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 is the most important such as fabric softness and wettability by varying the chemistry, location, and concentration of the side chain, reactivity and chain length of the silicone polymer, the droplet size in the emulsion. Silicones with primary amino groups are generally more efficient in rendering fabric softness than those containing secondary amino groups or amine derivatives or reactivities.
Compared with primary amino groups, secondary amino groups are not as effective in increasing the attractive interaction (and therefore the softening performance) of amino-functional siloxanes with cotton surfaces. Besides the chemical character of the functional group, the amine content, viscosity and particle size may have an effect on the softening effect and wettability, the most important parameter being the amine content, followed by viscosity.
High viscosity amino silicone oils give a more oily and silky touch but low viscosity amino silicone oils give a dry hand feeling.
The decisive chemical character of amino silicone oil is the amino content, viscosity and particle size may affect textiles as softening, silkiness, hydrophilicity. The nitrogen content of common amino silicone oils is below 1%.
There are two types of amino-functional silicone oils. One of them is nonreactive amino-functional silicone oil which contains 100% of actives, 0.40meq amine, and 1000cSt viscosity. 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 which contains 100% of actives, 0.20meq amine, and 4000cSt viscosity. Used mainly in textile applications to provide silk touch without any color change and with high stability.
Another topic is that amino silicones can undergo thermo-yellowing, the extent of color change being strongly dependent on the structure of the amino side-chain on the amine content and, of course, on curing temperature and time. To minimize or to avoid yellowing, a series of alternative structures have been evaluated. Starting with amino silicones, non-yellowing structures can be produced in different ways, 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 Ac2O however do show gelling tendencies. Therefore, butyrolactone can be used as an alternative acylating agent.
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