Amino Functional Silicone Oils
Amino functional silicone oils are important auxiliary chemicals for softener formulations in a broad class of finishing applications of textiles. They provide "supersoft" hand feelings in textiles in addition to other important benefits. Their chief drawback is yellowing with loss of water absorbency.
The silicone structure, the chemistry and concentration of the side chain, the reactivity and the chain length of the silicone polymer, and the droplet size in the emulsion are very crucial for the properties such as the fabric softness and wettability. Silicones with primary amino groups are generally more efficient in rendering fabric softness than those containing secondary amino groups or amine derivatives.
Compared to primary amino groups, secondary amino groups are not as effective in increasing the attractive interaction (therefore the softening performance) between amino-functional siloxanes and cotton surfaces. Besides the chemical character of the functional group, the amine content, viscosity and particle size have an effect on the softening effect and wettability, the most important parameter being the amine content, followed by the viscosity of the polymer.
High viscosity amino silicone oils give a more oily and silky touch and the low viscosity amino silicone oils give a dry hand feeling.
The decisive chemical character of the amino silicone oil is the amine content; the viscosity and the particle size may effect textiles in terms of softness, silkiness and hydrophilicity. The nitrogen content of common amino silicone oils is below 1%.
There are 2 types of amino functional silicone oils. One of them is non-reactive amino functional silicone oil with 100% of active, 0.40 meq amine, and viscosity of 1000 cSt. This oil is used mainly in textile applications to provide softness and silkiness. The second type of amino functional silicone oil is the reactive amino functional silicone oil with 100% of active, 0.20 meq amine, and 4000 cSt viscosity. Used mainly in textile applications to provide silk touch, it causes no color change and has high stability.
Another point is that amino silicones can undergo thermo-yellowing, the extent of color change being strongly dependent on the structure of the amino side-chain, the amine content and the curing temperature and duration. To avoid or to minimze the yellowing, a series of alternative structures have been evaluated. Starting with amino silicones, non-yellowing structures can be produced in different methods, such as by alkylation, acylation or by trapping the N-atom in a ring structure. Regarding acetylation, acetic anhydride reacts fast and with such a high selectivity, that it can even be applied in already emulsified formulations. Unemulsified oils treated with acetic anhydre however, do show gelling tendencies. Therefore, butyrolactone can be used as an alternative acylating agent.
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