Preparation and characterisation of poly(ethylene terephthalate) and poly(vinyl alcohol)/clay nanocomposites.

DOPPERS, Leena-Marie. (2004). Preparation and characterisation of poly(ethylene terephthalate) and poly(vinyl alcohol)/clay nanocomposites. Doctoral, Sheffield Hallam University (United Kingdom)..

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Abstract

The formation of poly (ethylene terephthalate) (PET)/organo-montmorillonite and poly (vinyl alcohol)(PVOH)/ montmorillonite nanocomposites and the diffusion behaviour of water and acetone/water mixtures into the latter have been investigated. Nanocomposites of PET and various, commercially available, organoclays have been prepared by solution intercalation and the structure of the resulting composite investigated in dependence of surfactant on the organoclay, clay loading, solvent, stirring time, polymer concentration, polymer type and drying temperature. All samples prepared had an intercalated structure with layer spacing depending mainly on the type of surfactant present on the clay. Thermal stability of the samples was similar to that of PET, yet decomposition was found to start at temperatures up to 40 °C lower than for the pristine polymer.Formation of nanocomposites of PVOH and montmorillonite has been achieved by solution intercalation from aqueous solutions. For these samples the influence of molecular weight of the PVOH, clay loading, clay structure and interlayer cations has been investigated. PVOH/ clay (nano-) composites have been prepared over the full range of compositions, from "true" nanocomposites to PVOH adsorbed on clay. For clay loadings up to 10 wt% XRD silent nanocomposites have been obtained. Clay loadings between 20 and 40 wt% resulted in intercalated nanocomposites with wide ranges of layer spacings, while clay loadings of 45 - 75 wt% resulted in intercalated composites with a narrower distribution of spacings. Above this loading adsorption of PVOH onto clay with two distinct layer spacings could be observed. Results were similar for higher molecular weight PVOH. Thermal stability of these samples was also found to depend on the clay loading. An increase of the degradation onset temperatures by 10-20 °C was measured for nanocomposite samples. Lithium and sodium montmorillonites showed similar dispersion patterns. Charge reduction of the lithium clay had a strong influence on the dispersion of the clay. Lower charged layers resulted in poorer dispersion. Li+ MCBP fired at 210 °C did not form nanocomposites with PVOH independent of the clay loading. Diffusion measurements of water into PVOH showed strong influences of swelling, gelling and dissolution of the samples. Generally, diffusion into the nanocomposites showed shorter time delays before it became measurable, yet the diffusion coefficient decreased with increasing clay content. Diffusion was found to be dependent on the dispersion of the clay with microcomposite structures resulting in better barrier properties than their nanocomposite counterparts. Higher temperatures resulted in faster diffusion rates. During the diffusion of water crystalline regions of the PVOH were dissolved and the clay remained dispersed in the swollen PVOH.Diffusion of acetone/ water mixtures was found to be strongly dependent on the concentration of water in the diffusant. In mixtures with an excess of water or a molar ratio of acetone: water of 1:1 the diffusion of acetone and water proceeded at the same time in PVOH and its nanocomposites. This has been attributed to formation of acetone/ water complexes. At excess levels of acetone in the diffusant acetone diffusion is delayed and occurs at a slower rate. Presence of clay in these samples leads to longer delay times before diffusion can be measured and slower diffusion rates. Microcomposite samples were again found to have better barrier properties than the nanocomposites and it is assumed that partial delamination of the clay layers in these samples increases the aspect ratio of the clay. Swelling is found to decrease with decreasing water content as well as increasing clay content. Crystallinity of the polymer is initially decreased, yet some crystallinity is recovered over the course of the experiment in the neat polymer. Presence of clay reduced the extent to which crystallinity was recovered. Analysis of the hydrogen bonding of the water within the polymer in the equilibrium spectra showed decrease of strongly and weakly hydrogen bonded water with increasing acetone/ contents in the diffusant. In the nanocomposites only decrease of the weakly hydrogen bonded water could be observed. Following the changes in hydrogen bonding over the course of the experiments showed increases in weakly hydrogen bonded water while strongly hydrogen water decreased due to break down of the hydrogen bonding network. Hydrogen bonding of the polymer also decreased due to swelling of the polymer.

Item Type: Thesis (Doctoral)
Additional Information: Thesis (Ph.D.)--Sheffield Hallam University (United Kingdom), 2004.
Research Institute, Centre or Group: Sheffield Hallam Doctoral Theses
Depositing User: EPrints Services
Date Deposited: 10 Apr 2018 17:19
Last Modified: 10 May 2018 10:20
URI: http://shura.shu.ac.uk/id/eprint/19671

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