EOW May 2014

Technical article

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.

Topography

Topography

Topography

Phase

Phase

Phase

▲ ▲ 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

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.

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 .

▼ ▼ 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

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May 2014