Collapse in Wood . . . Exploratory Experiments in Its Prevention

The occurrence of collapse during drying of many species is a major limiting factor preventing the, adoption of accelerated kiln schedules and rapid unorthodox methods of moisture removal. This paper describes part of a program to investigate the basic cause and nature of collapse, with an ultimate view to preventing its occurrence even when rapidly drying wood. Consideration of the liquid tension collapse theory suggests that lowering the surface tension of the drying liquid in wood will reduce collapse. Experiments in which water in wood was replaced with various organic liquids and then dried, showed that collapse was prevented with certain liquids even under very severe drying conditions. The reduction in collapse was qualitatively consistent with predictions from capillary theory, but other effects were also involved. Tensile compressive type drying stresses were also reduced, and some anti-shrink effect occurred, suggesting modified elastic and plastic behavior of the wood during drying. The implications from this behavior are that in addition to the possibility of influencing the development of collapse during drying, it may eventually be possible to completely modify the normal drying stress pattern, thus leading to substantial reduction of ordinary drying defects.

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