Effect of structural features of poly(butylene terephthalate) tubes on the useful properties of the loose tube/optical fibers system in the tubular optical fiber cables

Abstract

ABSTRACT:To verify a hypothesis that a relationship exists between the useful properties of the loose tube/optical fibers system and the structural features of poly(butylene terephthalate) (PBT) tubes, optical attenuation of optical fibers was studied both in the tubular optical fiber cable and in the tube proper. Examinations of the tube material structure was also performed by the DTA, SEM, and WAXD techniques. The results obtained allowed conclusion that during the standard industrial PBT tube extrusion process a finely dispersed crystalline ␣ phase is formed in a quantity of ϳ29%. The value is much less compared with the literature value of 66% (Yasuniwa et al., J Polym Sci B 1999, 37, 2420 1 ) reported for a possible maximal content of the crystalline phase in PBT. Accordingly, it was assumed that the quantity of the crystalline phase in the tubes can be made to increase by their heating at a temperature above the glass transition temperature (T g ) of PBT. Results of the study corroborate the soundness of the assumption that during the optical cable conditioning process over its working temperature range, i.e., from Ϫ40 to 70°C, crystallisation of PBT tubes is likely to occur to result in their shrinkage which, as proven, affects the optical fibers attenuation, which is a major useful property of optical cables.

The crystallinity of poly(butylene terephthalate) in mass‐scale extrusion products as seen by differential scanning calorimetry

“…In telecommunication, PBT is commonly used for the production of optical fiber loose buffer tubes. The function of these tubes is to protect single or a bunch of optical fibers against mechanical and thermal stresses and water penetration in order to ensure data transmission performance of optical fiber cables in outdoor applications 5,20‐23 . PBT satisfies wide range of requirements for a material for an optical fiber buffer tube, combining excellent processability with smooth surface, proper cold bend, crush, creep and impact performances, and low costs 5,20,21,23 .…”

“…The function of these tubes is to protect single or a bunch of optical fibers against mechanical and thermal stresses and water penetration in order to ensure data transmission performance of optical fiber cables in outdoor applications 5,20‐23 . PBT satisfies wide range of requirements for a material for an optical fiber buffer tube, combining excellent processability with smooth surface, proper cold bend, crush, creep and impact performances, and low costs 5,20,21,23 . These tubes are produced in high‐speed screw extrusion process where optical fibers (typically together with a water blocking material) are pulled through the crosshead die of an extruder and the tube is continuously formed around them from extruded PBT melt.…”

“…These tubes are produced in high‐speed screw extrusion process where optical fibers (typically together with a water blocking material) are pulled through the crosshead die of an extruder and the tube is continuously formed around them from extruded PBT melt. After short air‐cooling section, hot tube with fibers is then rapidly quenched, solidified, and cooled in a series of water baths or showers, pulled by wheel capstans and/or belt caterpillars and collected by take‐up devices on reels or pans 5,6,20,21 …”

“…PBT can crystallize in two forms in triclinic systems: strain‐free, α‐form, and extended β‐form, found in samples subjected to stretching 17,18,21 . β phase tends to transform into more stable relaxed α form even at room temperature if stress is removed 17,21 . The equilibrium melting point T m 0 of α‐form of PBT is 245.0 ± 2.0°C, determined from the extrapolation of the relationship between the temperatures of melting T m and crystallization T c .…”

“…Almost all properties of PBT that are crucial for its industrial applications are strongly dependent on the degree of crystallinity and on the resulting morphology after processing 17 . An increase of crystalline fraction of PBT results in serious changes of mechanical performance (increasing modulus, hardness, and dimensional stability and decreasing flexibility, ductility, and impact resistance), 17,22,26,27 decrease post‐production shrinkage, 5,6,21‐23 and decrease optical transparency 6,26 . For these reasons, precise control of the degree of crystallinity of PBT products is a matter of great importance to ensure good quality of the products.…”