Preparation Of Hydrophobic PP/PVDF Fiber Film And Its Filtration Properties Of Insulating Oil

The insulating oil is continuously aging during long-time operation under the condition of high temperature,electric field,copper and iron catalyst,which generate various impurities and cause faults of electrical equipments.In order to reduce the waste of resources and environmental pollution that are caused by oil exchange,the insulating oil could be purified after a period of operation.Polypropylene(PP)fiber films have simple manufacturing process,low cost,good thermal and chemical stability.However,the filtration effect of moisture and impurities below 1 ?m is not good due to the weak hydrophobicity and large pore of PP films.In this paper,the fluorinated PP/PVDF composite fiber films with super-hydrophobicity and high charge stability were fabricated by fluorination treatment and electrospinning,and the properties of oil filtration were measured.The main contents of this paper are as follow:(1)The influences of fluorination on the chemical composition,pore size,morphology and crystal structure of PP fiber films were studied,and the hydrophobicity and charge stability of the films were measured.The results show that the hydrophobicity and charge stability of the fiber films can be effectively improved by controlling the fluorination concentration.When the concentration reaches to 2%,the fiber films have super-hydrophobicity and the charge stability is significantly improved.However,the fluorination treatment will slightly increase the pore size of the PP fiber films,and only part of impurities in the insulating oil can be removed.(2)The double-layer micro-nano composite fiber films were fabricated by electrospinning process,in which the PVDF nanofibers were supported by the fluorinated PP fiber films.The effects of different electrospun parameters(PVDF concentration,applied voltage,feeding speed and receiving distance)on the morphology,pore size and hydrophobic property of the fiber films were investigated.The results show that the PVDF nanofiber films have small pore size,uniform diameter distribution and superhydrophobicity were prepared under the conditions of 12 wt% PVDF concentration,20 kV applied voltage,0.5 mL/h feeding speed and 15 cm received distance.(3)The effects of different PVDF concentrations on the crystal structure and surface charge decay of nanofiber films were studied.The results show that when the concentration of PVDF increases from 8 wt% to 12 wt%,the crystallinity of the fiber films increases,and the charge stability also increases.When the concentration exceeds 12 wt%,the crystallinity and charge stability of the fiber films decrease.(4)The insulating oil filtration performance of the fabricated filter films was evaluated by the measurement of moisture content,breakdown voltage,the relative dielectric constant and dielectric loss factor of the oil before and after filtration.The results show that the filtration effect of fluorinated PP/PVDF micro-nano composite fiber films is improved significantly.The moisture content in the aging oil samples decreased from 38.8mg /L to 14.2mg /L,the breakdown voltage increased by 56%.The frequency spectrum of relative dielectric constant and dielectric loss factor showed an obvious decrease at low frequency.The above studies show that the hydrophobicity and charge stability of PP fiber films can be improved by fluorination,which enhance the effect of oil/water separation.But the tiny impurities such as the charged colloids can't be filtered by PP films due the large pore size.Therefore,fluorinated PP/PVDF micro-nano composite fiber films with nanometer diameter and submicron pore size are fabricated by electrospinning to further enhance the effect of oil/water separation and impurity retention.It has a good application prospect in the field of insulating oil filtration.