Properties of polyketone/polypropylene blends

Blends of polypropylene and two polyketone grades with low and medium-high viscosities were prepared by melt extrusion. To obtain good compatibility, a maleic-anhydride-polypropylene copolymer was added to the blends. Polyoxy propylenediamine was added to some of the blends to further enhance compati bility. The blends were analysed with differential scanning calorimetry. In a second step, the blends were compression or injection moulded. Scanning electron microscopy, shear viscosity, density measurements and infrared spe ctroscopy were used to characterise the moulded blends and their oxygen per meabilities were assessed. Impact strength and hardness were measured on in jection-moulded blends. It was shown that the oxygen barrier properties of polypropylene could be greatly enhanced by a small addition of primarily th e low-viscosity polyketone. A content of 23.9% by volume of polyketone was sufficient to lower the permeability by 70% compared to pure polypropylene. This was because a polyketone-rich surface layer was formed during compres sion moulding. The incorporation of polyoxypropylenediamine had a profound effect on the morphology. The polyketone particles in this case were very s mall, and the absence of "pull-outs" suggested an enhanced phase adhesion b etween the different components. Further, the incorporation of polyoxypropy lenediamine had no impact on the oxygen permeability but the impact roughne ss and hardness were increased and the shear viscosity was also increased i n its presence. This indicated that chemical bonds were formed between poly ketone, polyoxypropylenediamine and the maleic-anhydride-polypropylene copo lymer. This network suppressed crystallisation of primarily the polyketone component. (C) 2001 Elsevier Science Ltd. All rights reserved.