Glycerol-plasticized films prepared from starch- poly(vinyl alcohol) mixtures: effect of poly(ethylene-eo-acrylic acid)

Equations were obtained from response surface models to show how the ultimate tensile strength (UTS) and percent elongation at break (%E) of solution-cast films vary with relative amounts of starch. poly(vinyl alcohol) (PVA). poly(ethylene-co-acrylic acid) (EAA) and glycerol in the formulation. Equations found from the response surface methodology were used to optimize the relative amounts of the four components with respect to the physical properties of cast films. The model showed that only glycerol content was important to predict the UTS of the films. The model for %E was more complicated. since there \vas a three-way interaction between EAA. PYA and glycerol. This model also contained two other terms: a two-way interaction evolving glycerol and EAA. and a (PVA)3 term. In generaL %E increased as EAA. PYA and glycerol were increased together. However. increased amounts of EAA could decrease %E if EAA was the only component increased. It is believed that EAA forms complexes with both starch and PVA. thereby increasing compatibility of the two polyhydroxy polymers. As %E increases. UTS of the films decreases. All the films produced in this paper were made with starch contents above 50% to insure an optimum film formulation with at least 50% starch. A mixture of 55·6% starch. 2·8% EAA. 28·3% PYA and 13·3% glycerol is believed to be close to the optimum formulation to obtain films having at least 100%E and UTS of 25 MPA. while still maintaining starch concentrations above 50%.