Recycled polyethylene is coming up more and more often in bag production. Some businesses ask for it by their own choice; others face it as an expectation from their buyers or from changing regulations. Whatever the reason, working with recycled material is different from working with virgin raw material and raises questions of its own.
This post offers a checking framework for businesses considering a bag that contains recycled PE. The aim is not to praise or criticise the material, but to ask the right questions.
Where does the material come from?
“Recycled” does not describe a single material but a group of materials of different origins. In the industry, the term regranulate is also widely used for these materials. The first and most important question is where the material comes from.
- Production scrap: Edge trims, set-up waste and defective products generated during film and bag production. These materials have never been used, their source is known and they are generally clean. Many plants collect this scrap and reuse it in their own production.
- Post-consumer material: Polyethylene collected and sorted from used packaging. Its sources are more varied; it may contain different types of plastic, ink, labels and dirt.
These two groups differ both in their properties and in the claims that can be made about them. Finding out from the supplier which group the material belongs to and how it has been processed is therefore the basis of every assessment that follows.
Consistency: batch-to-batch differences
Virgin raw material is produced within narrow limits set by its producer and comes with a technical data sheet. With recycled material, by contrast, properties can vary from batch to batch depending on the mix of material collected.
This variability shows up most in flow behaviour. Two batches with different melt flow indices behave differently in the extruder and in the bubble; line settings may need to be reviewed for each batch. Differences in density also affect the stiffness and strength of the film. A supplier that works in an orderly way should be able to share basic measurements for each batch.
Appearance: colour, odour and gels
Films made from recycled material can look different from those made with virgin raw material. In post-consumer material, because packaging of different colours is mixed together, the granule is usually greyish or coloured. That is why such films are often produced in dark colours; light-coloured and transparent film is difficult to achieve.
Odour is another issue that should not be overlooked. Traces left from the material’s previous use can make themselves felt during melting. Small unmelted or differently melted spots called gels may also appear in the film; these both spoil the appearance and create weak points in the film. Good filtration of the material significantly reduces the gel problem.
How is it used in film production?
Recycled material is often used not on its own but blended with virgin raw material. The blend ratio is set according to the bag’s intended use, the expected strength and the buyer’s specification. Some manufacturers state that they set this ratio directly according to the customer specification.
Co-extrusion offers a useful route here. In a multilayer film, recycled material can be placed in the middle layer and virgin raw material in the outer layers. This way, the surface to be printed and the inner face to be sealed remain more predictable, while the recycled content sits in the body of the film.
Differences in strength must also be taken into account. A film with recycled content may show different tear strength and impact strength from a film of the same thickness made from virgin raw material. If necessary, the thickness or the raw-material blend is adjusted accordingly.
What to watch in production and inspection
A production line working with recycled material needs more frequent monitoring than one working with virgin raw material. Screens can clog faster, so melt pressure and screen changes are closely monitored. Because moisture in the material can show up as bubbles and holes in the film, keeping the granule dry is important.
Quality control also looks at a few points in particular. The film is checked by eye and against the light for gels, holes and stains. Thickness is measured at different points of the film; with a variable material, the thickness distribution can vary too. Seal seams are tested separately, because the different materials in the blend can affect sealing behaviour. Recording the results with the batch number makes it possible to trace which material was used when a problem arises.
Storage should not be overlooked either. Recycled granule should be kept in its closed packaging, protected from moisture and dirt. Labelling is kept orderly so that different batches do not get mixed.
Claims and legislation
What is said about a bag with recycled content is at least as important as the bag itself. Every statement written on the bag or in promotional texts needs to be verifiable. If a content percentage is to be stated, it is expected to be backed by supplier documents.
General and absolute statements about environmental impact should be avoided. Using recycled content does not by itself make a bag better in every respect; the outcome depends on the source of the material, how it is processed and how the bag is used and disposed of. Recycled content and environmental claims on packaging are subject to the relevant legislation, and these regulations can change over time.
Why is testing with a sample important?
It is difficult to work out fully from technical documents how a bag with recycled content will behave. That is why requesting a sample before series production and testing it in real use becomes even more important than with virgin raw material.
In the test, fill the bag with the real product, carry it and close it. Check whether the colour and appearance meet expectations and whether there is a noticeable odour when the bag is opened. If possible, compare samples produced from different batches side by side; this comparison gives the clearest information about consistency.
Questions to ask the supplier
When talking to the manufacturer about a bag containing recycled PE, the following questions are a good starting point:
- Does the material come from production scrap or from post-consumer packaging?
- What is the recycled content percentage in the bag, and how is it documented?
- How are differences in flow, colour and odour between batches monitored?
- In which layer is the material used, and how are the printing and sealing surfaces protected?
- Can a strength and appearance test be carried out on a sample before series production?
Approached with the right questions and realistic expectations, recycled PE is a material that can find a place in bag production. What reduces uncertainty is knowing the source of the material, testing with samples and saying only verifiable things about it.