ISO-249-1995.pdf

INTERNATIONAL STANDARD IS0 249 Third edition 1995-l 2-15 Rubber, raw natural - Determination of dirt content Caoutchouc nature/ brut - Dgtermination de la teneur en impwet or beaker, of capacity 250 cm3 or 500 cm3, and a clockglass of appropriate diameter as cover. 4.2 Short air condenser (optional). 4.3 Thermometer, reading to at least 200 “C. 4.4 Heater, for heating the conical flask or beaker (4.1) and its contents (see the note to 5.3.4). Hotplates which provide uniform heating surfaces, or infra-red lamps, are recommended. Infra-red lamps (250 W) can be placed in rows, with the base of the conical flask about 20 cm from the top of the lamp. Individual control of each lamp is recommended to prevent localized overheating. Alternatively, a sand- bath may be used. 4.5 Sieve, of nominal size of openings 45 pm, of corrosion-resistant wire gauze, preferably stainless steel, complying with IS0 565. 4.5.1 The wire gauze shall be mounted across the end of a metal tube about 25 mm in diameter and greater than 20 mm long. 4.5.2 The sieve shall be constructed in such a way that the gauze is free from distortion and is protected from accidental damage. A suitable construction is shown in figure 1. 4.5.3 Sieves and holders may also be constructed by removing the bottom of a metal crucible having the appropriate dimensions, and soldering the screen to the crucible. This results in an ample container for the rubber solution during filtering. 4.5.4 A coarse screen may also be soldered under the 45 pm gauze to protect it from accidental damage. This “guard” screen shall not hinder the filtration in any way but only provide a support for the gauze. 4.5.5 Commercially available filtration apparatus (having 45 pm gauze) is acceptable, provided it can be used as specified in this International Standard. 4.6 Ultrasonic equipment, for cleaning sieves (op- tional but desirable). 5.1.1 Prepare a homogenized laboratory sample of raw natural rubber in accordance with IS0 1795. From the homogenized laboratory sample take about 30 g, and pass it twice between the cold rolls of a labora- tory mill, the nip being adjusted to 0.5 mm * 0,l mm by means of a lead strip (see IS0 2393). 5.1.2 Immediately weigh a test portion of 10 g to 20 g to the nearest 0,l g. (For “clean” rubbers of low dirt content, a 20 g test portion is recommended. For heavily contaminated rubbers, a smaller test portion should be used.) 5.1.3 Carry out the determination in duplicate. 5.2 Preparation of the peptizer 5.2.1 If xylyl mercaptan (3.5.1) is used, use 1 g of the solution per test portion and 150 cm3 to 230 cm3 of solvent (3.1 or 3.2). 5.2.2 If 2-mercaptobenzothiazole (3.5.2) or di-(2- benzamidophenyl) disulfide (3.5.3) is used, use 0,5 g per test portion. Prepare a solution by dissolving 0,5 g of solid in 200 cm3 of solvent (3.1 or 3.2) and filtering off any insoluble material. 5.2.3 If tolyl mercaptan (3.5.4) is used, use 1 g to 1,5 g of the solution per test portion and 200 cm3 of solvent (3.1 or 3.2). 5.3 Determination 5.3.1 To the conical flask or the beaker (4.1) add solvent and peptizer according to 5.2.1, 5.22 or 5.2.3. 5.3.2 Cut the test portion into pieces each about 1 g and drop each piece, separately, flask or beaker containing solvent (5.3.1). of mass into the 5.3.3 Heat the flask or beaker and its contents (see 4.41 at 125 “C to 130 “C until a smooth solution is obtained, or stopper the flask or cover the beaker with a clockglass and stand for several hours at room temperature before heating to 125 “C to 130 “C. A short air condenser (4.2) may be used during the heating, to reduce evaporation of the solvent. 2 Copyright International Organization for Standardization Provided by IHS under license with ISO Licensee=NASA Technical Standards 1/9972545001 Not for Resale, 04/25/2007 01:32:54 MDTNo reproduction or networking permitted without license from IHS -,-,- IS0 249:1995(E) Braze on outside d 39.7 Dimensions in millimetres 31.8 N Pi , l- 2994 SO.0 Sieve holder for inspection of sieve 1 Sieve: Stainless steel sieve ring with wire gauze soldered on to it. Arecesslmmaroundtheinneredgeofthetopandtheouteredgeofthelower end is allowed for easy stacking of the sieves. 2 Sieve holder: Stainless steel or brass cylinder of dimensions: 30 mm external diameter, 2 mm to 3 mm wall thickness ond 13 mm height. Figure 1 - Details of suitable sieve and holder for dirt determination 3 Copyright International Organization for Standardization Provided by IHS under license with ISO Licensee=NASA Technical Standards 1/9972545001 Not for Resale, 04/25/2007 01:32:54 MDTNo reproduction or networking permitted without license from IHS -,-,- IS0 249:1995(E) Q IS0 5.3.4 Agitate the flask or beaker occasionally by hand. 5.4 Care of sieves Boiling or overheating of the rubber solution may re- sult in the formation of a gel-like substance which renders subsequent filtration difficult and may result in a higher apparent dirt content; hence avoid appar- atus and conditions which can cause local overheat- ing. 5.4.1 At all stages, handle the sieve carefully. In- spect it after each determination to check for damage, for example under a microscope or with a slide pro- jector (to throw an image of the gauze on a screen). If noticeable distortion of the wire gauze has occurred, replace it by a new gauze. 5.3.5 When the rubber is completely dissolved (and the solution is adequately mobile), decant the hot solution through the sieve (4.51, which has been weighed to the nearest 0,l 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 (3.1 or 3.2) 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. 5.4.2 After each determination, remove loose dirt by careful brushing. Partially blocked sieves can usually be cleaned by boiling in xylene, but more effectively with ultrasonic equipment (4.6). If, in spite of this treatment, the gauze is badly blocked and the mass of the sieve has increased more than 1 mg, replace the wire gauze. 5.4.3 Sieves may be stored in warm toluene to lessen build-up of rubber. 6 Expression of results The dirt content, expressed as a percentage by mass, of the test portion is given by the formula 5.3.7 Remove any gelled rubber which will not pass through the sieve by one of the following methods: $4 100 where a) gently brushing the underside of the gauze with a small sable brush while hot solvent remains in m, is the mass, in grams, of the test portion; the sieve; ml is the mass, in grams, of the dirt. b) standing the sieve in a beaker containing about 10 mm depth of toluene (3.4) and gently boiling for 1 h, covering the beaker with a clockglass. Express the result to the nearest 0,Ol %. 7 Precision These operations should preferably be carried out un- der a hood. 5.3.8 Wash the sieve twice, either with light petro- leum (3.31, in which case dry at 100 “C for 30 min, or with white spirit (3.2), in which case dry at 100 “C for 1 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 5.3.7 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,l mg. 7.1 General The precision calculations to express repeatability and reproducibility were performed in accordance with ISO/TR 9272. Consult this Technical Report for pre- cision concepts and nomenclature. Annex A of this International Standard gives guidance on the use of repeatability and reproducibility. 7.2 Precision details 7.2.1 An interlaboratory test programme was organ- ized in late 1984 by the Rubber Research Institute of Malaysia. Two separate programmes were con- ducted, one in March and one in July. Two types of material were sent to each laboratory: a) blended samples of two rubbers “A” and “B”; 4 Copyright International Organization for Standardization Provided by IHS under license with ISO Licensee=NASA Technical Standards 1/9972545001 Not for Resale, 04/25/2007 01:32:54 MDTNo reproduction or networking permitted without license from IHS -,-,- 0 IS0 Is0 249:1995(E) b) unblended (normal) samples of the same two 8 Test report materials “A” and “B”. The test report shall contain the following information: 7.2.2 For both the blended and the unblended sam- ples, a test result was taken as the mean of five separate determinations. a) a reference to this International Standard; 7.2.3 A “type 1” precision was measured in the interlaboratory test programme. The time period for repeatability and reproducibility was on a scale of days. A total of 14 laboratories participated in the programme for blended samples and a total of 13 laboratories in the programme for unblended samples. b) all details necessary for the identification of the sample; c) the mean of the two results; d) the solvent and peptizer used; e) any particular points observed in the course of the test; 7.3 Precision results The precision results for the blended-sample pro- gramme are given in table 1 and the results for the unblended-sample programme in table 2. f) any operation not specified in this International Standard or in the International Standards to which reference is made, and any operation re- garded as optional. Table 1 - Type 1 precision - Blended-sample testing Average dirt Rubber sample content Within-laboratory repeatability Interlaboratory reproducibility % (m/m) r (4 R (R) A 0,ll 0.018 5 16.4 0,031 27.0 B 0,16 0,038 5 24.4 0,065 40.9 Pooled values 0,14 0,031 22,4 0,051 37,l r = repeatability, in percent by mass (r) = repeatability, in percent (relative) of the average R = reproducibility, in percent by mass (R) = reproducibility, in percent (relative) of the average , Table 2 - Type 1 precision - Unblended-sample testing Average dirt Rubber sample content Within-laboratory repeatability Interlaboratory reproducibility % (m/m) r (4 R (RI A 0,04 0,013 31.5 0,035 86.2 B 0.04 0,017 39,3 0,029 67.7 Pooled values 0.04 0,015 35,6 0,032 77.1 See table 1 for symbol definitions. Copyright International Organization for Standardization Provided by IHS under license with ISO Licensee=NASA Technical Standards 1/9972545001 Not for Resale, 04/25/2007 01:32:54 MDTNo reproduction or networking permitted without license from IHS -,-,- iSO 249:1995(E) Annex A (informative) Guidance for using precision results A.1 The general procedure for using precision re- sults is as follows, with the symbol IX, - +I desig- nating a positive difference in any two measurement values (i.e. without regard to sign). A.2 Enter the appropriate precision table (for what- ever test parameter is being considered) at an average value (of the measured parameter) nearest to the “test” data average under consideration. This line will give the applicable r, (r), R or (R) for use in the de- cision process. A.3 With these r and (r) values, the following gen- eral repeatability statements may be used to make decisions. A.3.1 For an absolute difference: The difference IX, -+I between two test (value) averages, found on nominally identical material samples under normal and correct operation of the test procedure, will exceed the tabulated repeatability I on average not more than once in 20 cases. A.3.2 For a percentage difference between two test (value) averages: The percentage difference I? - %d/(+ + x2)/2 x 100 between two test values, found on nominally identical material samples under normal and correct operation of the test procedure, will exceed the tabulated re- peatability (I) on average not more than once in 20 cases. A.4 With these R and (R) values, the following general reproducibility statements may be used to make decisions. A.4.1 For an absolute difference: The absolute difference Ix, - XJ between two independently measured test (value) averages, found in two labora- tories using normal and correct test procedures on nominally identical material samples, will exceed the tabulated reproducibility R not more than once in 20 cases. A.4.2 For a percentage difference between two test (value) averages: The percentage difference I? - xzll (x, + x2)/21 x 100 between two independently measured test (value) averages, found in two laboratories using normal and correct test procedures on nominally identical material samples, will exceed the tabulated reproducibility (R) not more than once in 20 cases. Copyright International Organization for Standardization Provided by IHS under license with ISO Licensee=NASA Technical Standards 1/9972545001 Not for Resale, 04/25/2007 01:32:54 MDTNo reproduction or networking permitted without license from IHS -,-,- IS0 249:1995(E) ICS 83.040.10 Descriptors: rubber, natural rubber, crude rubber, tests, determination of content, impurities, sieve analysis, Price based on 6 pages Copyright International Organization for Standardization Provided by IHS under license with ISO Licensee=NASA Technical Standards 1/9972545001 Not for Resale, 04/25/2007 01:32:54 MDTNo reproduction or networking permitted without license from IHS -,-,-