Functionalization of halloysite nanotubes (HNTs) via mussel-inspired surface modification and silane grafting for HNTs/soy protein isolate nanocomposite film preparation

The use of a catechol derivative (dopamine) for surface modification of the internal/external halloysite nanotubes (HNTs) and facilitating epoxy-functionalized silane grafting on the HNTs surfaces via a poly(dopamine) (PDA) ad-layer were demonstrated in this study. Aqueous dopamine was bound to alumina/silica at the tube and self-polymerized to form a thin, surface-adherent PDA ad-layer in an alkaline environment. The silane agent (KH560) was then supplied to the PDA-coated HNTs (PDHNTs) surface to introduce epoxy groups. The versatile promotion of the PDA layer in the PDHNTs was confirmed by the X-ray photoelectron spectroscopy (XPS), Fourier transform infrared spectroscopy (FTIR), thermogravimetric analysis (TGA), and transmission electron microscopy (TEM). The surface modification of the PDA coating and silane grafting was successfully carried out. The natural components-based PDHNTs-O/soy protein isolate (SPI) nanocomposite film was obtained due to the penetration and entanglement of the SPI chains to the PDHNTs-O nanotubes and their lifting luminal and interfacial adhesions via covalent/physicochemical bonding. Compared to the unmodified SPI film, the tensile strength of the PDHNTs-O/SPI nanocomposite films increased from 5.90 MPa to 8.73 MPa, the Young's modulus improved by 54.5% and moisture absorption decreased by 47.1%. The functionalized surfaces also improved the dispersion and compatibility of the PDHNTs-O to the SPI matrix.