Structure modification of montmorillonite nanoclay by surface coating with soy protein

To achieve exfoliated and/or intercalated structures, montmorillonite (MMT) was surface-coated by soy protein at 60 °C, at MMT/soy protein powder mass ratios of 49:1, 9:1, 4:1, and 2:1 and pH 2.0-10.0. The protein-coated MMT was triple-washed and lyophilized for characterization. Protein coating was observed at all pH conditions, based on data from X-ray diffraction, Fourier transform infrared spectroscopy, zeta potential, and quantification of protein remaining in the continuous phase and present in the triple-washed MMT. At a mass ratio of 4:1, >90% protein bound with MMT, with the largest d-spacing at pH 9.0. When the mass ratio was increased to 2:1, protein-coated MMT at pH 9.0 demonstrated the highest degree of intercalation/exfoliation, corresponding to disappearance of the diffraction peak characteristic of pristine MMT. This study thus demonstrated that intercalation/exfoliation of MMT can be easily achieved by coating with low-cost soy protein for manufacturing nanocomposite materials.