Studies on pre-treatment by compression for wood drying II: effects of compression ratio, compression direction and compression speed on the recovery rate and mechanical properties of wood

As a follow-up report, the pre-treatment by compression for wood drying was systematically studied in terms of effects of compression ratio, compression direction and compression speed on the recovery rate (RR) and mechanical properties. The results showed: the RR decreased 0.18 and 0.20 % every 1 % compression ratio when the compression ratio was lower than or equal to 50 and 40 % for Poplar and Chinese fir, respectively, over this compression ratio, the RR decreased rapidly; the RR had the maximum value in tangential compression for Poplar, while had the minimum value in 45° compression for Chinese fir; the RR of specimens compressed at 3, 5 and 10 mm/min were bigger than those in 0.5 and 1 mm/min for Poplar. For Chinese fir, the RR difference among all the compression speed was quite small compared with that for Poplar. The RR at all conditions was no less than 73.3 and 79.7 % for Poplar and Chinese fir, respectively; The mechanical properties difference was not significant between the specimen compressed in different compression ratio, while was significant between the specimens compressed in different direction and different speed except the modulus of rupture (MOR) of Poplar between different compression direction. For Chinese fir, MOR and modulus of elasticity (MOE) in 45° compression specimen showed the maximum value. The mechanical properties at all conditions retained at least 83.1 and 88.1 % of MOR, 84.9 and 83.7 % of MOE for Poplar and Chinese fir, respectively. After all, the pre-treatment by compression for wood drying is viable in terms of RR and mechanical properties at all compression ratio, compression direction and compression speed we tested.