J Therm Anal Calorim DOI 10.1007/s10973-017-6294-4 Analysis of flammability and smoke emission of rigid polyurethane foams modified with nanoparticles and halogen-free fire retardants 1 1 2 1 Kamila Salasinska • Monika Borucka • Milena Leszczyn´ska • Wojciech Zatorski • 1 1 2 Maciej Celin´ski • Agnieszka Gajek • Joanna Ryszkowska Received: 30 November 2016 / Accepted: 8 March 2017 Ó The Author(s) 2017. This article is an open access publication Abstract Using one-step method, rigid polyurethane Introduction foams were made, modified with developed fire retardant systems containing halogen-free flame retardants and Rigid polyurethane foams (RPUF) are used in many areas, nanofillers in the form of multi-walled carbon nanotubes or including construction industry as one of the best com- nanoscale titanium dioxide. The materials were subjected mercially available insulation materials. RPUF have very to a test using a cone calorimeter and smoke-generating good mechanical properties, resistance to aging and water chamber, and selected samples were further analyzed via and also atmospheric factors [1–4]. Unfortunately, rigid thermogravimetry and oxygen index. Moreover, the prod- polyurethane foams have also some disadvantages, among ucts of thermal degradation of selected samples were which special attention should be paid to flammability and identified using gas chromatography with mass spectrom- toxicity of the gas products emitted during thermal degra- eter. Conducted flammability tests confirmed the presence dation and combustion [5]. of a synergistic effect between the used nanofillers and Combustion of polymeric materials is an exothermic halogen-free flame retardants. It has been observed that the reaction of the catalytic oxidation of organic compounds carbonized layer, the formation of which favored the carried by energy supplied in the form of heat and forming presence of nanoadditives, inhibits the combustion process. free radicals. This phenomenon is accompanied by heat, Furthermore, nanofillers influenced favorably reduction in light and combustion products (gases, smoke). The ability the amount and the number of occurring products of ther- to ignite the polymer depends primarily on the availability mal degradation. of oxygen, temperature and its physicochemical properties. In contrast, the combustion process is conditioned, among Keywords Rigid polyurethane foams Á Halogen-free flame others, by composition, chemical structure and density of retardants Á Oxygen index Á Cone calorimetry Á Smoke the material, porosity, size, shape and structure of the chamber Á Thermal analysis product [6]. The thermal decomposition of non-fire retarded poly- urethane foams in air is generally quite well understood. Generally, the initial decomposition of the foam ([300 °C) results in the volatilization of isocyanates, amines and ‘‘yellow smoke’’, leaving behind polyols in the condensed phase. These polyols are fragments and volatilize as the & Kamila Salasinska temperature increases ([600 °C), leaving behind a char. [email protected] This char can decompose further, leaving behind a residue, to produce simple organic fragments and some polycyclic 1 Central Institute for Labour Protection – National Research Institute (CIOP-PIB), Czerniakowska 16, 00-701 Warsaw, aromatic hydrocarbons (PAHs). In the gas phase, iso- Poland cyanates, amines and ‘‘yellow smoke’’ are begun to 2 Warsaw University of Technology, Wołoska 141, decompose at [600 °C into low molecular weight nitro- 02-507 Warsaw, Poland gen-containing fragments (such as benzonitrile, aniline and 123 K. Salasinska et al. hydrogen cyanide (HCN)). At [800 °C these compounds nanomaterials exhibit improved rheological properties, further fragment into simple molecules (such as HCN, CO, higher mechanical strength and lower emission of fumes CH4 and CH2O) and PAHs [7, 8]. [22–24]. The most commonly used nanofillers are layered Rigid polyurethane foams are carbonized during com- silicates [25], nano-SiO2 [26], titanium oxide and carbon bustion. This process leads to the reduction in the amount nanotubes (CNT) [4, 27, 28]. During combustion, com- of heat released during the combustion of polymers and posite nanoparticles can migrate to the surface of the affects the amount and type of the emission. Formation of polymer and assist in the formation of carbon layer carbon by restricting access of the flame to the deeper [29, 30]. The combination of nanomaterials with conven- layers of the material prevents the formation of low tional flame retardants, leading to the formation of syner- molecular weight organic compounds, which support the gistic effect between those substances, is currently the fuel process. Unfortunately, the amount of formed carbon subject of numerous studies [23, 25, 31–33]. layers in the combustion of rigid polyurethane foams is Wang et al. [34] reported that the introduction of gra- relatively low [6]. phene nanoparticles to polybutylene succinate (PBS) con- Research and development units and chemical corpo- taining melamine poliphosphate favorably affects the rations around the world are currently carrying out formation of carbon and increases the thermal stability of numerous works related to the improvement in thermal the polymer. On the basis of the cone calorimeter testit was stability and fire resistance of rigid polyurethane foams. found that the values of maximum rate of heat release RFUP flame retardancy can be achieved by the addition of (pHRR) and total heat generated (THR) of polybutylene flame retardants [1–6, 9], the task of which is usually to succinate containing 18% melamine phosphate and 2% of delay ignition, slow the process of combustion and pyrol- graphene were, respectively, 63 and 23% lower compared ysis, reduce emissions of smoke, and reduce the phe- to the results obtained for pure PBS. The paper also pre- nomenon of dripping. The group of fire retardants includes, sents the results for the materials modified with polyhedral among others, compounds containing halogens such as oligomeric silsesquioxane (POSS), but the synergistic bromine and chlorine, compounds of phosphorus and effect in combination with melamine poliphosphate was nitrogen, and hydroxides of aluminum and magnesium significantly lower in comparison with graphene. In addi- [10]. Most flame retardants with built-in halogen atoms tion, increased quantities of fumes are released, which is currently attract a lot of controversy, mainly because of not observed in the case of materials of melamine phos- their safety and corrosion properties of gases released [11]. phate and graphene. The most frequently used halogen-free flame retardants, These results are contrary to those described by apart from aluminum hydroxide and magnesium, contain- Didane et al. [35]. The authors reported the results for ing compounds are phosphorus/nitrogen. Flame retardants flammability testing of polyethylene terephthalate (PET) based on Mg(OH)2 and Al(OH)2 prevent heating up of the using a 9 mass% of flame retardant agent based on the zinc material to the ignition temperature, and the water vapor, phosphinate, and three types of POSS, which have referred along with degradation products, is released into the to the unmodified PET and PET with 10 mass% a/m combustion zone reducing the concentration of com- retardant. It has been observed that the introduction of bustible products and oxygen. As a consequence, the flame 1 mass% POSS contributed to the reduction in the maxi- temperature is lowered and the resultant oxides form a mum HRR from 500 kW m-2 for PET and 365 kW m-2 protective layer, on the surface of the material, limiting the for PET with flame retardant to 214 kW m-2 in the case of movement of the volatile degradation products to the flame one of the types of nanofillers. In addition, for the same and oxygen to the burning material. The group of flame kind of POSS emissions of carbon dioxide at a level similar retardants containing phosphorus and nitrogen includes, to the values obtained for unmodified PET was observed. among others, phosphaphenanthrene phosphonamidates The aim of this study was to produce nanocomposites of [12], ammonium polyphosphate [13, 14], polydopamine rigid polyurethane foams modified with halogen-free fire [15], triphenylphosphate [16], dimethyl methylphospho- retardants with reduced flammability and smoke emissions. nate [17], dimethylpropanphosphonate [18], hexaphenoxy Prepared materials were analyzed using the cone cyclotriphosphazene [19] and aluminum phosphinate calorimeter and the single-chamber test; under obtained [4, 20, 21]. results, the initial selection of the proposed flame retardant A relatively new group of measures that increase the systems was done. In the next stages of work, for the thermal stability and reduce the flammability of polymers, selected compositions, thermogravimetric analysis and are nanoparticles. The advantage of nanocomposites is the oxygen index were performed. Also, specified were the possibility to obtain satisfactory results using only a few nature and quantity of the substances present in the exhaust percent of the filler, while in the case of traditional flame fumes and emitted during the thermal decomposition. The retardants these quantities reach up to 60%. Otherwise, analysis made it possible to assess the effectiveness of the 123 Analysis of flammability and smoke emission of rigid polyurethane foams modified with… proposed system on the behavior of materials containing to the component A in individual materials. Additionally, a them in the conditions of pyrolysis and combustion.