Journal of Plastic Film & Sheeting

Metallocene polyethylenes are well known for providing superior toughness, heat sealing, and clarity when compared to the conventional polyethylenes. Their unique attributes have been employed for over a decade in the manufacture of many different types of blown and cast films for numerous end-use applications. A new family of very low density metallocene polyethylenes, defined here as mVLDPE, exhibits outstanding toughness and surprising heat seal and hot tack performance. Both monolayer and coex blown film studies have demonstrated that the unique properties of these mVLDPEs can be used to produce high-performance films for a wide variety of packaging applications. Selected data from these studies are used to demonstrate that the properties of these mVLDPEs are superior to those of conventional very low density polyethylenes (VLDPEs), linear low density polyethylenes (LLDPEs), metallocene linear low density polyethylenes (mLLDPEs), and ethylene vinyl acetate copolymers (EVAs).

This study investigates the effect of extrusion processing conditions and comonomer type on the gas permeation properties of LLDPE films containing polyisobutylene (PIB). The results show improved gas barrier properties with increasing polymer density and with increases in film crystallinity and orientation as a result of extrusion processing conditions such as blow-up ratios.

Polyethylene films, prepared from a range of mLLDPE, LLDPE, and ULDPE resins containing 4% polyisobutylene (PIB) from a masterbatch, are manufactured using a Killion cast film extrusion system. FTIR, DSC, and mechanical analysis techniques are used to investigate the effect of comonomer type, density, and melt flow index (MFI) on the mechanical performance, orientation, and crystallinity of these films. The study established that comonomer type and MFI are the greatest factors influencing the mechanical performance and crystallinity. Crystallinity has been found to be the most influential factor governing PIB migration in these films and this in turn is related to polymer type, density, and MFI.

The effect of molecular weight on the migratory characteristics of polyisobutylene (PIB) additive from the bulk to the surface of a range of monolayer and multilayer extruded polyethylene films has been analyzed by FTIR-ATR and peel cling analysis. Migration rates are shown to be higher for lower molecular weight PIB additive, and cling strength increases as the PIB molecular weight increases.

A range of EVA-mLLDPE-EVA coextruded films, with polyisobutylene (PIB) masterbatch content of 0-20% and vinyl acetate (VA) comonomer content of 6, 12, and 18%, is manufactured. The films are aged at 45 C for up to 28 days to enable tack (cling) development. The results show that film tack strength improves significantly with aging. Increased VA concentration in the surface layer also shows significant improvement in film tack strength. The film tensile strength, elongation, and tear properties in both machine direction (MD) and transverse direction (TD) are not significantly affected by increase in PIB concentration. Increased VA content shows slight improvement in MD mechanical performance of the films, although TD properties are relatively unaffected.