Self-healing natural rubber/silica composites based on ionic supramolecular network
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Date
2019-07
Authors
Pitiphong Srisuwan A/L Ia Lun
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Abstract
Introducing reversible ionic supramolecular network is an effective approach to impart self-healing for natural rubber. In this work, the silica was grafted with Poly(methyl methacrylate-co-methacrylic acid) (PMMA-co-MAA) to introduce carboxyl groups on the silica surface and the natural rubber was grafted with zinc thiolate to introduce Zn2+ ion rich domain on the rubber molecular chains. The amount of PMMA-co-MAA was varied at three different concentration (1%, 3% and 5%) relative to silica content to assess the optimum amount of grafting between PMMA-coMAA and silica. Evidence of grafting between PMMA-co-MAA and silica was identified by Fourier Transform Infrared (FTIR) and grafting percentage was determined by Thermogravimetric Analysis (TGA). The results revealed that 3% PMMA-co-MAA produced the highest grafting percentage. Subsequently, the grafting of zinc thiolate with rubber molecular chain was carried out in an internal mixer at 135 oC and 60 rpm. The rubber was mixed with PMMA-co-MAA modified silica and other additives on two-roll mill. The compounds were then compressed at 150 oC. The results revealed that the developed self-healing natural rubber/silica elastomeric composites able to regain 60% of their properties in 5 minutes and almost 90% in 10 minutes at room temperature without the aid of any external stimuli. Scanning electron microscope (SEM) images showed that the fractured areas was recovered with intermolecular diffusion on the crack surface. Furthermore, the effect of silica content on healing efficiency and mechanical poperties were measured using universal tensile tester. The results showed that higher silica content decreased healing efficiency while improved mechanical properties of self-healing natural rubber/silica elastomeric composites. This study provide a new method to fabricate self-healing natural rubber with improved mechanical properties that may have bigger potential applications.