Novel treatments of solid wood - studies into the use of imidazole and succinimide

Abstract

Recent activities have focussed on the use of ionic liquids (ILs) in wood treatments and bioprocessing. Most ILs are based on imidazolium systems, so it was decided to investigate the potential of imidazole as a treatment, along with another heterocyclic compound, namely succinimide. Thus, modification of Scots pine sapwood (Pinus sylvestris L.) with heterocyclic compounds, imidazole and succinimide, was investigated. Pressure-impregnation with aqueous solutions containing imidazole, imidazole + citric acid, succinimide, succinimide + citric acid, and citric acid + sorbitol at 5%, 10%, and 15% solid content was followed by oven-curing at 220 °C for 1 hour. Mass changes during treatment steps, bending properties, and anti-swelling efficiency (ASE) were examined. Results indicate that solid concentrations within the range of 5% to 10% were optimal. Results seem to show there are two differing mechanisms in the modification of imidazole and succinimide, respectively. Mass loss due to the heat treatment was highest in imidazole-treated specimens, whereas it remained low and concentration-independent in succinimide-treated specimens. ASE after three cycles reached 31% for imidazole-treated specimens and improved to 38% with the addition of citric acid. For succinimide, ASE increased from 17% to 41%. Bending properties generally showed improvement, except for succinimide + citric acid and citric acid/sorbitol, which displayed a reduced modulus of rupture. Chemical analyses are warranted to fully understand the reaction mechanisms of the treatments. Imidazole treatment's positive effects are suggested to stem from a thermal reaction between the chemical and wood, indicated by substantial mass loss during leaching and specimen darkening. Succinimide and citric acid might exhibit polymerisation with each other and wood components, akin to the citric acid/sorbitol process. Studies into the effectiveness of these treatments against fungi and termites showed that whilst fungal protection was reasonable to exceptional, results for termites were less effective, unless higher levels of imidazole were present.