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Types of Quaternary Ammonium Softeners

Nov 29, 2021

Quaternary ammonium salts used as softeners, according to their
In terms of learning structure, there are mainly the following:
Among the above four quaternary ammonium softeners, except for the first type of alkyl trimethyl quaternary ammonium salt, which tends to be eliminated, the other three are full of vitality. Their applications on textiles are divided into three types, namely; washing softener, household softening conditioner and fabric softener. The softening effect of dialkyl dimethyl quaternary ammonium salt is the best. When fabric softening and finishing, use imidazoline quaternary ammonium salt softener, which has excellent antistatic effect and good rewetting property. Dialkyl dimethyl quaternary softening effect. And because of its low toxicity and low irritation, it is used in the soft processing of baby diapers. It was used in the United States in 1955 and in Japan in 1960. Trial production began in the 1970s in China, and mass production was put into production in the 1980s. The
Dialkyl dimethyl quaternary ammonium salt is currently the most used softener. Dialkyl quaternary ammonium salt contains two saturated alkyl groups with appropriate carbon chain length in its molecular structure, so it has excellent softness. In addition to being used as a household fabric softening conditioner and washing softener, it is also widely used in the modification of bentonite with an ammonium salt dosage of 0.1% to 0.2% to improve its lipophilicity, lubricity and viscosity. It is widely used in Adsorption separation, casting, grease, paint, daily cosmetics, etc. The development and application of this product in China started late. Currently, it is organized in Shanghai, Dalian, Changzhi, Shanxi and other places. The main production routes at home and abroad are as follows:
(1) Fatty acid route
Of the two routes, the former has a long process, large equipment investment and high operating costs. The latter fatty alcohol method can produce dialkyl secondary alcohols by one-step ammonialysis at normal pressure, with simple process and low equipment investment. However, considering the price of raw materials, fatty acids are much cheaper than fatty alcohols, so the final production cost is relatively low.
Of course, the dialkyl dimethyl quaternary ammonium salt softener has shortcomings in application.
(1) For the cellulose fibers and polyester, polyamide and polypropylene fibers that have been resin-finished, the absorption of softeners is very small due to their hydrophobicity, the surface of the fibers is hardly modified, and the softening effect is not good.
(2) Common fiber products are treated with optical brighteners. Because they are anionic, the use of quaternary ammonium salt softeners tends to reduce the whitening effect, which in turn makes the fibers yellow or gray.
(3) Cotton fibers finished with quaternary ammonium salt softeners not only obtain softness, but also increase the hydrophobicity of the fiber surface, reduce the moisture absorption of the fibers, and increase the uncomfortable feeling of wearing.
(4) The inherent shortcomings of quaternary ammonium softeners are yellowing and discoloration, which can easily make fabrics yellow and fade, especially for light-colored fabrics and dyed fabrics with anionic dyes.
Examples of commercial specifications of dialkyl dimethyl quaternary ammonium salt are excerpted as follows:
Adsorption on the interface is the instinct of surfactants. After the surfactant is added to the liquid, the surface energy of the liquid (that is, the surface tension δLG) decreases. Generally, although the surface active agent is adsorbed on the solid, the surface is still difficult to expand. However, the fiber is a material with a large specific surface area composed of linear polymer materials, and it is easy to adsorb the surface active agent (softening agent), which reduces the fiber interfacial tension δLS. According to Young's equation.
For the solid surface (fiber) to expand on the surface and easily absorb the softener, the above formula COSθ must be reduced. Since the surface tension of the solid (fiber) δSG is constant on a certain fiber, the fiber becomes easy to expand its surface. As a result, the fabric becomes fluffy and plump, giving a soft hand feeling.

According to the theory of thermodynamics, the substance that can reduce the interfacial energy of the fiber has the strongest adsorption effect on the surface of the fiber, and the formed adsorption film is also strong. The quaternary hinge salt softener is strongly adsorbed on the surface of the fiber by electrostatic attraction, and has a greater effect on reducing the surface energy of the fiber. Its adsorption on the fiber surface is based on the polar groups (cations) in the molecules facing the fiber, and the hydrophobic groups facing the air. Other types of softeners only rely on physical adsorption to reduce fibers. Of course, the adsorption effect is much smaller than that of quaternary ammonium softeners.

For alkyl groups with the same number of carbon atoms, the straight-chain type has a better softening effect than the branched chain; in addition, the unsaturated carbon chain will also reduce the flexibility. So hydrogenated tallow is often used instead of tallow. Because there are unsaturated alkyl groups in the ingredients of beef wax (tallow ingredients are: myristic acid 2-3%, hexadecanoic acid 24-32%, octadecanoic acid 14-32%, hexadec-9-enoic acid 1-3 , Cis-octadec-9-enoic acid 35-48%, octadec-9,12,2-dienoic acid 2-4%).
The quaternary ammonium salt with a long carbon chain (C16-18) has very low solubility in water, and the solubility of double-long carbon chain quaternary ammonium salt in water is lower. Usually the effective ingredient is only 4-8%, which is dioctadecyl Stable dispersion state of dimethyl quaternary ammonium salt.
The state of dioctadecyl dimethyl quaternary ammonium salt in water is very special, unlike other ionic surfactants that exist in the form of micelles, but in the state of liquid crystals. Therefore, when its concentration increases, it will cause the viscosity to rise sharply, which is why it cannot be made into a high-concentration aqueous solution.

The melting point of the liquid crystal state of dioctadecyl dimethyl quaternary ammonium salt in water is about 37°C, which is close to the body temperature of the human body, which is considered to be the reason for the waxy feeling.

The influence of the hydrophobe alkyl carbon chain on the softening effect can be considered that the C-C single bond can rotate around the single bond while maintaining the bond angle of 109°28', so that the long bond becomes a random arrangement of curled states. Thereby forming the flexibility of the molecule, when under the action of external force, due to the flexibility of the long-chain molecule, it can be endowed with the activity of extension and contraction. In this way, the softener molecules are distributed on the fiber surface to play a lubricating effect, reduce the dynamic and static friction coefficient between the fiber and the fiber, and increase the smoothness and softness of the fabric.
If the hydrophobic carbon chain is a slender chain, it is conducive to the cohesion and contraction of the molecular chain, which increases the flexibility of the molecule, thus improving the softness effect.

Although softening and reducing the fiber friction coefficient are two concepts, they are closely related. Reducing the friction coefficient between fibers can obtain a soft hand. However, the friction coefficient can be used as the main factor to evaluate the softness of the fiber and cannot be the only factor. The coefficient of friction is divided into the coefficient of dynamic friction and the coefficient of static friction. The low coefficient of static friction means that when the fabric is held in the hand, it can start sliding between the fibers with a small amount of force, so that it feels soft. The coefficient of kinetic friction refers to the value of fibers that are pressed together with a weak force when sliding slowly. In soft finishing, both static and dynamic friction coefficients are required to be reduced, but the relationship between softness and the reduction of static friction coefficient is greater. For example, two different softeners are applied to the viscose filaments, the softener A contains polydimethylsiloxane, and the softener B is a cationic softener.

The strength of the lubricating film is inversely proportional to the thickness d of the lubricating film. If the viscosity of the lubricating layer is too large, the thickness of the fluid lubricating layer will increase accordingly, which will cause the strength of the lubricating film to decrease, and the friction between the fibers will change from fluid friction and semi-fluid friction to The transition of boundary friction and too much viscosity will also affect the penetration and spread of the lubricating film on the fiber surface, which will ultimately affect the softening effect. Increasing the amount of softener not only increases n, but also increases the viscosity (that is, increases the thickness of the lubricating film d); the former is beneficial to the strength, and the latter is conversely, and the dosage should be balanced. Therefore, a certain amount of softener should be applied, but it should be appropriate and not excessive or too small.

The amount of softener has the following relationship: the oil content of boundary friction is 0.05-0.3% (owf), the thickness of the oil film is about 1μm (l0-6mm) to form a monomolecular adsorption layer; the oil content of fluid lubrication is 0.3-2% ( owf), the thickness of the oil film formed by the accumulation of the multi-molecule adsorption layer is about 100μm (10-6mm). The amount of softener is generally above 0.3 (owf), and most of the fiber lubrication is fluid lubrication. The dosage of mono- or double-long carbon chain alkyl (C16-18C) quaternary ammonium salt is 0.1-0.2% (owf), and an oil film with a thickness of 5-lOμm is formed on the surface of the fiber, which has sufficient flexibility. The problem is to use a softener Spread evenly on all fiber surfaces to obtain better softness.
The thickness of the oil film formed on the fiber surface is not only related to the amount of softener, but also related to the fiber denier and specific surface area. The fiber with finer denier has a larger specific surface area, such as ultra-fine fiber fabric or cashmere, which requires a certain thickness of film. For more softeners, the dosage will be increased.
The fabric structure also has a great influence on the softening effect. After the loose fabrics such as knitted fabrics, velvet fabrics, woolen fabrics, woolen cloth, etc. are softened and finished, the fibers can be stretched freely, resulting in softness, smoothness, fluffy, plump and increased Thick and other effects. For compact fabrics such as khaki, canvas and other fibers, it is difficult to stretch and slide, and the soft effect is not as good as the former.
2. Compounding of quaternary ammonium salt softener
(1) Combination of quaternary hinge salt and silicone softener
Silicone softeners, especially amino silicone oils, have smoothness, elasticity and softness to fibers, and quaternary ammonium salt softeners also have the same characteristics. However, the amino silicone oil makes the fabric slippery, and the softness and fullness are not as good as the quaternary ammonium softener, and the quaternary ammonium softener is on the contrary. Therefore, if two different types of softeners are used or compounded at the same time, a satisfactory softening effect can be obtained.
Their compound formulation is to apply the quaternary ammonium salt softener to the amino silicone oil microemulsion. Because there is enough emulsifier in the amino silicone oil emulsion, it is enough to emulsify the quaternary ammonium salt and the amino silicone oil to obtain a compound. Emulsion.

The surface tension of amino silicone oil is very low, 15-22 mn/m, which is not comparable to any other polymer except fluorine-containing polymer; and the solubility parameter is very small, about 7-8Cal/cm3, so it is equivalent to Many polymers are incompatible, including quaternary ammonium salts containing long carbon chain fatty alkyl softeners. Therefore, it is finished on the fabric with a compound amino silicone oil and quaternary ammonium salt softener. The amino silicone oil component always floats on the top layer, and the quaternary ammonium salt softener is on the bottom layer, which acts as a leveling substrate and makes the amino group float on it. The methyl groups in the silicone oil are aligned more neatly, show more slippery, better gloss, and better elasticity, and the amount can be reduced.

Types and characteristics of various softeners
Softener requirements
1. Under various soft processing conditions, the working fluid should be very stable. 2. Does not reduce the whiteness and color fastness of fibers or fabrics.
3. The softened fiber or fabric is not easy to be discolored by heat, and there should be no changes in color, feel, or odor during storage.
4. If the softener is emulsion, its emulsion stability is better.
5. According to different processing requirements, it can have proper water absorption or water repellency, anti-static properties and other properties (should be selected according to the different requirements of the fabric). It is resistant to washing or dry cleaning.
6. There is no adverse effect after human skin contact.

Due to the wide variety of textiles, different fibers used, different fabric specifications, different fabric uses, and different finishing requirements, the selection of softeners cannot be generalized. On the basis of the softening mechanism and functions of various softeners, choose the one that meets the requirements. Softener. In addition, the performance of each softener is always limited. To obtain multiple good performance effects, two or more softeners can be used in combination (or compounded into a new softener). Agent products). For example, the compound application of silicone softener and long-chain aliphatic softener can achieve soft, plump and smooth hand feeling. It can also combine the application of softener with mechanical softening, which can often achieve good results. Effect.
Types of softener

Softener is a kind of auxiliary agent with the largest variety in dyeing and finishing auxiliaries. According to reports, among the 920 samples of domestic and foreign additives collected by the Shanghai Institute of Printing and Dyeing Technology from 1990 to 1999, there were 350 softeners, accounting for 38%. So many varieties of softeners, based on their chemical structure, basically fall into two categories: long-chain aliphatic or high-molecular polymers. The long-chain aliphatic softeners in the molecular structure of the hydrocarbon long chain can be irregularly arranged in a crimped state, forming molecular flexibility, and the flexible molecules adsorb on the fiber surface to play a lubricating role, reducing the fiber and The dynamic and static friction coefficient of the fiber.

Therefore, the long-chain aliphatic structure generally has a good softening effect. In the softening agent, there are not only many varieties, but also a relatively large amount. Such softeners can be divided into anionic, cationic, nonionic and amphoteric types according to their ionicity. In addition, for natural oils and paraffin softeners, because they are natural lubricating substances, they can also be regarded as a separate category, but they are also classified into different ionic categories according to the ionicity of the emulsifier used. . There are mainly two types of molecular polymer softeners: polyethylene and silicone. The variety of polyethylene softeners is relatively single, with less dosage, less dosage, and more use; the main thing is silicone softener. Since the main chain of polysiloxane is a helical linear structure that is easy to bend, it can rotate freely in 360 degrees, and the energy required for rotation is almost zero. Therefore, the molecular structure of the polysiloxane alone conforms to the softness mechanism of textiles, which can not only reduce the static and dynamic friction coefficients between the fibers

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