There is a growing concern about carbon source after the depletion of fossil fuels in the world of polymeric materials, as the majority of the commercialized polymer products are related to petrochemical resources, such as polystyrene, polyvinyl chloride, polypropylene, and polyethylene terephthalate. Renewable resources, such as carbohydrate, lignin, cellulose and plant oils, gain attention for the production of polymeric materials, due to their short term of reproducibility from biomass. Plant oils, mainly constituting of triglycerides, are extracted primarily from the seeds of oilseed plants. Besides the basic consumption as food, other applications are developed from this bio-renewable resource, like lubricants, biofuels, plasticizers, and construction materials. These triglycerides are also candidates as the building block of polymeric materials considering their natural abundance and inherent functionality, like the unsaturated double bond and ester groups. Challenges still present, including their heterogeneous and non-uniform structures.
Various kinds of biomass have been applied to prepare polymeric materials, such as cellulose, hemicellulose, lignin, starch, chitin, rosin acid, lactic acid, and plant oils. Among them, plant oils are one of the most abundant raw materials, which can be obtained primarily from plant seeds. Due to the unsaturation of fatty acid chains, plant oils have been widely used in the preparation of thermoset polymeric materials. Cationic polymerization of conjugate low saturation plant oils or copolymerization with divinylbenzene leads to thermosetting polymers. However, the reactivity of the unsaturated fatty acid double bonds is not high enough to obtain strong thermosetting polymers.
Another important method is to transfer the double bonds of plant oils to epoxy groups. The epoxy group can be further modified to obtain high reactive multi-functional monomers, such as acrylate plant oils. These acrylate plant oils can be used in the design of thermoset polymers. Epoxy resins are unique among all thermosetting resins with excellent resistance to chemicals and good thermal properties, which are widely used in coatings, adhesives, and matrices for composite materials. Epoxidized soybean oils are commercially available and have been used as plasticizers in plastic industry. However, the preparation and application of epoxy resins from plant oils is still limited, due to the poor mechanical properties of the epoxy resins derived from plant oils. There are two main reasons: the reactivity of the plant oil epoxy groups is too low; the number of epoxy groups in an epoxidized plant oil is too low.