Biobased novolac resins cured with DGEBA using water-insoluble fraction of pyrolysis bio-oil: Synthesis and characterization

The bio-oil obtained from combining two separation methods (fractional condensation and water extraction) of intermediate pyrolysis beech wood was used to synthesize bio-oil phenol acetaldehyde (BOPA) resins to replace petroleum-based phenol precursor. Simultaneously, two different concentrations of hydrochloric acid catalyst (1% and 10%) were applied to better understand the reaction between bio-oil and aldehyde. Bisphenol A diglycidyl ether (DGEBA) was used as a formaldehyde-free cross-linker for bio-oil based novolac resins. The kinetic parameters of the curing reaction were determined with model-free methods using data obtained from differential scanning calorimetry. The physicochemical and thermal properties of uncured and cured BOPA resins as a function of bio-oil ratio and catalyst concentration were analyzed and compared. As the proportion of bio-oil increases in resins, the properties deviate more and more from phenol acetaldehyde resin (PA) resin. The high catalyst content reduced these differences and produced excellent bio-based resins with less free phenols and aldehydes, higher molecular weight, and lower activation energy (Ea) of curing. An optimal proportion of bio-oil (50% bio-oil) in BOPA resin promoted the curing reactions and provide the lowest Ea.