GB/T 12008.3-2026Plastics—Polyether polyols for use in the production of polyurethane—Part 3:Determination of hydroxyl number (English PDF)

1.2 Method A is phthalic anhydride method. It is recommended for polyether

polyols, polymer polyols and polyols with ammonia as initiator. But for polyols with steric hindrance, the result shall be lower. If corrective measures can be taken, other polyols can also apply this method.

1.3 Method B specifies the determination of hydroxyl value in polyether polyols

by near infrared spectroscopy. It describes the steps of sample selection, data collection, establishment and verification of calibration models.

3.1 Polyurethane

a polymer made by reacting organic diisocyanates or polyisocyanates with compounds containing two or more hydroxyl groups

4.1 Principle

The hydroxyl groups in the sample are esterified by refluxing in the pyridine solution of phthalic anhydride.

4.2 Interference

4.2.1 Excessive water shall destroy the esterification reagent and interfere with the determination. If the moisture content of the sample is greater than 0.2%, use a reagent that shall not introduce acid or alkali into the sample to dry.

4.2.2 Primary, secondary amino and long-chain fatty acids react with reagents

to form stable compounds, which shall be included in the results.

4.3 Reagents

Unless otherwise stated, only use analytical reagents. The test water shall conform to grade three water specification in GB/T 6682-2008.

4.3.1 Imidazole.

4.4 Instruments

4.4.1 Potentiometer or pH meter. the accuracy is not less than 0.1mV, equipped

with a pair of electrodes or glass-calomel composite electrodes, a burette with a capacity of 100mL or a burette that can be automatically backfilled.

4.4.2 Syringe. 2mL, 5mL and 10mL, with a hole suitable for processing viscous

polyols.

4.4.3 Magnetic stirrer

4.4.10 Erlenmeyer flask. 300mL, standard 24/40 ground mouth.

4.4.11 Air condenser. 400mm, standard 24/40 ground.

4.4.12 Oil bath. keep the temperature at (115±2)°C.

4.5 Steps

4.5.2 Accurately pipette 25mL of phthalic anhydride acylation reagent (4.3.3)

into each test material and blank Erlenmeyer flask. Shake the flask until the test material dissolves. Each Erlenmeyer flask is connected to an air condenser (4.4.11). Put it in the (115±2)°C oil-bath (4.4.12) for 30min.

4.5.3 After heating, take the device out of the oil bath and cool to room

temperature. Use 30mL of pyridine (4.3.2) to rinse the condenser and remove the condenser tube. Quantitatively transfer the solution to a 250mL beaker (4.4.8). Use 20mL of pyridine to rinse the Erlenmeyer flask.

4.5.4 Titrate the solution in one of the following methods.

4.5.5 Measure the acid value C according to ASTM D7253:2006.If the solution

for determining the acid value is pink, follow the steps below to determine the base value L.

4.6 Result calculation and expression

4.6.1 Hydroxyl value OHV, in milligrams of potassium hydroxide consumed per gram of sample, is calculated according to formula (2).

4.7 Precision

See Annex A for precision data.

4.8 Test report

The test report shall contain the following.

5.1 Principle

Near-infrared spectroscopy is mainly generated when the molecular vibration transitions from the ground state to the higher energy level due to the non-resonance of the molecular vibration.

5.2 Instruments

5.2.1 Near-infrared hydroxyl value analyzer and supporting software.

5.2.2 Constant temperature unit.

5.2.3 Sample pool.

5.3 Application

5.3.1 General rules for use

5.3.2 Limitation

5.3.2.1 Before calibration, first determine the influencing factors of the near-

infrared spectrum of the analyzed polyol. In order to properly select the sample, it is necessary to understand the chemical structure, interference, any non-linear relationships, the influence of temperature, and the interaction of the analyte with other components such as catalysts, moisture and other polyols, so as to simulate these uncontrollable factors.

5.4 Selection of calibration samples

5.4.1 The samples of the calibration set shall be selected according to the following guidelines as far as possible.

5.4.1.1 Sample selection includes all components expected to appear in the sample of interest.

5.5 Steps

5.5.1 Data collection

5.5.1.1 Chemical method data collection

Measure the hydroxyl value of the polyether polyol sample according to Method A of this Part and use it as raw data for backup.

5.5.2 Spectrum collection

5.5.3 Model establishment

Build a model according to the operating requirements of the instrument manual.

Optimize the variables in the model. In the process of model calibration, use mathematical and statistical methods to identify outliers. And remove all outliers before the model is finalized. Correct the model.

5.5.4 Model verification

Model verification is done by predicting the concentration of the analyte in the independent sample set and the known analyte concentration, and statistically analyzing the response of the model. Select the validation set samples according to the same conditions as the calibration set samples. In addition, the following conditions must be observed.

5.5.5 Conversion of calibration model

5.5.5.1 The conversion of the calibration model involves the steps of establishing the calibration model. It refers to the process of using the data obtained from the near-infrared hydroxyl value analyzer for spectral data collection and analysis.

5.5.5.2 When establishing a calibration model conversion, it is necessary to demonstrate it to ensure that the performance of the model does not degrade during the conversion process. Each calibration conversion step at least uses a converted model to conduct a complete verification.

5.6 Result expression

Conduct parallel determination of the same sample. Report results in arithmetic average, to the nearest of 0.1.

5.7 Test report

The test report shall contain the following.