Journal of the Korean Wood Science and Technology

The Korean Society of Wood Science & Technology (한국목재공학회)
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Performance of Hybrid Adhesives of Blocked-pMDI/Melamine-Urea-Formaldehyde Resins for the Surface Lamination on Plywood

  • Received : 2019.01.17
  • Accepted : 2019.03.04
  • Published : 2019.03.25
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Abstract

To improve the water resistance of melamine-urea-formaldehyde (MUF) resins, different levels of blocked polymeric 4,4 diphenyl methane diisocyanate (B-pMDI) were blended with MUF resins to prepare B-pMDI/MUF hybrid adhesives, and their adhesion performances were evaluated for the surface lamination of fancy veneer on plywood. FT-IR spectra showed that the de-blocked -NCO groups reacted with the -OH of hydroxymethyl groups of the MUF resins to form urethane bonds at 2% B-pMDI/MUF, which was detected before and after their hydrolysis. The mass loss after the hydrolysis consistently decreased as the B-pMDI level increased, indicating an improvement in the water resistance. As the B-pMDI level increased, the activation energy of hybrid adhesives decreased, which improved the reactivity of the hybrid adhesives. Additionally, the water resistance improvement of the hybrid adhesives increased the tensile shear strength of the surface laminated plywood in semi-water proof and water-proof by 23 % and 8 %, respectively, at 2% B-pMDI level. This was likely due to the urethane linkages in the hybrid adhesives. However, the formaldehyde emission from plywood panels bonded with the hybrid adhesives increased in the dry state, indicating incomplete curing of the hybrid adhesives.

Keywords

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Fig. 1. ATR-FTIR spectra of B-pMDI (a), and cured B-pMDI/MUF adhesives with different contents of B-pMDI (b).

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Fig. 2. Typical ATR-FTIR spectra of B-pMDI/MUF resins at different levels of B-pMDI after hydrolysis (a), and their mass loss (b).

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Fig. 3. DSC thermograms of B-pMDI/MUF resins at different contents of B-pMDI and different heating rates: neat MUF resins (a), 1% B-pMDI/MUF adhesives (b), 2% B-pMDI/MUF adhesives (c), typical DSC thermograms of B-pMDI/MUF adhesives at 10°C/min (d).

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Fig. 4. Kissinger plot and Ea values of B-pMDI/MUF resins as a function of B-pMDI level.

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Fig. 5. TSS and formaldehyde emission (FE) of surface laminate plywood bonded with B-pMDI/MUF resins as a function level of B-pMDI: Dry TSS (a), semi water proof TSS (b), water proof TSS (c), and FE values (d).

Table 1. Basic properties of B-pMDI/MUF hybrid adhesives as a function of B-pMDI content

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