Environment Fibre

Examples of creep effects covering environment, fibre type, resin type, effects of temperature, effects of strain and effects of overload are given in a variety of references at the end of this section. Creep effects are also affected by cyclic and intermittent loading. At cyclic frequencies above a few hertz the effects of heating of the material from hysteresis can be a factor in increasing creep. 

A wide variety of thermoplastics have been used as the base for reinforced plastics. These include polypropylene, nylon, styrene-based materials, thermoplastic polyesters, acetal, polycarbonate, polysulphone, etc. The choice of a reinforced thermoplastic depends on a wide range of factors which includes the nature of the application, the service environment and costs. In many cases conventional thermoplastic processing techniques can be used to produce moulded articles (see Chapter 4). Some typical properties of fibre reinforced nylon are given in Table 3.2. 

Caution is needed in applying the results of general chemical tests for glass durability across a wide spectrum of glass properties. Glass fibre strengths, for example, are sensitive to the physical, as well as the chemical, nature of the environment and should only be assessed by the direct strength measurements in conditions which closely approximate the final application situation . 

In the uniaxially oriented sheets of PET, it has been concluded that the Young s modulus in the draw direction does not correlate with the amorphous orientation fa or with xa "VP2(0)> 1r as might have been expected on the Prevorsek model37). There is, however, an excellent correlation between the modulus and x,rans,rans as shown in Fig. 15. It has therefore been concluded 29) that the modulus in drawn PET depends primarily on the molecular chains which are in the extended trans conformation, irrespective of whether these chains are in a crystalline or amorphous environment. It appears that in the glassy state such trans sequences could act to reinforce the structure much as fibres in a fibre composite. 

Aqueous scouring is expensive in terms of water use and effluent treatment and it can cause entanglement of delicate wool fibres. Solvent scouring offers an effective alternative but it is essential that the solvent does not enter the environment. Earlier solvent-based processes included the use of perchloroethylene in which 8-18% water had been emulsified with a surfactant. Current processes are based on hexane (de Smet process), 1,1,1-... 

Advanced materials can be used in extreme conditions, e.g., high temperatures (> 200°C), severe chemical environments (e.g., polytetrafluoroethylene (PTFE) with concentrated H2SO4). They are often used as a critical component in a workpiece and are frequently reinforced with glass, carbon or aramid (e.g., Kevlar ) fibres. 

The attenuation of an optical fibre results from physical phenomena either occurring within the fibre or coming from the environment. This is the sum of light lost by scattering in the fibre, absorption by the fibre materials, leakage of light out of the core due to environmental factors (e.g. microbends). Scattering and absorption losses dominate in every fibre. 

A fusion splice is a connection in which minimal losses can be obtained. Such a connection is made in a fibre optic splicer (usually controlled by a computer). Two fibres are put into an electric arc where they melt and create a low-loss splice. The splice obtained must be covered with a protective layer in order to prevent the junction from the damage and from the influence by the environment. 

Special optical fibres have been intensively investigated during recent years because of their potential wide-range use for on-line monitoring of material properties or processes in a number of areas of human activity (environment protection, food industry, medicine etc.) Their technology can be considered an integral part of the team-work on optical fibre sensors development. Despite special optical fibres represent a unique and often indispensable tool for a variety of sensor applications, special fibre production still represents only a small fraction of the market. Probably it is because of their low consumption (in comparison with standard telecommunication fibres), the need for much more advanced know-how and lower reproducibility. 

Ahmad M., Narayanaswamy R., Fibre Optic Reflectance Sensor for the Determination of Aluminium (III) in Aqueous Environment, Anal. Chim. Acta 1994 291 255-260. 

Ritchie L.J., Ferguson C.P., Bessant C., Saini S., A ten channel fibre-optic device for distributed sensing of underground hydrocarbon leakage, J.Environ. Monitor. 2000 2 670-673. 

Optical fibre based optical detection systems offer a number of advantages over bulk optical sensing systems. The principal one is that a robust passive sensing head may be remoted from the monitoring station a factor giving particular advantages in severe environments. This also allows... 

As ToF-SIMS is a surface analytical technique, it is well suited to the study of surface interaction between a material and its environment or between a material and products applied to it. The surface modifications can then be studied, making it possible to establish links with degradation processes. Published papers on the study of natural fibres related to cultural heritage typically illustrate this aspect of ToF-SIMS analysis. 

The colour of indigo depends dramatically upon its physical state and environment for example, the vapour is red but the colour on the fibre is blue. The marked solvatochromism of indigo (Table 6.4) is attributable mainly to hydrogen bonding. A progressive bathochromic shift of the visible absorption band is observed as the solvent polarity... 

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