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What are thermoplastic polymers?


To understand what thermoplastic polymers are, the structure of polymers will help. A feature of the structure of the polymer molecule is the repeatability of the monomers that are polymerized in the compound. Briefly, the structure of the polymer can be represented by the formula: 2 short-lived radicals of the methylene group are polymerized, creating a strong ethylene monomer (CH2 = CH2). Several identical monomers are also able to create a strong bond, but not a double one.

n monomers can participate in polymerization (their number varies from 1 to over 1000), then the formula of the resulting element will be shown as follows: (CH2-CH2) n is the formula of the simplest polymer – polyethylene. If one type of monomer is involved in the structure of the polymer, it is a homopolymer, if two or more types are involved, it is a copolymer.

Polymers: properties and classification

The most common classification of polymers according to their composition:

  • high molecular weight organic;
  • organoelement;
  • inorganic high molecular weight.

Classification of polymers by origin:

  • natural origin, in the natural environment of natural polymers (fundamental in this form are protein polymers, where the monomer is an amino acid, polysaccharides);
  • artificial origin in macromolecular substances – altered chemically modified natural substances (this is how plastic is made from cellulose);
  • obtained synthetically using polymerization or polycondensation of various structures and lengths. The property and application of the polymer depends on the length of the chain .

Monomers can be located in space in different ways, hence the differences in structures. She may be:

  • linear;
  • staircase;
  • spatial.

Watch a video about what polymers are.

The linear structure can be a straight chain, stretching in a zigzag or spiral. Sections of the chain are repeated and firmly connected between similar sections of the same chain.

The characteristic feature of the first structure is the possession of flexibility. Hence the peculiarity of the products – high elasticity and low changeability of the structure at low temperatures, there is no fragility, brittleness in the cold. (For example, polyethylene).

The second structure involves two chains chemically bonded to each other. Properties of this type of polymers: Rigidity, endurance of high temperatures and insolubility in organic solvents.

A spatial compound is formed from not small monomers, but whole molecules transversely. Outwardly, this structure resembles a grid with cells of different sizes. Rigidity and heat resistance in this connection is much higher than that of a linear structure.

Polymers and their characteristics

When heated, different substances behave differently. Some have a thermosetting reaction. The initial linear structure, under the influence of high temperature, changes the structure into a spatial one, becoming a solid substance, retaining high hardness in the future. The resulting compound cannot be melted and dissolved. The resulting joints are not subject to reheating. Their examples are various resins, epoxy, phenol-formaldehyde, etc.

Unlike thermoset compounds, thermoplastic compounds can be heated many times. Each time they melt on cooling, they solidify again. The reason for this is their original structure. A linear connection is not burdened by strong chemical bonds. Heating destroys the existing weak bonds, and when cooled, they are restored in their previous or modified form.

A substance with a thermoplastic characteristic (for example, polyethylene, polyamide, polystyrene, etc.) becomes amorphous when heated, and even liquid when the temperature is raised. This property is often used for injection molding, extrusion, extrusion, blowing, to fuse several parts by welding.

Thermoplastic polymers

In practice, the ability to become liquid or soft at any time is applied very effectively. But in order for the process to pass without difficulty, it is necessary to understand the temperature of the thermal decomposition of the substance. For different polymers, it is different, it directly depends on the structure of the molecule of the substance.

For the efficiency of the softening process, technologies are used that reduce the low viscosity of the substance or increase the reduction temperature by conducting the process in rooms with an inert gas.

The thermoplastic is able to swell and shred in the solvent. The reason is the same – the linear structure of its molecule and its large size. When the solvent evaporates, the molecular structure of the thermoplastic takes on its original form. This property is used in the creation of glue, a binder component of mastic, polymer-based colorants.

Negative features of polymers having a thermoplastic characteristic:

  • low heat resistance;
  • increased brittleness at low temperatures;
  • increased fluidity, at high temperatures;
  • loss of properties when exposed to ultraviolet rays;
  • air oxidation;
  • reduced surface hardness.

Application examples of thermoplastic properties

The most popular thermoplastics in construction sites and in domestic use are polyethylenes, polypropylenes and polystyrenes.

The creation of polyethylene is possible during the polymerization of ethylene. By maintaining the pressure at a high level, the oil gas is treated at a very high temperature or the extracted oil product is hydrolyzed. For the process, it is important to maintain the optimal degree Celsius, add a process-promoting substance and introduce oxygen.

Negative characteristics of polyethylene:

Products used in everyday life – pipes, films, electrical, sound, heat insulation, etc., other polymers and plastics.

Polypropylene is obtained by gas polymerization using a solvent. Harder and stronger than polyethylene, but becomes brittle already at -20. It is used in the form of bitumen, rubber. And polystyrene is obtained from styrene and is used for a heat-insulating layer, to create facing tiles and small fittings. In variations with solvents, adhesives can also be obtained.