ADDITIVES | FLAME RETARDANTS


and 90° angle. Requests from automotive industry experts for burn through times, were initially set at a minimum of 10 minutes and extended to 20 and 30 minutes. Nabaltec performed the tests to a maximum 30 minutes where it discovered that, when a polymer filled with its Actilox HTB ceramify- ing fillers was torch tested for 20 minutes at 1,000°C it remained solid with no expansion, intumescence, cracks, or holes visible. A hard, ceramic-like layer was formed during the torch testing that created a stable ash crust. Comparable results occurred with the test extended to 30 minutes. It is expected that an increased glass fibre content would further improve stability.


Antimony concerns The long-term use of antimony trioxide (ATO) is a topic of concern to PVC compound suppliers and their end user customers, says Christian Panofen, Global Marketing Director for Huber Advanced Materials. Existing and emerging regulatory mandates continue to drive an industry-wide effort to minimise use of ATO in PVC while maintaining adequate fire performance in applications such as rigid profiles, pipes, laminated textiles, thin films, adhesives and the production of wire and cable products, he says. ATO alone has no useful fire retardant (FR)


function. However, when used together with halogenated compounds, a synergistic effect creates improved FR properties. ATO reacts with a halogenated compound to form antimony chlorides and oxychlorides, which function as radical scaven- gers in the gas phase. Finding a safe and cost-effec- tive alternative in PVC on a 1:1 basis has been a major challenge for the global research community for decades, according to Panofen. Kemgard products from Huber have been specifically designed to be effective smoke suppressants, char formers and fire retardants. They are manufactured using a process in which molybdates are precipitated on a functional core


Figure 2: Replacing equal parts of CaCO3 +ATO + zinc borate in a PVC cable compound with Kemgard 605 results in reduced smoke generation and improved fire performance Source: Huber Advanced Materials


material, making more efficient use of the molyb- date species by maximising its active surface area, and combining it with a selected core material that can offer additional benefits such as additional fire retardancy, improved processability or increased thermal stability, Panofen says. This technology has successfully replaced ATO and zinc borate in some demanding PVC applications. Huber’s Kemgard 605 smoke suppressant is


offered as a cost-effective solution to fully replace ATO and zinc borate in PVC wire and cable applications. Replacing equal parts of CaCO3


+


ATO + zinc borate with Kemgard 605 results in a significant reduction in smoke generation and improved fire performance while maintaining LOI performance, says Panofen (Figure 2). Kemgard 3001 can be used where even more smoke suppression is required. Evonik has expanded its range of liquid


Above: Images showing the improved char formation resulting from the addition of 3% of Evonik’s Tegomer FR100 additive in a cable compound sample (right)


18 COMPOUNDING WORLD | December 2023


organo-modified siloxanes for surface treatment of hydroxide, nitrogen, and phosphorus flame retardant under its Tegopren product line, says Dr Michael Hagemann, Segment Head Compounds at Interface & Performance. The technology is finding increasing use in halogen-free flame retardant compounds (HFFR) where the additives are used for in-situ hydrophobisation and dispersion of hydroxides such as ATH and MDH. Evonik has two solid products for the cable compounding industry available in addition to the standard liquid product Tegomer V-Si 4042. It now offers Tegomer FR 100 and TegomerFR 120 for cable products with the possibility to provide improved flame resistance determined by UL 94, pronounced charring which leads to a delayed HRR (heat release rate), and less smoking with an


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IMAGE: EVONIK


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