Evolution of the interfacial stress transfer ability between a glass fibreand a polypropylene matrix during polymer crystallization

A rigorous evaluation of the influence of a transcrystalline interphase on the adhesion between a fibre and a polymer matrix is difficult because it i s generally not possible to consider this parameter without other factors. Indeed, in the case of a reinforcing material allowing spontaneous transcry stallization of a thermoplastic matrix, the inhibition of this phenomenon i s, for instance, possible by modifying the surface topography or the physic o-chemical nature of the fibre by appropriate coatings. In the same way, th e fibres which do not intrinsically favour transcrystalline growth can beha ve as active substrates by applying a shear stress onto the fibre-matrix in terface. In this case, however, processing of the sample for the classical micromechanical tests remains extremely difficult. In order to understand b etter the participation of a transcrystalline interphase in the interfacial adhesion in a polypropylene-glass fibre system, an experimental protocol h as been developed which allows us to evaluate the evolution of the interfac ial shear stress during the matrix crystallization, the latter being spheru litic or cylindritic. The results show that a transcrystalline interphase i n a polypropylene-glass fibre composite does not significantly alter the ad hesion between the two materials after total crystallization of the matrix. Nevertheless, it is shown that an important hooping of the fibre occurs du ring the development of a transcrystalline superstructure.