Reactive Compatibilization of PA6/LDPE Blends with Glycidyl Methacrylate Functionalized Polyolefins

Blends of polyamide-6 (PA6) and low-density polyethylene (LDPE) were compatibilized by melt mixing with various polyolefins functionalized with glycidyl methacrylate (GMA), i.e. GMA grafted LDPE (LDPE-g-GMA), GMA grafted styrene-ethylene/butylene-styrene block copolymer (SEBS-g-GMA) and ethylene-co-glycidyl methacrylate copolymer (E-GMA). The blends with PA6/LDPE composition ratios 25/75 and 75/25 wt.-%/wt.-% were prepared in a Brabender internal mixer and their properties were evaluated by SEM, rheological measurements and DSC calorimetry. Morphological investigation by SEM showed a neat improvement of phase dispersion and interfacial adhesion in all compatibilized blends when compared to PA6/LDPE binary blends. The variation of dispersed phase size was analysed as a function of blend composition, compatibilizer concentration and GMA content. The emulsification curves of compatibilized blends showed that the equilibrium size of dispersed particles at saturation concentration of copolymer was lower when PA6 is the major component. The finest dispersion of LDPE phase (< 0.25 µm) was observed in the presence of SEBS-g-GMA copolymer. LDPE-g-GMA and E-GMA displayed similar compatilizing efficiency. In all cases the blends with polyamide matrix presented a marked rise of torque and melt viscosity with increasing the compatibilizer content. These effects were accounted for by the reaction between the epoxide groups of LDPE-g-GMA and the carboxyl/amine end-groups of PA6 leading to the formation of an interchain graft copolymer. The phase transition processes of PA6 in the blends resulted to be influenced by the compatibilizer content and the interfacial interactions between the polymer components, suggesting a different role of the compatibilizers at the PA6/LDPE interface.