GB/T 2793-1995The method for determination of nonvolatile content of adhesives (English PDF)

4.1 Oven

For samples that may release flammable volatiles, explosion-proof equipment shall be used and operated under effective ventilation.

For test temperatures not exceeding 150°C, the oven shall be maintained within ±2°C of the specified or agreed temperature. For test temperatures exceeding 150°C, the oven shall be

5.1 Pretreatment of test apparatus

5.1.1 After cleaning the flat-bottomed dish, dry it in an oven at 120 °C for 30 min to 60 min.

Remove it and place it in a desiccator to cool to room temperature before weighing. If a lid and/or leveling tool are used, treat them together with the flat-bottomed dish throughout the pretreating, weighing, and heating processes; and include them in the mass.

5.1.2 Record the sum of the mass of the flat-bottomed dish (including the lid if used) and the leveling tool (if applicable) as m0, accurate to 0.1 mg.

5.2 Specimen weighing

5.2.1 The sample shall be placed under standard test conditions, i.e., temperature (23±2) °C and relative humidity (50±5) %, for at least 24 h before sampling.

5.2.2 The standard specimen quantity shall be weighed according to the provisions of Table A.1.

Non-standard specimen quantities may also be used, such as use the agreed specimen quantity or specimen quantity after calculation using a flat-bottomed dish with a non-standard inner diameter.

5.2.3 When sampling single-component samples, ensure that the sample is homogeneous.

5.2.4 For multi-component (including two-component) samples, mix each component sample

thoroughly according to the manufacturer's specified ratio before weighing. To ensure more accurate mixing of the components, it should mix them according to the mass ratio. If it is required to determine the non-volatile content of each component separately, samples shall be taken separately and noted in the report.

5.2.5 For rapidly reacting samples, each component can be accurately weighed separately into the same flat-bottomed dish according to the proportions, and then mixed thoroughly.

5.2.6 If the manufacturer specifies a range of proportions, follow these principles.

a) For reactive components (such as curing agents), use the midpoint of the range;

b) For non-reactive components (such as diluents), use the upper limit of the range.

5.2.7 For volatile samples, the weighing by difference should be adopted.

NOTE. The weighing by difference refers to determining the mass of the sample transferred to the flat- bottomed dish by weighing the difference in mass of the sealable container before and after sampling, thus reducing evaporation losses during the weighing process.

5.2.8 The time from sampling to completion of weighing shall not exceed 5 min. Record the total mass m1 after adding the sample to the flat-bottomed dish, accurate to 0.1 mg.

5.2.9 Spread the sample evenly and thoroughly over the bottom of the flat-bottomed dish.

5.3 Pretreatment before heating

5.3.1 Non-reactive samples do not require pretreatment.

5.3.2 Reactive specimens (such as multi-component, moisture-curing adhesives) require

pretreatment. Pretreatment should involve weighing the sample and placing it in the flat- bottomed dish under standard test conditions (see 5.2.1) for 24 h; the time can be shortened if the pretreatment purpose is met. If the manufacturer specifies otherwise, adjustments can be made accordingly; however, the placement temperature shall not exceed (50±2) °C; and the cumulative pretreatment time shall not exceed 3 d.

NOTE. The purpose of pretreatment is not to remove volatile substances, but to improve the stability of the sample in subsequent processes by allowing partial reaction to occur beforehand. Proper pretreatment can reduce the formation of crusts and boiling over in samples, as well as reduce the evaporation loss of active monomers, which is beneficial for obtaining more realistic test results.

5.4 Heating

5.4.1 Set the oven temperature according to the provisions of Table A.1 or the conditions agreed upon by the relevant parties. Place the weighed sample, along with the flat-bottomed dish, into the preheated oven at the set temperature; and maintain the temperature for the specified or agreed time.

5.4.2 Observe the changes in the appearance of the specimen during heating. For specimens with surface crusting that may affect the results, gently puncture the surface film using a leveling tool. Avoid specimen loss during operation and minimize the time the oven door is opened to reduce temperature fluctuations; and prevent specimen splashing that could cause danger.

5.4.3 If the specimen undergoes violent boiling and results in specimen loss, the test shall be terminated; and the test conditions adjusted before retesting.

5.5 Weighing after heating

After the specified or agreed heating time has been reached, immediately remove the flat- bottomed dish containing the specimen; transfer it to a desiccator to cool to room temperature, and weigh it. Record its mass as m2, accurate to 0.1 mg.