An Automated Installation for Measuring the Complex Thermal Expansion Coefficient of Polymers by the Modulation Dilatometry Technique

An installation designed for measuring the relaxation component of thermal expansion, a typical feature of polymers due to the conformational mechanism of thermal expansion inherent in them, is described. The relaxation component manifests itself as a shift in the expansion variation phase relative to the temperature variations. The installation allows variations of the temperature-oscillation frequency and amplitude in the ranges of 10^–3 to 10^–1 Hz and 1–5 K, respectively. The expansion variation amplitudes were measured using a mechanotron with a sensitivity of at least 10^–2 m. The serviceability of the installation was demonstrated in studies of the thermal expansion of a polymer (polyvinylacetate, PVA). In these studies, a shift in the expansion–temperature phase in the polymer-vitrification region and its dependence on the temperature-oscillation frequency were recorded.     

Synthesis and long-term stability of acrylic acid and N,N-methylene-bis-acrylamide radiation grafted polypropylene fibers

New carboxyl ion-exchange fibers prepared by acrylic acid (AA) and N, N-methylene-bis-acrylamide (MBAA) monomer grafting to polypropylene (PP) fibers based on the method of γ-rays pre-irradiation in air followed by a Mohr's salt redox initiation of grafting reaction were studied. Grafting degree, homopolymer quantity, monomer conversion and grafting efficiency were determined. FTIR spectroscopy was used to establish the nature of the grafted fibers. The thermal stability of the materials was investigated based on DSC analysis in N₂/O₂ mixture. The long-term stability during 6–8 years of storage was examined by the measurement of the tensile strength and the elongation at break of the fibers, and the chemical oxygen demand in water extracts as well as in the oxygen uptake experiments. The influence of some factors on the useful life of the grafted fibers was studied: a MBAA cross-linking, exposure to day light, the Fe (III) residue presence, a grafting reaction temperature. It was found that small amounts of the adsorbed Fe (III) ions increase the deterioration rate of the grafted fibers, while small amounts of MBAA delay this negative process.