Microwave vacuum drying of small round logs of plantation-grown species for the production of handicrafts

Sawing and conversion of round logs to lumber and planks results in huge waste in the form of sawdust, offcuts, etc. One feasible solution to avoid waste is to use low-girth plantation logs without sawing for the making of various products. The main obstacle in adopting this strategy is the occurrence of severe drying defects. In this study, microwave vacuum drying was used to explore the feasibility of low-girth log drying. Three Populus deltoides (poplar) logs with girths of 0.46 m, 0.64 m, and 0.75 m and two Eucalyptus hybrid logs (girths of 0.55 m and 0.6 m) were taken for microwave vacuum drying. Log temperature and pressure levels were monitored. Results suggest that poplar logs with initial moisture content 73.4–125% could be dried defect-free within 30–43 h of drying, whereas eucalyptus logs (initial moisture content 45%) could be dried in 24–40.83 h of drying. Moisture content drop per hour in poplar ranged from 1.5%/h (0.75 m girth) to 3.74%/h (0.46 m girth), whereas that of Eucalyptus was 0.7%/h (0.60 m girth) and 0.86%/h (0.55 m girth). The mean electrical energy consumption to evaporate water from poplar logs was 0.183 kg/unit, whereas that of Eucalyptus was 0.111 kg/unit. Internal cracks were the main defects found in poplar logs, whereas surface checks dominated in Eucalyptus logs. The low-girth plantation timber logs were successfully dried using a microwave vacuum dryer for the production of decorative handicrafts.