Abstract
Lignin is the abundant woody biomass next to (hemi)cellulose and is degraded to a specific dibasic acid, 2-pyrone-4,6-dicarboxylic acid: PDC, as a metabolic intermediate. In the present paper, the tensile adhesive strength of PDC-epoxy adhesives was studied. Relationships among curing temperature, species of curing agents, and tensile adhesive strengths of the PDC-epoxy adhesives were estimated. These values were compared to those of similar epoxy monomer of isophthalic acid, IPA, carrying a benzene ring instead of a 2-pyrone pseudo-aromatic ring of PDC as a reference. When succinic anhydride or 4-methylhexahydro-phthalic acid anhydride was used as curing agent, the PDC-epoxy adhesives exhibited larger tensile adhesive strength than IPA-epoxy adhesives at relatively low curing temperature of 130 °C. However, this situation is vice versa at elevated temperature. The tendency of the PDC-epoxy adhesive with pyromellitic anhydride was similar to the corresponding IPA-epoxy adhesive, the tensile adhesive strength became larger with increasing the curing temperature. By contrast, the PDC-epoxy adhesive with maleic anhydride exhibited the opposite tendency, i.e., the curing temperature increment caused smaller tensile adhesive strength. Against the plastics, the PDC-epoxy adhesives adhered polar materials, such as polycarbonate or polyamide. These characteristics might be derived from the polar nature of the 2-pyrone ring in PDC nucleus.
