Synthesis and performance evaluation of nanocomposite soy protein isolate/carbon nanotube (SPI/CNTs) adhesive for wood applications

Abstract In this article, effect of the incorporation of carbon nanotubes (CNTs) into soy-based adhesive, obtained from soy protein isolate (SPI), on the performance of the nanocomposite adhesive is presented. Multifunctional and exceptional properties of carbon nanotubes (CNTs) in nanofiller in polymer matrix were explored in this study to develop nanocomposite soy-based adhesive with improved shear strength and water resistance. Consequently, nanocomposite SPI/CNT adhesives having different CNT loading were synthesized and evaluated. Morphology, thermal stability and chemical functionalities of the synthesized nanocomposite adhesives were checked using scanning electron microscopy (SEM), thermogravimetric analysis (TGA) and Fourier transform infrared (FTIR) spectroscopy, respectively. The bond strength test of the adhesives was carried out according to European standards, EN-204 and EN-205. The results showed that CNTs improved the shear strength of the nanocomposite SPI/CNT adhesive at reduced percentage loading. About 100% increase in the shear strength and water resistance was recorded for the nanocomposite SPI/CNTs adhesive when compared with an alkaline modified adhesive without carbon nanotubes. The shear strength of the nanocomposite adhesive increased from 3.48 MPa (adhesive without CNTs) to 6.91 MPa (adhesive with 0.3 wt% CNT loading) and then decreased afterwards as the CNT loading was increased beyond 0.3%. Enhanced shear strength of soy-based adhesives using different fillers has been reported in the literature, but at relatively high loading of the filler. In this study, relatively small amount of CNTs (0.3%) has shown a substantial enhancement in shear strength as compared to other fillers. It is expected that the newly developed adhesive could pave the way to solving the challenge of low shear bond strength and poor water resistance of soy-based adhesives for wood applications in the industry.