Pusat Pengajian Kejuruteraan Bahan dan Sumber Mineral - Tesis

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Browsing Pusat Pengajian Kejuruteraan Bahan dan Sumber Mineral - Tesis by Author "Abdul Rehman"

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    Investigation of halloysite nanotubes reinforcement in self-healing natural rubber composites.
    (2025-03)
    Abdul Rehman
    Formulating rubbers with both self-healing abilities and excellent mechanical performance poses a significant challenge, as optimizing one property often comes at the expense of the other. The self-healing performance of rubbers relies on a flexible and dynamically reversible cross-linked network. In contrast, mechanical strength is influenced by the rigidity and stability of this network, creating a delicate balance. This research aimed to investigate the reinforcement effect of halloysite nanotubes (HNTs) on the self-healing performance of natural rubber (NR) composites based on metal thiolate ionic networks. The initial work involved characterization of raw halloysite particles which emphasis on particle size, shape, structure and chemical composition, and characterization of self-healing behavior of unfilled natural rubber. The unfilled self-healing NR showed excellent self-healing performance (98.5%) however, the tensile strength was low at ∼1.2 MPa. The halloysite nanotubes reinforced self-healing NR composites were prepared using conventional rubber processing. Materials were compounded using internal mixer and two-roll mill and subsequently vulcanized by compression moulding. The self-healing rubber composites were thoroughly examined and characterized by Fourier transform infrared spectroscopy (FTIR), scanning electron microscope (SEM), universal testing machine (UTM), dynamic mechanical analysis (DMA), Anton Paar rheometer, and compression set testing. The results revealed that, addition of 8 phr HNTs in the self-healing NR was found to be an optimum reinforcement to the better tensile performance of 4.12 MPa with 89.8% healing efficiency. Furthermore, the surface modification of halloysite nanotubes with acrylic acid (AA) was carried out to improve the compatibility between halloysite and natural rubber, since the major disadvantage of halloysite is poor compatibility with the non-polar rubber. The strategy was to reduce the surface hydroxyl groups on the HNTs and enhanced the interfacial adhesion between filler and rubber. Additionally, AA treatment on HNTs generates massive Zn2+ salt bonding between zinc thiolate grafted NR and carboxylic (COOH) groups of treated HNTs which enable electrostatic interaction and allows additional reversible ionic networks. It was found that the self healing rubber composites filled with 6% (AA) treated HNTs increased tensile strength to 5.56 MPa (increased by 34.9%) with 98.9% healing efficiency (increased by 10.1%) compared to untreated HNTs filled self-healing NR composites. Finally, the thermal stability and flame retardancy of self-healing rubber composites were investigated using thermal constants analyzer, thermogravimetric analysis (TGA), differential scanning calorimetry (DSC), flammability test, and limiting oxygen index (LOI) measurements. Altogether, the results revealed that the addition of HNTs into self healing NR nanocomposites enhanced 17.5% of their thermal conductivity, 19% of thermal stability, 27.7% of LOI, and 29% reduction in burn rate compared to the unfilled self-healing NR. A two-phase Lewis–Nielsen model was also utilized to simulate efficiency of the thermal conductivity of self-healing natural rubber containing halloysite nanotubes. The utilization of halloysite nanotubes as a reinforcement in self-healing natural rubber is promising for rubber products that experience high temperature environments especially for seals and gaskets.