Application of polyurethane sealant in construction

Polyurethane sealant is one of the three major elastic sealants (silicone, polysulfide, polyurethane) in the world. It is mainly used for sealing between building components or materials, such as caulking, connection sealing of concrete components, filling of expansion joints of highways and airports, bridges, waterproof materials for tunnel projects, bonding and sealing of double-layer glass, etc.The use of these sealing materials not only solves the problem of leakage of buildings and extends their service life, but also improves their thermal insulation performance and achieves the purpose of energy saving.Polyurethane sealant has developed rapidly because of its excellent performance, wide range of uses and cheap price. Its price is only half that of silicone, which is much lower than that of polysulfide sealant.

Polyurethane sealants appeared in the U.S. market in the 1970s. Two-component and one-component polyurethane sealants appeared in Japan in 1967 and 1970, respectively. Due to their excellent performance and low prices, production and sales in developed countries have been increasing. In less than 10 years, it has reached the level of annual consumption of more than 10,000 tons in industrial developed countries such as Japan and the United States. In the United States, polyurethane sealants have dominated the construction sealants.

1.Characteristics of polyurethane sealant

Silicone sealant has the advantages of high elastic recovery rate, small shrinkage, weather aging resistance, low temperature resistance and high temperature resistance, but its own strength is low, the adhesion to the adhesive material is poor, and the price is high; polysulfide sealant has the advantages of small shrinkage, low temperature vulcanization, good water resistance, and low moisture permeability, but it has odor, compression deformation, easy aging, and high price, making it difficult to meet the requirements of the construction industry.Compared with other sealants, polyurethane sealants have the following characteristics: high strength, good elasticity, wear resistance, insulation, cold resistance, high adhesion to general building materials, and can be used in almost all fields of construction.Especially for those materials with obvious expansion and contraction and large thermal expansion and cold shrinkage, the high elongation and good elastic resilience of polyurethane sealants can meet the sealing requirements of materials or components.Moreover, among high-end sealing materials, the price of polyurethane sealants is relatively low. For example, in the United States, the price of polyurethane sealants is 70% lower than polysulfide and 50% lower than silicone. Therefore, the application of polyurethane sealants in the construction industry is growing day by day.

2.Classification of polyurethane sealants

Polyurethane sealants occupy a dominant position in sealing materials. There are also sealing belts, gaskets, and water stop belts. They are mainly suitable for sealing with ±25% seam deformation and displacement. They are high-end products in sealants.

There are two main types of polyurethane sealants, namely one-component and two-component.What first appeared on the market was a two-component polyurethane sealant.Two-component polyurethane sealant has the advantages of fast crosslinking speed and good performance, but it also has its own disadvantages. For example, it takes a long time to mix. If the proportion of components A and B is wrong or the mixing is uneven, it will cure poorly, affect its physical and mechanical properties, and shorten its service life.Two-component polyurethane sealants are generally divided into two types of construction in summer and winter, because the seasons are different.The temperature is different, and the content of catalyst in the curing agent component should be adjusted to ensure the safety of operation and the quality of the cured product.One-component polyurethane sealant is convenient for construction and does not have mixing problems, so its proportion in polyurethane sealant is gradually increasing.According to the different structure and curing mechanism, it can be roughly divided into three types:

1.Solution type: It is generally an organic solvent glue or a water-dispersible liquid glue of terminal hydroxyl polyurethane elastomer, and its curing mechanism is solvent or water volatilization.

2.Solvent-free type: terminal isocyanate polyurethane prepopolymer solvent-free glue.The curing mechanism is that the active terminal isocyanate group in the prepolymer reacts chemically with moisture in the air or in contact with the material to obtain crosslinking.This kind of glue was successfully developed and popularized in the late 1970s and early 1980s. It has the advantages of solvent-free, environmental protection, safety, hygiene, and energy saving. It meets the general new requirements for sealants in the world and is a representative of the current one-component polyurethane sealant.

3.Two-component, single-packaging type: A single-packaging mixture composed of a prepoler and a curing agent after passivation or closure of the active group by a certain physical and chemical method.The curing mechanism is that when heated to a certain temperature, the active group can be passivated or closed, the activity of the original functional group can be restored, and a chain-expanding crosslinking reaction similar to that of a two-component polyurethane sealant occurs and it is cured. It is also known as a thermosetting one-component polyurethane sealant.