Some anatomical and physical aspects of wood-plastic (pMMA) combination of spruce

Test-pieces of spruce ( Picea abies (L.) Karst.) were vacuum-impregnated with commercial grade methylmethacrylate which was then polymerized by the application of heat. The position of the polymer (pMMA) was identified fight microscopically and with the aid of the scanning electron microscope; in the latter work macerated material was also used. In general, the lumina of longitudinal tracheids and raytracheids and of the pit cavities were well filled with the plastic; parenchymatous cells were only rarely filled. Although the polymer may be in contact with (attached to) the cell walls, there are no signs of a close interaction of cell wall and polymer. By means of interference microscopy a varying, but low-averaged, value of volume percentage of polymer in the cell wall was determined. Swelling tests have been carried out on sections of untreated material and of wood impregnated in the oven-dry state and at 14% moisture content. Results of these tests indicate that pMMA does not influence, especially reduce, the hydrophyllic nature of the cell wall substantially. The considerable reduction of swelling in radial and tangential direction of solid wood-plastic test pieces must be ascribed to mechanical hindrance by the polymer, in which the presence of non-aspirated bordered pit pairs must play a very important role. Additional data are presented for Scots pine.