Fibres chemical stability

Sapphire fibres have a slightly wider spectral range. The main argument for their application is their outstanding thermal stability, up to 2000 K. Also, their chemical stability is superior to most other waveguide materials. 

More important, from the practical point of view, was the extensive work of Psenica [8] devoted to the question of nitrating fibres of cellulose isolated from nettle, fibres of little interest for the textile industry. By nitrating nettle cellulose in the same way as cotton, nitrocellulose containing 13.4% of nitrogen was produced, of adequate chemical stability provided the cellulose was well purified before the nitration. 

Polyester Good temperature and chemical stability. High physical strength with glass fibre reinforcement. 

In the present paper are presented the results of the investigation of their physico-chemical and mechanical properties, chemical stability, as well as the data on water and sulphur dioxide sorption as a function of their concentration in the gas phase. Influence of different parameters on the efficiency of absorption of SO2 from air by COg and HCOj foimofthe fibres has been tested. These parameters are gas flow rate, concentration, and air humidity. The optimal condition for regeneration has been established. It has been shown that the fibrous ion-exchange materials made of strong-base fibres are highly efficient means for removal of SO2 from air. 

The chemical stability, solubility and affinity of optical brightening agents depend on effective pH value in solution. For example, for wool and polyamide fibres, optimum pH is on the acidic side for better exhaustion. 

The chemical weak spots and the corresponding types of damage vary greatly with synthetic fibres depending on their structure. Thus they are described in the next section in relation to the type of fibre. However, a general difference in chemical stability exists between fibres formed by polymerization or polycondensation. At extreme pH values polycondensate fibres are hydrolytically degraded, for example... 

G L Hart, The Chemical Stability of Carbon Fibres and their Composites, PhD Thesis, Kingston Polytechnic, 1975. See also G L Hart and G Pritchard, Mechanisms of corrosion in carbon fibre-reinforced phenolic resins , in Developments in Composite Materials-1, ed. G S HoUster, London, Applied Science, 1977. 

Polytetrafluoroethylene (PTFE) is available in highly concentrated dispersions which have to be sintered at temperatures up to 400°C.This means that only glass fibre substrates are suitable for PTFE coatings. Modified PTFE types with thermoplastic properties can be welded. PTFE displays very good chemical stability but reduced mechanical stability. It is transpar-... 

Some extremely expensive fibres have been developed for specialized situations, notably for the aerospace market. They exhibit very high strength and modulus combined with unusually high thermal and chemical stability. Of these, the polybenzobisoxazole (PBO) fibres are at present the most readily available. 

Polypropylene (PP) is, besides polyesters, one of the most widely used polymers for producing synthetic fibres, especially for technical applications. PP fibres are mostly used in different technical fields due to their excellent mechanical properties, high chemical stability and processability. However, because of low surface energy, lack of reactive sites and sensitivity to photo- or thermal oxidation the polymer properties are insufficient for some applications. Therefore, several techniques for fibre modification have been reported, e.g. plasma treatment, chemical modification and nanomodification, i.e. production of nanocoated and nanofilled materials. 

The chemical name for such materials is poly(bisbenzimid-azobenzophenan-throlines) but they are better known as BBB materials. Such polymers have a Tg in excess of 450°C and show only a low weight loss after aging in air for several hundred hours at 370°C. Measurements using thermal gravimetric analysis indicate a good stability to over 600°C. The main interest in these materials is in the field of heat-resistant films and fibres. 

---