Scope:

This document specifies two methods for the determination of ash from raw rubbers, compounded rubbers and vulcanizates using a thermogravimetric analyser (TGA). The methods are applicable to raw, compounded or vulcanized rubbers of the M, O, R and U families described in ISO 1629:

— Method A is applicable for the determination of the ash from raw rubbers.

— Method B is applicable for the determination of the ash from compounded or vulcanized rubbers.

The methods are not applicable for the determination of the ash from raw rubbers, compounded or vulcanized rubbers containing chlorine, bromine or iodine.

This document does not cover the interpretation of the ash results from the inorganic chemical contents of compounded or vulcanized rubbers.

Principle: 

A weighed test portion is heated in an atmosphere of nitrogen. After complete decomposition of the polymer, the atmosphere is switched from nitrogen to oxygen or air and the test portion is further heated until all the carbonaceous matter has been burnt off and a constant mass is reached. The mass of the residue represents the ash.

Reagents:

5.1 Dry nitrogen, purity ≥ 99,99 %.

5.2 Dry oxygen, purity ≥ 99,99 %, or air.

Apparatus:

1. Thermogravimetric analyser, comprising the following elements:

a) Thermo-balance;

b) Heating furnace;

c) Temperature programmer;

d) Gas flow controller, for controlling the purge gas to the balance and furnace, and keeping a constant flow rate.

2. Sample pan, platinum pan or alumina ceramic pan.

3. Analytical balance, capable of weighing to the nearest 0,1 mg.

Preparation of the test sample:

1. For raw natural rubber, test samples shall be cut from the homogenized piece prepared in accordance with ISO 1795. For raw synthetic rubber, test samples shall be cut from the dried rubber obtained after carrying out the determination of volatile-matter content in accordance with the hot-mill method of ISO 248-1.

Take a test portion of about 2 g to 5 g from the homogenized sample and cut into pieces by hand.

2. Test samples of rubber compounds shall be sheeted on a mill and cut into pieces by hand.

3. Test samples of vulcanizates shall be sheeted or crumbed on a mill or comminuted by hand.

4. Care shall be taken to ensure that test samples of rubber compounds and vulcanizates are representative of the sample.

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