Application of silicone oil in silicone sealant

With the rapid development of industry and construction in China, silicone sealant, as a new type of elastic sealing material for on-site filling, bonding joints, and curing at room temperature, has become increasingly widely used in various fields. Silicone sealant is composed of five main components: basic polymer, cross-linking agent, filler, coupling agent, and plasticizer.

With the promotion of silicone sealant production technology and the intensification of competition among enterprises, some manufacturers have adopted white oil instead of dimethyl silicone oil as the plasticizer for silicone sealants in order to reduce costs. Using a large amount of white oil instead of silicone oil in silicone sealants can greatly reduce many properties of silicone sealants, such as weather resistance, high and low temperature resistance, and the performance of high-performance silicone sealants. This greatly reduces the performance and service life of the originally high durability and high-performance silicone sealant. After being used in engineering, this type of white oil sealant has poor aging resistance, large volume shrinkage, and is prone to cracking, embrittlement, and hardening of the sealant, affecting the sealing and appearance of curtain walls, and even causing serious engineering accidents.

Dimethyl silicone oil is a colorless and odorless transparent liquid, whose molecular formula is mainly composed of dimethylsiloxane segments. Its structure is very similar to the base 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, the temperature range is wide, and it can be used for a long time within - 50~200 ℃.". Dimethyl silicone oil has excellent electrical properties, especially in various frequency ranges with low time 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 a plasticizer and 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 construction fluidity and lubricity of the adhesive, so dimethyl silicone oil is selected as a plasticizer. At the same time, adding plasticizers can also improve the comprehensive properties of the cured adhesive layer, and improve the impact resistance and fatigue resistance of the bonded joint.

On the other hand, the addition of plasticizers can also have an impact on other properties of silicone sealants. Generally, as the amount of plasticizer increases, the tensile strength of silica gel gradually decreases, and the elongation at break gradually increases. The reason is that the addition of non reactive dimethyl silicone oil plasticizer reduces the number of connection points between polymer molecular chains, resulting in a decrease in cross-linking density and ultimately in tensile strength. In addition, the decrease in crosslinking density reduces the stiffness of the three-dimensional structure, causing molecules to slip easily, 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 in the amount of plasticizer. The reason is that the plasticizer used is a non reactive plasticizer that dilutes the active molecules of silica gel, resulting in a decrease in the number of active groups per unit volume.

In order to adapt to the larger development of construction in the future and maintain the market growth of silicone sealant, enterprises should continuously improve product quality, enhance their sustainable development ability, and jointly adhere to industry self-discipline and standardize the market. Dimethyl silicone oil has been widely used as a plasticizer in silicone sealants. Using white oil instead of silicone oil as a plasticizer can significantly reduce the performance of silicone sealants. In engineering use, the use of white oil sealant should be rejected and silicone oil sealant should be selected.