VISCOELASTIC PROPERTIES OF SHORT CARBON-FIBER THERMOPLASTIC (SBS) ELASTOMER COMPOSITES

The determination of viscoelastic property variation in short fiber-re inforced composites, as a function of strain, temperature, and frequen cy, constitutes a useful tool when the existence or the strength of ma trix-fiber interfaces are to be examined. In this work, these properti es are studied in thermoplastic elastomer matrix materials (SBS) fille d with commercial carbon fiber (PAN), oxidated, and subsequently treat ed with diazide, which generates SO2N3 groups on the fiber surface, th eoretically capable of chemical reaction with the polymeric chain. For the composite containing diazide-treated oxidated fiber, certain phen omena have been proven to occur, such as lesser storing modulus losses in case of increasing strain, greater equivalent interfacial thicknes s values, and higher mechanical energy loss values than those of compo site containing oxidated fiber. An increase in glass transition temper ature and apparent activation energy of the relaxation process, with r espect to composite-containing commercial fiber, are also observed, wh ich, altogether, allow for the statement that new matrix-fiber bonds a re generated through the sulfonyl azide group, conferring greater stre ngth to the interface, although it is less stiff than the one formed w ith oxidated fiber. Finally, the experimental results are in agreement with those obtained from Huet's theological model. (C) 1995 John Wile y and Sons, Inc.