Aftertreatment Aids

After the washing process has been completed and soil removal has been accom-plished, fabrics are sometimes subjected to some type of aftertreatment. The goal is to increase the usefulness of laundry by restoring textile characteristics that have suffered in the course of the wash. Needs in this respect can vary considerably, depending on the

Table 31. Frame formulations of all-fabric bleaches in the USA

Ingredients Composition, %

Powders Liquids

Builders 60 – 75 –

(sodium carbonate, zeolite, sodium citrate, sodium silicate)

Anionic surfactants 5 – 15 2 – 10

(alkylbenzenesulfonates, alcohol sulfates, alcohol ether sulfates)

Nonionic surfactants 0 – trace 0.3 – 5

(alcohol ethoxylates, amine oxides)

Bleach 3 – 15 3 – 4^*

(sodium perborate, sodium percarbonate, hydrogen peroxide)

Fillers 5 – 20 0 – 2

(sodium sulfate, sodium chloride)

Fluorescent whitening agents 0.2 – 0.5 0.1 – 0.2

Enzymes 0 – 1 –

Dyes, fragrances, pH-regulators + +

Water balance balance

*Hydrogen peroxide.

Table 32. Frame formulations of laundry boosters in the USA

Ingredients Composition, %

Powders Liquids

Builders

Sodium carbonate 30 – 40 –

Sodium borate 0 – 50 0 – 1

Sodium silicate 0 – 5 –

Anionic surfactants 0 – 10 0 – 5

(alkylbenzenesulfonates, alcohol sulfates, alcohol ether sulfates)

Nonionic surfactants – 0 – 1

(alcohol ethoxylates, amine oxides)

Hydrotropes – +

Fluorescent whitening agents 0 – 1 0 – 0.5

Enzymes 0 – 2 0 – 1

Dyes, fragrances, neutralizing agents + +

Water balance balance

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fabric involved. Thus, products in this category may be called on to provide elastic stiffness, improved fit and body (shirts and blouses); smoothness, sheen; good drape (curtains); fluffiness and softness (underwear, towels, bath gowns); or antistatic prop-erties (garments, underwear, hosiery, and other easy-care articles made from synthetic fibers). To achieve such effects, the following product groups are marketed:

Fabric softeners Stiffeners

Laundry dryer aids

4.3.3.1. Fabric Softeners

Textiles washed by machine are subjected to greater mechanical stress than those washed by hand. Indeed, machine-washed laundry may be so severely jammed that the pile of the fibers at the fabric surface is reduced to an extreme state of disarray, especially in the case of natural fibers such as cotton and wool. During subsequent drying in static air (e.g., when laundry is dried hanging indoors), this condition tends to become fixed in the fabrics, and the laundry acquires a harsh feel. Addition of a liquid fabric softener in the final rinse (rinse-cycle softener) results in fabrics that feel softer.

The conditions described above are frequently found in Europe, Japan, and other regions of the world. Fabric softeners play another role in the USA, where laundry is mostly dried in mechanical dryers. The tumbling of the laundry in the dryer accom-plishes its own softening effect. The chief task of household fabric softeners in the USA is rather to impart antistatic properties and a pleasant odor to the laundry. Therefore, fabric softeners in the USA are frequently applied as sheets impregnated with active material which are added to the moist laundry at the beginning of the dryer cycle (see Section 4.3.3.3)

The principal active ingredients in commercially available rinse-cycle softeners are usually cationic surfactants of the quaternary ammonium type [60] – [63], [155], [156].

When applied in appropriate concentrations, cationic surfactants are adsorbed nearly quantitatively onto natural fibers, in contrast to their behavior with synthetic fibers (Table 33) [132] – [134].

To prevent undesired interactions between the anionic surfactants of a detergent and the cationic surfactants of a fabric softener, the latter must be introduced only in the last rinse cycle. Overuse of fabric softener must be avoided. Otherwise, the absorbency characteristics of the textiles decrease which in turn adversely affects the function of towels.

Conventional softeners, which contain on average 4 – 8 % active material, have been partially replaced in many countries by softener concentrates having some 12 – 30 % active material. This development is an answer to the increasing public environmental criticism centered on the bulky plastic packaging of conventional softeners. Bottles with

LaundryDetergents

volumes of 4 – 6 L of conventional fabric softener need large amounts of plastic for their manufacture, and also present waste disposal problems.

Due to its poor biodegradability the formerly widespread distearyldimethylammo-nium chloride (DSDMAC) [60], the former active material of most softeners in Europe, the USA, and Japan, has been replaced by the readily biodegradable (see Section 10.5.1) esterquats in the 1980s and 1990s. Frame formulations of liquid fabric softeners are given in Table 34.

The formulation of products with higher amounts of active material requires a well-balanced system of selected emulsifiers to maintain good dispersion stability upon storage.

Fabric softeners have additional benefits. They impart good antistatic properties on fabrics. They prevent the build-up of electrostatic charges on synthetic fibers, which in turn eliminates such unpleasant phenomena as fabric cling during handling and wearing, crackling noises, and dust attraction. Also, fabric softeners make fabrics easier to iron and help reduce wrinkles in garments. In addition, they reduce drying times so that energy is saved when softened laundry is tumble-dried. Last but not least, they also impart a pleasant fragrance to the laundry. That is why branded softeners are frequently offered with different fragrances.

4.3.3.2. Stiffeners

If stiffness and body are desired rather than soft and fluffy laundry, stiffeners can be added as aftertreatment. Usual agents for this purpose include natural starch derived from rice, corn, or potato, which can be used to impart extreme stiffness to fabrics.

Synthetic polymeric stiffeners are good alternatives. They impart a more modest degree of stiffness than natural starch does, which is more closely attuned to contemporary taste. Products of the latter type are generally liquid and are easier to apply than natural starch. Stiffeners are supplied as dispersions and contain, in addition to a small amount of starch, substances such as poly(vinyl acetate), which has been partially

Table 33. Sorption of distearyldimethylammonium chloride^*[58]

Textiles Adsorbed amount^**

mg/g mol/g mg/m² %

Wool 1.20 2.06 301 100

Resin-finished cotton 1.18 2.01 133 98

Cotton 1.17 2.00 169 96

Polyester/cotton 1.17 2.00 110 98

Polyamide 0.96 1.63 66 79

Polyacrylonitrile 0.90 1.53 68 74

Polyester 0.57 0.97 109 47

* Equilibrium conditions: time = 60 min, t = 23
C, bath ratio = 1 : 10; initial concentration: 120 mg/L.

** Based on the mass and geometric surface of the textiles.

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hydrolyzed to poly(vinyl alcohol). Table 35 shows a frame formulation for typical European liquid stiffeners. Such products are offered not only as dispersions, but also as aerosol sprays. The latter allow local treatment of garments, for example, collars and cuffs.

Synthetic polymeric stiffening agents are called permanent stiffeners because, unlike starch, their effectiveness endures through several wash cycles. This property also has its negative aspects, however, since poly(vinyl acetate) film on a fabric can attract both soil and dyes, thereby leading to discoloration.

Table 34. Formulations of fabric softeners in Europe, the USA, and Japan Ingredients Composition, %

Europe USA Japan

Regular Concentrate Conditioner Regular Concentrate Conditioner Quaternary

Water balance balance balance balance balance balance balance

aEsterquat type: triethanol amine, diethanol amine, or epichlorohydrine esterified with tallow-based acids or oil-based acids are preferred in Europe. Diesters are preferred due to superior softening performance. Aside from esterquats, distearyl dimethyl ammonium chloride (DSDMAC) types, imidazolines, and amino ester salts are used in some countries.

bFatty alcohols, fatty acids, triglycerides.

cSilicone oils, dispersed polyethylene.

dMagnesium chloride, calcium chloride, sodium chloride, sodium acetate.

Table 35. Formulation of liquid stiffeners in Europe

Ingredients Composition, %

Alkyl/alkylaryl polyglycol ethers 0.1 – 2

Poly(vinyl acetates)

(partially hydrolized) 10 – 30

Starch 0 – 10

Poly(ethylene glycols) 0.5 – 1.5

Fluorescent whitening agents

+/-Dyes

+/-Water balance

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4.3.3.3. Laundry Dryer Aids

Laundry dryers are far more widespread in the USA than in Europe. They have held a significant place in the U.S. market since the early 1970s. Dryer aids are introduced into the dryer along with the damp, spin-dried laundry. During the drying process, they impart to the laundry both softness and a pleasant odor. Most importantly, however, they prevent static buildup on the fabric. The latter point is particularly significant in the USA, where synthetic fabrics are quite frequently used. Synthetic fabrics are less popular in Europe and elsewhere.

Laundry dryer aids are almost exclusively applied as sheets, which serve as carrier.

The sheets are made from nonwoven material and impregnated with both fabric softeners and temperature-resistant fragrance oils. During the drying process, active ingredients from the dryer sheet are transferred to the laundry through frictional contact. The sheet materials are designed for single use and are discarded at the end of the drying cycle.

An additional reason for the popularity of dryer aids in the USA is the fact that washing machines in the USA often lack dispensers for automatic addition of liquid fabric softeners to the rinse cycle.