Synthesis of a bio-based polyamidoamine-epichlorohydrin resin and its application for soy-based adhesives

In view of sustainable development and environmental protection, renewable itaconic acid was used to synthesize a bio-based curing agent for soy-based adhesives. The bio-based curing agent, i.e., itaconic acid-based polyamidoamine-epichlorohydrin resin (IA-PAE), was characterized by RSV and 1H-NMR. Results showed that IA-PADA and IA-PAE had much lower molecular weights than commercial PAE (C-PAE). Both N-(3-chloro-2-hydroxypropyl) groups and azetidinium rings of IA-PAE could perform as functional groups in IA-PAE modified soy flour adhesive (IA-PAE-SF). The pH values affected the viscosities of IA-PAE-SF adhesives significantly but had little effect on the wet strengths. Wet strength of IA-PAE-SF on plywood (0.95 MPa) was comparable to that of C-PAE-SF and met the requirements of Chinese National Standards for type-II applications. Cross-linking networks were formed during hot-pressing process and thus, improved water resistance of IA-PAE-SF on plywood. Measurement of water-insoluble solid content of cured adhesives and observation of SEM confirmed the formation of cross-linking networks in cured IA-PAE-SF.