Preparation of Poly(acrylic acid-co-acrylamide)-Grafted Deproteinized Natural Rubber and Its Effect on the Properties of Natural Rubber/Silica Composites

This work aims to enhance the polarity of natural rubber by grafting copolymers onto deproteinized natural rubber (DPNR) to improve its compatibility with silica. Poly(acrylic acid-co-acrylamide)-grafted DPNR ((PAA-co-PAM)-DPNR) was successfully prepared by graft copolymerization with acrylic acid and acrylamide in the latex stage, as confirmed by FTIR. The optimum conditions to obtain the highest conversion, grafting efficiency, and grafting percentage were a reaction time of 360 min, a reaction temperature of 50 degrees C, and an initiator concentration of 1.0 phr. The monomer conversion, grafting efficiency, and grafting percentage were 91.9-94.1, 20.8-38.9, and 2.1-9.9%, respectively, depending on the monomer content. It was shown that the polarity of the natural rubber increased after grafting. The (PAA-co-PAM)-DPNR was then mixed with silica to prepare DPNR/silica composites. The presence of the (PAA-co-PAM)-DPNR and silica in the composites was found to improve the mechanical properties of the DPNR. The incorporation of 10 phr of silica into the (PAA-co-PAM)-DPNR with 10 phr monomer increased its tensile strength by 1.55 times when compared to 10 phr of silica loaded into the DPNR. The silica-filled (PAA-co-PAM)-DPNR provided s higher storage modulus, higher Tg, and a lower tan delta peak, indicating stronger modified DPNR/silica interactions and greater thermal stability when compared to silica-filled DPNR.

Automated summary

This study successfully achieved graft copolymerization of poly(acrylic acid-co-acrylamide) onto deproteinized natural rubber, which enhanced the polarity of natural rubber and improved its compatibility with silica. The mixture of (PAA-co-PAM)-DPNR and silica improved the mechanical properties of DPNR.