Impact of hygrothermal aging on the dynamic mechanical properties of Sheet Molding Compound

Sheet Molding Compound, (SMC), is a composite material comprised of an unsaturated crosslinked polymer, reinforcing fiber such as glass, thermoplastic processing aids, mineral fillers, and lubricant (release agent). Mechanical properties for service requirements are developed through fiber reinforcements randomly aligned in between two polymer sheets. Service requirements for the SMC material are necessary for specified amounts of time. For example, SMC used for automotive parts have upwards of a 10 year service life; therefore, the study of how the SMC material changes with time and environmental exposure is of interest. In the current study, hygrothermal aging is used to accelerate normal environmental aging and dynamic mechanical thermal analysis (DMTA) is used to study the mechanical and chemical changes as a function of temperature and aging time. Results from the current study show through high performance liquid chromatography (HPLC) analysis that poly(vinyl acetate) (PVAc) does not chemically react with water in the SMC material and DMTA data show that water has two roles in the thickening reaction in the SMC between MgO and carboxylic acid functional groups adding an additional step to what has been previously reported.