# Microwave-Assisted Bio-Based Chemical Recycling of Fiber-Reinforced Composites from Construction and Demolition Waste

## TL;DR

This paper introduces a microwave-assisted chemical recycling method for fiber-reinforced composites from construction waste, using green solvents to recover fibers with minimal damage.

## Contribution

A novel microwave-assisted solvolysis method using green solvents for efficient and low-temperature recycling of fiber-reinforced composites is proposed.

## Key findings

- Glacial acetic acid + ZnCl2 achieved over 94% degradation efficiency in small-scale trials.
- Recovered fibers from pultrusion-based composites retained up to 84% of their original tensile strength.
- The method supports circular economy goals through solvent reuse and reduced environmental impact.

## Abstract

Fiber-reinforced polymer composites (FRPCs) are increasingly used in construction due to their high performance and low environmental footprint. However, their widespread adoption has raised concerns over end-of-life management, particularly under European regulations mandating high recycling rates for construction and demolition waste (CDW). This study evaluates different systems for the chemical recycling of FRPCs through microwave (MW)-assisted solvolysis using green solvents, including deep eutectic solvents (DESs) and biobased acetic acid. The process targets thermoset resin depolymerization while preserving fiber integrity, operating at reduced temperatures (≤230 °C) and lower energy demand than conventional techniques, such as pyrolysis. A systematic experimental design was applied to CDW-derived polyester composites and extended to industrial epoxy and vinyl ester composites. Among the tested solvents, glacial acetic acid + ZnCl2 (5 wt.%), achieved the highest degradation efficiency, exceeding 94% in small-scale trials and maintaining over 78% upon upscaling. Recovered fibers showed moderate property retention, with tensile strength and elongation losses of ~30% and ~45% for infusion-based epoxy composites, while those from pultrusion-based epoxy composites exhibited 16–19% and retained similar properties to the virgin material, respectively. The method facilitates fiber recovery with limited degradation and aligns with circular economy principles through solvent reuse and minimizing environmental impact.