DURABILITY OF SHEET MOLDING COMPOUNDS - INFLUENCE OF HYDROTHERMAL AGING ON MORPHOLOGY AND MOLECULAR MOBILITY AT MICROSCOPIC SCALE

The physicochemical aging for parts of Sheet Molding Compound should b e considered for their lifetime management and reusability. This mater ial has a complex morphology and contains porosity due to the process and to shrinkage compensation. This SMC study has two complementary ap proaches. One describes the morphological consequences of water uptake , showing the decrease in the total amount and the fractal dimension o f micro-voids by scanning electron microscopy and image processing. Th e other shows, by mechanical spectrometry, the effect of water on phys ical or chemical bonds. In both cases, the ''low profile agent'' in SM C plays an important role. The molecular mobility was taken as a senso r parameter for the structural changes at the molecular scale, highlig hting and quantifying the first steps of the aging. The loss factor le vel increases, and the activation energies are modified, even for the first aging days. The analysis shows recovery for the material near th e relaxation peak of the low profile agent, since the curve recovers i ts initial shape.