Polymer Composites of Poly(p-Phenylene Terephthalamide) and Nitrile Butadiene Rubber: (I) Preparation and Properties
Microfibrillar poly(p-phenylene terephthalamide) (PPTA) was uniformly dispersed in a matrix of nitrile butadiene rubber (NBR) by coagulating a homogeneous solution of N-sodium PPTA and NBR in common solvent of dimethylsulfoxide and N,N-dimethylformamide (DMF) with acidic water, being accompanied by regeneration of metalated PPTA. The observation with polarization optical microscope showed that the image of the polymer composite was uniformly birefringent under crossed nicois. The electron-microscopic observation on the residue remaining after extraction of uncured NBR with DMF from the polymer composite revealed a network of microfibrills with a diameter of 10 ~ 30 nm. In a cured sheet of the PPTA/NBR composite, PPTA microfibrils tend to align along the milling direction, giving rise to the anisotropics of modulus and swelling ratio in organic solvent. The reinforcing effects of microfibrillar PPTA in NBR are superior in modulus and strength to those of carbon black at the same reinforcement content. The improvement in tear strength was noticeable in microfibrillar PPTA-reinforced NBR. The fractography supported the view that microfibrils of PPTA impede the crack growth by bifurcation or deflection of crack.
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