Characterization of the Liquid Products from Hydrolyzed Epoxy and Polyester Resin Composites Using Solid-Phase Microextraction and Recovery of the Monomer Phthalic Acid

Abstract

A method to recover the fibers and monomers from epoxy-based and unsaturated polyester-based composites and characterize the liquid products using solid-phase microextraction has been investigated in this study. Experiments were performed using near-critical water in a batch reactor (1 L) at temperatures and pressures up to 350 °C and 170 bar. In-situ sampling was performed. The samples collected at temperatures in the range of 300 to 350 °C were divided into an aqueous phase and an oil phase. It was possible to identify various phenolic and aromatic compounds in both phases. In the samples collected during degradation of the polyester composites, the monomer phthalic acid precipitated nearly purified at temperatures in the range of 250−325 °C. By the recovery of fibers, an oil product, and the possibility to recover phthalic acid, the polymer composite end-of-life cycle is a step closer to completion.

Sustainable End-of-Life Management of Wind Turbine Blades: Overview of Current and Coming Solutions

“…In the fluidized bed pyrolysis, a “bed”, fluidized by hot air is used, which allows quick heating of the materials [ 90 , 91 ]. Oxidation in the fluidized bed is carried out by combusting the polymeric matrix in a hot and oxygen-rich air flow of 450 to 550 °C [ 92 , 93 ]. The fibers are then contained in the air flow, and can be separated.…”

Investigation of degradation products produced by recycling the solvent during chemical degradation of fiber-reinforced composites

“…29 Purification and separation of valuable monomers in the resin have also been reported in a recent study by Sokoli et al. 44 The authors obtained nearly pure phthalic acid after solvolysis of polyester resin simply by storing the reaction liquid for several weeks in dark, without the use of any unit operations. Development of viable methods to recover monomers from the resin increases the potential for using the solvolysis process to recycle fiber reinforced polymer composites.…”

“…Although the resin elimination efficiency seems to increase, recovery of the glass fibers without resin on the surface requires higher process temperatures. 15,21,22,44 This study shows that the solvent can easily be recycled up to eight times. In fact, the recycling results in more efficient degradation of the composite, the more the solvent is recycled.…”

“…Although the resin elimination efficiency seems to increase, recovery of the glass fibers without resin on the surface requires higher process temperatures. 15,21,22,44…”

“…(3) The acetone left after eight recycles can be distilled and purified for reuse, as also shown in the investigations conducted by Sokoli et al 15 Furthermore, the solvent lost through absorption to the composite and evaporation to the environment could be recovered using a more advanced recovery system. This includes a closed recovery system, where all the evaporating acetone is condensed and collected 15 (4) The solubilized epoxy resin degradation products in the solvent can potentially be separated at the end and re-cured to produce new composite materials, as shown in the investigations conducted by Okajima et al 29 Purification and separation of valuable monomers in the resin have also been reported in a recent study by Sokoli et al 44 The authors obtained nearly pure phthalic acid after solvolysis of polyester resin simply by storing the reaction liquid for several weeks in dark, without the use of any unit operations. Development of viable methods to recover monomers from the resin increases the potential for using the solvolysis process to recycle fiber reinforced polymer composites.…”