Synthesis and characterization of phenol-furfural resins using lignin modified by a low transition temperature mixture

摘要

A new modification method based on an oxalic acid/choline low transition temperature mixture was used to activate the chemical groups of lignin as a substitute for phenol in phenol-furfural resins. The optimum modification conditions were 100 degrees C and 6 h at a molar ratio of oxalic acid to choline chloride of 1:2. The content of phenolic -OH in the modified lignin increased from 1.75 to 3.01 mmol g(-1) and the content of -OCH3 decreased from 10.86 to 8.57 wt%, increasing the reactivity of lignin. The modified lignin was partially substituted for phenol at various substitution rates in the synthesis of phenol-furfural (PFU) resins. When the substitution rate of lignin to phenol was 50%, the lignin-PFU had a high bond strength (up to 1.84 MPa) and a low free phenol content and the lignin-PFU showed a higher curing rate and thermostability than PFU alone. The oxalic acid/choline chloride low transition temperature mixture was shown to be an efficient and green lignin modification method for the synthesis of PFU.