Fabrication Of Nuclear Track Membrane And Its Application In Tea Filtration

Drinking tea is closely related to human health.How to drink tea healthily and scientifically has gradually aroused people's concern.There are three main causes of residue in tea soup.During processing and transportation,some contaminants are brought in,such as hair,mud and coal ash.During the tea processing,broken tea slag and tea stalk hair are introduced into.Incrustation in drinking water is also an important factor affecting the quality of tea soup.For the removal of residue in tea soup,common methods for brewing tea are stainless steel strainer filtration and tea washing.The former has low filtration accuracy,and the latter results in component loss of tea.The solutions in tea drinks are the centrifugal clarification and microfiltration process,both of which are not enough for clarification and need further processing.The ultrafiltration process obviously leads to the loss of tea flavor and soup color.Therefore,it is very necessary to explore new technologies that are more suitable filtration accuracy to solve this problem.Nuclear track membrane?NTM?is a type of polymer membrane with uniform pore size,thin membrane thickness,and high flux.It has many important applications.For example,the use of the NTM in precision infusion can reduce some infusion diseases caused by foreign substances entering the blood vessels.The NTM also can be a means of cell detection in medicine and biology to diagnosis many types of diseases.There are two major steps in the preparation of the NTM,namely the irradiation and etching of polymer membranes.In this study,a series of NTMs were prepared using NaOH solution and polyethylene terephthalate?PET?film irradiated by Kr ion(⁸⁶Kr²⁶⁺,25 MeV·u^-1)beam in the laboratory.The indicators of the NTM,such as pore density,pore size,porosity,can be strictly controlled so that the NTM has a good retention characteristic.In addition,other features of the PET-NTM are consistent with the requirements of tea filtration,such as no shedding,no adsorbing.Therefore,these NTMs were used as filtration membrane for the following tea filtration experiments.In this study,a spiral plate tester with NTMs differing from pore size served as a main filter to separate jasmine tea.It was found by the turbidity and colority analysis that the colority of tea soup was rarely affected by the NTM of pore size lager than4?m.It was calculated by the particle size analysis that the total particulate matter in the tea soup reduced by 1/5 after filtration through the 40-?m NTM,and reduced by2/3 after the 15-?m NTM,reaching basic filtration requirement and meticulous filtration requirement,respectively.Scanning electron microscopy analysis showed that the tea stem-hairs in the tea soup were trapped in the filtration and the NTM was slowly plugged.The transmembrane flow rate decay curve during the NTM filtration process revealed important features that the initial flow rate was large,and the flow rate decayed quickly.In response to that,the influence of the initial flow rate on transmembrane flux was explored.It was concluded that the flux of the membrane could be increased if the initial flow rate was controlled.That operation strategy could improve the economy of the NTM and guide the industrial production.In addition,durability tests and verification of cleaning methods were carried out with the 15-?m NTM whose flux is large.The results showed this membrane could be used for about2 weeks and cleaned to restore to more than 80%of the original performance after severe clogging.In parallel with the filtration experiment,the design and development of the NTM filter was carried out.NTM tea filter was made by the ultrasonic welding method,and it applied the 40-?m NTM,which had the features such as high filtration accuracy,large flow and easy cleaning.Stainless steel inner and outer filter cartridges were designed to meet the gravity filtration requirement of large area NTM.Pressure filtration device could achieve high precision and large flux filtration requirement.These designs provided experimental data and design references for product development.