Study On The Synthesis And Properties Of Phosphorus-containing Flame-retardant Polyurethane

Polyurethane is widely used due to its good physical and chemical properties.However,the limiting oxygen index(LOI)of polyurethane is only 16.5%.It is extremely easy burning material with fast burning rate,this greatly limits the application of polyurethane materials.Therefore,the flame retardant modification of polyurethane is an effective means of expanding its application.At present,most used polyurethane flame retardant is containing halogen flame retardants with excelent flame retardant efficiency.However,this kind of flame retardant will produce large amounts of toxic gas in the combustion process,which will damage to the environment and people's life safety.Small phosphorus containing molecules compounds as a kind of environmental protection adding flame retardant also has been widely used in PU,but this kind of flame retardant tend to affect the mechanical properties of polyurethane materials.In view of these weaknesses,here we designed and synthesized three type of reactive phosphorous-containing flame retardant,the first category is DOPO-containing polyester,the second one is CEPPA-containing polyester and the third category is P-N synergy flame retardant including phosphorus melamine Schiff base(P-MSB)and N,N-((bis-(2-hydroxyethyl)amino)methyl)phosphonate diethyl(BHAPE).And these phosphorous-containing flame retardants were applied in polyurethane by reacting with polyisocyanates and other addition agents.The properties of the thermal stability and flame retardant of modified polyurethane with above three kind phosphorous-containing flame retardants were investigated by TGA and LOI.And the mechanism of flame retardants was further discussed.Main conclusions are as follows:1.Against the problem of complex process,acid value lowering hard and the deep color in synthesis of phosphorus polyester polyol,we design and optimize the synthesis process of phosphorus polyester polyols,by adjusting the ratio of reactants and introducing of appropriate catalyst the acid value of phosphorus polyester polyol can be lowered to 6.5 mgKOH/g.Which was applicated in polyurethane showing excellent flame retardant effect.2.Compare to DOPO derivatives diacid with high price and complex synthesis peocess,the CEPPA can be directly used for synthesis of polyester polyol.Although the CEPPA shows poor thermal stability which will pyrolysis at low temperatures,but it is because of the low temperature pyrolysis produce much more material containing phosphoric acid,these phosphate material induce the substrate material dehydration into carbon as result these process give better flame retardant effect.3.The P-N synergistic flame retardants in this thesis consume can combust the reaction heat by absorbing heat and cooling effect.At the same time,the forned small molecules such as water and NH3 reduce the temperature of the combustion area,suppress the formation of combustible gas and lower the heat release rate through evaporation heat.The most amounts phosphorus form the phosphorus acid by P-N-Pand P-O-P bonds.This kind of phosphorus acid catalytic dehydrate of compounds containing hydroxyl into charcoal slows the mass loss of material and fuel production,while most of the phosphorus residue in coal layer in carbon residue,which play a good flame retardant effect.