Micro-analysis Of Wood Under Different Percentage Of Moisture

Based on the relationship between wood mechanical properties and moisture content,this paper through the analysis of the microscopic changes in the mechanical properties of wood under different water content conditions,and the purpose of exploring the existence and mode of moisture in the amorphous cellulose region.First of all,the static tensile relaxation test of wood with different moisture content was carried out to explore the effect of moisture on wood relaxation properties,crystallinity and micro fibril angle.After that,selective removal of chemical constituents from wood,under the premise of ensuring less damage to cellulose,the optimum process is obtained.Finally,micro mechanics test of treated wood and through comparative analysis,demonstration that the absorption form of water molecules and the influence mechanism of water molecule adsorption on mechanical properties of wood.The main conclusions are summarized as follows:1.As the water content increases,the amorphous region of the wood expands due to the entry of water molecules and the arrangement of the microstructures becomes loose,and the macroscopic manifestation is that the crystallinity is reduced and stress relaxation is more likely to occur.When the water content is between 6% and 8%,the adsorption of water molecules will fill in pores produced by drying.When water swells the cell wall,the unstable hydrogen bonds in the cell wall break and reconnect,and the fibrils will undergo some degree of orientation.Desorption test piece did not show this phenomenon because it did not undergo a drying process.Stress relaxation increases the crystallinity of wood.2.After removing the lignin from Pinus sylvestris,take the processed material into a 6% NaOH boiling water bath was used for 4 hours,this is the best way to extract cellulose fiber.The results showed that the cell structure and tissue did not change,but there was shrinkage and fibril exposure.The hygroscopic was significantly improved,showing the characteristics of the type II adsorption isotherm.3.With the increase of moisture content,the tensile elongation at break of untreated wood increases,the tensile strength decreases,and the stress-strain curve appears plastic deformation.When the water content was less than 8%,the treated sample showed elastic deformation and rupture,and when the water content was more than 8%,the treated sample exhibited a certain degree of plasticity.4.When the water content of the extracted cellulose sample is between 6% and 8%,its mechanical properties significantly change.The elastic modulus increases significantly.The mechanism is due to the attachment of water molecules,and the original twisted cellulose molecular chains in the amorphous region are stretched and rearranged.That is,the micro voids in the early drying process are filled with water molecules,which makes the fiber arrangement more ordered,the elastic modulus increases drastically,and the ability to resist external damage increases.5.Computer simulations confirm this conclusion and show that with the increase of moisture content,the volume of amorphous region increases.But the amorphous cell volume decreases when the water content is 5% But the amorphous cell volume decreases when the water content is 5%,and the molecular chain of cellulose is more dense.