Furfural is an efficient lignin-crosslinking agent and the following research demonstrates how it can replace formaldehyde in wood glues.
Hot water extraction (HWE) of sugar maple dissolves ~15% of lignin in the extract which is subsequently subjected to acid hydrolysis. In this study, lignin will be separated from the extracts of HWE before and after acid hydrolysis and its potential to produce formaldehyde-free lignin-based adhesives will be evaluated.
Extracts are ultrafiltrated to remove low-molecular-weight compounds in permeate. The retentate (Insol fraction) contains a mixture of lignin and carbohydrates (mainly xylose-originated). Depending on the conditions of HWE, acid hydrolysis, and ultrafiltration, the Insol fraction varies in lignin-to-carbohydrate (L/C) ratio.
Acid hydrolysis and dehydration of xylose-based carbohydrates in the Insol fraction produce furfural, an efficient lignin-crosslinking agent. Furfural may be added to the Insol fraction in case of low xylose content (i.e. high L/C ratio). The resulting lignin-furfural product is analyzed for the condensation level and thermal properties by spectral methods (FTIR and NMR) and DSC to assess its potential as an adhesive.