Among some interesting recent developments at Teknor Apex Co. is a new PVC elastomer compound for cable jacketing, particularly for use in extreme low-temperature environments. Teknor Apex claims the Flexalloy 9614-73 grade can withstand frigid outdoor and rugged industrial conditions, while providing enhanced flexibility and flame performance.
The 73 Shore A compound is UV-stabilized and exhibits a brittle point of -65°C or below, the company said. It is designed to pass the UL 1685 Vertical Tray test and Canadian Standards Association's FT-4 vertical tray flame test.
“There is a gap in the market for PVC jacketing for cable compounds that meet stringent flammability standards, but at the same time can have the flexibility and a very low brittle point,” said Michael Roberts, industry manager for the vinyl division of Teknor Apex.
Creating this compound was difficult because the target properties work against each other; typically, the more flame retardant a compound is, the more brittle the product becomes, and the softer the material is, the more flammable it is.
Balancing those three properties, Roberts said, offers cable makers a very soft, flexible compound that can be used in all sorts of challenging applications, such as in the colder regions of Canada. This type of performance, he said, typically requires polymers that cost 50 to 300 percent more than a PVC-based elastomer.
The shipbuilding and off-shore oil and gas sectors are at the forefront in requiring halogen-free, flame-retardant cable sheathing materials that offer flexibility and oil resistance—even in Arctic conditions.
According to Lanxess A.G., this trend is driving demand for blends of hydrogenated nitrile (HNBR) and ethylene vinyl acetate (EVM) rubbers, which also offer enhanced levels of resistance to oils, lubricating greases and drilling chemicals.
“Engineers today demand cable sheathing materials that remain flexible at temperatures below minus 40°C,” said Joerg Stumbaum, technical marketing manager at Lanxess' high performance elastomers business. “There are various materials that can break through this mark. However, if there are also special safety requirements, then 50-50 blends of our Levapren (EVM) and Therban HNBR elastomer ... not only remain flexible at temperatures well below minus 40°C, they also exhibit high oil resistance and outstanding flame-retardant properties.”
“Due to their high polarity, Therban/-Levapren blends can incorporate large quantities of inorganic halogen-free fillers, such as aluminum hydroxide,” Stumbaum added. “Should an external fire ignite these flame-retardant cable sheathings, only limited amounts of smoke will develop, which is important for keeping evacuation routes visible as long as possible.”
Fire safety is the focus for specialty materials distributor Velox GmbH, which has extended its partnership with the Tolsa Group, a Spanish supplier of flame retardant and thermal insulation synergists.
The Hamburg, Germany-based firm will supply Tolsa's Adins Clay and Adins Fireproof flame retardant synergists, in Europe. The inorganic halogen-free products boost char formation during combustion and protect polymers from further fire propagation, the company said.
The additives, said Velox, combine a high surface area and special morphology with a tailored functionality for wire and cable as well as electronics applications.