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Description
Surfactants (organic polar compounds with at least one hydrophobic part and at least one hydrophilicgroup) are widely spread in textile finishing industry. All types of surfactants (anionic, non-ionic,cationic and amphoteric) are in use. However, anionic and non-ionic dominate. Surfactants in textileindustry serve mainly as detergents, wetting agents, deaeration agents, levelling agents, dispersingagents, softening agents, emulsifying agents, spotting agents, anti-electrostatics, aftertreatment agents for fastness improvement, felting agents, fixing acceleration agents for continuous dyeing and printing.
Surfactants can be the essential active part of a textile auxiliary or used as an additive in textileauxiliaries or dyes, printing pastes and coating pastes (dispersing agents in dyestuffs, emulsifiers inpreparation agents etc.).
Following chemical components are mainly in use:
Anionic surfactants: alkyl sulfates, alkyl ether sulfates, alkane sulfonates, alkyl aryl sulfonates, fatty acid condensationproducts, alkali salts of fatty acids (soaps), lignine sulfonates, condensation products of formaldehydeand naphthaline sulfonic acid.
Non-ionic surfactants:
hydrophilic part: polyethylenoxide or polypropylenoxide; hydrophobic part: fatty alcohol, fatty amine,fatty acid amide, fatty acid, alkylphenol, alkylnaphthol.
Cationic surfactants: derivatives of quaternary ammonia salts.
Amphoteric surfactants (very rare):
Betain derivatives. Due to their surface activity, aquatic toxicity of surfactants has to be taken into account. Fish toxicitybetween different types of surfactants can vary within a large range. For non-ionic surfactants withincreasing ethylene oxide part, fish toxicity decreases but biodegradation decreases also [Schöberl,1988; Stache 1990]. Cationic surfactants have by far highest fish toxicity compared to other classes of surfactants.
The rate of biodegradation also strongly depends on the chemical structure of the surfactants. For nonionic surfactants chain length and number of side chains is a crucial point.
Substances with a low rate of biodegradation/bioelimination are adducts of ethylene oxide andpropylene oxide (EO/PO´s; mainly used in preparation agents), lignine sulfonates and condensationproducts of naphthaline sulfonic acid and formaldehyde (mainly used as dispersing agents in dyestuffsand as levelling agent and aftertreatment agent for fastness improvement) and in the majority of casesfatty amine ethoxilates (mainly used in levelling agents).
The ethoxy chain in alkyl phenolethoxilates (APEO´s) is readily biodegradable but nonylphenol whichis the main intermediate compound during biodegradation shows a very low degree of biodegradation,a high fish toxicity and reproductive toxicity [Schäfer, 1996]. Therefore TEGEWA (Germanassociation of textile auxiliaries suppliers) and other German associations decided in 1986 to phase outAPEO´s in detergents [TEGEWA, 1986].
To minimise ecological load in wastewater caused by surfactants the following principles should be regarded: - 189 -
- No use of APEO-containing products (with exception to APEO- containing coating pastes which are not released to wastewater).
- Use of readily biodegradable surfactants (OECD 301A-F tests: pass level > 60 resp. 70%; OECD 303 A: DOC or COD degradation > 80%; mod. Zahn-Wellens test: DOC-elimination > 80% in 7 days) if effectiveness of products is comparable to common products. For the choice of the products the ARS classification scheme (4.2.1.1.1) can be helpful.
- Aquatic toxicity of the products should be taken into consideration as well as possible critical byproducts concerning working place atmosphere.
Main achieved environmental benefits
Degree of biodegradation of wastewater increases. Fish toxicity of the wastewater is reduced.
Applicability There are manifold application fields for surfactants in textile finishing. Recipes and application techniques are process specific. There is no general difference for the application of ecologically optimised products. However if common surfactants are substituted by more environment-friendly products the process reliability and possible differences in effectiveness of the products should be regarded.
For textile finishing industries, the influence on the selection of surfactants is low if the products are used only as additives in textile auxiliaries and dyestuffs and a declaration in the Health and Safety Data Sheet is not needed.
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