With the use of adhesive technology more and more widely, the aging problem of adhesive joints has received more and more attention. The reasons for aging adhesive joints can be divided into the following aspects: the impact of mechanical loading on joints, the impact of the natural environment on joints, and the transfer of adhesive components. Today, let's talk about how the natural environment contributes to the aging of bonding joints:

1) Temperature and radiation

Temperature has a great influence on chemical reactions. The higher the temperature, the higher the likelihood of a chemical reaction and the faster the reaction. This reaction leads to poor performance changes in the bonding joints. The mechanical stress also leads to the accelerated failure of the bonding joint at high temperature. It is generally believed that the high temperature accelerates the rapid aging of the adhesive joints. The other side is radiation, especially ultraviolet radiation in the sun. The high molecular chain segments in adhesives and plastic substrates are vulnerable to ultraviolet light and lead to the destruction of molecular chains. In particular, polyurethane is very sensitive to ultraviolet light.

2) Water

Moisture can penetrate(diffuse) into the cemented layer and be absorbed by the layer. These absorbed water molecules reduce the cohesive strength of the glue. Because water acts as a lubricant between polymer chains(plasticizer effects), the molecular chains slide more easily to each other. The rate of water infiltration into the colloid layer is very low, but it is very persistent. At an ambient temperature of 40 °C, for cross-linked polymers, the water permeability rate is about several millimeters per month. When the adhesive joint is dry, the cohesion strength rises again and returns to its original level. The biggest problem caused by the exposure of adhesive joints to moisture is that water penetration reduces the adhesion of substrate and adhesive. After water penetration into the adhesive joint, the adhesion becomes smaller. Weakening the adhesion of the adhesive and substrate is usually a slow process. Chemical bonds formed on the surface of glue and substrate are more resistant to water vapor than physical interactions. Once the chemical bond is destroyed, its adhesion can not be restored after drying. The best way to prevent the glue from being affected by water vapor is to stay away from water vapor. If this is not possible, seal the connector.

3) Corrosion

For metal joints, the corrosion of the substrate is mainly caused by the penetration of water vapor. Corrosion of substrate leads to fast failure of bonding joint in a short period of time. Salt, acid, alkali, water vapor and other substances accelerate the occurrence of decay. These materials can not only corrode the substrate but also slowly penetrate into the interior from the outside of the rubber layer and affect the cohesion and adhesion of the rubber layer. Therefore, on the one hand, we need to protect the substrate and adhesive layer as much as possible. On the other hand, we need to improve the corrosion resistance of adhesives and substrate.

4) Chemical medium

Acid rain, acidic smog, or commonly used detergents in nature can also accelerate the aging of bonding joints. On the one hand, these substances containing chemicals will corrode the surface of the substrate of the adhesive, and on the other hand, they will cause irreversible damage to the adhesive layer and the cohesive layer.