Solvolytic recycling of unsaturated polyester resin-based sheet moulding composites

New regulations on low emission vehicles has incentivized a push towards reducing the weight of vehicles. While the implementation of lightweight Sheet Moulding Compounds (SMC's) in the automotive industry is taking shape, a recycling strategy that does not downgrade the fibers is not commercially applied yet. This paper investigates a broad scope of reaction conditions for the solvolysis of SMC's based on unsaturated polyester resins (UPR).

The Hansen Solubily Parameter theory was used to model and select prospective solvents for the project. A method is disclosed for recovering the glass fibers from SMC's, using base chemicals such as monoethoxyamine (MEA) and potassium hydroxide (KOH), and relatively mild conditions. Tensile testing is used to assess the effect of solvolysis on the fibers. Thermogravimetric analysis was used to determine residual material on the fibers.

The best solvolysis results were obtained with MEA/KOH at 170 °C. As a result of the mild conditions used, the strength of the fibers is not affected. TGA analysis shows that the removal of fiber sizing depends on the nature of the used catalyst. It also showed that the use of acetophenone as solvent raised the decomposition temperature of the resin.

An effective and mild method for the solvolysis of UPR based sheet moulding compounds was developed. The removal of the sizing of the fibers can be influenced by choosing an appropriate catalyst. It is postulated that acetophenone reacts with the resin and as a result makes it more thermally stable.