Synthesis and Characterization of Bio-Based Phenol-Formaldehyde Resol Resins from Bark Autoclave Extractives

Abstract

Abstract With the growing concern for fossil fuel depletion and environmental carbon footprint, there is a strong interest in exploring the renewable biomass materials as substitutes for petroleum-based feedstock. In this study, bark autoclave extractives from the mountain pine beetle (Dendroctonus ponderosae Hopkins)–infested lodgepole pine (Pinus contorta Dougl.) were used for partially replacing petroleum-based phenol in the phenol-formaldehyde (PF) resol resin synthesis. The structural characteristics of the bark autoclave extractives were examined using liquid-state 13C nuclear magnetic resonance (NMR). The curing behavior and curing kinetics, bonding strength, and bond development of the resulting bio-based bark extractive–PF resol resins were investigated using differential scanning calorimetry (DSC), lap shear, and dynamic mechanical analysis (DMA) tests, respectively. Results showed that bark autoclave extractives were a complicated mixture containing tannin, degraded hemicellulose, and degraded lignin components. The bark extractive–PF resins exhibited a higher molecular weight, higher viscosity, shorter gel time, and faster curing rate than the laboratory-made PF resin without bark components. The bark extractive–PF resins had comparable bonding strength to a commercial PF resin even when the phenol replacement rate was as high as 50 percent by weight. Bark autoclave extractives obtained from the beetle-infested lodgepole pine are suitable as a partial replacement of petroleum-based phenol in making PF resol adhesives.