How is PP air filter material tested？
PP (polypropylene) air filter media, with its advantages of acid and alkali resistance, low resistance, and ease of processing, is widely used in fresh air systems, automotive air conditioning, industrial dust removal, and other fields. Its filtration effectiveness and operational reliability require validation through scientific testing. This article outlines key testing items, methods, and criteria—from fundamental metrics to specialized scenarios—centered on the core performance of PP air filter media, providing reference for enterprise selection and quality control.
Appearance Quality Inspection
Primarily inspects the color uniformity, mesh structure integrity, and surface defects of the filter material:
- Color must meet design requirements with no noticeable color variation within the same batch;
- Mesh should be uniform, free of burrs, breaks, wire overlaps, or severe flattening;
- Edge trimming must be neat, with flash at the mesh frame junction ≤2mm (≤1.5mm for high-density mesh), and no delamination or brittle fractures.
Structural Dimension Inspection
For different types of PP filter materials, inspect weave density, mesh wire diameter, and dimensional tolerances:
- Weave Density: Flat injection-molded: 32 threads/inch warp, 34 threads/inch weft; Pleated injection-molded: 39 threads/inch warp, 33 threads/inch weft; High-density: 48 threads/inch warp, 37 threads/inch weft, etc. Tolerance: ±2–3 microns;
- Mesh wire diameter: Standard mesh: 0.20 ± 0.02 mm; High-density mesh: 0.05–0.10 mm; Machine room air conditioner filter mesh II: 0.15–0.20 mm;
Physical Properties Testing
Physical property testing of PP filter media primarily focuses on mechanical strength and durability, specifically including the following items:
First, tensile property testing (including tensile strength and elongation at break) aims to verify the material's resistance to damage during installation and use (such as cutting and exposure to air pressure). Testing methods follow GB/T 1040.3-2006 "Plastics—Determination of Tensile Properties—Part 3: Test Conditions for Films and Sheets." Tensile strength testing must be conducted according to application-specific requirements: — For standard PP filter materials: longitudinal tensile strength ≥1.5MPa, transverse ≥1.0MPa. Materials used in high-wind-pressure applications (e.g., industrial fan filters) require longitudinal tensile strength ≥2.0MPa to prevent tearing under wind pressure. Testing may involve either cutting a 150mm×25mm standard specimen and stretching it at 50mm/min using a universal tensile testing machine, or cutting a 30mm-wide specimen along the longitudinal direction and stretching it at the same speed while recording the maximum tensile force;
Second, burst strength testing: Place the filter mesh horizontally. Apply vertical downward pressure to the center of the mesh using a push-pull gauge with a disc-shaped thrust terminal until rupture occurs. Record the pressure value at rupture, which must be ≥70N. Third, bending performance testing: Simulate the installation scenario by assembling and disassembling the sample 20 times. The sample must show no signs of delamination, cracking, or fracture.
Filter Efficiency and Resistance Characteristics Testing
Core Performance Metrics for Validating Particle Capture Capacity and Airflow Resistance of Filter Materials:
Filter Efficiency: Employing the laser particle counter method, aerosols with multi- or mono-dispersed particle sizes (e.g., 0.3μm, 0.5μm particles) are generated using a Laskin nozzle atomization system. Simultaneous detection of particle concentrations upstream and downstream of the sample calculates the filtration efficiency (e.g., ≥99.95% indicates high-efficiency filter material). Compliant standards include GB 2626-2019, EN1822-3:2009, ISO 29463-3:2011, etc.;
Resistance Characteristics: Measures the pressure differential (ΔP) across the sample using a differential pressure sensor, calculating the resistance per unit area (ΔP/S, unit: Pa/m²). Resistance values must meet application requirements; low-resistance, high-efficiency filtration materials typically exhibit resistance ≤100 Pa.
Flame Retardant Performance Testing
PP (polypropylene), being a flammable material, requires the addition of flame retardants (such as bromine-antimony systems, nitrogen-phosphorus systems, intumescent flame retardants, etc.) to enhance its flame-retardant properties. The UL94 vertical burning test is the most commonly used method for evaluating flame retardancy. It simulates the combustion behavior of materials under flame exposure to assess their self-extinguishing capability, burning rate, and dripping risk.
The most widely applied plastic flame retardant rating standards are categorized as HB (horizontal burning), V-0/V-1/V-2 (vertical burning), and 5VA/5VB (enhanced requirements). During testing, the specimen (with specified thickness, e.g., 3–13 mm) is vertically secured and ignited with a defined flame (e.g., V-0 grade flame height 8.5 mm) for 10 seconds. After removal, the burning time with flame (not exceeding 60 seconds per ignition) is recorded. This ignition is repeated five times while observing whether molten droplets ignite the underlying cotton wool. For example: - V-0 requires flame extinction within 30 seconds after two ignitions with no molten droplets - V-2 permits molten droplets but prohibits ignition of the cotton wool
