What is it ?
What is mechanical recycling?
Mechanical recycling is the processing of used material into recycled material (recyclate). This recyclate can then be reused for the same or new applications, depending on its quality.
There are different qualities of the recyclate. This depends on how often it is already recycled and which contaminations are included, e.g. other materials or colours, but also non-washable residues from the filled-in product.
Before the recyclate can be used for new products, it needs to fulfill requirements, e.g. migration limits for food-contact, but also process ability on certain machines, because the recyclate could behave slightly different during processing.
If through mechanical recycling it’s not possible to gather a high quality recyclate, it goes to energetic recycling. It is described as gaining energy through incineration of the non-recyclable material e.g. for the cement industry.
What are the advantages of recycled material?
Recycled material has a lot of advantages compared to virgin material:
1. Recycled plastic saves raw materials (crude oil or renewable raw materials)
2. Recycled plastic saves energy consumption: the recycling process needs 2/3 less energy than the conversion from crude oil to virgin PET
3. This way of acting will protect the climate, because less raw materials, CO2 and energy are needed
4. Instead of burning the packaging or store it in landfills, recycled plastic can be used as valuable material again, e.g. for durable products, which is in line with the circular economy targets of Europe.
What are the different steps of the recycling process?
The recycling process has 3 major steps, which are the followings:
Part A. How is the collection working?
For plastics: There is post-consumer waste (PCR) and post-industrial waste (PIR).
Industrial waste, PIR, has usually a higher purity, because it is good separated after usage. And it isn’t disposed to household waste, so it won’t be contaminated through residues.
Post-consumer waste, PCR, is usually separated collected in paper, plastics/ metals, residual waste, organic waste, glass. The plastics/metals are used for the further described recycling steps. PCR material is every material, which was already used by consumers, e.g. also PET-bottles from deposit systems. Every contamination with other types of waste may result in less quality of the recyclate, depending on the type of contamination.
A separate system and almost closed recycling loop is the deposit PET-bottle collection and recycling. The PET material and caps will be produced after usage into new PET-bottles and caps. It’s currently the most efficient existing recycling process.
Part B. How is the sorting working (in countries with a recycling system)?
Sorting has usually the following steps to separate plastics and metal:
1. Sieve: removes organic waste (e.g. maggots etc.) and small pieces like broken fragments of glass. Caps won’t be separated.
2. Wind sifters: separates flexible packaging and flat objects from 3D-objects. A NIR-detector separates PE and other plastics subsequently.
3. Metal sorting, 2 steps: magnetic metals (iron, tin) will be removed by a magnet and non-magnetic metals as aluminum will be removed by eddy current separator using the polarity of the non-magnetic metals.
4. NIR (near infra-red): sorts plastics by polymer type. This works, because plastics reflect a specific light spectrum, which is specific for a certain type of polymer.
How the identification/ detection works by NIR?
The overarching part of the packaging is identified by specific light sensors (NIR = near infra-red), which identify the material by reflection of a specific light spectrum. Packaging products may still contain or have components of other materials, e.g. caps, labels, etc.
Packaging with plastic caps, e.g. PP will probably be sorted into the stream of the packaging body, because the size of the body is larger than of the cap.
The label is as well important, because the producer has to make sure, that the label-material and print don’t disturb the detection. Each label needs to be checked, because it’s not possible to give general instructions to make it detectable. Size, print, label thickness & adhesive are relevant characteristics.
Important: this is why products with large labels often can’t be identified and black and dark coloured products with the carbon black pigment can’t be detected, because the colour absorbs the NIR-light and doesn’t reflect.
5. Optical colour sorting: after sorting by material, the colour sorting happens. Sorting of plastics generally depends on:
- shape – flexible or rigid
- material / polymer type – PET, PE, PP, mix
o PET: transparent & mixed streams.
o PE / PP: all (detectable) colours are accepted. No carbon
black containing colours
Which rigid plastics are usually recycled by separate streams?
The following plastics are recycled, because there are markets for the recycled materials. For other recycled materials, there currently aren’t existing markets, so it’s not worthy for the recycling companies to put effort in recycle them. This could be change in the future, if applications and markets will further develop.
- PET transparent, together with bio-PET & rPET. PET coloured or opaque won’t be recycled! The only colour which will probably be recycled is transparent light-blue.
- PE (HDPE, LDPE), together with bio-HDPE & rHDPE.
- PS, in Germany, Austria and some regions of France.
Part C. How is the mechanical recycling working?
1. Shredding: the material into small pieces
2. Washing: a bath with circulating water (ca. 40°C) removes most of the residuals, labels and adhesives.
3. Separation by density in water: different plastics have different densities. So, they can be separated in water, because some are sinking and some are floating. PE and PP have a density < 1 g/cm3, so it floats in water. The floating plastic will be separated. PET has a density > 1 g/cm3, so it sinks in water.
Density ranges may overlap (PE & PP; PVC & PET), that makes it challenging to guarantee a material purity, if the NIR-detection wasn’t correct.
5. Melting: the sorted plastic flakes will be melted and filtered.
6. Pellets: the plastic is pressed into pellets, that’s the recyclate.
7. New product: these pellets will be sold and processed into new products.
How the customer can improve his packaging design for recycling?
See Pont’s presentation “How to improve the sustainability of my PET/ PE packaging” for detailed information the internal version is available, for forwarding to your customer, please only use the external version.