Pusat Pengajian Kejuruteraan Bahan dan Sumber Mineral - Tesis

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Intrinsic self-healable and recyclable rubbers based on ionic crosslinked network
(2023-08-01)
Mohd Hafiz Bin Zainol
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.
Investigation of the resistive switching properties and mechanisms of polymannose based memory devices
(2023-05-01)
Ilias Ait Tayeb
Resistive random access memory technologies (ReRAM) are promising candidates for next-generation non-volatile memories owing to their simple device structure, low operational cost and power consumption and their compatibility with CMOS technologies. In addition, bio-organic materials are considered as prominent alternatives due to their biodegradability and benign environmental impacts. As such, the motivation behind this research is to determine the applicability of polymannose as a suitable bio-organic material for ReRAM applications utilizing a two-terminal structure. Polymannose thin-films were produced via drop casting a D-mannose powder and aqueous ethanol solution on ITO/PET substrate and dried at 160oC for different duration followed by Ag deposition as top electrode. Current–voltage (I–V) characterization was carried out and displays that resistive switching characteristics are achieved in the device when the precursor is dried between 4 - 7 h. The optimal drying time of 7 h provided optimal resistive switching characteristics, with a READ window of 2.2 V, high ON/OFF ratio of >105 at relatively low READ voltage of 0.01 V, acceptable endurance cycles of approximately 102, and a long retention time of >104 s. Further I-V analysis and HRTEM-EDS characterization reveal that high-resistance states (HRS) are governed by space charge limit current conduction resulting, while the low resistance states (LRS) are dominated by Ag metallic filaments. Furthermore, by modulating the compliance current, the polymannose successfully demonstrated twelve distinct and reliable LRS states at a READ voltage as low as -0.05 V. Moreover, the effect of fullerene (C60) on enhancing the performance of polymannose based ReRAMs has been studied. A memory device with Au-Pd/polymannose:C60/ITO/PET structure containing 5 vol% C60 has shown optimal ON/OFF ratio reaching ~105, a smaller read-memory window of 6.5 V and stable retention characteristics reaching 104 s. The electrical characteristics of the Au-Pd/polymannose:C60/ITO/PET shows a governing electronic conduction mechanism, and a model is proposed to explain the resistive switching mechanism for both device types. These results not only demonstrate the suitability of polymannose as a candidate bio-organic material for environmentally friendly high-density next generation non-volatile memories, but also show competitive performances that can potentially rival current materials used in ReRAM applications.
Thermoresponsive shape memory blend of polylactic acid/styrene-butadiene-styrene copolymer with fillers or crosslinker
(2023-08-01)
Fathin Hani Binti Azizul Rahim
Shape memory polymers from biodegradable polymer blends have captured interest among researchers. However, there are some issues especially, related with responsive rate and repeatability that need to be considered. To solve the issue, a study of thermoresponsive shape memory polymer blend was prepared from the melt-blending of polylactic acid/styrene-butadiene-styrene copolymer (PLA/SBS) and morphology, thermal, shape memory, tensile, rheological and viscoelastic properties were evaluated. With the variation in the compositions, two-phase morphologies were observed due to the immiscibility of the blend. 70PLA/30SBS blend which possesses intermediate storage and loss moduli indicated optimum shape fixity ratio (Rf) and recovery ratio (Rr) with good tensile properties due to the formation of SBS droplets in the continuous PLA phase. In the second stage, 5 wt.% of erbium oxide (Er2O3), halloysite nanotube (HNT) and tungsten carbide (WC) was added separately into the binary blends of 70PLA/30SBS. 70PLA/30SBS-HNT has the highest tensile strength due to the reinforcing feature of the HNT but caused the reduction in Rf with the increasing immersion time. 70PLA/30SBS-Er2O3 showed an improvement in Rf and Rr possibly due to the spherical structure of Er2O3 and low viscosity that facilitates the chain movement during the deformation and recovery phase. The introduction of WC in 70PLA/30SBS blend led to high crystallinity and the optimum recovery time for Rr of 5 min. Meanwhile, the crosslinked 70PLA/30SBS blend was prepared by introducing different dicumyl peroxide (DCP) contents (i.e. 0.5, 1.0, 1.5 and 2.0 wt.%). The gel content and swelling density were measured to investigate the crosslinking density in the crosslinked 70PLA/30SBS blends. The presence of DCP led to high gel content value indicated the crosslinking reaction happened in the 70PLA/30SBS blends. The SBS droplet phase elongated in PLA domain as more DCP was added. The shape memory behavior was examined in three cycles. The Rf of the uncrosslinked blend increased with shape memory cycles. However, for crosslinked 70PLA/30SBS blend exhibited a reduction of Rr with test cycles. For this part, 70PLA/30SBS/1.5DCP blend is considered as the best system with optimum tensile properties, highest Rf value and intermediate Rr value. To summarize, thermoresponsive shape memory PLA/SBS blend properties were influenced significantly by the various composition, the presence of different fillers and the amount of crosslinker.
Characterization and properties of sepiolite/organo-modified sepiolites filled natural rubber-styrene butadiene rubber and natural rubber-epoxidised natural rubber blends
(2023-12-01)
Diana Adnanda Nasution
This research work investigated the effect of sepiolite as nanofillers on curing, mechanical, thermal, and morphological properties of natural rubber-styrene butadiene rubber (NR/SBR) and natural rubber-epoxidized natural rubber (NR/ENR-25) blends. The effect of sepiolite loading on properties of sepiolitefilled NR/SBR and NR/ENR-25 was analysed and compared. Subsequently, a comparative investigation on water uptake on properties of NR/SBR and NR/ENR- 25 blends containing sepiolite was carried out to assess the efficiency of sepiolite as reinforcing filler in the blend. The effect of surface modification on sepiolite particles in a concentrated solution of cetyltrimethylammonium bromide (CTAB) to produce organo-modified sepiolite was carried out to investigate further enhancement of properties for NR/SBR blends. It was observed that sepiolite-filled NR-SBR blends at optimal loadings (3phr) has optimal mechanical properties even under prolonged water exposure. The nanosize sepiolites, containing hydrous silicates and metal groups, act as accelerators for vulcanization. While sepiolite serves as a reinforcement at low loadings, agglomeration effects become dominant at higher loadings, in which reducing filler-rubber interaction. Moreover, in thermal analysis, it was found that, sepiolite accelerates char formation, acting as a flame retardant during combustion. In NR/ENR25 blends, sepiolite functions as an accelerator for vulcanization, exhibiting similar as NR/SBR blends. It was also found that sepiolite reinforced NR-ENR25 blends and acted as thermal stabilizer with higher water uptake ability compared to NR/SBR blends. The findings emphasize the potential applications of sepiolites in optimizing rubber blend properties, offering insights into their roles as reinforcement, thermal stabilizer, and flame retardant in various industrial applications. Keywords: sepiolite fillers, CTAB-sepiolites, natural rubber blends, epoxidized natural rubber, styrene-butadiene rubber, water uptake, blending properties
Asymmetrical porous polycaprolactone/ silver nanoparticle-hydroxyapatite composite membrane for periodontal guided bone regeneration
(2023-08-01)
Bee Soo Ling
Guided bone regeneration (GBR) procedure using barrier membrane is the most common method used to treat periodontal defects in clinical practice. Nevertheless, the currently available GBR membranes are still suffer from few drawbacks, including their lack of crucial properties such as suitable surface morphology, antibacterial and bioactivity to aid periodontal regeneration. Therefore, this research aimed to fabricate a novel asymmetrical porous polycaprolactone/silver nanoparticle-hydroxyapatite barrier membrane that possess bioactivity and antibacterial properties to overcome the shortcoming of conventional GBR membrane. Briefly, hydroxyapatite (HAp) with optimum physio-chemical properties was successfully extracted from fish bone waste via calcination approach at 650 oC. Thereafter, pandan leaf extract was used to induce the in-situ synthesis of silver nanoparticle-hydroxyapatite (AgNPs-HAp) composite through a green bioreduction approach in silver nitrate solution. The influence of filler loading content and filler types on the surface morphological, mechanical, surface hydrophilicity, swelling, degradation, in vitro bioactivity, antibacterial, biocompatibility and cell barrier properties of the resulting membranes were evaluated. Scanning electron microscopy (SEM) showed that all composite membranes displayed an asymmetric “macro-micro porous” surface morphology regardless of their filler type and content added. Compared to pure PCL membrane, incorporation of HAp or AgNPs-HAp also significantly enhances the bioactivity of PCL membrane, in which the AgNPs-HAp filler have better impact for enhancing the bioactivity of membrane over HAp filler. After 56 days of degradation period, the tensile strength and Young’s modulus of all prepared composite membranes were maintained at range of 1.36−1.93 MPa and 10.4−14.9 MPa. Meanwhile, all PCL/AgNPs-HAp composite membranes showed antibacterial activity against E. coli, while only PCL/AgNPs-HAp composite membranes with AgNPs-HAp content > 5 pphr showed antibacterial property against S. aureus. The addition of AgNPs-HAp filler also improved the attachment of Saos-2 cells on the surface of membrane. Furthermore, all PCL/AgNPs-HAp composite membranes showed the ability to inhibit the penetration of fibroblast cells in a period of at least 28 days. Due to the suitable mechanical, biodegradability, bioactivity, antibacterial properties, biocompatibility and cell barrier property along with the unprecedented “macro-micro porous” membrane’s morphological structure that meet the requirement for GBR, the developed asymmetrical porous PCL/AgNPs-HAp composite membrane has the potential to be applied for periodontal GBR application.

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