Biodegradable Composite Filter Media for Air Filtration

The patent employs composite materials by combining biodegradable polyester fibers with electrospun nanofiber layers. The base layer uses biodegradable polyester spunbond nonwoven fabric, while the filtration layer uses electrospun nanofibers made from biodegradable polymers such as polylactic acid (PLA) or polyhydroxyalkanoates (PHA). This composite structure maintains filtration performance through the nanofiber layer's fine pore structure while ensuring biodegradability of both layers, resolving the contradiction between performance and environmental harm.

The patent changes the material parameters from conventional non-biodegradable polypropylene/polyester to biodegradable alternatives. Specifically, it uses biodegradable polyester with controlled molecular weight and crystallinity to maintain mechanical strength during use, then degrades after disposal. The electrospun nanofibers use polymers with specific degradation rates tailored to maintain filtration performance during service life while enabling complete biodegradation afterward, thus resolving the reliability versus environmental harm contradiction.

The patent utilizes porous electrospun nanofiber materials with controlled pore sizes (50-500 nm) and high porosity (50-80%). These nanofibers create a three-dimensional network structure that provides extensive surface area and numerous filtration pathways. This porous structure enables high filtration efficiency at very low material weights (0.01-1.0 g/m²), achieving over 99.9% filtration efficiency with minimal material usage, thus resolving the contradiction between environmental burden and filtration efficiency.

The patent transitions from traditional two-dimensional flat filter media to three-dimensional electrospun nanofiber networks. This dimensional change creates a volumetric filtration structure with vastly increased surface area-to-volume ratio. The nanofibers form a random three-dimensional mat that provides multiple scattering and interception opportunities for particles, achieving superior filtration efficiency at ultra-low weights compared to conventional planar structures, thereby resolving the environmental burden versus filtration efficiency contradiction.

The patent introduces an intermediary bonding mechanism through surface treatment of the biodegradable polyester spunbond substrate. The substrate surface is treated with plasma, corona discharge, or chemical agents to increase surface energy and create anchoring sites. This intermediary treatment enhances the bonding strength between the electrospun nanofiber layer and the substrate, preventing delamination while maintaining the low-weight biodegradable structure, thus resolving the contradiction between environmental burden and bonding strength.

The patent merges the electrospun nanofiber layer with the biodegradable polyester spunbond substrate through simultaneous thermal processing. Both layers are heat-treated together at temperatures below the melting point of the nanofiber polymers but above the softening point of the substrate, creating strong thermal bonding between layers. This merging process ensures intimate contact and strong adhesion between the nanofiber filtration layer and the substrate support, resolving the bonding strength issue while maintaining the lightweight biodegradable design.