ساخت و ارزيابي ويژگي هاي مكانيكي- ديناميكي و گرمايي نانو چند سازه هاي كريستال سلولز- PVA

Preparation and Evaluation of Dynamic - Mechanical and Thermal Properties of Cellulose Nano-crystals / PVA Copolymers Nano-composites

The goal of this work was to compare the mechanical and thermal properties of biopolymer based nanocomposites prepared from cotton whiskers and copolymers of polyvinyl alcohol. The cotton whiskers, prepared by acid hydrolysis of cotton linter, consisted of slender rod-like nanoparticles. The average length and width of these whiskers were about 172 and 15 nm, respectively, leading to an average aspect ratio around 11-12. After blending the suspension of cotton whiskers with the solution of PVA, nanocomposite films were prepared by a casting/evaporation technique. The degree of hydrolysis of the matrix was varied to change the hydrophilic character of the polymer matrix and then the degree of adhesion between the filler and the matrix. Nanocomposite materials were conditioned at various moisture contents in order to evaluate the effect of this parameter on the composite structure. The dynamic mechanical and thermal properties of the films were characterized using DMA and DSC, respectively. Tensile tests were performed to estimate mechanical properties of the films. The storage modulus of nanocomposite materials was improved by adding reinforcement. However, the glass transition temperature was not changed. Increasing relative humidity decreased Tg and had negative effect on mechanical properties.The degree of crystallinity and the values of the melting temperature are found to decrease with increase in loading level. Properties improvement in fully hydrolyzed copolymers was more significant than partially hydrolyzed copolymers.