Synthesis And Pyrolysis Kinetics Of Etherified Melamine-Formaldehyde Resin With Low Free Formaldehyde

Nowadays,etherified melamine-formaldehyde resin is widely used in many fields,such as preparation of coatings,flame retardant materials,etc.However,formaldehyde,one of the raw materials for resin production,is a well-known"three-cause"substance,that is,long-term exposure to a certain amount of formaldehyde is easy to cause cancer,gene mutation,deformity.Therefore,reducing the content of free formaldehyde in resin is the research focus of many scholars.In addition,the application of etherified melamine-formaldehyde resin mostly needs to be heated and cured.Therefore,while working to reduce the free formaldehyde content of etherified melamine-formaldehyde resin,it is very important to study the synthesis process and pyrolysis characteristics of the resin.In this paper,a new two-step synthesis process was selected to prepare melamine-formaldehyde resin with low free formaldehyde.The optimum synthesis conditions were determined by orthogonal test,single factor test and repeated two-factor test.The main components of the product in the reaction phase were determined by LC-MS and the functional groups of each reaction phase were analyzed by FT-IR.Finally,the pyrolysis kinetics of the resin was studied,and the kinetic parameters and mechanism functions of the main pyrolysis stages were determined,and the pyrolysis characteristics of the resin were compared with 325 resin from Allnex company,USA.The findings are as follows:1.The optimum conditions of hydroxymethylation were as follows:The molar ratio of melamine to formaldehyde is 1:3.3,the reaction temperature and time are 60?and 30 min respectively,and the reaction p H is 10.Under the optimum conditions,the content of free formaldehyde,bound formaldehyde,moisture and yield of hydroxymethyl melamine are 0.22%,0.424,6.21%and 63.62%respectively.The optimum conditions of etherification reaction are as follows:The molar ratio of methanol to hydroxymethyl melamine is 6:1,the etherification temperature and p H are50?and 4 respectively,the vacuum time and temperature are 60 min and 70?respectively.The solid content of low free formaldehyde etherified melamine formaldehyde resin is 70.46%and the viscosity is 3060 m Pa.s.Free formaldehyde is only 0.08%,and the interaction of vacuum time,temperature,time and temperature had significant effect on the viscosity and solid content of the resin.2.The content of different hydroxymethyl in the optimized melamine is different,and the content of middle and low hydroxymethyl melamine is the most.Low free formaldehyde etherified melamine formaldehyde resin contains-NH-,-OH,triazine ring,ether bond,ether and other functional groups.And the content of-NH-,-OH is higher than that of 325 resin and 327 resin of Allnex Company.3.The thermal decomposition process of etherified melamine formaldehyde resin with low free formaldehyde can be divided into four stages,the maximum weight loss temperature is 300?380?,and the main pyrolysis stage is 250?400?.The thermal decomposition process of 325 resin can be divided into four stages.The first stage has higher weight loss than the etherified melamine-formaldehyde resin with low free formaldehyde.The maximum weight loss temperature ranges from 380?to 480?,300?500?is the main pyrolysis stage of 325 resin.4.The average activation energy of etherified melamine-formaldehyde resin with low free formaldehyde at the main pyrolysis stage is 229.17k J·mol^-1 by using FWO method,KAS method and more than 30 mechanism functions of C-R method.The mean preexponential factor is 9.71×10²⁰min^-1,The activation energy of the reaction increased with the increase of the conversion of weightlessness.The average activation energy of 325 resin is 257.11k J·mol^-1,and the average preexponential factor is1.71×10¹⁸min^-1.The activation energy decreased at first and then increased with the increase of the conversion of weightlessness.The reaction mechanism functions of both of them accord with P-T equation,that is G(?)=[-ln(1-?)]²,and the reaction mechanism is dendritic nucleation.The thermal stability of 325 resin is better than that of low free formaldehyde etherified melamine formaldehyde resin.The low free formaldehyde etherified melamine formaldehyde resin synthesized by a new two-step method has very low free formaldehyde content and rich functional groups.Low free formaldehyde is good for people's health,the rich functional groups are helpful to the compounding of low free formaldehyde etherified melamine formaldehyde resin with other matrix resins and to improve their application properties.The results of free formaldehyde content and water content of hydroxymethyl melamine are better than those of the former laboratory workers.The pyrolysis characteristics and kinetic parameters of 325 resin and low free Formaldehyde etherified melamine formaldehyde resin were studied,the reaction activation energy and the maximum weight loss temperature of 325 resin were higher than those of low free formaldehyde etherified melamine formaldehyde resin,which showed that the thermal stability of 325resin was better than low free formaldehyde etherified melamine formaldehyde resin.Through the analysis of the experimental results,in the follow-up study,materials such as inhibitor can be added to low-free formaldehyde melamine-formaldehyde resin for compounding,so as to improve the thermal stability of low-free formaldehyde melamine-formaldehyde resin.