Sandwich Compression of Wood by Hygro-thermal Control

For more efficient utilization of wood from plantations, Chinese white poplar (Populus tomentosa) was cut from Shandong Province. China. Changes of the position of the compressed layer, distribution of density and changes of hardness, as well as relations between surface density and surface hardness under the hygro-thermal control were studied. By means of controlling surface and inner MC of wood and pre-heating time before compression, the position of the compressed layer can be controlled and the number of compressed layers can be controlled to 1 or 2. The average density ranges from 0.79 g/cm(3) to 0.89 g/cm(3) of the compressed layers and from 0.61 g/cm(3) to 0.65 g/cm(3) in other parts, which shows a large difference with the compressed layers. The increase of density at compressed layers differs according to the position of the compressed layer. When it is at the surface, the density and hardness increased most compared with the controlled samples. showing a 78.1% and 127.6% increase. respectively, and the maximum density reached 1.00 g/cm(3). When the compressed layer is in the center, the density increased 57.1% compared to the controlled sample. The surface hardness increased exponentially with the increase of surface density.