1、BRITISH STANDARD BS 6057-3.6: 1993 ISO 506:1992 Rubber latices Part 3: Methods of test Section 3.6 Determination of volatile fatty acid number of natural rubber latices NOTEAttention is drawn to BS 6057-0 “General introduction”, issued separately” UDC 678.031.5:543.852.1BS6057-3.6:1993 This British
2、Standard, having been prepared under the directionof the Plastics and Rubber Standards Policy Committee, was published underthe authority ofthe Standards Board and comes intoeffect on 15 January 1993 BSI 10-1999 First published May 1982 Second edition January 1993 The following BSI references relate
3、 to the work on this standard: Committee reference PRM/51 Draft announced in BSI News, February 1991 ISBN 0 580 21510 5 Committees responsible for this British Standard The preparation of this British Standard was entrusted by the Plastics and Rubber Standards Policy Committee (PRM/-) to Technical C
4、ommittee PRM/51, upon which the following bodies were represented: British Rubber Manufacturers Association Malaysian Rubber Producers Research Association Medical Sterile Products Association Tropical Growers Association Amendments issued since publication Amd. No. Date CommentsBS6057-3.6:1993 BSI
5、10-1999 i Contents Page Committees responsible Inside front cover National foreword ii 1 Scope 1 2 Normative references 1 3 Definition 1 4 Principal 1 5 Reagents 1 6 Apparatus 1 7 Sampling 1 8 Procedure 1 9 Expression of results 2 10 Test report 2 Figure 1 Steam-jacketed distillation apparatus (Mark
6、ham still ) 3 List of references Inside back coverBS6057-3.6:1993 ii BSI 10-1999 National foreword This Section of BS 6057 has been prepared under the direction of the Plastics and Rubber Standards Policy Committee and is identical with ISO 506:1992 Rubber latex, natural, concentrate Determination o
7、f volatile fatty acid number, published by the International Organization for Standardization (ISO). It supersedes BS 6057-3.6:1982, which is withdrawn. A British Standard does not purport to include all the necessary provisions of a contract. Users of British Standards are responsible for their cor
8、rect application. Compliance with a British Standard does not of itself confer immunity from legal obligations. Cross-references International Standard Corresponding British Standard ISO 123:1985 BS 6057 Rubber latices Part 2:1987 Sampling (Identical) ISO 124:1985 Part 3 Methods of test Section 3.2:
9、1992 Determination of total solids content of rubber latices (Identical) ISO 126:1989 Section 3.4:1990 Determination of dry rubber content of natural rubber latices (Identical) Summary of pages This document comprises a front cover, an inside front cover, pages i and ii, pages1 to 4, an inside back
10、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.BS6057-3.6:1993 BSI 10-1999 1 1 Scope This International Standard specifies a method for the determination of
11、the volatile fatty acid number of natural rubber latex concentrate. The method is not necessarily suitable for latices from natural sources other than Hevea brasiliensis and is not applicable to compounded latex, vulcanized latex, artificial dispersions of rubber or synthetic rubber latices. 2 Norma
12、tive references The following standards contain provisions which, through reference in this text, constitute provisions of this International Standard. At the time of publication, the editions indicated were valid. All standards are subject to revision, and parties to agreements based on this Intern
13、ational 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 of currently valid International Standards. ISO 123:1985, Rubber latex Sampling. ISO 124:1992, Rubber latices Determination
14、of total solids content. ISO 126:1989, Natural rubber latex concentrate Determination of dry rubber content. 3 Definition for the purposes of this International Standard, the following definition applies. 3.1 volatile fatty acid (VFA) number of latex concentrate the number of grams of potassium hydr
15、oxide equivalent to the volatile fatty acids in latex concentrate containing 100 g of total solids NOTE 1If substances have been added to the latex which produce volatile acids on acidification with sulfuric acid, the volatile fatty acid number is high and does not represent the volatile fatty acid
16、content without correction. 4 Principle A test portion is coagulated with ammonium sulfate and a portion of the resultant serum is separated and acidified with sulfuric acid. The acidified serum is steam-distilled and the volatile acids present in the test portion are determined by titration of the
17、distillate with a standard volumetric barium hydroxide solution. 5 Reagents During the analysis, use only reagents of recognized analytical quality, and only distilled water or water of equivalent purity. 5.1 Ammonium sulfate, approximately 30 % (m/m) solution. 5.2 Sulfuric acid, approximately 50 %
18、(m/m) solution. 5.3 Barium hydroxide, standard volumetric solution, cBa(OH) 2 = 0,005 mol/dm 3 , standardized by titration with potassium hydrogen phthalate and stored in the absence of carbon dioxide. 5.4 Indicator solution: either bromothymol blue or phenolphthalein solution, 0,5 % (m/m) in a mixt
19、ure of approximately equal volumes of ethanol and water. 6 Apparatus Ordinary laboratory apparatus and 6.1 Steam-jacketed distillation apparatus (Markham still), conforming essentially to Figure 1. As an alternative to the one-piece apparatus illustrated, a ground-glass joint may be inserted between
20、 the distillation vessel and the condenser. 6.2 Steam-bath, or 6.3 Water-bath, capable of being maintained at a nominal temperature of 70 C. 6.4 Pipettes, of capacity 5 cm 3 , 10 cm 3 , 25 cm 3and 50 cm 3 . 6.5 Burette, of suitable capacity. 7 Sampling Carry out the sampling in accordance with one o
21、f the methods specified in ISO 123. 8 Procedure 8.1 If the total solids content and dry rubber content of the latex concentrate are not known, determine them in accordance with ISO 124 and ISO 126, respectively.BS6057-3.6:1993 2 BSI 10-1999 8.2 Into a beaker weigh, to the nearest 0,1 g, about 50 g o
22、f latex concentrate. Accurately add 50 cm 3of the ammonium sulfate solution (5.1) from a pipette (6.4), while stirring the latex concentrate. Either place the beaker on the steam-bath (6.2) or in the water-bath (6.3), maintained at 70 C, and continue stirring the latex concentrate until it coagulate
23、s. Cover the beaker with a watch-glass and leave it on or in the bath for a total period of 15 min. Decant the serum which exudes through a dry filter paper. Transfer the coagulum to a mortar and press out more serum by kneading it with a pestle. Filter this serum through the same filter. Pipette 25
24、 cm 3of the filtered serum into a dry 50 cm 3conical flask and acidify it by accurately adding 5 cm 3of the sulfuric acid solution (5.2). Mix well by swirling the flask. With certain latex concentrates, in particular those preserved with potassium hydroxide, a fine precipitate may form during the ac
25、idification step. This precipitate shall be removed by filtration through a fresh dry filter paper before proceeding with the distillation process. Pass steam through the apparatus (6.1) for at least 15 min. With steam passing through the outer jacket of the apparatus (steam outlet open), introduce
26、into the inner tube 10 cm 3of the acidified serum by pipette (6.4). If foaming is a difficulty, 1 drop of a suitable antifoaming agent may be added. Place a 100 cm 3graduated cylinder under the tip of the condenser to receive the distillate. Partially close the steam outlet to divert steam into the
27、inner tube. Pass steam gently at first, then fully close the steam outlet and continue distilling at a rate of 3 cm 3 /min to 5 cm 3 /min until 100 cm 3of distillate has been collected. Transfer the distillate to a 250 cm 3conical flask and eliminate any dissolved carbon dioxide from the distillate
28、by passing through it a stream of air free from carbon dioxide at a rate of 200 cm 3 /min to 300 cm 3 /min for approximately 3 min. Titrate with the barium hydroxide solution (5.3), using one of the indicators specified (5.4). 8.3 Carry out a duplicate determination (see 8.2) with a fresh 50 g test
29、portion of latex concentrate. 9 Expression of results Calculate the volatile fatty acid (VFA) number using the formula where Repeat the test if the results of the duplicate determinations do not agree to within 0,01 units when the actual VFA number is 0,10 units or less; within 10 % when the actual
30、VFA number is greater than 0,10 units. 10 Test report The test report shall include the following particulars: a) a reference to this International Standard; b) all details necessary for the identification of the test sample; c) the results, and the units in which they have been expressed; d) any un
31、usual features noted during the determination; e) any operations not included in this International Standard or in the International Standards to which reference is made, and any operations regarded as optional. c is the actual concentration, expressed in moles per cubic decimetre, of the barium hyd
32、roxide solution (5.3); V is the volume, in cubic centimetres, of barium hydroxide solution required to neutralize the distillate; m is the mass, in grams, of the test portion; DRC is the dry rubber content, expressed as a percentage by mass, of the latex concentrate; TSC is the total solids content,
33、 expressed as a percentage by mass, of the latex concentrate; is the density, in megagrams per cubic metre, of the serum a ; 134,64 is a factor derived from the relative molecular mass of potassium hydroxide, its equivalence to barium hydroxide and those parts of the serum acidified and distilled. a
34、 = 1,02 Mg/m 3for centrifuged or creamed latex concentrates.BS6057-3.6:1993 BSI 10-1999 3 Symbol A B C D E F G H I J K External diameter 29 to 32 13 to 14 9 to 10 5 to 6 25 to 27 44 to 48 9 to 10 15 to 17 20 to 22 11 to 12 9 to 10 Wall thickness 1 to 1,5 1 to 1,5 0,75 to 1,25 0,75 to 1,25 1 to 1,5 1
35、 to 2 0,75 to 1,25 1,5 to 2 1 to 1,5 0,75 to 1,25 0,75 to 1,25 Figure 1 Steam-jacketed distillation apparatus (Markham still)4 blankBS6057-3.6:1993 BSI 10-1999 List of references See national foreword.BS 6057-3.6: 1993 ISO 506:1992 BSI 389 Chiswick High Road London W4 4AL BSIBritishStandardsInstitut
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