INDUSTRIAL A N D ENGINEERING CHEMISTRY
84
Vol. 19, No. 1
The Freeness of Groundwood Pulp’ By D. S. Davis BUREAUOF TESTS,INTERNATIONAL PAPER Co., GLENSFALLS, N.Y.
S BROUGHT out in the first paper of this series,2 of groundwood and the stock does not contain the ‘(flour,” one of the most important properties of stock for or fine:particles of mechanical pulp. Consequently the mechpaper-making purposes is its freeness, or the rate of anism of the drainage of water from the two types of fibers drainage of the water from the fibers on the Fourdrinier wire. must differ greatly. The effect of change of consistency of the fiber suspension This difference is evident from a very superficial examinaupon freeness was discussed in the case of sulfite stocks. I n tion of the contents of the tester cup,2 during a test on each the second paper3 the effect of temperature upon the free- stock. When the liter sample of sulfite at 0.400 per cent conness of sulfite was taken up. sistency and 20” C. is poured into the cup and the valve It is the purpose of the present paper t o show the effects tripped all the fibers have formed a mat upon the wire at of consistency and temperathe time of cut-off. The ture upon the freeness of water passing to the gradugroundwood stocks. ate is quite clear and the sum Data presented show that increasing consistency-deWith sulfite and the of the volumes of water in creases the freeness (rate of drainage) of groundwood Model “B” Williams freethe graduate and that passstocks in a manner similar to that for sulfite stocks and ness tester it was f o u n d ing to waste is almost 1liter, that the mathematical relationship between consistthat freeness decreases with the remainder adhering to ency and freeness is the same for the two stocks. The increasing consistency and the fibers in the mat. I n paper contains a chart which enables freeness values that the reciprocal of the the case of g r o u n d w o o d determined at one consistency to be converted to freefreeness is a linear function tested a t the same consistness at other consistencies. This chart holds over a of the consistency of the ency a n d t e m p e r a t u r e ; fairly wide temperature range. stock. It was further found relatively few of the fibers The freeness of groundwood is-affected independently that freeness increases with have formed a mat upon and simultaneously by the temperature and viscosity increasing temperature, but wire a t the time of cut-off. of the suspending medium. Freeness-temperature and not linearly, for the rate of I n spite of this fact the mat freeness-viscosity plots are included. The freeness of change of freeness decreases is of a very dense character groundwood stock is shown to decrease stightly upon with increasing t e m p e r a and water drains through it standing. ture. In addition it was very slowly, so slowly that shown that increasing temthe water passing into the perature increases freeness conical chamber-overflows almost entirely by virtue of the attendant decreasing viscosity. into the measuring orifice and graduate only for a few seconds after the valve is tripped. The level then falls below the Work of Other Investigators edge of the measuring orifice and any water which slowly Very little work on freeness has been described in the seeps through the fiber mat is amply taken care of by the literature. What has appeared has referred entirely to a side- waste orifice. I n addition, the water passing into the outlet type of tester. With such a tester, Monroe4determined graduate is always very cloudy, although the water which the variation of freeness of groundwood between 45” and 90” later drains only through the waste ori6ce is much clearer, F. He found the freeness-temperature curve to be concave a denser fiber mat having been formed meantime, which to the temperature axis; that is, the rate of change of free- acts as a better filter. At the time of cut-off, practically ness with temperature dropped off slightly with increasing all the water is still in the tester cup and nearly all the fibers temperature. Brawn,6 using a Green side-outlet tester, are stili in suspension. Groundwood stocks, then, test infound the reverse to be true-that the rate of change of free- variably “slower” (less free) than sulfite stocks, the difference ness with temperature increased with increasing tempera- being due to the shorter fibers and to the presence of “flour.” Bearing in mind these differences, no other predictions ture. He also gave data which showed the extent to which the freeness of groundwood stocks was decreased by the about the influence of consistency and temperature were utilization of white water of various consistencies instead of made except that it was expected that freeness of groundwood fresh water. He ascribed this decrease in freeness to the would be found to increase with decreasing consistency and presence of the fine ‘(flour,” always present in groundwood with increasing temperature but that the manner of the white water, which filled up the voids between fibers and thus change would probably not be that found for sulfite. Nothing at all could be said about the effect of viscosity as dismade the fiber mat on the wire of the tester much denser. tinct from that of other effects attendant upon temperature.
A
Differences between Groundwood and Sulfite Pulp
On account of the striking dissimilarity of the two stocks, it seemed almost impossible to predict at all exactly the influence of consistency, temperature, and viscosity upon the freeness of mechanical pulp from the effect of these variables upon sulfite. Sulfite fibers are invariably longer than those Received August 24, 1926 :THISJOURNAL,18, 631 (1926). 8 Page 162, this issue. Paper Trade J . , 74, 235 (1922). 8 Ibid , 76, 50 (1923). 1
Freeness-Consistency Data
The procedure was almost identical with that previously reported. For the freeness-consistency work, three master stock suspensions of about 0.5 per cent were diluted to several other consistencies on which freeness determinations were made at 20” C. The data of runs 12, 14,and 15 are plotted in Figure 1. The forms of the curves are similar to the freeness-consistency curves for sulfite although the data lie in a much lower freeness range. The best lines were drawn on the assumption that the curves should all pass through 925, the
INDUSTRIAL A N D ENGINEERING CHEMISTRY
January, 1927
freeness of stock at zero consistency, or water, and that the curves were hyperbolic. MATHEMATICAL DIscussIoN-The general form of the equation is - = KC+A
85 Table I
I
c. 40.5 36.3
C
Fat C
consistency
0,308 0.307
F cor. to
0.400%
72.5 67.5
57 52.5
F a t 0.400% detd. at 200 c.
58.5 55.0
F
where A , H , and K are constants. As in the case of the corresponding sulfite data, H is chosen to be 1000 for convenience and, since all the hyperbolas have a common intersection a t 0, 925, we may substitute these values for C and F , respectively, in the general equation and solve for A . The value of A is 1.081 and the general equation becomes
'Oo0 = K C + 1.081 F
The equations of the individual curves are R u n 12
' 0 0 '= 35.6C + 1.081 F
Run14
'Oo0 = 41.1C
Run15
+ 1.081 'Oo0 = 43.9C + 1.081 F F
F i g u r e 2 was cons t r u c t , e d from the general equation
F
The method followed in the freeness-temperature work was similar t o that in the case of sulfite. Figure 3 presents data on several determinations made a t intervals in the range of 10' to 50" C. Both runs show that the freeness of groundwood is a linear function of the temperature. This was not the case with sulfite pulp, where the freeness-temperature curves appear to approach a freeness asymptote. However, even in the case of sulfite the lines straighten out a t low temperatures and freeness values, which makes it seem reasonable that a very slow stock such as groundwood should show a linear freeness-temperature relation. The equations of the curves are
F
Run 16 Run 17
FREE N E SS-CONSISTESCY CHART-
loo0 = KC
Freeness-Temperature Data
+ 1.081
and since the equations of the functions plotted along the axes are
= 0.937t F = 0.8781
+ + 29.3 27.1
where F is the freeness in cubic centimeters and t is the temperature in O C. It is seen that the rate of change of freeness of groundwood with temperature is constant and has an average value of 0.91 unit per degree. I n the case of sulfite the rate of change was not constant. It was a function of the freeness and required a differential equation for its expression: dF
dt = K(+ - F)
where K and 9 are constants, the latter representing the freeness asymptote.
x = qc
Y
= 7 (1000 4
t h e c u r v e s a r e all &straight lines with a c, PKR cm7 c o ~ s / s r ~ w c r common p o i n t of Figure 1 convergence. The use of the chart is as follows: 3 -~ 020
025
030
03
041
0.95
Given the freeness of a stock as 55 determined a t 0.44 per cent consistency. What is the freeness at the standard 0.400 per cent? Follow the 55 line horizontally t o its intersection with the 0.440 per cent line and read the freeness along the slant lines t o be 60. What is the freeness at 0.340 per cent? Follow along the slant lines from the 0.440 per cent, 55 intersection to the 0.340 per cent line, and read 70.
Obviously, the chart enables one to dispense with the adjustment of consistencies to exactly 0.400 per cent. The actual consistency need only be known, for the apparent freeness a t this consistency may a t once be converted to freeness a t the standard 0.400 per cent. Considering the extreme dissimilarity of the two stocks, it is remarkable that the freeness of groundwood should follow the same law, with respect to consistency, as does sulfite. USE O F CHART FOR OTHER TEMPERATURES-[rhe data for the freeness-consistency chart of Figure 2 were determined at 20" C., but, as in the case of the chart for sulfite, theresults may be used at other temperatures with reasonable accuracy. Table I bears out this statement. Freeness determinations were made a t about 40" C. a t consistencies of about 0.31 per cent and corrected to 0.400 per cent by means of Figure 2. These values were compared with others determined a t consistencies much closer to 0.400 per cent. The agreement is considered satisfactory.
09
03
C,
PLX
CENT
05
CONS/STfNCY
Figure 2
Figure 4 is a plot of the freeness data of runs 16 and 17 against the viscosity of water a t the temperatures involved. The lines show a much greater curvature than do the corresponding ones for sulfite and the shape is that of the temperature-viscosity curve for water. This is not surprising, since freeness is a linear function of temperature, for i t amounts only to defining a new temperature scale. It is exactly
I N D U S T R I A L d S D ESGISEERI-VG CHEMISTRY
86
analogous to stating that the shape of the viscobity-' F. curve should be similar to that of the viscosity-" C. curve. Relation of Viscosity
Vol. 19, No. 1
paper machines on Monday if the stock has stood since Saturday night. In the preceding paper data were presented dealing with the decrease in freeness of sulfite upon standing 3 and 4 weeks. Table I1 contains similar data for groun&ood. The decrease is probably due to slight fiber decomposition.
I n working with sulfite the question arose a3 to xhether temperature influenced freeness solely by virtue of its effect upon viscosity. That this was alm o s t exactly the case w a s e s t a b lished by determining the freeness of a stock suspended By A. M. McCollister and C. R. Wagner in a sugar solution, the temperature of THE PUREOIL Co., CHICAGO,ILL. which was high e n o u g h t o cause T7ERYuseful piece of apparatus for use on gas-analyzing the viscosity to be outfit's is shown in the accompanying sketch. It can the same as that of be easily made by any machinist from parts found in the shop. water at a much It was designed and is being used by the authors on a Fisher lower temperature. Universal gas analyzer, which is the Bureau of Standards This freeness value Orsat apparatus, but it can be applied on any gas-analyzing I was found to agree outfit or other appara'0 20 x, 40 so closelywiththatof tus where the accurate t DEGR[S C the same stock de- adjustment of a leveling Figure 3 termined in aque- bulb is desirable. ous suspension a t the lower temperature bqt a t the same The device consists viscosity. It was therefore concluded that for the same briefly of the following: stock suspending mediums of equal viscosities gave rise to A sliding block carrynearly equal freeness values, regardless of the temperatures ing the ring for the bulb, involved. which is actuated by a
Device for Adjusting the Leveling Bulb on a Gas-Analyzing Apparatus'
A
ol
b
Table I1
Run
Days
F, 20" C.
16 17 19
0 9 36
48 45 41
This conclusion is not valid for groundwood stocks. Freeness determinations were made in aqueous suspensions and the contents of the cup were combined with the effluents from the two orifices and filtered through a weighed cloth. The excess water was removed by suction and the damp fibers were suspended in a 20 per cent sugar solution, made up to 1 liter and again tested for freeness. As the average of two determinations, it was found that at a concentration of 19.70 per cent sugar, a temperature of 40.0' C., and a viscosity of 1.185 centipoises the freeness mas 46.0. With a water suspension, the freeness was 35.5 at 13.6' C., at which temperature the viscosity was the same as before. When the t e m p e r a t u r e Fvas 40.0' C., which corresponded to a tiscosity (for water) of 0.656 centipoise, the freeness was 59.5. At constant viscosity, then, freeness decreases with decreasing temperature, and a t constant temperature, freeness increases with decreasing viscosity.
I
"Slowing" of Stock
It is the experience of paperm a k e r s t h a t stock becomes somewhat slower upon standFigure 4 kgin the beaters and in the beater and machine chests even over a week-end. The effect is great enough to make itself evident in the operation of the
screw f i t t e d w i t h a k n u r l e d w h e e l . The main body of the device is carried on an ordinary r i n g - s t a n d c l a m p for coarse adjustments. An ordinary split ring was sawed in two about the middle of the shank and both of these ends were threaded. The sliding block was drilled and tapped to receive the ring and the m a i n b o d y was fitted with the clamp portion of the original ring. Rough adjustment is obtained by moving the whole device-and clamping t o the ring stand and very accurate adjustment is obtained by means of the screw and sliding block.
The accompanying cut shows ring actuated by rack and pinion which is an alternative method of construction. Either method should be satisfactory and need only to depend upon material available. 1
Received October 1, 1926.
Definition for Cultured Skimmed Milk Proposed by Standards Committee The Food Standards Committee has proposed the following definition and standard for cultured skimmed milk, "cultured buttermilk :" CULTURED SKIYMED MILE, "CULTURED BUTTERMILK." is the product obtained by souring skimmed milk, or partially skimmed milk, by means of special cultures of the streptococcus laclicus type. It contains not less than eight and five-tenths per cent (8.5%) of milk solids not fat.
Criticisms and suepestions regarding the DroDosed definition and- standard are i&ited from- food -officiais, consumers, the trade, and all interested parties. Communications should be addressed to the Secretary of the Food Standards Committee, B~~~~~ ,,f Chemistry, Washington, D. c., and reach him not later than February 15, 1927.
