Characterization of the Microstructure of Bimodal HDPE Resin

Abstract

In this work, two industrial bimodal high density polyethylene resins, resin A and resin B, having similar molecular weight (Mw), molecular weight distribution (MWD, and short-chain branching (SCB) content but different mechanical properties, were fractionated through cross-fractionation. The fractions were further characterized by GPC, 13C NMR, DSC and FT-IR techniques. These two resins were firstly fractionated into two fractions, i.e., high-temperature and low-temperature fractions, via preparative solution crystallization fractionation. Resin A with much better mechanical properties contains more high-temperature fractions with longer crystallizable sequences. The SCB content in the low-temperature fraction of resin A is lower than that of resin B. Both low-temperature fractions were then further fractionated using solvent gradient fractionation (SGF). The characterization of SGF fractions indicates that most of the branches fall into the high molecular weight chains in both low-temperature fractions. However, the high molecular weight chains in the low-temperature fraction of resin A contain less SCB than that of resin B.