Plastics - Polyether polyols - Part 3: Determination of hydroxyl number
Warning: Persons using this part shall be familiar with normal laboratory practice. This part does not purport to address any of the safety problems, if any, associated with its use. In case of any problems in the application, it is the responsibility of the user of this part to establish appropriate safety and health practices and to ensure compliance with any national administrative regulations.
1 Scope
1.1 This part of GB/T 12008 specifies two methods for determining the hydroxyl number of polyether polyols.
1.2 Method A, the phthalic anhydride method, is recommended for polyether polyols, polymer polyols and amine-initiated polyols, but may give low results for sterically hindered polyols. Other polyols may be analyzed by this method if precautions are taken to verify applicability.
1.3 Method B specifies the determination of hydroxyl number in polyether polyols by near infrared spectroscopy, and describes the steps of sample selection and data acquisition, as well as establishment and verification of calibration model.
2 Normative references
The following normative documents contain provisions which, through reference in this text, constitute provisions of this part of GB/T 12008. For dated references, subsequent amendments (excluding corrections) to, or revisions of, any of these publications do not apply to this part of GB/T 12008. However parties to agreements based on this part of GB/T 12008 are encouraged to investigate the possibility of applying the most recent editions of the normative documents indicated below. For undated references, the latest edition of the normative document referred to applies.
GB/T 601-2002 Chemical reagent - Preparations of reference titration solutions
GB/T 2035-2008 Terms and definitions for plastics (ISO 472: 1999, IDT)
GB/T 6682-2008 Water for analytical laboratory use - Specification and test methods (ISO 3696:1987, MOD)
ASTM D 7253: 2006 Standard test method for polyurethane raw materials: Determination of acidity as acid number for polyether polyols
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3 Terms and definitions
For the purposes of this part, the terms and definitions given in GB/T 2035-2008 and the following apply.
3.1
polyurethane
polymer prepared by the reaction of an organic di- or polyisocyanate with compounds containing two or more hydroxyl groups
3.2
hydroxyl number, hydroxyl value
number of milligrams of potassium hydroxide equivalent to the hydroxyl content of 1g of a sample
4 Method A - phthalic anhydride method
4.1 Principle
Hydroxyl groups in the sample are esterified when refluxing in pyridine solution of phthalic anhydride, the reaction is catalyzed by imidazole. Excess anhydride is hydrolyzed with water, and the resulting phthalic acid is titrated with sodium hydroxide standard volumetric solution. The hydroxyl number is calculated from the difference in titration of the sample and a blank solution.
4.2 Interferences
4.2.1 Excess water will interfere by destroying part of the esterification reagent. If the sample contains more than 0.2% water, dry the sample with a reagent that will not add acidity or basicity to the sample.
4.2.2 Primary/secondary amino group and long-chain fatty acids react with the reagent to form stable compounds that will be included in the results.
4.3 Reagents
Unless otherwise specified, only analytical reagents shall be used and the water used for test shall meet the requirements specified for Grade III water in GB/T 6682-2008.
4.3.1 Imidazole.
4.3.2 Pyridine: with moisture content of less than 0.1%.
4.3.3 Phthalic anhydride acylating reagent: Weigh 116g of phthalic anhydride into a 1-L brown flask, add 700mL of pyridine and shake violently until it dissolves, add 16g of imidazole and shake carefully until it dissolves, and the solution shall be let stand overnight before use. The reagent shall not be exposed to air for a long term to avoid moisture absorption, and it shall be discarded when its color becomes darker. In blank titration, 25mL of this reagent shall consume 95mL~100mL of 0.5mol/L sodium hydroxide standard volumetric solution.
4.3.4 Hydrochloric acid standard volumetric solution c(HCl)=0.1 mol/L: Prepare and standardize according to GB/T 601-2002. This solution is required only if a calibration is to be applied for the presence of strong base in the sample being analyzed.
4.3.5 Sodium hydroxide standard volumetric solution c(NaOH)=0.5 mol/L: Prepare and standardize according to GB/T 601-2002.
4.3.6 Phenolphthanlein indicator solution 10g/L: 1g of phenolphthalein is dissolved in 100mL of pyridine.
4.4 Apparatus
4.4.1 Potentiometric titrator or pH-meter: accurate to 0.1mV or better, equipped with a pair of electrodes or a combination glass-calomel electrode and a piston burette having a 100mL capacity or capability for multiple automatic refilling.
4.4.2 Syringe: 2mL, 5mL and 10mL, with an orifice suitable for handling viscous polyols.
4.4.3 Magnetic stirrer.
4.4.4 Analytical balance: accurate to 0.1mg.
4.4.5 Volumetric pipette: 25mL.
4.4.6 Measuring pipette: 1mL.
Foreword i
1 Scope
2 Normative references
3 Terms and definitions
4 Method A - phthalic anhydride method
5 Method B - Near infrared spectroscopy
Annex A (Informative) Precision determined with phthalic anhydride method
Bibliography
