Characterization of stearic acid modified soy protein isolate resin and ramie fiber reinforced ‘green’ composites

The effects of stearic acid on the physical, tensile, moisture, thermal and micro-structural properties of the soy protein isolate (SPI)-based resin have been investigated. Fully biodegradable, environment-friendly, unidirectional, ramie fiber reinforced ‘green’ composites were also successfully fabricated using SPI and stearic acid modified SPI (MSPI) resins and characterized for their tensile and flexural properties. The fiber/resin interfacial shear strength was characterized using microbond technique. The mechanical and thermal properties and moisture resistance of the MSPI resin were significantly better than the SPI resin. It was observed that part of the stearic acid crystallized in SPI resin and that the crystallizability was affected by the glycerol added as a plasticizer. The replacement of glycerol with stearic acid did not affect the fiber/resin interfacial interaction. The ramie/MSPI composites showed significantly better mechanical properties compared to ramie/SPI composites. While the Young’s modulus of ramie/MSPI composites was closer to the theoretically calculated values, both composites had lower values than predicted. The ramie fiber/MSPI resin composites may be used as ‘green’ composites for certain indoor applications.