Fractography of poly(methyl methacrylates).

For convenience in clinical manipulation, it is the practice to fabricate PMMA protheses from mixtures of powder and monomer. When the monomer is subsequently polymerized an unusual 2-phase polymeric material results in which grains of PMMA are dispersed in a matrix of the same polymer. The mechanical properties of the 2-phase materials are inferior in certain respects relative to 1-phase polymers. The purpose of the present work is to evaluate the failure of 2-phase materials by microscopical examination of their fracture surfaces. A granular microstructure was clearly distinguishable and a distinction made between materials which fail exclusively by transgranular fracture and others which additionally exhibit intergranular fracture. In order to interpret markings observed on the fracture surfaces of the complex 2-phase systems a study was made of the influence of molecular weight on the fractography of 1-phase PMMA. Molecular weight was reduced by degradation of samples by exposure to gamma-rays. The spacing of periodic rib markings on fracture surfaces was found to decrease with molecular weight and this relationship used to provide an estimate of the molecular weight of polymer in the matrix of 2-phase materials.