The study of chemical modifications on the properties of soy protein isolate (SPI) / kapok husk (KH) biocomposite films for agriculture applications

Abstract

In this research, the utilization of kapok husk (KH) as a filler in soy protein isolate (SPI) was studied to replace the plastic and petroleum based polymer films for packaging. The effect of KH loading, crosslinking agents such as phthalic anhydride (PA), adipic acid (AA) and formaldehyde (FA), and chemical modification of KH with 2-ethylhexyl acrylate (EA), methyl methacrylate (MMA) and sodium dodecyl sulphate (SDS) on tensile properties, morphology, thermogravimetry analysis (TGA), moisture content, total soluble matter, gel fraction and enzymatic biodegradation properties of SPI/KH biocomposite films was studied. Glycerol was used as a plasticizer to give flexibility to the biocomposite films. The experimental results showed that the increases of KH loading have increased the tensile strength, modulus of elasticity, and gel fraction of control SPI/KH biocomposite films, whereas the elongation at break, char residue, moisture content, total soluble matter and weight loss of enzymatic biodegradation decreased. The morphology of tensile fracture surface of control SPI/KH biocomposite films at higher KH loading showed better interaction between KH filler and SPI matrix. The addition of different crosslinking agents such as PA, AA and FA had increased the tensile strength and modulus of elasticity of crosslinked biocomposite films. The gel fraction of all crosslinked biocomposites films higher than uncrosslinked biocomposite films. However, crosslinked biocomposites exhibited decrement in elongation at break except AA, char residue, moisture content, total soluble matter, and weight loss of enzymatic biodegradation than uncrosslinked biocomposite films. The SEM studies of crosslinked SPI/KH biocomposite films with PA, AA and FA indicated the rough surface, due to the enhanced crosslinking. The FTIR spectra of all crosslinked biocomposite films illustrated the changes in functional group. The treated KH with EA, MMA, and SDS biocomposite films have higher tensile strength and modulus of elasticity in comparison with untreated SPI/KH biocomposite films. Nevertheless the elongation at break, char residue from TGA, moisture content, total soluble matter and weight loss of enzymatic biodegradation reduced. All treated SPI/KH biocomposite films performed slight changes in gel fraction as KH loading increased. The treated KH with EA, MMA and SDS had enhanced the interfacial bonding between KH and SPI matrix in biocomposite films, which were proved by SEM analysis. It can be summarized that incorporation of KH in SPI film has the ability to improve the properties of SPI/KH biocomposite films. However in comparison, SPI/KH biocomposite films treated with EA could give the highest improvement in all characterization.