Surface-modified ATH quality testing covers quick on-site screening methods and formal laboratory tests. The tests verify coating uniformity, hydrophobicity, powder properties, and the final composite performance, ensuring the ATH meets requirements for LSZH cables, plastics or artificial stone.
1. Quick on-site qualitative test: Water floating test
This is the simplest and most widely used field check.
- Procedure: Add a small amount of modified ATH powder into clean water and stir gently.
- Good quality: Most powder floats on the water surface, does not wet and sink rapidly.
- Poor quality: Powder quickly sinks, which means large fractions remain unmodified.
- Limitation: Qualitative only, cannot quantify coating coverage rate.
2. Powder physical property tests
Contact angle measurement
Measure the water contact angle on compressed ATH powder tablet. Higher contact angle = stronger hydrophobicity and better surface coating. Silane-modified ATH typically shows much higher contact angle than raw ATH.
Oil absorption value
Modified ATH has lower oil absorption than unmodified ATH. Lower oil absorption reduces melt viscosity during polymer compounding and allows higher filler loading.
Particle size distribution (PSD)
Use laser particle size analyzer to test D50, D97 and particle size span. Confirm grinding and classification quality remains unchanged after modification; verify no over-grinding or agglomeration occurs in the modification mill.
Moisture content
Karl Fischer or oven drying method. Free moisture should stay within 0.2–0.5%. Excess moisture indicates poor storage stability and may cause agglomeration in polymer blends.
3. Chemical analysis for coating quality
FTIR (Fourier Transform Infrared Spectroscopy)
Detect chemical bonding between modifier and ATH surface hydroxyl groups. For silane-modified ATH, FTIR can confirm Si-O-Al bonds, proving chemical coupling instead of simple physical adsorption.
Thermogravimetric analysis (TGA)
TGA quantifies the weight loss of organic modifier on ATH surface, to calculate actual modifier loading. It also checks whether ATH crystal water is intact, confirming no thermal decomposition during modification.
XPS (X-ray photoelectron spectroscopy, optional advanced test)
Analyze elemental composition on particle surface, to directly calculate surface coverage percentage. Used for high-end R&D, not routine production inspection.
4. Composite compound performance tests (most critical acceptance test)
Mix modified ATH with target polymer matrix (EVA/PE/PP) at the designed loading ratio, then prepare test specimens for mechanical and electrical tests.
- Mechanical properties: Tensile strength and elongation at break. These are the core indicators for LSZH cable-grade ATH.
- Melt flow index / Melt viscosity: Check extrusion processability.
- Electrical properties: Volume resistivity, dielectric constant (mandatory for cable ATH).
- Aging test: Thermal aging to evaluate long-term stability and modifier migration (blooming).
- Flame retardant & smoke density test: Confirm ATH flame and smoke suppression performance is preserved after modification.
5. Common quality judgment checklist
✅ Water float test passes
✅ PSD matches target specification
✅ Moisture ≤0.5%
✅ Oil absorption within specification range
✅ TGA shows modifier dosage matches recipe
✅ FTIR confirms successful surface reaction
✅ Composite tensile & elongation meet requirements
✅ No blooming after thermal aging
Common quality defects and corresponding root causes
- Powder sinks in water: insufficient coating / uneven modifier atomization
- High oil absorption: incomplete de-agglomeration before modification
- Low elongation of composite: poor silane bonding or under-coating
- Blooming on composite surface: excess free modifier
- High moisture absorption: incomplete coating or powder contamination
Quality testing of surface-modified ATH combines fast water float screening, powder characterization (PSD, moisture, oil absorption, contact angle), chemical analysis (FTIR, TGA), and polymer composite mechanical/electrical validation. The composite compound test is the most reliable final check for industrial production. Stable testing ensures consistent coating quality and predictable performance in LSZH cables and plastic composites.
