Abstract
The aim of this work was to investigate the influence of different types of carbon filler on the thermal stability and flammability of rigid polyurethane foams. As a filler, multi-walled carbon nanotubes and graphite fakes were used. Scanning electron microscopy was used to observe the structure of foam and dispersion of nanofiller in polymer matrix. Thermal stability of these composites was determined by thermogravimetry analysis. Test was carried out under both nitrogen and air atmosphere. The degradation products were evaluated by thermogravimetry (TG) combined with infrared spectroscopy (TG–IR) measurements. The activation energy was measured by the Flynn–Wall–Ozawa method from the TG curves. Flammability tests like limiting oxygen index and smoke density were also measured. No significant changes in the thermal stability of the composites were observed. The activation energy of sample containing carbon filler increased. Based on TG–IR, one can notice that there were no differences in the emitted volatile products during thermal degradation. Carbon filler enhanced fire retardancy of polyurethane foam; however, graphite gives better results.
Highlights
Polyurethanes possess specific chemical structures consisting of stiff and flexible segments, whose fraction strongly influence their properties
On the bottom of the foams—the arrows indicate the direction of foam rise in the mould—a porosity-free region, can be observed, the samples were all produced using the same conditions. The presence of these regions is a result of the addition of carbon fillers which slows down the crosslinking reaction in the foams
It was found that both carbon nanotubes (CNTs) and graphite have a minor impact on the decomposition process during thermal degradation of polyurethane
Summary
Polyurethanes possess specific chemical structures consisting of stiff and flexible segments, whose fraction strongly influence their properties. Depending on the fraction of each segment, two types of polyurethanes, namely elastomers and plastomers, can be distinguished. As a result, they can exhibit various mechanical and physical properties; polyurethanes are widely used in industry. Rigid polyurethane foams appear to be very promising materials for the transport industry, where the reduction in elements mass is of prime importance, as the lighter vehicles will use less fuel. The major disadvantage of polyurethanes which prevents them being used in the automotive industry is high flammability. When ignited, they emit toxic gases like carbon monoxide, carbon dioxide and hydrogen cyanide. Much emphasis has been placed on the safety regulations applicable to flame-retardant materials in relation to their toxicity and smoke products [1]
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