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ISO 249-2014 pdf free download
ISO 249-2014 pdf free download.Rubber, raw natural Determination of dirt content Caoutchouc naturel brut — Determination de Ia teneur en impuretés.
5.3.4 Agitate the flask or beaker occasionally by hand.
Boiling or overheating of the rubber solution can result in the formation of a gel-like substance which renders subsequent filtration difficult and can result in a higher apparent dirt content; hence, avoid apparatus and conditions which can cause local overheating.
5.3.5 When the rubber is completely dissolved (and the solution is adequately mobile), decant the hot solution through the sieve (4.5), which has been weighed to the nearest 0,1 mg, retaining the bulk of the dirt in the flask or beaker.
5.3.6 Wash the flask or beaker and the retained dIrt with hot solvent (11 or 32) until the rubber has been completely removed. Again, retain the bulk of the dirt in the flask or beaker. (About 100 cm3 of hot solvent is normally required for effective washing.) During the later stages of the washing operation, rinse the dirt from the flask or beaker into the sieve. Loosen any dirt adhering to the flask or beaker with a glass rod, so it can be rinsed on to the sieve.
5.3.7 Remove any gelled rubber which will not pass through the sieve by one of the following methods:
a) gently brushing the underside of the gauze with a small sable brush while hot solvent remains in the sieve;
b) standing the sieve in a beaker containing about 10 mm depth of toluene (14) and gently boiling for 1 h, covering the beaker with a clock glass.
These operations should preferably be carried out under a hood.
5.3.8 Wash the sieve twice, either with light petroleum (3), in which case dry at 100 °C for 30 mm, or with white spirit (32), in which case dry at 100 °C for I h.
5.3.9 The dirt on the sieve after drying should be loose and, apart from fibrous matter, be free-flowing. It should be readily dislodgeable from the wire gauze. If this is not so, treat the sieve with boiling toluene as in 5.12 item b.
5.3.10 If gelled rubber still remains, abandon the determination and carry out a repeat determination.
5.3.11 Cool the sieve and residue in a desiccator and weigh to the nearest 0,1 mg.
5.4 Care of sieves
5.4.1 At all stages, handle the sieve carefully.ISO 249-2014 pdf free download.
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