ISO 247-1:2018 download.Rubber-Determination of ash – Part 1 : Combustion method.
1 Scope
ISO 247-1 specifics three methods for the determination of’ ash from raw rubbers, compounded rubbers and vulcanizates. The methods are applicable to raw, compounded or vulcanized rubbers of the M, N. 0. R and U families described in ISO 1629, except that:
— Method A is not used for the determination of ash from compounded or VukafliZed rubbers containing chlorine, bromine or iodine;
— Method B is used or compounded or vulcanized rubbers containing chlorine, bromine or iodine. It shall not he used for uncompounded rubbers;
— Method C is intended to he used for the determination of ash from raw, compounded or vulcanized rubber not containing chlorine, bromine or iodine by wrapping the test forl ion in ishless lilter paper;
— Lithium and fluorine compounds might react with silica crucibles to form volatile compounds. giving low ash results. Platinum crucihles shall therefore be used for ashing fluorine-containing and lithium-polymerized rubbers.
ISO 247-1 oes not cover the interpretation of the ash results as to the inorganic chemical content of’ a compound or vulcanizate. This is the responsibility of’ the analyst, who has to be aware of the behaviour of rubber additives at elevated temperatures.
2 Normative references
The following documents are referred to in the text in such a way that some or all of their content constitutes requirements of ISO 247-1. For dated references, only the edition cited applies. For undated references, the latest edition of the referenced document (including any amendments) applies.
ISO 248-1, Rubber, raw — Determination of volatile-matter content — Part 1: Hot-mill method and Oven tH(’t hod
ISO 1795. Rubbe,; raw ncztural and raw synthetic — Susnplin.ij and further preparative procedures
4 Principle
4.1 Method A
A weighed Lest portion is heated in a crucible over a gas burner. Alter expulsion of the volatile decomposition products, the crucible is transferred to a motile turnace where it is heated until all the carbonaceous matter has been burnt off and constant mass is attained.
4.2 Method B
A weighed test portion is heated in a crucible in the presence of sulfuric acid, first by means of a gas burner and then in a muffle furnace Lilitil all the carbonaceous matter has L)ecn burnt off and constant mass is attained.
4.3 Method C
A weighed test portion is wrapped in ashless filter paper, pre-ignited at 300 °C i 25 °C for 1 h, followed by incineration in a muffle furnace at about 550 °C ± 25 °C for 2 h to 4 h until all the carbonaceous matter has been burnt off and constant mass is attaiilL?d.
4.4 Test results
The three methods of .ishing do not give identical results in all cases, and it is necessary to state in the
test report the method ofashing employed.
5 Reagent
5.1 Sulfuric acid (for method K only), analytical grade,p = 1,84 g/cm3.
6 Apparatus
Ordinary laboratory apparatus, plus the lollowing,
Heat a clean empty crucible .b.1) of appropriate size for about 30 mm in the muffle furnace (4), maintained at 550 °C ± 25 °C, allow to cool to .lnll)idnt temperature in a desiccator and weigh to the nearest 0,1 mg. Take a test portion of about 5 g of raw rubber or I g to 5 g of compounded rubber or vulcanizate, according to the mass of ash to be expected, and weigh to the nearest 0,1 mg Place the weighed test portion in the crucible mounted in the hole in the heat-resistant, thermally insulating hoard (62). I leat the crucible gently with the mimer &3) in a hood for proper ventilation, taking care that the rubber does not ignite. Ii any iiiatcri.il is lost due to spurting or frothing. repeat the above procedure with a new test portion.
When the rubber has decomposed to a charred mass, gradually increase the heat Ironi the burner Lint II the volatile decomposition products have been substantially expel led and a dry carhoiiaceous residue remains. Transfer the crucible and its contents to the muffle furnace, maintained at 550 °C ± 25 °C (for compounds and vulcanizates, a temperature of 950 °C ± 25 °C may be used), leaving the door of the furnace slightly open for I iiiin to provide sufficient air to oxidize the carbon.
t.ont intie heating tint ii (lit’ carbon is completely oxidized and a clean ash is obtained. Remove the crucihle and its contents from the furnace, allow to cool to ambient temperature in the desiccator .ln(l weigh to the nearest 0,1 rng. Then heat the crucible and its contents again for about 30 miii in the muffle furnace, maintained at 550°C ± 25°C (for compounds and vulcanizates, a temperature of 950°C ± 25°C may be used), allow to cool to ambient temperature in tile desiccator and reweigh to the nearest 0.1 mg. This mass shall not (tiller from the previous mass by more than 1 mg in the case of raw rubbers or by more than 1 % relative to the amount of ash for compounds and vulcanizates. If this requirement IS not Itillilled, repeat the heating, cooling and weighing l)rocetiti rt’ tint II the LliflelTflce hetweemi two successive weighing meets this requi remnent.
8.2 Method B
Heat •i clean empty crticible (1) of appropriate size for about 3() mm in the muffle furnace (hA), maintained at UJ5() Cc ± 25 °C, allow to cool to ambient temperature in a desiccator and weigh to the nearest 0,1 111g. Take a test portion nt about I g to S g of the compound or vulcanizate and weigh to the nearest 0,1 nig. Place the test portion in the crucible and pour about 3.5 cm3 of concentrated sulfuric acid (ii) over it so that the rubber is completely wetted. Place the crucible and its contents in the hole in the heat-resistant, thermally insulating board (h2) and heat gently with the burner in a hood for proper ventilation. If, during the initial reaction, the mixture swells excessively, withdraw the flame to avoid possible loss of niateria I.
When the reaction becomes more gentle, increase the heat from the burner until the excess sulfuric acid is volatilized and a dry, carbonaceous residue remi ins. Transfer the crucible and its contents to the I11LIIIIC furnace, maintained at LJ5() °C ± 25 °C. leaving the door of the furnace slightly open for I in in to provide suiricient air to oxidize the carbon and heat br about I Ii until all the carbon is completely oxidized and a clean ash is obtained. Remove the crucible and its contents from the furnace, allow to cool to ambient temperature in a desiccator and weigh to the nearest OJ mg. Then heat thii’ crucible and its contents again for about 30 mm in the muffle furnace, maintai,wd at 950 °C ± 25 ‘C, allow to cool to ambient temperature in the desiccator and re-weigh to the nearest 0,1 mg.
II this mass differs from the previous mass by more than 1 % relative to the amount of ash, repeat the heating. cooling and weighing procedure until the difference between two successive weighing is less than I % relative to the amount of ash.
8.3 Method C
Weigh, to the nearest 0,1 mg, a test portion of 5 g to 10 g of the homogenized rubber. Wrap in ashli’ss filter paper (Ii.S) and place in a crucible (bJ) which has been previously ignited and weighed. Introduce the crucible into a muffle furnace (b.4) at controlled temperature of 300 C ± 25 °C for 1 h pre-ignition followed by inciflerat loll in a muffle furnace at 550 °C ± 25 t for 2 h to 4 Ii until free from carbon. When ashing is completed, allow the crucible to cool in a desiccator and weigh to the nearest 0,1 mg.
This mass shall not differ from the previous iiiass by more than I rug. If this requirdnwnt is not fulfilled, repeat the heating, cooling and weighing procedure until the (litlerence between two successive weighing meets this requl reitwnt.
9 Expression of results
The ash content is given, as a percentage by mass, by Formula (1).