Fibrous filters are widely used in manufacturing and separation industries to remove aerosol particles produced in the production process. However, due to the complex internal structure of fibrous filters, there are still some problems to be investigated. In the first part of this review, the different theoretical analyses of the flow field distribution around the fiber is summarized. In a comparison of the various theoretical models of flow fields with the simulation results, the Kuwabara-Happel flow field model has the best applicability. The theoretical models of single fiber filtration by five mechanisms: diffusion, interception, inertial impaction, gravity settling, and electrostatic effects are summarized. One of the other outstanding questions is the effect of fibrous microstructure characteristics on filtration efficiencies, such as the composite layer structure, the heterogeneity of the fibrous filters, and the fiber orientation. Finally, critical gaps in the literature and necessary directions for future investigations are also given.

No abstract

Compared to natural leather, microfiber synthetic leather has many excellent qualities, such as chemical resistance and physical and mechanical properties. However, preparation of microfiber synthetic leather with a high water vapor transmission rate (WVT), moisture absorption and wearing comfort property is still a challenge. In this study, we prepared thermoplastic polyurethane (TPU)/sulfonated polysulfone (SPSf) electrospun nanofibers and applied them to a microfiber synthetic leather base (MSLB). The effects of TPU/SPSf nanofiber content on the structure and properties of the MSLB were investigated. The results indicated that the TPU/SPSf nanofibers with an average diameter of 0.12 µm were well distributed at all directions in the MSLB. Differential scanning calorimetry analysis showed four Tg peaks, further demonstrating the existence of TPU/SPSf nanofibers. With the increase of TPU/SPSf nanofiber content from 0 to 30 wt%, the contact angles decreased gradually from 111.64° to 67.07°, leading to 55.19% improvement in the WVT value (from 2868.96 to 4452.24 g/(m2•24 h)) and 26.25% improvement in the moisture absorption (from 628.70% to 793.75% mm/s). Simultaneously, when the nanofiber content was 30 wt%, the nanofibers tended to bundle and 6.79% decrement of air permeability was observed. Specifically, the softness of the MSLB was improved by 88.55%. Moreover, the thermal stability and the tear strength were also obviously enhanced. Consequently, this research provided a feasible and promising way to prepare a high-performance MSLB using TPU/SPSf nanofibers.

The microfiber synthetic leather base (MSLB) was prepared by mixing hollow segmented pie microfibers and polyacrylonitrile electrospun nanofibers. Micro/nano hybrid leather base was prepared to simulate the three-dimensional (3D) structure of natural leather. The diameter of the polyacrylonitrile nanofibers was 950 nm, 450 nm and 200 nm, respectively. The effects of nanofibers of different diameters on the performances of MSLB were investigated. The results indicated that polyacrylonitrile nanofibers were randomly dispersed in MSLB. Differential scanning calorimetry further demonstrated the presence of polyacrylonitrile nanofibers in MSLB, and thermogravimetric analysis showed that the addition of polyacrylonitrile nanofibers had a little influence on the thermal stability of MSLB. There was no significant change in the water contact angle of the MSLB surface before and after the addition of nanofibers. As the diameter of the nanofibers decreased from 950 nm to 200 nm, the static water vapor transmission rate was increased by 28.2%, the softness was increased by 39.74%, and air permeability was decreased by 17.16%. When the nanofiber diameter is 950 nm, the moisture absorption performance of MSLB was better, which was 768.99%. Moreover, the tear strength was also significantly enhanced by 105.76%.

Diffusion is an important filtration mechanism of fibrous filters for removing fine particles from gas streams. An analytical model is proposed in this work, based on fractal theory, to quantify the effective diffusion coefficient (EDC) across micro/nanofibrous filters with a layered structure. To show the influence of macroscopic parameters of fibrous filters on EDC, the present models are expressed in terms of fiber diameter. Polyacrylonitrile (PAN) nanofibers were prepared by electrospinning on melt-blown polypropylene (PP) microfiber filter materials to form micro/nanofibrous filters. To validate this model, a three-dimensional (3D) fiber model with physical parameters of the samples was reconstructed using the GeoDict code, and the Brownian movement of nanoparticles was simulated to calculate the EDC. Two kinds of pore size distributions for the layer-structured fibrous filters have been identified, which also shows the internal heterogeneity of the filter media. With decreasing fiber diameter, the tortuosity of the pore channel increases, while the EDC decreases. Compared with the numerical simulation and the experimental data reported in the literature, the current model gives a better theoretical prediction. In addition, the diffusion mechanism in classical filtration theory was modified to reduce the deviation between theoretical prediction and experimental results.