How to choose amino silicone oil correctly?
Polysiloxane is a twisted helical straight chain structure that can rotate freely around the main chain, so the main chain is very soft, which determines that polysiloxane can be an excellent softener for fabrics.
The high polarity of the amino group in amino-modified polysiloxane enables it to interact with hydroxyl groups, carboxyl groups, cyano groups, ester groups, amide groups, etc. in the fibers to form firm adsorption and orientation, thereby reducing friction between fibers factor, making it smooth and soft. The structure is shown in the figure below.
Mechanism of action of amino silicone oil
The structural characteristics of amino silicone oil can be characterized by three important parameters, namely ammonia value, viscosity and reactivity. It basically reflects the quality of amino silicone oil and affects the performance of the treated fabric.
Part.2 Ammonia value
The various properties that amino silicone oil imparts to the fabric are brought by the amino group in the polymer.
The amino group content can be expressed by the ammonia value. The higher the amino content, the higher the ammonia value, and the softer and smoother the finished fabric feels. This is because the increase in the amino functional group increases the affinity for the fabric, thereby giving the fabric a soft and smooth feel.
However, the active hydrogen in the amino group is easy to oxidize to form a chromophore, causing the fabric to be yellowish or slightly yellowish. In the case of the same amino group, it is obvious that with the increase of the amino group content (or ammonia value), the probability of oxidation increases, and the yellowing phenomenon is serious.
Of course, if the degree of oxidation of the active hydrogen in the amino group is reduced, the yellowing phenomenon can be reduced. For this reason, there are various modified products of amino groups, such as secondary amino modification and tertiary amino modification.
At the same time, it also affects other properties, such as hand feel, whiteness, water absorption, decontamination, etc. Conventional amino silicone oil is better than primary ammonia and secondary ammonia in hand feel, slightly inferior to tertiary ammonia modified amino silicone oil, but in Whiteness, water absorption and easy decontamination performance have greater disadvantages.
As the ammonia value increases, the polarity of amino silicone oil molecules increases, which provides favorable prerequisites for the emulsification of amino silicone oil, and can be made into microemulsions. The choice of emulsifier is related to the size and distribution of particle size and ammonia value in the emulsion.
Viscosity is related to polymer molecular weight and molecular weight distribution.
The greater the viscosity, the greater the molecular weight of amino silicone oil, the better the film-forming property on the surface of the fabric, the softer the hand feel, and the better the smoothness; but due to the excessive molecular weight, its permeability will become poor, especially for strong For tight-twisted fabrics and strong-twisted fine-denier fabrics, it is difficult for amino silicone oil to penetrate into the fiber, which will affect the performance of the fabric.
Excessive viscosity also makes it more difficult to prepare stable microemulsions. When adjusting the product, generally you can’t just choose to increase or decrease the ammonia value to adjust the hand feeling, you need to change the ammonia value and viscosity together.
Usually the ammonia value is low and the viscosity must be high to balance the softness properties of the fabric. Slippery feel requires high viscosity amino-modified silicone oil.
During softening and finishing baking, some amino silicone oils are cross-linked to form a film, thereby increasing the molecular weight. Therefore, the initial molecular weight of the amino silicone oil is different from the molecular weight of the amino silicone oil that forms a film on the final fabric.
Therefore, the same amino silicone oil is processed under different process conditions, and the slipperiness of the final product may be quite different.
On the other hand, low-viscosity amino silicone oil can also improve the feel of the fabric by adding a crosslinking agent or adjusting the baking temperature.
Low-viscosity amino silicone oil has good permeability, and through cross-linking agent and process optimization, the advantages of high and low-viscosity amino silicone oil can be combined.
The molecular weight distribution of amino silicone oil may have a greater impact on product performance.
After the fabric is finished, the low molecular weight amino silicone oil penetrates into the fiber, while the high molecular weight is distributed on the outer surface of the fiber, so that the inside and outside of the fiber are wrapped by amino silicone oil, giving the fabric a plump, soft and smooth feel, but the problems may be If the molecular weight difference is too large, it will affect the stability of the microemulsion and the choice of emulsification conditions.
Reactive amino silicone oil has self-crosslinking property during treatment, increasing the degree of crosslinking helps to increase the smoothness, softness and fullness of the fabric, especially the improvement of elasticity is more obvious.
If the hydroxyl group is introduced on the side chain, the performance in this respect can be improved. If there is no hydroxyl group in the side chain of the molecule, and the hydroxyl group is used for wool fibers, it can also increase the adsorption; if the terminal group is methyl, it can be used for cotton fabrics; if the terminal group is methoxy group, it can be used for synthetic fabrics .
Generally, the pH value of the amino silicone oil microemulsion is controlled at about 4 to 6. At this time, repulsion occurs between the emulsion particles to prevent particle aggregation, which is beneficial to the formation of the microemulsion.
When nonionic surfactants are used as emulsifiers, acid is usually added to form an emulsion. However, the addition of acid in the microemulsion will affect the ionicity of the microemulsion.
When the pH value is 7, the emulsion is non-ionic; when the pH value is <7, it is cationic, and the lower the pH value, the stronger the cationic charge, which increases the adsorption to fibers.
However, the acid and amino silicone oil form a quaternary ammonium salt, which is easily affected by alkaline substances or electrolytes and hard water during processing, thereby affecting the stability of the microemulsion, causing oil floating, sticking to the roller, and the like.