Preparation And Application Of Polyurea Microencapsulated Ammonium Polyphosphate And Aluminum Hypophosphite

Ammonium polyphosphate（APP）and aluminum hypophosphite（AHP）have become an indispensable part of the flame retardant field of polymer materials due to their high flame retardant efficiency,low smoke,non-toxicity,and low addition amount.Although these flame retardant have better flame retardant efficiency,it has the disadvantages of poor competitive with polymer composites and poor water resistance.Aiming at the defects of intumescent flame retardants,this paper adopts the interfacial polymerization method,using APP and AHP as core materials and polyurea polymer materials as wall materials to prepare polyurea microencapsulated APP（PUAPP）and polyurea microencapsulated AHP（PUAHP）,applied them to low-density polyethylene（LDPE）and EVA/LDPE/EPDM heat-shrinkable composites and explored the effect of microencapsulated flame retardants on the properties of polymer composites.（1）We adopted the single-factor method to investigate the influence of type of emulsifier,dosage of emulsifier,type of isocyanate,type of amine compound,reaction time,coating amount and other factors on microencapsules,determined the optimal reaction conditions and adopted the water solubility test,fourier infraud spectroscopy（FT-IR）,scanning electron microscopy（SEM）and thermogravimetric test（TGA）to characterize the chemical structure,microscopic morphology and stability.The results of FT-IR show that PUAPP and PUAHP not only have their own characteristic peaks,but also those of polyurea.The results of SEM show that the surface of PUAPP and PUAHP had changed from tough to smooth,and particle size had increased slightly.The results of TGA show that,co MPared with APP and AHP,the initial decomposition temperature of PUAPP and PUAHP is reduced,but the thermal decomposition rate is reduced,and the thermal stability is improved.The results of water solubility test show that the solubility of PUAPP and PUAHP decreased from 49.15g·L^-1H₂O and 14.17g·L^-1H₂O to 11.34g·L^-1H₂O and 4.22g·L^-1H₂O,respectively,and the degree of decrease was76.9%and 70.2%,respectively,the water resistance is effectively improved.（2）We formulated PUAPP,PUAHP and pentaerythritol（PER）as intumescent flame retardant,applied them into LDPE composites,explored the optimal formelationthe and adopted the UL-94,LOI,tensile performance,TGA and cone calorimetry to test the properties of LDPE composites.The results show that when PUAHP:PUAPP:PER=1:4.5:1.5,the synergistic flame retardant effect between the components of the intumescent flame retardant is stronger;When the amount of flame retardant is 35phr and LDPE is 100phr,the UL-94 of PUAHP/PUAPP/PER/LDPE composite material passes the V-0,the LOI reaches 27.3%,the tensile strength is8.20MPa,and the elongation at break is 36%.Co MPared with the material prepared with APP as the main flame retardant,its LOI is increased by 1.6%,the tensile strength is increased by 0.57MPa,and the elongation at break is increased by 22%,indicating that PUAPP effectively improves the flame retardant properties of the material.Improved the problem of decreased mechanical properties caused by fillers.（3）We adopted PUAPP as the main flame retardant,PUAHP as the synergistic flame retardant,PER or triazine macromolecular compound（CFA）is a char-forming agent,designed different intumescent flame retardant formulations according to the content and types of different char-forming and explored the influence of the content and type of the char-forming agent on the performance of the materials in EVA/LDPE/EPDM heat-shrinkable material,the results show that when the content of char-forming agent decreases,the flame retardant and mechanical properties of the material decrease to a certain extent;when the same content of PER is substituted for CFA,the flame retardant and mechanical properties of the material decrease,indicating the flame retardancy of CFA The efficiency is better than PER,and the damage to the mechanical properties of the material is less.By exploring the influence of the amount and type of carbon source on the heat-shrinkable material,the formula was optimized.The results showed that when PUAHP:PUAPP:CFA=1:4.5:1.5,the synergistic flame retardant efficiency between the components of the intumescent flame retardant system.On the basis of the above optimized formula,the influence of its dosage on the performance of the heat-shrinkable material has been explored through the tests of UL-94,LOI,tensile properties,cone calorimetry and TGA.The results show that when the dosage is 26%,the tensile strength is 7.78 MPa,the elongation at break is 762%,the LOI is 27.7%,the UL-94 grade has passed the V-0 level.At this time,the synergistic flame retardant effect between the intumescent flame retardants is better,the resulting carbon layer is denser and has the function of oxygen and heat insulation,effectively preventing further combustion of the material,improving the thermal stability of the material,and improving the flame retardant performance of the material.