Compatibility Studies in Binary Blends of PA6 and ULDPE-graft-DEM

Abstract

In order to study the compatibility promoted in polyamide 6 (PA6) and ultra low-density polyethylene (ULDPE) blends by grafting polar groups into the ULDPE, several blend compositions were prepared in a twin screw extruder. The grafting agent was diethylmaleate (DEM), and the blend compositions prepared were 0, 20, 50, 80 and 100 wt.-% of PA6. The compatibility was evaluated by studying the rheological, thermal, morphological, and spectroscopic (infrared and dielectric) properties of the blends. The formation of a copolymer was observed by infrared spectroscopy after selective extraction of the components, presumably by the interaction of terminal NH 2 groups of PA6 and carbonyl groups of ULDPE(graft-DEM. Thermal properties showed changes due to compatibilization. For instance, fractionated crystallization of the PA6 component was observed when it formed the dispersed phase in reactive blends in view of the enhanced dispersion. Nucleation of the ULDPE component by the PA6 component was observed for reactive and non-reactive blends. The DSC melting results showed the presence of two crystalline forms of the PA6 in the blends. These were the less stable γ-form, predominant over the more stable α-form, in reactive blends, especially for the 20/80 and 50/50 wt.-% blend compositions. Dynamic rheological experiments provided data for fitting the Carreau viscosity model; the results revealed that longer characteristic times are obtained for compatibilized system. This was reinforced by the more elastic behavior that such systems presented in G'-G plots, as compared to the non-reactive ones. Dielectric spectroscopy revealed a noticeable shifting of the α-mode of the PA6 to lower temperatures for the 50/50-g, together with an enhancement of the β over the γ-mode which indicates the presence of tightly bound water. The T g depression could be due to the plasticization effect resulting from the substitution of intramolecular PA6 H-bonds by either water molecules or physical interactions across the interphases.