Plastics – Basics and Introduction

Plastics – material of the 21st century

Plastics belong to the group of polymers. A polymer is an organic material and consists for the most part of carbon and hydrogen. Polymers are big molecules that have the shape of a chain (chain molecule) in which a great many identical subunits (the monomers) repeat themselves.

Since the introduction of the term “plastic” for an initially not clearly defined group of substances (for the first time by the journal “Kuststoffe”, founded in 1911) this term is written down in the German language and refers to artificially produced materials with polymeric material structure.

The model presentation about the structure of the plastic molecules goes back to Hermann Staudinger. The German laureate has created the basic for new methods of synthesis with this model formation in the early 20s and thus significantly helped the material to gain greater economic significance.

In the middle of the 19th century, the industrial processing of plastics began with the production of rubber. The emerging automotive industry was the catalyst behind the rapid growth of the rubber industry. It was not until the mid-thirties that synthetically produced thermoplastics camo onto the market, which have since been experiencing an unstoppable growth.

The production of plastics is based on the three reactions processes polymerization, polyaddition and polycondensation. Petroleum is used primarily as a raw material for the production of plastics, but only 4% of the annual oil reserves are used to produce plastics. Although the production of plastics based on renewable raw material is growing at a rate of 4-5%, it is still uncertain whether complete substitution of the petrochemical plastics will ever occur.

Plastics – elastomers, thermosets and thermoplastics

Plastics are divided into the three major groups of thermoplastics, elastomers and duromers. Thermoplastics differ significantly from the elastomers and duromers due to the fact that thermoplastics can be converted into the plastically deformable state as often as required by the application of temperature.

Furthermore, the properties of the plastic groups differ considerably. While elastomers have considerable extensibility at low strengths, the thermosets represent a high-strength but often brittle material. Due to the fact that these materials chemically decompose (burn) when the temperature is applied, further processing can only be carried out after the shaping by means of machining processes.

Thermoplastics are characterized by very good mechanical properties, combined with excellent processability in mass production processes. No other construction material offers such diverse possibilities for shaping, combination and functional integration in a component as thermoplastics.

The process of thermoplastics takes place mainly through the processing methods of extrusion and injection molding.


Processing – Extrusion

During the extrusion, a usually powdery or granulat plastic raw material is melted by supplying energy and pressed the thus continuously resulting viscous plastic melt through a molding extrusion die.  The so formed out profile is cooled either directly, so that a half stuff originates (e.g. window profile, pie) or the still deformable mass is transformed by subsequent process to the end product (e.g. bottles, hollow bodies, foils).

For this purpose, processing methods used are, for example, the blow molding, in which a deformable plastic tube is got caught between two cooled mold holves and a product is formed by inflating and applying the hose to the mold jaws of the tool.

Another plastic processing method is tubular film extrusion, in which a deformable plastic tube is inflated so much in a continuous process that the wall thickness of the tube decreases sharply and a thin-walled film is formed.


Processing – Injection molding

In the injection molding of thermoplastics, a liquid plastic melt is injected into a cooled forming tool and fixed there by temperature removal in its form. After the cooling process, the forming tool opens and a finished often multi-coloured or made of different materials product can be removed from the tool. In this way, the discontinuous injection molding process can in some cases produce more than 100 individual parts in a single cycle of a few seconds.


Plastic industry in Germany

The plastic industry consists of plastics producers, plastic processors and plastics machinery manufacturers and is one of the most important economic sectors in the Federal Republic of Germany with a turnover of approx. 90 billion euros and almost 500,00 employees. For other industries, such as automotive and mechanical engineering, packaging, electrical engineering or the construction industry supplies innovative solutions with specially tailored product properties.

Plastic products are among the high-tech products of German industry, although this is often hidden from the user. Today, a food packaging film combines up to eleven different plastics, thereby contributing to the excellent shelf life characteristics of the packaged food.

In other areas, heavy metal components are substituted by light fiber reinforced plastics such as in aircraft, racing or the automotive industry.

Plastics are an integral part of today’s world. The excellent processing possibilities coupled with a very economical production and a vast variety of possibilities for functional integration or combination of materials with different properties makes plastics the material of the 21st century!

Further information, checklist and Excel tools for extrusion can be found in our free download area.



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