Phenolation of lignins: Effect of structure on reactivity
The material utilization of lignin for high value products is one attempt to enhance the efficiency of lignocellulosic biorefineries. Lignin could function as a structural backbone in phenol formaldehyde resin prepolymers. However, the low number of reactive sites with respect to phenol-formaldehyde chemistry hinders effective condensation reactions. Organosolv, Kraft, soda and sulfite lignin were phenolated to increase their cross-linking ability. The products were characterized concerning their functional groups by 31P-NMR spectroscopy as well as sulfur and ash content. The results revealed that the degree of phenolation differs significantly due to structural features of the lignins. Additionally, the cross-linking ability of phenolated lignin was studied by synthesizing a lignin phenol formaldehyde resin and comparing its wood bonding properties with plain PF and LPF with unmodified lignin.