A new wood-modification process based on in situ grafting of urethane groups: biological resistance and dimensional stability of carbamylated Scots pine wood

Abstract

Chemical modification of wood typically requires the impregnation of wood with reactive compounds capable of undergoing covalent bonding to functional groups present in the cell wall. Creating such reactive agents in situ, with the use of low-priced chemicals, would prove more attractive for commercial applications. In this study, Scots pine (Pinus sylvestris L.) sapwood was impregnated with an aqueous solution of urea (30%), dried at 40°C for 24 h, and subsequently heat treated in an oven at 150°C for 24 h to produce the reactive isocyanic acid. By using accelerated fungal tests under laboratory conditions, provisional tests demonstrated a high biological resistance against selected moulds and rots. Migration of urea into the wood structure and grafting to its polymers during subsequent heat treatment, led to a bulked cell wall and enhanced resistance to water swelling, even after cycling water treatments. The bending strength (MOR) of modified pine wood was reduced by the treatment applied, while its modulus of elasticity (MOE) remained unchanged.