Microfibrillated cellulose (MFC) is an alternative material that has been widely studied to enhance the mechanical properties of a polymer matrix due to a number of perceived advantages over traditional plant fibre forms. Mechanical properties of MFC networks were found to depend on parameters such as the modulus of fibrils, bonding strength, porosity, degree of crystallinity, contact area of fibrils and possibly the modulus of the cellulose crystals of the raw materials (cellulose I or II). Even though the longer processing time used to produce MFC was found to yield networks with fewer fibre aggregates, finer fibrils and higher density, some properties, for instance thermal stability and degree of crystallinity, decreased due to the degradation of fibrils caused by the harsh treatment. The aims of this thesis were to assess the mechanical properties and interfaces of composites produced using of a range of MFC materials, prepared using different treatments and from different sources. Raman spectroscopy has been used to detect the molecular orientation of cellulose chains within an MFC network, and to monitor the deformation micromechanics of MFC networks. The Raman band initially located at ~1095 cm-1 obtained from MFC networks was observed to shift towards a lower wavenumber position upon the application of tensile deformation. The intensity of this band as a function of rotation angle of MFC networks was similar, indicating randomly oriented networks of fibrils. From the Raman band shift rate data, the effective moduli of MFC single fibrils produced from pulp were estimated to be in the range of 29-41 GPa. Poly(lactic acid) (PLA) composites reinforced with MFC networks were prepared using compression moulding. Enhanced mechanical properties of MFC reinforced composites were reported, compared to neat PLA films. The mechanical properties of these composites were found to mainly depend on the interaction of the PLA matrix and the reinforcement phase. The mechanical properties of the composites reinforced with dense networks were shown to be dominated by the network properties (fibril-fibril interactions), while matrix-fibril interactions played a major role where more opened networks were used to reinforce a polymer matrix. The penetration of the matrix into the network was found to depend on the pore sizes, fibre width and porosity within the network. It was found that the matrix easily penetrates into the network with a range of mean fibril dimensions, rather than for networks with only fine fibrils present. The stress-transfer process in MFC reinforced PLA composites was monitored using Raman spectroscopy. Greater Raman band shift rates with respect to tensile deformation for the composites were observed compared to pure MFC networks. This indicates that stress is transferred from the PLA matrix to MFC fibrils, supporting the enhancement of the mechanical properties of the composites.
| Identifer | oai:union.ndltd.org:bl.uk/oai:ethos.bl.uk:553533 |
| Date | January 2012 |
| Creators | Tanpichai, Supachok |
| Contributors | Eichhorn, Stephen |
| Publisher | University of Manchester |
| Source Sets | Ethos UK |
| Detected Language | English |
| Type | Electronic Thesis or Dissertation |
| Source | https://www.research.manchester.ac.uk/portal/en/theses/micromechanics-of-microfibrillated-cellulose-reinforced-polylactic-acid-composites-using-raman-spectroscopy(51fc47fa-fcb4-43cd-accc-3c559b5a0a2e).html |
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