GB/T 38138-2019Test methods of fiber grade polycaprolactam (PA6) chip (English PDF)

3.1 Bright polycaprolactam chip

Polycaprolactam chip with a titanium dioxide content (mass fraction) of less than or equal to 0.05%.

3.2 Semi-dull polycaprolactam chip

Polycaprolactam chip with a titanium dioxide content (mass fraction) greater than 0.10% and less than or equal to 0.60%.

3.3 Full-dull polycaprolactam chip

Polycaprolactam chip with a titanium dioxide content (mass fraction) greater than or equal to 1.20%.

3.4 Irregular chip

Polycaprolactam chip that is 4 times or more longer than normal chip in length, 2 times or more larger than normal chip in thickness, width or diameter, 1/4 smaller than standard particle (or a specified size), and of irregular shape.

4.1 Sampling

Perform according to GB/T 6678, with a sample quantity of not less than 0.5 kg.

4.2 Reagents or materials

Unless otherwise specified, the reagents and water used in this Standard shall be analytical reagents and grade-III water as specified in GB/T 6682.

Unless otherwise specified, all solutions used in this Standard shall be expressed as the mass fraction, except for ethanol (95%), which shall be expressed as a volume fraction.

Unless otherwise specified, the standard titration solutions, preparations and products used in this Standard shall be prepared in accordance with the provisions of GB/T 601 and GB/T 603.

5.1 Moisture content

5.1.1 Method A (Karl Fischer volumetric method)

5.1.1.1 Principle

Heat the sample under specific conditions, and the water vapor that evaporates is carried by dry nitrogen gas into a titration cup containing equilibrated anhydrous methanol for absorption. Use a Karl Fischer moisture analyzer to determine the moisture content.

5.1.1.2 Instruments and apparatuses

5.1.1.2.1 Karl Fischer moisture analyzer. including control unit, titration cup, sample bottle or sample boat, capable of measuring samples with a moisture content of 0.01% ~ 100%.

5.1.1.2.2 Balance. minimum division value, 0.1 mg.

5.1.1.2.3 Drying oven. including heating unit capable of heating to at least 250 °C, temperature control unit, gas flow meter, and gas drying tube containing desiccant, etc. It is recommended to control the temperature at (175±5) °C and set the nitrogen flow rate to 50 mL/min.

5.1.1.2.4 Micro-syringe. 10 µL.

5.1.1.3 Reagents or materials

5.1.1.3.1 Anhydrous methanol.

5.1.1.3.2 Karl Fischer reagent (K·F reagent).

5.1.1.3.3 Nitrogen. purity, 99.99%.

5.1.1.4 Test procedure

5.1.1.4.1 Water titration F of K·F reagent

Use a micro-syringe (see 5.1.1.2.4) to draw 10 µL of water and inject it into a titration cup (see 5.1.1.2.1) containing 40 mL of equilibrated anhydrous methanol (see 5.1.1.3.1); determine the mass of the water injected into the titration cup based on the mass difference before and after the micro-syringe draws water; weigh it to an accuracy of […]

5.2 Relative viscosity

5.2.6.2 Reproducibility

For the absolute difference between two independent test results obtained under reproducibility conditions, when the relative viscosity is 2.42 ~ 2.49, the absolute difference between the two test results shall not exceed the reproducibility limit of 0.051, and the number of cases exceeding the reproducibility limit of 0.051 shall not exceed 5%.

5.3 Content of hot water extractables

5.3.1 Method A (Gravimetric method)

5.3.1.1 Principle

Extract the sample in hot water at >=97 °C. Calculate the content of hot water extractables by the mass difference of the sample before and after extraction.

5.3.1.2 Instruments and apparatuses

5.3.1.2.1 Balance. minimum division value, 0.1 mg.

5.3.1.2.2 Oven. capable of maintaining the temperature at (120±2) °C.

5.3.1.2.3 Constant temperature water bath. capable of maintaining the temperature at 97 °C ~ 100 °C, with an inlet and an outlet, and capable of controlling the inlet and outlet water rates at 250 mL/min.

5.3.1.2.4 Covered stainless steel perforated cylinder.

5.3.1.2.5 Dryer. equipped with allochroic silicagel.

5.3.1.3 Test procedure

5.3.1.3.1 Measure the moisture content W of the sample according to 5.1.

5.3.1.3.2 Place the covered stainless steel perforated cylinder (see 5.3.1.2.4) into an oven (see 5.3.1.2.2) at (120±2) °C and dry it to constant weight (start weighing after drying for 2 h, weigh once every 10 minutes, and the difference between two consecutive weighings shall not exceed 0.05% of the last weighing). Then transfer it to a dryer to cool to room temperature for 30 min ~ 45 min; weigh it, to an accuracy of 0.1 mg.

5.3.1.3.3 Weigh approximately 20 g of the sample, to an accuracy of 0.1 mg; place it in a cylindrical container; seal the container; place it in a constant temperature water bath at >=97 °C (see 5.3.1.2.3) to extract for 8 h. Water shall flow through the water bath at a rate of 250 mL/min.

5.3.1.3.4 After extraction, remove the covered cylinder; when there are no water droplets at the bottom, dry it in an oven at (120±2) °C to constant weight (start weighing 5.5.2.2.3 Magnetic stirring device with heating. temperature control accuracy, (65±2) °C.

5.5 Amino content

5.5.2 Method B (Polypotential titration - m-cresol-isopropanol system)

5.5.2.2.4 Stoppered conical flask. 150 mL

5.5.2.2.5 Volumetric flask. 1 000 mL

5.5.2.2.6 Single-mark pipette. 100 mL

5.5.2.2.7 Graduated cylinder. 100 mL

5.5.2.3 Reagents or materials

5.5.2.3.1 m-cresol.

5.5.2.3.2 Isopropanol.

5.5.2.3.3 Ethanol (95%).

5.5.2.3.4 Hydrochloric acid.

5.5.2.3.5 m-cresol-isopropanol mixture. mass ratio, 2.1.

5.5.2.3.6 Hydrochloric acid-ethanol standard titration solution (0.5 mol/L). Prepare and calibrate according to GB/T 601; for the calibration method, potentiometric titration is recommended.

5.5.2.3.7 Hydrochloric acid-ethanol standard titration solution (0.05 mol/L). Transfer 100 mL of 0.5 mol/L hydrochloric acid-ethanol standard titration solution and use ethanol (95%) to dilute it to 1 000 mL.

5.5.2.4 Test procedure

5.5.2.4.1 Weigh 0.8 g of the sample, to an accuracy of 0.1 mg; place it in a 150 mL conical flask (see 5.5.2.2.4); add 80 mL of m-cresol-isopropanol mixture (see 5.5.2.3.5).

5.5.2.4.2 Heat the sample under reflux on a magnetic stirring device (see 5.5.2.2.3) with the temperature adjusted to (65±2) °C until it is completely dissolved; then cool it to room temperature.

5.5.2.4.3 Perform potentiometric titration using hydrochloric acid-ethanol standard titration solution (see 5.5.2.3.7). Do a blank test at the same time.

5.5.2.5 Result calculation

Calculate the amino content of the sample according to Formula (10). Where.

X3 - amino content of the sample, in millimoles per kilogram (mmol/kg);

V3 - the volume of hydrochloric acid-ethanol standard titration solution consumed by the sample, in milliliters (mL);

V2 - the volume of hydrochloric acid-ethanol standard titration solution consumed in the blank test, in milliliters (mL); c(HCl) - concentration of the hydrochloric acid-ethanol standard titration solution, in moles per liter (mol/L); m - mass of the sample, in grams (g).

Express the calculation results as the average of the test results of two parallel samples, and round it to one decimal place in accordance with GB/T 8170.

5.5.2.6 Precision

For the absolute difference between two independent determination results obtained under repeatability conditions, when the amino content is 46.2mmol/kg ~ 48.9mmol/kg, the absolute difference between the two test results shall not exceed the repeatability limit of 1.75mmol/kg, and the number of cases exceeding the repeatability limit of 1.75mmol/kg shall not exceed 5%.

5.6 Carboxyl content

5.6.1 Method A (Potentiometric titration)

5.6.1.1 Principle

In the sample solution where the amino content titration (see 5.5.1) is completed, use potassium hydroxide-ethanol standard titration solution to neutralize the excess hydrochloric acid; further titrate the carboxyl content. Calculate the carboxyl content based on the volume of standard titration solution consumed. […]

5.6.1.2 Instruments and apparatuses

5.6.1.2.1 Automatic potentiometric titration apparatus.

5.6.1.2.2 Volumetric flask. 500 mL.

5.6.1.2.3 Single-mark pipette. 100 mL.

5.6.1.3 Reagents or materials

5.6.1.3.1 Potassium hydroxide.