| Nonwovens are often chosen as preferred air filtration materials recently and spunbondedand melt-blown nonwovens are widely used because of their unique advantages. Researchpriorities and development trend of nonwovens are concentrated in two aspects. On one hand,diameter and distribution of fiber in nonwovens are studied. On the other hand, composite orfunctional nonwovens are two main kinds of nonwovens in the future as a result of people’s highrequirements for air filtration materials.In light of this, structure and filtration performance of single-layered spunbonded andmelt-blown nonwovens were studied in this thesis. Meanwhile, laminated composite nonwovenswere prepared under different lamination process and optimal lamination parameters wereattained. Structure fractal dimensions were calculated to quantitatively characterize fiberdistribution in spunbonded or melt-blown nonwovens and the relation between structure fractaldimensions and pore structure, air permeability can be obtained. Furthermore, structure andfiltration performance of various composite nonwovens with different composite models weretested and analyzed. The following conclusions can be drawn.(1)The optimally selected spunbonded nonwovens are produced under metering pumpspeed30Hz and apron frequency7Hz. The mean pore size of the selected one is36.00μm andthe largest pore size54.74μm. The filtration efficiency is17.7139%while the pressure drop is8.68Pa. And the tensile breaking strength comes to be4.40N/5cm. Different melt-blownnonwovens are produced using L9(34) orthogonal table and the selected melt-blown nonwoven isprepared under metering pump speed15Hz, crossing wind temperature265℃and DCD20cm.The mean pore size of the optimally selected one is17.42μm and the largest is21.22μm.Thefiltration efficiency is85.5413%while the filtration resistance is30.47Pa. The tensile breakingstrength is1.10N/5cm.(2)The filtration efficiency of SMMS laminated composite nonwovens under variousparameters exceeds94%while the pressure drop is also more than290Pa. Compared withsingle-layered melt-blown nonwovens, the filtration efficiency of SMMS is a little larger and itcan be improved by15%maximumly while the pressure drop is much larger and it can increaseby90%minimally. It can be seen that the filtration resistance goes up rapidly. The optimallamination parameter is temperature135℃, pressure1Mpa and time3s according to thecomprehensive index. (3)Matlab is used to get binary images of SEM of spunbonded and melt-blown nonwovens.Structure fractal dimension of these images are calculated through pixels covering method toquantitatively characterize fiber distribution in nonwovens. Furthermore, linear relations betweenstructure fractal dimension and mean pore size, largest pore size, porosity, air permeability canbe obtained. The correlation coefficient ranges from0.7to1, showing that its linear relation isvery obvious.(4)The influence of different composite models (namely spunbonded, melt-blown andmixed) on structure and filtration property is studied. For spunbonded model, the mean pore size,the largest pore size and air permeability decrease while the filtration efficiency and pressuredrop increase as the number of layer increases. When the layer number is four, the mean poresize is15.68μm and the largest pore size is45.28μm. The filtration efficiency is57.2400%andpressure drop is44.80Pa. For pore size distribution, spunbonded nonwovens are moreconcentrated when the layer number is two or three. For melt-blown model, the changing law issimilar with spunbonded nonwovens. When the layer number is four, mean pore size is9.88μmand the largest pore size is15.00μm. The filtration efficiency is99.9863%and the pressure dropis120.90Pa. For pore size distribution, melt-blown nonwovens are concentrated when the layernumber is three or four. For mixed model, there is a very big difference in pore size distributionand filtration property among structures with different layers. While the layer number of S or Mis certain, different sequence has obvious effects on structure. Judging from comprehensiveindex, the filtration performance of spunbonded model is worse and the others are much better.Among these, the indexes of MMM, MMMM, SSMM, SMMM and MSMM are all above zeroand the order from high to low is respectively MMM, MMMM, SMMM and MSMM, followedby SSMM. The SMMM, MSMM and SSMM are adopted due to the poor mechanical property ofmelt-blown nonwovens. The filtration efficiency of SMMM, MSMM, SSMM is respectively99.8068%,99.6038%,99.2610%while the pressure drop is respectively105.40Pa,100.80Pa,82.40Pa. |
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