«EUROPEAN COMMISSION Integrated Pollution Prevention and Control (IPPC) Reference Document on Best Available Techniques for the Textiles Industry July 2003 ...»
1.3 Carpet 1.3.1 Sector organisation The strong specialisation of this well integrated sector has already been mentioned. The carpet manufacturing, carpet yarn spinning and associated dyeing industry can be divided into a number of basic sub-sectors, although there may be considerable variations. All sectors may process combinations of 100 % synthetic fibre, 100 % natural fibre and/or blends of the two, as many of the processes and techniques used are not fibre specific.
As Table 1.4 shows there are five main different categories of companies where wet processes
are normally carried out (in italics in the table):
· commission loose fibre dyehouses · commission yarn dyehouses · integrated yarn manufacturing mills, which in addition to the dyeing processes perform onsite conversion of the loose fibre to yarn, selling the finished yarn as end-product · commission piece dyeing mills · integrated carpet manufacturing mills, which carry out all the mechanical processes, dyeing and finishing operations required to convert natural and synthetic fibres into finished carpet.
Table 1.4: Basic structure of the carpet manufacturing industry [32, ENco, 2001] Table 1.
5 indicates the locations of trading entities within the EU. Note that individual units may be part of a larger group, providing services to other members of the same organisation. In a similar way, a yarn spinning company with its own dyeing facilities may, if production schedules require, also have work carried out by a commission dyer or may carry out commission work for other companies if spare capacity is available.
Table 1.5: Sector Location and number of trading entities within the EU [32, ENco, 2001] 1.
3.2 Production and economics As Figure 1.3 shows, European carpet industry accounts for 38 % of world production (after the United States, with 58 %).
4% Figure 1.3: Worldwide production of carpets and rugs in 1999 [63, GuT/ ECA, 2000] Belgium, France, Germany, the Netherlands and the United Kingdom are all major producers for both internal EU consumption and world export markets. European carpet production exceeds carpet consumption by a significant margin (Figure 1.4), indicating the importance of export markets to the European industry.
Figure 1.4: Carpet production and consumption in some EU Member States [32, ENco, 2001] Among the three typical end-products of the carpet manufacturing industry - tufted carpet, woven carpet and needle felts - tufted carpets account for 66 % of EU production.
This is shown in the 1995 production below in Figure 1.5 and Figure 1.6.
Figure 1.5: European carpet and rug production in 1995 for the major producers of carpets and rugs in Europe [63, GuT/ ECA, 2000] Figure 1.
6: Total carpet and rug production in Europe in 1995 [63, GuT/ ECA, 2000]
1.4 Main environmental issues The main environmental issues arising from the activities in the textile industry which are covered in this document regard primarily emissions to water and air and energy consumption.
Among these, water is the most important concern. The textile industry uses water as the principal medium for removing impurities, applying dyes and finishing agents, and for the generation of steam.
Losses to the product are negligible, therefore, apart from a minor amount of water which is evaporated during drying, the bulk is discharged as aqueous effluent. The main concern is therefore about the amount of water discharged and the chemical load it carries.
An overview of these environmental loads is given in Table 1.6. The reported data have been extrapolated to European level from the results of a research study in Germany and Austria.
Natural fibres impurities (including biocides) and associated 50000 - 100000 material (e.g. lignin, sericine, wax, etc.) Sizing agents (mainly starch, starch derivatives, but also 80000 - 100000 polyacrylates, polyvinylalcohol, carboxymethylcellulose and galactomannans) Preparation agents (mainly mineral oils, but also ester oils) 25000 - 30000
Special auxiliaries with more or less ecotoxicological properties 5000 Source: [77, EURATEX, 2000] Table 1.6: Main charging loads from textile industry in Europe From the reported figures it appears that a large percentage of the total emission load from textile industry activities is attributable to substances that are already on the raw material before
it enters the finishing process sequence. Typically these are:
· sizing agents · preparation agents · natural fibres impurities and associated material.
Sizing agents are used to assist the weaving process. They are removed from the woven fabric before the finishing process, thus producing high levels of organic load in the water.
Preparation agents and spinning oils, are applied to fibres in various steps of the process, from the manufacture of the fibre itself (for synthetic fibres only) to the formation of the yarn. These organic substances are removed during pretreatment at the finishing mill either through wet processing (washing) or through dry processing (heat-setting). In the former case they contribute to the increase of the organic load of the final water effluent, in the latter case they become airborne.
All natural fibres contain a percentage of impurities and associated material. Associated materials are an essential part of natural fibres (e.g. grease for wool, pectin and hemicellulose for cotton, lignin for flax and sericine for silk). Impurities are metals, mineral and pesticides. All these substances have to be removed from the fibre before it can undergo finishing processes.
They therefore also have the potential for considerable environmental impact.
The input of chemicals and auxiliaries added at the finishing mills can be up to 1 kg per kg of
processed textiles, which appears to be high. The range of these substances is very extensive:
the latest issues of TEGEWA lists more than 7000 auxiliaries. However, as shown in Figure 1.7, in a typical finishing mill, 80 % of the annual consumption is covered by only 20 % of the product types used.
Figure 1.7: Auxiliaries pattern usage in a typical finishing mill [179, UBA, 2001] On the basis of the data reported in Table 1.
6, among the products applied during the process, the highest environmental loads arise from salts, detergents and organic acids (in that order).
Dyestuffs are not mentioned in the table because they do not represent a significant load compared to other substances used in the process. Nevertheless they are responsible for the colour of the effluent – which is mainly an aesthetic problem, although high doses of colour may also reduce light transmission to aquatic plants. Their presence in the water is therefore important, not only because of the colour, but also in relation with other environmental concerns (e.g. difficult-to-eliminate organic load, AOX, metals), particularly for certain classes of dyestuffs.
A number of chemicals that may be used in the textile process are worth specifically mentioning
for their potential negative effects on the environment. These are:
· alkyl phenol ethoxylates (detergents, wetting agents, levelling agents, etc.): their metabolites (octyl- and nonyl phenols) are highly toxic to aquatic life and are reported to disturb the reproduction of aquatic species by disrupting the endocrine system (octyl and nonylphenol are on the list of “Priority Substances” targeted for priority action under the Water Framework Directive 2000/60/EC, in particular nonylphenol is identified has “Priority Hazardous Substance”) · polybrominated diphenyl ethers and chlorinated paraffins (flame retardants), halogenated phenols and benzenes (reagents in the production of flame retardants): some members of these classes of substances (e.g. pentabromodiphenylether, C10-13 chloroparaffines) have already been identified as “Priority Hazardous Substances” for their toxicity, persistency and liability to bioaccumulate or they have been evaluated under the scope of Regulation (EEC) 793/93 on the evaluation and control of the risks of existing substances. For other members of these classes the debate about their potentially negative effects on the environment is still on-going (see Section 8.8.4)
· mothproofing agents based on permethrin and cyfluthrin (carpet sector) and other biocides:
these are highly toxic to aquatic life · sequestering agents such as EDTA and DTPA and NTA: these are capable of forming very stable complexes with metals (EDTA and DTPA are also poorly bioeliminable) · chlorine and chlorine-releasing compounds such as sodium hypochlorite (bleaching agent) and sodium dichloroisocyanurate (wool anti-felting agent): these are capable of reacting with organic compounds to form adsorbable organic halogens (AOX) · metal-containing compounds such as potassium dichromate · substances with carcinogenic potential, such as a number of aromatic amines, formed by cleavage of some azo dyes (see Section 18.104.22.168), or vinylcyclohexene and 1,3-butadiene, which can be present in polymer dispersions due to an incomplete reaction during polymerisation · carriers such as trichlorobenzene, o-phenylphenol, etc.
It is reported that [77, EURATEX, 2000]:
· more than 90 % of the organic chemicals and auxiliaries in pretreatment and dyeing operations does not stay on the fibre, whereas the reverse is true in the finishing treatment · nearly 90 % of the organic raw material load entering the textile process ends up in the waste water, the remaining amount being released to air.
With regard to emissions to air, volatile organic compounds are released from particular
activities such as:
· printing processes, in cases when organic solvents are used (e.g. they are contained in pigment printing pastes) · cleaning with organic solvents · heat treatments (e.g. thermofixation, drying, curing) when the textile materials contain substances that evaporate or degrade thermally (for example, oils, plasticisers, finishing agents and residues from upstream processes). Emissions of formaldehyde and uncombusted methane can be particularly significant in poorly maintained, directly heated stenters · vulcanisation of the backing layers (carpet sector).
Moreover, emissions of CO2, SOx, NOx and particulates associated with the on-site burning of fossil fuels to produce thermal energy are also to be taken into account.
Energy is consumed primarily in raising the temperature of the baths (e.g. pretreatment, dyeing, etc.) and in drying and curing operations. To this aim steam is produced on-site. Electrical energy is required for driving the machinery.
2 APPLIED PROCESSES AND TECHNIQUESThe textile chain begins with the production or harvest of raw fibre. The basic steps in this chain are schematically represented in the following diagram and will be described in this chapter.
Figure 2.1: General diagram of processes in the textile industry The main part of this chapter will describe those treatments that are broadly referred to as "finishing processes" (that is pretreatment, dyeing, printing, finishing and coating, including washing and drying).
As the diagram shows, they can take place at different stages of the production process: the substrates for finishing can be fabrics, yarns or loose fibres.
“Textile finishing” cannot be defined as a standard sequence of treatments, but rather is a combination of unit processes that can be applied within the production of a textile product, depending on the requirements of the final user. For this reason finishing treatments will be described (from Section 2.6 to Section 2.11) as unit processes without considering the possible sequences in which they can be applied.
Textiles Industry 15 Chapter 2 In the second part of this chapter (see Section 2.14) a distinction has been made between the carpet finishing sector and the rest of the finishing industry. Some typical categories of industries have been identified within each sector. The wool scouring industry has also been identified as a stand-alone sector. These categories have typical features that are described in brief.
As well as fibres, the raw materials of the textile industry include a wide range of chemicals and auxiliaries. These chemicals and auxiliaries are often not process-specific and can be found in different steps within the process cycle. For this reason it has been considered more practical to report the description of these issues in separate annexes (ANNEX I Textile Auxiliaries and ANNEX II Dyes and Pigments). Only general information about textile raw materials, including common procedures for storage and handling is given in this chapter.
In the same way, because most of the machines have a multifunctional use within the
production cycle, equipment is also described in a specific annex (ANNEX III Wet Processes:
Machinery and Techniques).
Two general categories of fibres are used in the textile industry: natural and man-made. Manmade fibres encompass both purely synthetic materials of petrochemical origin, and regenerative cellulosic materials manufactured from wood fibres. A more detailed classification
of fibres is:
Fibres included in this document are described in more detail below, highlighting in particular the typical impurities present on them. Part of these impurities will enter the textile process and will influence the associated emissions.
22.214.171.124 Polyester fibres (PES) Polyester fibres (PES) are made of linear macromolecules containing at least 85 % of an ester in
the chain. To date three polyester polymers are commercially available:
· poly(ethylene terephthalate) (PET), which is based on ethylene glycol · poly(butylene terephthalate) (PBT), which is based on butyl glycol · and polytrimethylene terephthalate (PTT), which is based on trimethylene glycol.
However, only one of these three polymers, poly(ethylene terephthalate), also known as PET, has so far been widely applied in the textile industry. Therefore in the following sections, unless otherwise specified, the term PES is used to indicate standard polyester fibres based on PET.
PET fibres have a very high degree of crystallinity, which allows for excellent heat-resistance and other mechanical properties. On the other hand, this compact structure inhibits the diffusion of the colourants into the fibre during dyeing. As a result, PET fibres cannot be dyed below 100 °C, unless dyeing accelerants (so-called carriers) are used. Carriers are harmful for the environment and in many cases are toxic for humans. Their use is now in decline, but it has been common practice for many years (see also Sections 126.96.36.199 and 8.6.7).
Carrier-free dyeable PES fibres are now available on the market. They include the “modified PES fibres” and the PTT fibres (see list above). “Modified PES fibres” are based on PET.
Thanks to physical and chemical alterations made to the structure of the fibre during the manufacturing process, they show lower crystallinity, which makes them easier to dye without need for carriers. Because of their high cost, however, these fibres are applied only in specific segments of the market.