Sustainable production of densified wood as advanced structural materials through oxygen delignification

Abstract

This study demonstrated a sustainable and commercially scalable low temperature (∼100 °C) oxygen delignification (O₂-delig) technology for delignifying pristine wood boards to produce advanced superstrong wood structural materials through subsequent densification. Sustainable dimensional wood delignification is the prerequisite first step with a significant barrier to commercialization due to great economic and environmental costs, though the groundbreaking concept of substantial wood densification through delignification has been well established and demonstrated. O₂-delig was conducted at low temperatures of 90–110 °C under semi-gas–solid phase reaction conditions with a lower base chemical charge of 28–56 g kg⁻¹, achieving approximately 20% lignin removal. Subsequent densification of the delignified basswood at a low pressure of 2 MPa for only 20 min resulted in a densified wood with double the density, a bending modulus of rupture over 220 MPa, and a Brinell hardness over 80 MPa. This study for the first time revealed that gains in wood strength by wood densification need to be greater than the “mathematical enhancing factor” (MEF) to avoid actual loss in wood load-bearing capacity due to the loss in wood thickness by densification. Life cycle assessment showed that densified O₂-delig wood has substantially low environmental impacts compared with metals even with high recycling content.