While there is increasing demand for low-smoke, halogen-free, flame-retardant (LS HFFR) compounds in many cable applications, fiber optics present special requirements for these types of materials. Tight buffer compounds must be tough yet elastic to protect the optical fiber from mechanical damage and the signal losses caused by micro-bends. Jacket compounds must exhibit a low degree of post-extrusion shrinkage, which can impose stress on the sensitive fibers during post-extrusion temperature cycling and over time during end use.
Added to these requirements are considerations that apply to all cables, whether fiber optic or copper. Chief among these, particularly in mass transit, cell tower, data center, and other infrastructure applications, is flame behavior. The growing demand that cable materials in such uses be halogen-free poses a challenge to compounders, who must meet this demand while still providing high levels of flame retardance.
Because of highly efficient gas-phase flame suppression mechanism provided by the presence of halogens, halogenated materials such as PVC (which is inherently flame retardant) have long been effective in applications with some of the highest FR requirements.
The polyolefin resins used for metal hydrate-based LS HFFR compounds, on the other hand, must be formulated with non-halogenated flame-retardant materials, generally at fairly high loadings, without compromising other application requirements, such as processability, mechanical performance, flexibility, and cost.
Teknor Apex Company has developed a wide range of LS HFFR products for wire and cable under its Halguard® brand, including a portfolio of compounds designed specifically for fiber optic cables. The portfolio provides choices for a broad range of end-use performance and flame retardancy, as well as low-cost options for buffer and jacket applications.
Passing flame tests on cables have been achieved by using the appropriate grade, ranging from VW-1, to vertical tray, to riser. All of the jacket compounds exhibit low-shrink behavior. Some of the compounds exhibit superior char formation under burning conditions, and others incorporate an innovative flame retardant system which facilitates their ability to offer cost-effective alternatives to premium grades.
Download a copy of the publication article from the November 2016 issue of Wire & Cable Technology International.
