From granulate to garbage bag
A product can only ever be as good as the material it is made from. So what exactly is polyethylene? How is it made? How does recycling work? And how are the raw materials converted into the finished products?
All of us encounter polyethylene on a daily basis as it represents over a third of the total worldwide consumption of plastic materials. It is versatile in its application - ranging from extremely thin plastic film to sturdy drums and bottles.
- doneresistant to aggressive substances
- donealmost indestructible
- doneresistant to strong climatic variations
- doneversatile in its applications
- donenon-toxic combustion into carbon
- donedioxide and water vapour
From naphtha to ethylene
Raw gasoline - also called naphtha - is derived from crude oil. Intense heating of the naphtha ("cracking") creates gaseous ethylene.
From ethylene to polyethylene
In the next step, the gas is fed into a reactor. Using a constant temperature and a pressure level dependent on the production technique used, this creates a white polyethylene powder. Melting and cooling of the powder then results in solid polyethylene, which is finally broken down into a granulate. This granulate is the raw material used for the manufacture of a wide diversity of products.
Recycling of plastic material
The recycling process transforms used plastic materials into new resources for production purposes. The chemical structure of the material remains unchanged and the new granulate created in this process is named regranulate.
- donesorted plastic fraction
- doneseparation by float/sink technique
- donemechanical/thermal drying
The process begins with the grinding of the sorted plastic packaging. Afterwards, the grist is washed and foreign matter removed in a water tank using the float/sink separation technique. Polyethylene has a lower density than water and floats, thereby simplifying the separation from other plastic material types. After the washed and sorted grist has been dried, it is granulated in the so-called extruder. This operates in the same way as a meat grinder. The plastic material is first melted in the extruder screw, thus creating a moulding material that is then pressed through a perforated plate. The emerging strands - similar to spaghetti - are then cooled underwater and cut. This creates the regranulate.
The production of plastic film
The extruder is again used for the production of plastic film. First, the (re-)granulate is fed through the extruder screw and heated externally thus creating a moulding material. A tool placed before the screw cylinder then forms the grouted mass into a film. This takes tubular form and is ejected balloon-like via a blower. The resulting plastic-film tube is then cooled, laid flat, and finally wound up onto a roll.
Bag production / Blow film extrusion
A special finishing machine turns the "endless" roll of plastic film into garbage bags. Depending on the type of end product, the plastic film tubing is folded (side gusset, star bottom etc.) before a combined welding and perforation machine adds the bottom and tear-off seams. Finally, a set number of connected bags or liners is wound up onto a roll.
The production of high and low density polyethylene creates suitable material types for all kinds of applications. The most common polyethylene types are PE-LD, PE-HD and PE-LLD, which are used in 90% of all cases.
PE-LD – Low density polyethylene
PE-LD is produced under high pressure of between 1000 to 3000 bar, and at a temperature of 150 to 300°C.
This is our standard material as it is relatively soft and easy to process. The end products are extremely penetration resistant and elastic. Mixed with PE-LLD, some of these bags gain even greater penetration resistance and, in addition, the welding seam is strengthened further.
PE-HD – High density polyethylene
PE-HD is produced under low pressure of between 1 bar to 50 bar, and at a temperature of 20°C to 150°C maximum.
This has greater penetration resistance than PE-LD. However, if punctured, it is also more likely to rip further. Compared to PE-LD, the material characteristics of PE-HD allow for it to be created with a lower strength, making it a more economical alternative for certain applications.
PE-LLD – Low density linear polyethylene
PE-LLD is produced under a slightly higher pressure of between 50 and 100 bar using a modified catalyzer. It possesses extreme elasticity and is used in particular for the production of stretch films.
PE-MD – Medium density polyethylene
This is a material very similar to PE-HD but with a reduced density. Compared to PE-HD it feels softer but its actual strength is only marginally weaker.
Metallocen is a catalyst used in the transformation process from ethylene to polyethylene and significantly improves the characteristics of the polyethylene. Colloquially, the term metallocen also refers to the types of plastic material that are made using this catalyst.
Occasionally the produced polyethylene does not meet the exact specifications of the manufacturer. This PE is referred to as non-standard and traded at a reduced price on the spot market. While the quality of non-standard goods is perfectly suitable for the production of various plastic films, such non-standards are not always available as they are ultimately an unintended product outcome.
Distinctive features of plastic regenerates
As is the case with paper, regrinding plastic results in a loss of quality each time it is recycled. After frequent recycling the polyethylene begins to clump: the granulate ceases to melt completely, thereby creating small granules; or it combusts partially during the manufacturing process and leaves a malodorant smell on the plastic film. To prevent this from happening, the various regenerated plastics are pre-sorted in accordance with their quality.
The regenerates used for our PREMIUM products originate from process waste that enables excellent quality characteristics.
120 l garbage bag
Garbage bag measuring 700 x 1100 mm
Brand-new granulate that meets its strict quality requirements.
Substances added to the base material in the extrusion process. Additives create specific characteristics such as improved penetration resistance, discharge capacity, UV-stability, etc.
Anti-static plastic film
Such plastic films contain an added substance which gives the film its discharge capacity, either permanent or temporary.
Colloquial term for plastic film that is made from biodegradable and compostable materials.
A manufacturing technique for the production of plastic film whereby melted plastic is inflated into large tubular form.
A mix of at least two different granulates melted together in the extrusion process. In Germany, blend is also referred to as a plastic alloy.
Cast film extrusion
A manufacturing technique for the production of plastic film whereby melted plastic is poured onto a smooth surface and the film sheeting pulled off.
Coextrusion creates two different films which are welded together flat while still in melted form.
Processing of plastic materials
A technique to extract ethylene
Measures the resistance of the plastic film against abrupt localised mechanical impact stress. It is determined by using a falling weight tester and measured in g/->my.
Defined recycling material
These are recyclable materials of which the composition, source and melting point are known.
See dart-drop value
A gaseous hydrocarbon with the chemical formula C2H4. It is the chemical precursor for the production of polyethylene.
The extruder increases the density and temperature of the polyethylene. Colloquially, the term is also used to describe the entire machine that is used for the production of plastic film.
The process which takes place inside the extruder. Colloquially, the term is used to describe the entire process of plastic film production.
Plastic film elasticity
The elastic capacity of the plastic film before it reaches tearing point measured in percent.
A substance used to influence the reaction of chemical processes.
A chemical compound of carbon and oxygen with the chemical formula CO2. A non-combustible, acidic, colourless and odourless gas that dissolves easily in water.
A glued bottom ensuring maximum upright stability of the bag. It provides an even bottom area, particularly for paper bags.
Unit to measure thickness of the plastic film. 1 µ = 0.001 mm
Also called raw gasoline. A relatively light fraction of crude oil which is used to extract ethylene.
Due to manufacturing errors, non-standard goods neither meet their specified quality requirements nor have the necessary properties for their intended purpose. Hence they are used for a variety of other purposes and are only available on the spot market.
Opacity / Opaque
Opacity refers to the level of light transmission through a plastic film. Opaque means impervious to light.
High density polyethylene
Low density polyethylene
Linear low density polyethylene
Medium density polyethylene
A polymer made of ethylene. One of the most widely used plastic materials in the world.
A chemical compound consisting of branching or chain molecules.
Waste that occurs during the production process, such as offcuts.
The use of recycling material for the production process
Products made from recycling material
A granulate created from regenerate
The temperature at which polyethylene liquefies.
A manufacturing process in which the produced plastic film tubing is split to create two tubes.
Direct delivery, acceptance and payment in a minimum timeframe. Longer-term availability of the products is unlikely.
UV-stabilized plastic film
Constant exposure to UV light invariably makes PE-film brittle. UV-stabilizers are substances added to the PE during the extrusion process to slow down this process.
Bags with perforations on the filling line to enable fastening with knots.
Bags with an inserted circumferential plastic string for fastening