Journal of the Korean Wood Science and Technology

The Korean Society of Wood Science & Technology (한국목재공학회)
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Performance of Urea-Formaldehyde Resins Synthesized at Two Different Low Molar Ratios with Different Numbers of Urea Addition

  • Jeong, Bora (Department of Wood and Paper Sciences, Kyungpook National University) ;
  • Park, Byung-Dae (Department of Wood and Paper Sciences, Kyungpook National University)
  • Received : 2019.02.06
  • Accepted : 2019.03.06
  • Published : 2019.03.25
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Abstract

This study reports the performance of urea-formaldehyde (UF) resins prepared at two different low formaldehyde/urea (F/U) mole ratios with different numbers of urea addition during synthesis. The second or third urea was added during the synthesis of UF resins to obtain two different low molar ratios of 0.7 and 1.0, respectively. The molecular weights, cure kinetics, and adhesion performance of these resins were characterized by the gel permeation chromatography, differential scanning calorimetry, and tensile shear strength of plywood, respectively. When the number of urea additions and F/U molar ratio increased, the gelation time decreased, whereas the viscosity and molecular weight increased. Further, the UF resins prepared with the second urea and 1.0 molar ratio resulted in greater activation energy than those with third urea and 0.7 molar ratio. Tensile shear strength and formaldehyde emission (FE) of the plywood that bonded with these resins increased when the number of urea additions and molar ratio increased. These results suggest that the UF resins prepared with 0.7 molar ratio and third urea addition provide lower adhesion performance and FE than those resins with 1.0 mole ratio and the second urea addition.

Keywords

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Fig. 1. GPC chromatograms of UF resins prepared at different numbers of urea addition and F/U mole ratios.

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Fig. 2. Peak areas per the total peak area of UF resins synthesized at different numbers of urea addition and F/U mole ratios. Four bars per each group at the retention time are corresponding to the Peak 4, 3, 2, and 1 as shown in Fig. 1.

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Fig. 3. Mn, Mw, and PDI of UF resins at different numbers of urea addition and F/U mole ratios.

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Fig. 4. Changes of Ea values of UF resins at different numbers of urea addition and F/U mole ratios.

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Fig. 5. Change in Eα values of UF resins as a function of α with different numbers of urea addition and F/U mole ratios.

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Fig. 6. Tensile shear strength of plywood bonded with UF resins synthesized with different numbers of urea addition and F/U mole ratios.

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Fig. 7. Formaldehyde emission of plywood bonded with UF resins prepared with at different addition of urea.

Table 1. Properties of UF resins synthesized at different numbers of urea addition and F/U mole ratios

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