DHTDMAC

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. 

ECETOC. DHTDMAC. Aquatic and Terrestrial hazard (Technical report no 53). European Centre for ecotoxicological and Toxicological Safety Assessment of Chemicals, Brussels, Belgium, 1993. 

Choose fabric softeners based on their softening power, which decreases in the order of DHTDMAC > imidazoline quaternary > amidoamine quaternary > TEA ester quaternary. 

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

Gerike P., H. Klotz, J.G.A. Kooijman, E. Matthijs, and J. Waters. 1994. The determination of dihard-ened tallowdimethyl ammonium compounds (DHTDMAC) in environmental matrices using trace enrichment techniques and high performance liquid chromatography with conductometric detection. Water Res. 28, 147-154. 

ECETOX Technical Report No. 53 (1993) DHTDMAC Aquatic and Terrestrial Hazard Assessment, CAS No. 61789-80-8, February, Brussels, Belgium. 

PARCOM 93/4(1993) Phasing out of cationic detergents DTDMAC, DSDMAC and DHTDMAC in fabric softeners. OSPAR Commission for the Protection ofthe Marine Environment ofthe North-East Atlantic, http //www.ospar.org/documents/dbase/decrecs/recommendations/pr93-04e.doc (19 Aug 2004). 

Table 8.7 Release amount (tonnes/year) from PRTR data and the comparison between actual concentration in environment and maximum allowable toxic concentration (MATC) concerning LAS, AE, DHTDMAC and AO... 

DHTDMAC Bis(hydrogenated tallow) dimethylammonium chloride AO N,N-dimethyldodecylamine N-oxide... 

No. 251 Bis (hydrogenated tallow) dimethylammonium chloride CAS-RN=61789-80-8 (hereinafter referred to as DHTDMAC)... 

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. 

Di-hard tallow dimethylammonium chloride (DHTDMAC), where R is a hydrogenated tallow alkyl (C /Cig chain). 

The replacement of DHTDMAC by esterquat in fabric softening compositions represented a turning point. Before then, only two actives accounted for 95% of the cationic softeners in use. Since then, every manufacturer has had its own active ingredient [11,12],... 

Many authors give details of the synthetic procedures for the manufacture of DHTDMAC [3,37,38], It is prepared by a rather complicated process, detailed in Figure 12.2. 

Although DHTDMAC fully meets all the needs and expectations criteria listed above, its use has dramatically decreased because of changes in European regulations, which led to its replacement by esterquats in the early 1990s to avoid adverse labeling. Moreover, the formulation of DHTDMAC-based concentrated softeners was not possible without the help of cosofteners. With other actives the technical constraints do not exist or are less stringent. 

FIG. 12.2 Synthesis of softening active molecules (a) DHTDMAC (b) esterquat. 

Among the many other molecules used for fabric softening, only two have been a commercial success imidazolinium salts and diamidoquaternary ammonium salts [26], Imidazolinium methylsulfate (DHTIMS) has been a useful alternative to DHTDMAC in the U.S., and in Europe to a lesser extent. Both actives indeed deliver similar benefits. The counterion here is always methylsulfate. 

The main limitation linked to DHTDMAC is that formulating concentrates with a solid content exceeding 15% is generally not possible without using cosofteners. To exceed this concentration, amidoamine quats or imidazolines must be introduced in the system [6],... 

Nonionic and even anionic surfactants have also been added in small amounts to DHTDMAC to boost a product s softening efficacy. For example, it was shown in the late 1970s that the performance of a 6% DHTDMAC composition is matched by a mixture of 4.4% DHTDMAC and 0.6% anionic [56] 1.6% DHTDMAC could then be replaced by 0.6% anionic, which is less expensive. That was quite unexpected, as it was generally accepted that fabric softeners must be introduced in the last rinse of the laundering process to avoid their neutralization by the anionic detergent residues on the fabric, which causes the formation of insoluble species. 

Likewise, a dispersion of 3.6% DHTDMAC-0.9% tallow alcohol blend delivers as much softness as a 6% DHTDMAC dispersion [57], From a performance standpoint, 0.9% fatty alcohol in the mixture is equivalent to 2.4% DHTDMAC, while it contains as many fatty chains as 0.8% DHTDMAC (tallow alcohol mol wt = 259, 1 chain DHTDMAC mol wt = 569, 2 chains). Fatty alcohols alone are not better than DHTDMAC in fabric softening. Due to the insolubility of fatty alcohols in water, this equivalence has been evidenced by spraying alcoholic solutions of actives onto textiles. Actually, the DHTDMAC-cosoftener synergy results from a modification of the DHTDMAC dispersion structure. A dispersion of straight DHTDMAC is made of large multilamellar vesicles while only small... 

This synergy has been systematically investigated and exploited to enhance the cost efficiency of fabric softeners, delivering either better performance at equal cost or the same performance at improved cost. It has also opened the door to the formulation of DHTDMAC-based concentrates, which without cosofteners is not possible for viscosity reasons. 

The main nonionic cosofteners are fatty alcohols, fatty acid esters, ethoxylated fatty amines, or lanolin derivatives. To the cationic-anionic systems belong ether sulfates, alkyl sulfonates, or fatty acids [5,6,10]. In all the blends, the weight ratio of DHTDMAC to the cosoftener is always greater than unity [10]. 

In esterquat-based and more so in DHTDMAC-based softening compositions, PDMS improves the wettability of the treated cotton at low PDMS/quaternary ratio. This property is surprising, considering the strong hydrophobicity of the material. Since PDMS is not very substantive, it is easily removed in the subsequent wash. 

The best trade-off between softening and affinity of the treated fabric for water is obtained at 1 g DHTDMAC/kg dry load [13,18,71],... 

For these reasons surfactants such as DHTDMAC have been safely used worldwide for decades. For instance, despite an annual DHTDMAC consumption of 27,000 tons in 1980 in Germany, there has been no clear evidence of any negative impact on the environment [10],... 

Nevertheless, as already mentioned, esterquats replaced DHTDMAC in the early 1990s. This move, a voluntary initiative from the industry, allowed the use of materials not classified as dangerous for the environment instead of materials classified as very toxic to aquatic organisms and potentially having long-term effects on the environment. 

Replacing DHTDMAC by esterquats required a full reformulation of fabric softeners to keep the softening performance and the aesthetic attributes of products. For instance, esterquat hydrolysis may occur upon storage of a product. The reaction is hindered by maintaining the product at slightly acidic pH values (2 to 3.5). Since 1996, the rest of the world has also started to remove DHTDMAC from softening compositions [16], As a result, DHTDMAC annual consumption has dropped by over 70%. 

Liquid fabric softeners are formulated by dispersing the melted raw material in well-stirred hot water. Although DHTDMAC aqueous dispersions are not emulsions in the strict sense, chemical and mechanical principles of emulsification apply to control the viscosity and phase stability [10]. 

Dispersion of the hot premix of DHTDMAC or esterquat, cosoftener, fragrance, and other water-insoluble ingredients, if any, in the well-stirred aqueous phase. Overheating should be avoided, as it is detrimental to the product s stability. The stirring is maintained until a homogeneous dispersion is obtained. 

The particles are usually composed of lamellar or gel phases [3,90,91], Electron micrographs (TEM or freeze fracture) show that most DHTDMAC particles exhibit a liposome-like structure called a vesicle (Figure 12.8). In this structure, the surfactant fatty chains form one or several highly organized hydrophobic areas... 

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