Improved compatibility of high-density polyethylene/poly(ethylene terephthalate) blend by the use of blocked isocyanate group

The blocked isocyanate group (BHI) was synthesized to improve the storage s tability of HI (2-hydroxyethyl methacrylate combined with isophorone diisoc yanate) and characterized by Fourier transform infrared spectroscopy (FTIR) . High-density polyethylene grafted with the blocked isocyanate group (HDPE -g-BHI) was used as a re active compatibilizer for an immiscible high-densi ty polyethylene/poly(ethylene terephthalate) (HDPE/PET) blend. A possible r eactive compatibilization mechanism is that regenerated isocyanate groups o f HDPE functionalized by BHI react with the hydroxyl and carboxyl groups of PET during melt blending. The HDPE-g-BHI/PET blend showed the smaller size of a dispersed phase compared to the HDPE/PET blend, indicating improved c ompatibility between HDPE and PET. This increased compatibility was due to the formation of an in situ graft copolymer, which was confirmed by dynamic mechanical analysis. Differential scanning calorimetry (DSC) analysis repr esented that there were few changes in the crystallinity for the continuous PET phase of the HDPE-g-BHI/PET blends, compared with those of the HDPE/PE T blends at the same composition. Tensile strengths and elongations at the break of the HDPE-g-BHI/PET blends were greater than those of the HDPE/PET blends. (C) 2000 John Wiley & Sons, Inc.