Role of molecular architecture in interfacial self-adhesion of polyethylene films

Abstract

The influence of molecular architecture on interfacial self-adhesion above polyethylene film melt temperature was examined in this study. The investigated molecular structures include molecular weight (Mw), molecular weight distribution, long chain branch amount and distribution and short chain branch among and along polyethylene chains. The long chain branches concentration was quantified using gel permeation chromatography and short branches concentration using nuclear magnetic resonance techniques. The adhesion strength was measured immediately after melt bonding using a T-Peel test. The results showed that increasing Mw resulted in higher adhesion strength in linear metallocene ethylene α-olefins. Low long chain branch concentrations hinder reptation motion and diffusion, and result in lower adhesion strength. Low density polyethylene with highly branched chains yielded very low self-adhesion. A drastic difference in adhesion strength between metallocene and conventional linear low density polyethylene is attributed to homogeneity versus heterogeneity of composition distribution. The low interfacial self-adhesion in conventional polyethylene was concluded to be due to enrichment of highly branched low molecular weight chains at the film surface. These segregated chains at the interface diffuse before the high molecular weight chains located in the bulk.