Trade-offs in Blown Film Processing-Structure-Property Behavior of LLDPE Type Resins from Chromium, Metallocene and Ziegler-Natta Catalysts

Abstract

Within the family of PE resins, linear low density PE (LLDPE) resins have found extensive applications in the areas of food packaging (for example, bakery, candy, frozen foods, ice-bags, etc.), non-food packaging (for example, garment bags, heavy duty sacks, stretch and shrink wrap, etc.) and non-packaging (for example, industrial can liners, agricultural films, medical, trash bags etc.). These numerous applications demand a vast range of application performance benefits that cannot be met by a single resin. A high molecular weight (Mw), broad molecular weight distribution (MWD) and often very low levels of long chain branching (LCB) typify chromium catalyst PE resins. Ziegler–Natta (Z–N) resins are typically narrower in MWD than chromium resins and contain no LCB. Metallocene resins are typically even narrower in MWD than Z–N resins and may or may not contain any LCB depending on the catalyst and process employed. Thus, it is clear that these three catalysts viz. chromium, Z–N and metallocene can yield PE resins with widely different molecular and rheological properties. This chapter examines the blown film processing–structure–property behavior and trade-offs with three different LLDPE resins from each catalyst mentioned.