20240830145908.gif)
Worker safety and chemicals
Potential risk of injury due to hazards associated with chemicals includes both immediate and chronic exposure. Hazards resulting from worker exposure to solvents and dyes require careful design of textile mills to protect human health. The problems associated with most of the chemicals are primarily related to skin contact with or inhalation of harmful chemicals.Exposure and toxic effects should be avoided, preferably through prevention
Adoption of worker Training for pollution Abatement; The training programs should include handling of chemicals, correct procedures for pasting, dissolving, and emulsifying of chemicals. These procedures should be subject to auditing and record keeping.In addition, policies regarding receipt, storage, and
About theauthor:
Mr. AbhishekJadhav is a student of M.Tech. in Fibre and Textile Processing in Mumbai.
5.1)Flame retardants
Fire retardancy involves the disruption of the burning process so that it is terminated within an acceptable time period. In designing polymeric flame-retardant, three approaches can be adopted:
1. Designing the basic polymer so that exposure to heat and oxygen will not produce combustion. This requires thermally stable polymers with high decomposition temperatures. 30
2. Transforming the existing polymer with either chlorination or substitution or Polyol. (This category is called the reactive type flame-retardant.) 37
3. Adding either inorganic salts or organic compounds so that the polymer performs satisfactorily when exposed to fire. (This category is called the additive type flame retardants).Silicone is considered a universal additive to improve the flammability properties of polymers. The uniqueness of silicon flame-retardant is that the hydrogen chloride formed in the combustion zone immediately takes part in flame inhibition and is thus very effective. Flammability of a large number of materials is reduced in the presence relatively small concentrations of silica gel and potassium carbonate. 29, 20
Flame-retardant finishing has become more and more important and is compulsory for some articles. Flame-retardant treatments should protect the fiber from burning, without modifying the handle, the color or the look of the fabric.
They are generally applied to cotton and synthetic fibers (e.g. they are important in the furniture sector for upholstery fabric). In some specific cases, in particular in the carpet sector (e.g. contract market, aviation), they can also be required for wool, even though this fiber is already inherently flame resistant. Flame-retardant properties are achieved by the application of a wide range of chemicals, which either react with the textile or are used as additives.
Conclusions
Textile wet processing industry being the chief cause of pollution needs to be looked carefully from ecological point of view. Eco-substitutes for these chemicals will not only help the consumer but also the society,which is directly, affected by it. Also a close look at workers safety should be given, since they are the first who get affected by any immediate exposure. Some substitutes are even better and economical as far as their precursors are concerned. Hence use of such products should not be delayed. From environment and ecological point of view the use of enzymes also serve as substitutes, especially for preparatory process. These eco-friendly auxiliaries however are difficult to imply because of technical and cost issues. But the latest technologies as well as the impetus for environment care will definitely make these substitutes grand success. The motto of the textile process should then be Substitution is better than cure "
Reference:
1) Achawal W.B; Colourage annual (1998), 97.
2) Nolan Etters; colourage annual (1998), 87.
3) Shenai V.A; Colourage September (2002), 61.
4) Nadiger G.S.; Indian journal of fiber and textile research March-June (2001), Vol.26, 55.
5) Natrajan T.S.; Colourage June (1998), 17.
6) Doshi Rashesh, Shelke V.; Indian journal of fiber and textileresearch March-June, (2001), Vol.26, 202.
7) Nalankilli G.; Colourage October (1998), 17.
8) Patel Sudhakar B.. Colourage December (1996), 57.
9) Shenai V.A, Indian journal of fiber and textile research March June (2001), Vol. 26, 50.
10) Saraf Naresh M. ;.Alat Deepak V .colourage September (1998) 27.
11) Teli M.D.; landge Sachin M.; Aich Arnab. Indian journal of fiber and textile research March-June (2001) ,Vol.26 ,101.
12) Schramm Christian,; Bischof Sandra Vukusic; katovic Drago.; Coloration Technology (2002).,Vol. 118, 244.
.Mairal A.K ; .Patel M.J, ,Man .made textiles in India March (2001),103.
mixing, should be established. This training helps to keep wastage within the factory to minimum, and encourages workers to suggest other improvements, which reduce pollution.
1.2 Chemicals Especially Used in Textile Wet Processing
Textile preparatory process includes:
2.1) Desizing
The sizes have to be removed from the fabric because they interfere with subsequent processing steps. Three methods frequently used in textile processing are acid desizing, enzyme desizing, and oxidative desizing. Good desizing is the first and most important step to achieve a good and soft washing result. Desizing operations represent large contribution to pollution, accounting for 40-50 % of the total pollution load from preparatory processing. The use of acrylates as a size in place of starch reduces the BOD, due to the recovery of size. 2, 3, 7
Starches can be partially substituted by polyvinyl alcohol to reduce pollution in effluents. The use of low viscosity sizes, such as PVA, CMC enables the recovery instead of up to 50% of the size in the effluents of the desizing process. The use of newer enzymes, which degrade the starch size to ethanol of anhydroglucose, enables the recovery of ethanol by distillation, thereby reducing the BOD load in the desized effluent considerably. Acids should be replaced by enzymatic and/or oxidative desizing to render the vegetable or animal size water-soluble (hydrolysis), starch from all sources can be removed. 9, 19
2.2) Scouring: Scouring is typically performed in an alkaline solution and high temperature environment. The removal of natural impurities is based upon saponification at high pH. The removal of natural impurities can be done in a single process or can be combined with desizing and/or bleaching. This makes the fabric more absorptive without undergoing any chemical or physical change. 2, 5, 6
The main processes occurring during scouring are
1) Proteins are hydrolysed into soluble degradation products
2) Simpler ammonia compounds are hydrolyzed to ammonia.
3) Saponifiable oils are converted into soaps.
4) Pectose and pectin are changed into soluble salts of pectic or metapectic
5) Dust particles are removed and held in stable suspension form in the kier liquor by the detergent present.
6) Unsaponifiable waxes and oils are emulsified by the soluble soaps formed from saponifiable oils
Ways to minimise pollution in scouring:
1) The optimum amounts of alkaline recipes should not be exceeded.
2) Alkalis should be recycled and reused as much as possible; rinsing water should be reused for preparing the scouring bath. 9
3) Combining the desizing and scouring processes can save water and energy and reduce processing time.
4) A reduction of 25% in sodium hydroxide can be obtained by substitution with sodium carbonate.
5) Alkylphenolethoxylates (APEO) in detergents and dispersants should be substituted by readily biodegradable surfactants, or should at least not reach the final effluent. Similar restrictions for other non-readily biodegradable surfactants should be considered.
6) Solvents having environmental impact that is more damaging than available alternatives should be avoided.
7) Mineral acids (sulphuric acid, hydrochloric acid) should only be used for neutralisation when no better options are available. 18
2.3) Bleaching
Almost all fabric containing cellulosics are being bleached to remove the natural coloured matter. After scouring, cotton becomes more hydrophilic. However, the original colour stays unchanged due to coloured matter that cannot be completely removed by washing and alkaline extraction. When the material has to be dyed in dark colors it can be directly dyed without need of bleaching
Three chemicals are commonly used:
1) Hydrogen peroxide (H2O2)
2) Sodium hypochlorite (NaClO)
3) Sodium chlorite (NaClO2).
Ways to reduce pollution in bleaching:
1) Fabrics that need to be colored in deep shades should not be bleached extensively, thus reducing the consumption of bleach and consequently reducing the pollution load.
2) The use of continuous knit bleaching ranges, to replace batch preparation of knitted fabrics reduces the water and chemical consumption, and consequently contributes to less pollution load.
3) Peroxide bleaches should be used instead of reductive sculpture- containing bleaches which are more hazardous.
4) Hydrogen peroxide (H2O2) should be used as the bleaching agent in preference to chlorine- containing compounds, such as hypochlorite. Also, the use of hypochlorite is banned by many certifying agencies. Hydrogen peroxide also minimises the content of hazardous organhalogen substance in the final effluent, and eliminates a toxic and hazardous chemical from the workplace and improve working environment.
5) The wetting agents, emulsifiers, surfactants and all other organic chemicals should be readily biodegradable without producing metabolites, which are toxic to aquatic species.
6) The installation of holding tanks for bleach bath reuse, where the bath is reconstituted to correct strength after analysis by titration. Using this technique decreased BOD over 50%, and reduced the water use.
7) In case of bluish and bright qualities (76% on Berger-scale) of fabrics, alternatives for chlorine bleach are not always available. Hazardous organohalogen substances production needs to be reduced or treated adequately.
8) Precursors (proteins and pectines) should be removed in order to prevent the formation of hazardous organohalogen substances in bleaching with chlorine.
9) Hydrogen peroxide in effluents from bleaching can be reused in the treatment of the (combined) wastewaters as a clean oxidant in the activated sludge process or chemical oxidation processes. 16
2.4) Mercerisation
Mercerisation is the treatment of pure cotton fabrics or yarn with a strong caustic soda solution (usually 280-300 gpl) to improve strength, dye substantivity, strength and smoothness. The effects of mercerization
1. Improved luster
2. Increased ability to absorb dye
3. Improved reactions with a variety of chemicals
4. Improved stability of form
5. Improved strength/elongation
6. Improved smoothness
Ways to minimise pollution in mercerising
1) Dilute alkali from mercerizing should be reused in scouring, bleaching or dyeing operations, so that discharges from alkaline treatment can be minimised, resulting less polluted effluents.
2) Liquid ammonia is a low pollution substitution for conventional mercerisation (NaOH).
3) Heavy cotton fabrics treated with liquid ammonia require less dye for a given depth
of shade, and consequently contribute to pollution abatement due to using less chemical for the same requirement. 19
4) Alkali should be recovered and recycled or reused after regenerative treatment to remove dirt (coagulation, flotation, microfiltration, nanofiltration) and after concentration.
3) Dyeing
Several auxiliary chemicals are added to the bath during the dyeing processes.
The mixtures are often developed to solve problems specific to the process. Some specialty chemicals are developed to counteract or enhance the effects of other chemicals. In other cases, the specialty chemicals cause side effects that are detrimental to the overall process. For example, wetting agents are often added to preparation and dyeing steps to ensure penetration of chemicals. Apart from a few exceptions (e.g. the thermosol process, pigment dyeing, etc.), most of the emissions originating from the dyeing process are emissions to water. Water-polluting substances can originate from the dyes themselves (e.g. aquatic toxicity, metals, colour), auxiliaries contained in the dye formulation (e.g. dispersing agents, anti-foaming agents, etc.). Basic chemicals and auxiliaries used in dyeing processes are alkali, salts, reducing and oxidising agents, etc and residual contaminants present on the fiber (e.g. residues of pesticides on wool, spin finishes on synthetic fibres). 4, 8
Important precautions in dyeing for reducing pollution,
1) Dyes found to be containing PCBs (e.g. certain sources of Cu-phtalocyanine) should be substituted immediately.
2) Cadmium containing pigments should not be used.
3) Benzidine-based azo-dyes should not be used at all.
4) Carriers containing chlorine should not be used.
5) Reduction of dyes by sulphide should be avoided. Dichromate oxidation of vat dyes and sulphur dyes should be substituted by peroxide oxidation.
6) Azo dyes, which can, under reductive conditions, release aromatic amines, which are suspected carcinogens, should not be used.
7) Halogenated solvents and dispersants for dyes and chemicals should be substituted where possible by water-based systems.
8) Metal containing dyes (Cu, Cr, Ni, Co, etc.) should be substituted by other dyes or techniques.
9) In order to minimize the discharges of BOD, COD, etc. as well as of colored substances in case of repeated dyeing, the rinsing bath should be used as next dye bath, it the after-treatment chemicals are compatible with the dye bath chemicals.
4) Printing
Printing, like dyeing, is a process for applying colour to a substrate. However, instead of colouring the whole substrate (cloth, carpet or yarn) as in dyeing, print colour is applied only to defined areas to obtain the desired pattern. This involves different techniques and different machinery with respect to dyeing, but the physical and chemical processes that take place between the dye and the fiber are analogous to dyeing.
Pollutant encountered in exhaust air are
1) Aliphatic hydrocarbons (C10-C20) from binders.
2) Monomers such as acrylates, vinylacetates, styrene, acrylonitrile, acrylamide, butadiene.
3) Methanol from fixation agents.
4) Other alcohols, esters, polyglycols from emulsifiers.
5) Formaldehyde from fixation agents.
6) Ammonia (from urea decomposition and from ammonia present, for example, in pigment printing pastes).
7) N-methylpyrrolidone from emulsifiers.
8) Phosphoric acid esters.
9) Phenylcyclohexene from thickeners and binders. 28
5) Finishing
Ways to reduce pollution in finishing,
1) Finishing chemicals should be reused whenever possible
2) Reducing the use of formaldehyde releasing chemicals as much as possible. Formaldehyde should be replaced with polycarboxylic. Alkylphenol should be replaced with fatty alcoholethoxylates
3) Replacement of acetic acid (used for pH adjustment in resin finishing bath) with formic or mineral acids to reduce BOD load.
4) Using formaldehyde- free cross-linking agents for cellulose textiles and formaldehyde- free dye fixing agents
1) Using formaldehyde scavengers during application and storage of resin finished goods.
2) Dimethylol or dihydroxythlene urea used in anti-wrinklefinishing should be substituted by polycarboxylic acids, mainly 1,2,3,4-butanetetracarboxylic acid or glyoxales.
3) MAC Complexing agents like DTDMAC, DSDMAC, DHTDMAC used in softening finishing should be replaced with cellulose enzymes.
4) Asbestos, halogenated Compounds like bromated diphenylethers and heavy metal containing compounds used in flame retardant finishing should be replaced by inorganic salts and phosphonates. 20
5) Biocides such as chlorinated phenols, metallic salts (As, Zn, Cu, or Hg), DDE,DDT and benzothiazole used in preservation finishing should be substituted by UV treatment and, or mechanical processes or by enzymatic finishing.
6) In case of using fireproofing chemicals, the best technique is that which consumes minimal amounts of water (such as Vacuum, back coating, foam) or techniques leading to minimal of residues particularly (e.g. foam).
7) The use of hazardous chemicals for the conservation of textiles should be minimized, either through substitution or through tailor-made selective use to only those textiles which are exposed to possible environmental degradation.
8) Limitation of the chlorination stage in wool shrink proofing by substitution of other techniques (e.g. peroxygen treatment).
9) It is more recommended to build in the finishing chemicals into the fiber during production or during spinning than applying the finish at a later stage
10)Concentrated residues from finishing should not be discharged. They should be reused or treated as waste.
In case of mothproofing agent-contaminated water, the volume of bath should be reduced by employing e.g. mini-bowls, modified centrifuges or foam treatment during back coating laminating or carpets. 26
In case of mothproofing finish, wastewater should be treated in such a way that excessive sludge is avoided. This sludge should preferably be incinerated as chemical waste or detoxified by wet (catalysed) oxidation
5.1)Softening
Softeners - Softeners give a soft feel to the fabric. They are also used with starch and other additives to give softness and body to the fabric. Different types of softeners like cationic, reactive and emulsion are available. Except silicone softeners, all others are temporary and get washed off after two or three washes. Silicones also give water repellency, which is fast to washing and dry cleaning. It is compatible with other finishing agents. It can be easily applied on the cloth. Air porosity is not altered in fabrics treated with silicones. 1
Problems associated:
1) Many times the exhaustion of the softening agent is low which causes health problems if the softener is hazardous.
2) Unpleasant odor of the softening agents.
3) Skin irritation.
4) Softener is not biodegradable.
5.1)Durable press finishes
Purpose:
Cellulosic fibers like cotton dont have natural bridges or cross-links between them. When deformed under stress (washing or wrinkling) the cellulose chains do not return to their original position. Therefore durable press finishes are given to the cotton fabrics to impart smooth drying properties and dimensional stability. Cross-linking agents are used to produce wash and wear and durable press properties. They are applied on fabrics which can be washed easily and dried to a smooth state. They exhibit excellent crease recovery. For preparing rein finished fabric the textile is impregnated with a solution of resin containing a catalyst, dried and cured at high temperature Examples: Urea formaldehyde resin, dimethyl dihydroxy ethylene urea. 12,22,23,25
Problems associated with durable press finish:
1) Most of the DP finishes contain formaldehyde as a cross linking agent . Formaldehyde is at toxic substance when present in gaseous as well as dissolved form.
2) Formaldehyde is believed to be carcinogenic causing lung cancer when the test was performed on rats.
3) It is a severe eye irritant dissolves in eye fluid resulting in inflammation.
Remedy:
1) Partial replacement of N-methylol group with zero formaldehyde content. 1,3,9
2) Formaldehyde scavengers.
3) Efficiency of local ventilation.
4) Control of atmospheric conditions since high temperature and humidity increase rate of formaldehyde release.
5) Extensive use of steam pressing and forming operations in garments forming.
Comments