Thermoplastics (or thermoplastic polymers or thermoplastic resins) are those plastic materials that acquire malleability, that is, they soften under the action of heat. At this stage they can be molded or formed into finished objects and then by cooling they become rigid again. This process, theoretically, can be repeated several times according to the qualities of the different plastic materials. These polymers are formed from linear or loosely branched chains that are not bonded to each other (i.e., not cross-linked).
Thermoplastic polymers are amorphous or semi-crystalline polymers characterized by linear or loosely branched non-cross-linked (i.e., unbonded) polymer chains. These characteristics define the thermoplasticity of this material, or their susceptibility to temperature, which if sufficiently high involves a melting principle that makes them viscous enough to deform plastically (or irreversibly).
Amorphous thermoplastic polymers
Amorphous thermoplastic polymers are typically transparent and made up of intertwined and twisted chains, below their melting temperature they have a certain strength and elasticity. The behavior of amorphous polymers is strongly influenced by temperature.
Crystalline thermoplastic polymers
Crystalline thermoplastic polymers, on the other hand, are typically opaque and composed of crystalline zones (in which the polymer chains are arranged in an orderly manner, all following the same orientation) interspersed with amorphous zones. In order to be semi-crystalline, polymers must have two criteria for crystallizability: regularity of constitution (along the polymer chain, there must be an order in which the atoms are repeated) and configuration (the monomer must have the same atoms in the same place along the chain).
Morphology of thermoplastic polymers
- fringed micelles: the base material is divided into two parts: crystalline zone and amorphous zone. As the length of the chains is typically greater than the length of the crystalline zones, the same chain is part of several crystalline zones;
- with folded chains: from the solidification of a very dilute solution it was discovered that the single crystal had the shape of a lamella, which had a height of 100 Å (Armstrong), less than the thickness of the chains. In the case of polymer obtained from melt a “superstructure” is formed, in which the lamella is the basic element, called spherulite.