Technical article
May 2014
56
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.
