The influence of cross-link density on the creep compliance of an advancedpolyimide

The effect of cross-link density on the visco-elastic performance of an adv anced polymer matrix (LaRC(TM) -PETI-SI) was investigated through creep com pliance tests. Testing consisted of short-term isothermal creep and recover y with the creep segments performed under constant load. The tests were con ducted at three temperatures below the glass transition temperature of each material with different cross-link density. Through the use of time-aging- time superposition procedures, the material constants, material master curv es and aging-related parameters were evaluated at each temperature for a gi ven cross-link density. It was shown that the high cross-link density mater ials have increased creep compliance and creep compliance rate, and are les s sensitive to physical aging than the low cross-link density materials. Th e temperature sensitivity of the time-temperature superposition (TTSP) shif t factor was shown to increase monotonically with increasing cross-link den sity. Furthermore, at the highest temperature, a separation in the TTSP shi ft factors was apparent between different cross-link densities. This separa tion occurred at a molecular weight (M-c) of similar to 3321 g/mol.