Polymer Composites of Poly(p-Phenylene Terephthalamide) and Nitrile Butadiene Rubber: (II) Calculation of Anisotropic Moduli Based on Microfibrillar Lattice Model

Abstract

Preparation and properties of polymer composites of poly-(p-phenylene terephthalamide) (PPTA) and nitrile butadiene rubber (NBR) were reported in the previous paper. Morphological observation proved that PPTA is uniformly dispersed in a form of microfibrillar network in NBR matrix. The diameter of the microfibrils was about 10–30 nm. The milling process induced the anisotropy in modulus of the polymer composites owing to the preferential orientation of PPTA microfibrils along the milling direction. With increasing molecular weight, the anisotropy was increased due to the stress concentration onto the high modulus PPTA microfibrils with high molecular weight. Anisotropy of modulus with respect to the milling direction was calculated by using the quasi-three-dimensional lattice model. Lattice parameters of the unit cell were evaluated by the aid of anisotropy of the swollen rubber composite. It was necessary to take into account the decreasing modulus with decreasing molecular weight of PPTA by introducing a very small, low modulus fraction of the matrix into each lattice element of the model. The temperature dependence of moduli of the polymer composites with various molecular weights of PPTA and various degrees of anisotropy were successfully calculated by the lattice model over the whole temperature range from glassy to rubbery state.