Technical article
May 2014
58
This suggests that SA2 lowers the COF
by making the resin surface smoother.
The topography image of the sample B
plaque shown in
Figure 2b
with just SA1
as the additive reveals globular features
mushrooming from the surface. The
random size of the features points to
a bulk-to-surface segregation process
of SA1 present in the masterbatch. The
corresponding phase image (
Figure 2e
),
clearly reveals these segregated globular
droplets, which appear as the bright (hard)
aggregates. The surface roughness of this
sample is 8.5nm, which is higher than
the surface roughness of the neat HDPE
plaque. This suggests that reduction of
COF by SA2 works differently than SA1.
The surface segregated globules lower the
surface energy of the resin surface, thus
reducing the COF.
The surface topology in the sample
containing both the additives (sample
C) is a hybrid between both the surface
features seen in the prior two cases
(
Figure 2c
). Most of the surface looks
fairly smooth, like that shown in
Figure
2a
, suggesting that the surface is covered
by a segregated layer of SA2. There are
also regions of “exposed boulders,” which
look like the surface segregated SA1
“mushrooms.”
However, the spherulite structure of the
HDPE surface is not visible, unlike the
topology seen in sample A. This suggests
that the HDPE layer is pushed further
down by the presence of the surface
segregated SA1 globules (more than 20nm
away from the surface), which dominate
the surface topology along with SA2. This
is further supported in the corresponding
phase image (
Figure 2f
) where the phase
difference is diminished as compared to
sample B as shown in
Figure 2e
.
The circled areas depict patches of surface
exposed SA1, not yet submerged in SA2.
The surface roughness of this sample is
measured at around 4.2nm, because of the
presence of SA2 at the surface.
The initial studies were focused on
testing the friction between compression
moulded plaques of the cable jacket and
duct substrate materials used in fibre optic
cable installation. To simulate installation
of a real cable in a duct situation the
testing capabilities of Plumettaz Inc in
Switzerland were used with a specially
designed micro-duct testing system under
various conditions.
The tests were performed on dummy fibre
optic cables, consisting of FRP strength
member (Neptco LIGHTLINE. LFH 230) as
the core and a layer of outer jacket.
Through the tests, the coefficients of
friction between the cables and inner
duct surfaces were obtained. Jetting
distances for the cables under each of the
test conditions were predicted utilising a
model developed at Plumettaz.
The correlation plot between COF
measured on plaques in the lab and on
cables at Plumettaz is shown in
Figure
3
. The plot shows correlation between
the two measurements, suggesting that
laboratory plaque data is a good indicator
of COF performance during installation of
cable through a duct.
Based on the correlation it can be
concluded that jacketing formulations
containing both the slip additives, SA1
and SA2, are most likely to show the best
COF performance. To optimise the COF
performance two different formulations
EXP1 and EXP2 were made, with 1.25 per
cent and 2.25 per cent additive levels.
Cables made from both these formulations
were tested at Plumettaz for COF and
jetting distance in microducts.
The COF of cables are shown in
Figure 4
.
The control cable used is made from HDPE
DGDA-6318 BK. The control cable reflects
the COF performance of fibre optic jacket
used currently. The COF of these cables
have a mean value of 0.22. The second
sample tested was the lubed control,
which is the HDPE jacket with jetting
lube applied. The jetting lube reduces the
COF by ~60%, and represents the COF
performance in a lubed cable installation
scenario.
The third sample, EXP1, is the low COF
formulation having a 1.25 per cent slip
additive content, resulting in a 50 per cent
reduction in COF from the control. The
fourth sample is EXP2, having a 2.25 per
cent slip additive content which results in
a 55 per cent reduction in COF.
▲
▲
Figure 2
:
AFM micrographs of surface topology of plaques with (a) sample A, (b) sample B, and (c) sample C and
phase image of plaques with (d) sample A, (e) sample B, and (f) sample C
▼
▼
Figure 3
:
Correlation plot between COF measured in the lab on plaques on a tribometer and at Plumettaz on cables
Lab Plaque COF
Plumettaz Cable COF
Topography
Topography
Topography
Phase
Phase
Phase
