Study On The Copolycondensation Of Furfuryl Alcohol,Phenol And Resorcinol With Urea-formaldehyde

The urea-formaldehyde resin in the modern wood-based panel industry has been affected by its fatal defects and has affected its wider application.The use of polyphenols for modification is a hot topic.However,there are still doubts about the structures and mechanism of copolycondensation,affecting the ultimate Structure and performance regulation.In this paper,the copolycondensation structure and reaction mechanism of furfuryl alcohol,phenol,resorcinol and urea-formaldehyde resin were studied in detail by ESI-MS and 13CNMR.At the same time,the competition relationship in the polycondensation reaction was systematically described and relevant.Relevant conclusions have been drawn.The main results and conclusions are as follows:(1)In alkaline system of UF,as the reaction time prolongs,a large number of methylene bridges are formed,and some of the ether bonds are converted into bridges,which are acidic.The resin formation observed under the conditions is similar.It shows that resinization under alkaline conditions is feasible.There is a large amount of competing reactions during the synthesis of urea-formaldehyde resins.The distribution of these products is determined by their thermodynamic properties.The pH level affects the rate of various reactions and changes the end-point(non-equilibrium state)of various chemicals.The relative content of the structure does not affect the chemical balance of the reaction.(2)Under alkaline conditions,furfuryl alcohol and formaldehyde in the sterol-formaldehyde system hardly react,but there is a large amount of self-condensation structure of formaldehyde.Under acidic conditions,the furfuryl alcohol and formaldehyde in the sterol-formaldehyde system undergo hydroxymethylation,while furfuryl alcohol undergo a certain degree of self-condensation reaction.(3)Mapping of ESI-MS and 13CNMR revealed that the furfuryl alcohol and urea hardly reacted under acidic conditions and no cocondensed structure could be fomed.The corresponding copolycondensation structures at the chemical shifts of 38-39 ppm and 42-43 ppm in the 13CNMR spectra mainly originate from the polycondensation reaction of methylol urea carbon cations and sterol 5-carbon,and the corresponding structure of 38-39 ppm is a linear structure.The corresponding structure of 42-44ppm is a branched structure.(4)In the alkaline system,there are two routes for the polycondensation reaction of urea and formaldehyde.One is the elimination of methylol urea under basic conditions through E1CB to form a conjugated methylene urea structural intermediate,and the methylol urea is Hydroxy is used as a nucleophile to attack the intermediates;one is that methylol urea forms an oxygen anion under alkaline conditions and is attacked by the hydroxyl group of the nucleophile methylol urea.The former is more advantageous than the latter in terms of dynamics.(5)Furfuryl alcohol are protonated preferentially to the alpha carbon of the furan ring under less acidic conditions,it is difficult to form sterol carbocations,and the degree of self-condensation reaction is also very low.The preferential hydroxymethylation of urea is beneficial to the polycondensation reaction in the sterol-urea-formaldehyde system.The contents of various polycondensation structures are increased to varying degrees,and the formation of co-condensation structures is facilitated with the decrease of pH value.(6)In the phenol-formaldehyde-urea copolycondensation system,the self-condensation reaction between methylol urea and hydroxymethyl phenol is the main monomer in alkaline conditions,and the degree of copolycondensation is very limited;under weak acid conditions The main self-condensation reaction between methylol urea monomers,methylol phenol self-condensation structure is very small,did not occur co-condensation reaction.Under strong acid conditions,the copolycondensation reaction between phenol-urea-formaldehyde and the respective self-condensation reaction form a clear competition relationship.(7)Under strong acidic conditions,the activity of carbocation intermediates produced by hydroxymethyl resorcinol is higher than that of resorcinol phenolic ring carbon,which makes the self-condensation reaction of RF more efficient.It is advantageous that,at pH=1,co-polycondensation structures are formed,but they do not occupy a major position.Under weakly acidic conditions(pH=3-4),the copolycondensation structure is obviously superior to the self-condensation structure.With the increase of pH,there is a cocondensation structure formed at pH=5,but it does not occupy a major position.Under alkaline conditions,the self-condensation between the RF monomers is predominant,and the co-polycondensation reaction can occur,but the degree is very limited.The formation of copolycondensation structure mainly depends on the degree of difficulty in the formation of different reactive intermediates and their relative activities in the self-condensation and copolycondensation reactions.Among them,the concentration of hydroxymethyl urea carbon cations is likely to be a key factor in determining the degree of copolycondensation reaction.