With the promotion of silicone sealant production technology and the intensification of competition among enterprises, some manufacturers use white oil instead of dimethyl silicone oil as the plasticizer of silicone sealers in order to reduce costs. The use of a large amount of white oil instead of silicone oil in silicone sealant will greatly reduce many properties of silicone sealant, such as weather resistance, high and low temperature resistance, and high-performance silicone sealant. This greatly reduces the performance and service life of the silicone sealant with high durability and performance. After being used in the project, this kind of white oil sealant has poor aging resistance, large volume shrinkage, and is very easy to crack, become brittle and hard, which affects the sealing and appearance of the curtain wall and even causes serious engineering accidents.
Dimethyl silicone oil is a colorless and odorless transparent liquid. Its molecular formula is mainly composed of dimethylsiloxane segments. Its structure is very similar to the basic polymer of silicone sealant, so it has good compatibility with the base adhesive. Dimethyl silicone oil is odorless, non-toxic, nonvolatile and has good chemical stability. In a wide temperature range, the viscosity changes little, and the boiling point is high, the freezing point is low. As a liquid, it has a wide temperature range and can be used for a long time within - 50~200 ℃. Dimethyl silicone oil has good electrical performance, especially in a variety of frequency ranges, with small time rate factor. Its surface tension is small and its shear resistance is excellent. Based on the above excellent properties, dimethyl silicone oil is particularly suitable for use as plasticizer and thinner in silicone sealant.
In the application of silicone sealant, considering the construction needs, it is often necessary to adjust the viscosity of the sealant, reduce the viscosity of the adhesive, improve the construction fluidity and the lubricity of the adhesive, so dimethyl silicone oil is selected as the plasticizer. At the same time, the addition of plasticizer can improve the comprehensive properties of the cured adhesive layer, and improve the impact resistance and fatigue resistance of the adhesive joint.

On the other hand, the addition of plasticizer will also affect other properties of silicone sealant. Generally, with the increase of plasticizer content, the tensile strength of silica gel will gradually decrease and the elongation at break will gradually increase. The reason is that the addition of non reactive dimethyl silicone oil plasticizer reduces the number of connecting points between polymer molecular chains, which reduces the cross-linking density, and finally reduces the tensile strength. In addition, the decrease of crosslinking density reduces the stiffness of the three-dimensional structure, and the molecules are easy to slip, leading to an increase in elongation at break. In addition, it was also found that the adhesive strength of silica gel generally decreased with the increase of plasticizer dosage. The reason is that the plasticizer used is a non reactive plasticizer, which dilutes the active molecule of silica gel and will reduce the number of active groups in 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 constantly improve product quality, enhance the ability of sustainable development, and jointly adhere to industry self-discipline and regulate the market. Dimethyl silicone oil as a plasticizer has been widely used in silicone sealant, and white oil instead of silicone oil as a plasticizer will greatly reduce the performance of silicone sealant. In engineering use, white oil sealant shall be rejected and silicone oil sealant shall be selected.

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