The topic of using resources and materials as efficiently and sustainably as possible is more topical than ever due to the current global political situation, rising energy prices and the partially disrupted supply chains, and is currently a concern for us in almost every product development.
The right choice of material plays an important role in the design of products, their recyclability and the use of raw materials that have already been recycled.
However, the planned purpose of the product, the mechanical loads that occur and the planned service life must also be carefully considered and these factors and the technical material properties must be taken into account at an early stage during development and production planning.
In addition to the positive aspect of conserving resources, recyclates also offer differences in terms of processability and mechanical properties, meaning that a product cannot simply be converted from virgin material to recycled raw material "during the ongoing process". Rather, the use of recycled materials - which may only be planned in the further course of production - must be taken into account as early as the article design stage.
This article is intended to provide a few points of reference:
1. definition
Recycled materials (from thermoplastics) are plastics that have already undergone a processing process as virgin/original material by forming and are to be used again.
By material:
- Single-variety industrial waste: (rejects, production waste) Material type and color usually known
- Post-consumer material: e.g. from the Yellow Bag; usually a mixture of different but similar plastics (usually PE/PP mixture)
After processing:
- Regrind 1: Rejects and production waste (sprues) are crushed in impact mills, sieved (according to particle size and dust removal) and usually fed directly back into the production process.
- Regrind 2: Post-consumer material is collected, shredded and delivered to the processor.
- Regranulate: Shredded plastic waste is re-melted, extruded and reprocessed into granules.
- Chemical recycling: Chemical recycling no longer refers to recyclate as a result. Here, the plastics are broken down into their basic chemical components by pyrolysis, for example, and reassembled into "original identical material". However, this is still a long way off. Chemically recycled plastics can only be expected in significant quantities in 2-3 years' time.
According to quality:
- Off-spec goods: The manufacturer cannot precisely define material properties due to fluctuating composition or similar. Significant process and property fluctuations are to be expected
- Spec goods: The manufacturer can guarantee material properties within technically reasonable limits. A material data sheet is also available from the manufacturer for these materials.
2. fundamental influence of recycling on material properties
The shortening of the molecular chains generally results in the following changes in properties: deterioration in tensile strength, elongation, impact strength and chemical resistance. Resistance, partial improvement of stiffness and flowability.
In particular, the shift in mechanical properties towards "brittleness" must be taken into account during product development.
For the manufacture of our mostly high-quality products with high demands on functionality, appearance, haptics and service life, only spec goods, i.e. materials with a guaranteed property profile, can be considered as recyclate. The material characteristics and properties listed in the data sheet help with material selection and comparability with other recyclates or original materials.
3. application example
Upper table:
ABS virgin material Terluran GP22
Red: ABS recyclate SPEC material
Comparison of mechanical properties (notched impact strength at room temperature)
Lower table:
ABS, recyclate, Spec-Ware
Here you can see a clear difference in the notched impact strength between the material types. A 54% lower value indicates that the material is considerably more brittle than virgin material.
While the products made from virgin material survived drop tests from a height of 1 m without damage, the boxes made from recycled material regularly broke in the main stress zones (see Fig. 01 + 02 in the slider).
Depending on the application, it is not easy to switch between recycled and virgin material. If recycled material is to be used, the design must be adapted to the sometimes significantly changed material characteristics:
- Adapted wall thicknesses
- Consistent avoidance of notches, transition radii as large as possible
- Reinforcement of load zones
These factors must be taken into account as early as the article design stage. This is the only way to ensure that the use of recyclates makes a product more resource-efficient without jeopardizing its functionality - otherwise it would end up "in the garbage can" much sooner than planned.
