Both melt viscosity (ηo) and elasticity (correlated here with the longest melt relaxation time λ1) were found to control the diameter distribution of meltblown fibers. Fibers were formed by melt blowing binary polystyrene (PS) blends containing widely differing component molecular weights using a custom-built laboratory apparatus. Varying the concentration and molecular weight of a high molecular weight PS provided independent control over ηo and λ1. These rheological parameters influence the average diameter (dav) and the distribution of diameters (coefficient of variation, CV) of meltblown fibers in different ways. Increasing ηo leads to an increase in dav but has little impact on CV. On the other hand, increasing λ1 beyond a threshold value reduces CV while simultaneously increasing dav. A one-dimensional slender-jet theoretical model with both upper convected Maxwell and Phan-Thien and Tanner constitutive equations was developed to investigate the influence of viscoelasticity and processing parameters on the properties of meltblown fibers. This model predicts a strong dependence of fiber diameter on the air shear stress and variations in fiber diameter with viscoelasticity that are in qualitative agreement with the experimental results. We believe these results suggest that carefully controlling the viscoelastic profile of polymers used in melt blowing is a viable approach for producing nanofibers with narrow fiber diameter distributions using current commercial equipment.
Bibliographical noteFunding Information:
This work was funded by Cummins Filtration. Parts of this work were carried out in the Institute of Technology Characterization Facility, University of Minnesota, which receives partial support from NSF through the NNIN program.
- Bimodal blend
- Fiber diameter distribution
- Melt blowing
- Polystyrene blend
- Slender-jet model