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℃, 150℃ and 180℃, 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.

Study on machining properties and surface coating properties of heat treated densified poplar wood

In this study, a modification combining densification and heat treatment of poplar wood (Populus tomentosa Carr.) was carried out, and the machining properties of the unmodified poplar wood (control) and the heat treated densified wood (HTD) were tested and evaluated. In addition, the water-based UV paint was covered on the control and HTD respectively, and the surface coating properties of them were evaluated. The results showed that: (1) The machining properties of poplar wood were improved after the heat treatmentdensification modification. The score of comprehensive machining properties of the HTD was 45 (excellent grade), while the score of the control was 36 (good grade). (2) The abrasion resistance, hydrophobicity and adhesion were improved after heat treatment-densification modification. Therefore, the modification combining densification and heat treatment played a significant role in enhancing the value of wood.

Relationship between cell lumen area and lignin content of alkaline-treated densified timber of Paraserianthes falcataria

In this study, low-density plantation timber, Paraserianthes falcataria was pretreated with 3%, 6% and 9% NaOH before densification process. Alkaline pretreatment leads to lignin reductions and cell wall structure becomes more porous. Densification was done by crushing the cell wall with hot-press machine, resulting in reduction of thickness to about 60%. Scanning electron microscopy images were captured and processed through ImageJ software. As to support the data, lignin content determination was conducted according to TAPPI T222 and the correlation coefficient between cell lumen areas and lignin content were studied statistically.

Some mechanical properties of densified and laminated Lombardy poplar (Populus nigra L.)

In this study, it was studied the effects of densification and then lamination processes on some mechanical properties of Lombardy poplar (Populus nigra L.), which is one of the low density tree species. Densification temperatures were 80, 100, 120 and 140ºC and ratios of densification were 15, 30 and 50 %. Furthermore, lamellas with a thickness of 4 mm cut from densified materials were laminated by bonding one on top of the other with urea formaldehyde (UF) and polyvinyl acetate (PVAc) adhesives. Bending, modulus of elasticity, compression and tensile tests were applied by preparing specimens from the pieces. According to test results, the most suitable temperature level was 120°C. As the ratio of densification was increased at this temperature level, increase were observed in the mechanical properties. Also, lamination provided significant increases in the mechanical values compared to laminated but undensified Lombardy poplar. Increases were observed in the mechanical properties reaching 444 % with application of densification and lamination processes.

Densification and heat treatment of maritime pine wood

Pine (Pinus pinaster Ait.) wood samples were subjected to a combined treatment by densification and heat treatment. Samples were densified before and after heat treatment. The heat treatment was made inside an oven at 190ºC during 2 to 6 h and wood densification was made in a hot press at around 48 bar pressure and temperatures between 160ºC and 200ºC for 30 min. Compression-set, compression-set recovery after three cycles of water soaking followed by oven drying, density, hardness, bending strength and stiffness and durability against subterranean termites were determined after the treatment. Results show that densification increases density, hardness, bending strength, stiffness and durability against termites. Heat treatment applied after the densification is more effective in reducing compression-set recovery than if applied before.

Effects of poplar f ibres as solid bridge on the physical characteristics of biomass briquette made from sawdust and bamboo powder

At room temperature, on condition that the die be within temperatures of 200 – 300°C biomass briquette production made from sawdust (S) and bamboo powder (B) was conducted by a briquette extruder using post-heating method, fibre with steam explosion poplar fibres used as additive. As observed through the microscope, fibres as additive has the micro-mechanism of promoting mechanical properties of biomass briquette during densification. For verifying the feasibility and effect of fibre as additive, BBD experimental design was macroscopically adopted to compare the indicators of surface quality, relaxation density, maximum radial compression pressure, and hydrophobicity. Response surface model was used to deduce the reasonable heating temperature range for exploring the suitable condition of fibre as additive. The result showed that fibre as additive has apparent effect on briquette densification of sawdust and bamboo powder within a given temperature range. Through microscopic observation, it was found that fibres acted as solid bridges which played a positive role in densification in the heating temperature of 200∼250°C. At the temperature of 240°C, the fibres started to be carbonized. And within the temperature range of 250-300°C, the carbonized fibre mainly acts as lubricant between the briquette and the channel surface of the die.

Effect of the temperature and pressure on properties of densified medium density fiberboards

The objective of this work was to evaluate the physical and mechanical properties of thermally compressed MDF (medium density fiberboard). For this purpose, MDF boards were subjected a combination of two temperatures (150°C and 170°C) and two pressures (25% and 50% of the perpendicular compression strength). After the treatment the following properties were assessed: bending strength and stiffness, compressive parallel strength, surface hardness, thickness swelling and water absorption after 2, 24 and 72 hours of immersion in water. It was found that in general, the results did not show any significant improvements regarding physical properties. However, mechanical properties were positively affected by treatments and densified boards had higher values than untreated boards, reaching a fourfold value in the case of the surface hardness. Regarding physical properties, there were no improvements compared to the untreated board for the thickness swelling, despite all treatments have showed lower water absorption. In general, temperature was the most important factor for physical properties and the pressure was the most important factor for mechanical properties.