Aligned ramie fiber reinforced arylated soy protein composites with improved properties

To enhance the strength, ramie fibers aligned in vertical (V), horizontal (H) as well as both vertical and horizontal (X) directions were used to reinforce soy protein materials (SC), coded as VSC, HSC and XSC. The soy protein isolate was arylated with 2,2-diphenyl-2-hydroxyethanoic acid through the process of “dip-coating”, coded as SC-B. The SC and SC-B composite films were characterized by Fourier transform infrared spectra, scanning electron microscopy, thermogravimetric analysis, dynamic mechanical thermal analysis, and tensile testing. Substantial improvement in the water uptake (from 100% to 25%) and the increased modulus (from 125 to 942 MPa) of the VSC-B composite were observed. This could be attributed to the formation of phase separation induced hydrophobic microparticles of DPHM on the surface of the SC-B films upon arylation, leading to the hydrophobicity. The thermal stability of the arylated composites increased compared to non-arylated ones. The VSC-B materials exhibited the highest water resistance and mechanical properties compared to HSC-B and XSC-B. Therefore, the arylation of SPI and alignment of the ramie fibers in the composites played an important role in the improvement of mechanical properties. This work provided a novel idea to improve the water resistance and modulus by reinforcing the protein matrix with natural fibers.