Synthesis of phenolic resin using furfural as a sustainable partial alternative to formaldehyde and its impact on wood dimensional stability

The application of wood as a material is often hindered by its dimension changes due to wood-water interactions and its biological and physical degradation. These effects can be reduced by wood modification with impregnation resins, such as phenol-formaldehyde resins. However, formaldehyde is highly toxic and obtained from non-renewable resources. In this study, furfural was used as a partial substitute for formaldehyde in resin synthesis and applied in wood impregnation modification. The properties of the synthesized resins with furfural substitution ratio from 0 to 100% were investigated. The chemical structure of the synthesized resins was analyzed using Fourier transform infrared spectroscopy and electrospray ionization-mass spectrometry, and solid content, pH value and curing behavior (studied by differential scanning calorimetry) were compared. Further, Scots pine (Pinus sylvestris) sapwood was modified with the synthesized resins via vacuum pressure impregnation followed by high temperature curing. The weight percent gain, cell wall bulking coefficient, leaching ratio and anti-swelling efficiency of the modified woods were determined. The results indicated that substituting up to 25% of formaldehyde with furfural reduces formaldehyde usage while maintaining an ASE of up to 47%, which is comparable to that of conventional PF-modified wood (53%). The use of furfural as a renewable alternative to formaldehyde in phenolic resin synthesis meets the needs of sustainable development, indicating that partially substituting formaldehyde with furfural may be a viable strategy for developing more sustainable phenolic resins for wood modification applications.