MECHANICAL AND VISCOELASTIC PROPERTIES OF BUTADIENE-STYRENE THERMOPLASTIC AND OXIDIZED CARBON-FIBER COMPOSITES

The mechanical and dynamic properties of oxidized carbon fibre and but adiene-styrene thermoplastic elastomer (SBS) composites were studied a s a function of the level of fibre oxidation and in comparison with th e properties of composites reinforced with untreated commercial carbon fibre. As a general rule, fibre oxidation gives rise to materials wit h improved mechanical properties-greater tensile and tear strengths. T he improvements accomplished depend on the degree of fibre oxidation. The effects of long exposure times to oxidizing agents were tested on the experimental samples, i.e. increase in the number of functional su rface groups and loss in mechanical strength due to a decrease in the L/d ratio, properties which act in opposite directions in the composit e. Storage modulus retention with increasing strain amplitude is direc tly proportional to the number of functional groups incorporated into the fibre surface, whereas at low strain amplitude it is proportional to fibre strength, measured in terms of the L/d ratio after processing . It is suggested that improved adhesion at the matrix-fibre interface is obtained through the functional groups of the oxidized fibre. As a consequence of fibre-matrix interface and at any frequency, the dampi ng peak temperature is shifted towards higher ranges and at the same t ime the apparent activation energy of the relaxation process is observ ed to increase.