What does HDPE

HDPE, LDPE, PP, PVC, EPS, PUR - a material science of plastics

Worldwide in 2016 335 million tons of various types of plastic are produced. Plastic is an important material that continues to gain in importance and in many areas there is no alternative, even if research is always experimenting with new materials to solve the problem of plastic pollution in the future.

We meet many in practice Abbreviations, in very different life situations. In the following, we will take a closer look at the most important petroleum-based plastics, briefly explain their production and properties and show where they are typically used in everyday life.

Classification of the types of plastic

There are various ways in which conventional plastics (i.e. plastics based on petrochemical raw materials) can be classified. In chemistry, for example, the classification is primarily based on the development reactions:

  • Polymers. They do polymerisation after all. Monomers with double bonds turn into long polymer chains in a chain reaction that takes place without any discernible steps. To put it simply: the double bonds are broken in order to form new connections in these free places. Individual monomers are added to form a long chain. There is no rearrangement or splitting off.
  • Polycondensates. They arise through polycondensation. This reaction takes place in stages and with elimination of by-products (often H.2O). This means that not only can single monomers be added to a chain, but two chains can also be built into a longer chain without ending the growth reaction.
  • Polyadducts. They arise through polyaddition. This reaction also takes place in stages, but without splitting off by-products. The monomers react at both ends, so first short chains (oligomers) are formed, which then react with one another or with longer chains.

In addition, the classification according to the mechanical-thermal behavior, i.e. the properties. Since this is more important in our industry, this classification is used in the following. The assignment is made into three large groups: the thermoplastics, the thermosets and the elastomers.

As described, all three types of plastic consist mainly of macromolecules, the polymers, which are repeated over and over again. The polymers are obtained from natural substances or produced purely synthetically. Depending on which raw material is used and which additives are added, the characteristics of the finished product vary greatly. This is why plastic is such an attractive material because you can produce countless variants with very different properties. It is precisely this peculiarity that sometimes makes an exact assignment of the finished products to the individual types of plastic a little difficult.

Thermoplastics

The biggest difference between thermoplastics and the other 2 groups lies in the Malleability of the material. The more energy (e.g. heat) that is added, the easier it is for the thermoplastics to be deformed. This property is based on the arrangement of the molecules. The molecular chains are mainly arranged linearly and have almost no cross-links. These chains can become move more easily against each other and are thus easier to deform and melt with enough heat, such as a Plastic bowl on the stove top.

Polyethylene, also polyethene (abbreviation: PE)

PE is the most commonly produced plastic and by far the one most important thermoplastic for production of Foil. Polyethylene is produced by the polymerization of ethene, in simplified terms:

In general, polyethene is a very soft thermoplastic and very stable to chemicals. For example, many acids are sold in PE plastic containers. The density is between 0.90 and 0.95 g / cm3, it so swims in water. Due to their physiological harmlessness, they become very strong in the Food sector used.

A distinction is made between PE-LD (LDPE) = low density polyethylene (Low density) and PE-HD (HDPE) = high density polyethylene (High density). The density (crystallinity) determines the flow behavior, processing properties and quality of the subsequent film. HDPE is therefore always more stable, tear-resistant, scratch-resistant and wear-resistant than LDPE.

Examples for PE-HD: Canisters, bottle crates, carrier bags, (very thin) foils, food packaging, transport containers, components, furniture parts, household appliances, toys.

Examples for PE-LD: Packaging and construction films, buckets, pipes, bottles, cans.

Polypropylene, also polypropene (Abbreviation: PP)

Polypropylene is very similar to PE-LD, it is characterized by high stability and is resistant to many chemicals. It is also physiologically harmless and, in the recycling process, harmless to the environment. Polypropylene is, however harder and more heat resistant as PE-LD. However, below 0 ° C, PP becomes brittle. The density is approx. 0.9 g / cm3. Polypropylene results in the polymerisation of propene, in simplified terms:

Areas of application for this plastic: The main area of ​​use is as a carrier material for adhesive tapes (available here in the shop). Furthermore: packaging of food, vegetables, pastries, disposable cups, battery boxes, components in the car, shoe heels, packaging films of all kinds, but also coffee machines, kettles, carpets and artificial turf.

Polyvinyl chloride (Abbreviation: PVC)

Polyvinyl chloride is the best-known plastic alongside PE, PS and PP, especially in the packaging sector, where the first PVC adhesive tapes were. Polyvinyl chloride is created through the polymerization of chloroethene (also known as vinyl chloride). Vinyl chloride is a highly toxic and carcinogenic substance. Residues have to be washed out of the PVC with a lot of effort. Pure PVC is a white, hard powder. To be used to manufacture the stable PVC products Plasticizers used. These substances push themselves between the molecular chains of PVC and hold them together. The more plasticizers, the more flexible the later plastic is.

The stability and elasticity with the addition of plasticizers also means a lower resistance to many chemicals, as these can wash the plasticizers out of the PVC.

That's why PVC has a lot different purposes, depending on elasticity: Packaging foils, drainage and sewer pipes, construction profiles and chemical apparatus construction, but also floor coverings, profiles, hoses, foams and adhesive tapes in the packaging area (order now in the shop). Not to forget the record, hence the name "vinyl record".

Polystyrene (abbreviation: PS)

Polystyrene is an inexpensive mass-produced plastic that is granulated and used in many areas. Pure PS is hard, colorless, brittle and has a high surface gloss. It is resistant to acids, alkalis and alcohol, but not against non-polar solvents (e.g. nail polish remover). The density is greater than 1 g / cm3, it so does not swim in water. Polystyrene is produced by the polymerization of styrene, to put it simply:

Areas of application: Food packaging, mugs, cases, CD cases, cans, toys.

Expanded polystyrene (Abbreviation: EPS)

Expanded polystyrene, is better known under the protected brand name Styrofoam® (BASF). Here blowing agent is worked into the polystyrene beads, which foams up through heat.

Areas of application for EPS plastics: packaging chips, inserts for constructive packaging, thermal insulation.

Polyamide (abbreviation: PA)

Polyamides are macromolecules, which by the way are also used in natural form: Peptides and proteins, such as hair, wool, egg white. Polyamide fibers are easy to dye, elastic, rot-proof, alkali-proof and tear-resistant. Polyamides are synthetically produced through polycondensation. In contrast to the natural fibers, the synthetically produced fibers are also moth-proof and crease-free. They are therefore particularly suitable for the manufacture of clothing. The triumphant advance of polyamide was with the Nylon stockings which came onto the market in the USA around 1940. Perlon® Incidentally, it hardly differs from nylon 6,6. It is a competing product that was patented by German companies after World War II.

The application goes far beyond the textile sector: the automotive industry, electrical engineering and surgical instruments are made from PA. In the packaging and food sectors, polyamides are used as barriers and to improve puncture resistance, as well as in all kinds of transparent films.

Polyester (abbreviation: PES)

All plastics that contain ester compounds are called polyester. Their different properties and thus their use depend on the monomers that are used for production. Accordingly, the area of ​​application is also very large. Polyesters are formed by polycondensation, either from hydroxycarboxylic acids or from dicarboxylic acids and dialcohols.

Areas of application: fibers for textiles, foils, strings of tennis rackets, food packaging, CDs. Probably the most important polyester is PET (polyethylene terephthalate), what the Pet bottle is made.

Some polyesters, depending on the materials used in their manufacture, can also be added to the Thermosets counted, such as the Polyester resin (UP).

Polyurethane (abbreviation: PUR, often also PU)

Polyurethane is produced by polyaddition from dialcohols and diisocyanates, often also from polyethers. Depending on which materials are used, the finished PUR is one of the thermoplastics, thermosets or elastomers. The areas of application are correspondingly diverse.

Polyurethane is a thermoplastic used in the manufacture of rollers and cylinders.

Thermosets

Thermosets (also known as thermosets) are polymers that have a The components melt or dissolve. This is an irreversible cross-linking reaction. That is, the molecular chains are strongly interlinked with each other and the reaction is irreversible close. This results in the typical property: If you try to heat thermosets, they do not melt like thermoplastics, but they do decompose. When you exercise, you are not stretching, but rather they shatter. After hardening, thermosets can only mechanically changed using files or saws.

Because of this mechanical and chemical resistance, thermosets are often found in Electrical installations or protective helmets. Another very well-known example of these plastics is the Trabant, whose outer body skin was made from a thermoset.

Melamine-formaldehyde resin, also phenoplasts (Abbreviation: MF)

Formaldehyde resin is produced by the polycondensation of formaldehyde with z. B. urea or phenol. Probably the best known product of this reaction is Phenoplast or bakelite called. A result of the processing of phenoplast resin are the Chipboard. Here the resin is mixed with wood chips and pressed. The result can be seen in many apartments and office buildings: pieces of furniture.

Further areas of application for MF plastics: Hard paper and fabric, wooden spoons, surfaces of kitchen furniture, electr. Insulating material.

Polyurethane (abbreviation: PUR)

If higher-quality alcohols are used in the production, stable plastics with many cross-linked molecular chains, i.e. thermosets, are created.

Typical areas of application are adhesives, paints and varnishes for furniture, floors and boats, but also components of printing inks.

Polyester resin (abbreviation: UP)

Polyester resins are condensation products from di- or polyhydric alcohols. Depending on the composition, there are polyester resins in very soft to hard. They are resistant to weak acids and bases (e.g. gasoline). Polyester resins are flammable plastics.

The area of ​​application ranges from lacquer binders, laminate and kitchen worktops to insulation material, for example in handles for pots and irons and drainage channels.

Elastomers

The main characteristic of elastomers is that special elasticity. Elastomers can be briefly to at least twice their length stretch and they then return to the original state. Elastomers are wide-meshed, cross-linked molecular compounds, they do not soften when heated, do not melt and are not soluble in most solvents. Main uses of elastomers are Tires. All types of rubber belong to this group.

Polyurethane (abbreviation: PUR)

As an elastomer, polyurethane is found in fibers, e.g. B. as elastane. The main area of ​​application, however, is use in foamed form. Polyurethane is a permanently elastic soft foam (e.g. for sports shoe soles) or known as a hard assembly foam.

Other areas of application for flexible PUR: cushions, mattresses, upholstered furniture, foams and upholstery materials (also for packaging), construction foam for thermal insulation and coating of carpets.

Elastane (abbreviation: PUE)

Elastane is an elastomer that consists of at least 85% polyurethane. Hence the abbreviation PUE = P.olyUrethane E.elastic. The elasticity of elastane is 500 - 700% and it then largely returns to its original state.

The reason for this elasticity is the structure of the fibers. Elastane is made up of stiff and loose, rubbery sections. The latter are often tangled and stretched during the stretching process, then they contract again.

Typical uses are therefore stretchable items of clothing, such as socks, tights, swimwear. Whereby elastane is often known under the trade names Lycra® and Dorlastan®.

This article provides an overview of the types of plastic. We explain information about bioplastics in the article “The EU plastics strategy - what is behind recyclable, oxo-degradable and bio-based plastics?”.

Posted UnderTagged