Effect of freezing and freezing-thawing pretreatment on wood properties and drying characteristics of Eucalyptus urophylla x E. grandis

Eucalyptus wood has uneven density and poor permeability, which can lead to defects such as wrinkling and cracking during the drying process, limiting applications. Freezing and freeze-thaw treatments can improve wood permeability by disrupting its microstructure, thus enhancing drying quality. In this experiment, Eucalyptus urophylla x E. grandis was subjected to cold trap freezing (CF), refrigerator freezing (RF), cold trap freeze-thaw (CFT), and refrigerator freeze-thaw (RFT) pretreatments. The pretreated materials were then dried and tested to investigate properties such as permeability, moisture absorption, shrinkage, and drying characteristics. The results indicated that the moisture content (MC) during pre-freezing, with lower freezing temperatures leading to greater reductions in MC. The water absorption rates for the CF, RF, CFT, and RFT pretreated wood increased by 16%, 7%, 16%, and 14%, respectively, showing significant improvement in permeability, which in turn resulted in increased drying rates of 24%, 11%, 26%, and 13%, respectively, when the MC exceeded the fiber saturation point (FSP). The shrinkage ratios were reduced by 8%, 2%, 4%, and 8%, respectively, but increased the equilibrium moisture content (EMC) by 5% for all groups. Overall, the improvement in drying rate from freeze-thaw treatment was greater than that from freezing treatment.