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Aug 5, 2019
With the rapid development of China's industrial and construction industry, silicone sealant is a new type of in-situ embedded, adhesive joint, room temperature curing elastic sealing material, and its application field is more and more extensive. Silicone sealant is composed of five main components: basic polymer, crosslinker, filler, coupling agent and plasticizer.
With the promotion of silicone sealant production technology and the intensification of competition among enterprises, some manufacturers use white oil instead of dimethicone as a plasticizer for silicone sealers in order to reduce costs. The use of a large amount of white oil in silicone sealant instead of silicone oil has greatly reduced the performance of silicone sealant, such as weather resistance, high and low temperature resistance, and performance of high performance silicone sealant. This greatly reduces the performance and service life of the inherently high durability, high performance silicone sealant. After being used in engineering, such white oil sealant has poor aging resistance and large volume shrinkage, and is prone to cracking, brittleness and hardening of the sealant, affecting the sealing and appearance of the curtain wall and even causing serious engineering accidents.
Dimethyl silicone oil is a colorless and odorless transparent liquid. Its molecular formula is mainly composed of dimethyl silicone segment, and its structure is very similar to that of silicone sealant, so it has good compatibility with base rubber. Dimethicone is odorless, non-toxic, non-volatile, and has good chemical stability. It has a small viscosity change over a wide temperature range, a high boiling point, a low freezing point, and a wide temperature range as a liquid, and can be used for a long period of time at -50 to 200 °C. Dimethyl silicone oil has good electrical properties, especially in various frequency ranges. It has small surface tension and excellent shear resistance. Based on the above excellent properties, dimethyl silicone oil is particularly suitable for use as a plasticizer and a diluent in silicone sealants.
In the application of silicone sealant, considering the needs of construction, it is often necessary to adjust the viscosity of the sealant, reduce the viscosity of the adhesive, improve the fluidity of the construction and the lubricity of the adherend, so use dimethyl silicone oil as the increase. Plasticizer. At the same time, the addition of plasticizer can also improve the comprehensive performance of the adhesive layer after curing, and improve the impact resistance and fatigue resistance of the bonded joint.
On the other hand, the addition of plasticizers can also have an effect on other properties of silicone sealants. Generally, as the amount of plasticizer increases, the tensile strength of silica gel will gradually decrease, and the elongation at break will gradually increase. The reason for this is that the addition of the non-reactive dimethyl silicone oil plasticizer reduces the number of joints between the polymer molecular chains, so that the crosslink density is reduced, and finally the tensile strength is reduced. In addition, the reduction in crosslink density reduces the stiffness of the three-dimensional structure, and the molecules are easily slipped, resulting in an increase in elongation at break. In addition, it has also been found that as the amount of plasticizer increases, the bond strength of the silicone gel generally decreases. The reason for this is that the plasticizer used is a non-reactive plasticizer which acts to dilute the active molecules of the silica gel, resulting in a decrease in the number of reactive groups per unit volume.
In order to adapt to the larger-scale development of buildings in the future and maintain the market growth of silicone sealant, enterprises should continuously improve product quality, enhance their ability to sustain development, and adhere to industry self-discipline and regulate the market. Dimethicone has been widely used as a plasticizer in silicone sealants. The replacement of silicone oil as a plasticizer by white oil can greatly reduce the performance of silicone sealant. In engineering use, white oil sealant should be rejected and silicone sealant should be selected.