The pit membrane changes of micro-explosion-pretreated poplar

Abstract

A new technique, micro-explosion, was used to pretreat fast-growing poplar wood and improve membrane porosity. Poplar lumber with a thickness of 20 mm was pretreated 10 times at pressures of 0.4, 0.6, 0.8 and 1.0 MPa. Subsequently, the test and control groups were dried in air to equilibrium moisture content. Several slices of 2–3 mm long at depths of 0, 2, 4, 6 and 8 mm were cut from the samples of both the pretreated and control groups for use in the scanning electron microscope. Numerous fine fractures were found at the weak parts of the cells, the pit membranes, following an instantaneous exhaust process which used pressurized air. With the increase in depth, the fractures became fewer and finer. Regardless of the fracture extent, at each level of pressure, the fractures could reach a depth of 8 mm. According to the diversity of fracture extent and location, the fractures could be classified into three main types: radial fracture opening along the pit membrane, ring fracture opening along the pit membrane and crush. The SEM photographs illustrated that the large capillary system of the micro-explosion-treated samples was widened, which could reduce resistance to moisture movement. Thus, micro-explosion treatment could be applied not only in the wood drying industry, but also to wood impregnation, as an effective method for improving impregnation efficiency.