| Polyurethane(PU)is widely used in various fields because of its excellent physical and chemical properties,but its flammability limits the application of this material,so it is necessary to study the flame retardant modification of PU.With the development of nanocomposites,nano-silica has been gradually used in the field of flame retardant PU because of its excellent interface effect,surface effect and other advantages.When combined with phosphazene compounds with special phosphorus and nitrogen skeleton structure,they can show excellent flame retardant and smoke suppression properties.Based on the flame retardant advantages of nano-silica and cyclotriphosphazene,six kinds of nano-silica hyperbranched modified P-N-Si flame retardants were prepared in this paper.The flame retardant agent with excellent performance was selected to study the flame retardant modification of PU.The main research contents are summarized as follows:(1)using tetraethyl orthosilicate as silicon source and ammonia as alkaline medium,silica microspheres were prepared by St?ber method,mesoporous silica was prepared by sol-gel method,and hollow silica was prepared by hard template method.The epoxy groups were introduced into the surface of three kinds of nano-silicon spheres by modification.Secondly,two kinds of hyperbranched polymers were prepared by nucleophilic substitution reaction of hexachlorocyclotriphosphazenewith4-minodiphenylmethaneand m-phenylenediamine respectively.Six kinds of hyperbranched cyclotriphosphazene modified nano-silica flame retardants were synthesized by ring-opening reaction between the epoxy group of modified silicon spheres and the residual-NH2 in hyperbranched polymers.The structure and composition of the target flame retardant were characterized by FTIR,XRD,XPS and so on.The results show that the target flame retardant has been successfully prepared.The thermal degradation process of flame retardant was characterized by TGA/DTG,the morphology of flame retardant was characterized by SEM,and the composition of flame retardant was analyzed quantitatively and qualitatively by EDX and Mapping.It was characterized by SEM that the grafting ratio of phosphorus and nitrogen was high.(2)Polyurethane foam was prepared by all-water foaming method using isocyanate and polyether polyol as main raw materials,butyleneditin dilute silicate and triethylene diamine as catalyst,1,2-propanediol as chain extender,glycerol as cross-linking agent and 2051 as surfactant.Six kinds of flame retardants were added to polyurethane to prepare flame retardant PU.The results of limiting oxygen index and vertical combustion test show that the loi value increases with the increase of the amount of flame retardant.When the content of the flame retardant is 20%,the LOI value of some flame retardants is close to the non-flammable grade,and the UL-94reaches the V-0 grade.According to the test results of LOI and UL-94,h SiO2-EPO-DHPCT/PU,m SiO2-EPO-DHPCT/PU and h SiO2-EPO-MHPCT/PU were selected to compare the thermal and flammability of the flame retardant system by TGA/DTG and Cone.Cone tests show that compared with blank PU,when the addition amount is 20%,the PHRR values of h SiO2-EPO-DHPCT/PU,m SiO2-EPO-DHPCT/PU and h SiO2-EPO-MHPCT/PU are reduced by 26.5%,23.2%,20.7%and THR by 18%,12.5%and 9%,respectively.The TSP,TSR,RSR and SPR values of the three systems also decreased accordingly,and the SPR value of20wt%h SiO2-EPO-DHPCT/PU decreased by 41.8%.Compared with the three flame retardant systems,the flame retardant and smoke suppression performance of h SiO2-EPO-DHPCT is the best.Through thermogravimetric analysis of the thermal decomposition of flame retardant PU,the T5%of the three flame retardant PU is lower than the decomposition temperature of pure PU,the Tmax of the flame retardant system is earlier than that of blank PU,and the carbon residue is increased at 800°C.The bending property test results show that the bending property of the system decreases with the addition of flame retardant,and the bending strength decreases with the increase of flame retardant content.(3)To compare the flame retardant efficacy of independent components of inorganic silicon ball,DHPCT,MHPCT and organic and inorganic physical mixture on PU.The results showed that when the addition amount was 20%,the loi values of SiO2,h SiO2 and m SiO2 were 22.3%,22.4%and 22.5%respectively.The LOI values of MHPCT and DHPCT are 23.2%and 22.9%respectively.In the composite system,the loi value of 10wt%m SiO2 materials 10wt%MHPCT/PU is 23.9%.It is obviously higher than that of single component.However,it is obviously inferior to20wt%h SiO2-EPO-DHPCT/PU(the LOI value is 25.7%).This shows that nano-silica modified by KH560 is further grafted with hyperbranched polymer with high P and N content,and the organic and inorganic components are chemically bonded to form a more effective P-N-Si synergistic flame retardant. |
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