Effect Of Extraction And Compression On Hygroscopicity Of Chinese Fir Heartwood

In order to improve the liquid permeability of chinese fir heartwood,such as mechanical properties, the combined method of extraction and compression was used in this study.Warm water and 1% sodium hydroxide were used as different solutions for extraction.Extracted chinese fir heartwood was adjusted to three differet moisture content that air-drying state,and water saturated state.Then it was radial compressed by diferent compression ratio(air-drying state(10%,20%),water saturated state (40%,50%)) and the same compression rate of 1 mm·min^-1.The effect of diferent extraction, moisture content,copmression ratio and compression rate to the liquid permeability of chinese fir heartwood was discussed.The hydroscopicity and permeability of treated fir were tested and analyzed referring to relevant standards.The swelling rate and fractal dimension of internal wood surfaces(Dfs) were catulated and compared.At last,the structure of treated fir was characterized by the X-ray Diffraction(XRD) and Scanning Electron Microscope(SEM).The following results were obtained:①The hydroscopicity speed of extracted or conpressed heartwood of chinese fir in initial period was high.But their final water absorption was smaller than that of untreated heartwood.Because of the recovery of deformation during water absoption,the initial water absorption of drying-compressed smaples was biggest.The initial water absorption of drying-compressed and water-saturated compressed after NaOH extacted samples imprved to a great extent.But the mechanism of combined compression and extraction is complicated.②The equilibrium moisture content of hot water or NaOH extracted without conpressed heartwood of chinese fir increased.And the effect of NaOH extraction was more obviously.The equilibrium moisture content of compressed samples improved.The influence of water-saturated compresstion was more significant.The fractal dimension of internal wood surfaces(D_fs) of water-saturated compressed samples was almost invariant or slightly increased.③The crystalline region of extracted and conpressed heartwood of chinese fir was almost invariant.The non-crystalline region of hot extracted samples had no change,but that of other treated wood changed differently.In the aspect of microstructure,there was no crack on pit membrane of hot water extracted samples,but there were different extent of cracks on pit membrane of other treated samples.And the position and size of cracks were different.