Crystalline | What is crystalline?

In a crystalline substance, the particles of a material are arranged in an ordered pattern relative to one another. The folded chains then exist side by side in their folded state. As plastics are chain molecules, they are difficult to structure. Consequently, most plastics are (partially) . There are three conditions under which a plastic can crystallise: the chain must be linear (i.e. it must not have any branches), the side groups must not be bulky, and the chain must have a regular arrangement of the side groups relative to the main chain (tacticity).

However, complete crystallisation is not possible in macromolecular substances. This is because the chains never exhibit a completely regular structure and entanglements occur between the chain molecules, which disrupt the crystal pattern. In addition to the crystalline phase, plastics therefore always contain an phase. Crystallinity is consequently expressed as the percentage of crystallised material relative to the total amount of polymer.