Chemical Recycling of Class A Surface Quality Sheet-Molding Composites

International audienceThis article describes the solvolysis of sheet-molding composites (SMC) consisting of an unsaturated polyester-styrene (UP) thermoset resin associated with glass fibers, filler (calcium carbonate), and a low-profile additive (LPA) (thermoplastic poly(vinyl acetate)). Preliminary studies have shown that glycols, diacids, and bisphenols are poor solvolytic reagents. On the contrary amino alcohols and polyamines allow much higher depolymerization yields, leading to a total digestion of the polymers. Diethylenetriamine (DETA), at boiling temperature (205 degreesC) was then chosen as solvolytic reagent. Pure poly(vinyl acetate) (PVAc) is readily converted to soluble products. A total dissolution of cured UP requires high yield of ester cleavage. Longer reaction times are needed with styrene content enhancing. The introduction of PVAc in the UP resin does not alter the kinetics of solvolysis of the thermoset but affects the rheological behavior in intermediate states and enhances the viscosity of the final liquid. A greater effect is observed with higher molecular weight poly(vinyl acetate). Treatment of SMC chips with DETA at 205 degreesC for 10-14 h leads to a mixture that can split into three fractions, viz. glass fibers, filler, and an organic liquid. Organic contamination of glass fibers and fillers is very low. The organic liquid may be used as a curing agent for epoxy resins. The course of the solvolytic process is affected by the nature of the LPA and the original sizing of the glass fibers.Keyword