Preparation And Properties Investigation Of Rigid Polyurethane Foam Composites Modified By Typical Phytic Acid-based Flame Retardants

With the rapid development of the world economy,energy consumption is increasing day by day.Energy issues have become the key to restrict the high-quality development of China and other countries.According to the "China Building Energy Consumption Research Report(2019)",building energy consumption in 2017 is 947 million tons of standard coal equivalent(tce),accounting for 21.11%of the country’s total energy consumption.Therefore,conducting energy-saving research in the construction industry could effectively reduce building energy consumption and improve building energy efficiency,which has become the focus of the industry,and the development of high-performance building insulation materials is an important strategy to achieving building energy conservation.Rigid polyurethane foam(RPUF)is widely used in the field of building insulation because of its excellent thermal insulation properties and simple construction.However,due to belonging to organic material and with porous structure,RPUF is extremely flammable and releases lots of toxic gases and smokes during the combustion process,causing serious personal injury and property loss.The above deficiencies seriously restrict the application of RPUF in related fields,so it is imperative to modify RPUF and improve its fire safety performance.Phytic acid(PA),as a phosphorus-rich organic biomass,has the advantages of non-toxic,degradable,and renewable.From the perspective of environmental protection,a series of phytic acid-based flame retardants,including aluminum phytate(PA-Al),copper phytate(PA-Cu),zinc phytate(PA-Zn),iron phytate(PA-Fe),cobalt phytate(PA-Co),nickel phytate(PA-Ni),piperazine phytate(PA-Pi)and melamine phytates(MEL-PA)were prepared from phytic acid.The phytic acidbased flame retardant and its compound system were further used to modify RPUF,and their effects on cell structure,physical properties,thermal stability,flame retardant properties,combustion properties as well as smoke toxicity suppression of RPUF composites were systematically studied.The main work are as follows:(1)A series of phytate metal salts(PA-M)were prepared by using the chelating properties of phytic acid,which were further introduced into rigid polyurethane foam system.A series of rigid polyurethane foam/phytate metal salts composites(RPUF/PAM)were prepared by one-step water-blown method.The results showed that PA-M had nucleation effect,and appropriate addition of PA-M could effectively improve hydrophobicity and service performance of the composites.Thermogravimetric analysis(TG)results showed that PA-M could improve thermal stability of the composites at high temperature.Compared with RPUF,the char residues of RPUF/PACu30 increased from 12.4 wt%to 26.2 wt%at 700℃.Cone calorimeter confirmed that the addition of PA-M could significantly reduce the heat release rate(HRR)and total heat release(THR)of composites in the middle and later period of combustion,and reduce the formation of smoke particles.TG-FTIR test showed that PA-Co was the most effective in reducing combustible gas and toxic gas produced during the combustion process.The carbon residue investigation showed that with the addition of PA-M,the compactness as well as graphitization degree of char layer of RPUF/PA-M were enhanced.(2)Ammonium polyphosphate(APP)and PA-Co were combined to form a flame retardant synergistic system(APP/PA-Co),which was further used to modified RPUF.It was found that PA-Co could promote the compatibility between APP and RPUF matrix.The LOI of RPUF/APP40/PA-Co10 was increased to 22.8 vol%with UL-94 reaching V0 level,the char residues of RPUF/APP40/PA-Co10 was 35.2 wt%at 700℃,which was 11.4%higher than that of RPUF/APP50.Cone calorimeter test implied that APP could reduce the pHRR and THR of composites during combustion,but its smoke suppression performance was limited.The addition of PA-Co could reduce heat release and inhibit the formation of smoke particles in combustion process of composites.Smoke density test indicated that the maximum smoke density(MSD)and smoke density grade(SDR)of RPUF/APP40/PA-Co10 were decreased to 50.56%and 33.77,which were significantly lower than the counterparts of RPUF/APP50.TG-FTIR test showed that the combination of APP and PA-Co could effectively reduce the release of toxic gases(CO,HCN)and flammable gases(hydrocarbons and esters)during combustion process of composites.It was further confirmed that APP/PA-Co synergistic system could reduce the thermal hazard of composites while reducing their non-thermal hazards,effectively improving fire safety of RPUF composites.Based on the above investigation,the synergistic flame-retardant mechanism of APP/PA-Co was proposed.(3)PA-Pi was synthesized by PA and piperazine(PI)and used to modify RPUF.When 20 phr PA-Pi was added,RPUF/PA-Pi20 exhibited the best physical properties.TG test showed that the addition of PA-Pi improved thermal stability of composites at high temperature.Compared with RPUF,the char residues of RPUF/PA-Pi20 at 700℃was increased from 12.3 wt%to 25.8 wt%.Cone calorimeter and smoke density tests showed that PA-Pi could promote the pyrolysis products of composites into condensed phase to form char,reducing the total heat release and total smoke production of RPUF/PA-Pi.TG-FTIR test showed that toxic and combustible gases of RPUF/PA-Pi20 in degradation process were significantly decreased compared with those of RPUF.Char layer investigation showed that PA-Pi promoted to the formation of P-N-C,C=C stable structure in the combustion process of composites,improving the graphitization degree of the char layer,and played an important role in condensed phase flame retardancy mechanism.(4)Melamine phytates(MEL-PA)was prepared by supramolecular self-assembly technology,which was further used to modify RPUF.SEM test showed that MEL-PA had good compatibility with RPUF matrix.TG test showed that the addition of MELPA could promote the initial degradation of composites into char,and the higher the MEL-PA loaded,the higher the char residues and the better high-temperature thermal stability of the composites.On this basis,the pyrolysis kinetic analysis of the RPUF/MEL-PA composites were conducted,which indicated that the degradation mechanism of composites in the main degradation stage was random nucleation reaction.Smoke density tests and TG-FTIR analysis implied that MEL-PA possessed good smoke toxicity suppression characteristics.With the increase of MEL-PA loading,the MSD and SDR of composites decreased gradually.MSD and SDR of RPUF/MELPA30 were decreased by 53.3%and 52.5%compared with RPUF,and the release of toxic and combustible gases was significantly reduced.The char residues investigation showed MEL-PA could promote the formation of char layer and inhibit the heat and mass transfer.On the basis of above investigation,gas phase condensation phase coworked flame retardant mechanism of MEL-PA was proposed.