1/5 composition and a drawn 1/1 blend with 2=8. To avoid this phenomenon, cross-linking of PV A chains was carried out by formal- ization under formaldehyde vapor. Significant improvement could be established by the cross-linking of PV A chains. For the 1/1 blend, the amount of ST dissolved in water at 23degC was less than 3% for the undrawn state and 25% for the drawn film. The decrease in the ST content was enough for use as biodegradation materials. Namely, the water content relating to the biodegradation in soil is obviously different from such a serious ex- perimental condition that a piece of blend film was immersed in a water bath. At temperatures above 0degC, the storage modulus of the formal- ization blends became slightly higher than those of the nonfor- malization blends. The Young's modulus of the drawn films with a draw ratio of 8 times was 2 GPa at 20degC.