As the core material of medical masks, the filtration efficiency of meltblown fabric directly affects the protective effect of masks. There are many factors that affect the filtration performance of meltblown fabrics, such as fiber line density, fiber mesh structure, thickness, and density.
However, as an air filtration material for masks, if the material is too tight, the pores are too small, and the breathing resistance is too high, the user cannot smoothly inhale air, and the mask loses its value.
This requires the filter material not only to improve its filtration efficiency, but also to minimize its respiratory resistance as much as possible, and respiratory resistance and filtration efficiency are a contradictory pair. The electrostatic polarization treatment process is the best way to solve the contradiction between respiratory resistance and filtration efficiency.
The filtration mechanism of meltblown fabric
In the filtration mechanism of melt blown filter materials, the commonly recognized mechanisms mainly include Brownian diffusion, interception, inertial collision, gravity settling, and electrostatic adsorption. Due to the fact that the first four principles are all mechanical barriers, the filtration mechanism of meltblown fabrics can be simply summarized as mechanical barriers and electrostatic adsorption.
Mechanical barrier
The average fiber diameter of polypropylene meltblown fabric is 2-5 μ m, and droplets with a particle size greater than 5 μ m in the air can be blocked by the meltblown fabric.
When the diameter of the fine dust is less than 3 μ m, the fibers in the meltblown fabric are randomly arranged and interlayered to form a multi curved channel fiber filter layer. When the particles pass through various types of curved channels or paths, the fine dust is adsorbed on the fiber surface by the mechanical filtration van der Waals force.
When the particle size and airflow velocity are both large, the airflow approaches the filter material and is obstructed, causing it to flow around, while the particles detach from the streamline due to inertia and collide directly with the fibers, being captured.
When the particle size is small and the flow rate is low, the particles diffuse due to Brownian motion and collide with the fibers to be captured.
Electrostatic adsorption
Electrostatic adsorption refers to the capture of particles by the Coulomb force of charged fibers (polarizations) when the fibers of the filter material are charged. When dust, bacteria, viruses and other particles pass through the filter material, electrostatic force can not only effectively attract charged particles, but also capture induced polarized neutral particles through electrostatic induction effect. As the electrostatic potential increases, the electrostatic adsorption effect becomes stronger.
Introduction to Electrostatic Electrification Process
Due to the filtration efficiency of ordinary meltblown non-woven fabrics being less than 70%, relying solely on the mechanical barrier effect of the three-dimensional aggregates of fibers with fine fibers, small voids, and high porosity produced by meltblown ultrafine fibers is not enough. Therefore, meltblown filtration materials generally add electrostatic charge effects to the meltblown fabric through electrostatic polarization technology, using electrostatic methods to improve filtration efficiency, making it possible to achieve 99.9% to 99.99% filtration efficiency. A very thin layer can meet the expected standards, and the respiratory resistance is also low.
At present, the main methods of electrostatic polarization include electrospinning, corona discharge, friction induced polarization, thermal polarization, and low-energy electron beam bombardment. Among them, corona discharge is currently the best electrostatic polarization method.
The corona discharge method is a method of charging the meltblown material through one or more sets of needle shaped electrodes (voltage generally 5-10KV) of an electrostatic generator before winding the meltblown fiber mesh. When high voltage is applied, the air below the needle tip produces corona ionization, resulting in local breakdown discharge. Carriers are deposited on the surface of the meltblown fabric under the action of the electric field, and some carriers will be trapped by the traps of the stationary mother particles deep into the surface, making the meltblown fabric a filter material for the stationary body.
Increasing the surface charge of the meltblown fabric can be obtained through the corona discharge method for electrostatic discharge treatment, but in order to prevent the decay of this electrostatic storage, the composition and structure of the meltblown electrode material need to be conducive to charge retention. The way to improve the charge storage capacity of electret materials can be achieved by introducing additives with charge storage properties to generate charge traps and capture charges.
Therefore, compared with ordinary melt blown production lines, the production of melt blown materials for air filtration requires the addition of high-voltage electrostatic discharge devices in the production line, and the addition of polar masterbatch such as tourmaline particles to the production raw material polypropylene (PP).
The main factors affecting the effect of electrospinning treatment on meltblown fabrics
1. Charging conditions: charging time, charging distance, charging voltage;
2. Thickness;
3. Electrified materials.
Dongguan Liansheng Non woven Technology Co., Ltd. was established in May 2020. It is a large-scale non-woven fabric production enterprise integrating research and development, production, and sales. It can produce various colors of PP spunbond non-woven fabrics with a width of less than 3.2 meters from 9 grams to 300 grams.
Post time: Oct-26-2024