Publication: Intrinsic self-healable and recyclable rubbers based on ionic crosslinked network
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Date
2023-08-01
Authors
Mohd Hafiz Bin Zainol
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Abstract
In modern technologies, rubbers play a significant role to serve various main manufacturing industrial products, for instance vehicles tires, damping systems, wearable electronics, safety gears and many more. In order to fabricate a component which offers high toughness, great damping properties, chemical and thermal stability, rubbers need to be chemically crosslinked through vulcanization process. However, vulcanized rubber with permanent covalent crosslinked network cannot be reprocessed, reshaped or recycled. As a result, waste rubber products have become a serious threat towards ecological and environmental systems. This problem has driven towards emerging of a self-healing rubber technology which has the ability to restore the damage and can be recycled and reprocessed at the same time. The work carried out started with investigation of the potential of self-healing non polar natural rubber (NR) based on zinc thiolate ionic network. The Zn2+ is a potential metal ion candidate for formation of reversible ionic network, thus self-healing ability, recyclability and reprocessing ability would be achievable. In the next work stage, carboxylated nitrile butadiene rubber (XNBR) was chosen to investigate self-healing ability for polar rubber. The strategy is to generate massive Zn2+ salt bonding between zinc thiolate and COOH group on XNBR in order to create electrostatic interaction that allow thermo reversible ionic network. For NR, the samples achieved 100% self-recovery within 10 minutes at room temperature. Evidence for reversible metal thiolate ionic networks was provided by Fourier Transform Infra-Red (FTIR) and swelling density. Followed by mechanical performance assessment which include tensile test, tear strength, fatigue lifespan and creep behaviour. As for the recycled and reprocessed assessment, the vulcanised rubber was recycled and reprocessed for few times and the tensile test, scanning electron microscope (SEM) and welding test were evaluated. Interestingly the rubber was able to be reprocessed for three times and recovered its initial mechanical performance up to 60%. For XNBR, the sample achieved 97.87% self-recovery within 10 minutes at 150ºC. Evidence for thermo reversible ionic network was provided by FTIR and swelling density assessment. Followed by mechanical performance assessment which include tensile test, tear strength, fatigue lifespan and creep behaviour. As for recycle and reprocessing assessment, the results showed that XNBR were able to be reprocessed for three times with significant mechanical performance recovery up to 70%. From the work carried in this research, it was found that NR self-healing rubber enables more potential for final application as the healing occur at room temperature. For potential application stage, NR self-healing rubber was chosen as candidate material for puncture proof application. The self-healing natural rubber was able to recover the puncture spot ranging from 0.8 mm to 2 mm nail diameter at 100% recovery rate throughout pressure test, temperature test, repeatability test and stability test. Evidence for healed punctured spot was provided by SEM. Both self-healing NR and XNBR had exhibit significant performance on self-healing capabilities and mechanical properties. While on puncture-proof application, self-healing NR had shown a promising performance throughout all the test that has been conducted in this research.