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Information about Thermoplastic

For other uses, see Plastic (disambiguation).
A thermoplastic is a plastic that melts to a liquid when heated and freezes to a brittle, very glassy state when cooled sufficiently. Most thermoplastics are high molecular weight polymers whose chains associate through weak van der Waals forces (polyethylene); stronger dipole-dipole interactions and hydrogen bonding (nylon); or even stacking of aromatic rings (polystyrene). Thermoplastic polymers differ from thermosetting polymers (Bakelite; vulcanized rubber) as they can, unlike thermosetting polymers, be remelted and remoulded. Many thermoplastic materials are addition polymers; e.g., vinyl chain-growth polymers such as polyethylene and polypropylene.

Temperature dependence

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Stress strain graph of thermoplastic material
Thermoplastics are elastic and flexible above a glass transition temperature Tg, specific for each one — the midpoint of a temperature range in contrast to the sharp freezing point of a pure crystalline substance like water. Below a second, higher melting temperature, Tm, also the midpoint of a range, most thermoplastics have crystalline regions alternating with amorphous regions in which the chains approximate random coils. The amorphous regions contribute elasticity and the crystalline regions contribute strength and rigidity, as is also the case for non-thermoplastic fibrous proteins such as silk. (Elasticity does not mean they are particularly stretchy; e.g., nylon rope and fishing line.) Above Tm all crystalline structure disappears and the chains become randomly inter dispersed. As the temperature increases above Tm, viscosity gradually decreases without any distinct phase change.

Thermoplastics can go through melting/freezing cycles repeatedly and the fact that they can be reshaped upon reheating gives them their name. This quality makes thermoplastics recyclable. The processes required for recycling vary with the thermoplastic. The plastics used for pop bottles are a common example of thermoplastics that can be and are widely recycled. Animal horn, made of the protein α-keratin, softens on heating, is somewhat reshapable, and may be regarded as a natural, quasi-thermoplastic material.

Some thermoplastics normally do not crystallize: they are termed "amorphous" plastics and are useful at temperatures below the Tg. They are frequently used in applications where clarity is important. Some typical examples of amorphous thermoplastics are PMMA, PS and PC. Generally, amorphous thermoplastics are less chemically resistant and can be subject to stress cracking. Thermoplastics will crystallize to a certain extent and are called "semi-crystalline" for this reason. Typical semi-crystalline thermoplastics are PE, PP, PBT and PET. The speed and extent to which crystallization can occur depends in part on the flexibility of the polymer chain. Semi-crystalline thermoplastics are more resistant to solvents and other chemicals. If the crystallites are larger than the wavelength of light, the thermoplastic is hazy or opaque. Semi-crystalline thermoplastics become less brittle above Tg. If a plastic with otherwise desirable properties has too high a Tg, it can often be lowered by adding a low-molecular-weight plasticizer to the melt before forming (Plastics extrusion; molding) and cooling. A similar result can sometimes be achieved by adding non-reactive side chains to the monomers before polymerization. Both methods make the polymer chains stand off a bit from one another. Before the introduction of plasticizers, plastic automobile parts often cracked in cold winter weather. Another method of lowering Tg (or raising Tm) is to incorporate the original plastic into a copolymer, as with graft copolymers of polystyrene, or into a composite material. Lowering Tg is not the only way to reduce brittleness. Drawing (and similar processes that stretch or orient the molecules) or increasing the length of the polymer chains also decrease brittleness.

Although modestly vulcanized natural and synthetic rubbers are stretchy, they are elastomeric thermosets, not thermoplastics. Each has its own Tg, and will crack and shatter when cold enough so that the crosslinked polymer chains can no longer move relative to one another. But they have no Tm and will decompose at high temperatures rather than melt. Recently, thermoplastic elastomers have become available.

List of thermoplastics

See also

Plastic may refer to:
  • Plastic, a polymerized material
  • A thermoplastic
  • A thermoset
  • Any material that has plasticity
  • A genotype that has phenotypic plasticity

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Melt can refer to:
  • Melting, in physics, the process of heating a solid substance to a liquid
  • "Melt!", a 1982 song by Siouxsie & the Banshees
  • "Melt", a song by Leftfield on their 1995 album Leftism

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brittle if it is liable to fracture when subjected to stress. That is, it has little tendency to deform (or strain) before fracture. This fracture absorbs relatively little energy, even in materials of high strength, and usually makes a snapping sound.
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Glass is a noncrystalline material that can maintain indefinitely, if left undisturbed, its overall form and amorphous microstructure at a temperature below its glass transition temperature.
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molecular mass (abbreviated Mr) of a substance, formerly also called molecular weight and abbreviated as MW, is the mass of one molecule of that substance, relative to the unified atomic mass unit u (equal to 1/12 the mass of one atom of carbon-12).
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polymer is a substance composed of molecules with large molecular mass composed of repeating structural units, or monomers, connected by covalent chemical bonds. The word is derived from the Greek, πολυ, polu, "many"; and μέρος, meros,
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The term Chain (sequence) may refer to:
  • Chain sequence (continued fraction), numbers in the mathematical study of continued fractions
  • Chain of thought, continuous thought process where ideas follow one from the other

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van der Waals force is sometimes used as a synonym for the totality of non-covalent forces (also known as intermolecular forces). These forces, which act between stable molecules, are weak compared to those appearing in chemical bonding.
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In physics, force is an action or agency that causes a body of mass m to accelerate. It may be experienced as a lift, a push, or a pull. The acceleration of the body is proportional to the vector sum of all forces acting on it (known as net force or resultant force).
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"Polythene" redirects here. For the Feeder album, see Polythene (album).


Polyethylene (IUPAC name polyethene) is a thermoplastic commodity heavily used in consumer products.
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dipoles (Hellènic: di(s)- = twi- and pòla = pivot, hinge). An electric dipole is a separation of positive and negative charge. The simplest example of this is a pair of electric charges of equal magnitude but opposite sign, separated by some, usually small,
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hydrogen bond is a special type of dipole-dipole bond that exists between an electronegative atom and a hydrogen atom bonded to another electronegative atom. This type of bond always involves a hydrogen atom, thus the name.
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Nylon is a generic designation for a family of synthetic polymers first produced on February 28, 1935 by Wallace Carothers at DuPont. Nylon is one of the most common polymers used as a fiber.
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Aromaticity is a chemical property in which a conjugated ring of unsaturated bonds, lone pairs, or empty orbitals exhibit a stabilization stronger than would be expected by the stabilization of conjugation alone.
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Polystyrene IPA: /ˌpɒliˈstaɪriːn/ is a polymer made from the monomer styrene, a liquid hydrocarbon that is commercially manufactured from petroleum by the chemical industry.
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For other uses of the word, see plastic (disambiguation).


Thermosetting plastics (thermosets) are polymer materials that cure, through the addition of energy, to a stronger form.
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Bakelite /ˈbɛkəˌlaɪt/ is a material based on the thermosetting phenol formaldehyde resin, polyoxybenzylmethylenglycolanhydride developed in 1907–1909 by Belgian-American Dr. Leo Baekeland.
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Vulcanization refers to a specific curing process of rubber involving high heat and the addition of sulfur. It is a chemical process in which polymer molecules are linked to other polymer molecules by atomic bridges composed of sulfur atoms.
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Natural rubber is an elastic hydrocarbon polymer that naturally occurs as a milky colloidal suspension, or latex, in the sap of some plants. It can also be synthesized. The entropy model of rubber was developed in 1934 by Werner Kuhn.
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An addition polymer is a polymer which is formed by an addition reaction, where many monomers bond together via rearrangement of bonds without the loss of any atom or molecule.
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A vinyl compound is any organic compound that contains a vinyl group (also called ethenyl), −CH=CH2. These are derivatives of ethylene, CH2=CH2, with one hydrogen atom substituted with some other group.
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Polypropylene or polypropene (PP) is a thermoplastic polymer, made by the chemical industry and used in a wide variety of applications, including food packaging, ropes, textiles, stationary, plastic parts and reusable containers of various types, laboratory equipment,
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The glass transition temperature is the temperature below which the physical properties of amorphous materials vary in a manner similar to those of a solid phase (glassy state), and above which amorphous materials behave like liquids (rubbery state).
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trillion fold).]]

Temperature is a physical property of a system that underlies the common notions of hot and cold; something that is hotter generally has the greater temperature. Temperature is one of the principal parameters of thermodynamics.
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The melting point of a crystalline solid is the temperature range at which it changes state from solid to liquid. Although the phrase would suggest a specific temperature and is commonly and incorrectly used as such in most textbooks and literature, most crystalline compounds
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CRYSTAL is a quantum chemistry ab initio program, designed primarily for calculations on crystals (3 dimensions), slabs (2 dimensions) and polymers (1 dimension) using translational symmetry, but it can be used for single molecules.[1] It is written by V.R. Saunders, R.
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Water is a common chemical substance that is essential to all known forms of life.[1] In typical usage, water refers only to its liquid form or state, but the substance also has a solid state, ice, and a gaseous state, water vapor.
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An amorphous solid is a solid in which there is no long-range order of the positions of the atoms. (Solids in which there is long-range atomic order are called crystalline solids or morphous). Most classes of solid materials can be found or prepared in an amorphous form.
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A random coil is a polymer conformation where the monomer subunits are oriented randomly while still being bonded to adjacent units. It is not one specific shape, but a statistical distribution of shapes for all the chains in a population of macromolecules.
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Hooke's law of elasticity is an approximation that states that the amount by which a material body is deformed (the strain) is linearly related to the force causing the deformation (the stress).
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