Humination Modification: A Green Approach to Improve the Material Properties of Scots Pine (Pinus sylvestris L.) Sapwood

Recently, wood modification with environmentally friendly modification agents has received special attention. To this end, this study was conducted to use humin fractions, in combination with citric acid (CA) and succinic acid (SA), as reaction catalysts for the modification of Scots pine (Pinus sylvestris L.) sapwood. The effects of humination modification were evaluated by means of dimensional stability, static and dynamic mechanical properties, thermal stability, crystalline structure, and biological durability tests on modified samples and compared with the unmodified reference ones. According to the results, the dimensional stability of the huminated samples significantly increased, and this increase with the presence of catalysts was higher than the sole humin-modified samples. The static mechanical properties were considerably improved by 17-24% in the modulus of rupture (MOR) and by 11-12% in the modulus of elasticity (MOE). An apparent increase in the storage modulus of huminated wood was also determined by dynamic mechanical analysis (DMA). Although the thermal degradation of the samples was slightly shifted to lower temperatures after humination, the modification effect was more pronounced on the residual mass retention compared to the unmodified samples. The biological durability against white and brown rot fungi was also significantly improved by the humination modification. Overall, the humination modification showed huge potential as a green approach to enhance the wood properties for outdoor applications.