Study On Structure And Filtration Properties Of Polypropylene Melt-blown Nonwoven

With the rapid development of technology and industry and the improvement of living standards,people are paying increasingly attention to air quality.The atmospheric haze will cause great harm to human health and social production and life,therefore,the development of air filter materials that can filter finer particles and have high efficiency and low resistence has become the focus of research in the field of meltblown nonwoven air fitration today.Meltblown electret fiber material is one of the mainstream air filter materials at present market.It uses electrostatic effects to improve its filter efficiency without increasing the pressure drop;however,its electret charge is easily attenuated by environmental influences.Studies have shown that the crystallinity of polypropylene is related to the heat treatment process.The microcrystalline structure of the material will affect the charge storage density and stability,that is,heat treatment can improve the electret charge storage stability and slow charge decay.It is envisaged to improve the filtration performance of meltblown nonwovens by the methods of electret at high temperature and nucleating agent modification.The thesis explores the effects of electret temperature on the structure and the filtration performance of materials;the effects of different proportions of nucleating agents on the structure and the filtration performance of materials are explored.The influence of electret temperature and different proportions of nucleating agents on the structure and filtration performance of meltblown nonwoven materials provides a theoretical reference for future studies that want to improve the filtering performance of materials through high temperature electret and nucleating agent modification.This paper first analyzes the physical properties of meltblown polypropylene resin.The melting point and decomposition temperature of polypropylene are the basis for setting the temperature parameters of the meltblown process.Therefore,DSC and TG tests are performed on polypropylene master batches.Next,the influence of the electret temperature on the structure and filtration performance of the meltblown polypropylene nonwoven fabric was studied.Changing electret temperature,polypropylene meltblown nonwoven fabrics charged in different temperature(20??70??75??80??85??90??95??100??105??110?)were prepared.The apparent morphology,fiber diameter,pore size and distribution,surface density,porosity,crystallization and filtration properties of polypropylene meltblown nonwoven fabrics were evaluated respectively by SEM,capillary flow porometer,fabric thickness tester,electronic balance,XRD,automatic filter tester.Finally,the effects of different transparent nucleating agent ratios on the structure and filtration performance of meltblown polypropylene nonwoven materials were studied.Four kinds of PP meltblown nonwovens were prepared by charging at the optimal temperature,containing transparent nucleating agent 0%,0.2%,0.5%,and 0.8%respectively.The apparent morphology,fiber diameter,pore size and distribution,permeability,thermal properties,crystallization properties,filtration properties of Nucleating agent modified polypropylene nonwoven material were studied respectively with SEM,capillary flow porometer,air permeability instrument DSC,XRD,automatic filter tester.The physical properties of PP utilized in this study were as following:melt flow rate(MFR)of 1500g/10min,melting point of 163.75?,Initial decomposition temperature about 400?.The processing temperature of the meltblown polypropylene nonwoven should be controlled between 163.75??400?.Charging in high temperature would affect the structure of the polypropylene meltblown nonwoven fabric,which would increase the surface structure unevenness of the fiber web,and the effect on the fiber diameter was not obvious;the average pore diameter of the fiber web became slightly larger.The pore size distribution range was widened;the thickness of the fiber web first became larger and then decreased,but the variation range was small;as the electret temperature increased,the areal density first increases and remains relatively stable,the porosity decreases,and the filtration resistance first increased then remained relatively stable;The filtration efficiency of fabric charged at 70??105? was higher than that of room temperature;the fabric charged at room temperature had highest quality factor which means it had the best filtration performance.The addition of nucleating agent made the fiber diameter smaller,the pores between the fiber aggregates became smaller,the average pore diameter and the gas permeability of the material decreased;the crystallization peak temperature of the material increased which made it easy to crystallize,and the crystallization speed was accelerated;the melting enthalpy decreased first and then increased,the nucleating agent makes the peak profile of the crystal plane of polypropylene(130)clearer.With the increase of nuclear agent,the filtration efficiency and the dust holding capacity of the material increased while the filtration resistance increased slightly.The change of the nucleating agent to the structure of the fiber network was the main reason for the change of filtration performance.