How to inspect cotton? Detailed explanation of cotton inspection methods and standards

Cotton is one of the world's most important agricultural crops. Its high yield and low production costs make cotton products relatively affordable. Cotton fiber can be used to weave a wide range of fabrics, from lightweight voile to heavy canvas and velveteen, for a wide range of uses in clothing, home textiles, and industrial fabrics. China, the United States, India, Brazil, Mexico, Egypt, Pakistan, Turkey, Argentina, and Sudan are the world's top cotton producers. Cotton quality requires professional testing to determine its quality. So how is cotton tested?

1. Basic knowledge of cotton

(1) Classification by length and fineness:

1. Upland cotton (also known as upland cotton): the main cultivated variety in my country.

2. Long-staple cotton (also known as sea island cotton): Xinjiang is my country's main production base.

3. Cotton: It is no longer grown in my country.

(2) Classification by fiber color:

1. White cotton: Normal mature cotton fiber, which is white, milky white or light yellow in color.

2. Yellow cotton: Due to frost and other reasons, the pigment of the boll shell is stained on the fiber, most of which are yellow and are of low grade.

3. Gray cotton: The fiber becomes grayish due to factors such as rain and mildew.

(3) Other categories:
Including infertile seed recycled cotton, moldy cotton, peach-peeled cotton, frost-yellow cotton, gray-stained cotton, burnt cotton, oil-stained cotton, ground cotton, water-stained cotton, hail-damaged cotton and rain-rusted cotton, etc.

The main components of cotton fiber:
Cellulose (chemical formula: (C6H10O5)n) accounts for about 94%, and also contains small amounts of pentosan, wax, protein, fat, water-soluble substances, ash and other accompanying substances.

2. Technical terms for cotton inspection

(1) Product standard terminology:

1. Long-staple cotton: length 33-45 mm, fineness 9000-8500 Nm, single strength 3.9-4.9 cmN, mostly roller ginned, can be divided into extra long-staple cotton (≥35 mm) and medium-staple cotton (33-35 mm).

2. Fine-staple cotton: length 23-33 mm, fineness 6500-5000 Nm, single strength 2.9-4.4 cmN, mostly sawtooth ginning.

3. Coarse cotton: length <23 mm, fineness <4000 metric tons, single strength 4.4-6.9 cmN.

4. Sawtooth cotton: cotton fiber processed by a sawtooth gin.

5. Roller cotton: cotton fiber processed by roller ginning machine.

6. Naturally colored cotton: cotton fibers that are naturally colored during growth.

7. Dyed fiber: colored fiber that has been dyed or processed with masterbatch.

8. Grade: It is divided into seven grades according to maturity, color characteristics and rolling quality (GB1103-1999). Grade three is standard grade and grades below seven are out-of-grade cotton.

9. Length: The distance between the two ends of a fiber after it is straightened.

10. Natural length: The distance between the two ends of the fiber including the natural twist.

11. Main body length: The length of the most abundant fiber in a cotton sample (mode length).

12. Quality length: the weighted average length of the part longer than the main body length (the average length of the main body).

13. Upper quartile length: The length at one quarter of the length-weight cumulative distribution.

14. Average Length: Weighted average of fiber lengths.

15. Uniformity: the uniformity of fiber length.

16. Short fiber rate: the percentage of fibers shorter than a specific length. The limit for long-staple cotton is 20 mm, and for fine-staple cotton is 16 mm.

17. Wool fraction: the percentage of lint cotton weight to seed cotton sample weight.

18. Officially defined cloth content rate: the cloth content rate after deducting the water content and impurity content according to national standards.

(II) Terminology of inspection methods:

1. Batch sample: A sample taken from a batch of cotton.

2. Laboratory sample: Derived from batch sample.

3. Test sample: a sample derived from a laboratory.

4. Test sliver: a test strip formed by stretching and combining the slivers through an extender.

5. Test specimen: Cotton sample used for testing.

6. Constant weight: The mass when the difference between two consecutive weighings is less than 0.05% of the latter.

III. Cotton Inspection Items and Methods

1. Classification and inspection:
Long-staple cotton, fine-staple cotton, and coarse-staple cotton can be comprehensively judged by sensory inspection combined with instrumental measurement of length, fineness, strength, micronaire value, and curvature.

2. Classification and inspection of types:
Roller cotton and serrated cotton are identified based on their appearance, defects, and the type and content of impurities.

3. Maturity and color characteristics inspection:

• Maturity: Determined by feel, visual inspection and hand pulling.

• Color characteristics: Based on visual inspection, most of them are white, yellow or gray and are respectively classified as white cotton, yellow cotton or gray cotton.

4. Rolling quality inspection:

• Contents: uniformity and cleanliness of the fiber layer, fiber breakage, short fiber rate, and content of defects (strings, neps, sterile seeds, etc.).

• Method: The manual method is expressed as the number of defective particles per 100 grams of lint; the short fiber rate is tested by instrument.

Short fiber rate test:

• Sampling: Take 1-3 laboratory samples according to the batch size to form a 200-250g test sample in accordance with GB/T6097-2006.

• Inspection: According to GB/T6098.1-2006, the weight is calculated in two groups: 16 mm and below and above.

Defect inspection:
Sampling shall be carried out in accordance with GB/T6097-2006 and inspection shall be carried out in accordance with the manual method of GB/T6103-2006.

5. Clothing content test:

• Sampling: 30 cm deep, multi-point sampling, take 1.5-25 kg in batches, divided into 5-12 samples.

• Trial rolling: After trial rolling, weigh the net weight of the lint (accurate to 1 gram).

• Calculation: Calculate the standard cloth content based on the actual and standard moisture and impurity contents.

6. Moisture regain test:

• Electric measuring instrument method : Use the resistance characteristics of the fiber to measure, take 50±5 grams of sample, and add the temperature correction value to the reading to get the regain.

• Oven method : Take 50 g of sample (accurate to 0.01 g), bake at 105℃±3℃ to constant weight, and calculate the moisture regain.

7. Micronaire test (GB/T6498-2004):

• Principle: The air flow rate or pressure difference through the fiber plug indicates the air permeability.

• Steps: Calibrate the instrument with calibration cotton, load the sample and test, the reading should be accurate to ±1%, if it exceeds the tolerance, retest.