GB/T 14337-2022Man-made fibre—Test method for tensile properties of staple fibre (English PDF)

5.1 Constant elongation single fibre extensometer (CRE)

5.1.1 The extensometer shall be equipped with the following devices:

a) A device capable of indicating or recording the tension applied to the specimen and the corresponding elongation value;

b) A device that can make a stretching curve or a data acquisition system;

c) A gripper suitable for holding individual fibres at the desired nominal gauge length;

d) A device for changing different stretching speeds;

e) A device for precise calibration of the instrument.

5.1.2 The instrument shall meet the following technical requirements:

a) The indication error of applied force shall not exceed 1%;

b) The indication error of elongation does not exceed 0.1mm;

c) The error of clamping length does not exceed 0.2mm;

d) The instrument shall maintain constant elongation. 1s after the force tester is started, the difference between the speed of the lower gripper and the specified speed shall not exceed 5%;

e) The gripper shall have adjustment device. It can give the fibre proper clamping force when clamping the fibre, so as to prevent the fibre from slipping or crushing.

The surface of the gripper jaws in contact with the specimen may have a lining.

Minimize slippage or damage to the specimen within the gripping area;

f) Adjustable automatic grippers shall be used during arbitration;

g) The mass error of the pretension clamp does not exceed 10% of the nominal value.

5.2 Other test tools and materials

5.2.1 Tweezer, fleece board, brush, stopwatch.

5.2.2 Water container, for immersing the specimen in water.

5.2.3 The laboratory water is in accordance with grade three water of GB/T 6682. The temperature is (20 ± 2)°C.

5.2.4 Nonionic surfactants.

6.1 Sampling

Sampling regulations are as follows:

- Take loose laboratory samples as needed. The minimum shall not be less than 10g;

- The extraction of laboratory samples in batch samples shall be in accordance with the provisions of GB/T 14334.

Do not extract the packages that have been accidentally dampened, contaminated, scratched, or packaged open during transportation.

6.2 Preconditioning, standard atmosphere for humidity conditioning and testing, humidity-conditioning time

6.2.1 Preconditioning

Preconditioning is required when the sample meets one of the following conditions:

- The moisture regain of the specimen exceeds the official moisture regain;

- The sample is in an atmosphere with a relative humidity higher than the upper limit of the laboratory relative humidity;

- The sample temperature is 5°C lower than the laboratory temperature.

The preconditioning conditions are that the temperature does not exceed 50°C, the relative humidity is 10%~25%, and it is placed for at least 30min. The official moisture regain is specified in GB/T 9994.

6.2.2 Standard atmosphere for humidity conditioning and testing

For staple fibre with a conventional moisture regain less than 4.5%: the temperature is (20±2)°C, the relative humidity is (65±5)%.

For staple fibre with a conventional moisture regain greater than or equal to 4.5%: the temperature is (20±2)°C, the relative humidity is (65±3)%.

6.2.3 Humidity-conditioning time

The humidity-conditioning time is according to Table 1. If the staple fibres are pre- conditioned, the humidity-conditioning time shall be subject to the upper limit. It can also be weighed every 30min until constant weight.

7.1 Determination of linear density

According to the provisions of GB/T 14335, determine the average linear density of the same laboratory sample or the single fibre linear density of a single specimen.

7.2 Dry state test

7.2.1 Use tweezers to randomly remove a fibre from the conditioned sample. One end of the fibre is clamped with a tension clamp according to the pretension value in 6.3.1 (when holding the fibre with tweezers and tension clamps, do not touch the test part of the fibre, and avoid accidental stretching or damage to the fibre). Place the fibre in the upper holder of the instrument. Ensures fibre elongation in the axial direction. Then close the lower gripper for the tensile test.

7.2.2 When the specimen is tested, the number of fibre breaks in the jaws (the broken end cannot be seen when the fibre breaks) or in the gripping head shall not exceed 10% of the number of test pieces. If it exceeds, check whether the gripper is abnormal. Repair or replace it. Re-test. If it does not exceed 10%, the results obtained from specimens with fibres breaking in the jaws or slipping in the gripping head are rejected.

7.3 Wet state test

7.3.1 Samples do not need to be conditioned. Remove a random fibre from the sample with tweezers. Immerse it in the grade 3 water that is in accordance with GB/T 6682 at a temperature of (20±2)°C. Add non-ionic surfactants up to a maximum concentration of 0.1% in water. Submerge the entire specimen. Immersion lasts for 2min.

7.3.2 Remove fibres with tweezers. One end of the fibre is clamped with a tension clamp according to the pretension value in 6.3.1 (when holding the fibre with tweezers and tension clamps, do not touch the test part of the fibre, and avoid accidental stretching or damage to the fibre). Place the fibre in the upper holder of the instrument. Ensure fibre elongation in the axial direction. Wet the specimen again for 10s. Remove the water glass. Then close the lower gripper. Push on the water glass to allow the fibre to be submerged for tensile testing (when the fibre is immersed, the water level shall not be in contact with the upper gripper, but the distance from the lower end face of the upper gripper shall not be greater than 1mm).

7.3.3 If the specimen is abnormally fractured, it shall be handled in accordance with the provisions of 7.2.2.

7.4 Determination of hook breaking force

The modulus is calculated according to formula (4):

Where, CMi - The single fibre modulus, in centi-Newton per decitex (cN/dtex);

deltasigmadi - The increment of the stress of a single fibre, that is, the increment of the breaking strength, in centi-Newton per decitex (cN/dtex);

deltaepsilondi - The increment of the strain of a single fibre, that is, the increment of the ratio of the elongation at break to the spacing length.

When calculating the wet modulus, the usual stress increment deltasigmad is the breaking strength at a fixed elongation. Use 5% for viscose. The increment of strain deltaepsilond is the corresponding elongation at break.

NOTE: The wet modulus can also be directly expressed by the constant elongation strength.

However, it is necessary to specify the value of the constant elongation, such as: expressed as 0.62 cN/dtex/5%.

8.4 Initial modulus

Near the origin of the stretch curve, take the maximum point of change in force with elongation. Find the slope of the tangent at this point, that is, the ratio of the difference between the force and the elongation at any two points on the tangent. The initial modulus is calculated according to formula (5):

Where, - The initial modulus of a single fibre, in centi-Newton per decitex (cN/dtex); ki - The slope of the tangent line of the maximum point of the change of force with the change of elongation on the tensile curve of a single fibre, in centi-Newton (cN);

rholi - The average linear density or the linear density of a single fibre measured in the same laboratory sample, in decitex (dtex).

8.5 Result expression

All test results are expressed as the arithmetic mean of valid test values.

8.6 Calculation of statistical values

The arithmetic mean, standard deviation, coefficient of variation and other statistical values are calculated according to Annex B.

8.7 Numerical rounding

Breaking force, breaking strength, constant elongation, modulus and initial modulus are rounded to two decimal places.

Elongation at break and coefficient of variation are rounded to one decimal place.