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PROPERTIES OF CHITIN WHISKER REINFORCED POLY(ACRYLIC ACID) COMPOSITES
[Thesis]. Manchester, UK: The University of Manchester; 2015.
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Abstract
Composites, in which the matrix and the reinforcing fillers are respectively, poly(acrylic acid) (PAA) with two different molecular weights, and chitin whiskers (CHW) were successfully prepared using an evaporation method. The weight fraction of CHW was varied from 0.03 to 0.73. Mechanical and thermal properties and crystallinity of the composites were characterised using tensile testing, differential scanning calorimetry, thermogravimetric analysis and X-ray diffraction. The tensile strength of the composite increased up to 11 wt % CHW after which it decreased. XRD characterisation showed a decrease in crystalline index, crystalline size, chitin crystalline peak and intensity as the content of PAA and its molecular weight increased. Raman spectroscopy was used for the first time to monitor the deformation of chitin film and CHW reinforced PAA composites. The Raman band located at 1622 cm^(-1) was monitored for deformation. On application of tensile deformation the Raman band initially located at 1622 cm^(-1) shifted toward a lower wavenumber. Raman band shift rates of -1.85 cm^(-1)/% for chitin film and -0.59 and -0.25 cm^(-1)/% for 73 and 23 wt % CHW content, respectively, were measured. The modulus of a single chitin whisker and composites were found to be 115, 37 and 16 GPa respectively, for a two dimensional (2D) in-plane distribution of CHW. CHW within a PAA matrix did not show any preferential alignment in a polarised Raman. The Raman intensity ratio〖 I〗_1698 /I_1622 showed that the strongest interaction of the carboxylic group in the composites occured at 3 wt % CHW content. The interaction gradually reduced as the CHW content increased. 〖 CaCO〗_3 crystals were grown in CHW, PAA and CHW/PAA composites by a solution and evaporation casting method. In the absence of PAA and CHW, rhombohedral calcites were observed while rod-like aragonite polymorphs were seen when only PAA was used as a template. In the presence of only CHW, a morphological mixture of ellipsoidal and disc shape with traces of rhombohedral aggregate calcite were the features. In the presence of both PAA and CHW, the rhombohedral shape showed roughness with irregular faces while the vaterite polymorph continued to agglomerate with the observation of porosity at higher CHW content. The vaterite particles gradually decreased as the CHW content was decreased. At lower CHW content aragonite polymorph growth was favoured to the detriment of calcite. The results showed that the vaterite polymorph can be grown even at higher filler loading.The effect of 〖 CaCO〗_3 growth on the mechanical properties of CHW reinforced PAA indicated that better mechanical properties can be achieved at a CHW content of 3 wt % when compared with neat PAA and when 〖 CaCO〗_3 was not incorporated into the CHW/25PAA composites.