Recycled material testing by Save Plastic

One of the things that the TRANSFORM-CE project and we, Save Plastics in the Netherlands, want to know is the best mix of reused plastics to create a material that has the optimal qualities for its intended purpose, and whether it can in turn be recycled and if so, how many times. We were particularly interested in seeing if fibres have a positive effect on the flexural – or bending – strength of materials. To this end we asked Materia Nova in Belgium to test a few mixes containing fibres for us. As fibres consist of long chains, they help strengthen material. The general rule of thumb is that the longer the fibres, the stiffer the material.

We had three types of materials tested at Save Plastics’ Green Plastic Factory.

  • A mix with added fibreglass waste from fibreglass linings. The fibreglass linings waste consists of the offcuts of rolls that were cut to size and rolls that were rejected because of defects. The offcuts and rejected rolls are still strong though and can hugely improve the qualities of the mixed plastics.
  • A mix with added fibres from car recycling. Car bumpers contain a lot of fibres to make them thin, strong and lightweight. The fibres can vastly improve the qualities of the mixed plastics.
  • A fibre-free test mix to serve as a baseline.

As part of the research, we first produced a material from each mix which we then shredded and recycled five times. This allowed us to see if and how much the material deteriorated after being recycled several times. After that we ran tests to measure the Young’s modulus of the various mixes and the number of recycling rounds. Young’s modulus is a mechanical property that measures the resistance of a material to stretching and tension under pressure exerted lengthways. The assumption is that the Young’s modulus deteriorates each time the material is recycled. This is a known issue in products containing fibres as recycling shortens the length of the fibres, which then weakens the strength of the material.

The results were interesting. The mix containing the car recycling fibres did not demonstrably perform better in the Young’s modulus than the standard mixed plastics. In contrast, the mix with the added fibreglass was twice as stiff as the mixed plastics, a significant outcome in terms of applications for the material. The Young’s modulus was shown to be marginally worse after five rounds of recycling. This means that it can be said with great certainty that the material can be recycled and reused at least five times without causing the end product to deteriorate too much.

Save Plastics will carry out more research into optimising the use of the fibreglass mix for use in the Green Plastic Factory.

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