Esterquats biodegradation

In 1991, the European fabric softener market took a sharp turn. Producers in Germany, the Netherlands, and later in Austria and Switzerland voluntarily gave up the use of DHTDMAC (238) because of pressure from local environmental authorities, who gave an environmentally hazardous classification to DHTDMAC. A number of esterquats were developed as candidates to become successors to DHTDMAC (see Fig. 1). The ester group facihtates biodegradation. 

The toxicity of these compounds [ 173,175] can be relatively high compared to other surfactants, but their poor solubility and their tendency to adsorb to solids or to complex with anionic substances considerably reduce the real risk and adverse effects for the aquatic environment. [30,31,176]. The use of alkylquats has been substituted by the more easily biodegradable and less toxic esterquats that are nowadays the cationic surfactants produced in higher volumes. 

However, since DTDMAC also shows a pronounced resistance to biodegradation (see Chapter 1.7), it has been almost completely replaced by the more environmentally acceptable esterquats. 

Taking into consideration its physico-chemical properties, removal efficiencies, low biodegradability, predicted environmental levels, toxicity, and the need to provide sufficient safety margins for aquatic organisms, the demand for alternative cationic surfactants arose. Since 1991, DTDMAC has been replaced in some European countries due to producer s voluntary initiatives with new quaternary ammonium compounds, the esterquats. These contain an ester function in the hydrophobic chain (Table 1.3) that can be easily cleaved, releasing intermediates that are susceptible to ultimate degradation [24-26]. The effects of the phasing-out and replacement of DTDMAC can be demonstrated by the results of a Swiss study, where the surfactant... 

Simms et al. [119] employed an integrated approach to determine the mechanism and kinetics of surfactant biodegradation by FAB-MS and liquid scintillation counting. Two compounds, the esterquat A -octadecyl-A - [palmytoyloxyethyl]-A V-dimethyl ammonium chloride and AM2-hydroxyethyl)-AyV-dimethyloctadecyl ammonium chloride,... 

The anaerobic biodegradability and toxicity on anaerobic bacteria of cationic surfactants such as ditallow dimethylammonium chloride (DTDMAC) and two esterquats have been investigated in a recent study [52], For the esterquats studied, high biodegradation levels were obtained and no toxic effects on anaerobic bacteria were observed even... 

Choose esterquats over DHTDMAC for environmentally friendly products, since they biodegrade more rapidly and are less toxic to aquatic life. 

As more and more attention was paid to the environmental impact of every product, the biodegradability profile of DHTDMAC was scrutinized. In the early 1990s, as the result of changes in European regulations, fabric softener manufacturers in Europe voluntarily replaced DHTDMAC with the more biodegradable esterquats. Since 1996 manufacturers in the rest of the world have also started to remove DHTDMAC from products and to replace it with esterquats. Replacing DHTDMAC with esterquats is not a simple one-to-one replacement in a formula. It requires full reformulation to maintain product aesthetics and performance. This is discussed in detail in Chapter 12. 

Quats are usually less easily biodegraded than anionic or nonionic surfactants, or esterquats, as they are less prone to be attacked by bacteria. Nevertheless softeners are not detrimental to the environment, since, besides their elimination by biological degradation, their concentration in effluents remains very low [15],... 

The new quats generation presents readily biodegradable surfactants the long chains of which are interrupted by ester groups, thus named "esterquats" [102, 108]. Esterquats are derived frequently from the diester of triethanolamines and the partially hydrogenated tallow or oleic acid followed by a diester quaternisation. The final product, N-methyl-N,N-di[2-(Ci6-i8-acyIoxy)-ethyl]-N-(2-hydroxyethyl)ammonium methosulphate (VIII), of the formula... 

As described above, esterquats differ structurally from DTDMACs by the presence of ester linkages in the alkyl chains. These linkages allow a rapid and complete biodegradation of esterquats. For example, DEEDMACs reached about 80% CO2 evolution in the modified Sturm test. With respect to the other criteria, DEEDMACs can be classified as readily biodegradable. In addition, a rapid and high anaerobic biodegradability of DEEDMACs was found (22). Similar results were reported from biodegradation tests with esterquats, DEQs and DTIEs. There was almost a complete mineralization and stable metabolites were not formed. 

In contrast to alkyl-based cationics, esterquats contain ester groups in the molecule. Owing to this hydrolytically unstable function in the molecule, esterquats are much better biodegradable than alkyl-based cationics. In the European detergent industry, this fact and its lower toxicity to water organisms [21] led to a nearly complete replacement of DSDMAC by esterquats in household rinse cycle softeners since 1991. 

During the last decade, the dialkyl esterquats have to a large extent replaced the stable dialkyl quats as rinse cycle softener, which is the single largest application for quaternary ammonium compounds. The switch from stable dialkyl quats to dialkyl esterquats represents one of the most dramatic changes of product type in the history of surfactants and it is entirely environment driven. Unlike stable quats, esterquats show excellent values for biodegradability and aquatic toxicity. Esterquats have also fully or partially replaced traditional quats in other applications of cationics, such as hair care products and various industrial formulations. Normal esterquats are covered in a special chapter of this book and are not discussed further here. 

As a consequence of this specific structure, esterquats upon hydrolysis decompose into non-surface-active fragments. They may be referred to as cleavable surfactants. As a matter of fact, esterquats usually biodegrade more rapidly than the related alkylquats. The hydrolytic instability, on the other hand, comprises a challenge to the user and formulator. While traditional alkylquats are virtually stable under the conditions of use, esterquats... 

The esterquats discussed are readily biodegradable and effects are found only at concentrations greater than their water solubility. The (bio)degradation pathway demonstrates that formation of persistent toxic compounds is circumvented. The main degradation products, i.e., polyalcohol quaternary ammonium salts, are not toxic. The ready biodegradability and determined effect concentration strongly indicate that esterquats are safe at the intended maximum usage volumes. PEC/PNEC ratios are lower than 1 for all esterquats examined. 

Softener esterquats based on alkanolamines have been extensively investigated for their environmental properties. A number of very comprehensive studies has been published [14,37,41]. All materials biodegrade rapidly and show comparatively low toxicity to aquatic organisms. It has been suggested that abiotic degradation (hydrolysis of esterbonds) contributes to the favorable environmental profiles of these esterquats [37],... 

In the last years the behavior of chemical substances in the environment gained increasing importance for nearly all kinds of consumer products. Therefore the industry has developed new raw materials with a better environmental profile. For cosmetic products the biodegradation, toxicity, and dermatological behavior (especially for leave-on products) are the major issues. New classes of cationic surfactants that fulfill the new demands are the esterquats [107]. 

Esterquats with improved stability and biodegradability are prepared by quaternization of a fatty acid (partially hydrogenated tallow) alkanolamine ester with an alkylating agent (dimethyl sulfate) in the presence of nonionic emulsifiers [126] or cosmetic oils [159]. This procedure avoids problems associated with the use of lower alcohols as solvents in the reaction, such as low ignition point, poor emulsifying capacity for perfume oils, poor skin compatibility, and a defatting action on the skin. Formulations of a triethanolamine-based Coco esterquat, oil, and a Ci-Cg alcohol are useful in cosmetic and sunscreen formulations [160]. 

Like other quaternaries, esterquats exhibit fabric softening properties. They are also claimed to be nonsensitizing agents in the dermatological sense and are readily biodegradable. 

Applications. The esterquats are suitable substitutes for straight quaternaries they present an improved environmental profile and comparable softening properties compared to straight quaternaries. Indeed, the esterquat molecules show faster biodegradability compared to the ditallow-dimethyl-ammonium compound (DTDMAC) which has been the... 

Within the last 5 to 8 years, there has developed a need for efficient fabric softening agents with better enviromnental compatability than the most extensively used softening material, dhtdmac [1,5]. Several new types of fabric softener molecules which exhibit rapid biodegradation were developed [6,7], The esterquat shown in Figure 1 is based upon triethanolamine (TEA), while similar diesterquat molecules are in use based upon methyldiethanolamine (MDEA) and l-dimethylamino-2,3-propandiol (dmapd). 

Alcohol amines such as methyldiethanolamine and triethanolamine react with fatty acids to form esteramines. The esteramines have found limited utility and are mostly quaternized to yield the corresponding quats (Figure 2.3). Esterquats are used predominantly in fabric softening, paper softening and hair conditioning applications due to their substantivity and biodegradability [16]. 

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