Modification of urea-formaldehyde resin adhesives with blocked isocyanates using sodium bisulfite

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• 作者：Muhammad Adly Rahandi Lubis^a ; Byung-Dae Park^a ; ^{byungdae@knu.ac.kr} ; Sang-Min Lee^b
• 关键词：Urea-formaldehyde resin ; Blocked isocyanate ; Sodium bisulfite ; Hybrid resin ; Plywood
• 刊名：International Journal of Adhesion and Adhesives
• 出版年：2017
• 出版时间：March 2017
• 年：2017
• 卷：73
• 期：Complete
• 页码：118-124
• 全文大小：840 K
• 卷排序：73

文摘

Polymeric 4-4 diphenyl methane diisocyanate (pMDI) was blocked with an aqueous sodium bisulfite solution to obtain water-dispersible blocked pMDI (B-pMDI) resin with different HSO3/–NCO mole ratios for the modification of urea-formaldehyde (UF) resin. Fourier transform infrared (FTIR) spectra of the B-pMDI resin clearly showed that all isocyanate groups of the pMDI resin were successfully blocked by sodium bisulfite. As the HSO3/–NCO mole ratio increased, the de-blocking temperature of the B-pMDI resin also increased. Two addition levels (1% and 3%) of the B-pMDI resin with different HSO3/–NCO mole ratios were mixed with UF resins and used as an adhesive for plywood. The gel time of the UF/B-pMDI resins decreased to a minimum at a mole ratio of 0.9 and then increased with the HSO3/–NCO mole ratio, and was consistent with the peak temperature (Tp). However, as the HSO3/–NCO mole ratio increased, the viscosity of the modified UF resins by 1% B-pMDI resin addition slightly increased, whereas those of modified resins with 3% B-pMDI resin addition rapidly increased. The adhesion strengths of plywood bonded with the hybrid resins were greater for 1% B-pMDI resin addition than for 3% B-pMDI resin addition. Formaldehyde emission of plywood bonded with the UF/B-pMDI resins significantly decreased up to 34% by the addition of B-pMDI resin at a mole ratio of 1.8. These results suggest that the modification of UF resins by mixing with water-dispersible B-pMDI resin can be a method for improving the water resistance and formaldehyde emission of UF resins for wood-based composites.