Thermoplastics

Thermoplastics are a class of polymers that become soft and deformable when heated and harden when cooled. Unlike thermosetting polymers, which form cross-linked networks during curing and cannot be remelted, thermoplastics consist of relatively linear or branched chains that can be repeatedly melted and reshaped without significant chemical change.

The behavior of thermoplastics is governed by glass transition temperature (Tg) for amorphous or semi-crystalline polymers, and melting temperature (Tm) for crystalline portions. Below Tg or Tm they are rigid; above, they flow. Molecular weight, degree of crystallinity, and additives influence properties such as stiffness, toughness, chemical resistance, and heat resistance.

Processing methods include extrusion, injection molding, blow molding, and thermoforming for parts and films. Thermoplastics can also be used in additive manufacturing, notably FDM and material extrusion. They are typically recyclable by re-melting and reforming, though recycling efficiency depends on purity, additives, and polymer type.

Common families include polyethylene (PE), polypropylene (PP), polystyrene (PS), polyvinyl chloride (PVC), polyethylene terephthalate (PET), polycarbonate (PC), polymethyl methacrylate (PMMA), and nylons (polyamides). They range from clear and stiff to tough and impact-resistant; crystallinity influences transparency and mechanical properties.

Applications span packaging, automotive components, pipes, electrical housings, and consumer goods. Environmental considerations include recycling rates, energy use for remelting, and issues related to additive migration and microplastic generation. Thermoplastics are widely used because of their versatility, processability, and potential for circular materials design.