Study On Synthesis, Structures And Performances Of MUF Co-condensation Resin

The effect of different synthetic process on the MUF co-condensation resin performance wasstudied, and based on the best synthetic process, to investigate in detail the structure formation,molecular distribution of MUF resin. With the help of modern apparatus, the curing and thermalproperties of MUF resin were studied, which provide powerful theoretical basis for theapplication of MUF resin.The main content were as follows:（1） The investigation on the synthetic process of MUF co-condensation resin。There was aclose relationship between different synthetic process and MUF resin properties, so the effect ofthree synthetic processes of MUF resin on the MUF resin performance, which was mainlystudied. The resin was separately named MUF1, MUF2, MUF3by synthetic process. The resinperformance evaluation mainly included basic performance, the structure distribution of MUFresin and the curing performance.（2） Study on the structure formation and distribution of MUF co-condensation resin. On thebase of best synthetic route, the structure formation and component distribution of MUFco-condensation resin were tracked with the help of FT-IR and MALDI-TOF MS, moreover, theformation mechanism of MUF co-condensation resin was also further analyzed by reaction ofmodel compound.（3） The characterization of MUF co-condensation resin curing performance. Curing was anvery important process for application of thermoset resin, and the curing characteristics of MUFco-condensation resin were studied by DSC, DMA. The structure and group change of MUFco-condensation resin during curing process were studied using FT-IR, and the curing mechanismwas analyzed.（4） Heat-resistant quality was another important index for appreciating MUFco-condensation resin performance. Use TG to investigate heat-resistant quality of MUF resin,and the effect of curing agent, storage time, sample state on that was mainly studied.（5） At last, the bonding strength and durability performance of MUF co-condensation resinwere studied by glulam preparation in laboratory. And the durability performance was evaluatedby comparing bonding strength after treated by different condition.The main results were as follows:（1） With the same F:（U+M） mola ratio, it was remarkable that effect of synthetic process onMUF co-condensation resin performance. The basic property results showed that syntheticprocess focally impacted the formaldehyde-free content and storage time of MUF co-condensation resin, and the minimum content was0.15%, the highest content was0.54%.Simultaneously, the storage time was different changed from one week to one month due tochange of formaldehyde-free content. The FT-IR,¹³C-NMR,1H-NMR characteristics results ofMUF1, MUF2, MUF3revealed that three resins included same group category, but its ratio wasdifferent, especially, the hydroxy-methyl group（-CH₂OH）, methylene bridge（-CH₂-）, methyleneether link（-CH₂-O-CH₂-）. Furthermore, DMA results showed that the maximum modulus ofMUF resin was different under the curing agent condition. Many performance showed thatsynthetic process of MUF3resin was best.（2） On the bases of synthetic process of MUF3resin, samples were taken in differentreaction time during synthetic process, the characteristic results of samples revealed thatformation of MUF resin included three key types of reaction, that was hydroxy-methyl reaction,resinification, co-condensation reaction, in fact, there was no obvious boundary for three reactiontypes. The co-condensation reaction not only existed in hydroxy-methyl reaction phase but inresinification phase, in other words, there was always co-condensation reaction of melamine andurea though the whole reaction. Especially, seconde melamine addition had an important role inthe resin structure formation and its performance. Reaction phenomena revealed that reactionspeed of melamine and basic resin was very fast, because solution could change clear in veryshort time. MALDI-TOF MS analysis of sample also confirmed that melamine mainly takenhydroxy-methyl reaction, as the extension of reaction time, abundance rise of high molecularmeaned that condensation reaction taken place. According to distribution of molecular weight, itcould be deduced that formation of methylene bridges between melamine and urea wasdominant.Using model compound reaction, seconde melamine action on matrix resin was furtheranalyzed, the results showed that melamine had an strong cohesion effect on hydroxy-methylcompounds, especially methylolurea, and had important effects on the resin molecular weightincrease. Moreover, condensation reaction between hydroxy-methyl of hydroxy-methylcompounds and residual active hydrogen was major condensation reaction type.（3） Curing characteristic of MUF co-condensation resin was characterized by DSC, resultsrevealed that test method, curing agent had different degree impact on the curing process of MUFco-condensation resin. Among them, under open testing condition, curing of MUF resin took intwo areas, lower temperature area（40¹000C） and higher temperature area（100²000C）. Butunder the close testing condition, curing mainly took place in higher temperaturearea（100²000C）, which was similar to the dried sample curing process. By linear fitting of peaktemperature at different heating rate, it was found that testing method did not affect peaktemperature of MUF resin curing（about1000C）. Curing agent could effectively reduced initialcuring temperature, and accelerated curing reaction. By FT-IR analyzing groups change of resinin different curing condition, it was found that curing agent did not change resin curingmechanism, but could effectively promote condensation reaction of active groups, especially consume the hydroxy-methyl group. DMA results showed when curing agent（NH4Cl） contentwas0.5¹%, the glue-line performance could achieve excellent.（4） TG thermal analysis results showed that under nitrogen protection, char residue rate ofliquid sample without curing agent was higher than solid sample’s char residue rate, but did notaffect resin thermal decomposition temperature and maximum decomposing rate. After adding1%curing agent, liquid thermal decomposition of the sample was divided into three regions, andthe decomposition of the solid sample mainly happened in a large area. Either liquid or solidsamples,1%curing agent addition, char residue rate of the resin could be effectively improved.Different storage time did not affect thermal decomposition properties of MUF resin, butslightly affect char residue rate of MUF resin. Under air condition, burned for7min at8000C, thechar residue rate of MUF resin was between6⁹%, so the decomposition degree and processwere different from the nitrogen atmosphere.（5） The results of glulam performance showed that MUF co-condensation resin had strongbonding strength and durability, which can satisfy the standards of timber performance.