Fiber length of pulp and paper by automated optical analyzer using polarized light

Transcription

1 T 27 om-2 PROVISIOA METHOD 99 OFFICIA METHOD 988 REVISED 2002 REVISED 2007 REVISED TAPPI The nformaton and data contaned n ths document were prepared by a techncal commttee of the Assocaton. The commttee and the Assocaton assume no lablty or responsblty n connecton wth the use of such nformaton or data, ncludng but not lmted to any lablty under patent, copyrght, or trade secret laws. The user s responsble for determnng that ths document s the most recent edton publshed. CAUTIO: Ths Test Method may nclude safety precautons whch are beleved to be approprate at the tme of publcaton of the method. The ntent of these s to alert the user of the method to safety ssues related to such use. The user s responsble for determnng that the safety precautons are complete and are approprate to ther use of the method, and for ensurng that sutable safety practces have not changed snce publcaton of the method. Ths method may requre the use, dsposal, or both, of chemcals whch may present serous health hazards to humans. Procedures for the handlng of such substances are set forth on Materal Safety Data Sheets whch must be developed by all manufacturers and mporters of potentally hazardous chemcals and mantaned by all dstrbutors of potentally hazardous chemcals. Pror to the use of ths method, the user must determne whether any of the chemcals to be used or dsposed of are potentally hazardous and, f so, must follow strctly the procedures specfed by both the manufacturer, as well as local, state, and federal authortes for safe use and dsposal of these chemcals. Fber length of pulp and paper by automated optcal analyzer usng polarzed lght. Scope. Ths s an automated method by whch the numercal and weghted average fber lengths and fber length dstrbutons of pulp and paper can be measured usng lght polarzng optcs n the range of 0. mm to 7.2 mm..2 The fber length can also be measured usng the followng methods: TAPPI T 232 Fber ength of Pulp by Projecton and TAPPI T 233 Fber ength of Pulp by Classfcaton. 2. Summary 2. The measurng prncple of ths method s optcal and s based on the ablty of the fber to change the drecton of lght polarzaton. 2.. The fbers suspended n water are routed through a fber orentng channel (F.O.C.) where the mage lengths of ndvdual fbers are measured A F.O.C. s placed between a lght source and a photosensor matrx. The elements of the matrx detect the length of the fber from the projected mage of the fber. 2.2 On ether sde of the F.O.C., crossed polarzers are postoned to elmnate the effect of objects other than fbers, e.g., non-optcally actve fllers and ar bubbles, whch are not able to change the drecton of polarzaton. 3. Sgnfcance 3. Pulp and paper made from wood conssts of fbers and fber fragments. The length dstrbuton of dfferent fbers n the pulp can contrbute to varous propertes of the fnal product. 4. Apparatus 4. The apparatus (Fg. ) conssts of a sample transport system and a measurement secton. 4.2 A transport system of a F.O.C. (), through whch fbers dspersed n a lqud are drawn. [umbers n parentheses refer to numbers on Fg..] The F.O.C. orents the fbers nto a plane, or tube, normal to the lght path and Approved by the Standard Specfc Interest Group for ths Test Method TAPPI

2 T 27 om-2 Fber length of pulp and paper by automated / 2 optcal analyzer usng polarzed lght no thcker than a nomnal 0.5 mm or less n the drecton of the lght path. 4.3 Measurement system: 4.3. A lght source (2) s located on one sde of the F.O.C. and a photosensor matrx (3) on the opposte sde of the F.O.C. The photosensor matrx ndcates the fber length from the mage of the fber passng by. The wavelength of lght for the lght source and the photosensor matrx must be spectrally matched Crossed polarzers (4, 5) are located between the lght source and the photosensor matrx An analyzer wth resoluton equal to, or better than, 00 μm (see ote ). OTE : Measurng cellulosc partcles between 0. mm and 0.2 mm wll requre an analyzer to have a resoluton of 50 μm or smaller. 5. Test specmen 5. If the pulp or paper s beng tested to evaluate a pulp or paper lot, obtan a sample n accordance wth TAPPI T 400 Samplng and Acceptng a Sngle ot of Paper, Paperboard, Contanerboard or Related Product. It s essental that the test specmens of dry pulp or paper do not contan any cut edges. Fg.. The apparatus/measurement prncple. 6. Procedures 6. Dsntegraton. 6.. Dry pulp samples. Dsperse the sample as descrbed n TAPPI T 205 or dsntegrate t n a manual dsntegrator (Fg. 2). For good fber dsperson of the dsntegrated sample, one method s to use the manual dsntegrator as follows: Put the sample ( g for long-fbered softwood pulps and g for hardwood pulps) and 50 m of dstlled water n the dsntegrator, and move the pston up and down untl the sample has been dsntegrated completely. Presoakng s to be preferred for pulps dffcult to dsperse. Fbers must be properly separated, wth no fber bundles or fber-to-fber bonds remanng n the test specmen. When the sample s completely dspersed, dlute wth dstlled water to a consstency of 0.02 ± 0.005% for softwood, and ± % for hardwood. The sample volume after dluton should be at least 5 to nsure a homogenous mxture. Treat mxed furnsh pulps as softwood pulps for determnng fnal consstency Wet pulp samples. Dlute to approxmate consstency per manufacturers recommendatons to gve accurate measurements Ordnary papers. Dsntegrate the paper accordng to method A as descrbed n TAPPI T 40 Fber Analyss of Paper and Paperboard. Treat paper samples as softwood pulps for determnng fnal consstency. 6.2 Test sample concentraton. Dlute to the suspenson concentraton recommended by the nstrument s manufacturer, or to that determned by tests over a range of concentratons to gve accurate measurements.

3 3 / Fber length of pulp and paper by automated T 27 om-2 optcal analyzer usng polarzed lght 6.2. Take a 50 m ± 0.05 m sample of the dluton usng a ppette wth a tp openng of at least 2 mm n dameter When takng the sample, agtate the dluton contnuously. Do not str wth a rotary movement, because the sample dluton wll not be homogenous. Move the ppette both horzontally and vertcally durng samplng. 6.3 Runnng the sample. The mnmum number of fbers to measure shall be that at whch the average fber length reaches a steady state varance of 0.0 mm. If the apparatus does not provde contnuous fber length values, then measure a mnmum of 5000 fbers. 7. Calbraton check Fg. 2. Manual dsntegrator (dmenson unts are n mm). Perform the calbraton check of the analyzer wth fbers that polarze lght, of known fber length dstrbuton. Durng the calbraton, measure the ntensty of the lght and use t to standardze the optcal path. (See nstrument manufacturer s recommendatons.) 8. Calculaton 8. Arthmetc average of fber length ( A ). Calculate the arthmetc average fber length from the number of measured fbers (n ) n dfferent length fractons ( = the total number of fractons, when resoluton s a mnmum of 50μm) and from the average length of the fracton (l ) (). = the maxmum number of fractons greater than or equal to 44. A = = = n 8.2 ength weghted average fber length ( ). The arthmetc average fber length s not always the most commonly used ndcator of the fber length because the effect of short fbers s emphaszed. The commonly used expresson s the length weghted average fber length (2,3).

4 T 27 om-2 Fber length of pulp and paper by automated / 4 optcal analyzer usng polarzed lght = = = Weght weghted average fber length ( W ) W = = = Frequency dstrbutons. Dstrbuton curves show the relatve amounts of fbers and fber related values n each length category along the measurement range. Populaton dstrbuton s based on the numbers of fbers n categores. Values n each category are calculated usng formula: P (%) = n J = n j 00 Iength-weghted dstrbuton total lengths of fbers n each category are used nstead of number of fbers. The formula to calculate values n dstrbuton s: where nl P l, (%) = 00 j= P l, s the percentage of length n category, n s the number of fbers n category I, and l s average fber length of the fbers n category. 9. Reports j j Report the average fber length by methods descrbed n or fber length dstrbuton by method n 8.4. If the upper and lower length lmts for whch the mean fber lengths are calculated are user-selectable, report these lmts wth the meaengths. 0. Precson 0. Precson statements for ths procedure were determned n accordance wth TAPPI T 200 Interlaboratory Evaluaton of Test Methods to Determne TAPPI Repeatablty and Reproducblty. 0.2 Samples of commercal bleached southern pne, Scandnavan pne, brch and eucalyptus pulp were used. The ndvdual samples were taken from the same batch of pulp. The same dluton was analyzed 0 tmes wth three devces conformng to the method s specfcatons. 0.3 Standard devaton and percent repeatablty were calculated as follows:

5 5 / Fber length of pulp and paper by automated T 27 om-2 optcal analyzer usng polarzed lght 0.3. For each unt: Average fber length = the average of the length weghted average fber length after beng analyzed 0 tmes = x. Standard devaton (S e ). Standard devaton of test results (S r = S e ). Repeatablty r = 2.77 S r. Repeatablty n % = 00 r/x. The result of the repeatablty tests are shown n Table. Measurements are made wth 50 μm resoluton. Table. Replcate measurements wthn a sngle laboratory. Unt Unt 2 Unt 3 Eucalyptus Average fber length, mm Standard devaton/mm Repeatablty % Brch Average fber length Standard devaton Repeatablty % Pne Average fber length Standard devaton Repeatablty % Southern pne Average fber length Standard devaton Repeatablty % Reproducblty. To measure reproducblty samples of Scandnavan pne and brch were analyzed n 6 laboratores. Each laboratory performed three analyses of each materal and reported the length-weghted average fber length. Results of the test are shown n Table 2. Table 2. Results from round robn tests n 6 laboratores. Scandnavan pne Brch Average fber length, mm Standard devaton (s n ), mm Average standard devaton (s e ), mm s R, mm Reproducblty, mm Reproducblty, %

6 T 27 om-2 Fber length of pulp and paper by automated / 6 optcal analyzer usng polarzed lght. Keywords Pulp, Paper, Fber length, Fber length dstrbuton, Optcal measurement, Polarzed lght 2. Addtonal nformaton 2. Effectve date of ssue: ovember, Related methods: TAPPI T 232 Fber ength of Pulp by Projecton, TAPPI T 233 Fber ength of Pulp by Classfcaton. 2.3 A precson statement has been added and revsons were made n the 998 update. There were no major changes other than edtoral to the 2007 verson or ths 202 verson. terature cted. TAPPI T 232 Fber ength of Pulp by Projecton. 2. Clark, J. D A., Pulp Technology and Treatment for Paper, Mller Freeman Publcatons Inc., San Francsco, Ilvessalo - Pfaffl. M.-S., v. Alffthan G., The Measurement of Fber ength Wth a Sem-Automatc Recorder, Paper ja Puu 39 (): s (957). Your comments and suggestons on ths procedure are earnestly requested and should be sent to the TAPPI Standards Department. g