SMOKE SUPPRESSANT MATERIALS FOR PLENUM APPLICATIONS

摘要

Poly (vinyl chloride) or PVC is a widely utilized material for wire insulation and cable sheathing. Plenum cables are electrical cables installed in confined spaces, such as the air handling plenums in buildings to provide electrical connections (both voice and data) between different parts of the building. These plenum cables require enhanced flame and smoke resistance. These formulations are typically complex and contain a wide variety of additives such as plasticizers (both flame-retardant and non-flame retardant), additional flame retardants, smoke suppressants, stabilizers, antioxidants, lubricants, pigments, etc. Plenum cables typically consist of a number of conductors protected by a primary insulation layer, which provides electrical/signal insulation between adjacent conductors and physical protection where optical fibers are used. The primary insulation may be PVC, a fluorinated polymer such as FEP (e.g. Teflon~RFEP, DuPont), PVDF (e.g. Kynar~RPVDF, Atofina), and ECTFE (e.g. Halar~R, Ausimont), or a polyolefin such as polypropylene or peroxide cured polyethylene, which may additionally contain flame retardants. Encapsulating the conductors is a jacket, which provides additional protection and assists in cable identification and installation. The jacket of a plenum cable is typically a formulated PVC compound or a fluoropolymer. Although unmodified PVC is thermally unstable, decomposing at about 150℃, unmodified PVC has relatively good flame retardant properties. Plasticizers are added to increase flexibility to PVC. However, these plasticizers increase the compound's flammability, especially if used at higher levels. Additionally, when PVC burns it produces a large amount of smoke, which not only contains toxic materials but also restricts visibility. To prevent the spread of smoke and flame through the building via the plenum spaces, the specifications of plenum cables are particularly stringent with regard to flame and smoke resistance. The most common standard for measuring the acceptability of cable formulations for this application is the UL 910 (Underwriters Laboratory Specification) test, which measures both flame retardancy and resistance to smoke evolution. Generally, failures to pass the UL 910 test are due to high smoke results, namely, Peak Optical Density and Average Optical Density. Our research concentrated on improvements in smoke reduction in highly-filled PVC formulations.