Characterization of Phytagel® modified soy protein isolate resin and unidirectional flax yarn reinforced "green" composites

The mechanical properties and moisture resistance of the soy protein isolate (SPI) resin and flax yarn reinforced composites were improved significantly by incorporation of a poly‐carboxylic acid based modifier, Phytagel®. SPI and Phytagel® were blended to form an interpenetrating network‐like cross‐linked complex. This complex showed significantly improved tensile and moisture properties as well as higher thermal stability as compared to the unmodified SPI resin. The incorporation of Phytagel® (40% w/w of SPI powder) in SPI resin and subsequent lowering of the amount of glycerol (from 30% to 12.5%) led to an overall 10‐fold increase in the tensile fracture stress and a nine‐fold increase in the Young's moduli of the SPI resin along with a seven‐fold decrease in fracture strain. The dynamic mechanical properties such as storage and loss modulus of the modified resin increased and the glass transition temperature also increased by about 56°C. The unidirectional flax yarn reinforced composites were made using two modified resins with 20% and 40% Phytagel® contents. Both resins contained 12.5% glycerol. The composites fabricated using resin containing 20% Phytagel® showed significantly higher tensile and flexural moduli as well as fracture stress in the axial direction than the composites with resin containing 40% Phytagel®, which was higher than the SPI resin based composites. POLYM. COMPOS., 26:647–659, 2005. © 2005 Society of Plastics Engineers