| Meta-aramid paper-based functional materials have various excellent properties such as good flame retardancy,electrical insulation,radiation resistance,thermal stability,and chemical stability.Therefore,they have been widely used in the fields of insulating materials,honeycomb structural materials,electronic materials and the like.However,due to their poor surface hydrophilicity and large length,meta-aramid fibers are easily entangled to form flocs,which seriously affects the formation and strength of meta-aramid paper and limits the application of meta-aramid paper-based materials in the high-tech fields.Therefore,how to improve the efficient dispersion and flow of meta-aramid fiber suspension and the efficient forming of meta-aramid paper are the key problems that need to be solved to ensure meta-aramid paper-based functional materials have excellent formation and properties.Based on this,it is necessary to study the hydrodynamic characteristics of meta-aramid fiber suspension that plays a key role in meta-aramid paper forming process.To investigate the yield properties of meta-aramid fiber suspensions,the critical flocculation concentration,shear and compressive yield stress of the single suspensions of meta-aramid staple fibers and fibrids as well as their mixed suspensions were examined,and relations between the formation index of aramid papers and rheological properties could be found,based on the rheological theory.Moreover,combined with the actual production,the effect of polyethylene oxide(PEO)on the yield rheological properties of aramid fiber suspensions and its relationship with aramid paper formation was examined.In addition,through the fluidization test of meta-aramid fiber suspensions,the conditions under which the suspensions reached critical fluidization were explored.The relationship between the critical turbulence Reynolds number and suspensions concentration,and that between the critical turbulence Reynolds number and fiber proportion were studied respectively.The energy dissipation factor of the suspensions was calculated,and the relationship between the energy dissipation factor and the shear yield stress of the suspensions was explored.After experimental exploration,the main research conclusions obtained in this paper are as follows:(1)The critical gel concentration of the single suspensions of meta-aramid staple fibers and fibrids as well as their mixed suspensions ranged from 0.37 to 0.68 g/L,and the gel crowding number ranged from 2.66 to 35.90.The compressive yield stress of the suspensions increased as the concentration increased.Moreover,the compressive yield stress Py was depend on the concentration C complying with a linear relationship Py=a+bC,the values of a and b were between-411.22?-80.78 and 127.69?1038.78,respectively.The shear yield stress of meta-aramid fiber suspensions increased as the concentration increased.Moreover,the shear yield stress ?y was depend on the concentration C complying with a power law relationship ?y=aCb,the values of a and b were between 0.54?1.42 and 1.31?1.64,respectively.In addition,the compressive and shear yield stress decreased as the proportion of fibrid increased at a certain concentration,with the exception of 100%staple fiber suspensions.The formation index of meta-aramid papers decreased as the shear and compressive yield stress of suspensions increased.In addition,the formation index Y was depend on the?y·Py complying with a power law relationship Y=18.85(?y·Py)-0.21.The Froude number of the suspensions decreased as the concentration increased and eventually approached a fixed value.In addition,the Froude number increased as the proportion of fibrid increased at a certain concentration.(2)With the addition of PEO,the critical gel concentration of the meta-aramid suspensions with mass ratios of fibrid and staple fiber of 1:4 and 1:1 increased by about 11%.The compressive yield stress of the suspensions still increased as the concentration increased.Moreover,the compressive yield stress Py was depend on the concentration C complying with a linear relationship Py=a+bC,the values of a and b were between-223.47?-211.38 and 323.27?544.79,respectively.The shear yield stress of meta-aramid fiber suspensions still increased as the concentration increased.Moreover,the shear yield stress ?y was depend on the concentration C complying with a power law relationship ?y=aCb,the values of a and b were between 0.70?1.22 and 1.39-1.79,respectively.Moreover,the compressive and shear yield stress still decreased as the proportion of fibrid increased at a certain concentration.In addition,with the addition of PEO,the compressive yield stress of the suspensions with mass ratios of fibrid and staple fiber of 1:4 and 1:1 decreased at a certain concentration,and the shear yield stress of suspensions decreased at a certain fiber proportion and concentration.However,the formation index of meta-aramid papers increased with the addition of PEO.The formation index of meta-aramid papers still decreased as the shear and compressive yield stress of suspensions increased.Moreover,the formation index Ywas depend on the ?y·Py complying with a power law relationship Y=23.40(?y·Py)-0.15.With the addition of PEO,the Froude number of the suspensions still decreased as the concentration increased and eventually approached a fixed value.Moreover,the Froude number still increased as the proportion of fibrid increased at a certain concentration.In addition,PEO had little effect on the Froude number of suspensions at a certain fiber proportion and concentration.(3)The critical Reynolds number of the single suspensions of meta-aramid staple fibers and fibrids as well as their mixed suspensions increased as the concentration increased.The energy dissipation factor of suspensions increased as the concentration increased.Moreover,the energy dissipation factor ?F was depend on the concentration C complying with a power law relationship ?F=aCb,the values of a and b were between 0.22?1.13 and 1.25?2.08,respectively.At a certain concentration,the critical Reynolds number and the energy dissipation factor of the suspensions with a mass ratio of fibrid and staple fiber of 1:1 were largest,while those of 100%fibrid suspensions were smallest.The energy dissipation factor of suspensions increased as the ?y2 increased.Moreover,the energy dissipation factor ?F was depend on the ?y2 complying with a linear relationship ?F=a+b?y2,the values of a and b were between 0.13?1.07 and 0.07-0.39,respectively. |
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