African tree bark exudate extracts as biohardeners of fully biosourced thermoset tannin adhesives for wood panels

A totally "bio" hardener derived from the exudate extract of the African trees Vachellia nilotica and Senegalia senegal was investigated. It hardened a maritime pine tannin resin without any obvious presence of an aldehyde thus obtaining a completely "bio" adhesive for wood panels. MALDI-ToF and CP MAS C-13 NMR analysis indicated that the hardeners cross-linking species was 2,5-dihydroxymethyl furan linked onto carbohydrate chains. The hydroxymethyl furan moieties reacted both after detachment from the carbohydrate chains but also with carbohydrate chains still attached. The carbohydrates too were then involved as part of the binder. The gel times were slower than what was obtainable with paraformaldehyde but sufficiently fast to possibly be of industrial significance.