ADDITIVES | RECYCLING
were cut from compression moulded sheets and tested on a TA Instruments DHR-2 using an SER3 elongational viscosity fixture. Elongational viscosity testing was performed at 180°C using a constant strain rate of 0.1s-1
. In the first stage of testing, one pass through the
Above: BASF’s IrgaCycle solutions address recycled resin quality issues and can improve processability, long-term thermal
stability and outdoor weathering protection
term thermal protection for recycled PP and polyolefin blends containing impurities; IrgaCycle UV 033 DD, which combines weathering stability with enhanced thermal and processing stability for reclaimed HDPE and PP blends for re-use in outdoor goods; and IrgaCycle XT 034 DD, which is said to “rejuvenate” processing, improve long-term heat stability and to help neutralise impurities to improve mechanical properties. BASF says one advantage of the additives lies in
their ready-to-use granulated non-dusting product form, which ensures safe and easy dosing during converting or compounding. The IrgaCycle range is offered as part of BASF’s newly-branded “high sustainability value” Valeras portfolio of additives.
Right: Fraunhofer LBF says novel additive solutions are needed to successfully recycle plastic parts such as car battery cases
High melt strength PP Improvement of properties in polyolefins contain- ing recyclate — specifically high melt strength PP — is the goal for the latest additive introduction from Cray Valley. Dymalink 9200 is an acrylate functional zinc salt that reacts with aliphatic polymers to form a carbon-carbon covalent link. The company says the polar zinc cations tend to assemble into ionic clusters within the polymer matrix, promoting the formation of a network that leads to improved melt strength, even at very low loadings. High melt strength PP (HMS-PP) is most com- monly used for extrusion of foams and thermo- formable sheet. Thermoforming in particular can produce a large amount of scrap, which can be added back to the original compound. But be- cause the regrind has lower low melt strength than the virgin polymer, only a relatively modest amount can be incorporated back into the base compound. Dymalink 9200 is said to combat this. Experi- ments carried out at Cray Valley simulated regrind material by passing a commercially available HMS PP through a twin-screw extruder up to four times. This was then compounded with Dymalink 9200 at 1%, 1.5% and 2% addition levels before specimens
64 COMPOUNDING WORLD | October 2021
extruder was enough for the HMS-PP to see a reduction in melt viscosity of 90%. During this study the 1.5% loading of Dymalink 9200 proved to be optimum for the material and increased the elongational viscosity by more than 800%, from 125,000 to 1,139,000 Pa.s. In the second stage, the regrind sample contain- ing 1.5% Dymalink was blended into virgin HMS PP and compared against compounded regrind containing no Dymalink. The regrind addition was increased by 5% increments up to 25% of the total compound. The elongational viscosity of the 95/5 base compound/regrind control was measured at 587,000 Pa.s. With 1.5% Dymalink 9200, an elonga- tional viscosity of 687,000 Pa.s was achieved with 25% regrind. The Dymalink-modified regrind at 5% level achieved a higher melt viscosity than the virgin HMS PP (1,565,000 Pa.s against 1,270,000 Pa.s).
Degradation expertise The plastics unit within the Fraunhofer Institute for Structural Durability and System Reliability (Fraun- hofer LBF) says it has used its expertise in degrada- tion 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 manufacturers, 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
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