The barrier, impact, morphology, and rheological properties of modified polyamides and their corresponding polyethylene?modified polyamide blends

Abstract

A systematic investigation of the effects of melt indices of polyamides (PAs) on the morphology, barrier, and impact properties of blow-molded polyethylene—polyamide and polyethylene-modified polyamide (PE—MPA) containers is reported. An appropriate alkyl carboxyl-substituted polyolefin was chosen as a compatibilizer precursor to modify PAs of varying melt indexes in a twin-screw extruder by the “reactive extrusion” process. The melt shear viscosities (ϵs) of MPAs increased with decreasing melt indices of their corresponding PAs and were higher than those of their corresponding PAs, respectively. The barrier properties of MPAs were better than those of their corresponding PAs, and the level of barrier improvement of PAs and MPAs increased consistently with decreasing melt indices of their corresponding PAs. The values of total impact energy (Et) of PAs and MPAs also improved with decreasing melt indices of PAs; however, MPAs exhibited lower values of Et than their corresponding PAs. The barrier properties of PE—MPA bottles were much better than those of PE—PA bottles. The order of barrier improvement of these PE—MPA bottles corresponded approximately to the order of barrier improvement of pure MPA when the viscosity ratio of MPA to PE was about equal to or less than one. However, regardless of exhibiting the best barrier improvement in all MPAs, a significantly smaller barrier improvement of PE—MPA5 bottles was observed when the viscosity ratio of MPA to PE was significantly greater than one. Finally, it is interesting to note that PE—MPA sheets exhibited significantly higher Et than their corresponding PE—PA sheets, although each PA was associated with a higher Et than their corresponding MPAs. Possible mechanisms accounting for the interesting behaviors noted above are suggested in this study. © 1997 John Wiley & Sons, Inc. J Appl Polym Sci 66: 2517–2527, 1997