Carbonate pre-treatment of wood for transformative structural applications through densification

This study investigated carbonate pre-treatment of wood followed by densification for producing advanced wood structural materials. Poplar wood blocks of 100 mm long and 20 mm wide with thickness of 10 mm were treated with sodium carbonate with and without sulfide at different carbonate loadings at 150 ºC for 30 min. Carbonate effectively removed lignin and hemicelluloses which facilitated subsequent wood densification for improving wood mechanical properties. Comparing with wood pre-treatment using sodium hydroxide, carbonate pre-treatment improved wood yield but achieved similar level of wood mechanical strength. Considering sodium carbonate is the key ingredient of commercial pulping process liquors such as spent pulping liquor (black liquor) and green liquor (an aqueous solution of the dissolved inorganic smelt from the combustion of concentrated pulping spent liquor), the present study indicated that low cost, effective, and cleaner wood pre-treatment can be achieved using spent process liquors rather than fresh and expensive sodium hydroxide (white liquor). Laboratory black liquor was used to pretreat the same poplar wood blocks, the good wood mechanical properties of the treated wood after densification confirmed this hypothesis. The practical significance of the present study is the utilization the residue alkali in spent process liquors rather than fresh NaOH for wood pre-treatment to reduce environmental impact. Furthermore, the spent liquor after wood-pretreatment can be directly feed into commercial pulp mill chemical recovery system to reduce capital and operation cost.