Investigation on curing kinetics, water diffusion kinetics and thermo- mechanical properties of functionalized castor oil based epoxy copolymers

In pursuit to develop sustainable, eco-friendly and high-performance toughened epoxy materials, a green reactive monomer, epoxy methyl ricinoleate (EMR) was synthesized through transesterification of epoxidized castor oil (ECO). Both ECO and EMR were used as co-monomers with petro based epoxy resin at 10, 20, and 30% and cured with triethylenetetramine (TETA) to achieve toughened samples with moderate stiffness. Compared to neat epoxy, tensile strength of EPECO20 and EPEMR20 co-polymeric systems increased by 21.6% and 30% along with enhancement in impact strength to the tune of 24.4% and 39.4% respectively. Non-isothermal kinetic methods, Iso-conversional method and autocatalytic model were used to find curing kinetic parameters of the optimized EPECO and EPEMR copolymer system. The effects of ECO and EMR on curing kinetics and thermo-physical properties of TETA cured epoxy has been studied in order to control the curing reaction and achieve adequate properties for structural applications, which are not explored so far. The inclusion of ECO as copolymer resulted in the increase of activation energy (E a ) of curing by 10.9%, wherein EMR incorporation reduced the E a value by 5% because of its low viscosity, better resin diffusion and reactivity. The water diffusion coefficient is increased with increase in bio-resin content and water absorption through these samples is found to be a reversible process. The dynamic mechanical analysis (DMA) showed a reduction in glass transition temperature ( T g ) with the improved damping ability of copolymers due to segmental mobility of the flexible aliphatic chains of bio-resins. TGA study revealed the reduction in decomposition rate on addition of bio-monomers without much change in derivative peak temperature. These greener materials can find space in structural composites applications, being eco-friendly and sustainable.