How to optimize the porosity of flame-retardant nonwoven fabrics?

2025-12-03 14:31:18

Optimizing the porosity of flame-retardant nonwoven fabrics requires systematic control from three dimensions: fiber characteristics, web-forming process, and consolidation method. Fiber fineness and length are fundamental factors affecting porosity. Finer fibers form a denser network structure, reducing the average pore size; while longer fibers increase pore connectivity through entanglement. By adjusting the fiber crimp and cross-sectional shape (e.g., hollow or irregular cross-sections), the spatial arrangement of fibers during stacking can be altered, thereby precisely controlling the porosity distribution. Mixing fibers with different properties (e.g., coarse-fine blends or long-short fiber composites) can achieve a tiered pore distribution, meeting the requirements of specific applications for air permeability and filtration accuracy.

The web-forming process plays a decisive role in the formation of the pore structure. Airflow web-forming, by adjusting the airflow speed and direction, can prepare fiber webs with isotropic or oriented arrangements. The former results in a uniform pore distribution, while the latter forms directional channels. Wet spinning, which disperses fibers in an aqueous medium, is suitable for producing high-density, low-porosity materials, but careful control of fiber migration during dehydration is necessary. Electrospinning can manufacture nanofiber webs composed of ultrafine fibers with porosities as low as 80% and concentrated pore size distribution, but its production efficiency is relatively low. Multilayer composite technology stacks fiber webs with different porosity characteristics, enabling functional zoning designs.

The consolidation process is crucial for determining porosity. Hot rolling consolidation, through precise temperature and pressure control, ensures sufficient bonding points between fibers while avoiding excessive compression that could lead to pore collapse. Hydroentangling uses high-pressure water jets to penetrate and entangle the fiber web, maintaining a high porosity (typically 60-90%) and producing pores closer to their natural state. The piercing depth and density of needle punching directly affect the three-dimensional connectivity of the pores; deeper piercing increases the proportion of through-pores, making it suitable for filtration applications. Chemical bonding regulates local pores through adhesive distribution; spraying is more effective than impregnation in maintaining the overall pore structure.

Post-processing steps can further optimize porosity. Plasma treatment can modify the pore walls at the micro- and nano-scale without significantly altering the macroscopic porosity, improving surface properties. Heat setting processes stabilize the pore structure by relaxing internal stress, preventing deformation during use. Functional coatings can selectively cover parts of the pores, achieving intelligent responsive porosity adjustment. Porosity optimization requires balancing flame retardant distribution requirements, ensuring that the flame-retardant components adequately cover the fiber surface without completely blocking the pore channels.