Abstract
The influence of composite materials of ethylene-vinyl acetate copolymer that do not maintain combustion and fire-retardant fillers on thermophysical processes was explored. Ethylene-vinyl acetate copolymer was used in the studies. The content of vinyl acetate is 18 % and 28 %; MFI is 2.5 g/10 min. and MFI is 5 g/10 min. Fire retardant fillers included aluminum oxide trihydrates with average diameter of particles of 1.5 µm and 3.0 µm; magnesium oxide dihydrates with average diameter of particles of 3.0 µm and 3.7 µm and hydromagnesite with average diameter of particles of 1.4 µm. Using the method of thermogravimetric analysis and differential scanning calorimetry TGA/DSC, temperatures of vitrification, melting and decomposition, crystallinity degree, specific thermal capacity, and activation energy were determined. It was found that temperatures of physical transformations (temperatures of vitrification, melting, and decomposition) of polymer compositions that do not maintain combustion depend on properties of ethylene-vinyl acetate copolymer. They increase with decreasing of fluidity indicator of copolymer of ethylene vinyl acetate. EVA 1 has lower values of the indicator of melt fluidity and content of vinyl acetate than EVA 2. During an increase in content of fire retardant fillers, temperatures of physical transformations are shifted in the direction of increasing: vitrification temperature increases from – 85 °C to 53 °C, melting temperature – from 68 °C to 90 °C. At the same time, crystallinity degree decreases from 8.8 % to 1.0 % and specific thermal capacity increases from 0.4 to 8.6 J/gK. This is due to formation of supermolecular structure of the derived compositions. The influence of the polymeric matrix, composition and dispersity of fire retardant fillers on thermal-physical characteristics of polymeric compositions was determined. In case of using a polymer matrix with lower MFI and fire retardants fillers with smaller average diameter of particles, temperature characteristics are shifted towards higher temperatures than in the case of selection of polymer matrix with large MFI and fire-retardant fillers with a larger diameter of particles. Obtained results will be useful during development of formulations of polymer compositions that do not maintain combustion for cable products, considering their thermophysical characteristics.
Highlights
Polymeric composites are widely used in modern manufacturing of cable products [1]
Analysis of the results shows that temperature of the beginning of decomposition in the case of using polymeric compositions based on ethylene-vinyl acetate (EVA) 1 is higher
Among polymeric compositions based on EVA 1, the polymer composition with fire retardant filler in sample No 5 – hydromagnesite, has the highest value of activation energy of the beginning of decomposition, samples No 1 and No 2 of aluminum oxide trihydrate have the lowest value, samples No 3 and No 4 of magnesium oxide dihydrate are in the middle
Summary
Technical requirements for cable products have increased lately and, so has the need for development of new advanced materials, including polymeric composite materials that do not maintain combustion. Polyolefin composite materials that do not maintain combustion are very promising This is due to the growing use of wires and cables for power industry, nuclear power industry, railway transportation, construction, etc. The principle of creation of formulations of halogen-free cable tracks is based on an increase in oxygen index up to the value of 35−40. This is achieved by introduction of fire retardants – hydroxides of metals – to the basic polymer. Research into dependence of thermal properties on the polymer composition, taking into account the chemical composition, dispersity and amount of fire retardant fillers, is an actual problem
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