Testing the bonding strength of hot melt yarn is critical for evaluating the performance of composite structures (e.g., core-sheath yarn, covered yarn), directly impacting product durability and functionality. Below are detailed testing methods, standards, and considerations:
1. Common Testing Methods
1.1 Peel Test
Application: Evaluates interfacial bonding strength between core and sheath (or between covering layer and core).
Standards:
ASTM D1876 (T-Peel Test)
ISO 11339 (Adhesive Peel Strength)
Procedure:
Sample Preparation:
Cut hot melt yarn into 25 mm × 150 mm strips (with separable core and sheath).
Clamp both ends to form a "T" shape.
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Test Conditions:
Temperature: 23±2°C, Humidity: 50±5% RH.
Tensile Speed: 100 mm/min (ASTM standard).
Data Analysis:
Record maximum force (N/cm) during peeling; calculate average peel strength.
Pass Criteria: Typically ≥5 N/cm (varies by application).
1.2 Lap Shear Test
Application: Measures bonding strength between hot melt yarn and other materials (e.g., fabric, metal).
Standards:
ASTM D1002 (Metal-to-Metal Shear Strength)
GB/T 7124 (China National Standard)
Procedure:
Sample Preparation:
Sandwich hot melt yarn between two substrates (e.g., fabric/metal) with a 25×12.5 mm overlap.
Cure in a hot press (temperature/time based on material).
Test Conditions:
Tensile Speed: 1.3 mm/min (ASTM D1002).
Data Analysis:
Calculate shear strength (MPa) = Maximum force / Overlap area.
1.3 180° Peel Test
Application: Quick evaluation of bonding between covering fibers and core.
Procedure:
Sample Fixing: Peel one end of the yarn to expose the core; clamp at a 180° angle.
Testing: Peel at 50 mm/min; record force-displacement curve.
2. Equipment Requirements
| Equipment | Key Parameters | |
|---|---|---|
| Universal Testing Machine | Load range 0.1–5 kN, ±0.5% accuracy | |
| Hot Press | Temperature control ±1°C, 0–10 MPa | |
| Environmental Chamber | Temperature (-40°C–150°C), RH 10–95% |
3. Key Factors & Optimization
Material Compatibility:
Issue: Core-sheath thermal expansion mismatch causes delamination.
Solution: Add compatibilizers (e.g., maleic anhydride-grafted polymers).
Process Parameters:
Issue: Excessive melting temperature damages cores; insufficient heat weakens bonding.
Solution: Set gradient temperatures based on MFI (e.g., TPU: 180–220°C).
Surface Treatment:
Issue: Contaminants (oils, moisture) reduce bonding.
Solution: Pre-treat with plasma cleaning or solvent wiping.
4. Industry Standards
| Application | Standard | Strength Requirement |
|---|---|---|
| Apparel Covered Yarn | GB/T 3916 | ≥4 N/cm (180° peel) |
| Industrial Core-Sheath Yarn | ASTM D7269 | ≥8 N/cm (T-peel) |
| Medical Nonwoven Fabric | ISO 22610 | ≥3 N/cm (wet peel) |
