ADDITIVES | MATERIALS
the virgin HMS PP (1,565,000 Pa.s against 1,270,000 Pa.s). The plastics unit within the Fraunhofer Institute
for Structural Durability and System Reliability (Fraunhofer LBF) says it has used its expertise in degradation mechanisms of plastics and additives to develop some novel stabiliser systems for recycled plastics. According to Prof Dr Rudolf Pfaendner, Division Director Plastics at the institute: “Plastic recyclates differ from virgin material through oxidative damage and new chemical groups on the polymer backbone, mixtures of polymers, even in single polymers through different manufactur- ers, and impurities from other polymers, adhesives, inks etc.” Pfaendner says an efficient stabiliser system for recyclates has to address this and is different from a 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 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 . “Through the high efficiency of these systems, the future challenge of multiple recycling is also already tackled as low concentra- tions will be beneficial to avoid accumulation of residues from stabilisers followed by incompatibili- ties and exudation.” Fraunhofer has partnered with additives company Brüggemann to commercialise the developments. The first series is designed for polypropylene, as well as for polyethylene films. Traditional car batteries are also the target of developments at Altana, which points out that these 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
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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
were exposed to artificially accelerated heat aging conditions at a temperature of 135 °C and the embrittling time measured. “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-den-
sity 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. 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 antioxi- dant masterbatches during these processes helps preventing yellowing, surface cracking, and can also help to preserve critical mechanical properties such as impact resistance, elongation and tensile strength. The company also highlights its Rejoin PCR masterbatch for polyolefin packaging applica- tions. Made with post-consumer recycled polyole- fin and polyester as a carrier resin, it can enable a bottle or part to be manufactured from 100% PCR.
Left: Altana’s RecycloByk 4371 restabi- lises PP and other polyolefin compounds exposed to aggressive substances, including PP waste from car battery cases
Below: Avient’s ReJoin masterbatches are made using post consumer recycled carrier resins
October 2021 | PLASTICS RECYCLING WORLD 55
IMAGE: AVIENT
IMAGE: ALTANA
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