Study On Optimization Of Synthesis Process And Thermal Degradation Mechanism Of Compound Film Of Methyl Etherified Melamine Resin

Methyl etherified melamine resin,due to its excellent cross-linking properties,is in great demand in the market.This project aimed to produce methyl etherified melamine resin using a two-step process,the first step is the methylolation process of melamine,and the second step is the methyl etherification process of methylol melamine.However,there is a certain gap between the processing and preparation methods of methyl etherified melamine resin and the advanced level abroad,so in the first step of production of methyl etherified melamine resin,there are some problems,such as excessive water content of the product after centrifugation,which needs large amount of energy for drying.In the second step of production,precisely,in the post-treatment of the resulting resin product,the water and organic solvents in the reaction system can be removed well by vacuum distillation at high temperature and high vacuum.But at high temperature and high vacuum conditions,there is excessive resin in the waste liquid,when the solid content of the product resin is not very high,the viscosity of the product resin increases obviously and there is a certain amount of free formaldehyde in the product.Above-mentioned problems have affected the quality of products and reduced the production revenue to a certain extent.This project is a sub-project under the cooperation project between the laboratory and Chongqing Jianfeng Haokang Chemical Co.,Ltd,focusing on the above mentioned problems encountered by the enterprise in the production of methyl etherified melamine resin and preliminarily exploring the application of methyl etherified melamine resin in the field of waterborne polyurethane.In this thesis,two orthogonal experiments were first used to screen and optimize the influencing factors of methylolation reaction of melamine,and the influencing rules of each factor on the hydroxymethylation degree and the water content of hydroxymethylmelamine after centrifugation were obtained.Next,the resin content in the waste liquid and the solid content of the product resin during the etherification process.Finally,the thermoelastic analysis?TG?method was used to study the thermal degradation kinetics of the composite film prepared by cross-linking and curing of waterborne polyurethane and high imino methyl etherified melamine formaldehyde resin,and the thermal degradation mechanism was deduced.?1?In the hydroxymethyl process of melamine,nine factors were screened through a preliminary experiment,the four orthogonal factors of formaldehyde and melamine molar ratio,temperature,pH and formaldehyde concentration were screened out for the next orthogonal experiment.The results of orthogonal experiments show that:the pH value has the greatest influence on the hydroxymethyl content of the product,followed by the concentration of formaldehyde,and the temperature has the least influence on the index;likewise,the value of pH has the greatest influence on the water content of the product after centrifugation,still followed by the formaldehyde concentration,differently,the ratio of raw materials has the least influence on the water content of the product after centrifugation.The degree of methylolation of the product has a maximum value when the molar ratio of formaldehyde to melamine is 9,the temperature is 50?,the pH is 9 and the concentration of formaldehyde is 25%,while the water content of the product after centrifugation has a minimum value at a molar ratio of formaldehyde to melamine of 9,a temperature of 60?,a pH of 9 and a formaldehyde concentration of49%.Considering all aspects,the optimum reaction conditions for the synthesis of hydroxymethyl melamine are as follows.the molar ratio of formaldehyde to melamine was 9,the temperature was 60?,the pH was 9 and the concentration of formaldehyde was 37%.The product obtained under the reaction conditions has a degree of methylolation of 50.13%,the water content of the product after centrifugation is only52.98%,and the water content of the final product reached 8.37%.?2?In the vacuum distillation process of methyl etherification of hydroxymethyl melamine,three levels are set respectively for the temperature T?°C?and the vacuum P?-MPa?,the experimental arrangement was carried out using a comprehensive experimental method,the crude resin content in the waste liquid,the viscosity of the product resin,the solid content of the product resin,and the free formaldehyde content of the product resin were determined in each experiment.Since no free formaldehyde was detected in the product resin,the crude resin content in the waste liquid,the viscosity of the product resin and the solid content of the product resin were analyzed as follows.Firstly,under the various indicators,the effects of temperature T???and vacuum degree P?-MPa?on the indicators were analyzed.Then,the Analysis of Variance was used to test the significance of different indicators,but there were some differences in the optimal factors under different indicators.Therefore,the three methods of Analysis of Variance,Factor Contribution Rate and Duncan's New Multiple Range Test were used to select the optimal level.The results show that the crude resin content in the waste liquid should be given priority,when screening the optimal level,and then the the viscosity of the product resin should be considered,and finally the solid content of the product resin should be considered.Therefore,the optimal horizontal combination is A₁B₂,that is,the temperature T=70?,and the vacuum degree P=-0.09 MPa,under these conditions,the crude resin content in waste water is 0.071%,the viscosity of the product resin is 1768 mPa·s,the solid content of the product resin is 91.06%,and the free formaldehyde content in the product resin is 0.?3?The degradation kinetics equations of the thermal degradation curve peaks of the cured film were calculated by TG and DTG curves at different heating rates,and the apparent activation energies and the stages of thermal degradation reaction of the respective thermal degradation peaks were determined.It was found that the thermal degradation process of the cured film was mainly controlled by nucleation and growth mechanisms.