sirSATCO Report 3: Textile Processing Techniques
In order to determine the true environmental impact of textile processing the main types of machinery in current u together with typical processing routes need to be described. The pollutants and waste generated by the process together with typical levels or concentrations emitted or discharged help to provide a more detailed picture of the polluting nature of the textile industry.
For convenience, the whole textile chain has been split into ven main ctions. The are fibre production, fibre to fabric, preparative treatments, textile coloration, finishing process, fabric aftercare and recycling and disposal.
• Fibre production – this includes details on cotton growing,sheep rearing, riculture and the generation of man-made fibres.
• Fibre to fabric- which contains information on the types of machinery ud in spinning, weaving, knitting and non-woven production.
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• Preparative treatments- which includes details of process such as desizing, scouring and bleaching.cas
• Textile coloration– contains information on the different methods ud for dyeing and printing.
• Finishing process– includes information on coating and lamination, wet chemical finishing and mechanical finishing process.
• Fabric aftercare– which contains information on the different types of commercial laundry and dry cleaning machinery ud.
• Recycling and disposal – looks at the process involved in textile recycling, the gregation techniques and the different end-us.
Fibre Production
parameterCotton is cultivated as a shrubby annual in temperate climates but can be found as a perennial in tree-like plants in tropical climates. The cultivated shrub grows from about one to two metres tall over a growing period of six to ven months.
neglectWarm and humid climates with sandy soil are the most suitable. Although cottton can be grown between latitudes 45 N and 30 S, yield and fibre quality are considerably influenced by climatic conditions, and best qualities are obtained with high moisture levels resulting from rainfall or irrigation during the growing ason and a dry, warm ason during the picking period. Rain or strong wind may cau damage to the opened bolls. Cotton producing areas vary in climate from arid to mi-humid. Some of the biggest include parts of
the USA, China, Russia, Brazil, Mexico, Egypt, Sudan, Turkey and India. African producers include the Ivory Coast, Nigeria, Uganda and Tanzania.
Every year, new ed is planted, the crop grown to maturity, the eds with their fibres harvested, the dead plants destroyed and the land prepared for the following ason. The lint or raw cotton, is s hipped to textile factories all over the world, while most of the ed is procesd for its food components (soaps, margarine and animal feed cake). Only a small quantity of ed is retained for planting.
Cotton is a key agricultural product in the world’s economy, and is particularly important to developing countries. Production in the Third World provides a livelihood to 125 million people. It ens
ures that developing countries have an important source of foreign exchange ($25 billion annually) and a major raw material to develop their own textile industries.
Cotton needs a lot of water to grow, over 50cm of rain in a ason. However, cotton can be grown with less rainfall by applying supplementary water from irrigation channels.
Pests in the cotton can be controlled by the regular application of pesticides sprayed onto the plants. Cotton is attacked by veral hundred species of incts. Limited inct control can be achieved by proper timing of planting, or by lective breeding of varieties with some resistance to inct damage. Chemical incticides, which were first introduced in the early 1900’s, require careful and lective u becau of ecological considerations but appear to be the most effective and efficient means of control.
Cotton plants are also subject to dias caud by fungi, bacteria and virus. The treatment of eds before planting is common, as is the practice of soil fumigation.
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A really good field of cotton ready for picking will yield about 1000 kg of cotton fibre per hectare. Yields vary, but the prent world average of only 400 kg per hectare could be improved. Crops could be incread without using any more land in developing countries if agricultural knowledge cou
ld be applied and supplies of pesticide and fertilir made available to the farmers there. Even in the more advanced countries, the improvements in ed varieties and farming techniques give better yields per hectare almost every year. The prent world production of cotton is about 13 million metric tonnes which is grown on about 32 million hectares.
On small farms cotton is hand picked. It is packed in loo bales and is marketed by farmers at local ed cotton markets. The buyer then provides the transport to national ginneries. In countries where labour costs are high and where the terrain is suitable, machine picking is ud. The machines collect immature bolls and other vegetable matter, which is called trash. To minimi the trash collected, the plants are sometimes sprayed with a chemical defoliant causing the leaves to drop prior to picking.
Ginning machines are designed to parate the cotton fibres from the ed. The paration of fibres from ed is effected by means of a row of circular saws passing through a ries of narrow grids. The saw teeth grip the fibres and draw them through the grids. The ed is too wide to pass through and the fibre is thus pulled from the eds.
Cotton is then baled in loads of 220kg. The bale which is fabric or plastic covered is cured by strong metal bands.
Wool is available in a wide range of fineness, crimp, length and colour. Types are denoted by quality numbers on a subjective scale related to fineness, spinnability, etc. Merino wool is usually about 60’s –64’s, crossbred wool is 48’s-60’s.
There are about 1000 million sheep of nearly 500 different breeds scattered about the world, with large concentrations in New Zealand, Australia, South Africa, South America, China and Russia. The British share of the world’s sheep is 3%, with a 2% share of the world’s wool, but British sheep have made contributions to the world’s flocks out of all proportion to the story the statistics alone tell.
In order to protect the sheep during its productive lifetime, regular treatment with pesticides is given in the form of a sheep dip. The pesticides, some of which are organo-phosphorus, can be harmful to humans and so great care must be taken when the sheep are being treated. Residual pesticides also find their way into surface and ground water supplies and are found in the waste liquors from raw wool scouring.
The basic steps in wool processing have remained unchanged for centuries. Wool obtained from different parts of the sheep varies in fibre fineness, length and crimp. There are variations between locks, or cohering bunches of wool, and between fleece from different areas of the sheep. The qualit
伞用英语怎么说y of wool obtained from the belly is short and burry; the shoulders yield the finest wool. Sorting is the paration of the different qualities of wool from the fleece. The most important property is usually fibre fineness, cloly related to softness of handle. The sorter unrolls the fleece on the sorters board, usually waist high, and cuts away any wool carrying tar or paint marks. He next removes the coarst wool, placing it in a parate basket, and finally reaches the fine wool on the shoulders. A sorter can generally sort up to 4500 kgs of Australian fleece in a week.
Flax requires a temperate climate free from heavy rains and frosts. Frequent moist winds during the growing ason are advantageous. Hot dry summers produce a short and harsh but strong fibre; moderately moist summers produce plants yielding fine, strong, silky linen.
Flax is difficult to grow becau of the soil preparation required before sowing, and the heavy applications of artificial fertilirs required. After a slow initial growth, the plants grow as rapidly as one inch per day for 30 to 40 days. Blossoms then begin to develop and stem growth ceas. Flax is normally a three month crop, although this growing time varies with climatic and other growing conditions.
It is attacked by veral fungal and viral dias, usually kept under control by chemical treatments
of the ed, or by cultivation of resistant varieties. Harvesting is usually carried out by pulling the plant from the ground. Pulling is considered superior to cutting since flax deteriorates at the cut. Yields of fibre per acre vary from 200 to 360 kgs.
Like other bast fibres, flax must be parated from the stalks by retting. Water retting, which is esntially bacterial, is practid in areas such as the Philippines, Taiwan and China; most of the crop grown in Russia and the United States is dew retted, which is predominantly fungal. In this method the harvested flax straw is left in the field and allowed to remain until the combined action of the moisture from dew and micro-organisms makes paration of the fibres possible. The process depends very much on the temperature and chemical nature of the water, but takes only six to eight days under controlled temperature conditions. After removal of the stalks from the retting medium, thorough drying is necessary to prevent further fermentation.
The retted and dried fibres are removed from the woody remainder of the stem by the process of scutching, in which the stems are first broken by passage through a ries of fluted metal rollers, and the fine pieces of the woody portion of the straw, called shives, are beaten out. About a tenth of the original flax stem is uful fibre.
Although the lifecycle of Bombyx mori is typical of most other silkmoth species, domestication over the ages has deprived the moth of its ability to fly. This feature is exploited in riculture to introduce an orderly quence into the whole cycle, for the moths can be put in desired places for egg laying.
The fully grown silkworm has two silk glands each filled with a concentrated solution of the silk proteins, fibroin and ricin, the latter forming a sheath around the former. The two glands unite in the spinneret, a minute aperture in the muzzle of the worm.
suddenlyImmediately prior to the process of pupation the worm first attaches silk fibre to various supports, to form a scaffolding, and then extrudes the silk thread and deposits it layer upon layer to form a cocoon around itlf. Most cocoons, except tho required for propagation purpos, are subquently heated by a process known as stifling to kill the chrysalis within and prevent the emergence of the moth which otherwi would make the cocoon unreelable. Following the stifling process the cocoons are inspected and graded, defective ones are parated for subquent treatment as silk waste.
Reeling consists of unwinding the fibre from veral cocoons together and reeling the baves so as to form a composite thread of the required denier. A Bombyx silk bave is only about 15 to 25 microns th
ick and it is too thin and weak to be ud singly. The reeling process consists esntially of softening the silk gum, by maceration in hot water, removing the loo outer layers until the free end of the bave has been located and then combining it with the baves from other cocoons.
Although much of the world’s silk is still reeled from hand operated basins, 99% of the silk produced in Japan (the world’s largest producer and consumer) is reeled on automatic reeling machines. With the machines the process is considerably less labour intensive.
Silk throwing involves the preparation of the raw silk into a form suitable for knitting and weaving. The first process is that of soaking the hanks in a warm emulsion of various oils and other softening agents in a slightly alkaline solution. During this process the oils are taken up by the silk gum. The objective is to make the yarns more supple and pliable. Following soaking and drying the hanks are rewound on to bobbins or cones. It is at this stage that twist is inrted to form different types of yarn.
Many silk fabrics are still produced on hand looms which can produce superior goods for which the purchar is obviously prepared t o pay the extra cost involved.
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Some 60% of the silk extruded by the silkworm is uless for the production of continuous filament y
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arns, and the spun silk process is bad on the utilisation of this material. The technique of spun silk production is quite distinct from that of thrown silk yarns, and many of the mechanisms involved in the process are cloly related to machines ud in the preparation and production of yarns from staple fibres such as cotton, wool, flax and jute. After degumming, cleaning a nd opening, the fibres are cut into short lengths and then combed into slivers. The are made into yarns by mixing, drafting and spinning.
The basic method of visco fibre production can be split into five stages. Firstly, sheets of cellulo in the f o rm of purified wood pulp are steeped in caustic soda solution and then presd to remove the excess and ground into crumbs. The crumbs are allowed to stand for a time during which ‘ageing’ occurs, the very long cellulo molecules are thus reduced in length to allow a satisfactory spinning solution to be prepared later.
The product ‘alkali cellulo’, is churned with the liquid carbon disulphide to form a soluble derivative of cellulo, cellulo xanthate. The crumbs turn orange in colour and are then dissolved in a cond caustic soda solution forming the syrupy liquid visco.
