Abstract
Part I. A range of polyethylene films were prepared from metallocene linear low density polyethylene (m‐LLDPE), linear low density polyethylene (LLDPE) and ultra low density polyethylene (ULDPE) resins, containing 0 and 8% polyisobutylene (PIB). FTIR, DSC and mechanical analysis techniques were used to investigate the effect of co‐monomer type, density and melt flow index (MFI) on the mechanical performance, orientation and crystallinity of these films. The study established that co‐monomer type and MFI were the greatest factors influencing mechanical performance and crystallinity. Crystallinity was found to be the most influential factor governing PIB migration in these films and this in turn was related to polymer type, density and MFI, High MFI, octene co‐monomer films exhibited the highest orientation, tear resistance and tack strength and would therefore be suitable for stretch film applications. Ultra low‐density polymers gave relatively low tack strength and poor overall mechanical performance.
Part II. A range of ethyl vinyl acetate (EVA)/m‐LLDPE/EVA co‐extruded films was manufactured, with vinyl acetate (VA) co‐monomer content of 6, 12 and 18% and PIB content from 0–20%. The films were aged at 45d̀C for up to 28 days, to enable tack (cling) development. The results show that film tack strength improved significantly with ageing. Increased VA concentration in the surface layer also showed significant improvement in film tack strength. The film tensile strength, elongation and tear properties in both machine direction (MD) and transverse direction (TD) were not significantly affected by increase in PIB concentration. However, increased VA content showed slight improvement in MD mechanical performance of the films, TD properties were relatively unaffected. Films with 12 to 18% VA in the surface layers produced high surface tack film and the mechanical performance of these films were comparable to mono‐layer polyethylenes. These films are suitable for stretch wrap applications and have reduced the overall concentrations of tack additives, though high VA films were more difficult to process.