Microwave Drying of Scots Pine Lumber: Structure Changes, Its Effect on Liquid Permeability

Abstract

Microwave (MW) drying method was adopted to enhance the liquid permeability of Scots pine lumber. Structure changes were characterized by stereoscope microscope, scanned electron microscope (SEM) and transmission electron microscope (TEM) examination. Pore parameters before and after MW treatment were detected by mercury intrusion porosimetry (MIP) method, and the effect of structure changes on liquid permeability were analyzed. As stereoscope microscope, SEM and TEM examination results shown, macro and micro checks mainly developed at intercellcular of tracheids, intercellular of ray parenchyma and tracheid, while these checks extend main along the radial-longitudinal plane. Pit border destruction, aspirated pits’ orus translocation and micro-checks in tracheid cell wall were also observed. MIP test shown that pore volume and pore area increased as macro and micro checks generated to form new cavities. Microstructure changes would increase the quantity of pores or enlarge the pore diameter. Liquid flow pathways increased as macro and micro checks generated, aspirated pits reopened to form new pathways; liquid flow efficiency improved as porosity, pore volume and pore diameter increase which facilitate the liquid flow.