Design Of Reactive-type Phosphorus And Nitrogen-containing Compounds And Study On The Smoke Toxicity Suppression Of Rigid Polyurethane Foam

Rigid polyurethane foam(RPUF),produced from the polyaddition between polyols and isocyanates,has been in commercial production for around sixty years.RPUFs are widely utilized in appliances and the construction industry such as building insulation,and structural portions of furniture due to their unique combination of brilliant mechanical properties and thermal insulation.However,after ignition,RPUFs generate a large amount of heat and gaseous products in a short period of time owing to the porous cellular structure and various components of RPUF,producing harmful smoke and toxic gases containing CO,NOx and HCN.The smoke and toxic gases will destroy the human health and even lead to a vast majority of fire deaths,which may superior over those from heat hazards.In recent years,the increasing high-rise building fire cases which caused great losses of human.Consequently,a considerable number of research efforts into the field of flame retardant and smoke toxicity suppression of RPUF composites are indispensable which is vital to human society and for the environment.In this dissertation,trying to solve the problem of rigid polyurethane foam by molecular design,we start from the following aspects.Firstly,a flame-retardant structural unit containing phosphorus,nitrogen or other flame retardant elements is introduced into the molecular structure of polyurethane.The pyrolysis mechanism accelerates the carbonization rate and increases the amount of carbon residue,which can effectively reduce the release of heat of combustion of the polymer,thus endows good flame retardant effect and heat resistance,and can be used to prepare intrinsic flame retardant polyurethane with excellent comprehensive properties;secondly,in order to reduce the toxic release during combustion of the RPUF material,we successfully synthesized several transition metal oxides,which can catalyze to form a stable carbonaceous layer;at the same time,the layered compounds with two-dimensional morphology,large specific surface area and excellent physical properties can be used as a novel carrier to improve the catalytic efficiency,Obtaining the physical barrier action of two-dimension materials and the catalytic char formation and elevated catalytic activity of the transition metal compounds.Specially,the inorganic nanoparticles supported on the layered sheets can effectively limit the agglomeration.Based on the above researches,this dissertation intends to combine molecular design,nanocomposite,synergistic flame retardant,catalytic carbonation and catalysts for reducing toxic gases generation,and it is expected to hunt for highly efficient catalysts for reducing fire hazards for rigid polyurethane foam composites.The research work of this dissertation is presented as follows:1.The investigation focused on the synergistic effect of phosphorus-containing polyol(BHPP)and nitrogen-containing polyol(MADP)in improving the flame retardancy of EG/rigid polyurethane foam(RPUF).BHPP and MADP were synthesized through dehydrochlorination and Mannich reaction respectively.The influence of the weight ratio of BHPP and MADP was studied by thermogravimetric analysis and limiting oxygen index(LOI)tests.The results demonstrated that the optimal weight percentage of BHPP and MADP in flame-retarding RPUF was 1/1.In addition,the incorporation of expandable graphite(EG)into the RPUF/BHPP/MADP composite could greatly improve the flame-retardant properties of RPUF composites.When the content of EG was 15 wt%,LOI value of RPUF composites reached 33.5%.Furthermore,the value of peak of heat release rate was reduced by 52.4%compared to that of pristine RPUF.Based on the analysis and discussion,a condensed flame-retardant mechanism was primarily proposed.2.Flame retardant rigid polyurethane foam with a reactive nitrogen-containing polyol denoted as MADP and DOPO was fabricated through free-rise technique.The thermal stability and fire behaviors of RPUF were investigated by TGA,LOI,and cone calorimeter.In comparison with the results of individual flame retardant agent(MADP or DOPO),RPUF/MADP-DOPO displayed higher compressive strength,owing to the reaction between isocyanate(-NCO)and P-H of DOPO that imparted the interfacial adhesion and further enhancement effect.Moreover,the RPUF/MADP-DOPO system endowed RPUF with enhanced the char formation,increased the LOI values and reduced heat release.SEM images,XPS analysis and Raman spectra of the char residues suggested that the formation of compact and continuous char layer.The flame-retardant mechanism was further confirmed by RT-FTIR and TG-IR analysis,disclosing that RPUF/MADP-DOPO promoted the formation of protective char layers with phosphorus-rich residues in condensed phase and diluted the flammable gases in gaseous phase.Based on the analysis and discussion,the introduction of MADOP/DOPO can endowed excellent flame retardancy to RPUF depending on bi-phase flame-retardant mechanism.However,the release of toxic gases and smoke production of modified RPUFs increased obviously,which is environmentally hazardous.3.Huge consumption of rigid polyurethane foam(RPUF)brings about two serious challenges for our society:fire hazards and toxicity hazard.To address these issues,metal oxides and bimetallic oxides used for reducing smoke toxicity was successfully synthesized.The structures and morphologies were confirmed and thermogravimetric analysis indicated that incorporation of 2 wt%NiO conspicuously increased the residual yield of RPUF nanocomposites by 63.8%due to its catalytic coupling effect.Additionally,through the thorough analysis of volatile and condensed products,the smoke toxicity suppression mechanism in the pyrolysis and combustion of RPUF was investigated so as to find out the conversion of CO to CO2 through a redox cycle,involving the reduction of Ni2+-Ni0 by CO and the oxidation of Ni0-Ni2+ by O2.Among all the additives,NiO and Cu20 are the best catalysts which facilitate the migration of fuel-N in RPUF into the pollution-free gas in pyrolysis and combustion process.4.Cu2O particles with different sizes,as a kind of active catalysts for reducing toxic gases and smoke suppression,were synthesized and well characterized.The flame retardant and smoke suppression properties were evaluated by LOI test and cone calorimetry.Specifically,with the addition of Cu20 microparticles,the HRR curve of the RPUF/Cu2O-1?m composites can not change too much.However,the PHRR of the RPUF/Cu20-100nm nanocomposite is reduced to 262 kW/m2,which may be due to the obvious catalytic carbon formation of the Cu2O nanoparticles and the formation of network structures in the RPUF matrix,thus forming more and the denser carbon layers and enhancing the protection effect.Particularly interesting is that when Cu2O nanoparticles with a size of 5 nm are added,the PHRR value is increased,which is caused by the surface area of the nanoparticle,thereby obtaining a better catalytic oxidation effect.These results indicate that the smaller nano-sized Cu2O has a greater catalytic oxidation effect.Although it has not a good flame retardant performance,it can be a good auxiliary effect on the catalytic effect of Cu2O in the thermal degradation process in RPUF matrix.For the release of toxic gas CO during thermal degradation of RPUF composites,different sizes of Cu2O nanoparticles have good attenuating effect,which is related to the catalytic carbonation and catalytic oxidation of Cu2O nanoparticles in RPUF matrix.5.A layered MoS2 decorated with Cu2O nanoparticles was creativity obtained by hydrothermal technology and facile wet chemical treatment,reducing the toxic product formations of polyurethane nanocomposites during combustion.Due to the low weight ratio of Cu2O to MoS2,the resulting Cu2O-MOS2 hybrid effectively prevented the MoS2 nanosheets from restacking.However,the Cu2O-MoS2-M hybrid was produced by increasing content of Cu2O,which has the characteristic stacked layer structure of MoS2.Reduced harmful organic volatiles and the toxic gases(e.g.a decrease of ca.28%and 53%for CO and NOx products,respectively)were obtained because of synergistic effect between the physical adsorption of MoS2 and catalysis action of Cu2O.Notably,the addition of Cu2O-MoS2 hybrids led to high char formation of the RPUF nanocomposite,indicating the effectively catalytic carbonization property.In this work,the N-Gas model for predicting fire smoke toxicity was developed and demonstrated.Furthermore,the research offers theoretical model and direct proofs of the negative influence of the stacked MoS2 on reducing the smoke toxicity for RPUF nanocomposites.