What process initiates cross-linking between thermoset molecule chains?

The correct answer is curing. Curing is a chemical process that involves the hardening or setting of thermoset resins through cross-linking. During curing, heat, light, or chemical additives are often applied to initiate a reaction between the thermoset molecule chains. This process results in the formation of a three-dimensional network of interconnected molecules, which gives thermosets their desirable mechanical and thermal properties.

In contrast, melting refers to the phase transition of materials from solid to liquid, which is pertinent to thermoplastics rather than thermosets. Printing generally refers to the additive manufacturing process itself without specifically addressing the chemical changes occurring in thermosets. Sintering is a process used primarily for ceramics and metals, where powdered materials are heated below their melting point to form a solid mass, which also does not involve the cross-linking process characteristic of thermosets. Understanding these differences highlights the unique importance of curing in modifying the structure and performance of thermoset materials.