INTERFACE AND MECHANICAL COUPLING EFFECTS IN MODEL PARTICULATE COMPOSITES

Dynamic mechanical spectra of polystyrene (PS) or styrene-co-methacryl ic acid copolymer (SAMA) filled by various amounts of raw or coated gl ass beads have been recorded in the glass transition (T-g) region of t he polymers used as the matrix. The relative contribution of the two k ey features governing the magnitude of the main mechanical relaxation, i.e., (i) the mechanical coupling between phases, and (ii) the physic o-chemical interactions at the polymer/filler interface, is separated by an original mechanical modeling, which gives evidence only for the reinforcement effect of the polymer matrix. Thus, by comparing experim ent and theory, it was shown that the decrease in the tan delta maximu m displayed by PS reinforced by high volume fractions of raw glass bea ds mainly results from an improvement of the reinforcement effect, bec ause of the presence of clusters of particles. In contrast, for SAMA c opolymer used as the matrix, it was found, in addition, a decrease in the molecular mobility of chains due to interactions at the polymer/co ated glass bead interface. Differential scanning calorimetry and scann ing electron microscopy analysis agree with this conclusion.