Conducting composites of polyurethane resin and polypyrrole: Solvent-free preparation, electrical, and mechanical properties

Abstract

Three methods were used for solvent-free preparation of conducting composites of PUR and PPy. In all cases, PUR was prepared from TDI and hydroxyl 15-W as polyol cross-linker, whereas PPy was obtained upon oxidative coupling of Py using ferric chloride as oxidant. In method 1, PPy powder was dispersed in hydroxyl. After addition of TDI the mixture was cured to yield the final product. In method 2, ferric chloride and Py were dissolved in hydroxyl and a PPy dispersion was obtained. The TDI was added and the final product was obtained upon curing. In method 3, Py was dissolved in TDI and ferric chloride dissolved in hydroxyl. Then the two solutions were mixed and cured resulting in the simultaneous formation of PPy and PUR. Method 1 led to composites with a specific electrical conductivity sigma of 10(-10) S (.) cm(-1) and a Shore A hardness of 40 to 55. Using methods 2 and 3, composites with sigma values of 10(-7) S (.) cm(-1) and a hardness of 30 to 40 were obtained. Presence of moisture increased the sigma values and decreased the hardness. Due to the solvent-free preparation, the maximum PPy content of the samples was limited to 10 wt.-%. The studies also demonstrated that the conductivity was mainly dependant on the amount of ferric chloride present in the sample and not on the PPy content, suggesting that the conductivity was ionic.