Correlating the Plastic Strain with the Properties of the Linear Low Density Polyethylene Blown Film, 1993 Polymers, Laminations & Coatings Conference Proceedings"

A. K. Babel, G. A. Campbell

Experiments are carried out to verify a theory developed to correlate the plastic strain history in the film blowing to the ultimate physical properties of the film. The theory predicts that the amount of strain put in the film once it starts to freeze, defined as plastic strain here, has the prominent effect on the film properties. A grade of linear low density polyethylene, an experimental resin supplied by Mobil chemical company, was used to produce the blown film runs yielding a 1.25 mil thin film at the outlet. Film surface and bulk temperatures were measured using the infra-red techniques to identify the points where film starts to crystallize. A video digitization technique was used to measure the bubble kinematics. Film properties were measured using standard ASTM methods. The results indicate that the film of superior quality is produced if the film is stretched to a greater extent in the neighborhood of freeze-line. This principal applies equally well to the film properties in the cross or transverse direction. The results obtained can be exploited by designing the blown-film equipment and processing conditions which result in maximum bubble stretching once the melts begin to crystallize.