Foam stabilizer (silicone oil)
1. What is silicone oil
Silicon oil is a kind of organic silicone surfactant. It was first called Foaming Spirit in China and Silicone surfactant in foreigners. Taiwanese and Hong Kong people call it Silicone. Later, the Chinese usually called it foam stabilizer or foam stabilizer. This type of surfactant can be divided into Si-O-C type and Si-C type. The Si-C bond does not hydrolyze, but the Si-O-C bond is easily hydrolyzed under strong acid or alkali conditions. The foam stabilizer prepared using this connection method is not suitable for formulating composite materials because it interacts with the tertiary amine catalyst and After the water mixture is stored for a period of time, the product will lose its foam-stabilizing effect due to the hydrolysis of the Si-O-C bond. Therefore, foam leveling agents used for hard foam, semi-hard foam, and high resilience are generally Si-C type. Its structure is generally:
In short, we say: silicone oil is a kind of oil that can make the foam rise stably during the foaming process, make the foam rise steadily without collapsing, and make the cell structure uniform and fine without breaking the foam. Silicone oil additives. Ten years ago, the domestic production of silicone oil was relatively low, and it did not enter the high-end market. The market was mainly controlled by European and American countries. After the efforts of the Chinese people over the years, the current market for hard foam silicone oil is mainly produced by domestic companies, and a series of products are supplied from low-end to high-end, from insulation to refrigerators. For example, our 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 rising. Many products are exported to European and American markets.
2. The role of silicone oil
Simply speaking, the function of silicone oil is to enable the foaming system to foam, to hold the foam stably, to make the foamed cells fine and uniform, and to have a high closed cell rate. Without silicone oil, the foam will collapse and there will be no foam.
So how does silicone oil control cells? The main aspects are as follows:
2.1 Emulsification
Silicon oil is an emulsifier, with one end being lipophilic and the other end hydrophilic, which enables the various components in the white material (especially polyether, polyester, and foaming agent) to form a uniform and stable consistency during the mixing process. solution so that the combined materials do not stratify. As shown below:
In addition, during the mixing process of black and white materials, it can also play a certain role in making the black and white materials evenly mixed. We all know that the more uniformly the black and white materials are mixed, the more complete the reaction will be, the more uniform the cells of the resulting foam will be, the better the fluidity will be, and the smaller the density distribution gradient will be.
2.2 Nucleation
As soon as the reaction occurs, the silicone oil reduces the surface tension of the system, causing the mixed air to form a certain number of bubble nuclei when the system is stirred. During the foaming process, the nucleated bubble nuclei will form. It acts like a “seed crystal”, allowing the foam to form smoothly and gradually grow in size. If the foam cannot form a bubble core, it will not form a uniform foam. Just like we blow soap bubbles, no one can blow out a string of bubbles without adding some washing powder or detergent. Only by adding a little washing powder can we blow out colorful bubbles.
2.3 The role of foam stabilization
The foam is very small when it first forms. As the foaming reaction proceeds, the foam continues to grow, and gas continues to enter the bubble. During the process before the foam is cured, the foam is still very fragile and will break if you are not careful. Silicone oil is a surfactant. With the presence of silicone oil, it can be oriented and arranged on the surface of the foam to protect the foam and avoid It prevents the merging of bubbles to stabilize the bubbles and prevent them from bursting, merging, and endless expansion, thereby ensuring the formation of independent bubbles;
On the other hand, silicone oil can dissolve the urea formed by the reaction between black material (MDI) and water, thereby making the tension of the bubble wall uniform and without stress points, ensuring that the foam does not break until the foam solidifies to form a uniform high closed cell structure. Foam.
2.4 Improve the fluidity and density distribution of foam
We say that silicone oil is a surfactant that can reduce the surface tension of the system. Reducing the surface tension is conducive to improving the wettability of the foam to the base material mold, thereby improving fluidity and density distribution and reducing dark bubbles. The following is a comparison of the liquid flow between the two groups with and without surfactant.
3. Classification of silicone oil
The classification of silicone oil is still based on its characteristics, which are generally divided into three categories: 1. Silicone oil with strong nucleation ability; 2. Silicone oil with strong emulsification ability; 3. Silicone oil with good fluidity. There are many classifications in other applications, such as classification according to foaming agent: F-11 system, 141B system, cyclopentane system, all-water system; classification according to use: home appliances, plates, spraying, etc. There are many classifications, but the essence is based on the characteristics given to the silicone oil by its own structure. We usually use different silicone oils for different foaming agents, and use different silicone oils for different purposes. In the final analysis, it is still based on the above three aspects of requirements and different.
Basic performance classification of silicone oil
For example: 1. We all say that the silicone oil used in the cyclopentane system is different from that of the 141B system. Why? A very important reason is that the compatibility between cyclopentane and conventional polyether systems is poor. So, to make the composite system stable, you either need to use special polyether, or you need to use silicone oil with strong emulsifying ability.
2. Some people say that our combination material does not have a high yield rate as others. That is because the fluidity and starting speed of your combination material are not good enough, and the silicone oil you choose is a silicone oil with poor fluidity. How can the power rate be high?
