Properties Research Of Rigid Polyurethane Foam Insulation Materials Modified By Aluminum Hypophosphite(Phosphinate)/Expandable Graphite

With the rapid development of the global economy,energy and environmental issues have become the two major themes of today's world development.Currently China's building energy consumption accounts for 30% of total energy consumption in the world,and building energy conservation has become an important measure for sustainable development in China.Rigid polyurethane foam(RPUF)is widely used in building exterior insulation due to its excellent thermal insulation properties.However,as an organic polymer,rigid polyurethane foams are extremely flammable,causing huge casualties and property losses in the fire.Therefore,it is necessary to conduct flame retardant modification research on rigid polyurethane foams.This paper first reviews the external wall insulation technology and flame retardant technology in recent decades,and discusses the feasibility of the above technology in the flame retardant of rigid polyurethane foam.Secondly,expandable graphite(EG),aluminum hypophosphite(AHP)and aluminum diethyl-phosphate(ADP)were used for flame retardant of rigid polyurethane foam,respectively.The effects of flame retardant loading on the cell structure,physical properties,flame retardant properties,combustion properties,thermal stability and smoke density of rigid polyurethane foam were studied.Finally,EG,AHP and ADP were composed to flame retardant synergistic system and introduced into rigid polyurethane foams.The effects of flame retardant synergistic system on the cell structure,physical properties,flame retardant,combustion performance,thermal stability and smoke density of rigid polyurethane foam were systematically studied.1.Expandable graphite was introduced into rigid polyurethane foam system and a series of rigid polyurethane foam/expandable graphite composite(RPUF/EG)were prepared by one-step water-blown method.Low loading of expandable graphite had little effect on the cell structure of the composite,while high loading of expandable graphite had an effect on the uniformity and integrity of the cells structure in the composites.With the increase of EG loading,the density and thermal conductivity of the composites were gradually increased.When the amount of EG added is 5 parts,the density and thermal conductivity of RPUF/EG5 composites are the smallest,59.7Kg/m3 and 0.0436 W/(m · k),respectively.With the increase of EG addition,RPUF/EG composites The density and thermal conductivity increase gradually,but the overall impact is small.Thermogravimetric analysis test showed that the addition of expandable graphite would reduce the thermal decomposition temperature of the RPUF/EG composites,but would increase the char residue of the composites,The amount of EG added is 30 parts,and the char formation rate at 800? is as high as20.2 wt%.Flame retardant tests show that expanded graphite can significantly improve flame retardant of the composites.When 30 phr of expanded graphite was added,the composites presented limiting oxygen index of 25.2 vol% with V-1 rating in Underwriters Laboratories 94 vertical burning test,indicating fire safety of the composites were significantly improved.2.Aluminum hypophosphite(AHP)was introduced into rigid polyurethane foams and a series of rigid polyurethane foam/aluminum hypophosphite composite(RPUF/AHP)were prepared by one-step water-blown method.Low loading of aluminum hypophosphate had little effect on the cell structure of polyurethane foam,but the high loading of aluminum hypophosphite had a certain influence on the uniformity and integrity of RPUF/AHP composites.The density and thermal conductivity of RPUF/AHP composites increased with the increase of aluminum hypophosphate loading.When the amount of ADP added is 30 parts,the density and thermal conductivity of RPUF/AHP30 composites are the highest,60.3 Kg/m3 and0.0466 W/m·k,respectively.Thermogravimetric analysis showed that the addition of aluminum hypophosphate reduced the thermal decomposition temperature and the temperature at maximal mass loss rate of the composite,and significantly increased the char residue of the composites,The highest carbon formation rate can reach 22.6wt%.Flame retardant test showed that the limiting oxygen index(LOI)of RPUF/AHP composites increased gradually with the increase of aluminum hypophosphite loading.When 30 hpr of aluminum hypophosphite was added,the LOI of RPUF/AHP composite reached 23.6 vol% with V-1 rating in UL-94 test.Cone calorimetry test showed that aluminum hypophosphate can effectively reduce the peak heat releaserate and total heat release of RPUF/AHP composites,and effectively improve the fire safety of the composites.3.Aluminum diethyl-phosphate(ADP)was introduced into the rigid polyurethane foams,and a series of rigid polyurethane foam/aluminum diethyl-phosphate composite(RPUF/ADP)composites were prepared by one-step water-blown method.Low loading of ADP had little effect on the cell structure of composites,but high loading of ADP caused partial damage of cell structure.At the same time,it was found that the addition of ADP had little effect on the density of the composites,but increased thermal conductivity of the RPUF/ADP composites.The addition of ADP resulted in decrease in the thermal decomposition temperature and char residue of the RPUF/ADP composites.Flame retardant test showed that the limiting oxygen index of RPUF/ADP composite increased with the increase of ADP loading.When 30 phr ADP was added,RPUF/ADP composite presented limiting oxygen index of 23.0 vol% and passed V1 rating in UL-94 test.MCC test showed that the addition of ADP significantly reduced the peak heat release rate of the RPUF/ADP composite,but had little effect on the total heat release.4.Aluminum hypophosphite(AHP)and expandable graphite(EG)were introduced into rigid polyurethane foams,and a series of rigid polyurethane foam/aluminum hypophosphite/expandable graphite composites(RPUF/AHP/EG)by one-step water-blown method.It was found that both AHP and EG have certain nucleation effect and decreased the cell size of RPUF/AHP/EG composites.Compared with EG,AHP had greater influence on the cell structure and increases the in-homogeneity of the cell structure.The AHP/EG system had little effect on the density of composites,The density of RPUF/AHP/EG composites does not exceed10.54% compared with the pure sample,but the thermal conductivity of RPUF/AHP/EG composites increases with the increase of EG addition.When 6 phr of AHP and and 24 phr of EG were added,the composite presented maximal thermal conductivity of 0.0461W/m·k,which was 15.6% higher than that of pure RPUF.In the RPUF/AHP/EG system,kept the total loading of flame retardant of 30 phr,With the decrease of AHP loading and increase of EG loading,limit oxygen indexincreased to 27.0 vol% for RPUF/ADP12/EG18,which was higher than the systems EG,AHP or ADP added alone,indicating significant synergistic effects in RPUF/AHP/EG system.MCC test showed that the combination of aluminum hypophosphite and expandable graphite in RPUF can effectively reduce the peak heat release rate and total heat release of RPUF/AHP/EG composites,improving the fire safety of composites.5.Aluminum diethyl-phosphate(ADP)and expandable graphite(EG)were introduced into rigid polyurethane foams,and a series of rigid polyurethane foam/diethyl-phosphate/expandable graphite composites(RPUF/ADP/EG)were prepared by one-step water-blown method.In RPUF/ADP/EG composites,the cell morphology was greatly damaged,the cell wall was ruptured and the uniformity of cell size was decreased.When 6 phr of ADP and 24 phr of EG were added s,the thermal conductivity of RPUF/ADP6/EG24 reached the highest value of 0.0474W/m·k,which was 20.9% higher than that of RPUF.Kept the total amount of flame retardant loading at 30 phr,with the decrease of ADP loading and increase of EG loading,the limiting oxygen index reached the maximal value of 25.9 vol% at RPUF/ADP10/EG20,which was significantly higher than the systems of EG,AHP or ADP added alone,indicating significant synergistic effect in RPUF/ADP/EG system.MCC test showed that when ADP and EG loading were 24 phr,and 6 phr,the peak heat release rate of the composite decreased to 137 W/g,which was 47.4% lower than that of the pure sample,indicating that the combination of ADP and EG could significantly reduce the fire safety of the composites.