Effect of heating on the structure of carbon fiber polyphenylenesulfide-matrix composite, as studied by electrical resistance measurement

Heating and cooling were found to affect the structure of carbon fiber polyphenylenesulfide-matrix composites, as shown by their effects on the DC electrical resistance of the composite in the fiber direction. Matrix flow during first heating above T_g and thermal stress buildup during cooling in any thermal cycle caused the resistance to increase, whereas isothermal crystallization at 180°C caused the resistance to decrease. Thermal stress buildup was reversible upon thermal cycling. Prior annealing at 180°C diminished the matrix flow because of improved fiber-matrix bond, and it increased the matrix crystallinity. Annealing at 180°C for 15 h or more was sufficient to eliminate the matrix flow.