RECYCLED MATERIALS | MATERIALS
Recyclates go back in the mix
Recent advances in recycled plastics include two projects to upcycle packaging waste into injection moulding grades and a rheology test that optimises stabiliser loadings
Recycled plastic has become a key commodity – with industries such as automotive, under pressure to use greater amounts in their products. While suppliers continue to develop new grades based, there are also efforts to encourage more use of recyclate. One, from researchers at Fraunhofer Institute
for Structural Durability and System Reliability (LBF), has led to better rheological tests for polypropylene (PP) – allowing more precise amounts of stabiliser to be used in recycled grades. Typically, the optimum amount of antioxidant needed is determined after extensive, costly testing. This is not profitable when producing recyclate from old material batches with variable quality and varying stabiliser content, says Fraun- hofer LBF. The approach of adding ‘enough’ stabiliser is unsuitable – and expensive – and there is also an upper limit for the compatibility of stabilisers and the polymer. During each life cycle, the stabilisers are used up as intended, with their by-products remaining in the plastic. This makes it more important to add only the necessary amount during recyclate production.
Online rheological tests speed the process of achieving exact stabilisation and optimising costs, say the researchers. They are characterising the melt online during compounding, which deter- mines useful information on the processing
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behaviour of plastics – such as the flow curves of both shear and elongational viscosity. In initial tests, a partially stabilised virgin PP served as a model. A clear link was found between the viscosity values and the stabiliser concentra- tion, or the viscosity values and the molecular weight. For recyclates, one post-industrial and one post-consumer PP were analysed. The post-indus- trial PP from start-up material and injection moulding sprues still had a high stabiliser content. This means no significant improvements in preserv- ing the molecular weight were achieved here with stabiliser additions of more than 0.1%. In the post-consumer PP, the antioxidants are consumed to a high degree, which shows significant damage during processing. For optimal stabilisation and minimal damage to the recyclate, a 0.5% additive loading is required.
Japanese goal A consortium of industry, government and aca- demia has set a target of using over 15% recycled plastic in the production of cars in Japan by 2031 – and over 20% from 2036 – according to a report in The Japan News. The goal is partly in response to new regulations
to be introduced by the European Union in 2031 – that would require at least 20% of the plastic used
September 2025 | INJECTION WORLD 23
Main image: FKuR now offers Paluren – an LDPE made from recycled of beverage cartons by Palurec
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