BS EN ISO 2554:1999. Plastics – Unsaturated polyester resins – Determination of hydroxyl value.
BS EN ISO 2554 specifies a method for determining the hydroxyl value of unsaturated polyester resins.
In fact, this method determines the difference between the hydroxyl value and t.he acid value; it is therefore necessary t.o determine the total acid value separately, in order to calculate the hydroxyl value.
NOTE 1 The hydroxyl value of saturated polyester resins (for example, polyester resin used for the manufacture of polyurethanes and polymeric plasticizers) and of certain types of alkyd resins may also be determined by this method.
3 Definitions
For the purposes of this international Standard, the following definitions apply:
3.1
hydroxyl value
the number of milligrams of potassium hydroxide necessary to neutralize the acetic acid which will combine, by acetylation, with 1 g of an unsaturated polyester resin
3.2
acid value
the number of milligrams of potassium hydroxide required to neutralize 1 g of a test sample under the test conditions
4 Principle
The hydroxyl groups in the resin are acetylated by reacting an ethyl acetate solution of the resin with acetic anhydride in the presence of toluene-4-sulfonic acid catalyst. The excess acetic anhydride is hydrolysed by a pyridine/water mixture and the resultant acetic acid is titrated with methanolic potassium hydroxide solution. In this titration, the free acid and free anhydride groups which exist in the resin are also neutralized by the potassium hydroxide.
The hydroxyl value is finally calculated by taking into account the total acid value determined separately by ISO 2114.
5 Reagents
During the analysis, use only reagents of recognized analytical grade and water of grade 3 purity as defined in Iso 3696.
5.1 Acetic anhydride acetylating solution, approximately l moIIl, in ethyl acetate.
Dissolve 1,4 g of pure, dry toluene-4-sulfonic acid in 111 ml of anhydrous ethyl acetate. When completely dissolved, slowly add, while mixing, 12 ml of freshly distilled acetic anhydride. Store in a dry atmosphere.
5.2 Ethyl acetate, anhydrous.BS EN ISO 2554 pdf download.