Morphology and mechanical properties of poly(vinyl alcohol) and starch blends prepared by gelation/crystallization from solutions |
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Authors: | T Nakashima C Xu Y Bin M Matsuo |
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Institution: | (1) Kinki University of Toyooka Junior College, Toyooka 668-8580, Japan, JP;(2) Department of Textile and Apparel Science Faculty of Human Life and Environment Nara Women's University, Nara 630-8506 Japan, JP |
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Abstract: | In an attempt to produce biodegradation materials, poly(vinyl alcohol) (PVA)–starch (ST) blends were prepared by gelation/crystallization
from semidilute solutions in dimethyl sulfoxide (Me2SO) and water mixtures and elongated up to 8 times. The content of mixed solvent represented as Me2SO/H2O (volume 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. The elongation up to 8 times could be done for the 1/1 blend but any elongation was impossible
for blends whose ST content was beyond 50%. When the blends were immersed in water at 20 or 83 °C, the solubility became considerable
for an undrawn blend with 1/5 composition and a drawn 1/1 blend with λ=8. To avoid this phenomenon, cross-linking of PVA chains
was carried out by formalization under formaldehyde vapor. Significant improvement could be established by the cross-linking
of PVA chains. For the 1/1 blend, the amount of ST dissolved in water at 23 °C 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 experimental condition that a piece of blend
film was immersed in a water bath. At temperatures above 0 °C, the storage modulus of the formalization blends became slightly
higher than those of the nonformalization blends. The Young's modulus of the drawn films with a draw ratio of 8 times was
2 GPa at 20 °C.
Received: 23 June 2000 Accepted: 30 October 2000 |
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Keywords: | Poly(vinyl alcohol) starch blends Gelation/crystallization Dimethyl sulfoxide and water mixtures Formaldehyde Cross-linking |
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