Anisotropic fibre spinning

Dopes like these exhibit mesomorphic behaviour they are solid at room temperature, but at higher temperature become less viscous and show optical anisotropy. If heated further, the clearing temperature (Td) is reached at which a phase transformation takes place from an anisotropic solution to an isotropic solution. With increasing polymer concentration both Ta and the melting point of the dope (T ) increase. Fibres of the highest quality (tenacity) are obtained by spinning at temperatures between and Ta, but as low as possible, The spun filament is solidified in a coagulating bath, preferably at temperatures below 5 °C. 

One further topic merits discussion in this section in view of its success in dealing with the mechanical properties of oriented fibres, which are after all anisotropic polymers. That is the theory of kinetic fracture, developed mainly by Zhurkov and co-workers. Evidence has been presented from electron spin resonance (e.s.r.X " mass spectrometry, and infra-red spectroscopy that when highly oriented fibres or heavily cross-linked rubbers experience a tensile stress (along the axis for fibres) an appreciable fraction of main-chain bonds are broken by the applied stress. These scission events are observed to occur more or less homogeneously throughout the fibre and are not localised in the fracture plane. Many sets of data show that the lifetime tb of a fibre under stress is described approximately by the following equation... 

Considering fibres based on poly(hydroxybutyrate) or higher PHAs, no successful process was reported for preparation of PHB fibres by conventional fibre processing technology, i.e. melt or gel spinning with subsequent hot drawing. Therefore, more sophisticated procedures have to be developed to achieve reasonable draw ratios, resulting in production of anisotropic material with important improvement of properties. 

Piezoceramic materials are chemically inert and physically strong. In fibre form, they have anisotropic structures. Usually, ceramic fibres are produced by the spinning of an organic or mineral precursor fibre, followed by heat treatment and pyrolysis (Hearle, 2001). Piezoceramic fibres comprising lead zirconate/lead titanate exhibit better sensitivity in terms of piezoelectric activity and elevated operating temperatures (Swallow et al., 2008). PZT fibres can be manufactured by various processes, such as sol-gel, viscous suspension spinning, extrusion and viscous plastic processing, some of which are already commercially available (Strock et al., 1999 Meyer et al., 1998 French and Cass, 1998 Meister et al., 2003 Bowen et al., 2006). 

Muraki, C, Niwa, M., Amino, N., and Kawabata, S., Changes in Anisotropic Elastic Moduli of Wool Fibres during Worsted Spinning, Weaving and Finishing , JoMrna/o/i/ze Textile Institute, 81,12-21, 1994. 

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