Effect of Fabrication Conditions and Molecular Orientation on Polyethylene Blown Film Properties, 1993 Polymers, Laminations & Coatings Conference Proceedings

Linear low density polyethylene (LLDPE) is a copolymer of ethylene and an alpha olefin, such as 1-butene, 1-hexene, or 1-octene. Primary molecular parameters such as molecular weight, molecular weight distribution (MWD), type and amount of short chain branching (SCB), short chain branching distribution (SCBD), etc. affect processing, the structure and properties of polyethylene blown and cast films. A significant amount of work in the area of characterizing the primary molecular structure of LLDPE has been carried out (1,2). In addition to these primary molecular parameters, the molecular orientation imparted during blown and cast film fabrication is well known to have a major effect on the mechanical and thermal properties of both glassy and semi-crystalline polymers. In this study, an experimental design is used to study the effects of blown film fabrication variables on the structure and properties of LLDPE films. A 3-variable Box-Behnken designed experiment was conducted to study effects of die gap, land-length, and blow up ratio (BUR) at constant final film thickness on key blown film properties. In addition, the differences in the molecular orientation in the films were studied using optical birefringence and shrinkage methods. The measured key film properties are correlated to the processing conditions and to the measured molecular orientation.