Poly fibre

Japanese workers have developed fibres from poly(vinyl alcohol). The polymer is wet spun from warm water into a concentrated aqueous solution of sodium sulphate containing sulphuric acid and formaldehyde, the latter insolubilising the alcohol by formation of formal groups. 

In addition to poly(methyl methacrylate) plastics and polyacrylonitrile fibres, acrylic polymers find widespread use. First introduced in 1946, acrylic rubbers have become established as important special purpose rubbers with a useful combination of oil and heat resistance. Acrylic paints have become widely accepted particularly in the car industry whilst very interesting reactive adhesives, including the well-known super-glues are also made from acrylic polymers. 

Today a very wide range of acrylic materials is available with a broad property spectrum. The word acrylic, often used as a noun as well as an adjective in everyday use, can mean quite different things to different people. In the plastics industry it is commonly taken to mean poly(methyl methacrylate) plastics, but the word has different meanings, to the fibre chemist and to those working in the paint and adhesives industries. Unless care is taken this may be a source of some confusion. 

These polymers, typical of polyamides with fewer than four main chain carbon atoms in the repeating unit, decompose before melting and have to be processed from solution. Several of the polymers may, however, be spun into fibres. Over thirty years ago Courtaulds produced silk-like fibres on an experimental commercial scale from poly-(L-alanine) and from poly-(a-methyl-L-glutamate). The latter material is also said to be in use as a synthetic leather in Japan. The... 

Japanese have also shown interest in poly-(L-glutamic acid) for the manufacture of silk-like fibres. 

In 1973 Du Pont commenced production of another aromatic polytunide fibre, a poly-(p-phenyleneterephthalamide) marketed as Kevlar. It is produced by the fourth method of polyamide production listed in the introductory section of this chapter, namely the reaction of a diamine with a diacid chloride. Specifically, p-phenylenediamine is treated with terephthalyl chloride in a mixture of hexamethylphosphoramide and V-methylpyrrolidone (2 1) at -10°C Figure 18.32). 

Carothers also produced a number of aliphatic linear polyesters but these did not fulfil his requirements for a fibre-forming polymer which were eventually met by the polyamide, nylon 66. As a consequence the polyesters were discarded by Carothers. However, in 1941 Whinfield and Dickson working at the Calico Printers Association in England announced the discovery of a fibre from poly(ethylene terephthalate). Prompted by the success of such a polymer, Farbenfabriken Bayer initiated a programme in search of other useful polymers containing aromatic rings in the main chain. Carbonic acid derivatives were reacted with many dihydroxy compounds and one of these, bis-phenol A, produced a polymer of immediate promise. 

In the late 1970s several developments occurred causing renewed interest in poly(ethylene terephthalate) as a plastics material. These included the development of a new mouldable grade by ICI (Melinar) and the development of a blow moulding technique to produce biaxially oriented PET bottles. In addition there appeared a glass-fibre filled, ionomer nucleated, dibenzoate plasticised material by Du Pont (Rynite) (see Chapter 26). 

In the early 1960s other terephthalates became available, particularly poly-(1,4-cyclohexylene terephthalate) Figure 21.10 (b)), with slightly higher and superior water and weathering stability to poly(ethylene terephthalate). Fibre and film forms became available. 

Polyesters are eneountered in many forms. They are important as laminating resins, moulding compositions, fibres, films, surface coating resins, rubbers and plasticisers. The common factor in these widely different materials is that they all contain a number of ester linkages in the main chain. (There are also a number of polymers such as poly(vinyl acetate) which contain a number of ester groups in side chains but these are not generally considered within the term polyester resins.)... 

Fibres are also available from poly-(l,4-cyclohexylenedimethylene terephthalate) and are marketed as Kodar (Kodak) and Vestan (Hills). 

As with poly(ethylene terephthalate) there is particular interest in glass-fibre-filled grades. As seen from Table 25.8, the glass has a profound effect on such properties as flexural modulus and impact strength whilst creep resistance is also markedly improved. 

For an aliphatic polyester, poly(pivalolactone) has a rather high of 245°C and for such a an unexpectedly low of -10°C. It is also claimed to have good hydrolysis resistance for a polyester and this appears to be one of the reasons for its manufacture on an experimental scale by Shell with a view for use as both a fibre and as a thermoplastics moulding material. 

As previously mentioned the initial research on polyurethanes was directed towards the preparation of fibre-forming polymers. Many poly hydroxy compounds and many di-isocyanates were used and the melting points of some of the more linear aliphatic polyurethanes produced cU"e given in Table 27.1. 

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. 

Turning now to other types of ceramic fibre, the most important material made by pyrolysis of organic polymer precursors is silicon carbide fibre. This is commonly made from a poly(diorgano)silane precursor, as described in detail by Riedel (1996) and more concisely by Chawla (1998). Silicon nitride fibres are also made by this sort of approach. Much of this work originates in Japan, where Yajima (1976) was a notable pioneer. 

Jones, F.R., Interfacial aspects of glass fibre reinforced plastics. In Jones, F.R. (Ed.), Interfacial Phenomena in Composite Materials. Butterworths, London, 1989, pp. 25-32. Chaudhury, M.K., Gentle, T.M. and Plueddemann, E., Adhesion mechanism of poly(vinyl chloride) to silane primed metal surfaces. J. Adhes. Sci. Technol, 1(1), 29-38 (1987). Gellman, A.J., Naasz, B.M., Schmidt, R.G., Chaudhury, M.K, and Gentle, T.M., Secondary neutral mass spectrometry studies of germanium-silane coupling agent-polymer interphases. J. Adhes. Sci. Technol., 4(7), 597-601 (1990). 

As stated in Section I, columns should be selected so the low molar mass portions of the samples in question can be sufficiently separated from the elution interval of the system peaks. This task cannot always be accomplished, e.g., dimethylacetamide often replaces dimethylformamide as a GPC eluent the analyzed, mostly polar, samples require a neutral salt (e.g., FiBr) (7). The calibration is usually carried out with poly(methylmethacrylate) standards... 

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.

In America there are promising signs for certain polymers. For example, poly(ethylene terephthalate) drinks bottles can be cleaned and recycled to give an acceptable grade of PET resin in a process that is economically viable. The recycled polymer is used as carpet fibre, furniture stuffing, or insulation. Waste nylon can also be recycled profitably. 

As a representative example of our current technological dependency, we can consider the manufacture of the polyester, poly(ethylene terephthalate) (PET) and its use in the production of synthetic fibre for clothing, and to examine the extent to which it might be possible to replace PET fibre by an equivalent quantity of the natural fibre, wool. Some... 

Poly(trimethylene terephthalate) (PTT) is a polymer with very useful properties. As a textile fibre it has excellent softness, stretch and recovery. As a resin it has excellent barrier properties. Developed over 60 years ago, PTT has not been very widely used compared to poly(ethylene terephthalate) (PET) as one of the key monomers 1,3-propanediol (PDO) has been expensive. 

GFR Glass-fibre reinforced PBMA PBT Poly(butyl methacrylate) Poly(butylene terephthalate)... 

Compared with wool and cotton, the scouring procedures for synthetic fibres are relatively simple since these fibres contain fewer impurities. Most of these have at least some degree of water solubility the most important are sizes and lubricants. The major sizes used are poly (vinyl alcohol), carboxymethylcellulose and poly (acrylic acid), all of which are completely or partially water-soluble. Sometimes aliphatic polyesters are used. 

---