Vacuum Drying Process And Characteristic Study Of Round Bamboo Under Electromagnetic Heating

As a new drying technology,electromagnetic heating and vacuum drying technology(EHVD)is widely used in medicine,food and other fields because of the advantages of fast drying,no pollution and continuous uniform heating.Compared with other bamboos,moso bamboo(Phyllostachys heterocycla(Carr.)Mitford cv.Pubescens)is denser and higher in tensile strength and tensile modulus,so moso bamboo has excellent physical and mechanical performance.In addition,moso bamboo has the bibulous low expansion coefficient and low dry shrinkage rate.The traditional drying has the problems of long drying cycle and discontinuous heating.Aiming at the problems,EHVD was applied and properties of round bamboo were studied.The effects of temperature and steam treatment conditions on the drying rate,final moisture content distribution and drying shrinkage of round bamboo were mainly expounded.The cracking phenomenon of round bamboo in the drying process was analyzed to determine the optimal process for rapid drying and avoid drying defects.The color change of moso bamboo was measured.Structural changes were analyzed by infrared spectroscopy and ultraviolet spectroscopy.The pyrolysis behavior change was explained by thermogravimetric analyzer.The mechanical properties were measured by dynamic thermodynamic analyzer.The results provided theoretical and scientific basis for its application in industry.The main conclusions of this study are as follows:(1)EHVD equipment was continuous and rapid when heating.The temperature distribution was uniform and easy to control.The equipment was mature and workable.It can meet actual production.(2)The drying rate increased with temperature changed.Vacuum and steam speeded up the drying rate.Temperature was the main reason for the moisture distribution and the difference in shrinkage rate.(3)When the temperature increased,the lightness L~*of bamboo decreased,the red-green quality index a~*moved from green to red,the yellow-blue quality index b~*moved from blue to yellow,and the overall color differenceΔE~*went larger.The color of the bamboo turned to yellow.(4)Vacuum and steam would lead to the structural change of hemicellulose and lignin,and the steam had a greater influence than vacuum.Structural changes were greatest in the SV40 condition.Changes in lignin structure led to the changes of color.(5)The thermal stability of V40 was higher than V30 and V50 under vacuum treatment.Hot air drying and steam treatment made the pyrolysis reaction of bamboo moved to the low temperature area,and the pyrolysis reaction was easier to occur.The thermal stability of bamboo was improved after steam treatment.(6)Vacuum treatment made the loss peak of bamboo move towards low temperature.At V40,αloss peak corresponded to the lowest temperature,whileβloss peak corresponded to the highest temperature.SV40 was the opposite of V40 under steam conditions.The energy storage modulus of V50 and SV50 changed the most at 150℃.