Co-authors​ :

 William DYER (NETHERLANDS), Baris KUMRU , Clemens DRANSFELD (NETHERLANDS) 

Epoxy based FRPCs have found use throughout engineering fields including aerospace, automotive and wind energy. Research into more sustainably sourced polymeric matrix materials will safe-guard composite industries and lead to the development of next-generation high-performance matrices. Ongoing research into the scalability of bio-based platform chemicals suggest some monomers could be commercially viable in the future. Biobased chemistries, obtained from sources including algae and lignin, have unique structures and reactivity that are otherwise difficult to obtain from classic petro-based feedstocks. These unique chemical structures could offer advanced material properties including ultra-high crosslink density and inherent toughness. In the following research three biobased epoxy monomers (vanillin diglycidyl ether (VDE), phloroglucinol triglycidyl ether (PHTE) and resveratrol triglycidyl ether (RTE)) are investigated for use as composite matrix materials. Comparison is made against three petroleum-derived commercial epoxies - the classic BADGE monomer, Tactix 742 (a high-performance triglycidyl ether used in aerospace structural composites), and trimethylolpropane triglycidyl ether (TPTE) as a baseline. DDS hardener is used to obtain high-performance resins. Furthermore, structure-property relationships are sought to be established using advanced characterisation techniques linking resin mechanical performance, free volume characteristics and network relaxation mechanisms with chemical structure. Engineered resins are characterised using non-destructive PALS, BDS, and DMA techniques. Tensile, Three-point bending and SENB destructive testing are performed to give a comprehensive understanding of material properties. Following this, processing behaviour of resins is characterised using rheological and thermal characterisation techniques, allowing for high-quality composite manufacturing. ILSS and impact tests are performed on carbon fibre composite materials to demonstrate the feasibility of FRPC production using biobased resins.
Initial DMA results from stoichiometrically-optimised resin formulations suggest that PHTE and RTE display slightly higher stiffness from 25-250°C than Tactix 742, the mechanism of which may be revealed through PALS and BDS characterisation. The biobased monomers also show a higher oligomeric content than Tactix 742 (n≈1.05) and BADGE (n≈1.03), with n≈1.14 for PHTE and n≈1.09 for RTE. The reason for this is due to the lab-scale production of biobased epoxy monomers compared to the more well-controlled industrial processing of BADGE and Tactix 742 synthesis. Higher oligomeric content leads to lower crosslink density, lower stiffness, lower strength, and higher toughness. Resin mechanical and processing comparisons will give a foundational understanding to the composite scientist of the applicability of biobased monomers in structural applications.