Absorbable fibres

Since 1976 the number of commercial odour adsorbent wound dressings has increased, but it was not until the late 1990s that they were available on prescription in the UK. There are a wide variety of odour adsorbent wound dressings available, but these can differ in construction, composition and, therefore, physical characteristics including odour adsorption. These dressings are composed of many different materials, ranging from the traditional naturally absorbent fibre types such as cotton and viscose, specialist materials such as polyurethane film, and fibres such as alginate and carboxymeth-ylcellulose fibres (CMC). 

Sorbtive extraction methods involve the extraction of compounds into a solid absorbent (fibre) and—for volatile compounds—a subsequent thermal desorption in a GC injector. The two main techniques are solid phase micro-extraction (SPME) (Pawliszyn, 1997) and stir-bar sorbtive extraction (SBSE) (Hanaoka et al, 2000). Both methods are good candidates for the automation required in the context of quality control, as commercially available robots are capable of controlling the sampling and injecting the extracted analytes into the GC. 

The problems of monomer recovery, reaction medium viscosity, and control of reaction heat are effectively dealt with by the process design of Montedison Fibre (53). This process produces polymer of exceptionally high density, so although the polymer is stiU swollen with monomer, the medium viscosity remains low because the amount of monomer absorbed in the porous areas of the polymer particles is greatly reduced. The process is carried out in a CSTR with a residence time, such that the product k jd x. Q is greater than or equal to 1. is the initiator decomposition rate constant. This condition controls the autocatalytic nature of the reaction because the catalyst and residence time combination assures that the catalyst is almost totally expended in the reactor. 

Fig. 25.6. Fibres toughen by pulling out of the fracture surface, absorbing energy os the crock opens.

To improve the resistance to ultraviolet light carbon black is often useful as a light screen. Its use in fibres and films is clearly very restricted and in these instances ultraviolet absorbers and/or quenching agents are used. Recent developments include the greater use of hindered amine and nickel compounds. 

This material has been known for many years, being used originally in the making of electric lamp filaments. In principle vulcanised fibre is produced by the action of zinc chloride on absorbent paper. The zinc chloride causes the cellulosic fibres to swell and be covered with a gelatinous layer. Separate layers of paper may be plied together and the zinc chloride subsequently removed to leave a regenerated cellulose laminate. 

Other estimates placed the film and bottle market to be of a similar size in Japan while globally the bottle market was about 20% of the total. Together with other data this suggests that the fibre and filament market absorbs about 72% of PET capacity, containers about 19%, film about 7% and mouldings 2%. Considerable quantities of PET bottles are, however, recycled into fibres for use, for example, in outdoor clothing. 

Typical applications for nylon include small gears, bearings, bushes, sprockets, housings for power tools, terminal blocks and slide rollers. An important design consideration is that nylon absorbs moisture which can affect its properties and dimensional stability. Glass reinforcement reduces this problem and produces an extremely strong, impact resistant material. Another major application of nylon is in fibres which are notoriously strong. The density of nylon is about 1100 kg/m. ... 

From this table it may be seen that carbon fibre has low energy absorbing capability compared with the other fibres. However, the other fibres are not as stiff. Hence it is... 

Figure 12.30 Potential uses of polyphosphazenes (a) A thin film of a poly(aminophosphazene) sueh materials are of interest for biomedical applications, (b) Fibres of poly[bis(trifluoroethoxy)phosphazene] these fibres are water-repellant, resistant to hydrolysis or strong sunlight, and do not burn, (c) Cotton cloth treated with a poly(fluoroalkoxyphosphazene) showing the water repellaney eonferred by the phosphazene. (d) Polyphosphazene elastomers are now being manufaetured for use in fuel lines, gaskets, O-rings, shock absorbers, and carburettor eomponents they are impervious to oils and fuels, do not bum, and remain flexible at very low temperatures. Photographs by eourtesy of H. R. Allcock (Pennsylvania State University) and the Firestone Tire and Rubber Company.

Internal At one time open-weave hessian cloth was very largely used as an internal reinforcement material, but experience showed that this is subject to rotting in the soil. Even when the material appears to be covered with enamel, some of the fibres must protrude, and thus moisture is absorbed so that after a period of years the hessian is generally found to be in a waterlogged condition and forming food for bacteria. 

In order to dry the crystals, the Buchner funnel is inverted over two or three thicknesses of drying paper (i.e., coarse-grained, smoothsurfaced filter paper) resting upon a pad of newspaper, and the crystalline cake is removed with the aid of a clean spatula several sheets of drying paper are placed on top and the crystals are pressed firmly. If the sheets become too soiled by the mother liquor absorbed, the crystals should be transferred to fresh paper. The disadvantage of this method of rapid drying is that the recrystallised product is liable to become contaminated with the filter paper fibre. 

Whatever the approach, the result is a difficult-to-analyse system. Such options suit polymer producers better than additive suppliers. Aromatic polymers (PPO) have been mentioned as char-forming FRs. Polymeric UV absorbers, blended in proper proportions with commercial plastics, have potential use as stabilisers for fibres, films and coatings. Several monomeric stabilisers containing a vinyl group were homopolymerised and used as stabilisers for PE, PVC, acrylates, polystyrene, cellulose acetate and several vinyl polymers [55]. 

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