EFFECT OF MOISTURE ABSORPTION ON THE DYNAMIC-MECHANICAL PROPERTIES OFSHORT CARBON-FIBER-REINFORCED NYLON 6,6

A study of hygrothermal aging in terms of the kinetics of moisture abs orption by nylon 6,6 and its carbon fiber reinforced composites has be en carried out. The single free phase model of absorption has been app lied to the kinetic data and thereafter the values of diffusivity have been evaluated. The diffusivity was found to be dependent on the cond itioning temperatures and the volume fraction of fibers. Dynamic mecha nical properties of unaged and aged samples were studied using a free resonance torsion pendulum which covers a temperature range of 350-deg rees-C. Incorporation of carbon fibers has led to an increase in struc tural rigidity of the nylon 6,6 matrix especially at higher temperatur es. This was reflected by the sharp increase in the relative shear mod ulus as the glass transition temperature of nylon 6,6 is approached. A bsorbed moisture was observed to plasticize the polymer matrix and dec reased the temperatures of all the transitions. For instance, the alph a-transition was shifted by almost 95-degrees-C. The intensities of th e transition peaks of both unaged and aged samples were found to decre ase with fiber volume fraction. Increasing the conditioning temperatur es has resulted in a reduction of the shear storage modulus and this e ffect was found to be more pronounced in the reinforced nylon 6,6. Thi s has been attributed to the increase in the extent of degradation at the fiber-matrix interface.