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, epsilon(b), 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 epsilon(b) compared to PP-MAH, while at high concentrations similar values of epsilon(b) were obtained. The higher values of epsilon(b) 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. (C) 2000 Elsevier Science Ltd. All rights reserved.