MATERIALS | FLAME RETARDANTS
A PE compound containing Byk Max CT 4260 clay (left) demonstrates highly effective char layer formation compared to a control without
Image: Byk
from HFFR cable compounds,” the company says. It has also been working on improvements in compound flow characteristics and extrudate surface quality. The result is a new cable grade — EcoPiren Plus — available for lab and small indus- trial scale testing. The benefits of clay as a char-forming material have long been recognised, but clay can be difficult to disperse and incorporate into polyole- fins. However, Byk says its clay products have been engineered specifically for use in polyolefins to maximise ease of dispersion and flame retardant efficacy. The company supplies organophilic phyllosilicate clays to provide flame retardancy in polyolefins used in applications as wire and cable, decking, construction panels, and pallets. Typical application for HFFR applications is 5%. Byk-Max CT 4260 prevents dripping in PE by forming a char layer, making it possible for com- pounds to achieve a UL94 V-0 rating, according to the company. It cites a study carried out to demon- strate char formation using CT 4260 in a typical ATH polyolefin formulation. This compared a control formulation with 65% ATH and a formula- tion with 58% ATH and 5% Byk Max CT 4260. The
compounds were prepared in a twin-screw extruder then processed to a sheet and 3mm test pieces prepared and burned in an oven. The compound containing Byk Max CT 4260 demon- strated formation of a much more highly effective char layer than the control. The addition level of ATH needs to be approxi-
mately 65% to provide required flame retardance, which negatively affects processability and me- chanical properties. Byk says the addition of Cloisite 20 A to the formulation can improve dispersion, resulting in better compounding and mechanical properties. In an internal study, it compared a typical 65% ATH formulation with one containing 55% ATH and 5% clay. Addition of 5% Cloisite 20 A resulted in a 250% increase in elongation without any adverse effects on tensile strength and lowered the viscosity of the com- pound.
Coating innovation It is well-known that long term water aging of flame retardant compounds containing mineral fillers such as aluminium hydroxide (ATH) impacts on electrical performance, according to German flame retardants producer Nabaltec. “HFFR compounds so far show inferior wet electrical properties compared to compounds based on halogenated flame retardants,” the company says. It has developed a range of surface treated
Figure 2: Water uptake of an LLDPE/EVA compound containing 60 wt% of three different surface modified Apyral fire retardant grades after four weeks at 90°C Source: Nabaltec
30 COMPOUNDING WORLD | December 2021
mineral flame retardants designed to improve compound performance after long term wet aging. The Apyral 40HS1 and newly developed Apyral 40H1 grades are said to show very promising results. Nabatec’s tests show the special surface treatments significantly reduce water uptake in an LLDPE/EVA compound compared to the same formulation using its untreated Apyral 40CD grade (Figure 2). Furthermore, the surface modified Apyral grades allow volume resistivity of the filled compounds to remain at a constant level even after water aging at 90 °C for four weeks. The company says both grades offer the same good flame
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