Management of SMC plastic waste by the process of recycling SYLTEC

The objective of this study was to improve the mechanical properties of SMC composite waste, recycled as fillers in a polypropylene matrix. A four stages process, called SYLTEC, was developed. The first step called conditioning step, aimed to extract glass fibres from the polyester resin and to obtain a cotton-like aspect for the ground material. The use of a shredding process allowed either to preserve a minimum fibre length or to maintain a constant rate of each SMC component, particularly glass fibres. The second step called reinforcement step, consisted in a controlled dissolution step of calcium carbonate by an acido-basic reaction and allowed to obtain a reinforcing glass fraction of 40-45% wt. The third step, called thermal treatment step, created an ionic adhesion, filler/filler (calcium carbonate-anhydride of thermally activated polyester) by polyester fonctionnalization and filler/matrix (calcium carbonate-anhydride of interfacial agent PPgma blended with PP). This entailed a significant reinforcement of composite and a strong improvement of mechanical properties. The last step, called chemical treatment step, lead in the case of PP, to a chemical fonctionnalization between the SMC filler, thermally modified and the polymer matrix made of a PP/PPgma blend, caused by an amine type polyfonctionnal agent. Condensation into imide allowed the creation of a chemical interface in comparison with the ionic one resulting from the third step. It was also noticed that this last step was unnecessary in the case of a polar polymer host matrix such as PA6 to achieve high mechanical performance. Finally, the whole process lead to very close mechanical properties for the reinforced thermoplastics to the same polymer reinforced with virgin fibres.