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 °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 δ peak, indicating stronger modified DPNR/silica interactions and greater thermal stability when compared to silica-filled DPNR.

This work aims to enhance the mechanical properties, oil resistance, and thermal properties of acrylonitrile butadiene rubber (NBR) by using the Nile tilapia fish scales as a filler and using bis(triethoxysilylpropyl)tetrasulfide (TESPT) as a coupling agent (CA). The prepared fish scale particles (FSp) are B-type hydroxyapatite and the particle shape is rod-like. The filled NBR with FSp at 10 phr increased tensile strength up to 180% (4.56 ± 0.48 MPa), reduced oil absorption up to 155%, and increased the decomposition temperature up to 4 °C, relative to the unfilled NBR. The addition of CA into filled NBR with FSp at 10 phr increased tensile strength up to 123% (5.62 ± 0.42 MPa) and percentage of elongation at break up to 122% relative to the filled NBR with FSp at 10 phr. This work demonstrated that the prepared FSp from the Nile tilapia fish scales can be used as a reinforcement filler to enhance the NBR properties for use in many high-performance applications.

Natural rubber (NR) is a renewable resource that is used in many products. In the production of NR products, other rubbers or fillers may be used to produce a product with required properties. However, most rubbers and fillers are synthetic which are non-environmentally friendly materials. To solve this problem, rice husk ash (RHA) from biomass power plant was used to prepare silica to be used as a filler in rubber by in-situ generation. The purer RHA was prepared by leaching with HCl to remove some metallics and increase silica contents by combustion. The purer RHA was dissolved in NaOH to obtain sodium silicate from RHA (RSS). Carboxylated styrene-butadiene rubber (XSBR) used as synthetic rubber was blended with NR in latex form. NR/XSBR at the ratio of 2:1 was mixed with RSS to obtain NR/XSBR/RSS mixture. Acetic acid was dropped into the mixture until neutral for precipitating silica to obtain NR/XSBR/RSi composite. The mechanical, morphological, and thermal properties of NR/XSBR/RSi composites at different contents of silica (5, 10, and 15 phr) were studied. The NR/XSBR/RSi composite with optimum content was compared with NR/XSBR/CSi composite which prepared silica from commercial sodium silicate (CSS) on mechanical, morphological, and thermal properties.