Fibre formation techniques polymers

As non-degradable polyesters are quite common as textile materials, it comes as no surprise that their degradable counterparts are also readily processable into fibres. Polymer fibres are particularly interesting for biomedical applications, including wound dressings, controlled-release formulations and tissue engineering. Several spinning techniques result in the formation of polymer fibres. 

Although the existing fibre-making technique is able to produce a bicomponent fibre of many cross-sectional structures, the production of bicomponent nanofibres has been limited to two basic types of cross-sectional structures, the core-sheath and the side-by-side . These bicomponent nanofibres are eiectrospun via special spinnerets. Two polymer solutions flow within the spinneret as the sheath and core, or side-by-side, to the tip of the nozzle and then are subjected to a co-electrospinning process. The formation of bicomponent nanofibres is determined by the laminar bicomponent jet. 

Polymers owe much of their attractiveness to their ease of processing. In many important techniques, sueh as injection moulding, fibre spinning and film formation, polymers are processed in the melt, so that their flow behaviour is of paramoimt importance. Because of the viscoelastie properties of polymers, their flow behaviour is much more complex than that of Newtonian liquids for which the viscosity is the only essential parameter. In polymer melts, the recoverable shear compliance, which relates to the elastic forces, is used in addition to the viscosity in the deseription of flow [48]. 

Raman fibre optics has been used to study the emulsion homopolymerisations of styrene and n-butyl acrylate (35). An IR spectroscopic technique for the examination of radical copolymerisations of acryl and vinyl monomers was developed. A comparative study of the copolymerisation of model monomer pairs was made using monofunctional and polyfunctional compounds. The data established the role of structural-physical transformations, involved in the formation of crosslinked polymers, on the copolymerisation kinetics and on the nonuniformity of distribution of crosslinks in the copolymers formed (151). Raman fibre optics of polymerisation of acrylic terpolymers was also used to monitor as well as an on-line measurement of morphology/composition (66). The high temperature (330 °C) cure reaction of 4-phenoxy-4 -phenyl-ethynylbenzophenone was monitored using a modulated fibre optic FT-Raman spectrometer (80). 

Finally, the coaxial electrospinning technique is suitable to prepare coreshell fibres with high-molecular-weight molecules, such as proteins, in-eorporated into them. In this case the formation of the high-molecular-weight fibres is aided by the electrospinning of homogenous polymer solutions. ... 

Abstract Polymers are macromolecules derived by the combination of one or more chemical units (monomers) that repeat themselves along the molecule. The lUPAC Gold Book defines a polymer as A molecule of high relative molecular mass, the structure of which essentially comprises the multiple repetition of units derived, actually or conceptually, from molecules of low relative molecular mass. Several ways of classification can be adopted depending on their source (natural and synthetic), their structure (linear, branched and crosslinked), the polymerization mechanism (step-growth and chain polymers) and molecular forces (Elastomers, fibres, thermoplastic and thermosetting polymers). In this chapter, the molecular mechanisms and kinetic of polymer formation reactions were explored and particular attention was devoted to the main polymerization techniques. Finally, an overview of the most employed synthetic materials in biomedical field is performed. 

An alternate design that uses a needleless spinneret to overcome the disadvantages of both needle-based and free-surface electrospinning, whilst controlling the Taylor cone formation is credited to Revolution Fibres Ltd [40], who scaled up this process to achieve continuous production of nanofibres from less than 100 nm to sub-micron range with more than 30 varieties of polymers. Elmarco developed similar techniques with coated wires as spinneret and recently Stellenbosch University has developed a regenerating bubble method [41] as an alternative to needle-based electrospinning. 

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