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Sep 4, 2020
The softening mechanism of quaternary ammonium softeners:
The adsorption on the interface is the instinct of the surfactant. After adding the surfactant to the liquid, the surface energy of the liquid (that is, the surface tension δLG) decreases. Although surfactants are generally adsorbed on solids, the surface is still difficult to expand, and fibers are substances with a large specific surface area composed of linear polymer substances, which are easy to adsorb surfactants (softeners) and reduce the fiber interfacial tension δLS.
According to thermodynamic theory, the substance that can reduce the interfacial energy δLS of the fiber has the strongest adsorption on the fiber surface, and the strength of the formed adsorption film is also large. The quaternary hinge salt softener is strongly adsorbed on the fiber surface by electrostatic attraction, and the effect of reducing the fiber surface energy δLS is also greater. Its adsorption on the fiber surface is directed towards the fiber with polar groups (cations) in the molecule, and its hydrophobic groups toward the air. Other types of softeners only rely on physical adsorption and can also reduce the δLG of the fiber. Of course, the adsorption is much smaller than that of quaternary ammonium softeners.
It can be imagined that the softener adsorbs a thin layer on the surface of the fiber, and the hydrophobic groups are arranged neatly outward.
The kinetic determination of quaternary ammonium softeners was carried out. The adsorption amount and adsorption speed of dialkyl dimethyl quaternary ammonium salt, dialkyl amide dimethyl quaternary ammonium salt and dialkyl amide imidazoline quaternary ammonium salt on cotton cloth basically the same.
The research on the adsorption amount and adsorption rate of quaternary ammonium softeners on cotton cloth shows that when they are in lower concentration, their adsorption rate is much faster than that in high concentration.
The absorption of quaternary hinge softener on various fabrics is different, mainly according to the negative surface charge (Zeta potential) of the fabric in water, for example: acetate fiber (-5lmv), wool (-48mv ), viscose (-2gmv), cotton (-27mv), so the amount of adsorption on these fibers is in the following order: acetate fiber>wool>viscose>cotton>polyester>acrylic fiber, due to the negative surface of synthetic fibers in water The charge is so weak that it has less adsorption. In order to improve the effect on synthetic fibers, there has been the development of a composite component softener product. The combination of cationic softener and anionic softener is one of them.