Study On Tribocharging Characteristics And Electrostatic Separation Of Waste Plastic Particles

With the increasingly consumption of plastic products,waste plastics keep growing in numbers.However,ninety percent of waste plastics could be recycled.Therefore,the research on recycling waste plastics is of great significance and extremely urgent.Triboelectric separation is a dry separation method based on the difference of electrical properties in material surfaces.Triboelectric separation and recovery process is superior to other approaches because the original properties of the material can be retained easily.Besides,it consume less energy than other methods and it can avoid secondary pollution,making it a suitable way for recovering waste plastics.In this paper,four kinds of simulated plastics and three kinds of actual waste plastics were employed to study the mechanism of fluidization tribocharging,the characteristics of fluidization tribocharging with different feed composition.Finally,the separation effect of plastics were studied.The charging characteristics of four simulated plastics and three actual plastics were studied by fluidization tribocharging method.And the tribocharging series of the simulated plastics was obtained as follows:?+?PE,PP,PET,PVC?-?;the actual plastic tribocharging series was:?+?PP,PET,PVC?-?.The research on the fluidization tribocharging rate of five different simulated plastic mixtures revealed that the fluidization tribocharge rate order was PE-PVC>PP-PVC>PE-PET>PP-PET>PET-PVC.Meanwhile,the order of saturation charge-mass-ratio of five mixtures is consistent with that of fluidization charging rate.XPS was employed to investigate the changes in surface elements of PE,PP and PET before and after tribocharging with PVC.The results show that during the tribocharging process,the Cl element which could be found on the PVC surface only,was transferred to the other three plastic surfaces,indicating that the fluidization tribocharging is,indeed,accompanied by material transfer.Subsequently,the PVC particles charged negatively were added to H⁺and Cu²⁺solutions respectively.The pH and current value in the H⁺solution showed an increasing trand,and the Cu elements were detected on the surface of PVC in Cu²⁺solution.These experimental results indicated that the charged PVC particles could increases the amount of electrons in the solution where the reduction reaction took place,and the electrons originally came from the transferred and accumulated surface electrons of plastic surface during fluidization tribocharging process.The electronegativity of side chain functional groups in the chemical structure of plastics determines the charging characteristics in tribocharging process.The greater the electronegativity of the group,the easier it would be to obtain electrons on the plastic surface,thus the more electronegative it tends to be in tribocharging process.In respect of tribocharging occurred among different plastics,the difference of electronegativity of side chain groups determines the charging rate and the saturated charge-to-mass ratio.Larger electronegativity difference could lead to stronger ability to transfer electron,faster charge rate,and larger saturated charge-to-mass ratio.Based on the aforementioned investigation,electrostatic separation of two and three components of actual material mixture were investigated.Specifically,the PP-PVC mixture showed an outstanding outcome,with grades of the positive?PVC?and negative?PP?products reached 95.79%and 86.90%respectively,and the recovery rates were 87.02%and 95.71%,respectively.In three-component separation,the result showed that the optimal separation efficiency when the fluidization time was 240 s,the fluidized gas velocity was 2.73 m/s,and the separation voltage was 60 kV.The grades of PP,PET and PVC products obtained under the optimal test conditions were 80.28%,79.18%and 80.17%,and the recovery rates are 89.86%,88.24%and 85.88%,respectively.There are 53 figures,16 tables,and 91 reference articles in this thesis.