Novel high-performance materials from starch. 3. Influence of degree of substitution and amylose/amylopectin ratio on performance

The improvements in mechanical properties obtained by orienting starch-ether films were further examined, specifically with regard to their dependence on degree of substitution of the starch and on its amylose/amylopectin ratio. It was found that the degree of substitution had little or no influence on the mechanical properties of these materials at comparable deformations during drying. On the other hand, there were clear dependences of the tensile strength and toughness on the amylose/amylopectin ratio. In particular, the larger this ratio, the stronger and tougher the materials were after orientation. In overall performance, the oriented starch-ether films can be described as tough plastics, with tensile strengths between 15 and 47 MPa, tensile moduli between 320 and 670 MPa, and elongations at break between 5 and 120%. These values are comparable to those of medium-density or even high-density polyethylene.