1、Viscometry Determination of kinematic viscosity using the Ubbelohde viscometer Viscosity relative increment at short flow times 1 Scope and field of application DIN 51 562 Part 1 specifies a minimum flow time of 200 s for the volume between the filling marks, as in almost all standards dealing with
2、capillary viscometers. Even greater flow times are specified for cases where the Hagenbach correction at 200 s is not negligibly small. The specification of minimum flow times leads to difficulties in fields where short flow times have in practice been customary and required. When frequent measureme
3、nts are made in practice, flow times for pure solvents of above 200 s are too long, especially when determining the Staudinger function (viscosity number, see clause 2) of polymer solutions (e.g. in accordance with the DIN 53 728 standard series), since the flow times of the solutions are even highe
4、r and, additionally, there are difficulties in the handling of the capillaries. Experience has shown that for such measurements it is better to operate with wider capillaries and shorter flow times. This standard specifies a method of determining and applying the Hagenbach correction, which is essen
5、tial at low viscosities and short flow times, and offers, together with experimental instructions, a uniform working base. oiN 51 562 Part 3 2 Concepts (see also DIN 1342) The viscosity relative increment is defined by where q is the viscosity of the solution; qs is the viscosity of the solvent; qr
6、is the viscosity ratio. When the viscosity relative increment is related to the concentration by mass of the substance dissolved in the solution, pi, the concentration-related viscosity relative increment, J, called Staudinger function (viscosity number), is obtained. 1 lV=(%-l)- ( 2) pi The concent
7、ration by mass, Pi, is mostly expressed in g/cm3, the Staudinger function, J, in cm3/g. 3 Calculation of viscosity relative increment and Staudinger function From flow times measured by the Ubbelohde viscometer, the kinematic viscosity, u, which is the ratio of dynamic viscosity, q, to density, e, i
8、s immediately obtained. Provided that the differences in density between the solvent and the solution are small, J, can be calculated from the ratio of the kinematic viscosities or that of flow times which are proportional to these viscosities. (3) IV= - .- (i I) ;i where t t, Only flow times correc
9、ted in accordance with clause 5 shall be used for 1 and t, in equation (31, not the flow times measured. is the flow time of the solution; is the flow time of the solvent. Continued on pages 2 to 5 Beuih Varlag GmbH. Berlin. has the exclusive right of sala for German Standards (DIN-Normen). DIN 51 5
10、62 Part 3 Engl. Price group 6 05.87 Sales No. O106 Page 2 DIN 51 562 Part 3 4 Hagenbach correction If the actual flow time is shorter than the minimum flow time to1 specified in DIN 51 562 Part 1, the individual values for the Hagenbach correction, A tHi, are to be determined for every capillary vis
11、cometer using suitable standard liquids of known viscosity, as follows: where tni is the flow time measured using the standard liquid, i; vi is the kinematic viscosity of the standard liquid; K is the apparatus constant of the viscometer. In accordance with DIN 51 562 Part 1, the flow times and the
12、Hagenbach corrections shall be expressed in s, the kinematic viscosities in mm2/s “1 and the apparatus constants in mm2/s2. By linear interpolation between thevalues ofAtH1 andAtHz determined for the two standard liquids i = 1 and i = 2 having flow times te, and tez respectively, the Hagenbach corre
13、ction A t, shall be calculated for another flow time, te, using equations (5) and (6) (see also figure 1): (5) (6) tg2 tg1 Flow time tg shall lie between flow times fel and tap. Curve a -correction equation (3) as in DIN 51 652 Curve b -true form of the individual Hagenbach Curve c - straight line t
14、o be interpolated from Part 1 (validity ranged) correction equation (5); it intersects curve b at points Figure 1. Example of the individual Hagenbach correc- tion for an Ubbelohde viscometer No. Oc in accordance with DIN 51 562 Part 1 Figure 1 represents an example of a typical form of the individu
15、al Hagenbach correction for an Ubbelohde viscometer No. Oc in accordance with DIN 51 562 Part 1, in which the transition from the capillary to the suspended level is funnel-shaped. 5 Correction of the measured flow times To determine the Staudinger function (viscosity number) by equation (31, the me
16、asured flow times of the solvent, te, and the solution, te, shall be corrected using the Hagenbach correction in accordance with clause 4 (see equations 7 and 8). ts = tgs - A tHs, t tg -AtH and (7) ( 8) where the subscript s represents the solvent. 6 Limitation of correction method For Ubbelohde vi
17、scometer No. O in accordance with DIN 51 562 Part 1, the method is applicable for the shortest flow times attainable in practice. For all other viscometers, attention shall be paid in cases of short flow times (see table 1) to disturbances which announce the imminent collapse of the suspended level.
18、 Figure 2 illustrates these disturbances in a simplified form. Table 1. Limiting values of the measured flow time, tg, and the Reynolds number, Re, in accordance with DIN 53 012, up to which generally no suspended level disturbances occur Ubbelohde viscometer as in DIN 51 562 Part 2 Limiting value o
19、f t, in s Corresponding Reynolds number Re Note. In some viscometers, the disturbances can occur even at slightly longer flow times, although the visual examination of the lower end of the capillary does not suggest such disturbances. 7 Apparatus and reagents The following apparatus and reagents sha
20、ll be used. 7.1 Ubbelohde viscometer with suspended level in accordance with DIN 51 562 Part 1. For measuring polymer solutions, viscometers shall be used for which the surface tension correction is sufficiently small (see also Explanatory notes). Viscometers with a lower capillary end, which is eit
21、her sharp-edged or funnel- shaped, may also be used. To reduce uncertainty of measurement, automatic measuring devices for the determination of flow times shall preferably be used. Determination of the Hagenbach correction shall be carried out in the same order as the tests. 7.2 Thermometer in accor
22、dance with DIN 51 562 Part 1. *) Previously centistokes (cSt); 1 cSt = 1 mm2/s. DIN 51 562 Part 3 Page 3 d) a) Undisturbed flow, measurement is usable b) Commencement of a disturbance at an excessively high flow rate c) Progress of the disturbance at an even higher flow rate d) Collapse of the suspe
23、nded level Figure 2. Formation of the suspended level The illustration shows the liquid alone without the glass wall of the viscometer enclosing it. Measurement cannot be used 7.3 Constant-temperature liquid circulator as specified in DIN 12 879 Part 1, capable of maintaining the test temperature co
24、nstant to within 0,Ol OC. See DIN 51 562 Part 1 for further details. 7.4 Timing device with an uncertainty of measurement of 0,02 s. The time base of the electronic measuring device shall be constant to to the nominal value. and shall correspond 7.5 Two to three lowviscosity standard liquids (see Ex
25、planatory notes) covering a range of kinematic viscosity which includes the kinematic viscosities of the solutions to be tested. The values of the ratio of surface tension to density of the standard liquids and of the solvent shall differ by less than 2 cm3/s2. 7.6 A solvent (not a mixture, if possi
26、ble) of an agreed degree of purity, suitable for preparing the solution to be tested shall be used. The surface tension and density at the test temperature shall be known. The use of one of the standard liquids as solvent is very advantageous. 8 Preparation of measurement 8.1 Preparation of viscomet
27、er The apparatus constant, K, shall be determined in compli- ance with the specifications given in DIN 51 562 Part 1. The experimental determination of the Hagenbach correction as specified in clause 4 using standard liquids (see subclause 7.5) is to be considered a special case of calibration of th
28、e viscometer for the field of application of this standard. 8.2 Preparation of samples The pretreatment of the sample supplied and the prep aration of the solution are governed by the relevant standards or they are to be agreed upon. The test solution shall be free from undissolved con- stituents. T
29、he agreed concentration by mass, i, at the agreed preparation temperature of the solution shall be kept to 0,1%. The use of filters (folded filters, fritted glass filters) in the filling of the viscometer reduces the risk of disturbances due to particles suspended in the liquid. When charging the vi
30、scometer through the filter, the first 10 ml shall be discarded in order to avoid fluctuations in its concen- tration. 9 Procedure The measurement of flow times tg8 (solvent) and tg (test solution) shall be carried out using the same viscometer. For this purpose, the capillary with the most suitable
31、 diameter shall be selected. The measurement shall be carried out as specified in DIN 51 562 Part 1. The flow times of the pure solvent shall be measured using a liquid taken from the same container as the liquid used for preparing the solutions. The number of measurements carried out on one and the
32、 same viscometer charge shall be not less than 3 and, because of solvent evaporation, not more than 5. If the flow times differ by more than 0,l % within this meas- urement series, this may be due to external influences. In such a case, the measurement shall be repeated after cleaning the viscometer
33、. Note. Disturbances due to solvent evaporation are more readily prevented if pressure rather than suction is applied. 10 Inter-laboratory testing When inter-laboratory tests of the viscosity relative increment are to be carried out on the same substances, the conditions specified in subclauses 10.1
34、 to 10.3 shall be observed. 10.1 Sampling All laboratories shall proceed in compliance with the same specifications for, or agreements on, the substances to be tested in respect of a) sampling, b) sample preparation, c) solution preparation. Page 4 DIN 51 562 Part 3 Substance 10.2 Procedure All labo
35、ratories shall observe the following standard test conditions: a) agreed type of viscometer type in accordance with b) agreed solvent (degree of purity and composition); c) agreed concentration of the substance to be tested; d) agreed test temperature; e) application of the Hagenbach correction in a
36、ccordance with this standard using the same standard liquids. DIN 51 562 Part 1; Kine- Surface matic tension1 Degree uring purity ature viscosity density OC mm2/s cmW of temper- 10.3 Expression of result The test result shall include the following information: a) identification of sample and its pre
37、paration in b) test parameters in accordance with subclause 10.2; c) relative viscosity and/or the Staudinger function accordance with subclause 10.1; (viscosity number) in compliance with the specifica- tions relating to the test report covering the substance tested; d) specifically agreed details,
38、 e.g. information concerning the apparatus constant, form of the lower end of capillary (sharp-edged or funnel-shaped), type of determination of flow times (manual or automatic). 11 Precision The precision cannot be characterized by values specified in DIN 51 562 Part 1. Irrespective of the inherent
39、 uncertainty of measurement caused by the samples themselves, these values are increased by: a) higher relative variations when measuring short flow times; b) the procedure of determining the difference between solution and solvent flow times when calculating the viscosity relative increment (see Ex
40、planatory notes); c) the uncertainty of the Hagenbach correction. Standards referred to DIN 1342 Viscosity of Newtonian fluids DIN 12 879 Part 1 Di N 51 562 Part 1 DIN 53 012 DIN 53 728 Electrical laboratory apparatus; constant-temperature liquid circulators; general and safety requirements, testing
41、 Viscometry; determination of kinematic viscosity using the standard design Ubbelohde viscometer Viscometry; capillary viscometry of Newtonian fluids; sources of errors and corrections Testing of plastics; determination of viscosity of solutions Other documents I Bauer, H.; Meerlender, G. Precise vi
42、scosity measurements of Newtonian liquids with V 1 mm2/s for the selection of suitable standards. Rheoi. Acta 23 (1984). pp. 514 to 521. Explanatory notes This standard has been prepared by NMP 831 Technical Committee Viskosimetrie because it was felt that IS0 1628- 1984, Guidelines for the standard
43、ization of methods for determination of viscosity number and limiting viscosity number of polymers in dilute solution. Part 1 : General conditions, dealing with the same range of problems, did not offer an adequate solution of the problems involved. According to IS0 1628, the Hagenbach correc- tion,
44、 AtH, should not exceed 3% of flow time t,; the correction is neglected. This may result in an uncer- tainty of measurement of the viscosity number of 4% to 6 %. Since in many cases the change in viscosity number over the whole manufacturing range of a product is less than 1 O %, this limit of error
45、 is considered too high. The Ubbelohde viscometers referred to in ISO/R 1628 do not correspond to those specified in DIN 51 562 Part 1, but to Ubbelohde viscometers specified in Inter- national Standard IS0 3105, Glass capillary viscometers; specification and operating instructions. The kinematic vi
46、scosities of suitable standard liquids of a defined degree of purity have been published l. For example, for determining the viscosity of polycarbonate (PC) dissolved in dichloromethane, the standard liquids specified in table 2 are recommended. The calculation of the viscosity relative increment is
47、 based on the difference between two numbers which Table 2. Standard liquids used for the experimental determination of the Hagenbach correction when measuring the viscosity of dissolved polycarbonate. I I I I I I I I Dichloro- Analytical methane (grade I 25*00 I 1 *O Trichloro- Analytical ethylene
48、(grade I 25,OO I 0,3683 I 200 Tetrachloro- Analytical ethylene brade I 25300 I 0,5257 I 19,5 differ only slightly from each other. This is the reason why some deviations have a significant influence on the final result, as illustrated in the following example of calculation. In an Ubbelohde viscomet
49、er No. Oc in accordance with DIN 51 562 Part 1, having an apparatus constant, K, of 0,003201 and being provided with a DIN 51 562 Part 3 Page 5 funnel-shaped lower capillary end, the measured flow time t, is 10346 sand ts is 12718 s.The differences in density between the solution and the solvent should be negligibly small. After the individual Hagenbach correction has been applied, the corrected flow times are t = 122,48 s and t, = 97.90 s. It follows that the relative viscosity is 1,251 1 and the viscosity relative increment is 0,251 1. Example a): A deviation, 6 t, of + 0,
