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Fiber Orientation Testing in Nonwoven Fabrics: How Does It Affect Material Anisotropy?

2025-08-04 08:31:14

I. Why is Fiber Orientation Important?

The alignment of fibers in nonwoven fabrics directly influences their anisotropy (directional property variations), which determines:

1. Mechanical properties: Longitudinal tensile strength can be 50% higher than transverse strength (typical data for spunbond processes)

2. Liquid penetration paths: When fibers are aligned parallel, liquid diffusion speeds increase by 2-3 times

3. Filtration efficiency: Random fiber orientation in melt-blown fabrics improves PM0.3 capture rates by 40%

Industry challenge: Traditional optical microscopy only observes surface features and cannot quantify 3D orientation distribution

II. Testing Methods Comparison and Breakthroughs in CT Scanning

Method

Principle

Resolution

Limitations

Optical microscopy

2D surface imaging

1μm

Cannot analyze internal structure

SEM + image analysis

Surface morphology statistics

0.1μm

Samples require conductive coating

Micro-CT scanning

X-ray 3D tomography

0.5μm

High equipment cost (¥2M+)

Ultrasonic anisotropy testing

Sound wave velocity differences

-

Only suitable for thick materials

Advantages of CT technology:

Quantifies orientation parameters (Herman factor: 0 = completely random, 1 = fully aligned)

Detects hidden defects

III. Quantitative Relationship Between Fiber Orientation and Mechanical Properties

Experimental data (PP spunbond nonwoven, 50 g/m² basis weight):

Orientation angle distribution

Longitudinal tensile strength (N/5cm)

Transverse tensile strength (N/5cm)

Anisotropy ratio

Random orientation (±30°)

35±2

32±3

1.09

Partial orientation (±15°)

48±3

36±2

1.33

High orientation (±5°)

62±4

28±1

2.21

Key conclusions:

Every 10% increase in orientation degree improves longitudinal strength by ~15%

Transverse tear strength correlates positively with the number of fiber crossover points

IV. Directions for Production Process Optimization

1. Spinning stage adjustments:

Increasing electrostatic separator voltage from 10kV to 15kV reduces fiber orientation standard deviation from ±25° to ±12°

At drafting air speeds >8 m/s, fiber orientation improves but breakage risk rises (requires balance)

2. Thermal calendering improvements:

Embossed roller pressure >3 MPa damages fiber orientation structure

Optimal process: 180°C + 2 MPa + 20 m/min (Herman factor up to 0.7)

3. Post-treatment effects:

Hydrophilic finishing sprays reduce fiber orientation by 5-8% (due to volumetric shrinkage)

V. Industry Case Study

Optimization at a filter material factory:

1. Problem: Melt-blown fabric filtration efficiency fluctuated significantly (85%-92%)

2. CT diagnosis: Uneven fiber orientation distribution (local Herman factor 0.2-0.6)

3. Improvements:

Modified drafting air channels (added flow guides)

Installed online ultrasonic orientation monitors

4. Results:

Filtration efficiency stabilized at 91±1%

Raw material consumption reduced by 8%


Tags: CT scanning, mechanical properties, production process optimization