Properties tailoring of biobased epoxy resins by regulating the degree of polymerization of oligomers

Epoxy oligomers are preferred in the industry, and biobased epoxy resins derived from renewable biomass particularly attract extra attention. Herein, a series of epoxy oligomers with different polymerization degrees, which originated from biomass magnolol, were synthesized by the tatty and fusion methods. As the degrees of polymerization increased, P-DBP-EP-n changed from a liquid with a viscosity of 11.7 Pa.s to a solid owing to its high molecular weight and poor chain mobility. Cured resins were prepared with a two-step curing process: an amine-epoxy reaction first, followed by an allyl polymerization. Due to the higher polymerization degree of PDBP-3 and P-DBP-5, the corresponding cured resins had glass transition temperatures of 334 C(P-DBP-EP-3/ DDM) and > 350 C (P-DBP-EP-5/DDM), indicating superior heat resistance in comparison with P-DP-EP-1/DDM (300 C). Additionally, the tensile strength and notched impact strength of P-DBP-EP-3/DDM (22.7 MPa, 2.9 kJ/ m(2)) and P-DBP-EP-5/DDM (25.2 MPa, 2.6 kJ/m(2)) were better than those of P-DBP-EP-1/DDM (20.7 MPa, 2.5 kJ/ m(2)). The initial degradation temperatures of the three P-DBP-EP-n/DDM samples exceeded 410 C, and the char yield maintained above 33% at 700 C. What's more, P-DBP-EP-n/DDM exhibited surprising intrinsic flame retardancy, with LOI values higher than 39% and V-0 rating for the UL 94 tests almost without any after-flame time. The synergy effect of nonflammable gases in the gaseous phase and tough protective char layer in the condensed phase simultaneously contributed to the intrinsic flame retardancy. This work offered a practical and promising method for synthesizing biobased epoxy oligomers with varying degrees of polymerization, obtaining cured resins with comprehensive properties including high heat resistance, excellent thermal stability, and intrinsic flame retardancy.

Automated summary

In this study, a series of biobased epoxy oligomers were synthesized using the tatty and fusion methods, and cured resins were prepared. The results showed that these biobased epoxy oligomers exhibited high heat resistance, excellent thermal stability, and intrinsic flame retardancy.