Tailored interfacial properties for immiscible polymers by hyperbranched polymers

The influence of hyperbranched polymer grafted polypropylene (PP-HBP) on the interfacial adhesion between fusion bonded bilayers of polypropylene (PP) and polyamide 6 (PA6) and on the properties of PP/PA6 blends was investigated. The interfacial adhesion between PP-HBP compatibilised bilayers was ten times higher compared to maleic anhydride grafted PP (PP-MAH) compatibilised bilayers. This is attributed to the higher diffusitivity and functionality of PP-HBP leading to the formation of more PP-PA6 copolymers at the interface. The elongation at break, epsib, of PP-HBP and PP-MAH compatibilised PP/PA6 blends were measured as a function of compatibiliser concentration. At low compatibiliser concentrations PP-HBP yielded a higher epsib compared to PP-MAH, while at high concentrations similar values of epsib were obtained. The higher values of epsib at low concentrations are explained by the higher functionality of PP-HBP yielding more copolymers and a higher interfacial adhesion. The similar values obtained at high concentrations show that similar properties are achieved for copolymer saturation at the interface using either compatibiliser. The high diffusitivity of PP-HBP is an asset for multilayer film extrusion, while for blends, the high functionality permits the use of less compatibiliser for similar property improvements.