From the raw material to the 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?
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Polyethylene
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.
The characteristics of polyethylene - strong, safe and versatile
- doneresistant to aggressive substances
- donealmost indestructible
- doneresistant to strong climatic variations
- donelightweight
- doneversatile in its applications
- donegroundwater-neutral
- donenon-toxic combustion into carbon
- donedioxide and water vapour
How is polyethylene made?
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
- donegrinding
- donewashing
- doneseparation by float/sink technique
- donemechanical/thermal drying
- donegranulation
- doneregranulate
Regranulation process
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
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.
Non-standard products
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.
About post-industrial recyclate
Optimised-thickness foil made from post-industrial recyclate – The solution for the future. By adding high-performance polymers, we have found the means of manufacturing a uniquely thin foil with approx. 95 per cent recyclate content that provides exceptional tear- and puncture resistance. As a consequence, we can offer you the most reliable, resource-efficient and CO2-friendly solution on the market – a garbage bag that leaves a significantly smaller ecological footprint than bags made from bio-plastic or paper with the same functionality (as per ifeu).
The material
Post-industrial recyclate (PIR) consists of high-quality industrial waste, arising, for example, during cutting operations. The utmost purity of the raw material ensures homogenous tactility and high stability in the end product. With the aim of lowering CO2 emissions, material requirements are thus reduced without any drop in stability.
About post-consumer recyclate
Foil made from post-consumer recyclate poses a challenge in the recycling process. In the complex field of PCR, DEISS can already look back on many years of expertise, and this is reflected in an extensive product range. The ultimate target has always been to obtain an even better end product comprising an even greater level of PCR. This has resulted in a top-quality garbage-bag with high tear resistance and over 80 % regenerated content in the form of post-consumer recyclate.
70 million of the bags marketed by DEISS have already displayed the Blue Angel – the best known and strictest eco label in the fields of plastic foil and paper. www.blauer-engel.de/en/emil-deiss-kg-gmbh-co
The material
Post-consumer recyclate (PCR) is a blended mixture of recycled material generated from household, industrial and agricultural waste. The increasing usage of PCR foils brings the recycling process around full circle and conserves resources. Due to the extremely heterogeneous quality of the starting material, however, the tear resistance of the end product poses a major challenge.
About biodegradable foil
Good biofoil contains the highest possible level of renewable raw materials (e.g. the bio-based BASF polyester ecoflex) and can be composted industrially without the creation of micro-plastics. It therefore provides a basis for the hygienic and safe disposal of organic waste. The decisive challenge before such material can be degraded at the composting plant is to ensure a stability comparable to that offered by plastic.
The material
- done100% biodegradability
- donepartially made from renewable raw materials
- donehigh wet- and tear resistance
Paper
It is possible to produce paper from almost any kind of organic fibre. Paper is biodegradable, often displays recognised eco-labels (such as the Blue Angel and FSC) and has a good image – but does not automatically offer greater ecological advantages than plastic.
In order to achieve the required stability, its production, as a rule, is extremely energy- , water- and CO2 intensive. But not all types of paper are alike. To ensure the high stability of the DEISS sack kraft paper, for example, we combine especially long paper fibres obtained from top-quality waste paper with cellulose fibres from managed forestry sources. The resultant material is extremely durable, elastic and – despite an extra coating to ensure a high level of wet strength – 100% recyclable.
Grass paper
Paper made from the rapidly regrowable raw material grass has now become the overriding research issue with enormous potential in the field of environmental protection: 97 % energy savings, 99 % water savings, zero chemicals, low logistic requirements due to regional availability, and a 75 % reduction in CO2 in comparison to fresh virgin-fibre paper.
Specialist terms
120 l garbage bag
Garbage bag measuring 700 x 1100 mm
Top quality
Brand-new granulate that meets its strict quality requirements.
Additives
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.
Biofilm
Colloquial term for plastic film that is made from biodegradable and compostable materials.
Blow extrusion
A manufacturing technique for the production of plastic film whereby melted plastic is inflated into large tubular form.
Blend
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/Coex film
Coextrusion creates two different films which are welded together flat while still in melted form.
Compounding
Processing of plastic materials
Cracking
A technique to extract ethylene
Dart-drop value
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.
Puncture resistance
See dart-drop value
Ethylene
A gaseous hydrocarbon with the chemical formula C2H4. It is the chemical precursor for the production of polyethylene.
Extruder
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.
Extrusion
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.
Catalyst
A substance used to influence the reaction of chemical processes.
Carbon dioxide
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.
Block bottom
A glued bottom ensuring maximum upright stability of the bag. It provides an even bottom area, particularly for paper bags.
my (µ)
Unit to measure thickness of the plastic film. 1 µ = 0.001 mm
Naphtha
Also called raw gasoline. A relatively light fraction of crude oil which is used to extract ethylene.
Non-standard goods
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.
PE-HD
High density polyethylene
PE-LD
Low density polyethylene
PE-LLD
Linear low density polyethylene
PE-MD
Medium density polyethylene
Polyethylene
A polymer made of ethylene. One of the most widely used plastic materials in the world.
Polymer
A chemical compound consisting of branching or chain molecules.
Process waste
Waste that occurs during the production process, such as offcuts.
Recycling material
Recyclable resources
Regeneration
The use of recycling material for the production process
Regrind
Products made from recycling material
Regranulate
A granulate created from regenerate
Melt index
The temperature at which polyethylene liquefies.
Slit sealing
A manufacturing process in which the produced plastic film tubing is split to create two tubes.
Spot market
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.
Wave-Top-Bags
Bags with perforations on the filling line to enable fastening with knots.
Draw-string bags
Bags with an inserted circumferential plastic string for fastening