The Effect of Sequential Ammonia and Methyl Formate Injection on the Strength Development of Phenol-Formaldehyde Bonds to Wood
Keywords:ABES, chemical injection, phenol-formaldehyde
AbstractIt has been reported in a companion paper that gaseous anhydrous ammonia may readily penetrate compressed wood fiber mats and that subsequent cell-wall softening is very rapid. Literature also shows that alkaline catalyzed phenol-formaldehyde (PF) resins of the resole type are stable at pH levels above nine. Methyl formate has, however, been shown to accelerate the rate of PF cross-linking, and its volatility (sea level boiling temperature 33°C) makes it well suited to vapor phase injection into resinated mats at near ambient temperatures. It was hypothesized at the outset of the reported investigation that mats may be treated with gaseous ammonia to affect softening without stimulation of resin cure, and that the PF could be subsequently catalyzed with methyl formate in the vapor phase. Before adopting this strategy in a sealed pressing system, the strength development characteristics of miniature PF-to-wood bonds exposed first to ammonia and then to methyl formate were explored. Bond formation and testing were conducted with an Automated Bonding Evaluation System (ABES) equipped with a computer-controlled fluid injection accessory. Results, in the form of room-temperature strength development plots, show that ammonia does not greatly stimulate PF cure (1.65 MPa after 600 s), but application of methyl formate significantly hastens strength development (3.5 MPa after 150 s). These results are aiding in the development of techniques for the rapid room-temperature formation of strong and dimensionally stable fiber composites using sealed pressing with sequential chemical injection.
Bariska, M., C. Skaar, and R. W. Davidson. 1969. Studies of the wood-anhydrous ammonia system. Wood Science2(2):65-72.nChowdhury, M. J. A. 1999. Sealed consolidation of natural fiber composites with chemical reactant injection and removal. Ph.D. thesis, Department of Wood Science and Engineering, Oregon State University, Corvallis, ORnChowdhury, M. J. A., and P. E. Humphrey. 1999. The effect of acetylation on the shear strength development kinetics of phenolic resin to wood bonds. Wood Fiber Sci.31(3):293-299.nChowdhury, M. J. A., and P. E. Humphrey. 2005. A sealed pressing system and its use to explore the ammonia plasticization of natural fiber mats. Wood Fiber Sci.37(1):42-50.nDavidson, R. W. 1968. Plasticizing wood with anhydrous ammonia. Brochure prepared by New York State University, College of Forestry at Syracuse University, Syracuse, NY.nDavidson, R. W., and W. G. Baumgardt. 1970. Plasticizing wood with ammonia—a progress report. Forest Prod. J.20(3): 19-25.nHumphrey, P. E. 1993. A device to test adhesive bonds. US patent number 5, 176,028. US Patent Office. Washington, DC. (and related patents).nHumphrey, P. E. 1999. The bonding speed of adhesives: An automated evaluation system. Pages 139-146 in Wolcott et al., eds. Proc. 33rd. International Particleboard and Composite Materials Symp. Washington State University, Pullman, WA.nLemon, P. H. R. B. 1990. An improved sand binder for sealed castings. Int. J. Mater. Prod. Tech.51:25-54.nPizzi, A., 1983. Wood adhesives: Chemistry and technology. Marcel Dekker, Inc., New York, NY.nPizzi, A., and A. Stephanou. 1994a. Phenol-formaldehyde wood adhesives under very alkaline conditions. Part I: Behaviour and proposed mechanism. Holzforschung48: 35-40.nPizzi, A., and A. Stephanou. 1994b. Phenol-formaldehyde wood adhesives under very alkaline conditions. Part II: Esters curing acceleration, its mechanism and applied results. Holzforschung48:150-156.nSkeist, I. 1977. Handbook of adhesives. 3rd. ed. Van Nostrand Reinhold, New York, NY.n
The copyright of an article published in Wood and Fiber Science is transferred to the Society of Wood Science and Technology (for U. S. Government employees: to the extent transferable), effective if and when the article is accepted for publication. This transfer grants the Society of Wood Science and Technology permission to republish all or any part of the article in any form, e.g., reprints for sale, microfiche, proceedings, etc. However, the authors reserve the following as set forth in the Copyright Law:
1. All proprietary rights other than copyright, such as patent rights.
2. The right to grant or refuse permission to third parties to republish all or part of the article or translations thereof. In the case of whole articles, such third parties must obtain Society of Wood Science and Technology written permission as well. However, the Society may grant rights with respect to Journal issues as a whole.
3. The right to use all or part of this article in future works of their own, such as lectures, press releases, reviews, text books, or reprint books.