Design for Reliability - Plastic recyclates in technical components

How do we ensure the reliability and service life of components made from recycled materials and thus bring them into more high-value applications?

Due to ecological and social obligations, the aim is to recycle a very large proportion of the plastic waste produced. In addition, legal obligations require a proportionate utilisation of plastic recyclates. In some areas, e.g., in the PET bottle sector, there are already established cycles. However, recycled plastics have so far only been used to a limited extent in technical applications.

Recycled plastics sometimes differ considerably from virgin plastics. The differences are due to pre-damage, impurities and mixing effects and have a direct influence on, for example, long-term durability, mechanics, operational stability, and other properties that are essential for technical components. To be able to use recycled plastics reliably in technical applications, a basic understanding of these interrelationships and methodological approaches for taking these influencing variables into account in component design is a basic prerequisite. However, these are often only available in a very incomplete form.

The driving questions here are, for example, how to deal with batch fluctuations. Larger scatter widths in the mechanical characteristic values can in turn lead to a greater probability of failure of a product and, in the worst case, be relevant to safety. These must therefore be considered when designing components. Currently, this leads to higher safety factors and the associated higher wall thicknesses, which counteract lightweight construction and thus economy and ecology.

Furthermore, the behaviour under long-term loading in highly stressed applications and possible changes in material behaviour due to external influences are not sufficiently known. These characteristics must be considered when verifying a product to be able to reliably estimate the product service life of a component.

→ This is precisely where this joint industrial project comes in, investigating two different recycled materials as examples. This could be rPP or rPA, for example, but will depend on the requirements of the project participants and will be agreed with them before the project starts.

Research questions on cause-effect relationships in highly stressed applications

The following research questions are intended to investigate fundamental interactions between material flow, processing, and long-term behaviour in highly stressed applications:

• How do batch fluctuations affect the properties?
• Which material properties of the recyclates are sufficient for my product?
• What long-term properties result for the respective material?
• How can the service life of components made from recyclates be assessed and what options are there for increasing it if necessary?
• How can the changed material properties be determined and estimated using a quantitative method and transferred to a design routine?

Focus & approach

Basic literature research and evaluation

Based on the recycled plastics selected in the network, orientating research of available materials is carried out and their property profile, (long-term) availability and known property fluctuations are compiled. This data is compared with the virgin material used and initial challenges are derived from this.

Determination of the scatter widths of different recycling batches and initial assessment of application-specific suitability

With the help of analytical and mechanical tests, the actual state of the material properties and their scattering width are determined using different material batches. This makes it possible to estimate whether the material properties are sufficient for the respective application and where there is potential for optimisation when transferring them to the component.

Investigation of the long-term properties

Further material tests will specifically investigate the long-term loads under the interactions of, for example, temperature, medial environment and superimposed mechanical cyclic stresses.

Documentation of the design methodology

The procedure for dimensioning the components is agreed and fixed in consultation with the partners. In this context, orientating research is also carried out on how the design of plastic recyclates is generally handled according to the state of the art.

Adaptation of the design methodology

The material properties determined are incorporated into an operationally stable design methodology for estimating the service life of a component-like demonstration body. With the help of material tests, a quick characterisation is to be derived with which an estimation of the material properties of different batches is possible in a short time.

Evaluation of the potential and possibilities for material modification

The potential of the plastic recyclates analysed will be presented and the critical weak points identified. This presentation enables the participating partners to address their requirements specifically to material suppliers. These in turn could adapt their formulations in line with requirements.

The tests are carried out in parallel on equivalent virgin material to enable a direct comparison between recycled and virgin material.

Build up expertise and stay on the market sustainably!

Participating partners in this joint project will be able to:

• assess the challenges and potential of using recycled plastics.
• derive the necessary material analyses for the qualification of recycled plastics.
• adapt their own design methodology for component design and thus design technical components made from recyclates for operational reliability.
• to be able to formulate very specific requirements for material manufacturers.

This joint project is aimed at companies along the value chain from the granulate to the finished component:

• OEMs and manufacturers of plastic components from the automotive, commercial vehicle or white goods industries, who will have to produce components from recyclates or blends in the future and ensure their reliability and service life.
• Recyclers, compounders, processors, additive manufacturers who want to further qualify their materials for demanding applications in the future.
• Players who want to tap into a new source in the future.

Benefit from working with us!

We at Fraunhofer LBF contribute our expertise, project experience and extensive equipment.

Recycled plastics in demanding applications:

In material and component tests, considering temperature and media influences, we prove that the service life and reliability of, for example, a dishwasher floor made from recyclates can withstand the stresses of daily use.