Recycling thermosetting polyester resin into functional polymer using subcritical water

Subcritical water and soluble alkali were applied to hydrolyze thermosetting polyester resins of fiber reinforced plastic (FRP) to recover a styrene-fumaric acid copolymer (SFC) in high yield. SFC is a functional polymer and has the same molecular structure as that of styrene-maleic acid copolymer, which is applied as high value-added additive. Potassium hydroxide (KOH) contributed to accelerate hydrolysis and to provide water solubility to the SFC. The optimized reaction conditions based on the SFC yield were at either a temperature of 230 °C, reaction time of 2 h, and with a KOH concentration of 0.38 mol/L, or 230 °C, 1 h, and 0.72 mol/L for sodium hydroxide (NaOH). It was verified that this method had the potential to recycle thermosetting polyester resin of FRPs to produce SFC.