What does the polymerization process involve for resins?

The polymerization process is a chemical reaction where small molecules called monomers join together to form a larger, more complex structure known as a polymer. In the context of resins, this means that the initially liquid resin, when subjected to certain conditions such as heat or the addition of a hardener, undergoes a transformation into a solid state. This transition from liquid to solid is fundamental to the curing process of resins in composite materials, as it defines the structural integrity and mechanical properties of the final product.

As for the other options, changing from solid to gas refers to sublimation or vaporization, which is not a characteristic of the polymerization process. Mixing with additives, while often part of preparing composites, does not describe the core chemical reaction of polymerization itself, which focuses on the transformation of the resin. Lastly, evaporation of solvents can occur in some resin systems but does not represent polymerization; instead, it can be a separate process that occurs in conjunction with or after polymerization, affecting final properties but not defining the polymerization process itself.