«EUROPEAN COMMISSION Integrated Pollution Prevention and Control (IPPC) Reference Document on Best Available Techniques for the Textiles Industry July 2003 ...»
544 Textiles Industry Annexes Padding machines (foulards) are used to apply dyestuffs or other chemicals onto the fabric in open-width form. The fabric passes through the pad trough where it picks up the liquor. After leaving the pad trough, the fabric is squeezed between rubber rolls. The amount of liquor picked up depends mainly on the pressure produced by the two rolls, the speed at which the fabric is transported and the type of substrate. The level in the trough is automatically maintained to compensate for liquor picked up by the fabric. The liquor is kept in circulation to avoid differences in temperature and/or concentration.
Different designs of foulards exist: some examples are shown in Figure 10.11.
Figure 10.11: Foulard types [18, VITO, 1998] Padding is the most common application technique in textile finishing, but other application systems (see figure below) are more common in the carpet industry.
Due to their higher ecological performance, some of them are increasingly used in the textile finishing sector.
Figure 10.12: Illustration of some of the most important dye/finish applicators [211, Kuster, 2001] 10.
4.2.1 Pad-batch process (semi-continuous) This process includes an impregnation step on a padding machine.
After being squeezed, the fabric is wound onto a roll and stored at room temperature. The roll is kept in slow rotation until the desired chemical processes (e.g. fixation of the dyestuffs, etc.) are complete. At the end the fabric is washed in an open-width washing machine.
This process is commonly used for pretreatment (e.g. desizing) and dyeing (mainly with direct and reactive dyes). It is characterised by low water and energy consumption (about 50 – 80 % less than conventional systems) and good repeatability.
Figure 10.13: Schematic layout of a pad-batch plant [69, Corbani, 1994] 10.
4.2.2 Pad-roll process (semi-continuous) This process is similar to pad-batch, but in this case the fabric, after padding, passes through an infrared oven. It is then rolled and kept in slow rotation in a hot steam chamber until fixation, or other chemical processes are complete. The fabric is then washed in an open-width washing machine.
10.4.2.3 Pad-jig process (semi-continuous) This process is generally used as a dyeing technique, mainly used for heavy weight fabrics with direct and reactive dyes.
In this process the fabric passes through a padding machine where it is impregnated with the dyeing bath, then the dyestuff is fixed on a jigger.
Sometimes the fabric can be dried in a hot-flue drier after padding, before entering the jigger.
The application of the dyestuff by padding allows for homogeneous dyeing and time saving when compared to traditional jigger dyeing processes.
10.4.2.4 Pad-steam process (continuous) This technique is mainly used for scouring woven fabric and dyeing. It is particularly suitable for the application of direct, vat, sulphur and reactive dyestuffs.
It includes the following steps:
· impregnation by padding · steaming (at about 100 ºC) · additional impregnation of the fabric with developing agents (e.g. reducing agents in vat or sulphur dyeing) · washing and rinsing.
Figure 10.14: Schematic representation of a pad-steam plant (wet steam) for dyeing with vat dyes [186, Ullmann's, 2000] 10.
4.2.5 Pad-dry process (continuous)
This process includes the following steps:
· impregnation by padding · intermediate drying (optional) · fixation in hot-flue · washing.
10.4.2.6 Thermosol process (continuous) This process is specific for dyeing with disperse dyestuffs polyester or cotton/polyester blends.
The process includes the following steps:
· impregnation in the dyeing liquor · pre-drying in an infrared oven · drying in hot-flue · passage through a stenter frame for thermal fixation at 200 ºC of the disperse dyes to the PES.
An alkaline reductive aftertreatment is then carried out or, in the case of cotton/polyester blends, the second dye is developed according to the procedure typical of its class, using in general padsteam, pad-jig or pad-batch processes.
11 ANNEX IV: TYPICAL RECIPES (WITH SOME ASSOCIATED
EMISSION FACTOR) IN THE TEXTILE SECTOR
The following information is based on [179, UBA, 2001] with reference to:
[7, UBA, 1994] Schönberger, H.; Kaps, U.
Reduktion der Abwasserbelastung in der Textilindustrie UBA-Texte 3/94 (1994)
11.1 Pretreatment 11.1.1 Cotton and cotton blends
WOVEN FABRICEnzymatic desizing
Table 1: Standard recipe for enzymatic desizing of woven fabric consisting of CO and CO blends Removal of water-insoluble sizing agents by cold oxidative desizing It is a semi-continuous process. The liquor for oxidative desizing is added at room temperature in a padder with a pick-up of 70 – 80 %. Reaction takes place with a retention time of 16 - 24 h (max. 72 h). The fabric is then thoroughly rinsed.
KNIT FABRIC Pretreatment of knit fabric does not need desizing because sizing agents are not present.
“Light scouring” is applied if bleaching is not needed; i.e. it is applied for fabric to be dyed in dark shades (black, brown, dark marine or turquoise etc.). “Light scouring” is also called “alkali pre-washing”; a precise definition is not available.
Usually bleaching is only applied for full bleach qualities which are not dyed subsequently or which are dyed in light and medium shades. However, because of logistics some mills bleach all kind of qualities. In the case of continuous processes bleaching is usually performed in a single stage. There are exceptional cases in which the combined bleaching process with peracetic acid/hydrogen peroxide/optical brightener is applied.
In many cases so-called combination bleaching, consisting of a two-stage bleaching with sodium hypochlorite and hydrogen peroxide has been replaced by two-stage hydrogen peroxide bleaching and one-stage bleaching with reducing agents. An acidic pretreatment, which requires a lower dosage of complexing agents in the subsequent bleaching stage is usually carried out in one-stage, similarly to woven cotton fabric or cotton blends.
The consumption of chemicals for pretreatment of knit fabric is similar to that for woven fabric.
Table 8: Standard recipe for neutral/acidic demineralisation of knit fabric consisting of CO and CO blends “Light scouring” process (alkali pre-wash)
Table 11: Standard recipe for bleaching with hydrogen peroxide of knit fabric consisting of CO and CO Blends 11.1.2 Viscose
WOVEN FABRICUsually viscose is treated with alkali. Only exceptionally is subsequent bleaching with hydrogen peroxide carried out. Thereby the applied quantities of chemicals are lower than for cotton because viscose does not contain natural by-products which need to be removed.
Table 12: Standard recipe for alkali treatment of woven fabric consisting of viscose Table 13: Standard recipe for scouring of woven fabric consisting of viscose KNIT FABRIC Knit fabric consisting of viscose is not a common product. The standard recipe for bleaching concerns cotton. However the dosage of caustic soda and hydrogen peroxide is reduced to 40 - 70 %.
11.1.3 Man-made fibres (woven and knit fabric) Woven fabric and knit fabric consisting of man-made fibres are usually washed in order to remove sizing agents and preparation agents which are normally water-soluble. Scouring is not carried out. The application of bleaching of PES and PAN with chlorite is no longer common.
STANDARD RECIPES FOR WASHING (CONTINUOUS AND DISCONTINUOUSPROCESSES) Woven fabric
Table 20: Standard recipe for wool washing and felting Bleaching For full bleach qualities, the standard process for wool bleaching is the application of a combination of oxidation (hydrogen peroxide) with subsequent reductive bleaching (3 g/l reducing agent, e.g. stabilised sodium dithionite and 0.5 g/l surfactant). For wool pre-bleaching either hydrogen peroxide or reducing agents can be used. With regard to the standard recipe for wool bleaching it has to be stressed that the dosage of chemicals can vary considerably depending on time and temperature of the process.
Table 21: Standard recipe for bleaching of wool In some cases acidic hydrogen peroxide bleaching is applied. Then an activator instead of a stabiliser is used. After bleaching rinsing takes place and reductive bleaching (40 – 80 g reducing agents/kg wool) at 60 °C for 30 minutes is carried out. Finally optical brighteners can be added.
In general, especially for bleaching of yarn and knit fabric with hydrogen peroxide, stabilisers based on protein derivates and modified phosphoric esters (lecithine types) are used. These stabilisers also act as dispersing agents. Also fatty acid amides are in use; they do no stabilise the bleaching bath only but also serve as a softening agent.
Table 23: Standard recipe for the pretreatment for printing of wool with chlorine-containing substances Pretreatment without chlorine-containing substances
Table 4: Typical recipe for padding liquors for the application of vat and disperse dyestuffs (for dyeing of cellulosics/PES blends with one padding liquor)
Table 4: Typical composition of printing pastes with disperse dyestuffs
11.4 Finishing Typical recipes for padding liquors in textile finishing are summarised in Table 1, while Table 2 to Table 17 report the substrate emission factors to air for some common auxiliary formulations listed in the “Textile Auxiliaries Buyers’Guide” ([65, TEGEWA, 2000]).
Table 3: Substance specific emission factors to air (organic carbon and formaldehyde) of easycare finishing agents based on dimethyloldihydroxyethen urea derivatives
13 ANNEX VI: AUXILIARIES CLASSIFICATION TOOLS
13.1 Tegewa scheme The "Method of classification of textile auxiliaries according to their waste water relevance"
provides a logic system for the classification of textile auxiliaries in 3 classes of relevance:
Class I Minor relevance to waste water Class II Relevant to waste water Class III High relevance to waste water The main criteria for the classification are the content of certain harmful (including bioaccumulative) substances, biological degradation or elimination and aquatic toxicity of the sold products (see scheme on next page).
The introduction of the classification concept rests essentially on the following pillars:
· Classification by producers on their own responsibility, guided by the association of textile auxiliaries suppliers, called TEGEWA (TEGEWA = Verband der TExtilhilfsmittel-, Lederhilfsmittel-, GErbstoff- und WAschrohstoff-Industrie e.V., D-60329 Frankfurt) · Screening of correct classification of textile auxiliaries in the three classes by an expert.
· A monitoring report on the effectiveness of the voluntary commitment which will be communicated to the authorities. For this purpose numbers and quantities of textile auxiliaries classified in classes I, II and III and sold in Europe are collected by a neutral consultant from the manufacturers.
· The triggering of market mechanisms towards the development of environmentally sounder products.
It is not claimed that the classification concept allows a differentiated ecotoxicological evaluation of textile auxiliaries. The purpose of the classification concept is rather to allow users to select textile auxiliaries also from ecological aspects. Ecological competition is intended to trigger a trend towards the development of environmentally more compatible textile auxiliaries.
The German Association of the Textile Finishing Industry (TVI-Verband, D-Eschborn) is officially supporting this concept and has signed and published a self-commitment to recommend the textile finishing industries to use classified products only and preferably such of classes I and II (“TVI-Verband, 1997”).
A classification of the textile auxiliary is possible both on the basis of data of the preparation and on the basis of data of the ingredients by calculating mean values for the ingredients. For data to be newly determined, it is recommended to determine those data on the basis of the ingredients.
Footnotes mentioned in the classification scheme:
1. Problematic substances are
1.1 CMR substances which are - according to Annex I to Directive 67/548/EEC · classified as "carcinogenic" cat. 1 or cat. 2 and labelled with R45 (May cause cancer) or R49 (May cause cancer by inhalation), · classified as "mutagenic" cat. 1 or cat. 2 and labelled with R46 (May cause heritable genetic damage) or R60 (May impair fertility), · classified as "toxic for reproduction" cat. 1 or cat. 2 and labelled with R61 (May cause harm to the unborn child).
1.2 Ingredients which have an aquatic toxicity (definition see footnote 4) of 0.1 mg/l and are not readily biodegradable (definition see footnote 3),
1.3 Low-molecular halogen hydrocarbons (halogen share 5 %, chain length C1 - C12),
1.4 Arsenic and arsenic compounds,
1.5 Lead and lead compounds,
1.6 Cadmium and cadmium compounds,
1.7 Tri- and tetra-organotin compounds,
1.8 Mercury and mercury compounds,
1.10 EDTA, DTPA.
2. In connection with classifications made within this voluntary commitment, substances shall be considered "accumulative" which are labelled either with R-phrase 53 "May cause long-term adverse effects in the aquatic environment" alone, or with R53 in combination with other R-phrases.
3. Readily biodegradable = OECD tests 301 A-F with 60 % BOD/COD or CO2 formation, respectively, or 70 % DOC reduction in 28 days.
4. Aquatic toxicity of textile auxiliaries = LC 50 daphnia (if not available to be substituted by fish).
5. Biodegradable/eliminable = OECD test 302 B: 70 % DOC reduction in 28 days, or OECD test 302 C: 60 % O2 consumption, or Proof of a 70 % reduction in precipitation typical of sewage treatment plants.
For textile auxiliaries the evaluation "readily biodegradable (3)", "aquatic toxicity" (4), and "biodegradable/bioeliminable" (5) can be made not only on the basis of test data of the readyfor-use preparation but also on the basis of valid data obtained by calculating mean values for the various ingredients.
13.2 SCORE System
1. SUMMARY The score system is an administrative method of sorting chemicals on the basis of information especially from the chemical supplier's specification sheets. The sorting permits a priority selection of chemicals which, because of actual consumption and information on environmental behaviour, should be subject to closer examination.
The score system is based on the parameters usually considered to be the most interesting in connection with characterisation of substances injurious to the environment of industrial sewage. The parameter A is a score on the estimated amount of chemical, which is discharged into the environment as waste water. B is a score on biodegradability, and C is a score on bioaccumulation. The structure of the score system appears from the table in Chapter 2.
Together, A, B and C indicate the potential presence of the substance in the environment;