Sealant is widely used in building curtain walls, doors and windows, interior decoration and other fields, and is an important auxiliary material for building joints and sealing. In order to give full play to its sealing performance, the adhesion between sealant and contact materials becomes very important. Theoretical Details At present, there are mainly the following theories in the industry:

1. Adsorption theory

According to adsorption theory, the main source of adhesive force is intermolecular force of adhesive system, that is, van der Waals force and hydrogen bond force. Firstly, the adhesive molecules diffuse to the surface of the adherend through Brownian motion, so that the polar groups or links at the two interfaces are close to each other. Then, when the distance between the adhesive and the adherend molecules reaches 5-10 Amy, the interface molecules will generate mutual attraction. Intermolecular force is the factor that provides adhesion, but it is not the only factor.

2. Theory of chemical bond formation

Theoretically, apart from intermolecular force, there are sometimes chemical bonds between sealant and adherend molecules. The strength of chemical bond is much higher than van der Waals force, and the formation of chemical bond is of great significance to improve bonding strength and durability. However, the formation of chemical bonds is not common, and the number of chemical bonds per unit bonding interface is much less than that of intermolecular interaction, so the bonding strength comes more from intermolecular interaction.

3. Diffusion theory

On the premise of compatibility, when the two polymers are in close contact with each other, mutual diffusion occurs due to Brownian motion of molecules or swing of chain segments. The result of diffusion leads to the disappearance of interface and the formation of transition zone. However, the diffusion theory can't explain the adhesion between polymer materials and metal, glass or other hardware, because it is difficult for polymers to diffuse to such materials.

4. Electrostatic theory

The main basis of this theory is that the energy consumed in peeling is consistent with the adhesion work calculated by electric double layer model. When the system of sealant and adherend is a combination of electron acceptor and donor, an electric double layer is formed on both sides of the interface region, thus generating electrostatic attraction. However, the electrostatic effect only exists in the adhesive system that can form an electric double layer, and it is not universal. Therefore, although electrostatic force does exist in some special bonding systems, it is not the dominant factor.

5, mechanical combination

Theoretical mechanical action is not a factor that produces adhesive force, but a method to increase adhesive effect. The adhesive penetrates into the cracks or concavities on the surface of the adherend, and after curing, it produces meshing force in the interface area. The essence of mechanical bonding force is friction force, which is particularly important when bonding porous materials, paper, fabrics, etc., but this effect is not significant for some solid and smooth surfaces. Simply understood, bonding includes two parts: bonding and bonding. Bonding refers to bonding strength and bonding refers to infiltration. The summary is shown in the following figure:

The adhesion of sealant is influenced by many factors in practical application, mainly including the following five factors: a. The properties of adhesive substrate: the substrate with greater surface energy and polarity is easier to adhere; B. Types of sealants: Different types of adhesives have different adhesion to different materials; C use environment of sealant: temperature and humidity of construction environment, chemical solvent, PH, ultraviolet aging, etc. D. Bonding interface: rough, porous, loose, smooth and dense, flat or curved; E. Construction: construction environment (temperature and humidity), substrate surface treatment (cleaning and primer coating), glue injection and finishing, etc. In practical application, we should standardize the construction, carry out the construction in strict accordance with the sealant construction technology, fully avoid the bonding failure caused by the unfavorable conditions in the above factors, and strengthen the quality control in the construction process.