Recycling of fiber reinforced plastics using depolymerization by solvothermal reaction with catalyst

Fiber reinforced plastics (FRP) have been widely used as a high strength material. However, it is well known that the FRP is one of the most difficult materials to fractionate into elemental components, namely fiber, filler, and polymers in the waste recycling process. Therefore, the wastes are treated in the incineration or landfilling without any recycling approaches. We have developed a new recycling method using subcritical fluids where unsaturated polyester (UP) resin in FRP can be efficiently depolymerized to separate glass fiber from filler and polymer. Reactions were carried out with or without a catalyst (K3PO4) in diethyleneglycol monomethylethter (DGMM) and benzyl alcohol under their subcritical state at temperatures 463–623 K for 1–8 h in a batch reactor. The conversion of UP became fast as the catalyst/solvent molar ratio increased and it was enhanced in the presence of K3PO4 catalyst in subcritical BZA. The glass fiber recovered after the FRP treatment in subcritical BZA was relatively long, while it became short and somewhat damaged at temperature higher than 573 K. The similar trend was observed when DGMM was used as a solvent.