Sustainable Thermosets and Composites Based on the Epoxides of Norbornylized Seed Oils and Biomass Fillers

Abstract

Thermosets and composites were fabricated from the epoxides of norbornane seed oils (linseed oil, soybean oil, high-oleic soybean oil, and non-modified seed oils). The epoxides were cured using a cationic initiator to mold thermosets. Thermosets were characterized for their curing behavior and T g by dynamic scanning calorimetry, crosslinking efficiency by Soxhlet extraction, and thermal stability by thermogravimetric analysis (TGA). Steric hindrance of the norbornylized seed oils had a perturbing effect on the extent of epoxidation. However, the higher ring strain energy of the norbornene moieties played a key role in epoxide curing, resulting in higher T g thermosets with higher crosslinking efficiency. To the epoxide system with the highest optimum balance of T g, crosslinking efficiency, and thermal stability, lignocellulosic sorghum-derived biomass fillers were added. The addition of biomass fillers increased the bio-based content and reduced the cost and weight of the composites. Further, torrefied and carbonized sorghum filler variants were used to study the effect of the extent of thermal treatment on curing and on the final thermoset properties. Fillers were characterized by TGA, IR, elemental analysis, and solid-state NMR. Glass fiber-reinforced composites were molded using the optimum formulation. The mechanical and thermal properties of the novel hybrid biocomposites were investigated using universal testing machine (UTM), impact tester, and TGA. Both the sorghum-filled thermosets and composites showed enhanced thermomechanical property as compared to the non-filled epoxy systems. Carbonized sorghum filler composites exhibited the highest mechanical properties and thermal stability. Elemental differences and biomass precursor differences such as the cellulose, hemicellulose, and lignin content were found to play a critical role toward the composite properties. The SEM images showed good interfacial adhesion between the polymer matrix, fillers, and fiber phase in the biomass-filled composites. Thus, the fabricated composites demonstrate the potential for being used as sustainable, greener, and lightweight composites.

Enabling Green Manufacture of Polymer Products via Vegetable Oil Epoxides

“…Another factor that merits consideration is how the purification and separation processes need to be applied to the vegetable oil epoxides as compared to the petroleum products which undergo huge downstream processing. At large, after the epoxidized vegetable oils are synthesized, they undergo a phase separation stage initially (mostly for biphasic reactions), vacuum filtration to remove any unreacted constituents or catalytic residue, followed by evaporation of solvent (rotary evaporation) and vacuum drying before use. ,, …”

“…At large, after the epoxidized vegetable oils are synthesized, they undergo a phase separation stage initially (mostly for biphasic reactions), vacuum filtration to remove any unreacted constituents or catalytic residue, followed by evaporation of solvent (rotary evaporation) and vacuum drying before use. 26,74,75 The oxirane ring, often known as the epoxy ring, is a highly reactive chemical moiety due to its ring strain and chemical structure. Multiple routes can be employed for the ring opening reaction of an oxirane ring.…”

“…16,93−95 Examples include epoxides of linseed oil, palm oil, and soybean oil. 13,26,96 Such vegetable oil based plasticizers were confined to laboratory scale, but lately, international tire companies like Goodyear have started to use it on a commercial scale, notably the soybean oil. Modified soybean oil, orange oil from orange peels, castor oil, and cashew derived resins, liquid guayule rubber, etc.…”

“…Further, vegetable oil epoxides are replacing the petroleum based carcinogenic oils in the rubber industries due to the latter’s toxicity and former’s environmental safe and biodegradable nature coupled with easy availability. ,− Examples include epoxides of linseed oil, palm oil, and soybean oil. ,, Such vegetable oil based plasticizers were confined to laboratory scale, but lately, international tire companies like Goodyear have started to use it on a commercial scale, notably the soybean oil. Modified soybean oil, orange oil from orange peels, castor oil, and cashew derived resins, liquid guayule rubber, etc.…”

“…Further, the degree of unsaturation (number of carbon–carbon double bonds per triglyceride of fatty acid present in oil) is a key parameter in the epoxidation conversion . Thus, a highly unsaturated oil like linseed oil would give an epoxide with more epoxy groups in the polymer backbone, whereas soybean oil with a lower unsaturation degree would make epoxides with lesser epoxy groups per polymer chain. , However, due to the versatile epoxidation level possible with vegetable oils, there is a primary significant epoxidation which holds among the functionalization of vegetable oil for several industrial product applications. It is therefore critical that as a scientific community, researchers across the globe are cognizant of its challenges, progress, and future opportunities.…”