Compatibility studies in binary blends of PA6 and ULDPE-graft-DEM

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. T he grafting agent was diethylmaleate (DEM), and the blend compositions prep ared were 0, 20, 50, 80 and 100 wt.-% of PA6. The compatibility was evaluat ed by studying the rheological, thermal, morphological, and spectroscopic ( infrared and dielectric) properties of the blends. The formation of a copol ymer was observed by infrared spectroscopy after selective extraction of th e components, presumably by the interaction of terminal NH2 groups of PA6 a nd carbonyl groups of ULDPE-graft-DEM. Thermal properties showed changes du e to compatibilization. For instance, fractionated crsytallization of the P A6 component was observed when it formed the dispersed phase in reactive bl ends 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 PA 6 in the blends. These were the less stable gamma -form, predominant over t he more stable alpha -form, in reactive blends, especially for the 20/80 an d 50/50 wt.-% blend compositions. Dynamic rheological experiments provided data for fitting the Carreau viscosity model; the results revealed that lon ger characteristic times are obtained for compatibilized systems. 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 r evealed a noticeable shifting of the alpha -mode of the PA6 to lower temper atures for the 50/50-g, together with an enhancement of the beta over the g amma -made which indicates the presence of tightly bound water. The T-g dep ression could be due to the plasticization effect resulting from the substi tution of intramolecular PA6 H-bonds by either water molecules or physical interactions across the interphases.