Process modification involving strong-acid step in urea-formaldehyde resin preparation
Keywords:UF resin, Plywood, Alkaline – Acid Process, Strong Acid Step
Urea-formaldehyde (UF) resin adhesive for wood-based panel industries are commonly manufactured using conventional alkaline-acid process. This paper reports a process modification of a conventional UF resin preparation by incorporating a strong-acid step, involving simultaneous methylolation and condensation reactions at very low pH at the beginning of the processing step. The experiment showed that this additional step should be carried out at short duration and at high enough temperature in order to avoid gelation or separation problems. In order to control temperature rise caused by the exothermic nature of the reactions, the modified process requires a higher initial formaldehyde-to-urea (F/U) molar ratio compared to the original. For the same reason, the first urea should be fed incrementally to ensure high F/U ratio at any time during the strong acid step. Using regular formalin concentration as raw material at the same F/U molar ratio, the modified resin showed lower free formaldehyde content thus have lower reactivity in comparison to those of the original. However, when the same procedure was applied using higher formaldehyde concentration at higher solid content, the produced resin showed comparable free formaldehyde content and shorter gelation time. Application test for making plywood showed that the modified process gave a very significant improvement in both the internal bonding strength and formaldehyde emission.
Akinyemi, B.A., Olamide, O., Oluwasogo, D. 2019. Formaldehyde-free particleboards from wood chip wastes using glutaraldehyde modified cassava starch as binder, Case Studies in Construction Materials 11, DOI: 10.1016/j.cscm.2019.e00236.
Carvalho, L.H., Magalhaes, F.D., Ferra, J. 2012. Formaldehyde emissions from wood-based panels - testing methods and industrial perspectives in Formaldehyde: Chemistry, Applications, and Role in Polymerization, Cheng, C.B. & Lin, F.H. (eds), Nova Science Publishers, Inc., New York.
Conner, A.H. 1996. Urea-formaldehyde adhesive resins, Polymeric Materials Encyclopedia 11, 8496-8501, CRC Press Inc, Boca Raton.
Costa, N.A., Pereira, J., Ferra, J. Cruz, P., Martins, J., Magalhaes, F.D., Mendes, A. & Carvalho, L.H. 2013. Sodium metabisulphite as a scavenger of air pollutants for wood-based building materials, International Wood Products Journal, 4 (4), 242-247, DOI: 10.1179/2042645313Y.0000000037.
De Rooij, A. H. 1963. Process for absorbing formaldehyde from a formaldehyde-containing gas, US Patent No. 3,151,960.
Dorieh, A., Mahmoodi, M.O., Mamaghani, M., Pizzi, A. & Zeydi, M. M. 2018. Effect of different acids during
the synthesis of urea-formaldehyde adhesives and the mechanical properties of medium-density fiberboards bonded with them, Journal of Applied Polymer Science, DOI: 10.1002/app.47256.
Dorieh, A., Mahmoodi, M.O., Mamaghani, M., Pizzi, A., Zeydi, M. M. & Moslemi, A. 2019. New insight into the use of latent catalysts for the synthesis of urea-formaldehyde adhesives and the mechanical properties of medium density fiberboards bonded with them, European Polymer Journal 112, 195-205, DOI: 10.1016/j.eurpolymj.2019.01.002.
Duan, H., Qiu, T., Guo, L., Ye, J. & Li, X. 2015. The microcapsule-type formaldehyde scavenger: the preparation and the application in urea-formaldehyde adhesives. Journal of Hazardous Material 293, 46-53, DOI: 10.1016/j.jhazmat.2015.03.037.
Dunky, M. 1996. Urea-formaldehyde adhesive resins, Polymeric Materials Encyclopedia 11, 8502-8510, CRC Press Inc, Boca Raton.
Dunky, M. 1998. Urea-formaldehyde (UF) adhesive resins of wood, International Journal of Adhesion and Adhesives 18, 95-107, DOI: 10.1016/S0143-7496(97)00054-7.
Edoga, M. O. 2006. Comparative study of synthesis procedures for urea-formaldehyde resins (part I), Leonardo Electronic Journal of Practices and Technologies 9, 63-80.
Ferra, J.M.M., Henriques, A., Mendes, A.M., Costa, M.R.N., Carvalho, L.H. & Magalhaes, F.D. 2012. Comparison of urea-formaldehyde synthesis by alkaline-acid and strongly acid processes, Journal of Applied Polymer Science, DOI: 10.1002/app.34642.
Gadhave, R.V., Srivastava, S., Mahanwar, P.A. & Gadekar, P.T. 2019. Lignin: Renewable Raw Material for Adhesive, Open Journal of Polymer Chemistry, 9, 27-38, DOI: 10.4236/ojpchem.2019.92003.
Gao, W., Du, G. & Kamdem, D.P. 2015. Influence of ammonium pentaborate (APB) on the performance of urea-formaldehyde (UF) adhesives for plywood, The Journal of Adhesion, 91 (3), 186–196, DOI: 10.1080/ 00218464.2013.874294.
Ghani, A., Bawon, P., Ashaari, Z., Wahab, M.W., Hua, L.S. 2017. Addition of propylamine as formaldehyde scavenger for urea formaldehyde-bonded particleboard, Wood Research, 62 (2), 329-334.
Giovanni, S., Mazzoleni, G., Nistri, U. & Vargiu S, 1974. Process for the preparation of resins from urea, formaldehyde, methanol and formic acid using three stages, US Patent No. 3,830,783.
Hse, C.Y., Xia, Z.Y. & Tomita, B. 1994. Effects of reaction pH on properties and performance of urea-formaldehyde resins, Holzforschung 48, 527-532.
Hatjiissaak, A. & Papadopoulou, E. 2007. Aminoplast resin of high performance for lignocellulosic materials, WO Patent Appl. No. 2007138364 A1.
Liu, M., Wang, Y., Wu, Y., He, Z., Wan, H. 2018. “Greener” adhesives composed of urea-formaldehyde resin and cottonseed meal for wood-based composites, Journal of Cleaner Production, 187, 361-371.
Nocanda, X.W. 1998. A synthetic and spectrometric study of the initial phases in urea-formaldehyde resin formation,” MS thesis, Rhodes University.
Norström, E., Demircan, D., Khabbaz, F., Fogelström, L. & Malmström, E. 2018. Green Binders for Wood Adhesives, in Applied Adhesive Bonding in Science and Technology, Ozer H. (ed), DOI: 10.5772/intechopen. 68926.
Nuryawan, A. Byung-Dae Park & Singh, A.P. 2014. Penetration of urea-formaldehyde resins with different formaldehyde/urea mole ratios into softwood tissues, Wood Sci. Technol 48, 889–902, DOI: 10.1007/s00226-014-0649-9.
Nuryawan, A., Risnasari, I., Sucipto, T., Iswanto, A.H. & Dewi, R.R. 2017. Urea-formaldehyde resins: production, application, and testing, IOP Conf. Series: Materials Science and Engineering, DOI: 10.1088/1757-899X/223/1/012053.
Pizzi, A. 2016. Wood products and green chemistry. Annals of Forest Science 73, 185-203.
Que, Z., Furuno, T., Katoha, S. & Nishino, Y. 2007. Effects of urea-formaldehyde resin mole ratio on the properties of particleboard, Building and Environment 42, DOI: 10.1016/j.buildenv. 2005.11.028.
Sun, W., Tajvidi, M., Hunt, C.G., McIntyre, G. & Gardner, D.J. 2019. Fully Bio-Based Hybrid Composites Made of Wood, Fungal Mycelium and Cellulose Nanofibrils, Scientific Reports 9(1):3766, DOI: 10.1038/s41598-019-40442-8.
Thoemen, H., Irle, M. & Sernek, M. 2010. Wood-Based Panels – An Introduction for Specialists, Brunel University Press, London, ISBN: 978-1-902316-82-6.
Valyova, M., Ivanova, Y. & Koynov, D. 2017. Investigation of free formaldehyde quantity in the production of plywood with modified urea-formaldehyde resin, Wood, Design & Technology, 6 (1), 72-77.
Wang, H., Cao, M., Li, T., Yang, L., Duan, Z., Zhou, Z. & Du, G. 2018. Characterization of the low molar ratio urea-formaldehyde resin with 13C NMR and ESI–MS: negative effects of the post-added urea on the urea-formaldehyde polymers, Polymers 10, 602, DOI:10.3390/polym10060602.
Williams, J. H. 1983. Hydrolytically stable urea-formaldehyde resins and process for manufacturing them, US Patent No. 4,410,685.
Williams, J. H. 1984. Low emitting aqueous formulations of aminoplast resins and processes for manufacturing them, US Patent No. 4,482,699.
Wu, Z., Lei, H., Du, G., Cao, M., Xi, X. & Liang, J. 2016. Urea-formaldehyde resin prepared with concentrated formaldehyde, Journal of Adhesion Science and Technology, DOI: 10.1080/01694243.2016.1193963.
Wu, Z., Xi, X., Yu, L. & Su, L. 2018. An eco-friendly urea-formaldehyde resin: preparation, structure and properties, Wood research 63 (1), 45-56
Xi, X., Wu, Z., Pizzi, A., Gerardin, C., Lei, H. & Du, G. 2018. Furfuryl alcohol-aldehyde plywood adhesive resins, The Journal of Adhesion, DOI: 10.1080/00218464.2018.1519435.
Zhang, J., Song, F., Tao, J., Zhang, Z., & Shi, 2018. Research progress on formaldehyde emission of wood-based panel, International Journal of Polymer Science, DOI: 10.1155/2018/9349721.
Zhong, R., Gu, J., Gao, Z., Tu, D. & Hu, C. 2017. Impacts of urea-formaldehyde resin residue on recycling and reconstitution of wood-based panels, International Journal of Adhesion and Adhesives 78, DOI: 10.1016/j.ijadhadh.2017.06.019.