SN/T 5239-2020 in English

Technical background and scope of application of the standard

This standard, as a special testing method issued by the General Administration of Customs in 2020, establishes a unified specification for the application of microprojectors in the quantitative analysis of kapok/cotton blended products. With the growth of international trade in natural fiber blended products, the traditional chemical dissolution method has limitations in distinguishing kapok (density 0.29g/cm³) from cotton (density 1.55g/cm³). This standard achieves accurate identification through microscopic morphological characteristics.

Core Detection Principle

Measurement system based on digital image analyzer or microprojector (≥500 times magnification):

Key Operation Points

1. Sample Preparation

Yarn samples need to be randomly selected from 10 bobbins to prepare suspension. Fabric samples are required to be 10×10cm and >10cm away from the edge of the fabric. Special attention should be paid to the kapok fibers being kept parallel and straight for measurement.

2. Diameter measurement specification

• Cotton fiber: take the average of the widest, narrowest and midpoint points within the torsion cycle
• Kapok fiber: only measure the non-deformed section, with a diameter range of 20-45μm
• Single sample measurement ≥200 pieces, total count ≥1000 pieces

Calculation result correction

Note when using the density correction formula:

X₁ = (n₁d₁²ρ₁k₁)/(n₁d₁²ρ₁k₁ + n₂d₂²ρ₂k₂) ×100

The values of the conversion coefficients k₁ (0.7289 for kapok) and k₂ (0.2939 for cotton) directly affect the accuracy of the results. A third measurement is required if the difference in parallel tests is >2%.

Implementation suggestions

1. Equipment selection

Preferably use a projection system with an automatic image analysis module to reduce manual counting errors.

2. Quality control

It is recommended to insert a standard substance (30%±1.5% kapok content) into every 20 samples for process verification.

3. Personnel training

Operators must pass the FZ/T 01057.3 fiber identification special assessment and have accumulated identification training of no less than 2,000 characteristic fibers.