Thermoplastic Polymers

A thermoplastic is a type of plastic made up of polymer resins that are hard at room temperature and become softer when they are heated, hardening again as they cool down. When thermoplastics are heated, their physical properties change and they become a homogenized liquid and can be shaped into different forms. Some thermoplastics are derived from theproduced by the petrochemical industry and are hard to dispose of in the environmentan environmentally friendly way, while some are produced from natural sources, such as corn starch, and are thus therefore compostable. Some thermoplastics, including some derived from petrochemicals, are recyclable.

The most common thermoplastic materials used in 3D printing include polylactic acid (PLA), PET/PET-G, nylon (polyamide or PA), acrylonitrile butadiene styrene (ABS), Acrylonitrile styrene acrylate (ASA), polycarbonate (PC) and polypropylene (PP). Some thermoplastics, including ULTEM (Polyetherimidepolyetherimide/PEI), PEEK and PEKK, can offer very high temperature and chemical resistance properties, which are comparable to some metals and are often referred to as technopolymers or high-performance plastics. Thermoplastics also include rubber-like materials used in 3D printing, such as thermoplastic polyurethane (TPU) and thermoplastic elastomers (TPE)PE.

Some additional categorizations define these materials used in 3D printing thermoplastics, which their molecular structure can classify: some are amorphous, while others are semi-crystalline. Thermoplastics can be amorphous, which means that they have a randomly ordered molecular structure that lacks a sharp melting point, which means they. The result is that amorphous materials soften gradually as the temperature increases. They are mostly translucent plastics such as PC, ABS, PMMA/acrylic, polystyrene (PS), polysulfone (PSU) and polyvinyl chloride (PVC). This category also includes high-performance PEI. Semi-crystalline thermoplastics have a structure that is part amorphous and part crystalline. Unlike amorphous thermoplastics, semi-crystalline polymers have a highly ordered molecular structure with a sharp melting point (i.e. a range of less than 5 °C)s. While amorphous materials soften gradually when the temperature rises, semi-crystalline plastics do not. Instead, they remain solid until a certain amount of heat is absorbed. Because of their strong intermolecular forces, semi-crystalline polymers form tough plastics. Common semi-crystalline thermoplastics used in 3D printing include polyethylene (PE), polypropylene (PP), polyethylene terephthalate (PET), polyether ether ketone (PEEK) and polyetherketoneketone (PEKK). PEEK and PEKK both belong to the family of PAEK high-performance engineered thermoplastics.

Thermoplastic materials used in 3D printing are available in three different material forms—filaments, pellets and powders—based primarily on the specific additive technologies that they are used for. Almost all thermoplastic materials are available as pellets (granules), as this is their common raw material form and, also the standard material form used in traditional injection molding processes. Many 3D printable pellet materials are generally also available as filaments developed specifically for thermoplastic filament extrusion 3D printing technologies. However, not all filament extrusion systems support all materials due to technical limitations (extrusion temperature, enclosed print chamber). Some thermoplastics are also available as powders for PBF processes. Today, these primarily include various types of nylon (PA), thermoplastic elastomers (TPU/TPE), polypropylene (PP), and PEEK.