Evaluating the processability of film blowing resins

Abstract

AbstractA key factor that limits the production rate in film blowing is bubble instability. Although processing conditions play an important role, it is well known that some resins are more resistant to instabilities than others. It is clear that long‐chain branching enhances stability, but it is not currently possible to model the process with sufficient accuracy to establish a quantitative relationship between rheological properties and blown film processability. It would thus be useful to be able to compare the processabilities of film resins by means of a laboratory measurement. We compared two laboratory tests that may be helpful in evaluating the ability of a resin to resist instabilities in the film blowing process. One of these was a film resin tester designed to simulate some aspects of the film blowing process, and the other was an extensional rheometer. We used a set of polyethylene resins that had been used previously in an extensive study of blown film stability. The extensional rheometer clearly shows the superiority of low‐density polyethylene but is not able to distinguish among polymers of other types. The melt tester, on the other hand, is sensitive to differences among linear polymers. POLYM. ENG. SCI., 2009. © 2009 Society of Plastics Engineers