Effects of pressing temperature and compression ratio on density distribution and hardness of surface densified poplar wood

Process parameters play an important role in wood surface densification. In this study, the poplar (Populus tomentosa Carr.) wood was heated on one side at 100 & DEG;C, 150 & DEG;C and 180 & DEG;C, and compressed in the radial direction with the speed of 10 mm/min. The initial thickness of the wood samples were 30 mm, 26 mm and 23 mm, and they were all compressed to 20 mm and resulting in three different compression ratios: 33.3%, 23.1% and 13.0%. When the surface densification completed, the density distribution and hardness of the densified and un-treated samples were measured and analyzed. Results show that the compressing temperature mainly decided the formation of the density distribution curve and the peak density increased with the increasing temperature; as the compression ratio increased, the peak density increased and the thickness of the densified zone broadened; the surface hardness was highly correlated with the density distribution which was affected by temperature and compression ratio, and as the peak density increased and the thickness of the densified broadened the hardness increased accordingly. Therefore, by optimizing the process parameters such as the compressing temperature and compression ratio could generate a targeted density distribution which has the desired hardness.