Curing/ Vulcanizing Agent and Crosslinking
Crosslinking or curing is the formation of chemical links between molecular chains to form a three dimensional network of connected molecules.
Crosslinking or Curing Agent is the formulation component that causes this reaction to take place. These terms are generally used with all polymeric materials that are capable of forming a thermosetting structure.
The crosslinking of rubber with sulfur is called vulcanization. Crosslinking bonds the chains together to form a network. The term “Vulcanizing Agent” is generally used with rubber or elastomers.
Crosslinking agents are multifunctional chemical compounds,that react with functionality of the molecular chains in the base polymer and thereby form a thermoset of three-dimensional polymeric materials.
The curing agents are of di- or higher functionality, and they become an integral part of the final thermoset material except for materials lost in a condensation crosslinking process. These crosslinking agents can range from low molecular weight to polymeric materials. Crosslinking causes changes in physical and chemical properties. It causes changes in hardness, tensile strength, modulus, elongation, solution, swelling and other properties.
The resulting product is called a thermoset, because it does not flow on heating. Crosslinking increases the thermal stability and mechanical properties of the polymer. It provides important effects on both the curing features and on the fundamental properties of the adhesive or sealant system.
The figure below illustrates a crosslinked resin and shows how the number of crosslink sites, the length of the crosslinking agent molecules, and the distance between crosslinks on the base polymer affect the properties of the final adhesive.
Functionality of Polymer