Thermoplasticization

Thermoplasticization is the process by which a material is rendered thermoplastic—capable of softening and flowing when heated—by increasing molecular mobility or reducing crosslink density. In polymer science, it is most commonly achieved by introducing plasticizers, small molecules that insert between polymer chains, weaken intermolecular forces, and lower the glass transition temperature (Tg) and melt viscosity. This enables melt processing and reprocessing, such as extrusion, injection molding, and recycling of materials that would otherwise be thermosetting or brittle.

In natural polymers, thermoplasticization is exemplified by thermoplastic starch, obtained when starch is heated in the presence of water and plasticizers (e.g., glycerol, sorbitol) to gelatinize and plasticize the granules, producing a processable, moldable material. Similar strategies apply to lignocellulosic fibers, proteins, and cellulose derivatives to improve processability or to form bio-based composites.

For thermosetting or crosslinked systems, true thermoplasticization requires modification of the network—such as partial depolymerization, cleavage of crosslinks, or the use of dynamic covalent bonds (vitrimers) that can rearrange under heat—to allow flow and reshaping.

Characterization typically involves differential scanning calorimetry to determine Tg, melt rheology or melt flow index to assess flow, and mechanical testing to evaluate property changes. Practical considerations include plasticizer compatibility, migration, moisture sensitivity, and potential loss of stiffness or strength upon plasticization.