Effects of cast film fabrication variables on structure development and key stretch film properties

The properties of films produced by the cast or blown film processes can be altered by varying the fabrication parameters. An experimental design is used to determine the effect of cast film fabrication variables on the performance of LLDPE stretch films. A three-variable Box–Behnken designed experiment was conducted to study the effects of air gap, melt temperature, and line speed on the key cast stretch film properties. In addition, the differences in molecular orientation in the films were studied using optical birefringence and shrinkage methods. The key film properties are correlated with the fabrication conditions using a statistical analysis program. The results of this study are explained in terms of web tensile stresses before solidification and the degree of molecular orientation developed in the film due to the stresses. © 1994 John Wiley & Sons, Inc.