Study On High Solids And Slow Reacting Polyurea Finishing Agent

Polyurea（PUA）is a new solvent-free,non-polluting and environmentally-friendly polymer material developed to comply with environmental requirements in recent years.It is prepared by reacting isocyanate component（A）with amino component（R）.Due to the high activity of the A and R components,the polyurea coating cures rapidly and the viscosity of the mixed liquid increases rapidly.It’s necessary to use professional spraying equipment,but sometimes the equipment is inconvenient because of the influence of space or environment in some construction occasions（such as narrow tunnel seepage control,etc.）.Simultaneously,due to insufficient wetting time between the polyurea and the substrate,the coating may crack or fall off.Therefore,the problem of adjusting the curing speed of polyurea has attracted widespread attention from researchers of domestic and foreign.The latent curing agent is prepared by blocking the amino group with a blocking agent,and can be deblocked under certain conditions.So far,there are few studies on slowing down the curing rate of polyurea by using latent curing agent and secondary amine at internal and abroad and the curing kinetics of latent curing agents and isocyanate components have rarely been reported.This paper uses ketone or aldehyde to block amino groups to prepare several latent curing agents,and discusses the curing reaction kinetics,which provides an academic reference for the reaction mechanism of slow reaction polyurea.Finally,the latent curing agent and secondary amine compound act as R component.Investigate the effect of the latent curing agent content on the reaction rate and coating properties.The conclusions are as follows:1)The oxazolidines were prepared by blocking 2-（ethylethano）ethanol or2-anilinoethanol with isobutyraldehyde;The ketimines were prepared by blocking ethylenediamine（EDA）,4,4’-diamino dicyclohexyl methane（PACM）and terminal amino polyether（D2000）with 4-methyl-2-pentanone,respectively.Finally,the factors affecting the amine conversion rate were investigated,and the synthesis conditions with higher conversion rate were obtained.2)The reaction kinetics of the latent curing agent curing polyurea was studied by DSC.It was calculated that Ea was 95.763 kJ·mol^-1,A was 3.4×10¹11 s^-1,n was 1.08 and dα/dt=3.4×10¹¹exp（-11.52/T）（1-α）^1.08,when oxazolidine was used as curing agent.When ketimine was used as curing agent,Ea=57.68 kJ·mol^-1,A=2.6×10⁶ s^-1,n=0.90 and dα/dt=2.6×10⁶exp（-6.94/T）（1-α）^0.90;Both system reaction stages are close to 1,which can be considered as an apparent first order reaction.The latent curing mechanism was inferred and confirmed that the deblocking reaction of the latent curing agent at a certain temperature is the control step of the curing process,and the deblocking reaction rate is mainly related to the LCA concentration.3)The performance test results of the oxazolidine-cured polyurea coating showed that when the content of the R component was 80%,the gel time at room temperature was 10 h,which satisfied the construction requirements of manual brushing at room temperature.The adhesion of the coating is grade 1,the flexibility is 1 mm,the impact resistance is 50 kg·cm,the hardness is 0.78,and the corrosion resistance is intact.4)The performance test results of the oxazolidine-cured polyurea coating showed,the reaction rate of ketimine to prepare polyurea is obviously slowed down,gel time is prolonged,and the curing temperature also affects the gel time of the reaction.The comprehensive performance of the coating is related to the molecular structure of the amine after deblocking.As the ketimine content increases,the gel time gradually prolongs,and the adhesion to the substrate also improves.And,the inert substance generated after the decomposition of the ketimine remains in the coating to promote plasticization.The effect of reducing the hardness and tensile strength of the coating.The comprehensive performance of PUA8,PUA13 and PUA15 prepared was superior（Table 1）.In summary,the reaction rate of the oxazolidine and ketimine-cured polyurea is controllable.On the basis of retaining the excellent performance of the coating,it not only meets the long time required for manual brushing,but also meets the construction requirements of high temperature and rapid curing in industrial production lines.The application of polyurea is no longer limited to professional spraying equipment,and provides data support for the application of latent curing agent in the polyurea field.