Plasticizing Wood with Ammonia–A Progress Report

The present state-of-the art for plasticizing wood with ammonia is described. The practicality of plasticizing with gaseous ammonia at room temperature is emphasized. Forming experiments with different species of solid wood, fiberboard, and particleboard show potential applications. Cutting experiments suggest new machining possibilities as well as the potential for whole new production systems. The essential features of a gaseous ammonia treating plant are presented, and the need for development work is discussed. Experience has led to the following qualitative observations: 1) Experiments using hard maple, white ash, yellow birch, red oak, black walnut, American beech, black cherry, basswood, Douglas-fir, southern yellow pine, red lauan, and teak indicate that, indeed, all wood is plasticized when exposed to ammonia and consequently can be formed at least to some extent. 2) Species that are known to be good bending woods using the steam process appear to be those most successfully formed using ammonia. 3) Species that are currently unsuited for steam bending operations can be formed to some extent using ammonia. 4) When proper forming techniques are employed (i.e., careful selection of bending stock and use of straps and end pressure) it appears that the ammonia process will lead to reduced breakage rates or conversely the ammonia process may permit the use of some what lower grade material in the bending stock. 5) Plasticizing with ammonia should permit forming with the use of less force than is required in a steam operation. 6) Because ammonia appears to enhance the rate of stress relaxation due to bending, the time the bent material needs to remain on the form will probably be reduced. For example, 3/4 inch thick maple bent to an 8-inch radius can be removed from the form after 1-1/2 hours without springback. It may be possible that an entirely new manufacturing system could be designed around the concept of doing most of the mechanical processing of the wood while it is in a plasticized state. Such a system might very well start with logs, cants, or flitches and end up with either finished or, semi-finished moulded components for structures, decorative items or combinations of the two.

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