Temperature-modulated thermomechanical analysis (TMA) is a technique which allows for separation of the temperature-dependent thermal expansion from the time and temperature-dependent creep or stress relaxation behavior. Extrusion during the cable production process may orient and stretch polymer chains which are rapidly cooled in water. Such frozen-in stresses might relax over a longer time period, or when the sample is heated up, the polymer chains are able to move back to their initial state. Using this method allows for measurement of both effects-irreversible stress relaxation and reversible thermal expansion-at the same time. Additionally, a reversible signal might be used for the determination of the coefficient of thermal expansion for different materials. This work compares polyethylene samples with and without frozen-in stresses measured on standard and temperature-modulated TMA.

The crystallinity affects the most of the properties of the products made of semi‐crystalline engineering polymers, such as poly (butylene terephthalate) (PBT) optical fiber loose buffer tubes. Precise control of crystallinity of PBT can be crucial for the quality of an optical fiber cable. Proper determination of crystallinity index from differential scanning calorimetry (DSC) measurements can be challenging for PBT as various processes occur between devitrification and melting that influence the initial crystallinity. Discrepancy between industrial and laboratory conditions leads to difficulties in transfer of laboratory‐scale procedures to technological processes. In this article, simple and time effective, small‐scale laboratory procedure based on Melt Flow Indexer was proposed for the preparation of samples with varying crystallinity indices to simulate industrial products of PBT extrusion, namely loose buffer tubes for optical fibers. Moreover, the conventional “linear” DSC method of characterization of PBT crystallinity index was revised with wide‐angle X‐ray scattering as the reference. Analysis showed the complexity of the thermal processes occurring in PBT melt‐extruded samples between Tg and Tm that strongly influenced the value of crystallinity index of PBT measured by DSC. These processes were identified and new semi‐empirical method of their extraction from the thermograms was proposed. Cold melting of the crystalline phase was found to have dominant contribution in the “pre‐melting” region that is between approx. 130°C and the onset of the fundamental melting peak, with only minor interrupting low‐intensity exothermic event. The contribution of this “pre‐melting” endotherm was more significant for the samples cooled at lower rates.

We studied the porous structures and thermal properties of spherical shaped cross-linked polymers. These novel polymeric microspheres were synthesized by emulsion-suspension polymerization of aromatic tetrafunctional monomer [2,7-(2-hydroxy-3-methacryloyloxypropoxy)naphthalene (2,7-NAF.DM)] with typical, commercially available monomers (styrene, divinylbenze ne and methyl methacrylate). The monomer 2,7-NAF.DM was obtained in the twostep process. In the first step, the epoxy resin was synthesized by treating epichlorohydrin with naphthalene-2,7-diol. In the second step, the obtained epoxy derivatives were subjected to esterification with methacrylic acid. Porous structures of the obtained microspheres in the dry state were studied by nitrogen adsorption-desorption measurements. Thermal stabilities and degradation behaviours of the obtained co-polymers were characterized by differential scanning calorimetry and thermogravimetric/derivative thermogravimetry analyses. In addition, we also present the photoluminescent properties of these microspheres.

Optical cables and fibers are extremely sensitive for mechanical, thermal and environmental conditions, which can affect their optical performance. This article describes known reasons and mechanisms responsible for dimensional changes in temperatures cycling, which can influence optical and mechanical performance and properties of the cables, including internal cable components. Understanding all physical and chemical mechanisms which meet different manufacturing parameters, various materials properties and external conditions allows to control and reduction of cable shrinking and as a result, improving mechanical and optical performance of optical cables.