On In-Situ Compatibilization Of HDPE/PC Blends By Macromolecular Reaction And Their Structure, Morphology And Properties

HDPE and PC are known to be incompatible polymer pair, therefore how to compatibilize and improve the properties of HDPE/PC blends have become the important problem. In this paper, ethylene vinyl acetate copolymer(EVA) and ethylene acrylic acid copolymer(EAA) were added into HDPE/PC blends through twin screw extruder. Grafted or co-crosslinked copolymers PC-EVA, PC-EAA were generated as compatibilizers in situ during reactive processing by transesterification between PC and EVA or EAA in the presence of catalyst- Dibutyltin Oxide.To generate the macromolecular compatibilizers during processing, the transesterification between PC and EVA or EAA was employed and studied in detail. The blends were compounded by means of Haake Torque Rheometer and the characteristics of the products were evaluated by Soxhlet extraction and FTIR,DSC, ~1H-NMR analysis. The results showed that the reaction did take place in PC/EVA or PC/EAA blends, grafted or co-crosslinked copolymers PC-EVA or PC-EAA were in-situ generated at the interface of the components during processing; the product of PC-EVA was mainly grafted copolymer, and EAA-g-PC-g-EAA copolymer generated mainly for PC/EAA blend. With more catalyst and reaction time, more co-crosslinked copolymers tended to be generated. However, too long time would aggravate the chain scission and instability of products. In the same condition, EAA was more reactive than EVA.Afterward, the morphology and mechanical properties of HDPE/PC blends were investigated. Except for the influence of EAA and DBTO, the advantage anddisadvantage of one-step processing and two-step processing were considered. The results indicated that EAA 3990 could improve the compatibilization of HDPE/PC blends, PC phase was more homogenously dispersed in HDPE matrix and the interfacial adhesion was enhanced; the addition of only lphr DBTO could decreased the particle diameter of dispersed phase and the surfaces of the two phases became illegible. A peculiar morphology was observed in the fracture surface of the blends through two-step processing, that the minor phase was broken after the interfacial adhesion was greatly enhanced by macromolecular reaction. But this did not lead to the big increase of mechanical properties. Whereas the blends through one-step processing possessed the better properties: when the content of PC was set 20%, the addition of EAA could increase the toughness and the elongation at break but the strength became worse; when the content of PC was set 30%, stress hardening phenomenon of blends was strengthened by EAA, so that the tensile strength at break of HDPE/PC/EAA/DBTO 39/30/30/1 reached such a high value-30.15MPa, and at the same time, the peak value of Izod notched impact strength occurred-29.85KJ/m2, approximately double one of HDPE/PC 70/30.Finally, the crystallization properties of blends through two-step processing were investigated preliminarily. It was found that with the addition of EAA, the melting enthalpy as well as the crystallizability for HDPE decreased gradually. Furthermore, the transesterification enhanced the compatibilization of blends which resulted in the continued decrease of melting enthalpy of HDPE when adding lphr DBTO.