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Title: High performance of silicone rubber nanocomposites with improved physical properties
Author: Ismail, Nik I. Nik
ISNI:       0000 0004 7971 0581
Awarding Body: Loughborough University
Current Institution: Loughborough University
Date of Award: 2015
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Highly extent exfoliated and intercalated silicone rubber (SR) nanocomposites based on natural montmorillonite (Cloisite Na+) and organically modified montmorillonite (Cloisite 30B and Cloisite 20A) were successfully prepared by melt-mixing technique. As indicated by the X-ray diffraction (XRD) and transmission electron microscopy (TEM) analysis, intercalation and exfoliation of the clay particles in the nanocomposites was achieved at less than 8 parts per hundred (phr) rubber by weight, irrespective of the initial interlayer spacing of the nanoclay particles. Cloisite 30B was spontaneously transformed into exfoliated nanostructures during the vulcanisation stage as suggested by X-ray diffraction (XRD), fourier transforms infra-red spectroscopy (FTIR) and differential scanning calorimeter (DSC) results. Overall, the use of the nanoclays in silicone rubber improved the Young's modulus, tensile strength and elongation at break by more than 50% as compared to the neat SR. However, the Cloisite Na+yielded outstanding mechanical properties with low hysteresis at the same loading of the exfoliated Cloisite 30B and intercalated Cloisite 20A organoclays, even though the filler had a tendency to produce mixture intercalated/exfoliated nanostructures in the SR matrix. It was concluded that the tensile strength and Young's modulus in this particular rubber nanocomposite are dominated bythe degree of crosslink density instead of filler dispersion. In addition, incorporation of the nanoclays in SR altered the wear mechanism of silicone rubber where addition of the fillers minimised the weight loss during abrasion testing, particularly at low filler loading (< 6phr). Moreover, this study showed that the SR/C30B nanocomposite exhibited excellent heat resistance in comparison to the other two nanocomposites and neat SR as revealed by higher retention strength. The thermal stability of the rubber in air was strongly dependent on the clay morphology and increased in the following order: highly intercalated/exfoliated SR/Na+MMT < highly intercalated SR/C20A < highly exfoliated SR/C30B. Furthermore, the performance of SR Abstractiiinanocomposites containing precipitated silica (PS)/montmorillonite (MMT) hybrid fillers were investigated as a function of PS/MMT hybrid filler weight ratio. Interestingly, the stress-strain properties of the nanocomposites with the hybrid fillers showed a large improvement at high deformation in comparison with the properties of those nanocomposites containing the PS and MMT fillers. The resistance to ageing of SR/PS/MMT was improved by gradually adding amounts of PS filler into the PS/MMT hybrid filler system. Finally, the comparative study demonstrated that the SR containing precipitated silica (PS)/multiwall carbon nanotube (MWMT) hybrid filler significantly improved stiffness of the rubber but accompanied by a small improvement in the tensile strength and elongation at breakwith regard to the SR/PS/MMT. In spite of that, the inclusion of PS/MWNT gave adverse effects to the cure efficiency of the SR compounds which is a drawback from processing point of view.
Supervisor: Not available Sponsor: Malaysian Rubber Board
Qualification Name: Thesis (Ph.D.) Qualification Level: Doctoral
EThOS ID:  DOI: Not available
Keywords: Materials Engineering not elsewhere classified ; Silicone rubber ; Nanoclay ; Nanocomposites ; Hybrid filllers ; Mechanical properties ; Thermal properties