ABSTRACT Urea-formaldehyde (UF) resin is widely used as an adhesive for the manufacture of a range of wood and fiber based products. Although the microstructure of this resin has been examined at high resolution by field-emission scanning electron microscopy and atomic force microscopy, transmission electron microscopy (TEM) has thus far not been used, perhaps because of difficulties in ultrathin sectioning this resin in cured (polymerized) state. In the technical note presented here, a novel sample preparation method is described which enabled us to examine the microstructural morphology of UF resin by transmission electron microscopy in ultrathin sections, revealing the presence of spherical particles within the resin. Our initial attempt to ultrathin section the resin directly was not successful as it was too brittle to trim blocks for sectioning. Then, we developed a sample preparation technique that involved impregnation ofPinus radiatawood tissues with the UF resin, and then embedding of resin impregnated wood tissues with Spurr’s low viscosity embedding medium, which has been widely employed in plant and wood ultrastructure work. The TEM images illustrated and the information on the microstructural morphology of the UF resin presented are based on this novel sample preparation approach.
Cite this paper
P. Singh, A. , Nuryawan, A. and Dae Park, B. (2013) Short Communication—A Novel Sample Preparation Method That Enables Ultrathin Sectioning of Urea-Formaldehyde Resin for Imaging by Transmission Electron Microscopy. Microscopy Research, 1, 1-6. doi: 10.4236/mr.2013.11001.
 B. D. Park and H. W. Jeong, “Influence of Hydrolytic Degradation on the Morphology of Cured Urea-Formal- dehyde Resins of Different Formaldehyde/Urea Mole ratios,” Journal of the Wood Science and Technology, Vol. 39, No. 2, 2011, pp. 179-186.
 A. Pizzi, L. Lipschitz and J. Valenzuela, “Theory and Practice of the Preparation of Low Formaldehyde Emis- sion UF Adhesives,” Holzforschung, Vol. 48, No. 3, 1994, pp. 254-261. doi:10.1515/hfsg.1922.214.171.124
 J. Y. Gu, M. Higuchi, M. Morita and C. Y. Hse, “Syn- thetic Conditions and Chemical Structures of Urea-For- maldehyde Resins II. Synthetic Procedures Involving a Condensation Step under Strongly Acidic Conditions and the Properties of the Resins Obtained,” Mokkuzai Gak- kaishi, Vol. 42, No. 2, 1996, pp. 149-156.
 J. Stuligross and J. A. Koutsky, “A Morphological Study of Urea-Formaldehyde Resins,” Journal of Adhesion, Vol. 18, No. 4, 1985, pp. 281-299.
 A. P. Singh, C. R. Anderson, J. M. Warnes and J. Ma- tsumura, “The Effect of Planing on the Microscopic Structure of Pinus radiata Wood Cells in Relation to Penetration of PVA Glue,” Holz als Roh-und Werkstoff, Vol. 60, 2002, pp. 333-341.
 L. F. Drummy, J. Yang and D. C. Martin, “Low Voltage Electron Microscopy of Polymer and Organic Molecular Thin Films,” Ultramicroscopy, Vol. 99, No. 4, 2004, pp. 247-256. doi:10.1016/j.ultramic.2004.01.011
 K. Yamauchi, S. Akasaka, H. Hasegawa, S. Koizumi, C. Deeprasertkul, P. Laokijcharoen, J. Chamchang and A. Kornduangkaeo, “Structural Study of Natural Rubber Thermoplastic Elastomers and Their Composites with Carbon Black by Small-Angle Neutron Scattering and Transmission Electron Microscopy,” Composites Part A, Vol. 36, No. 4, 2005, pp. 423-429.
 T. Yoshioka, M. Tsuji, Y. Kawahara, S. Kohjiya, N. Ma- nabe and Y. Yokota, “Morphological Study by TEM on Uniaxially Oriented Thin Films of PBT,” Polymer, Vol. 46, No. 14, 2005, pp. 4987-4990.
 L. Sawyer, D. T. Grubb and G. F. Meyers, “Polymer Microscopy,” 3rd Edition, Springer, New York, 2008.
 A. P. Singh, B. Dawson, C. Rickard, J. Bond and A. Singh, “Light, Confocal and Scanning Electron Micros- copy of Wood-Adhesive Interface,” Microscopy and Analysis, Vol. 22, No. 3, 2008, pp. 5-8.
 R. Adhikari and G. H. Michler, “Polymer Nanocom- posites Characterization by Microscopy,” Journal of Macromolecular Science, Part C: Polymer Reviews, Vol. 49, No. 3, 2009, pp. 141-180.
 G. E. Myers, “Hydrolytic Stability of Cured Urea-For- maldehyde Resins,” Wood Science, Vol. 15, No. 2, 1982, pp. 127-138.
 A. R. Spurr, “A Low-Viscosity Epoxy Resin Embedding Medium for Electron Microscopy,” Journal of Ultrastruc- ture Research, Vol. 26, 1969, pp. 31-43.
 E. Suzuki, “High-Resolution Scanning Electron Micros- copy of Immunogold-Labelled Cells by the Use of Thin Plasma Coating of Osmium,” Journal of Microscopy, Vol. 208, No. 3, 2002, pp. 153-157.
 O. Monticelli, Z. Musina, S. Russo and S. Bals, “On the Use of TEM in the Characterization of Nanocomposites,” Materials Letters, Vol. 61, No. 16, 2007, pp. 3446-3450.
 Y. Jiao and P. Akcora, “Assembly of Polymer-Grafted Magnetic Nanoparticles in Polymer Melts,” Macromole- cules, Vol. 45, No. 8, 2012, pp. 3463-3470.
 P. M. Carrasco, L. Tzounis, F. J. Mompean, K. Strati, P. Georgopanos, M. Garcia-Hernandez, M. Stamm, G. Ca- banero, I. Odriozola, A. Avgeropoulos and I. Garcia, “Thermoset Magnetic Materials Based on Poly(ionic li- quid)s Block Copolymers,” Macromolecules, Vol. 46, No. 5, 2013, pp. 1860-1867. doi:10.1021/ma302261c
 S. Coiai, D. Prevosto, M. Bertololo, L. Conzatti, V. Cau- sin, C. Pinzino and E. Passaglia, “Chemistry of Interfacial Interactions in a LDPE-Based Nanocomposite and Their Effect on the Nanoscale Hybrid Assembling,” Macromolecules, Vol. 46, No. 4, 2013, pp. 1563-1572.
 C. Xing, B. Riedl, A. Cloutier and S. M. Shaler, “Charac- terization of Urea-Formaldehyde Resin Penetration into Medium Density Fiberboard Fibers,” Wood Science and Technology, Vol. 39, No. 5, 2005, pp. 374-384.
 A. Despres and A. Pizzi, “Colloidal Aggregation of Aminoplastic Polycondensation Resins: Urea-Formalde- hyde Versus Melamine-Formaldehyde and Melamine- Urea-Formaldehyde Resins,” Journal of Applied Polymer Science, Vol. 100, No. 2, 2006, pp. 1406-1412.
 J. M. M. Ferra, A. M. Mendes, M. R. N. Costa, L. H. Carvalho and F. D. Magalhaes, “A Study on the Colliodal Nature of Urea-Formaldehyde Resins and Its Relation with Adhesive Performance,” Journal of Applied Polymer Science, Vol. 118, No. 4, 2010, pp. 1956-1968.
 B. D. Park and V. Causin, “Crystallinity and Domain Size of Cured Urea-Formaldehyde Resin Adhesives With Different Formaldehyde/Urea Mole Ratios,” European Polymer Journal, Vol. 49, No. 2, 2013, pp. 532-537.