Study On Preparation And Properties Of Intrinsic Flame-retardant Polyurea

Polyurea is a block copolymer composed of soft and hard segments,which has excellent mechanical and waterproof properties.It is widely used as a waterproof spraying material and a new type of explosion-proof material in various engineering projects.However,polyurea is an extremely flammable polymer material that releases smoke and toxic gases during combustion,resulting in droplet formation,which not only pollutes the environment but also endangers human safety.Therefore,the development of flame retardant polyurea is of great significance.Phosphorus based flame retardants have good flame retardancy and plasticization properties,which are conducive to carbonization.However,additive phosphorus based flame retardants are prone to migration and have poor compatibility.In this paper,three reactive phosphorus containing flame retardants were introduced into polyurea to prepare three intrinsic flame retardant phosphorus containing polyureas.Due to the excellent flexibility,water resistance,and thermal stability of polysiloxane,it can be introduced into the main chain of polyurea to combine the excellent properties of both,forming a material with better comprehensive performance.In this article,two intrinsic flame retardant silicon/phosphorus block polyurea were prepared by using polysiloxane and two phosphorus containing flame retardants,and their flame retardancy,thermal properties and mechanical properties were explored.The specific work is as follows:1.The relationship between the structure and properties of polyurea was studied for the preparation of flame retardant polyurea.A series of polyureas were prepared using polyurea prepolymers with different isocyanate content(NCO%)and curing agent formulations with different amino content.Research has found that an increase in NCO% of the prepolymer and the hard segment of the curing agent can lead to an increase in the hard segment content of the polyurea and an increase in intermolecular forces.When the NCO% of the prepolymer is 19.01%,the tensile strength can reach 44.3 MPa.The gel time and mechanical properties of polyurea can be adjusted by changing the NCO% of the prepolymer and the composition of curing agent,Using sterically hindered aromatic secondary amine 4,4’-bis(sec-butylamino)diphenylmethane(MDBA)as curing agent can reduce the reaction rate of polyurea synthesis,and the methylene group in the molecule has good flexibility.When the content of MDBA is 30%,the gel time of the prepared polyurea can be extended to 68 s,and the elongation at break can reach1253%.2.Three phosphorus containing flame retardants(OP550)containing reactive groups(-OH),diethyl bis(2-hydroxyethyl)aminomethylphosphonate(FRC-6),and tris(hydroxymethyl)phosphine oxide(THPO)were introduced into the polyurea structure to prepare three intrinsic flame retardant phosphorus containing polyureas.When the addition amount of flame retardant was 6%,the limiting oxygen index(LOI)values of FRC-6,OP550,and THPO flame retardant polyurea increased from 19.8% to about 23.8%,24.3%,and 24.1%,respectively.When the addition amount of flame retardant is 12%,the tensile strength of FRC-6 flame retardant polyurea is 14.2 MPa,and the elongation at break reaches 584%.The LOI value of OP550 flame retardant polyurea reaches about 25.4%,and the maximum smoke density decreases to 52.46%.Due to the catalytic effect of phosphorus containing flame retardant components on dehydration and carbonization of the polyurea material to form a dense carbon layer during thermal decomposition,the residual carbon rate increases from 3.28% to 11.36%,The maximum mass loss rate decreased from 1.20%/°C to 0.77%/°C,effectively reducing the thermal decomposition rate of polyurea and improving its flame retardancy.3.Two intrinsic flame retardant silicon/phosphorus block polyureas were prepared by introducing hydroxypropyl terminated polydimethylsiloxane(HTPDMS)and two reactive phosphorus containing flame retardants(FRC-6and OP550)onto the polyurea molecular chain.When 3% FRC-6 flame retardant and 10% HTPDMS were added,the tensile strength of silicon/phosphorus block type polyurea was 27.6 MPa,the elongation at break reached 539%,the LOI value reached about 23.9%,the time for smoke generation was delayed from 60.1 seconds to 117.0 seconds,and the residual carbon rate increased from 3.28% to 9.65%.When 3% OP550 flame retardant and 10% HTPDMS were added,the LOI value reached about 24.0%,and the maximum smoke density decreased from 76.72% to 51.71%,the residual carbon rate increased from 3.28% to 10.70%,the maximum mass loss rate decreased from 1.20%/°C to 0.85%/°C,and the water contact angle increased from 91.3° to 108°.Due to the silicon oxide silicon network structure in HTPDMS promoting the formation of a carbon layer,the residual carbon rate increases,while reducing the thermal decomposition rate,improving the flame retardancy and thermal stability of polyurea.Moreover,HTPDMS has a lower surface energy,which can improve the hydrophobicity of polyurea and increase the water contact angle.