Silicone softeners are the emulsion or micro-emulsion of polysiloxane and its derivates, which allows fabric to have a good sense of softness and smoothness. The products include some manufacturing techniques such as emulsion polymerization, polymer silicone oil emulsification, and modification and compound. All these have basically formed systems and there are many varieties and brands in supply. However, the application effect and properties are still quite different.
1. Dimethyl silicone emulsion
This is the earliest product applied in silicone softeners. The relative molecular weight of silicone oil used as a softener is generally 6,0000-7,0000. After finishing, it allows the fabric to have a sense of softness, straightness, and comfort and reduces the friction coefficient of the fabric, as well as improves the abrasive resistance and sewing adaptability of the fabric. As there is no reactive group on the molecular chain, it cannot react with the fiber, nor can it cross-link. As it can only adhere to the surface of the fiber by molecules, the washing resistance and elasticity are limited.
2. Silicone hydroxyl emulsion (hydroxy silicone oil emulsion)
This is the most widely used silicone softener in China in the 1980s. Its relative molecular weight is generally 60,000-80,000. The greater the relative molecular weight, the softer and smoother it is. Under the effect of cross-linking agent and catalyst, it can cross-link with the reactive base of the fiber or itself to form a polymer film with certain elasticity because of its end of the molecular chain and hong blocking. Therefore, it has washing resistance and can improve the elasticity of the fabric. Silicone hydroxyl emulsion is divided into cationic silicone hydroxyl emulsion and anionic silicone hydroxyl emulsion according to the ionicity of the used emulator. There is hydroxyl at the end of the molecular chain of organic silicone hydroxyl emulsion and it is helpful to improve the hydrophilia and emulsion stability, but because it is hard to control the slightness and homogeneousness of emulsion particles of organic silicone hydroxyl emulsion, it is also hard to control the emulsion stability. Therefore, the floating oil phenomenon easily appears when it is used, causing the occurrence of blemishes on the fabric such as unmovable oil stains. Therefore, the emulsion stability of silicone hydroxyl emulsion softener is also an important index to evaluate its quality.
3. Hydrophilic soluble silicone (polyether type hydrophilic silicone)
This kind of silicone softener is usually polysiloxane modified from polyether and epoxy groups. It is a colorless and transparent thick liquid and can give the fabric good moisture absorption, ventilation, and anti-static properties. Because belonging to the nonionic type, it can be mixed with a variety of accessory ingredients. When used together with resin, it can reduce the chlorine absorption and formaldehyde release of resin. In addition to resin finishing and soft finishing, it is also widely used in the pigment dyeing process. Not only can it improve the hand feeling of the fabric affected by adhesive, but also improve the shortcomings of the adhesive roller.
4. Amino-modified silicone
The properties of organosilicon can be greatly improved by adding the amino group to the macromolecular chain of the polysiloxane. The introduction of amino group can not only form a firm orientation and adsorption with the fiber, making the friction coefficient between the fibers decreases, but also can react with the epoxy group, carboxyl group, and hydroxyl group, so it can be applied to cotton, wool, silk, viscose fiber, polyester, nylon, acrylic, and other fibers and their blended fabrics. After finishing the fabric, it can obtain excellent softness and resilience with soft and plump, smooth and delicate hand feelings. Generally speaking, the higher the amino contents, the softer the fabric is. But higher amino content can increase the greater chance for the fabric to become yellow.
The main reason is that there are two amine groups (primary amino group and secondary amino group) in (CH2)NH(CH2)2NH2 on its side chain and three active hydrogen atoms in total, making it easy to oxidize and form chromophore, and this diamine structure has a more synergistic effect of accelerating oxidation. Therefore, there must be an optimal balance between the amino content and becoming yellow.
Making amino-modified silicone into microemulsion has developed rapidly in recent ten years. Due to the introduction of amino groups into siloxane molecules, the hydrophilicity of the microemulsion is improved. Therefore, the appropriate emulsifier and preparation process can make it become a microemulsion with particle size below 0.15μm. Because its particle size is smaller than the wavelength of visible light, it has no resistance to visible light, so it can make the emulsion transparent. Moreover, because the particle size of the microemulsion is only 1/10 of the particle size of the ordinary emulsion, the number of effective particles in the microemulsion is increased by 103 times (if the concentration is the same), the contact opportunity between the microemulsion and the fabric is greatly increased, and it can spread well on the surface of the fabric, making it easy to penetrate the fiber. Therefore, this product can give the fabric a good internal softness, which is also more durable. Generally speaking, microemulsion products are better in water solubility, storage stability, heat stability, and shear stability. Although the widely used bisaminosilicone softener has a good softness, the whiteness, water absorption, and soil release are poor and will become serious with the increase of amino functional groups in the polymer. We can change the type and number of amino-functional groups to improve these shortcomings. Changing the type of amino functional group is mainly to change the primary amine group into secondary amine group or tertiary amine group. For example, N-propyl cyclohexylamine (secondary amine) and N-propyl piperazine (tertiary amine) modified silicone softeners have been developed and applied to fabric finishing. These softeners can reduce yellowing during baking and are less hydrophobic than silicone softeners compared with primary amine groups, but it may make the texture a little drier. They are mainly used for the soft finishing of bleached and light-colored fabrics. In addition, in order to obtain a super smooth hand feeling, the two ends of dimethylsiloxane macromolecule are modified with amino to seal the ends, which can form a very neat directional arrangement on the fabric so as to obtain excellent smooth hand feeling. If the part side chain and two end groups of polysiloxane are substituted by amino modification, to create a fabric finishing agent, it can make the fabric softer.
Now as the development of organic silicon softener is fast with more and more varieties and declined price, the number of silicone softener applications has increased relatively. In addition to the above kinds of silicone softeners, there are epoxy modification, amide modification, and carboxyl modification, etc.