Commodity fibres

Successful construction of textile fabrics as substrates for the integration of solar cells has to take into account the type and grade of polymer used, the type of fibre extruded from it, and subsequent fabric construction. Fibre selection is very much determined by its ability to withstand successfully the elevated temperatures required for the deposition of the thin layers comprising a solar cell. Where these temperatures are as high as 400 °C or more, as in the deposition of many types of solar cell, selection is restricted to high-performance fibres, such as glass fibres, polyimides, polybenzimidazoles and polybenzoxazoles, but these types of fibre are expensive. However, it has been demonstrated that nanocrystalline silicon films can be successfully laid down at temperatures as low as 200 °C [4, 5], a factor that then broadens fibre choice to include a range of commodity fibres. 

The fibre must also be able to withstand prolonged exposure to sunlight, specifically irradiation by UV light. The twin considerations of thermomechanical stability up to 200 °C and resistance to UV radiation do rule out several types of commodity fibre. These fibres include most natural fibres, as well as commercial polyolefin and acrylic fibres, all of which melt or begin to decompose below 200 °C. Nevertheless, polyethylene terephthalate (PET) fibres are potentially suitable substrates they melt at 260-270 °C and exhibit good stability to UV radiation [6]. They are also commercially... 

Mixtures of nanocrystalline and amorphous silicon cells can usefully be deposited at temperatures as low as 200 °C (Koch et al., 2001 Lind et al., 2011), and under appropriate conditions even crystalline silicon may be grown, albeit epitaxially on silicon wafers (Ji and Shen, 2004). These two factors of UV resistance and temperature of deposition, therefore, restrict the use of some types of commodity fibres for the direct deposition of silicon cells. Commercial polyolefin fibres melt below 200 °C, and cotton, wool, silk and acrylic fibres start to decompose below this temperature. Amongst polyamide fibres, nylon 6 6 fibres, which melt at 255-260 °C, can withstand deposition temperatures of 200 °C, but they need to contain light stabilizers to avoid degradation by UV radiation. P-aramid fibres, which are also polyamides, can for practical use withstand temperatures up to ca. 400 °C, but they would probably not be sufficiently stable against UV radiation. 

In spite of the limitations imposed by the chemical structure upon the choice of fibre-forming polymers, the number of potentially useful polymers is extremely large. Yet, in reality, the majority of commodity fibres are produced from a few well-established polymers. In commerce, fibres are classified by generic names which sometimes employ chemical names in a more restricted sense than that which is common in polymer science. The generic names of the most important commodity... 

Polymers used for the manufacture of commodity fibres are also used in the production of multiconstituent fibres, sometimes in conjunction with a modified commodity polymer or a specialty polymer. These fibres consist of two or more polymers forming separate phases. There are essentially two types of such fibres. In the first type, each polymer occupies a discrete region of the fibre cross-section e.g. sheath/core-type fibres, where the sheath is a lower melting homopolymer or copolymer such fibres are used for thermal bonding). In the second type, the components are dispersed in a random way throughout the fibre, typically forming a matrix/fibril arrangement e.g. incorporation of dyeable polymer fibrils into polypropylene which forms the matrix). Detailed description of these fibres can be found elsewhere. 

Leaving aside rayon and artificial silks generally, the first really effective polymeric textile fibre was nylon, discovered by the chemist Wallace Hume Carothers (1896-1937) in the Du Pont research laboratories in America in 1935, and first put into production in 1940, just in time to make parachutes for the wartime forces. This was the first of several major commodity polymer fibres and, together with high-density polyethylene introduced about the same time and Terylene , polyethylene tereph-thalate, introduced in 1941 (the American version is Dacron), transformed the place of polymers in the materials pantheon. 

Over the past 20 years no new commodity polymer has been developed. This is because of the advances in fabrication, blends (both miscible and non-miscible), fibre reinforcement, etc. Thus films with up to 11 different polymer layers have been developed. 

As the demand for natural fibres declined due to the availability of synthetics, so did the supply of sisal waste and thus hecogenin. In due course, hecogenin became a more valuable commodity than sisal, and efforts were directed specifically towards hecogenin production. This has resulted in the cultivation of Agave hybrids with much improved hecogenin content. 

PE, being a commodity polymer, is used in its different physical forms viz. fibres, sheets, membranes, moulds with different backbone chemical configurations (LPE, LLDPE, LDPE, HDPE, UHMWPE, UHSPE etc). Each of these forms of PE requires surface modification at some stage of application. The surfaces of PE fibres are often modified to make them compatible in the composites, whereas PE sheets/tapes are modified to achieve adhesion. Moulds are frequently surface-modified for probability and membranes for selective permeation. In the same way, different chemical configurations of PE, by the virtue of their properties, are used for different applications after surface modification. 

PLA is a polymer that may not be well suited to injection moulding. Its rate of crystallisation is too slow to allow cycle times typical of those for commodity thermoplastics such as polystyrene. Stress induced crystallisation that can enhance PLA crystallisation is better suited to processes such as fibre spinning or biaxial orientation of film. 

The primary economic rationale underlying the production of cotton is the trade in cotton fibre, which accounts for around 8o% of a cotton farmer s mcome In addition to fibre, the world s cotton farmers produce around 34 million tonnes of cottonseed every year . This high protein commodity is not only used as an animal feed, but is also a source of cottonseed oil around 3.1 million tonnes is used in the preparation of food each year . In total, cottonseed oil represents approximately 8% of the world s vegetable oil consumption ", providing the major source of fat and oil in Mali, Chad, Burkina Faso, Togo, Ivory Coast, and Cameroon, and forms a significant part of the diet of the Middle East (3.8 g/day), Far East (0.5 g/day), and Latin America (0.5 g/day). In total, as much as 65% of harvested cotton produce may enter the human food chain. ... 

La demonstration donnee plus haut montre en mime temps que la classification des fibres constants tordus X sur S, quasi-isotriviaux et de type I, est equivalents k celle des fibres principaux galoisiens sur S, de groups G = Aut(l). C est mime lk une equivalence de categories, mais qui peut Itre mise sous une forme plus commode comme dans SGA1V. Pourceci, supposons S... 

In recent times, commodity thermoplastics have become signiflcant contenders as matrices for glass fibre composites where environmental resistance is sought for example, polypropylene is now available in a pre-preg form for fusion bonding. Since it has low polarity and is also partially crystalline, moisture absorption is very low. 

Unreinforced thermoplastics are ideal for mass production processing technology and together they constitute the great majority of plastics usage worldwide, although more than half of the output consists of commodity plastics, not intended for durable products. Although thermoplastics can be reinforced with fibres, they have until very recently not been well repre-... 

The nylon market can be divided into two segments resin products and fibre products. The total consumption of nylon in Western Europe was 913,000 tons in 1993, of which 560,000 tons were fibre products divided among textiles, carpets, and industrial fibre [22]. The total annual nylon consumption, as well as that of other engineering plastics, is small compared to that of high-volume commodity thermoplastics for example, the consumption of LLDPE/LDPE for 1993 was 5,548,000 tons [22]. Engineering plastics therefore constitute a minor share of the total plastics waste. Nevertheless, for an environmentally responsible company it is necessary to develop a clear strategy for the recycling of products and to help their clients do the same. 

Nylon resins have their primary applications in under-the-bonnet automotive applications and in durable goods, while nylon fibres are primarily used in textiles and carpets. These are all applications of lower volume compared to commodity plastics, with more or less complex material composition, and with disposal patterns that make them difficult to be recovered economically in sufficient amounts. 

Many of the commodities we take for granted are uniaxialfy oriented crystalline pofymers. Those we use most are the synthetic fibres—nylon. 

In terms of tonnage and use, poly(ethylene terephthalate) is these days virtually a commodity plastic, with widespread, large volume, use in food packaging, beverage bottle and fibres. Other aromatic polyesters have increased in volume production over the last decade or so, such as poly( butylene terephthalate) and poly(ethylene naphthalate). There is also the promise of large quantity use of the most recently commercialised member of the family, poly (trimethylene terephthalate). 

Due to their high molecular masses, macromolecular substances (polymers) show particular properties not observed for any other class of materials. In many cases, the chemical nature, the size, and the structure of these giant molecules result in excellent mechanical and technical properties. They can display very long linear chains, but also cyclic, branched, crosslinked, hyperbranched, and dendritic architectures as well. The thermoplastic behaviour or the possibility of crosslinking of polymeric molecules allow for convenient processing into manifold commodity products as plastics, synthetic rubber, films, fibres, and paints (Fig. 1.1). 

Shebani et al. [20] noted that removing extractives improved the thermal stability of different wood species. Therefore, using extracted wood for the production of wood-plastic composite (WPCs) would improve the thermal stability of WPCs. Because wood and other bio-fibres easily undergo thermal degradation beyond 200°C, thermoplastic matrix used in the composites is mainly limited to low-melting-temperature commodity thermoplastics like polyethylene (PE) and polypropylene (PP). However, the inherently unfavourable thermomechanical and creep properties of the polyolefin matrix limit some structural applications of the materials. 

Although composite forms of pipe may not have reached the same level of growth and widespread application as the commodity thermoplastic pipes, they have penetrated important market sectors and often attain a premium value. Composites can offer high performance for specific requirements. In the case of high pressure applications they are an alternative to steel pipe, especially where corrosion resistance and weight reduction are required. The chemical engineering construction industry with its need for conveyance of various fluids and applications in demanding environments, is a major consumer of composites, particularly fibre reinforced pressure pipes. 

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