Effect of naturally occurring proteins on graft copolymerization of vinyltriethoxysilane on natural rubber

• Published in: Polymer journal 2022-05, Vol.54 (5), p.633-641
• Main Authors: Thi Nghiem, Thuong, Nguyen, Thang Ngoc, Yusof, Nurul Hayati, Kawahara, Seiichi
• Format: Article
• Language: English
• Subjects: 140/131; 639/301; 639/638; Ammonia; Biomaterials; Bioorganic Chemistry; Butyl hydroperoxide; Chemical bonds; Chemistry; Chemistry and Materials Science; Chemistry/Food Science; Condensates; Copolymerization; Fourier transforms; Graft copolymers; Hydrogen bonds; Hydrolysis; Infrared spectroscopy; Initiators; Latex; Natural rubber; NMR spectroscopy; Original Article; Polymer Sciences; Proteins; Rubber; Silicon dioxide; Spectrum analysis; Surfaces and Interfaces; Tensile strength; Thin Films; Transmission electron microscopy; Water chemistry
• ISSN: 0032-3896; 1349-0540
• DOI: 10.1038/s41428-022-00616-0

This work presents insights into how naturally occurring proteins affect the graft copolymerization of vinyltriethoxysilane (VTES) on natural rubber (NR) latex. Four NR latexes with different protein contents were subjected to graft copolymerization catalyzed by tert -butyl hydroperoxide (TBHP)/tetraethylene pentamine (TEPA) initiators. The four NR latexes were freshly tapped natural rubber (fresh NR), high-ammonia natural rubber, deproteinized natural rubber (DPNR), and protein-free natural rubber (PFNR). During the graft copolymerization on the studied latexes, VTES conversion depended on the protein content of the NR latexes. The formation and morphology of silica were investigated by Fourier transform infrared spectroscopy, solid-state NMR spectroscopy, and transmission electron microscopy. Among the products, fresh NR- graft -poly(VTES) exhibited the highest tensile strength and highest protein content. Proteins were confirmed to function as catalysts for the hydrolysis and condensation of VTES when graft copolymerization was performed on fresh NR (ammonia-free), fresh NR containing ammonia, and DPNR without TBHP/TEPA initiators. Our work studied the effect of proteins on the graft copolymerization of vinyltriethoxysilane (VTES) on natural rubber (NR) latex. Stress at break of the graft copolymers was substantially higher when proteins were present; that is, the stress at break of fresh NR- graft -PVTES was higher than that of protein-free NR- graft -PVTES. Silica nanomatrix was formed more visibly in the presence of proteins, as observed by transmission electron microscopy. Furthermore, proteins were found to accelerate the formation of silica particles by forming hydrogen bonds with VTES molecules and enhancing hydrolysis with water molecules.