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 dimension wood delignification is the prerequisite first-step with a significant barrier to commercialization due to great economic and environmental costs, despite the ground breaking concept of substantial wood densification through delignification has been well established and demonstrated. O2-delig was conducted at low temperatures of 90-110°C in semi-gas-solid phase reaction conditions with lower base chemical charge 28-56 g/kg and achieved approximately 20% delignification. 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, bending modulus of rupture over 220 MPa, and Brinell hardness over 80 MPa. The study for the first time revealed that densification below a critical densification ratio (CDR) resulting in actual loss in wood loadbearing capacity for a giving wood mass 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.