PHOTO: Recycled materials are often not glossy; they may have spots, localised discolouration and only be available in a dark colour. To overcome these deficiencies a few strategies are used, including a frame and cover design where a frame forms the inside of the product and virgin material covers are used. For example, the Phillips Senseo Up coffee maker

By BERNARD REEKSTING

THE ‘circular economy’ use of plastics materials, from cradle to cradle, is attainable by considering two simple concepts: design for recyclability of products made from virgin materials, and design using recycled materials.

A prime driver for the use of recycled materials is the cost savings over the use of virgin materials. Other incentives are the reduction of environmental impact, customer requirements, marketing, and in some countries, legislation.

 

Design outcome

The general outcome for the use of recycled materials is to turn a low value material into a higher value product.

But, what grade of recycled material? There are different types of recycled materials, each of these have different performance properties that need to be understood:

• Pre-consumer waste, also named in-house scrap, which is used in-house or sold on to another processor.
• Post-consumer waste, which may be either household packaging with a mix of multiple materials, or from an industrial source, then of mostly uniform type.
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Technical data sheet

Materials are affected by exposure to degradation during prior use. The amount of degradation will be determined by, prior thermal exposure, environmental exposure such as sunlight and UV, and mechanical damage.  Further exposure to contaminants and chemicals will challenge the retention of the materials properties.

The recycling process adds to the sum of the materials degradation by shear during granulation, agglomeration, heating and drying.

Many materials contain some pigments and fillers that have an influence on the performance of the recycled material.

A technical data sheet of the materials should report the density, tensile strength, elongation at yield, E modulus, melt flow rate, impact strength and hardness.

 

Examples of materials and their primary and recycled use

Material	Original use	Recycled
TPO	Automotive  bumper	Automotive  wheel liner, spoilers, mud guards
PP	Packaging, automotive, furniture	Crates, automotive air ducts, battery housings, garden furniture
PEHD	Bottles, food packaging, crates, pipes	Crates, waste bins, pots, pipes, bags, wood simulants
PET	Soft drinks bottles, packaging film, food tubes	Soft drink bottles, fabrics, fleece, strapping
LDPE	Blown film shrink-wrap, agricultural film, toys	Bags, pipe, wood simulants
PS/XPS	Disposable cups, cutlery, packaging	Rigid mouldings, insulation materials, fillers in cement aggregates
PVC	Pipes, packaging, flexible vinyl	Tubes, floor tiles

 

Design considerations

The properties of the product to be made from recycled material need to clearly specified. A material that matches these requirements is selected. Additionally, the material needs to be able to be processed and possibly recycled once more at some future time.

Recycled materials, through their prior use and processing may have reduced elasticity and become more brittle. Properties related to long-term loads and strains are usually reduced. Thermal and UV exposure have more marked effects on the performance of recycled materials. Recycled materials often have an associated odour, either from degradation or from the previous use. It is possible to reduce this by masking, sequestering, neutralizing or stripping the odour.

Additives and fillers may be compounded into the recycled material to improve selected properties. This requires some expertise in selection to retain an economic motivation for using a recycled material.

For some required properties it may be required to make a blend using virgin material.

The fundamental principles for injection moulding design still apply to recycled materials. However, because of the possible decrease of elastic properties and an increased sensitivity to sharp radii, these are made more generous for recycled product design. Mould shrinkage and post moulding shrinkage may also increase for the recycled material. Incorporation of filler or adjustments of the processing parameters (cooling time and temperature) are required to retain the dimensions.

Many products made by extrusion processes require long-term load characteristics. These need to be assessed in the application with constructed measurement of the time dependency property.

 

Product design

Recycled materials are often not glossy; they may have spots, localized discoloration and only be available in a dark colour.

To overcome these deficiencies a few strategies are used:

• Frame and cover design, a frame forms the inside of the product and virgin material covers are used. For example, Phillips Senseo Up coffee maker.
• Strong colour contrasts for different parts of a product are employed to distract from surface imperfection
• Non visible parts for automobiles, for example, wheel housing liners and air ducts.
• Lighter colours can only be achieved from lighter colour materials, they still do tend to lack depth and intensity. Use of a filler, such as talc, may improve the appearance.
• The surface gloss is low when a recycled material is used. Textured surfaces are used disguise the lack of gloss.
• Labels and in-mould labelling may be used to disguise surface deficiencies.
• Techniques that ‘sandwich’ the recycled materials between thin layers of virgin materials are used for both injection moulding and extrusion processes.

 

Review the design considerations Evaluate if the performance properties adequately cover the intended application and do they accurately reflect the intended use.

 

Regulations governing food contact use of materials

• Recycled plastic materials and articles intended to come into contact with foods: Regulation EC No 282/2008
• Requirements for plastics materials and articles intended to come into contact with food: Regulation EU No 10/2011
• Good manufacturing practice for materials and articles intended to come into contact with food: EU No 2023/2006