Strengthening soy protein hydrogels filled with protein-coated montmorillonite nanoclay by glutaraldehyde crosslinking

To strengthen interactions in bio-nanocomposite systems, montmorillonite (MMT) was intercalated by surface-coating with soy protein before being incorporated within soy protein dispersions for cross-linking by glutaraldehyde (GA). Dynamic small strain tests were utilized as a non-destructive method to reveal the improvement of network structure in the bio-nanocomposite system. The storage modulus (G′) and loss modulus (G″) gradually increased with increasing GA concentration during isothermal treatment at 23, 60 and 90 °C. The incorporation of intercalated MMT resulted in an order of magnitude increase in the moduli. The moduli were higher at pH 5.5 than those at pH 6.5 and 10.0. At a GA concentration equal to 10 g/100 g mass of soy protein, G′ and G″ in the absence of MMT increased with an increase in temperature, while those in the presence of intercalated MMT showed the opposite trend due to restructuring of aggregated MMT. The present results confirmed that the mechanical strength of bio-nanocomposite systems can be significantly improved by first intercalating MMT with protein and subsequently cross-linking with the continuous phase protein molecules. The established chemical cross-linking method and conditions can be beneficial for preparing bio-nanocomposite materials with enhanced mechanical properties.

► Soy protein hydrogels with intercalated MMT were much strengthened by glutaraldehyde cross-linking. ► Addition of 1 g/100 mL MMT increased storage modulus by 1-2 decades. ► Stronger gels formed at a higher glutaraldehyde level and at pH 5.5 than at pH 6.5 and 10.0. ► Samples without MMT formed stronger gels at a higher temperature, opposite to those with MMT. ► At a high temperature, restructuring of aggregated MMT caused the weakening of gel network.