ADDITIVES | RECYCLING
stabiliser for virgin material. “The novel generation of additives with selected alditols as key chemistry directly addresses for the first time in recyclate stabiliser developments the oxidised structures, for example carbonyl and acidic groups. Thus, known accelerated degradation reactions originating from these structural defects are avoided. Moreover, the novel additive systems can cope with metallic impurities through complex formation and act as hydroperoxide decomposers to interrupt the autooxidation cycle of polymers,” he says. As a consequence, Pfaendner says, processing
Figure 1: Processing stability of post-consumer PP simulated through multiple extrusion (twin-screw extrusion at 230°C) Source: Fraunhofer LBF
stability of recycled plastics (he cites the example of PP from battery cases) is excellent as well as the long-term thermal stability compared to state-of- the-art stabilisers (Figure 1 and 2). “Through the high efficiency of these systems, the future chal- lenge of multiple recycling is also already tackled as low concentrations will be beneficial to avoid accumulation of residues from stabilisers followed by incompatibilities and exudation.” Fraunhofer has partnered with additives com- pany Brüggemann to commercialise the develop- ments. The first series is designed for polypropyl- ene, as well as for polyethylene films. Traditional car batteries are also the target of developments at Altana, which points out that traditional car batteries will not disappear with the advent of EVs since most use a 12V battery alongside high-voltage Lithium ion batteries to power on-board electronics. RecycloByk 4371 was especially developed for restabilising PP and other polyolefin compounds that are especially exposed to aggressive substances. It notes that even after PP recovered from battery cases is cleaned, it still contains acid and metal residues, albeit in very small quantities. “Reusing directly would signifi- cantly accelerate the aging of the plastic,” the company says.
In tests conducted by the company, specimens
Figure 2: Long-term thermal stability of post-consumer PP simulated through artificial aging Source: Fraunhofer LBF
were exposed to artificially accelerated heat aging conditions at a temperature of 135 °C and the embrittling time measured (Figure 3). “Without additives, the service life under accelerated heat aging is almost 700 hours, which is too short for a new battery case that is to be used over a period of several years,” according to Altana. “Adding 0.2% or 0.5% RecycloByk 4371 significantly prolongs this time to more than 1,000 hours or almost 1,300 hours, which is equivalent to an extension of more than 80% in service life.” Another RecycloByk grade, 4372 improves the recycling of high-density polyethylene (HDPE) material that can be employed, for instance, in pallets and bottle crates designed for outdoor use. All RecycloByk products come in a granular, dust-free form for safe handling and accurate dosage.
Figure 3: Time to embrittlement of PP exposed to accelerated heat aging at 135°C with and without Recyclobyk 4371 Source: Altana
66 COMPOUNDING WORLD | October 2021
Radical attention Repetitive extrusion and recycling of poylolefins causes a chain reaction that forms free radicals, breaks up the long polymer chains, and degrades the appearance and performance of the plastic. Avient says the addition of its Cesa Nox antioxidant masterbatches during these processes helps preventing yellowing, surface cracking, and can also
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