1、BRITISH STANDARD BS7164-7.1: 1990 ISO5945:1989 Chemical tests for raw and vulcanized rubber Part7: Methods for determination of polymer content Section7.1 Polyisoprene contentBS7164-7.1:1990 This British Standard, having been prepared under the directionof the Rubber StandardsPolicy Committee,waspub
2、lished underthe authorityof the Boardof BSI and comesintoeffecton 30September1990 BSI10-1999 The following BSI references relate to the work on this standard: Committee reference RUM/37 Draft for comment90/40973 DC ISBN 0 580 18940 6 Committees responsible for this British Standard The preparation o
3、f this British Standard was entrusted by the Rubber Standards Policy Committee (RUM/-) to Technical Committee RUM/37, upon which the following bodies were represented: Institute of Water and Environmental Management Laboratory of the Government Chemist Ministry of Defence Royal Society of Chemistry
4、Rubber and Plastics Research Association Amendments issued since publication Amd. No. Date CommentsBS7164-7.1:1990 BSI 10-1999 i Contents Page Committees responsible Inside front cover National foreword ii 1 Scope 1 2 Normative references 1 3 Principle 1 4 Reagents 1 5 Apparatus 2 6 Sampling 2 7 Pro
5、cedure 2 8 Expression of results 3 9 Test report 4 Annex A (informative) Bibliography 6 Figure 1 Digestion and distillation assembly 5 Figure 2 Aeration assembly 5 Table 1 Degree of interference of rubber compounding ingredients 4 Table 2 Behaviour of rubber-like materials in chromic acid oxidation
6、procedure 4 Publication(s) referred to Inside back coverBS7164-7.1:1990 ii BSI 10-1999 National foreword This Section of BS7164 has been prepared under the direction of the Rubber Standards Policy Committee and is identical with ISO5945:1989 “Rubber Determination of polyisoprene content”, published
7、by the International Organization for Standardization (ISO). BS7164 rationalizes all the methods that deal with chemical analysis of raw, compounded and vulcanized rubber, some of which have previously been published in BS903, BS1673 and BS5923. Relevant Parts of those standards will be withdrawn or
8、 deleted by amendment, as appropriate, when superseded by Parts and Sections of BS7164. This Part of BS7164 supersedes section1 of PartB12 of BS903-B11 andB12:1960 which is deleted by amendment. Annex A of this standard is for information only. The Technical Committee has reviewed the provisions of
9、ISO1407:1976, to which reference is made in the text, and has decided that they are acceptable for use in conjunction with this British Standard. It is envisaged that the revised edition of ISO1407 1)will be identical to BS7164-3. A British Standard does not purport to include all the necessary prov
10、isions of a contract. Users of British Standards are responsible for their correct application. Compliance with a British Standard does not of itself confer immunity from legal obligations. Summary of pages This document comprises a front cover, an inside front cover, pagesi andii, pages1 to6, an in
11、side back cover and a back cover. This standard has been updated (see copyright date) and may have had amendments incorporated. This will be indicated in the amendment table on the inside front cover. Cross-references International Standard Corresponding British Standard BS6057 Rubber latices ISO123
12、:1985 Part2:1987 Sampling (Identical) ISO124:1985 Section3.2:1987 Determination of total solids content (Identical) ISO1795:1974 BS6315:1982 Methods for sampling and sample preparation of raw rubber (Technically equivalent) 1) In preparation.BS7164-7.1:1990 BSI 10-1999 1 1 Scope 1.1 This Internation
13、al Standard specifies a method for the determination of polyisoprene occurring as natural isoprene rubber (NR) 2) , synthetic isoprene rubber (IR), balata and gutta percha, in the total solids from NR or IR latices, in solid raw rubbers, or in cured or uncured compounds. The method is applicable to
14、these isoprene rubbers alone or in blends. It cannot be used for hard rubber (ebonite) without modification. 1.2 Compounding ingredients, such as carbon black, mineral oil and sulfur, in soft rubbers do not interfere (see Table 1) (but see also8.2). If vinyl acetate polymers are present, the method
15、should not be used. 1.3 The method is applicable to blends of the rubbers mentioned in1.1 with SBR, BR and NBR. If halogenated rubbers are present, a slightly modified procedure, described in7.7.3, is used. Some interference may be expected, because these rubbers react with chromic acid in a manner
16、similar to polyisoprene. If these interfering rubbers are the major part of the blend, they may impede the reaction of the polyisoprene with the chromic acid. The digestion shall then be checked for completeness on known mixtures of these interfering rubbers. Milling of the test portion as finely as
17、 possible is advisable. 1.4 The method may be used for the determination of polyisoprene in reclaimed rubbers, but it has been found to give consistently lower values than the previously accepted estimates for the polyisoprene content. 1.5 If rubbers other than those mentioned in1.3 are present (CSM
18、, EPDM, IIR, CIIR and BIIR), the digestion time shall be modified. The estimates shall be corrected by comparison with results from similar rubber blends. If these interfering rubbers are present in the blend, they may impede the reaction of the polyisoprene with the chromic acid and the method is n
19、ot applicable. Greatest deviations are found if polysulfide rubbers are present as part of the mixture. (SeeTable 2.) 2 Normative references The following standards contain provisions which, through reference in this text, constitute provisions of this International Standard. At the time of publicat
20、ion, the editions indicated were valid. All standards are subject to revision, and parties to agreements based on this International Standard are encouraged to investigate the possibility of applying the most recent editions of the standards indicated below. Members of IEC and ISO maintain registers
21、 of currently valid International Standards. ISO123:1985, Rubber latex Sampling. ISO124:1985, Rubber latices Determination of total solids content. ISO1407:1976, Rubber Determination of solvent extract. ISO1795:1974, Raw rubber in bales Sampling. 3 Principle Quantitative oxidation of the polyisopren
22、e present in a test portion with a hot digestion mixture of sulfuric and chromic acids; distillation of the acetic acid formed, aeration of the distillate to remove carbon dioxide and titration of the acetic acid with sodium hydroxide solution. The calculation is based on the observation that a75% y
23、ield of acetic acid is always obtained in oxidation of the isoprene unit under the specified test conditions. 4 Reagents All recognized health and safety precautions shall be exercised when performing this method of analysis. During the analysis, use only reagents of recognized analytical grade and
24、only distilled water or water of equivalent purity. 4.1 Extraction solvents: acetone, chloroform (used in a closed extraction system) or dichloromethane. 4.2 Chromic acid digestion mixture Dissolve200g of chromium trioxide(CrO 3 ) in500cm 3of water. Carefully add, while stirring,150cm 3of sulfuric a
25、cid(H 2 SO 4 ), 20 =1,84Mg/m 3 . 2) For the meanings of the abbreviations, see ISO1629:1987, Rubbers and latices Nomenclature.BS7164-7.1:1990 2 BSI 10-1999 4.3 Potassium iodide solution Dissolve84g of potassium iodide in water and dilute to1000cm 3 . 4.4 Sodium thiosulfate solution Dissolve79g of so
26、dium thiosulfate(Na 2 S 2 O 3 ) in water and dilute to1000cm 3 . 4.5 Sodium hydroxide, standard volumetric solution, c(NaOH)=0,1mol/dm 3or0,05mol/dm 3 . The choice of concentration depends upon the size of the test portion, the amount of polyisoprene and the test assembly used. 4.6 Phenolphthalein,
27、2g/dm 3alcoholic indicator solution. Dissolve0,2g of phenolphthalein in50cm 3of95%(V/V) ethanol. Dilute to100cm 3with the same ethanol. 5 Apparatus 5.1 Balance, accurate to0,1mg. 5.2 Extraction apparatus, as described in ISO1407. 5.3 Digestion and distillation assembly A suitable assembly for the di
28、gestion and distillation apparatus is shown in Figure 1. Heating is by heating mantles. Any apparatus which will perform the same functions, in the same sequence, as the items shown, may be substituted. 5.4 Aeration assembly (seeFigure 2), containing a capillary tube, which, when connected to a redu
29、ced-pressure line, will maintain, through the receiving flask, an air flow of approximately33cm 3 /s. If the absolute pressure is less than4kPa(30mmHg), a capillary tube of length approximately100mm and of1mm bore will maintain the required air flow. A flowmeter shall be connected to the reduced-pre
30、ssure line to ensure that the prescribed air flow is obtained. Since it is essential to maintain the aeration at a rate within20% of33cm 3 /s, each capillary tube shall be tested before use. The following method may be used. Invert a graduated tube over a beaker filled with water and evacuate the ai
31、r through the capillary by means of a tube extending up into the graduated tube. The rate of air flow will be the same as the rate at which water fills the graduated tube. 5.5 Absorption device, to prevent carbon dioxide from entering the aeration assembly. 6 Sampling Sample raw rubber in accordance
32、 with ISO1795, or use any other method that provides a representative sample of the product to be analysed in the case of cured or uncured compounds. Sample latex in accordance with ISO123. 7 Procedure 7.1 Preparation of test sample Mill the test sample to as thin a sheet as possible, not exceeding0
33、,5mm. For a finished product, if milling to thicknesses of0,5mm or less is not practicable, cut the sample into the smallest possible pieces. The thickness limit of0,5mm shall not be exceeded; otherwise samples of some uncured NR or IR rubbers, or blends of CSM, EPDM, IIR, BIIR or CIIR compounds, cu
34、red or uncured, may not be sufficiently thin to allow complete oxidation by the chromic acid. For latex, prepare a film in accordance with ISO124. 7.2 Test portion Weigh, to the nearest0,1mg, a mass of test portion appropriate for the apparatus to be used and the expected polyisoprene content of the
35、 sample. For the apparatus shown in Figure 1, a test portion of0,15g to0,25g is normally satisfactory; if the expected polyisoprene content is particularly low, a larger test portion will be necessary. 7.3 Extraction If the sheeted test portion is coherent, place it in the extraction cup (see ISO140
36、7). If it is unmanageable, or sticky, wrap it in filter paper before placing in thecup. Extract the test portion for16h, or overnight, with acetone(4.1). Alternatively, place the unwrapped test portion in the required solvent and reflux directly for4h as for the rapid reflux extraction in accordance
37、 with ISO1407. If the presence of bituminous material (mineral rubber) or factice is suspected, carry out a further extraction for4h with chloroform, in a closed system, or dichloromethane(4.1). WARNING Do not mix acetone and chloroform. In the presence of bases, they mayform explosive mixtures. Raw
38、 rubbers which are not oil-extended, may be digested without prior extraction.BS7164-7.1:1990 BSI 10-1999 3 All test portions shall be thoroughly dried before proceeding to the digestion(7.4). 7.4 Digestion If necessary, unwrap the test portion. Bits of paper adhering to the test portion need not be
39、 completely removed: small amounts of cellulose do not interfere with the determination. Place the test portion in the digestion flask (see5.3) and add an appropriate volume of the digestion mixture(4.2). For the apparatus shown in Figure 1, use25cm 3 . Greater volumes may be used according to the t
40、ype of apparatus. Place the receiver flask, containing100cm 3of water, under the condenser and adapter of the distillation assembly. Heat the digestion mixture to100 C 5 C for a period sufficient to ensure complete digestion of the polyisoprene. Determine the correct heating-mantle setting by heatin
41、g the digestion mixture, without the sample, and measuring the temperature of the digestion mixture with a thermometer. For the apparatus shown in Figure 1, a digestion time of30min is sufficient. Other types of apparatus may need longer digestion times up to1h, for example. If the test portion is a
42、 mixture of NR and/or IR with the rubbers specified in1.5, complete digestion of these rubbers is not possible, but the polyisoprene will be digested. Although each apparatus may require different digestion times, the time shall be maintained consistent for each type of apparatus. 7.5 Distillation 7
43、.5.1 During the digestion step, heat the steam generation flask with the stopper removed, so that steam is available at the end of the digestion period. If the laboratory is equipped with a steam line, this is unnecessary. 7.5.2 After30min, replace the stopper and delivery tube in the mouth of the s
44、team generation flask, and allow steam to enter the digestion flask. Continue heating the digestion flask to maintain the total volume at about75cm 3 . The rate of distillation and cooling shall be controlled so that the temperature of the condensate is not more than30 C. 7.5.3 Collect150cm 3of dist
45、illate for the apparatus shown in Figure 1, and appropriately larger volumes for larger apparatus. 7.5.4 At the end of distillation (usually20min for the apparatus shown in Figure 1), remove the delivery tube from the receiver flask, carefully wash the tube with distilled water, collecting the washi
46、ngs in the receiver flask, and place the receiver flask on the aeration assembly. 7.5.5 Disconnect the steam delivery tube from the digestion flask as soon as the receiver flask is removed from the apparatus. This is to ensure that chromic acid mixture will not be sucked back into the steam generato
47、r when the heat source is removed. 7.6 Aeration Adjust the temperature of the distillate to room temperature and aerate for30min for all types of digestion and distillation apparatus. NOTEThe rates of loss of carbon dioxide and acetic acid during aeration have been investigated for temperature range
48、, type of aeration apparatus and recommended rate of air flow. Variation of any of these factors may lead to erroneous analytical results. 7.7 Titration 7.7.1 Remove the receiver flask from the aeration assembly, washing the delivery tube with distilled water and collecting the washings in the recei
49、ver flask. Add5drops of phenolphthalein solution(4.6). Titrate with0,05mol/dm 3sodium hydroxide solution(4.5), in the case of test portions of0,15g to0,25g, or with0,1mol/dm 3sodium hydroxide solution(4.5) for larger test portions. 7.7.2 Carry out a blank test of the digestion mixture reagents as often as necessary, or when a new supply of chromic acid is used. 7.7.3 If halogenated rubbers are suspected, add potassium iodide solution(4.3) to the distillate after aeration and remove any liberated iodine (indicated by a yellow solution) with sodium
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