What is a crosslinking agent?
1. Co-crosslinking agent refers to a type of auxiliary agent that improves the crosslinking efficiency of peroxides, most of which are compounds with polyunsaturated functional groups. The contribution of the auxiliary crosslinking agent to the crosslinking efficiency is generally understood as providing a higher concentration of reactive sites, inhibiting side reactions such as polymer radical disproportionation or chain scission, and helping to form more crosslinking bonds.
2. The specific use effect of the crosslinking agent is not only related to its chemical structure and added amount, but also related to various conditions such as the type of polymer and crosslinking peroxide.
1. The influence of crosslinking agent on physical properties
The use of cross-linking aids helps to increase the cross-linking density. In terms of physical properties, it is manifested as an increase in modulus, hardness, and a decrease in elongation at break and compression set. In some cases, it can also improve tensile strength, tear strength, heat resistance, abrasion resistance, or dynamic performance.
The effect of using auxiliary crosslinking agent on physical properties is mainly manifested in the following aspects: (Not all properties can be obtained at the same time, and some properties can be achieved by using specific auxiliary agents)
Reduce permanent compression set;
Increase the hardness;
Reduce rubber viscosity and improve processing performance;
Improve oil resistance;
Improve heat aging resistance;
Improve the adhesion of rubber and metal products;
Increase the vulcanization speed;
Reduce the amount of peroxide;
Increase tensile strength;
Improve tearing and hot tearing performance;
Improve dynamic flexing performance;
2. The influence of the structure of the crosslinking agent on the performance of the crosslinking agent
The structure of the crosslinking agent is closely related to the performance of the crosslinking agent. The type of functional group of the crosslinking aid, the number of functional groups, the structure of the bridge bond, the polarity of the molecule, the molecular weight, etc. will all affect the performance of the crosslinking aid.
The type and number of functional groups are the primary parameters that affect the vulcanization performance of the crosslinking agent, which directly affects the activity of the crosslinking agent, the solubility in the polymer and the physical properties of the product. Common crosslinking agents are mostly bifunctional and trifunctional additives;
The structure of the bridge bond, which includes the polarity of the bridge bond, the length of the bridge bond, and the molecular structure. Although the structure of the bridge bond usually has no direct effect on the activity of the crosslinking agent, it may affect the efficiency of the crosslinking agent, the solubility in the polymer, and the strength of the crosslinking bond, which are also very important parameters. ；
The molecular weight can have an impact on the efficiency of the crosslinking agent, and it can also be used as an important evaluation parameter for the volatility of the crosslinking agent. If the molecular weight is small, the volatility may be high;
The polarity of the auxiliary crosslinking agent can directly affect its solubility in the polymer and other factors, thereby affecting the vulcanization efficiency and performance;
3. Classification of crosslinking aids
According to their contribution to vulcanization, crosslinking aids can be divided into two categories. One is to increase the degree of vulcanization while also increasing the vulcanization speed, which is also called the first type of crosslinking aid; the other is to only increase the degree of vulcanization or crosslinking density without increasing the vulcanization speed, also known as The second type of crosslinking agent.