Development of the thermo-fluid method for flattening sweet-bamboo culms (Dendrocalamus asper Backer.) without cracking

Six Black-Sweet-Bamboo culms were randomly collected from Prachinburi Province. Each culm was approximately 3-4 years old. The culms were crosscut at every two-meter intervals along the culm starting from the level at 0.30-0.50 meter from ground for a total of seven locations. The third to the sixth crosscut portions were selected for experiment due to their uniform culm thickness. The internode and node portions of two pieces each were then removed from a crosscut portion which were subsequently split by half into two pieces. A total of 180 specimens of 3 to 4 milimeters thick and 230 milimeters long were obtained from the part without bark and inner skin of each split piece. The specimens were placed in a water-boiling vat for 14 to 18 hours, and then dipped in heated drying oil for 35 to 45 seconds. The specimens were flattened while heated in the drying-oil vat, and then stabilized by pressing in a hot press. The obtained specimens were finally tested at air-dried condition according to the produces in ISO standards. The data gathered were analyzed by the Statistic Analysis System (SAS) program based on the analysis of variance concepts. The results indicated that bamboo culms were flattenable without cracking by boiling in water for 18 hours and dipping in heated drying oil (Linseed oil or Tung oil) for 45 seconds. The specimens were flattened in the drying-oil vat and immediately stabilized by pressing in a hot press maintained at temperature of 210 deg C and pressure of 0.375 kg/square mm for 5 minutes. It was finally dried in an oven at temperature of 103 +- 2 deg C for 24 hours. Results from mechanical-properties tests of flattened bamboos from internode were higher than those from node, and that the flattened bamboss dipping in Linseed oil were better than those in Tung oil. From physical-properties tests of flattened bamboss, moisture content of 4.64-6.39 percent and specific gravity of 0.77-0.96 were obtained. It was concluded that the developed method could be employed in flattening bamboo culms without cracking. The obtained flattened bamboos had low equilibrium moisture content (5.62 percent), high specific gravity (0.88), and had mechanical properties in compression, tension, shear parallel to grain as well as static bending higher than the natural Sweet-Bamboo culms and all other wood species. These new products have great potential for application in industry.