Effect of the shape of filler particles on the strength of a polymer composite

When metallic or polymeric powder fillers are introduced into poly(2,6-dimethyl-1,4-phenyleneoxide) (PDPO), the strength of the filled composites is found to decrease, while when glass or polymeric fiber fragments are introduced into PDPO, the effect is reverse. The fracture activation energy of the composites is shown to coincide with the fracture activation energy of PDPO. The variation of the strength is caused by the dependence of structure-sensitive parameter gamma of the matrix on the concentration and shape of filler particles. On the one hand, filler particles are stress concentrators and their introduction decreases the strength. This effect prevails in the composites filled by spherical particles. On the other hand, when anisotropic particles are introduced, matrix molecules are arranged parallel to their axis, which decreases gamma and increases the strength. This effect is predominant in the composites filled by fiber fragments.