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 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.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 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