Major Project (1st Draft)

Preparation of silica-supported 2-mercaptobenzimidazole and its antioxidative behavior in styrene-butadiene rubber

Zhong et al. (2014) conducted a study to prepare silica-supported 2-mercaptobenzimidazole (SiO₂-s-MB) as a novel antioxidant in rubber and to investigate its properties and application in styrene-butadiene rubber (SBR). SiO₂-s-MB was synthesized by the reaction of 2-mercaptobenzimidazole (MB) with chlorosilane-modified silica (m-SiO₂). SiO₂-s-MB was then analyzed by Raman spectroscopy, Fourier transform infrared (FTIR) spectroscopy, X-ray photoelectron spectroscopy (XPS), and thermogravimetric analysis (TGA) to confirm the supporting of antioxidant MB onto the surface of silica particles. SiO₂-s-MB particles were filled in SBR and were vulcanized to obtain SBR composites. Confirmation of dispersion of SiO₂-s-MB in SBR matrix was performed by Scanning electron microscope (SEM) and compared to the results of SiO₂ in SBR matrix. The oxidative efficiency of SiO₂-s-MB during short-term oxidation was determined using oxidative reduction time (OIT) method. The change of mechanical properties before and after aging was used to evaluate the thermal oxidative stability of SBR composites. The results showed that MB has been successfully bonded onto the silica surface through chemical linkages between chlorosilane on the m-SiO₂ and MB. For SBR composites, the SiO₂-s-MB particles were homogeneous dispersed in SBR matrix and no agglomeration of SiO₂-s-MB particles was observed. The oxidative efficiency of SBR/SiO₂-s-MB was much higher than that of SBR/m-SiO₂/MB due to harder migratory and volatile of MB from rubber matrix. Additionally, mechanical properties retention of SBR/SiO₂-s-MB was significantly improved comparing to low molecular MB. The researcher suggested that SiO₂-s-MB might be used as a rubber antioxidant with high performance and environmentally friendly characteristic due to its lower migration and volatility, and homogeneous dispersion in rubber matrix.

            This study provides a novel antioxidant in rubber with high performance and environmentally friendly. However, there are some limitation.

1)               The researcher did not study the oxidative efficiency and mechanical property retention of pure SBR as reference. The researcher might miss some effect related to pure rubber. Normally, many research study in polymer nanocomposite field have to compare their results with pure polymer as reference. Kongsinlark et al. (2012) study the effect of heat aging on mechanical property retention of natural rubber (NR) composites filled with polyisoprene (PIP)-SiO₂ in comparison with pure NR.  It was found that PIP-SiO₂ could enhanced the improvement of the interaction between SiO₂ and NR resulting in an increase in mechanical property retention comparing with pure NR.

2)         This study did not investigate the thermal properties, such as glass transition temperature (T_g) and decomposition temperature (T_id and T_max), of composite materials which is important data to select the appropriate materials using in various application. All polymer composites should be analyzed because adding of filler or antioxidant in the polymer matrix significantly affect the thermal properties and stability of materials (Grassie & Scott, 1988).

3)         This study used only SEM to confirm the homogeneous dispersion of SiO₂-s-MB in SBR matrix. The researcher might have bias when selecting part of sample to analyze because some part of composite may obtained the agglomeration of SiO₂-s-MB. One of common method to observe the distribution of filler in polymer matrix is dynamic light scattering (DLS) technique. Using a combination of SEM and DLS is more effective for investigation of SiO₂-s-MB distribution in SBR matrix than using one of these method alone (Kongsinlark et al., 2012).

            The strength of this study is that the confirmation of supporting of MB onto silica surface used 4 techniques to analyze. These method are widely acceptable for research in the polymer nanocomposite field and are efficiency technique to specify functional groups and composition of material. Furthermore, this novel rubber antioxidant have possible potential for future applications, which could suppress the migration and volatility being major problem for low molecular weight antioxidant resulting in high performance and environmentally friendly.

References

Grassie, N., & Scott, G. (1988). Polymer degradation and stabilisation: CUP Archive.

Kongsinlark, A., Rempel, G. L., & Prasassarakich, P. (2012). Synthesis of monodispersed polyisoprene–silica nanoparticles via differential microemulsion polymerization and mechanical properties of polyisoprene nanocomposite. Chemical Engineering Journal, 193–194, 215-226.

Zhong, B., Shi, Q., Jia, Z., Luo, Y., Chen, Y., & Jia, D. (2014). Preparation of silica-supported 2-mercaptobenzimidazole and its antioxidative behavior in styrene-butadiene rubber. Polymer Degradation and Stability, 110, 260-267.