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Competitive Polycondensation of Model Compound MUF Resin System by 13C NMR

  • Corresponding author: Zhigang Wu, e-mail addresses:wzhiang9@163.com ;  Taohong Li, e-mail addresses:lith.cool@163.com
  • Received Date: 2019-09-11
    Accepted Date: 2019-11-02
    Fund Project:

    This work was supported by National Natural Science Foundation of China (No. 31800481 and No. 31870546), Education De-partment Foundation of Guizhou Province of China (NO.[2019]184), Science-technology Support Foundation of Guizhou Prov-ince of China (No.[2019]2308 and[2019]2325), and Forestry Department Foundation of Guizhou Province of China (No.[2017]14 and[2018]13).

  • Melamine-urea-formaldehyde (MUF) resin is an excellent adhesive in the field of wood adhesives, however the com-petition mechanism is questionable which affects the structure control and performance optimization of the resin. In this sduty, the competitive resin synthesis polycondensation reaction of MUF system under alkaline condition was studied based on the model compound 1,3-dihydroxymethyl urea (UF2) and melamine (M) system, and the competitive reaction mechanism in the system was deduced by 13C NMR quantitative analysis. The results show that the energy barrier of hydroxymethylation of melamine is lower than that of urea, and the priority of hydroxymethylation is lower; the addition of melamine results in a large amount of hydrolysis of UF2, and the formed free formaldehyde, resulting in hydroxymethylation of melamine; there is obvious polycondensation reaction in UF2+M system, mainly from the relationship between Hydroxymethylurea and melamine or hydroxymethylmelamine. The type I bridge bond structure of polycondensation mainly comes from the reaction of UF2 and M, which is difficult to form the type II bridge bond. At low molar ratio, the formation of bridge bond is superior to that of ether bond. With the increase of molar ratio, the formation of ether bond shows advantages, but there is obvious competition between them. There may be competitive presence of the UF self-condensation products, melamine-formaldehyde (MF) self-condensation products and MUF co-condensed products after the polycondensation reaction.
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    Li, T.H., Guo, X.S., Liang, J.K., Wang, H., Xie, X.G., Du, G.B., 2015. Competitive formation of the methylene and methylene ether bridges in the urea-formaldehyde reaction in alkaline solution:a combined experimental and theoretical study. Wood Sci. Technol. 49, 475-493.
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Competitive Polycondensation of Model Compound MUF Resin System by 13C NMR

    Corresponding author: Zhigang Wu, e-mail addresses:wzhiang9@163.com
    Corresponding author: Taohong Li, e-mail addresses:lith.cool@163.com
  • a Kaili University, Qiandongnan 556011, China;
  • b College of Forestry, Guizhou University, Guiyang 550025, China;
  • c Yunnan Provincial Key Laboratory of Wood Adhesives and Glued Products, Southwest Forestry University, Kunming 650224, China
Fund Project:  This work was supported by National Natural Science Foundation of China (No. 31800481 and No. 31870546), Education De-partment Foundation of Guizhou Province of China (NO.[2019]184), Science-technology Support Foundation of Guizhou Prov-ince of China (No.[2019]2308 and[2019]2325), and Forestry Department Foundation of Guizhou Province of China (No.[2017]14 and[2018]13).

Abstract: Melamine-urea-formaldehyde (MUF) resin is an excellent adhesive in the field of wood adhesives, however the com-petition mechanism is questionable which affects the structure control and performance optimization of the resin. In this sduty, the competitive resin synthesis polycondensation reaction of MUF system under alkaline condition was studied based on the model compound 1,3-dihydroxymethyl urea (UF2) and melamine (M) system, and the competitive reaction mechanism in the system was deduced by 13C NMR quantitative analysis. The results show that the energy barrier of hydroxymethylation of melamine is lower than that of urea, and the priority of hydroxymethylation is lower; the addition of melamine results in a large amount of hydrolysis of UF2, and the formed free formaldehyde, resulting in hydroxymethylation of melamine; there is obvious polycondensation reaction in UF2+M system, mainly from the relationship between Hydroxymethylurea and melamine or hydroxymethylmelamine. The type I bridge bond structure of polycondensation mainly comes from the reaction of UF2 and M, which is difficult to form the type II bridge bond. At low molar ratio, the formation of bridge bond is superior to that of ether bond. With the increase of molar ratio, the formation of ether bond shows advantages, but there is obvious competition between them. There may be competitive presence of the UF self-condensation products, melamine-formaldehyde (MF) self-condensation products and MUF co-condensed products after the polycondensation reaction.

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