Gypsum has been used almost exclusively as the mould material for casting sanitary-ware due to its high versatility, strength and homogenous pore distribution. However gypsum moulds have a number of disadvantages including deterioration on contact with water, deformation, long set times and short mould lives such that a large number of moulds are required for a commercial manufacturing processes. These drawbacks have led to attempts to find a new synthetic material to create moulds with similar properties to gypsum with respect to fine homogeneous pores, but with increased durability. Porous PMMA was developed in 1971 for the purpose of moulding ceramics. The basic approach to making the materials has remained unchanged since its commercial introduction with few academic studies undertaken on the formulations. This thesis describes an investigation into porous PMMA from an academic perspective studying the mechanism of formation of the materials and the role of the components in polymerisation. In particular: the surfactant type and level, monomer type, water to monomer ratio and bead size have been probed to assess their effect on the porosity and mechanical strength. A particular importance has been placed on the commercial viability of formulations because gypsum is a relatively inexpensive material and, due to its versatility and ease of manufacture, is still used throughout the ceramics industry. To increase cost competitiveness through spreading the higher cost of the raw materials and capital investment, the mechanical strength of porous PMMA materials has to be significantly greater to increase the number of casting cycles from each mould. In addition, to achieve competitive advantage in the marketplace, a deep understanding of the formulation was undertaken. This should allow for tailoring of the mould properties allowing for specialised moulds for different applications. In addition, this focused approach facilitates cost-savings allowing for the minimum input of raw materials. The thesis is a comprehensive body of work which looks individually at the components assessing their effect on the properties of the final material. In addition, the formation mechanism of the materials has been explored by breaking down the polymerisation into key stages. Highlighted is the excessive use of surfactant in a commercial formulation and the influence of plasticisation of the ligaments by the surfactant and excess monomer. The theory behind the polymerisation process, which generates the ligaments and traps the polymer beads in an immobile matrix, is developed; forming a comprehensive understanding of the formation of porous PMMA materials and factors influencing their development and final properties.
| Identifer | oai:union.ndltd.org:bl.uk/oai:ethos.bl.uk:764244 |
| Date | January 2013 |
| Creators | Gibson, Catherine |
| 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/synthesis-and-characterisation-of-porous-pmma-for-use-in-the-pressure-casting-of-ceramics(33eb67ad-c8fd-44ee-9e2c-a3c04a2efe53).html |
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