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

In an attempt to produce biodegradation materials, poly(vinyl alcohol) (PVA ) starch (ST) blends were prepared by gelation/crystallization from semidil ute solutions in dimethyl sulfoxide (Me2SO) and water mixtures and elongate d up to 8 times. The content of mixed solvent represented as Me2SO/H2O (vol ume percent) was set to be 60/ 40 assuring the greatest drawability of PVA homopolymer films. The PVA/ST compositions chosen were 1/1, 1/3, and 1/5. T he elongation up to 8 times could be done for the 1/1 blend but any elongat ion was impossible for blends whose ST content was beyond 50%. When the ble nds were immersed in water at 20 or 83 degreesC, the solubility became cons iderable for an undrawn blend with 1/5 composition and a drawn 1/1 blend wi th lambda = 8. To avoid this phenomenon, cross-linking of PVA chains was ca rried out by formalization under formaldehyde vapor. Significant improvemen t could be established by tile cross-linking of PVA chains. For the 1/1 ble nd, the amount of ST dissolved in water at 23 degreesC was less than 3% for the undrawn state and 25% for the drawn film. The decrease in the ST conte nt was enough for use as biodegradation materials. Namely, the water conten t relating to the biodegradation in soil is obviously different from such a serious experimental condition that a piece of blend film was immersed in a water bath. At temperatures above 0 degreesC, the storage modulus of the formalization blends became slightly higher than those of the nonformalizat ion blends. The Young's modulus of the drawn films with a draw ratio of 8 t imes was 2 GPa at 20 degreesC.