Study On The Effect Of Vacuum-Freeze Dried On The Permeability Of Bamboo

Environmental protection and innovation have become the theme of the 21 st century.Bamboo,as the second largest resource of biomaterials,has set a great potential and space for promoting green economy and developing green industry.Now,it is gradually promoting the advancement of "bamboo instead of wood" with its high quality natural and renewable nature.Nowadays,China is developing in the direction of beautiful country and the rejuvenation of rural areas.To promote the efficient use of bamboo and producing areas,performance protection and modification have become the most important technical link for bamboo processing and utilization.All involve as anti-mold,anti-corrosion,flame retardant and dyeing depend on the permeability of bamboo.In this paper,bamboo was used as a test material to study its permeation under vacuum freeze-drying method,and the changes of permeability were characterized from macroscopic and microscopic structures,pore characteristics.Then,the mechanism of bamboo's permeability after vacuum freeze-drying was revealed.This paper mainly research on the permeability of bamboo from three aspects:Firstly,the vacuum-drying process of bamboo was studied.Based on the analysis of the effects about freezing rate,freezing temperature and moisture content on the mechanical strength and water uptake of bamboo,the best technology of vacuum freeze-drying bamboo was obtained.Secondly,the correlation between pore structure and permeability of bamboo was analyzed by observing the microstructure and pore characteristics of the bamboo material after vacuum freeze-drying.Finally,the distribution and permeation curves of the dye liquor in the interior of the bamboo material were observed with a bulk microscope,SEM-EDS and optical microscope to quantitatively characterize and study the promoting effect of vacuum freeze-dried bamboo material permeability.We can draw the following conclusions through research:(1)The best process of vacuum freeze-drying to improve the permeability of bamboo:Pre-freezing rate of 1.2?/min,moisture content ranged from 85%to 115%and freezing temperature was-45?.(2)Observations of scanning electron microscopy showed that vacuum freeze-drying method did not affect the overall morphology of the bamboo,the main changes of bamboo were concentrated in the vascular bundle region,where the upper wall of the vessel appeared cracks,some collapsed on the wall of the vessel,and the pore size increased.The analysis of pore characteristics by mercury porosimetry showed that the specific surface area,mesopore diameter,and porosity of bamboo after vacuum freeze-drying treatment were significantly improved.The total pore area increased by 27.6%(from 73.6 cm~2/g to 93.9 cm~2/g),the pore size reached 101.5 nm,and the porosity increased to 73.48%(Raw bamboo:48.54%).(3)The observation of the dyed bamboo by stereoscopic microscope and optical microscope showed that the signs of the inner dyeing liquid in the bamboo material extending from the tube wall toward the parenchyma and the fibrous tissue were obvious.It can be preliminarily judged that the direction of fluid infiltration in bamboo is pipe,parenchyma and fiber in order,and the permeability of parenchyma is better than that of fibrous tissue.By local observation of the toluidine blue penetration in parenchyma,it was found that the flow of the dye solution between the parenchyma cells first flows into the intercellular layer,and then flows into the cell cavity through the cell wall.It can be inferred that the intercellular layer has a larger pore size than the thin layer,and pores appear on the walls.(4)The results of the SEM-EDS show that there is a significant difference in the permeability between the various components of the bamboo material,namely the catheter,fibers,and parenchyma.The difference in Cu distribution between the treated wood and the untreated wood was 54.5%and 854%,respectively,at the two time periods.Bamboo after vacuum freeze-drying,Cu element increased about 7.5%per unit time inner it.The promotion of the effect of vacuum freeze-drying on the permeability of bamboo was characterized by the correlation between the surface scan distribution of Cu element and the distribution of the original elemental surface distribution of bamboo,and no significant effect on the original structural components of the original bamboo was found.