Green, Christopher Duncan (2008) Polyethylene-montmorillonite nanocomposites. University of Southampton, School of Electronics and Computer Science, Doctoral Thesis , 186pp.
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Nanocomposite materials are currently attracting much interest due to their possibility of global property improvement – mechanical strength, toughness, electrical breakdown strength, electrical erosion resistance and flame retardancy. In order to disperse montmorillonite clay (MMT) into polyethylene
(PE), the clay sheets need to be rendered organophilic. Masterbatches with a high level (~40 %wt) of organomodified clay can then be dispersed into a host by a simple mechanical process. Two chemically different masterbatches were
purchased: Nanoblend 2101 from PolyOne Corp. and C30PE from Nanocor Inc. These were let down using a RandcastleTM single screw extruder with a patented mixing device to provide elongational flow. Wide angle X-ray diffraction was used together with transmission electron microscopy to evaluate the particle dispersion, which consisted of intercalated clay organised in clusters up to one micron in diameter.
The performance of these materials was assessed in terms of AC ramp breakdown statistics, dielectric spectroscopy, dynamic and tensile mechanical properties. Nanoblend masterbatch consistently improved the breakdown statistics, more than overcoming the inherent demerit of extrusion, which mildly
aged the unfilled material (as confirmed by Raman spectroscopy.) On the other hand, even low loading levels of Nanocor could result in reduced breakdown strength and increased scatter. Furthermore, both sets of materials demonstrated large dielectric losses at power frequencies and poorer performance under mechanical tension. These materials would therefore require considerable development before they could confidently be used commercially.
The nature of the PE-MMT interactions was examined by investigating the crystallisation kinetics and resulting morphologies with differential scanning calorimetry and scanning electron microscopy. By varying the masterbatch
type, loading level and crystallisation temperature, it was possible to study a wide range of supercrystalline morphologies using a permanganic etching technique. This is a useful contribution to the field of nanocomposites research. It is known that the morphologies of polymers can affect their mechanical properties and electrical treeing behaviour, and so it is possible
that controlled crystallisation could provide a route toward designer materials with optimised behaviour.
|Item Type:||Thesis (Doctoral)|
|Subjects:||Q Science > QA Mathematics > QA75 Electronic computers. Computer science|
|Divisions:||University Structure - Pre August 2011 > School of Electronics and Computer Science > Electrical Power Engineering
|Date Deposited:||27 Jan 2009|
|Last Modified:||08 Jun 2012 12:27|
|RDF:||RDF+N-Triples, RDF+N3, RDF+XML, Browse.|
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