Foam Stabilizer (Silicone Oil) Handout
What is silicone oil
Silicone oil is a kind of silicone surfactant, which was firstly called Foaming Spirit in China and Silicone surfactant in foreigners, Silicone in Taiwan and Hong Kong, and later on, it is usually called Even Foam Agent and Foam Stabilizer in Chinese. This kind of surfactant can be divided into Si-O-C type and Si-C type, the Si-C bond is not hydrolyzed, while the Si-O-C bond is easy to be hydrolyzed under the condition of strong acid or strong alkali, the foam stabilizer produced by this kind of connecting way is not suitable to be used in the preparation of the combination of materials, because it is stored for a certain period of time with the tertiary amine catalyst and the mixture of water, it will be hydrolyzed due to the hydrolysis of the Si-O-C bond, so the product loses the
stabilizing effect of the foam. Foam stabilizing effect. Therefore, the leveling agent used for hard foam, semi-hard foam and high resilience is generally Si-C type. Its structure is generally:
In a word, we say: silicone oil is a kind of organic silicone oil additives that can make the foam rise stably during the foaming process, make the foam body rise smoothly without collapsing the foam during the rising process of the foam, and make the structure of the bubble holes uniform and fine, and do not break the bubble. Ten years ago the domestic production of silicone oil is relatively low, and did not enter the high-end market, the market is mainly controlled by Europe and the United States. After years of national efforts, hard foam silicone oil market is now mainly done by domestic companies, and from low-end to high-end, from insulation to refrigerators have a series of product supply. Like us, Dongjun Chemical produces more than 2,000 tons of silicone oil every year, of which more than 500 tons are exported, and the export volume is still on the rise, and many products are exported to Europe and the United States market.
The role of silicone oil
The role of silicone oil is simply to make the foam system can send up the foam, can stabilize the foam, so that the foam issued by the bubble hole is fine and uniform, closed cell rate is high. Without the addition of silicone oil will collapse the bubble, is not able to send out the foam.
So how does silicone oil play a role in controlling the role of the bubble hole, mainly in the following aspects:
Emulsification
Silicone oil is a kind of emulsifier, one end of the lipophilic, one end of the hydrophilic, can make the white material in the components (especially polyether, polyester, foaming agent) in the mixing process can form a homogeneous, stable solution, so that the combination of materials do not stratify. As shown in the figure below:
In addition in the black and white material mixing process can also play a certain role in making the black and white material mixed evenly. As we all know, the more evenly mixed black and white materials, the more fully reacted, the more uniform the resulting foam holes, the better the fluidity, the smaller the density distribution gradient.
Nucleation
In the reaction just occurred, the silicone oil has to reduce the surface tension of the system, so that the system in the mixing of the air into the formation of a certain number of bubbling nuclei, in the process of foam development, the nucleation of the bubble nuclei play a similar role as the “crystal seed”, so that the foam can be formed smoothly, slowly get bigger, if the foam is not shaped bubble nuclei, then the shape of a uniform foam body. If the bubble is not formed into a nucleus, then it will not be formed into a homogeneous bubble body. Like we blow soap bubbles, do not add some washing powder or detergent, who can not blow a string of bubbles, only add a little bit of washing powder can be blown out of the colorful bubbles.
Stabilization of the role of foam
Foam is very, very small when it is first formed, and as the foaming reaction proceeds, the foam grows, and there is a constant flow of gas into the bubbles. In this process before the foam curing, the foam body is also still very fragile, a careless will break, silicone oil is a surfactant, the presence of silicone oil, it can be directed to arrange in the surface of the foam, to protect the foam, to avoid the merger of the bubbles and bubbles, so as to make the foam stabilization, is not a bubble rupture, merger, endless expansion, thus ensuring the formation of an independent bubble;;.
On the other hand, silicone oil can dissolve the urea formed by the reaction between black material (MDI) and water, so that the tension of the bubble wall is uniform and there is no stress point, which ensures that the foam does not break until the foam body is cured and forms a foam with uniform and high closed cell structure.
