Plastics - Phenolic resins - Determination of hexamethylenetetramine content - Kjeldahl method, perchloric acid method and hydrochloric acid method
1 Scope
This standard specifies three methods for the determination of the hexamethylenetetramine (“hexa”) content of phenolic resins. The three methods are equivalent. The Kjeldahl method described in Clause 3 is not applicable if there are other components containing nitrogen in the phenolic resin. The perchloric acid method and the hydrochloric acid method described in Clause 4 and Clause 5, respectively, are only applicable if there are no other basic or acidic additives in the resin. If the resin contains additives which can be oxidized by perchloric acid, only the hydrochloric acid method (Clause 5) is applicable.
2 Normative references
The following referenced documents are indispensable for the application of this document. For dated references, only the edition cited applies. For undated references, the latest edition of the referenced document (including any amendments) applies.
GB/T 12805 Laboratory glassware - Burettes (GB/T 12805-2011, ISO 385: 2005, NEQ)
3 Kjeldahl method
Warning——For safety reasons, the Kjeldahl determination must be carried out in a well ventilated fume cupboard.
3.1 General
This clause specifies a method for the determination of total nitrogen, expressed as hexamethylenetetramine, in phenolic resins. The method is applicable to phenolic resins with hexamethylenetetramine contents of ≥ 0.5 % (by mass).
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3.2 Principle
The hexamethylenetetramine in a test portion is converted to ammonium bisulfate by decomposition in hot concentrated sulfuric acid in the presence of a catalyst. The ammonium bisulfate is converted to sodium sulfate and ammonia by reaction with sodium hydroxide. The ammonia is distilled off and collected in hydrochloric acid. The excess hydrochloric acid is titrated with a standard volumetric solution of sodium hydroxide using a colorimetric indicator.
3.3 Reagents
