The Mechanism And Regulation Of The Environmental Factors On The Hydrophilicity/Hydrophobicity Transition Of The Modified Plastic Surface

The effective separation of waste plastics is the premise to ensure the quality and performance of recycled products.At present,there are many kinds of separation methods.Among them,the plastic flotation method is favored because of its simple process and less pollution.The plastic surface changes from hydrophobic to hydrophilic after modificiation.In order to minimize the surface energy,the migration and inversion of groups occur on the surface.The phenomenon of surface reconstruction will further restore the hydrophobicity of plastics,and the difference of hydrophilicity and hydrophobicity can affect the effect of flotation separation.In this paper,we select Fenton oxidation,alcoholysis and capping method to study the effect of environment on the change of hydrophilicity and hydrophobicity on the surface of modified plastics and the regulation of flotation separation.The study found that the difference in hydrophilicity of plastic surfaces was small in polar environments,further expanded in neutral environments,and maximized in non-polar environments.This mechanism is conducive to guiding and regulating the difference in the hydrophilicity and hydrophobicity of the plastic surface,which is of great significance for the recycling of plastics.In the environmental research on the transition mechanism of hydrophilicity/hydrophobicity on the surface of Fenton-modified plastics,after ABS,PC,PS,and PMMA are modified by Fenton,the buoyancy of the plastics does not change,and the contact angle changes slightly in the polar environment,the surface remains hydrophilic.The buoyancy of the plastic increases as the environmental polarity decreases.When the treatment time is 8h,the balanced contact angle values increase to 76°,80°,72.5° and 85°,respectively.The recovery degree of surface hydrophobicity is greater than that of the polar environment.In the non-polar environment,the buoyancy of the plastic increases the fastest,and the surface hydrophobicity is completely restored,which is the same as the hydrophobicity before the modification.It can be found that the hydrophilic groups obtained after the modification of the plastic surface are more likely to stay on the surface in a polar environment.As the polarity decreases,the hydrophilic groups gradually migrate to the bulk,and the plastic surface returns to hydrophobic.In the environmental study on the hydrophilicity/hydrophobicity transition mechanism of PET surface modified by alcoholysis method,alcoholysis introduced(C=O)-O on the surface of PET plastic,and hydrophilic PET at high induction temperature,long induction time and non-polar environments restore hydrophobicity more easily.During the hydrophobicity recovery process,the functional groups on the plastic surface did not change,and the phenomenon of(C=O)-O moving to the bulk was more obvious in nonpolar environment;when the temperature exceeded Tg,the hydrophobicity recovery rate of PET decreased.In the study of the mechanism of the environment on the hydrophilicity/hydrophobicity transition of the modified PVC surface by the capping method,the recovery law of the hydrophobicity of the PVC on the environment is roughly the same as that of the previous two methods.The process of hydrophobicity recovery is accelerated,in which environmental polarity is the decisive factor.The reason why PVC is hydrophilic is that hydrophilic calcium carbonate particles are introduced into the surface.When external force intervenes to peel the particles off the surface,the surface of PVC loses its hydrophilicity.Compared with the hydrophilic methods of introducing functional groups through oxidation and alcoholysis,PVC is more difficult to maintain hydrophilicity.The phenomenon of surface reconstruction has a great impact on the hydrophilicity of modified plastics.Polarity,low temperature,and instant can maintain the difference in hydrophilicity between target plastics and non-target plastics,ensuring the stability of the plastic surface during the flotation separation process.