PMMA PPTA MICROCOMPOSITES

Polymer composites of several concentrations of poly(methyl methacryla te) and poly(p-phenyleneterephthalamide) microfibrils have been prepar ed by blending a solution of the matrix polymer and a suspension of mi crofibrils obtained from a solution of commercial Kevlar fiber in H2SO 4. Scanning electron microscopy shows that a continuous network of fib rils with dimensions in the range 30-70 nm builds up starting at very low PPTA concentrations and that these fibrils tend to form larger glo bular aggregates at higher PPTA concentrations. The high connectivity of the network is reflected in the good reinforcing effect as shown by the values of the dynamic-mechanical storage modulus. Increased inter action between the constituent phases as the fiber content grows is re vealed by an increase of the calorimetric glass transition temperature and by thermogravimetric analysis, as well as by the growth of the sl ope of the Arrhenius plot of the main relaxation. The induced modifica tions of the matrix polymer's dynamic-mechanical spectrum are discusse d with the help of predictions of a modified block model. A consistent interpretation of the temperature shifts of the glass transition and the main dynamic-mechanical dispersion can be gained on this basis. Th e numerical values of the model parameters that fit the experimental b ehavior correlate well with the buildup of structure revealed in the m icrographs.