Polymeric fibre

14 Extension properties of plastic optical fibre with ten cycles. 

The core diameter varies according to the type of fibre, but is of the order of a millimetre, except in special cases. For economic reasons, the thickness of the cladding is much less, of the order of tens of micrometres. The surface of the core/cladding separation must be as even as possible. 

A possible classification of POF can be based on the principal core material. The principal types of POF are fibres with PMMA (polymethyl methacrylate) core, fibres with PS (polystyrene) core, fibres with PC (polycarbonate) core and fibres with deuterated core.  

Physical properties, such as tensile resistance, compression resistance, shock resistance, torsion resistance, the effect of permanent winding, bending resistance, etc., temperature property and the chemical properties of POF have been studied systematically.  

The mechanisms responsible for the formation of periodic structures in polymers have been explained. They can be classified into photolysis, oxidization and laser ablation for the surface relief gratings, while chain scission, cross-link and photopolymerization are considered to be responsible for bulk or volume gratings and in-fibre gratings. The cross-link in Bragg grating fabrication can be shown as  

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A. G. Causa, D. K. Kim, and R. S. Bhakuni, "Advances In MetaUic and Polymeric Fibre Reinforcement For Tyres," International Rubber... 

Cellulose trinitrate, 13.8% N, undergoes rapid denitration at room temperature when treated with dry pyridine. Segall and Purves [55a] have stated that in the presence of hydroxylamine the course of the reaction is changed one molecule of N2 is produced and a highly polymerized fibre-like dinitrate with a number of nitro groups 1.7 is formed. During this reaction denitration without degradation takes place. 

Van Wijk, R.J. De Weijer, A.P. Klarenberg, D.A. De Jonge, R. 8c Jongerden, G.J. Technique for Measuring Properties of Polymeric fibres World Intellectual Property Organization Patent Cooperation Treaty International Application WO 99/12019 Assigned to Akzo Nobel N.V. Piled in 1998. Priority Number NL 1006895 (1997). 

Conclusions. "R-factors" calculated between pairs of structure-factor sets determined by three different laboratories varied between 16 and 22%, and these large inaccuracies were the dominant contributor to errors in the parameters of the crystalline structure. Thus if the accuracy with which the structure of polymeric fibres is determined is to be improved, it is essential both to increase the accuracy of intensity measurement, and to quantify its errors. 

Another novel technique of making oxide fibres is called the inviscid melt technique [24], In principle, any material in a molten state can be drawn into a fibre shape. Organic polymeric fibres such as nylon, aramid, etc., as well as a variety of glasses can be routinely converted into fibrous form by passing a molten material, having an appropriate viscosity, through an orifice. The inviscid (meaning low viscosity) melt technique uses this principle to make oxide fibres. 

The moduli of polymers cover a wider range than those of other materials (from 105 N/m2 for rubber to 1010 N/m2 = 10 GPa for rigid polymers), which is one of the reasons why polymers are so versatile in application. Absolute stiffness and strength of polymers are much lower than those of metals, but on the basis of equal weight polymers compare favourably due to their much lower density. The specific moduli, defined as the moduli divided by the density, of isotropic polymers are of the order of one tenth of those of the stronger metals. The hyper-strong and hyper-stiff polymeric fibres such as fully extended polyethylene, stretched poly-(p-phenylene terephthalic amide) and carbon,... 

The values of E for polymer crystals are of the order of magnitude of 1011 N/m2 = 100 GPa, which is much higher than the values mentioned in Table 13.2 for commercial polymers. These values of the elastic moduli of single crystals must be considered as the limiting values of the tensile moduli of stretched polymeric fibres. 

TABLE 13.18 The basic elastic constants gd and ech, the highest filament values of the modulus, and the strength, average values of the creep compliance, j[t) (ratio of time dependent creep and local stress), at 20 °C and the interchain bond for a variety of organic polymeric fibres (after Northolt et al., 2005)... 

Understanding of the mechanism of creep failure of polymeric fibres is required for the prediction of lifetimes in technical applications (Northolt et al., 2005). For describing the viscoelastic properties of a polymer fibre use is made of a rheological model as depicted in Fig. 13.103. It consists of a series arrangement of an "elastic" spring representing the chain modulus ech and a "shear" spring, yd with viscoelastic and plastic properties... 

In practice, simple extension is found in melt spinning of polymeric fibres, although the situation is complicated by the non-isothermal character. 

The mechanical properties of paracrystalline aramides and other high-performance polymeric fibres are shown in Table 19.11. In comparison some other fibres are mentioned in this table (see also Sect. 13.6). Aramide fibres display a very high refractivity (refractive index and strong birefringence // 2.2, n 1.6). 

The most important polymeric matrices are linear and cross-linked polyesters, epoxy resins and linear and cross-linked polyimides the most important reinforcements are high-performance polymeric fibres and filaments (for polymeric composites), filaments of refractory metals and inorganic materials (E-glass, A12C>3, B, BN, SiC and Carbon) and whiskers (fibrillar single crystals of A1203, B4C, WC, SiC and C, exclusively for reinforcement of metals). 

The use of such small beams allows X-ray scattering patterns on single polymeric fibres with diameters down to a few microns to be collected in a few seconds. Thus scanning experiments across a fibre become feasible. It also allows study of individual spherulites or deformations near the edge of crack tips. Below are examples of work carried out on ID 13 at the ESRF. 

Polymeric microfibre mat. Until recently, the production of absorptive separators from 100% polymeric fibres was limited by the fact that fibre diameters of less than 1 pm could not be produced at reasonable cost. Further developments in polymers, as well as refinements in fibre production, have resulted in the manufacture of mats with a high percentage of fine fibres with a diameter below 1 pm [41]. As these organic fibres (usually polypropylene) are hydrophobic by nature, wettability has to be imparted by additional treatments such as grafting with hydrophilic agents or by co-extrusion with hydrophilic polymers [1]. 

H. Fong and D.H. Reneker in Structure Formation in Polymeric Fibres, Hanser Gardener Publications, Cincinnati, OH, USA, 2001, p.225. 

Rubber consumption is dominated by tyre production. In these, conveyor belts, and pressure hoses, thin layers of either steel wire or polymeric fibre reinforcement take the main mechanical loads. These layers, with rubber interlayers, allow flexibility in bending, whereas the reinforcement limits the in-plane stretching of the product. The applications are dominated by natural rubber and styrene butadiene copolymer rubber (SBR). Other rubbers have specialised properties butyl rubbers have low air permeability, nitrile rubbers have good oil resistance, while silicone rubbers have high and low temperature resistance. Rubbers play a relatively small role in this book, but the rubbery behaviour of the amorphous phase in semi-crystalline thermoplastics is important. 

Aerospace composite structures can also employ high-performance polymeric fibres such as the aramids Kevlar (DuPont) or Twaron (Teijin Twaron), poly(p-phenyl-ene-2,6-benzobisoxazole) (PBO) (Toyobo) and high-modulus polyethylene (PE) (Dynema, Certran and Spectra). Generally ultra-high-molecular-weight PE (UHMWPE) can be considered to be inert to most environments except that the service temperature is limited to <130 °C. 

Where polymeric fibres are mixed with natural fibres, the continuous multifilaments are cut into lengths according to the mean length of the natural fibres. The fibre-mix is then made into yams via ring spinning, rotor spinning or air-jet spinning. 

High performance heat and fire resistant organic polymeric fibres and blends 255... 

It depends on selective penneabUily rates of different gases through membranes (made from hollow polymeric fibres). Gases such as H2, NH3, CO2, and O2 are able to permeate through the membranes faster than N2. 

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