Microencapsulated Ammonium Polyphosphate Flame Retardant Modified Rigid Polyurethane Foam Composites And The Properties Investigation

According to the report of China Association of Building Energy Efficiency in2019,China’s building energy consumption accounted for 21.11%of the country’s total energy consumption in 2017.It is necessary to conduct energy-saving research in the building industry,and the development of high performance thermal insulation material for building exterior wall is an important way to building energy conservation.Rigid polyurethane foam（RPUF）,as an important building insulation material,has the advantages of low density,excellent insulation performance,easy processing,et al,which make it widely applied in building insulation.However,RPUF has the disadvantages of easy combustion and release of a large amount of toxic gas and smoke,so it is necessary to conduct flame retardant modification for RPUF.Ammonium polyphosphate（APP）,as a phosphor-nitrogen flame retardant,possesses the advantages of halogen-free and high efficiency,which is especially suitable for flame retardant of rigid polyurethane foam.However,APP presents the disadvantages of poor compatibility with polyurethane foam matrix,poor water resistance,et al.In practical application,APP is easy to agglomerate and migrate to the surface of the materials,which seriously deteriorate thermal insulation performance,mechanical performance and environmental resistance of flame retarded RPUF composites.Based on this,microcapsules technology is used as breakthrough point,and different capsule materials are chosen to encapsulate APP to prepare polyurethane microencapsulated ammonium polyphosphate（PUAPP）,melamine-formaldehyde microencapsulated ammonium polyphosphate（MFAPP）,silicone gel microencapsulated ammonium polyphosphate（Si APP）and glycidyl methacrylate microencapsulated ammonium polyphosphate（GMAAPP）,which can effectively improve the deficiencies of in the poor water resistance,poor compatibility with matrix and easy to moisture absorption,et al for APP.The prepared microencapsulated ammonium polyphosphate and its compounding system were applied to enhancing flame retardancy of RPUF,and the effects of flame retardant on cell structure,flame retardancy,water resistance,physical properties and combustion properties of RPUF are systematically investigated.The main research works are as follows:（1）Polyurethane microencapsulated ammonium polyphosphate（PUAPP）was introduced into polyurethane rigid foam to fabricate polyurethane rigid foam/polyurethane microencapsulated ammonium polyphosphate composite（RPUF/PUAPP）composites by one-step water-blown method.It was found that virgin RPUF presented Limited Oxygen Index（LOI）of 18.8 vol%without immersion,and the LOI value of RPUF was gradually decreased to 18.0 vol%with the increase of immersion time with no rating in UL-94 test all the time.When 30 php of APP and PUAPP were added,RPUF/APP30 and RPUF/PUAPP30 presented LOI of 23.3 vol%and 22.3 vol%,respectively,with V-0 ranting in UL-94 test.RPUF/APP30 showed LOI of 21.7vol%with V-0 rating in UL-94 test when it was soaked for 15 days.Meanwhile,RPUF/PUAPP30 presented inconspicuous decrease of LOI and V-0 rating in UL-94 test with with smooth surface and no migration of PUAPP particles,indicating higher flame retardancy,compatibility and water resistance of RPUF/PUAPP30 compared with those RPUF/PUAPP30.The physical performance test confirmed that the thermal insulation and mechanical properties of RPUF/PUAPP30 were obviously superior to that of RPUF/APP30（2）Melamine-formaldehyde microencapsulated ammonium polyphosphate（MFAPP）was introduced into polyurethane rigid foam to fabricate polyurethane rigid foam/melamine-formaldehyde microencapsulated ammonium polyphosphate（RPUF/MFAPP）compositesby one-step water-blown method.RPUF/MFAPP30 with30 php MFAPP loading possessed LOI of 21.3 vol%with V-0 rating in UL-94 test.RPUF/MFAPP presented unchangeable LOI value with V-1 rating in UL-94 test even immersed in water for 15 days.RPUF/MFAPP showed thermal conductivity of of0.0400 W/m·k with compressive strength of 0.295 W/m·k.At the same time,it was found that the maximum thermal decomposition temperature(T_max)of RPUF/MFAPP30 was significantly improved with compact and intact char layer compared with RPUF/MFAPP30,which endowed excellent fire safety of RPUF/MFAPP30.TG-FTIR analysis confirmed that the addition of MFAPP could significantly inhibit the release of toxic and combustible gases in combustion of RPUF/MFAPP composites.On this basis,the solid-gas flame retardant mechanism of RPUF/MFAPP composite was proposed.（3）Silicone gel microencapsulated ammonium polyphosphate（Si APP）was introduced into polyurethane rigid foam to prepare polyurethane rigid foam/silicone gel microencapsulated ammonium polyphosphate（RPUF/Si APP）composites by one-step water-blown method.RPUF/Si APP30 possessed LOI of 22.8 vol%with V-0rating in UL-94 test.After soaking for 15 days,the LOI of RPUF/Si APP30 was slightly decreased to 21.8 vol%with V-0 rating in UL-94 test,which were better than those of RPUF/APP30.It was confirmed from physical properties test found that RPUF/Si APP30 composite possessed thermal conductivity of 0.0398 W/m·k with compressive strength of 0.292 MPa.It was revealed from thermogravimetric analysis and char residue analysis that RPUF/Si APP30 presented higher char residue,T_-5wt%and T_max value compared with those of RPUF/APP30 with enhanced compactness and graphitization degree,indicating significantly improved thermal stability and flame retardancy of RPUF/Si APP30.（4）Glycidyl acrylate microencapsulated ammonium polyphosphate（GMAAPP）was combined with polyurethane microencapsulated expanded graphite（PUEG）and introduced into polyurethane rigid foamto prepare polyurethane rigid foam/glycidyl acrylatemicroencapsulatedammoniumpolyphosphate/polyurethane microencapsulated expanded graphite（RPUF/GMAAPP/PUEG）composite by one-step water-blown method.RPUF/GMAAPP30 showed LOI of 22.3 vol%with V-0 rating in UL-94 test,the thermal conductivity of 0.0412 W/m·k compressive strength of 0.273 MPa and heterogeneous cell structure.RPUF/PUEG30 presented LOI of 25.3 vol%with V-0 rating in UL-94 test,thermal conductivity of 0.0391W/m·k,compressive strength of 0.276 MPa,and relatively uniform cell structure.In comparison,RPUF/GMAAPP20/PUEG10 possessed LOI of 24.6 vol%with V-0 level in UL-94 test,thermal conductivity of 0.0395 W/m·k,compressive strength of0.292MPa and uniform and smaller cell structure.Thermogravimetric and char residue analysis indicated that RPUF/GMAAPP20/PUEG10 presented higher thermal stability with compacter and completer char residue,thus possessed excellent fire safety.