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Using one-step method, rigid polyurethane foams were made, modified with developed fire retardant systems containing halogen-free flame retardants and nanofillers in the form of multi-walled carbon nanotubes or nanoscale titanium dioxide. The materials were subjected to a test using a cone calorimeter and smoke-generating chamber, and selected samples were further analyzed via thermogravimetry and oxygen index. Moreover, the products of thermal degradation of selected samples were identified using gas chromatography with mass spectrometer. Conducted flammability tests confirmed the presence of a synergistic effect between the used nanofillers and halogen-free flame retardants. It has been observed that the carbonized layer, the formation of which favored the presence of nanoadditives, inhibits the combustion process. Furthermore, nanofillers influenced favorably reduction in the amount and the number of occurring products of thermal degradation.

The synergism between nanoparticles and different kinds of halogen-free fire retardants leading to reduction in flammability and smoke generation of polyethylene was investigated. The composites were evaluated by thermogravimetric analysis, oxygen index test, cone calorimeter measurements, and a single-chamber test. Moreover, the semivolatile and volatile compounds evolved in the thermal degradation processes of polyethylene were determined using a steady state tube furnace and gas chromatograph with mass spectrometer. Morphological and structural characteristics as well as thermomechanical properties of the composites were characterized using various techniques including scanning electron microscopy (SEM), X-ray diffraction (XRD), and dynamic mechanical thermal analysis (DMTA). The obtained data were compared to the results received for polyethylene and polymer with bromine-containing fire retardants. The incorporation of nanofillers and halogen-free fire retardants caused a reduction in combustibility as a consequence of the formation of char.Furthermore, the presence of nanoparticles has a beneficial effect on the inhibition of dripping. The polyethylene with carbon nanotubes, zinc borate, and aluminum hydroxide exhibited better combined properties of fire behavior and production of nontoxic smoke compared to the remaining composition and reference materials. K E Y W O R D Scombustibility, fire retardancy, nanocomposites, polyethylene, synergistic effects

2,3-Dibromo-2-butene-1,4-diol (DBBD) was found to be one of the most effective bromine ame retardants (FR) used to prepare re-resistant polyurethane foams (PU). The production and application of DBBD is environmentally friendly. The compositions of DBBD with other ame retardants available on market: tri(2-chloropropyl)phosphate and 2-(2-hydroxyethoxy)ethyl-2hydroxypropyl-3,4,5,6-tetrabromophthalate were investigated. The environmentally friendly blowing agent -pentane was applied. Computer Statgraphics 2.0 programme was applied for generation of variable quantities of ame-retardants used to prepare PU foams. The obtained foams had characteristics of good re-resistant materials without worsening of other useful properties. Four stop-burning chemical structures: aliphatic bromine, aromatic bromine, phosphorus and also aliphatic chlorine caused synergistic effects in re-extinguishing.

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