ASTM D1926-2000(2006) Standard Test Methods for Carboxyl Content of Cellulose《纤维素羧基含量的测试方法》.pdf

1、Designation: D 1926 00 (Reapproved 2006)Standard Test Methods forCarboxyl Content of Cellulose1This standard is issued under the fixed designation D 1926; the number immediately following the designation indicates the year oforiginal adoption or, in the case of revision, the year of last revision. A

2、 number in parentheses indicates the year of last reapproval. Asuperscript epsilon (e) indicates an editorial change since the last revision or reapproval.1. Scope1.1 These test methods cover the determination of thecarboxyl content, or ion-exchange capacity, of cellulose fromany source. Two test me

3、thods are described, the sodiumchloride-sodium bicarbonate method (1)2and the methyleneblue method (2). The test methods must be used within theirlimitations, and it must be recognized that there is no way ofdetermining the accuracy of any method for the determinationof carboxyl. The precision of th

4、e sodium chloride-sodiumbicarbonate method is low in the lower range of carboxylvalues. The methylene blue method can be used over the wholerange of carboxyl values; it is especially useful in the lowrange. It is not applicable to the determination of carboxyl insoluble carbohydrate material. Althou

5、gh these test methodsmay be used to determine the ion-exchange capacity ofunbleached pulps, the residual lignin will cause an undeter-mined error, especially the sulfonic acid groups in unbleachedsulfite pulps (3).1.2 The values stated in SI units are to be regarded asstandard. No other units of mea

6、surement are included in thisstandard.1.3 This standard does not purport to address all of thesafety concerns, if any, associated with its use. It is theresponsibility of the user of this standard to establish appro-priate safety and health practices and determine the applica-bility of regulatory li

7、mitations prior to use.2. Referenced Documents2.1 ASTM Standards:3D 1193 Specification for Reagent Water3. Significance and Use3.1 These test methods measure the amount of carboxylgroups present in wood or cotton linter pulp. Carboxyl groupsare indicative of the surface charge of the pulp which is a

8、 veryimportant quantity for use in the papermaking industry.4. Purity of Reagents4.1 Reagent-grade chemicals shall be used in all tests.Unless otherwise indicated, it is intended that all reagents shallconform to the specifications of the Committee on AnalyticalReagents of the American Chemical Soci

9、ety, where suchspecifications are available.4Other grades may be used, pro-vided it is first ascertained that the reagent is of sufficientlyhigh purity to permit its use without lessening the accuracy ofthe determination.4.2 Unless otherwise indicated, references to water shall beunderstood to mean

10、reagent water conforming to SpecificationD 1193.SODIUM CHLORIDE-SODIUM BICARBONATEMETHOD5. Summary of Test Method5.1 In the sodium chloride-sodium bicarbonate method thespecimen is deashed with hydrochloric acid, washed, soaked insodium chloride-sodium bicarbonate solution, filtered, and analiquot o

11、f the filtrate titrated with 0.01 N hydrochloric acid toa methyl red end point. The difference between the concentra-tion of the filtrate and of the sodium chloride-sodium bicar-bonate solution is a measure of the ion-exchange capacity ofthe cellulose.6. Reagents6.1 Hydrochloric Acid, Standard (0.01

12、 N)Prepare andstandardize a 0.01 N solution of hydrochloric acid (HCl).6.2 Hydrochloric Acid (1 + 99)Dilute 1 volume of con-centrated HCl (sp gr 1.19) with 99 volumes of water.6.3 Methyl Red Indicator Solution.6.4 Sodium Chloride-Sodium Bicarbonate SolutionDissolve 5.85 g of sodium chloride (NaCl) a

13、nd 0.84 g ofsodium bicarbonate (NaHCO3) in water and dilute to 1 L.1These test methods are under the jurisdiction of ASTM Committee D01 onPaint and Related Coatings, Materials, and Applications and are the directresponsibility of Subcommittee D01.36 on Cellulose and Cellulose Derivatives.Current edi

14、tion approved April 1, 2006. Published April 2006. Originallyapproved in 1961. Last previous edition approved in 2000 as D 1926 00.2The boldface numbers in parentheses refer to the list of references at the end ofthese test methods.3For referenced ASTM standards, visit the ASTM website, www.astm.org

15、, orcontact ASTM Customer Service at serviceastm.org. For Annual Book of ASTMStandards volume information, refer to the standards Document Summary page onthe ASTM website.4Reagent Chemicals, American Chemical Society Specifications, AmericanChemical Society, Washington, DC. For suggestions on the te

16、sting of reagents notlisted by the American Chemical Society, see Analar Standards for LaboratoryChemicals, BDH Ltd., Poole, Dorset, U.K., and the United States Pharmacopeiaand National Formulary, U.S. Pharmacopeial Convention, Inc. (USPC), Rockville,MD.1Copyright ASTM International, 100 Barr Harbor

17、 Drive, PO Box C700, West Conshohocken, PA 19428-2959, United States.6.5 Sodium Hydroxide Solution (0.4 g/L)Dissolve 0.4 g ofsodium hydroxide (NaOH) in water and dilute to 1 L.7. Procedure7.1 Condition the specimen in the atmosphere near thebalance for at least 20 min before weighing duplicate porti

18、onsof 2.5 6 0.01 g. At the same time, weigh specimens for thedetermination of moisture. Disintegrate the specimen in water,filter through fritted glass, and disperse to about 1 % consis-tency in HCl (1 + 99) at room temperature.After 2 h collect thespecimen on a fritted-glass filter funnel and wash

19、with watersaturated with carbon dioxide (CO2). Continue the washinguntil the filtrate, after boiling, does not require more than 1 or2 drops of NaOH solution to give an alkaline color with methylred.7.2 Weigh the wet pulp pad, transfer it immediately to a250-mL glass-stoppered Erlenmeyer flask, add

20、50 mL of theNaCl-NaHCO3solution with a pipet, and shake to obtain ahomogeneous slurry (Note 1). Allow the mixture to stand for 1h at room temperature. Filter through a clean, dry, fritted glassfunnel, pipet a 25-mL aliquot of the filtrate into an Erlenmeyerflask, and titrate with 0.01 N HCl, using m

21、ethyl red solution asan indicator. When the first change in color occurs, boil thesolution for about 1 min to expel the carbon dioxide andcontinue the titration to a sharp end point.NOTE 1If the cation-exchange capacity is very low, use a solutioncontaining about 5.85 g of NaCl and 0.42 g of NaHCO3p

22、er litre. It isimportant that the excess of NaHCO3be large enough that the pH does notfall below 7.0.7.3 Pipet 25 mL of the NaCl-NaHCO3solution into anErlenmeyer flask and titrate as described in 7.2.8. Calculation8.1 Calculate the cation-exchange capacity, c, of the speci-men in milliequivalents pe

23、r 100 g as follows:c 5Sb 2 a 2av50D2G(1)where:G = weight of oven-dry specimen, g,v = weight of water in the wet pulp pad, g,a = millilitres of 0.01 N HCl consumed by 25 mL offiltrate, andb = millilitres of 0.01 N HCl consumed by 25 mL of theNaCl-NaHCO3solution.9. Report9.1 Until more data are obtain

24、ed on the precision of this testmethod, it is suggested that the ion-exchange capacity bereported to 0.01 milliequivalent/100 g of pulp.10. Precision and Bias10.1 Work sponsored by ASTM, TAPPI, ACS, and ICCA(see Ref 4) found that precision decreased with decreasingcarboxyl content. For pulps varying

25、 in carboxyl content from5.75 to 0.40 mmol/100 g pulp, the repeatability (intralabora-tory) expressed as a percent coefficient of variance was 2.2 to8.1 %, respectively. Interlaboratory results based on differentmaterials and various test methods gave percent coefficient ofvariance of 9.0 to 33 % fo

26、r these same materials.10.2 No statement on bias can be made as no suitablereference material exists for determining bias.METHYLENE BLUE METHOD11. Summary of Test Method11.1 In the methylene blue method the specimen is treatedwith 0.0002 M methylene blue solution buffered to a pH of 8with diethylbar

27、bituric acid (barbital). The decrease in methyl-ene blue concentration, measured photometrically, is a functionof the ion-exchange capacity of the cellulose.12. Apparatus12.1 Spectrophotometer or Filter Photometer, capable ofmeasuring absorbance near 620 mm.12.2 Shaker or Mixer for agitating the spe

28、cimens in themethylene blue solution.Awheel or rod, to which the specimenvials can be attached, that rotates at about 15 r/min, has provensatisfactory.12.3 Centrifuge, capable of settling the cellulose from themethylene blue solution.13. Reagents13.1 Buffer, Stock SolutionDissolve 1.151 g of diethyl

29、bar-bituric acid (barbital) in water, add the equivalent of 0.16 g ofsodium hydroxide using a standard solution and buret, anddilute with water to 1 L in a volumetric flask.13.2 Hydrochloric Acid (1 + 99)Dilute 1 volume of con-centrated hydrochloric acid (HCl, sp gr 1.19) with 99 volumesof water.13.

30、3 Methylene Blue, Stock Solution (0.002 M)Dissolve0.640 g of methylene blue in water, making allowance formoisture, and dilute to 1 L in a volumetric flask.NOTE 2Information on the determination of the purity of methyleneblue is given in the literature (5).13.4 Methylene BlueBuffer Solution (0.0002

31、M)Mix 1volume of methylene blue stock solution with 1 volume ofbuffer stock solution and dilute to a total of 10 volumes in avolumetric flask. The volume of solution to be prepared willvary with the requirements. For example, pipet 10 mL of eachsolution into a 100-mLvolumetric flask, dilute to the m

32、ark withwater, and mix thoroughly. Prepare a fresh solution for eachdetermination.14. Preparation of Calibration Curve for Ordinary SizeSpecimens14.1 In order to prepare a calibration curve, make up a seriesof methylene blue buffer solutions containing the same amountof buffer but different amounts

33、of methylene blue, to cover thedesired range. Add 50 mL of the stock solution of buffer toeach of nine 500-mL volumetric flasks. Add to these flasks 10,15, 20, 25, 30, 35, 40, 45, and 50 mL, respectively, of the 0.002M stock solution of methylene blue. Dilute each solution to themark with water and

34、mix thoroughly.NOTE 3The concentrations suggested for preparing calibration curvesneed not be followed exactly as long as enough points are obtained toD 1926 00 (2006)2allow construction of an acceptable calibration curve.14.2 Pipet 10 mL of each solution into 100-mL volumetricflasks, add 10 mL of H

35、Cl (1 + 99), dilute to the mark withwater, and mix (Note 4). Measure the absorbance of thesolutions and prepare a plot of absorbance at 620 nm againstconcentration (Note 5).NOTE 4The procedure described for the colorimetric determination ofmethylene blue is based on the use of the Beckman DU spectro

36、photometerwith 1-cm absorption cells. The dilution procedure may have to bemodified for use with filter photometers or for cells with a longer lightpath.NOTE 5It has been reported (5) that Beers law is obeyed at 620 nm,and it is recommended that measurements be made at this wavelength.Measurements m

37、ay also be made at 675 nm, which is close to theabsorption peak, but Beers law is not obeyed at this wavelength.15. Preparation of Calibration Curve for SmallSpecimens15.1 In order to prepare a calibration curve, pipet 1 mL ofeach of the nine solutions mentioned in Section 14 into 10-mLvolumetric fl

38、asks, add 1 mLof HCl (1 + 99), dilute to the mark,mix, and measure the absorbance at 620 nm. If the volumetricapparatus is sufficiently precise, this calibration curve shouldbe identical with the one described in Section 14. Obviously,any specific procedure that gives solutions in the right concen-t

39、ration range for the colorimetric measurements should besatisfactory.16. Procedure for Ordinary Size Specimens16.1 Determine the approximate carboxyl content in apreliminary experiment. Weigh out three specimens, one esti-mated to give 50 % exhaustion of the dye solution, one 10 to15 % smaller, and

40、one 10 to 15 % larger, making allowance forthe moisture content. Weigh the specimens into 125-mLglass-stoppered flasks (any other convenient size flask may beused), and add 50 mL of 0.0002 M methylene blue-buffersolution from a pipet. Lubricate the stoppers with a littlepetroleum jelly and secure th

41、em with rubber bands. Place theflasks on a device that will turn them end over end or otherwiseagitate the solutions.16.2 After overnight agitation, centrifuge the solutions andpipet a 10-mL aliquot of the supernatant liquid into a 100-mLvolumetric flask. Add 10 mL of HCl (1 + 99), and fill the flas

42、kto the mark with water. Measure the absorbance of thesolutions at 620 nm.16.3 Using the observed absorbances, refer to the calibra-tion curve and read the concentration of methylene blue presentfor each of the three portions of specimen.16.4 Plot the specimen size against the concentration ofmethyl

43、ene blue in the supernatant liquid, and read from the plotthe specimen size that gives 50 % exhaustion of the dyesolution.NOTE 6It is not absolutely necessary to plot the specimen size againstmethylene blue concentration in order to calculate dye absorption. The dyeabsorption may be calculated from

44、two slightly different weights ofcellulose that will give approximately 50 % exhaustion, and the mean ofthe two results taken.17. Procedure for Small Specimens17.1 The general procedure is the same as for ordinary sizespecimens (Section 16). Weigh the specimens into glass-stoppered weighing bottles

45、of about 10-mL capacity and add 5mL of 0.0002 M methylene blue-buffer solution. After over-night agitation, centrifuge the solutions, remove a 1-mL aliquotwith an automatic pipet, and transfer to a 10-mL volumetricflask. Add about 1 mL of HCl (1 + 99), dilute to the mark, andmeasure the absorbance a

46、t 620 nm. Determine the specimensize that gives 50 % exhaustion of the methylene blue solutionas described in 16.4.18. Calculations18.1 Ordinary Size SpecimensThe size specimen thatgives 50 % exhaustion of 50 mL of 0.0002 M methylene bluesolution has used 0.005 millimole of methylene blue in ionexch

47、ange with carboxyl groups. Therefore the millimoles ofcarboxyl per 100 g of cellulose, M1, is calculated as follows:M15 0.005/W! 3 100 (2)where W = specimen to give 50 % exhaustion of 50 mL of0.0002 M methylene blue solution, g.18.2 Small SpecimensThe size specimen that gives 50 %exhaustion of 5 mL

48、of 0.0002 M methylene blue solution hasused 0.0005 millimole of methylene blue in ion exchange withcarboxyl groups. Therefore the millimoles of carboxyl per 100g of cellulose, M2, is calculated as follows:M25 0.0005/W! 3 100 (3)where W = specimen to give 50 % exhaustion of 5 mL of0.0002 M methylene

49、blue solution, g.19. Report19.1 Until more data are obtained on the precision of thistest method, it is suggested that the ion-exchange capacity bereported to 0.01 meq/100 g of pulp.20. Precision and Bias20.1 Work sponsored by ASTM, TAPPI, ACS, and ICCA(see Ref 4) found that precision decreased with decreasingcarboxyl content. For pulps varying in carboxyl content from5.75 to 0.40 mmol/100 g pulp, the repeatability (intralabora-tory) expressed as a percent coefficient of variance was 2.2 to8.1 %, respectively. Interlaboratory results based on differentmaterials a