GLYCEROL-PLASTICIZED FILMS PREPARED FROM STARCH POLY(VINYL ALCOHOL) MIXTURES - EFFECT OF POLY(ETHYLENE-CO-ACRYLIC ACID)

Equations were obtained from response surface models to show how the u ltimate 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 t he 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 th at only glycerol content was important to predict the UTS of the films . The model for %E was more complicated, since there was a three-way i nteraction between EAA, PVA and glycerol. This model also contained tw o other terms: a two-way interaction evolving glycerol and EAA, and a (PVA)3 term. In general, %E increased as EAA. PVA and glycerol were in creased 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 dec reases. All the films produced in this paper were made with starch con tents above 50% to insure an optimum film formulation with at least 50 % starch. A mixture of 55.6% starch, 2.8% EAA, 28.3% PVA and 13.3% gly cerol is believed to be close to the optimum formulation to obtain fil ms having at least 100%E and UTS of 25 MPA, while still maintaining st arch concentrations above 50%.