FLAME RETARDANTS | INNOVATION
Above: NeoGraf Solutions says GrafGuard 280-50N expandable graphite flake additive is widely used as a flame retardant in thermoformed and extruded thermoplastic panels used in the aerospace and automotive industries
Product Manager for NeoGraf. The company recommends using MgOH as a synergist.
Radical alternatives New FR developments at the Fraunhofer Institute LBF for Structural Durability and System Reliability focus on the extension of the oxyimide radical generator family. Previous oxyimide flame retard- ants comprising ester linkages influence process- ability of engineering plastics. The new family of oxyimide ethers is said to be compatible with polyamides and can provide UL 94 V-0 in PA6 at concentrations as low as 3%. Flame retardancy is provided through the formation of a glassy layer as a barrier, which Prof Dr Rudolf Pfaendner, Division Director Plastics at the institute, says seems to be a mechanism not seen before. Another advanced research topic at LBF is the design of flame retardants based on renewable resources. These novel molecules combine active phosphorus species as part of a polymer chain synthesised using readily available raw materials such as cellulose, lignin, and pentaerythritol. One application area is to provide flame retardancy for biopolymers, most notably PLA. Adding 5% of flame retardant to PLA results in UL 94 V-0, whereas with a commercial polyester flame retardant a 15% loading achieves only V-2 due to burning dripping.
Synergist developments Paxymer, which developed its own synergist for flame retardants, says it has been involved in several exciting developments during the year. “Due to improvements in the production of the syn- ergist there has been a significant improvement in efficiency of the synergist itself,” says CEO Amit Paul. “It improves residue levels in materials by more than 250% by adding 1-2 wt% of synergist in
28 COMPOUNDING WORLD | December 2020
combination with conventional P/N systems.” The main benefits come from reducing the flame spread, eliminating dripping, and increasing gas phase availability of the P/N systems, enabling compounders to meet fire standards with a lower total level of flame retardant. “This often means cost savings - sometimes up to 20% on HFFR formulations,” says Paul. Paxymer’s latest develop- ment has increased the thermal stability so that that the synergist can be processed at up to 300°C. It is now also said to be easier to handle and less sensitive to moisture. Preliminary trials have proven compatibility and
efficiency in polyamides and ABS. “We were previously focused only on polyolefin plastics, but the new product is compatible more or less across resins,” says Paul. The company has also developed new masterbatch formulations that are aimed at conduit and duct markets in PP and PE. Addition levels below 10% can achieve self-extinguishing performance. Bansi L Kaul, CEO of MCA Technologies, says applicability of the company’s morpholino- poly(piperazinyl-morpholinyl-triazine) proprietary universal fire retardant synergist and smoke and toxic gases suppressant has been extended beyond its original purposes. “It is now found that MCA PPM Triazine HF additionally acts as a heat stabiliser, beyond anti-oxidants, to retard visible and invisible degradation during melt-processing and reprocessing (recycling) of invariably high- loaded (and heat sensitive) FR compounds, such as PINFRs,” he says. Composed of C, H, N elements and characteristi- cally insoluble, MCA PPM Triazine does not bloom or bleed during the service life of the plastics compound. “No matter in what polymer we tested we always found the stabilising effect,” says Kaul. “PPM Triazine HF has also shown to be a facilitator for environmentally safer ultimate disposal of waste plastics, beyond recycling, thereby enabling energy extraction with least production of toxic gases.”
Table 2: Performance of novel polymeric bio-based flame retardants in PLA
PLA grade low viscosity low viscosity low viscosity high viscosity high viscosity
Flame retardant no
15 % Polyester 5 % LBF-Polymer no
15 % Polyester high viscosity 10 % LBF-Polymer
UL 94 V V-2 V-2 V-0
Not classified V-2 V-0
Source: R Pfaendner, Fraunhofer Institute
www.compoundingworld.com
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IMAGE: NEOGRAF SOLUTIONS
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