The in situ Compatibilization of HDPE/PET Blends

Abstract

Currently there are two main compatibilization routes for PET (polyethylene terephthalate (PET))/HDPE blends. One route is PET/HDPE-g-maleic anhydride/HDPE blends. Here HDPE-g-maleic anhydride (HDPE-g-MA) is synthesized by melt grafting of HDPE with maleic anhydride. Adding HDPE-g-MA in the blends can increase the polarity of nonpolar HDPE phase so that certain hydrogen bonding can be formed between the functional maleic anhydride group of HDPE-g-MA and polar structure of PET. Another technique is PET/EGMA/HDPE blends using EGMA (ethylene glycidyl methacrylate copolymer) as the precursor of compatibilizer. EGMA is a recently developed functional copolymer, which has reactive GMA units on polyethylene backbone. This system could achieve much better mechanical properties than the former one because of the chemical network formed between the epoxy group of GMA, and the carboxylic or hydroxyl end groups of PET. Unfortunately, the commercially available EGMA, which is synthesized by solution copolymerization, is relatively expensive. It is economically impractical to use this kind of compatibilizer in large quantity. In this chapter, epoxy group grafted HDPE (HDPE-g-epoxy) by melt grafting is used as reactive compatibilizer for the blends. Compared with EGMA, HDPE-g-epoxy has the same compatibilization mechanism but it offers two advantages: first, low synthesizing costs by melt grafting technique; second, HDPE-g-epoxy could be synthesized based on the HDPE to be compatibilized. The grafting does not change the original structure of PE backbone, therefore, it has quite similar molecular structure, molecular weight, crystallinity, and melt viscosity as its original HDPE.