EOW May 2014

Technical article

Low Coefficient of Friction Polyolefin FTTx Jacket for Improving Cable Installation in Ducts By Saswati Pujari, Anny Flory, Chester Kmiec, Mohamed Esseghir, Jeffrey M Cogen, Elastomers, Electrical and Telecommunications Research and Development

Abstract Underground fibre optic cables are utilised widely, from the central office through a distribution network to homes, office buildings, apartment complexes, etc. Popular installation methods for underground fibre optic cable include blowing or pulling cables through an existing or a newly installed duct. Cable jackets having a lower coefficient of friction (COF) with the inner surface of the duct can potentially make pulling through ducts easier and increase blowing distances in case of dry installation. Lubricants and lined ducts are commonly used to improve the blowing distance by reducing the COF of the inner duct surface. However, such solutions are inconvenient to handle, difficult to control and increase the overall cost of cable installation. In this paper, the properties of a polyethylene-based low COF jacket are compared against the current jacket grades utilised today. The comparative data includes COF measured on plaques and cables, and simulated blowing distances under various duct network designs. The results show ~50 per cent reduction in COF in both plaque and cable testing over dry cables which yielded an increase in simulated blowing distance. 1 Introduction Fibre-optic communication is a method of transmitting information from one place to another by sending pulses of light through an optical fibre.

First developed in the 1970s, fibre-optic communication systems have revolu- tionised the telecommunications industry. Due to their advantages over traditional copper data transmission, optical fibres have largely replaced copper wire communications in core networks and the use of fibre optics is growing at a rapid pace. A fibre optic cable is made up of one or more optical fibres. The optical fibre elements are typically individually coated with a polymer coating and contained in a protective tube. The entire construction is protected by an outer protective layer of plastic jacket or sheath. The most commonly used jacketing material is polyethylene (PE). Fibre optic cables within the FTTx infrastructure may be installed under- ground or in the air. Installation underground generally happens in one of two ways: either the cable is direct buried in the ground via trenches or it can be jetted/pulled within an existing duct. In either case installation is a costly step in developing the infrastructure. Reduction of installation cost can be achieved by longer “pushes or pulls” during cable installation, resulting in fewer duct openings or possibly less labour hours [1-4] . One way to increase the jetting distance during cable installation is by reducing the coefficient of friction between the cable jacket and the duct materials. Several techniques have been studied in the literature to reduce the COF of plastics [5-8] . These include use of surface migratory additives, low surface energy additives, modification of surface morphology, etc.

All of the methods work differently to reduce the COF of the PE surface. Surface migratory additives like fatty acid amides bloom to the surface forming a crystalline slippery layer, which reduces COF by slip of the crystalline layers past each other [7] . Low surface energy additives also reduce the COF of plastic surfaces by reducing their tendency to adhere to other surfaces [7-8] . Other techniques involve altering the surface morphology and aim at reducing the surface contact area and thus reducing the friction force. The COF of the PE jacket on the fibre optic cables was altered by modifying the jacket compound formulation to reduce friction for a ready-to-use system, eliminating further external modification during installation. COF measurements on plaques showed that the combination of two additives had a synergistic effect on COF reduction. COF measurements of cables made with this compound showed double performance improvement in terms of jetting distance in a duct based on using a simulation model.

2 Experimental 2.1 Materials

The base polymer resin utilised in this study is a high density polyethylene (HDPE) DGDA-6318 BK jacketing compound (0.6 dg/min, density = 0.956 g/cc) produced by The Dow Chemical Co, Midland, Michigan, USA. These jacket grades are primarily used in telecommunication fibre optic cable (FOC) applications.

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May 2014