Production of sustainable wood-plastic composites from the nonmetals in waste printed circuit boards: Excellent physical performance achieved by solid-state shear milling

Abstract As a byproduct of electronic waste, the accumulated millions of tons of nonmetals from waste printed circuit boards (referred to hereinafter as NPCB) have caused severe environmental issues. Here, we report a novel method for the production of wood composites reinforced by NPCB via a solid-state shear milling (S3M) process. The S3M pretreatment successfully exfoliated NPCB into single glass fibers with a high aspect ratio. Hemicellulose and lignin were liberated from the surface of the wood cellulose fibers, and the size was reduced to a submicron level. Both optical and electron microscopy revealed that the wood composites prepared by the S3M process exhibited excellent filler dispersion and excellent interfacial adhesion between the filler and the polymer. This NPCB-reinforced wood composite was thermally stable at temperatures below 200 °C. In addition, the exfoliated NPCB and wood flour provided a well-designed structure that improved the tensile strength of the composite to 32.4 MPa. This wood composite retained a high storage modulus of 616 MPa at 100 °C, expanding the upper service temperature limit for wood composites. The excellent interfacial adhesion and hydrophilic nature of NPCB led to water absorption as low as 0.21%, exceeding the values previously reported for NPCB-reinforced wood composites under the same conditions. Finally, this wood composite also contained negligible organic pollutants and low heavy-metal concentrations, which are far below the regulatory limits for hazardous waste. The above results show that the reuse of NPCB in high-strength wood composites is a promising choice for both resolving environmental pollution and reusing solid waste to create value-added products.