CA1103137A - Method of monitoring surface charge of suspended materials colloidal system - Google Patents

Abstract

ABSTRACT OF THE DISCLOSURE
A titration technique for measuring the surface in a papermaking colloidal suspensions, particularly on the furnish in a papermaking process. The surface charge measurements are used to determine the optimum conditions for maximizing the drainage rate and first pass retention on a papermaking machine. The amounts of a cationic and anionic polymer that adsorb onto the surface of the headbox furnish components are measured by a colloid titration technique and the surface charge is calculated. A furnish having a met positive surface charge on its suspended particles adsorbs more anionic polymer than cationic polymer. The opposite is true in a negatively charged system. The ratio of the amounts of each polymer adsorbed onto the surface of the suspended particles in the furnish is determined by the sign and magnitude of the surface charge of the system. The ideal surface charge is determined experimentally for each paper or board machine and then can be maintained on the papermaking machine by adjusting pH, alum level, broke addition and wet additives.

Description

BACKGROUND OF TII~ INVENTION
Controversy has existed for many years on the most appropriate way to effectively measure the surface charge on the solid components of a papermaking furnish in order to optimize drainage and retention.
At present, almost all existing methods utilize an electrical approach to obtain these measurements. See: Melzer, J., "Zeta-potential and Its Importance in Paper Manufacturing", Papier 26 (7):
305 (1972). Electrophoretic mobility measurements, initially developed for measuring the charge on suspended particles in river water systems, have had the most acceptance in the paper industry.
In water treatment, the particles being studied are generally col-loidal in nature and thus electrophoretic mo~ility measurements have proved adequate. In contrast, the paper machine headbox furnish contains large fibers that are not colloidal in nature and rapidly settle out of suspension if not adequately agitated. Consequently, such fibers are not well suited to electrophoretic mobility measuring techniques.
Papermakers have tried uasuccessfully for years to adapt procedures to make electrophoretic mobility measurements on the long fiber component of the headbox furnish. Systems, such as the mass transport analyzer, have not met with a great deal of overall success.
See: Britt, K.W., et al., "Electrophoresis in Paper Stock Suspensions as Measured by Mass Transport Analysis", TAPPI 57 (12): 81 (1974).
In lieu of measuring the charge of the fiber furnish, electrophoretic mobility measurements have generally been made on the colloidal particles of the headbox furnish (fines and filler) and then extra-polated to represent the charge on the total system. See: Anderson R., et al., "How to Maximize Drainage Through Zeta Potential Control", Paper Trade Journal 158 (38): 22 (197~) and Strazdins, E., "Critical Phenomena in the Formation of the Rosin--Aluminum Sizing Complex", TAPPI 48 (3): 157 (1965).
Disagreement still exists as to whether the charge on the q~

~Q313~

rines represents the charge on the to~al furnish. Strazdins recently showed that the charge on the fines is dependent on the amount of shear to which a sample is subjected. The electrical surface charge potential of a headbox sample and that which is measured on the fines of a tray water sample differ considera~ly because a large amount of shear occurs during fiber deposition on the paper machine wire. Laboratory prepared samples have been mea-sured for zeta potential, and correlations have been developed between electrophoretic mobility measurements and optimllm drainage and retention. However, in spite of numerous publications claiming the value of zeta potential measurements, many mills have had difficulty ;~
in using this method.
A method has been developed for measuring surface charge of ~uspended solids in water. The method is based on the re1ative amounts of a cationic polymer that adsorbs onto the suspended solids.
See: Xawamura, S., et al., "Coagulant Dosage Control by Colloid Titration Technique", Pu e Univ., ~ng. Bull., ~xt. Ser. 121: 381 (1966). Excellent correlations were shown to exist between the amount of the cationic polymer adsorbed and the electrophoretic mobility of suspended clay solids. However t Kawamura et al. did not employ anionic and cationic tests to obtain "colloid titration ratio", which is an important improvement allowing accurate deter-mination of true surface charge potential. Such a determination is particularly important in a paper making process in which control of the suræace charge i5 really the factor which determines optimum first pass retention and drainage.
United States Patent 3,576,713 describes a process for determining the ionic character of a paper mass employing metachromasy to determine the maximum amount of a cationic starch that can be adsorbed onto a papermaking furnish. ~lowever, this procedure only allows one to determine the maximum amount of cationic starch that a papermaking s~stem will adsorb and provides no means to 313~
dctermi~e the sign and magnitude of the charge on thc furnish.
GENER~L DI~SCRIPTION OF Tlll~ INVI~I~TIOI~
The present invention is directed to the use of adsorbed polymers to determine the electrical surface charge potential by means of colloid titration in colloidal systems such as the headbox furnish in a papermaking system. This method offers many advantages for papermalers when compared with current techniques of zeta potential measurement. In colloid titration, particle size is not a limiting factor, so the surface charge on the entire colloidal system, such as the furnish, can be easily measured.
Cationic and anionic demand of the paper machine furnish system have been measured using certain cationic and anionic dyes.
However, it is believed the dye molecules are small enough to penetrate and interact with charges on the internal cellulose sur-faces so that such a measurement is not that of the surface charge.
Even though the internal portions of the cellulose surfaces may be strongly anionic, the outer surface charge may be the same or oppositely charged. The surface charge is the needed measurement to accurately determine the system control required for best first pass retention and drainage rate. Larger molecules (charged polymers) that are physically too large to enter into the porous structure of the cell wall, and which adsorb only on the fiber surface are used to measure the surface charge in the headbox furnish. Anionic and cationic charges that exist in the interior of the fiber are inaces-sible, and only surface charges are measured. The presently preferred colloidal polymers are methyl glycol chitosan and potassium polyvinyl sulfate. Other polymers can be used, such as "Polybrene"* which i5 1, 5-dimethyl-1, 5-diazaundecamethylenepolymethobromide obtained from Aldrich Chemical Company, Inc., Milwaukee, Wisconsin. Poly-brene is cationic, and can be used instead of methyl glycol chitosan.
The method of the invention is based on the fact thatnegatively charged anionic polymers such as potassium polyvinyl sulfate interact in solution with certain positively charged cationic C

*Trademark 3:137 polymers such as methyl glycol chitosan in almost a stoichiometric relationship to produce a precipitate. This interactian exists even in very dilute polymer solutions (.0002 to .0005N~, and the precipitate forms near the isoelectric point, and is almost non-ionic.
Methyl glycol chitosan and potassium polyvinyl sulfate react almost stoichometrically to neutralize one another to form an insoluble precipitate, as set forth below:

Rl-S4 K+ + I (C~-I3)3 NR2 ~RlSO4 N-R2 + KI
(Potassium poly- methyl glycol (CH3)3 vinyl sulfate) chitosan (PP~ ) :

Toluidene Blue O ~ye is used as an indicator dye for titrating the cationic polymer with the anionic polymer. This dye changes color from blue to pin~ in the presence of an anionic polymeric system. It does not have any interaction in the presence of a ca~ionic polymeric system, so it remains blue.
In a cationic polymer system, the indicator dy~ (Toluidene Blue O) is blue. Titrating the cationic polymer system with an anionic polymer solution causes an insoluble precipitate to form, and both the anionic and cationic polymers are removed from solution.
At first, the anionic polymer does not cause the indicator dye to Change color because it is rapidly removed from the solution by interaction with the cationic polymer. ~owever, when the cationic polymer is totally precipitated, additional anionic polymer creates an excess of anionic polymer which interacts with the blue indicator dye to produce a color change to pink. This color change is called "metachromasy". It is easy to determine the amount of cationic polymer in solution from the amount of anionic polymer required to carry the titration to the point of color change.
The colloid titration technique can he readily used to measure the amount of polymer that remains in solution. By adding a fixed amount of polymer to a pulp furnish, the amount of a cationically ~313~

or anionically charged polymer adsorbed OlltO a pul~ furnish can also be determined in this way. It follows that a headbox furnish with an overall negative charge will adsorb more of an oppositely charged polymer (cationic polymer~ than a polymer of the same charge (anionically charged polymer). The reverse is true in a positively charged furnish.
The method developed is based on the adsorption of cationic and anionic polymers to measure the surface charge potential of the entire furnish of a papermal-ing system. The ratio with which each polymer adsorbs (colloid titration ratio) is correlated with machine performance characteristics, such as drainage and retention.
The papermaking system has optimum drainage and retention when this ratio (amount of anionic polymer charge adsorbed/amount of cationic polymer charge adsorbed) is c~lose to, or slightly greater than unity, and zeta potential is close to zero. Systems with colloid titration ratios greater or less than one were generally found to be more dispersive and consequently had lower retention and longer drainage times. Zeta potential measurement on the tray water fines by electro-phoretic mobility measurements did not always produce this same correlation.
: The surface charge potential determined by colloid titration can be used to optimize drainage and retention of a specific paper machin~. The surface charge on a measured sample of the headbox furnish is varied in a systematic way using a measured amount of wet-end additive such as alum or retention aids. The drainage or retention characteristics are then measured using a dynamic drainage jar and freeness tester. The surface charge is then measured by the colloid titration technique. Once the ideal surface charge has been determined experimentally, it is maintained on the papermaking machine by adjusting wet-end variables such as pH, alum level, broke addition and retention aids.

3~37 The adsorption characteristics of a cationic polymer (methyl glycol chitosan) and an anionic polymer (potassium polyvinyl sulfate) were investigated on the solids fraction of a tray water furnish for comparison with electrophoretic mohility measurements. The tray water samples were collected from a series of experiments designed to determine the effect of alum addition on first pass retention at a constant pH. The procedures and colloid titration technique described after Example 8 below were used.
The tray water fines adsorbed more of the anionic polymer as the alum content of the headbox furnish was increased because the fines fraction is normally negatively charged at low alum levels and thus does not attract an anionic polymer. Increase of the alum level created more cationic sites on the fines and more anionic polymer was adsorbed.
The cationic polymer adsorption was greatest at low alum levels in which the pulp was at its greatest negative character.
Surprisingly, the fines fraction adsorbed very little cationic polymer in the alum free condition, and essentially adsorbed no cationic polymer at levels higher than 20 lbs.ton.
Even in the alum free system which should be negatively charged, it was found that some cationic sites exist on the fines to interact with potassium polyvinyl sulfate. With the addition of alum, most of the negative sites disappear, since no cationic polymer adsorbed on the fines at levels greater than 40 lb./ton. These adsorption measurements indicate that there is no point where the fines fraction i5 non-ionic. Rather, it appears that the surface charge is made up of an accumulation of anionic and cationic sites which exist simultaneously.
When the particle surface in question has a net negative charge, then more of the positively charged polymer will adsorb and the ratio will be less than one. Conversely, if the particle surface contains more cationic sites than anionic sites, the net 11~13137 surface charge will be positive, and more of the anionic polymer will adsorb, and the colloid titration ratio will ~e greater than one.
The logarithm of the colloid titration ratio gives values less than zero for negatively charged systems, and values greater than zero for positively charged systems. Systems close to neutral will adsorb equal amounts of anionic and cationic polymer and the logarithm of the ratio will be close to zero.
This method is based on the amount of polymer charqe ads~rbed, and not on the actual weight of the polymer, so the wei~ht of each polymer adsorbed does not produce the desired ratios. The two polymer solutions were adjusted so that a predetermined volume of one polymer solution was neutralized by an equal volume of the other polymer solution so that the desired ratios could be obtained.
A system that is neutrally charged requires equal volumes of each polymer solution to saturate the surface, even though more of the methyl glycol chitosan, by weight, than polyvinyl sulfate is actually adsorbed. The volume of polymer solution required to neutralize the surface charges present on a sample is defined as ~he polymer charge adsorhed.

Polymeric adsorption following the method of Example 1 was performed on a fines fraction from a papermaking system headbox furnish, and the results compared to electrophoretic mobility measurements made on the same sample. Electrophoretic mobility measurements of the fines fraction showed a poor correlation with increases in alum level. The surface charge became zero only at alum levels where the first pass retention was already adversely affected. The zeta meter measurements for this sample indicated a negative charge still existed when the fines fraction no longer adsorbed any cationic polymer. Knowing the zeta potential of the fines for this system would not have aided the papermaker in pre-1~3137 dicting the optimum charge conditions for maximiæing retention,but the colloid titration of the headbox furnish did show that about 20 lbs./ton of alum should be added to improve first pass retention in this particular system.

A.
Another pulp sample was prepared and beaten in distilled water, and the fines fraction was collected after determining the first pass retention using the Britt dynamic drainage ~ar method described more fully~following Example 8 below. ~hen tested with the colloid titration method of Example 1, this fines fraction initially adsorbed more anionic charge than cationic charge, and hence the colloid titration ratio was greater than one. This showed that the fines had a positive charge, even in an alum free system. Iron from the beater may have helped to make the charge slightly cationic.
The maximum retention occurred where the fines adsorbed zero ml of the cationic charge.
B.
When the polymer adsorption ~as measured on the simulated headhox furnish of this same system, much more of the cationic polymer was adsorbed than was the case for the fines fraction. The amount of cationic charge adsorbed decreased to zero at an alum level of 320 lbs./ton.
Initially, the furnish adsorbed almost three times more of the cationic charge than the anionic charge. This was the expected result for a pulp beaten in distilled water with no alum present.
As the alum level increased, the furnish adsorbed more of the anionic charge, and less of the cationic charge. Consequently, the colloid titration ratio increased from a value of less than one to infinity, and the logarithm of this ratio increased from a negative value to a positive value.
At about 15 lbs./ton of alum, the amount of anionic and cationic ~i~3~3~
narge adsorbed was about equal. This corresponded to the maximum first pass retention. It appears from these results that measuring the charge on the headbox furnish by colloid titration is much more meaningful than measuring it on the fines for predicting the optimum alum level for achieving the maximum first pass retention. The fines fraction titration indicated that the system was highly cationic at the point of optimum first pass retention.
EX~MPLE 4 An attempt was made to measure zeta potential by electro-phoretic mobility measurements. ~his produced results similar toExample 2 above. However, at the point of maximum retention, the zeta meter indicated that the furnish was still highly negative.
Zero zeta potential occurred only at alum levels too high to give maximum first pass retention. These results were similar to those found by others. A zero zeta potential could be attained only at very high levels of alum.
No correlation could he established between actual first pass retention and zeta potential. In contrast to this, excellent cor-relation of first pass retention to colloid titration ratio of the headbox furnish was possible. In addition, the maximum first pass retention appears to occur at a colloid titration value close to zero.
The alum levels used in this experiment represent typical equilibriums which occur on the paper machine due to the recycling of the white water system. Alum concentrations in the S0 to 1~0 lbs./ton range have been found in several actual paper machine furnishes tested.

Wet End Starc _ A typical papermaking furnish containing alum, rosin, clay and titanium dioxide was made in the laboratory following the procedure described below (after Example 8). The effect of added increments of a cationic starch and an oxidized starch were then ~lU3~37 `~luated, using the colloid titration method described bclow (after Example 8).
The colloid titration ratio indicated that the papermaking furnish without any additives was negatively charged. The first pass retention increased to a maximum ~ith the addition of a small amount of cationic starch after which further incremental additions of the cationic starch reduced first pass retention. The fines fraction in this system had a surface charge slightly more cationic than the whole furnish. This indicates that the fines adsorb cationic starches in a similar manner to the fiber fraction, and that the surface charge on the fines, when due to adsorbed polymers, is not as susceptible to shear forces which occur on the paper machine wire.
The cationic starch initially neutralized the negative charge on the furnish and thus the system became less dispersive and drained more freely. Past a certain point, the cationic starch increased the dispersion of the system and the freeness again decreased. The addition of oxidized starch made the surface charge more negative than it already was, and the drainage rate decreased.
Measurements indicated that the freeness in this system was strongly dependent on surface charge, and that the optimum drainage rate occurred at the same colloid titration ratio that produced the maximum first pa~s retention.
The use of ionic starches appears to have a much greater effect on drainage than alum, and there is a very narrow range of surface charge where optimum drainage occurs.

Papermaking systems generally fall within the pH range of 3 to 8, so the stoichiometric relationship between the anionic and cationic polymers was checked to determine stability over this pH
range. Four ml of thecationic pol~ner solution was added to 25 ml of pl~ adjusted distilled water (pH adjusted with HCl or NaOH) and titrated with the anionic polymer solution. The 1:1 stoichiometric ...,~

~103~37 ~ relationship remained fairly constant irrespective of p~l, increasing only slightly from plT 3 to plI 8. This test shows that the t~pical mill furnish pH does not present a major problem in using the colloid titration technique.
The colloid titration ratio method of this invention elimin-ates the necessity of determining the amount of polymer adsorbed per gram of furnish. However, because headbox consistencies vary widely, the amount of polymer added per gram of furnish will affect the amount adsorbed. Fortunately, the proportion of each polymer adsorbed remains constant, and has little effect on the colloid titration ratio. Also, the dilution factor of adding up to 5 ml of polymer solution to 25 ml of furnish appears to have a minimum effect. The amount of polymer adsorbed per gram of furnish is useful in indicating the amount of a particular compound such as a wet strength resin, retention aid, dye or dry bonding agent th~t a particular furnish will adsorb.

Using the colloid titration method described herein, a mill furnish stuff hox sample was found to have a colloid titration log of the ratio -1.40 (highly negative) value measured before the addition of re~ention aid. After the furnisll was diluted with the recirculated tray water and the retention aid was added, the log of the colloid titration ratio increased to 0.3, which is within the range for optimum first pass retention.

The results of a trial on a fine paper machine using the subject colloid titration method are set forth below in Table I.
Headbox furnish samples were taken during and after a wet end starch trial and first pass retention was determined under controlled conditions using the dynamic drainage jar.

~la3~3~

T~LE 1 Effect of Colloid Titration Ratio of the First Pass Retention of a Fine Paper Machine Headbox Headbox Head- First Log Alum Consis- box Pass Colloid Colloid Concen- tency Filler Reten- Titration Titration Time pH tration g/100 ml % tion % Ratio Ratio During Cationic 5.1 42 lb./ton 0.522 21 78.0 1.54 +0.19 10 Starch Trial 17 hours after 5.1 46 lb./ton 0.555 32 68.6 0.83 -0.081 trial During the starch trial, the cationic starch maintained the colloid titration ratio in the range for optimum retention (1.54~
and first pass retention was 78.0%. Seventeen hours after the starch was removed from the system, the colloid titration ratio decreased to 0.83 and the first pass retention decreased to 68.6~. As a result of the decrease in retention, the headbox filler content increased from 21 to 32%.
Samples of the headbox furnish ~ere taken during and after the trial for retention evaluation using the dynamic drainage jar.
The drainage jar test procedure is described helow under "Procedures"
- First Pass Retention.
When an additional 8 lb./ton of the cationic starch was added to each sample, the sample taken during the starch trial showed very little improvement in first pass retention, increasing from 78.0% to 79.0%. This was probably due to the surface charge being slightly lower than its ideal value. The additional cationic charge coming from the 8 lb./ton of cationic starch added then took it past the surface potential that produced optimum first pass retention.
On the other hand, 17 hours after starch trial, the furnish had become negatively charged, and could easily accommodate the additional cationic charge coming from the cationic starch. The colloid titration ratio moved into ideal range for retention as the first pass retention increased from 68.8 to 84.1%.

.~ ~

Every paper or board machine has a characteristic colloid titration ratio that results in optimum performance of retention or drainage. To establish the optimum colloid titration ratio, a headbox sample should be evaluated using the constant conditions of the dynamic drainage jar. The pulp furnish surface charge should then be varied by adding different concentrations of anionic and cationic additives, and the results should be plotted to obtain a continuous curve showing the actual results, and what can be expected by each adjustment. The optimum colloid titration ratio may then be maintained on a paper machine by adjusting alum level, pH, broke `~ addition and wet end additives.
The colloid titration method of this invention measures the charge on the total headbox furnish, including the long fiber fraction, so that accurate and effective adjustments to the total system can be made. The system is inexpensive since no exotic equipment is required, and operators may be easily trained in the use of this technique, making it a feasible technique for in-process control, because the results are easily reproduced by different operators.
Even very opaque and disperse systems, and systems having a high specific conductance can be measured. Thick stock and tray water solids can be measured easily. Most important, the actual adsorption of wet end additives can be determined accurately.
The colloid titration method determines accurately optimum conditions for optimum drainage and retention improvement. The method is fairly rapid, only 10 minutes being necessary to make one measurement.
PROCEDURES
Furnish The simulated laboratory furnish used in these experiments consisted of a 50:50 mixture of bleached kraft softwood and bleached sulfite hardwood pulp. After refining in a laboratory Valley beater, 1~03137 10% clay and 5% titanium dioxide was added. When an alum free system was re~ui~ed, distilled water was used throughout. In making up a typical mill furnish, 10 lh./ton of rosin size and 20 lh./ton of alum was added to the above furnish. The desired pH
was adjusted to 4.5 with ~Cl or NaO~.
Freeness Tests Schopper-Reigler freeness tests were carried out at 25C. No dilution of the headbox sample was made since the consistencies used were close to 0.5~. The volume of free water collected ~in ml) was used instead of S.R.
First Pass Retention First pass retention was measured using Britt's dynamic drainage jar tester described in Britt, K.W. "Mechanisms of Retention During Paper Formation", TAPPI 56 (10): 46 (1973). The sample was introduced into the jar and stirred at 1200 rpm for 30 seconds before draining at 800 rpm. The first 50 ml coming through the jar was discarded. The next 100 ml was then collected for determining retention.
COLLOID TITRATION METHOD
Reagent Preparation Toluidene Blue 0 dye is prepared at a 0.1% solution in distilled water. The cationic polymer solution is made by dissolving approximately 760 mg of methyl glycol chitosan in 400 ml of distilled water. The anionic polymer solution is made by slowly adding 265 mg of potassium polyvinyl sulfate to 400 ml of hot distilled water.
The two polymer solutions have to be standardized so that one volume of cationic reagent will be neutralized exactly by one equivalent volume of the anionic reagent. To accomplish this, 5 ml of the cationic reagent is pipetted into 25 ml of distilled water and 1 or 2 drops of indicator dye is added. This sample is titrated with the anionic polymer reagent until the color changes from blue to pink. The volume of either the anionic or cationic polymer 11~3~37 & ~ution is adjusted so that 5 ml of the cationic polymer solution is neutralized by 5 ml of a~nionic polymer solution.
The cationic and anionic polymers were obtained from ICN
Pharmaceuticals, Inc., Life Science Group, 121-Express St., Plainview, New York 11803.
Another cationic polymer which can be used in 1,5-dimethyl-1, 5-diazaundecamethylene polymethobromide, brand name, Polybrene*
(Aldrich Cat. No. 10768-9), Aldrich Chemical Co., Inc., Cedar Knolls, N.J. 07927. Other polymeric reagents may be used in place of methyl glycol chitosan and potassium polyvinyl sulfate but caxe must be exercised in choosing them. Color end points may become less distinct, or molecular wei~hts may become so hi~h that Van der Waal's forces of attraction may obscure the effects of adsorption due to opposite charges. Low molecular weight polymers may penetrate into the fiber wall, which causes erroneous results. Also, it is important that the t~o polymers selected will interact stoichio- ;
metrically.
Test Method Measure out t~o 25 ml samples of headbox stock into two ;
centrifuge tubes. A recalibrated 25 ml graduated pipette that has been cut off at the tip to avoid fiber plugging may be used. To one of the samples, add 4 ml of the stanaardized cationic polymer solution. To the other sample, add 4 ml of the standardized anionic polymer solution. Agitate both slightly. After ahout one minute, centrifuge both samples until the liquid phase is clear. Transfer 10 ml ~f clear supernatant liquid from each sample into two separate 50 ml beakers and add one drop of indicator solution. For titration purposes, diluted standard reagents (5X) are used. Titrate `
each 10 ml sample with the dilute polymer solution of opposite charge. In the event that the endpoint is missed, the sample may be back titrated. For precise work a blank determination on a 25 ml clear supernatant headbox sample should be run.

.~
*Trademark :' 11(~3137 When t~le cationic nolymer ;n distilled water is neutralized by potassium polyvinyl sulfate, there is an ahrupt and distinct color change. With excess alum in the system, the color change becomes less distinct, going from blue to purple to pin}~. Since the indicator dye functions ~y adsorhing onto the negative sites of the titrated anionic polymer, the excess alum must interact to reduce the overall negative charge on potassium polyvinyl sulfate.
Therefore, it is more accurate when measuring a mill sample to take the first color change as the endpoint rather than wait until the 0 color has changed completely from blue to pink.
Formula The col~oid titration ratio (P~) is calculated using the following formula:

A - 2.9 x a A or A - 2.9 x a R = C - 2 _ x c where A is the ml of titrant necessary to neutralize 4 ml of the standard anionic polymer solution which has been added to 25 ml of distilled water. For more precise work, 25 ml of clear supernatant from the headbox furnish should be used in place of distilled water.
The symbol "a" is the ml of titrant necessary to neutralize 10 ml of the clear sup~rnatant from the centrifuged headbox sample con-taining the anionic polymer solution.
C is the ml of titrant necessary to neutralize 4 ml o the standard cationic polymer solution which has been added to 25 ml of distilled water or as mentioned for A, 25 ml of clear supernatant from the headbox furnish.
The symbol "c" is the ml of titrant necessary to neutralize 10 ml of the clear supernatant from the centrifuged headbox sample containing the cationic polymer solution.

The factor of 2.9 is estahlished by using only 10 ml of the original 29 ml sample that was centrifuged.
Soluble anionic or cationic compounds present in the super-11~3~37 natant can interact with the polymers used in the colloid titration technique and reduce the charge or precipitate the polymer from solution. By using the clear supernatant from the headbox furnish for values A and C, some of these effects are minimized. This is important since it is only the adsorbed polymer that will truly reflect the surface charge.
If A or C deviate appreciably from the values obtained with distilled water, adjustments have to be made to the amount of colloid added to the sample, since the colloid titration technique is based on,e~ual amounts of polymer charge being present to adsorb onto the furnish. If, for example, the difference between the distilled water hlank and the supernatant blank is 10 ml of anionic charge, than an additional 10 ml of anionic charge will have to be added initially to the furnish sample when performing the colloid titration. In this case, 6 ml of the anionic polymer solution should be added.to the headbox furnish sample instead of 4 ml. The cationic polymer should remain at 4 ml. As a result of this procedure, the headbox samples will agai~ have approximately equal amounts of both positive and negative charge present to adsorb onto the fiber, fines and filler.
The various features of the invention which are believed to be new are set forth in the following claims.

Claims (7)

The embodiments of the invention in which an exclusive property or privilege is claimed are defined as follows:-

1. In a papermaking process employing a papermaking machine wherein an ionic material is to be added to the paper mass aqueous suspension containing electrically charged sus-pended solids, the steps of:
a) taking equal first and second samples from said paper mass aqueous suspension from about the same point in the process stream;
b) adding to the first sample of the aqueous suspension a measured amount of a cationic colloidal polymer which adsorbs only on the surface of the suspended solids in said aqueous suspension; separating the treated aqueous suspension into a solids portion and an aqueous portion; then applying an indicator means to said aqueous portion which indicates the isoelectric point of said cationic colloidal polymer; then titrating the aqueous portion of said sample to the isoelectric point using an anionic colloidal polymer which interacts stoichiometrically with said cationic colloidal polymer remaining in said aqueous portion to precipitate said polymers from said aqueous portion; and recording the amount of anionic colloidal polymer used in said titration;
c) adding to the second sample of the aqueous sus-pension a measured amount of said anionic colloidal polymer which adsorbs only on the surface of the suspended solids of said aqueous suspension; separating the treated aqueous sus-pension into a solids portion and an aqueous portion; then applying an indicator means to said aqueous portion which indicates the isoelectric point of said anionic colloidal poly-mer; then titrating the aqueous portion of said sample to the isoelectric point of said anionic colloidal polymer using the cationic colloidal polymer; and recording the amount of cationic colloidal polymer used in said latter titration;
d) measuring the amount of anionic and cationic colloidal polymer adsorbed on the surface of the suspended solids portion of the first and second samples, respectively, by subtracting the titrated amounts of the respective colloidal polymers from the total amount of the polymer initially added to the respective sample; and e) adding ionic material comprising retention aids, fillers, wet and dry strength additives and other additives carrying electrical charges to said aqueous colloidal suspension in direct proportion to the amount of anionic and cationic colloidal polymers adsorbed on the surface of the respective suspended solids portions of said first and second samples to enable effective and continuous uniform deposition of said fibrous solids portion from said aqueous suspension with maximum retention of fines, and fillers and strength additives and maximum drainage rate.

2. The method of Claim l, in which the indicator means is a dye added to the aqueous portions of said samples which changes color at the isoelectric point of the said aqueous portion.

3. The method of Claim 2, in which the cationic colloidal polymer is selected from the group consisting of methyl glycol chitosan and 1,5-dimethyl-1,5-diazaundecamethylene-polymethobromide, the anionic colloidal polymer is potassium polyvinyl sulfate; and the indicator dye is Toluidene Blue O.

4. The method of Claim l, including the additional steps of taking third and fourth samples from said aqueous suspension; first filtering said third and fourth samples to remove suspended fibers; thereafter treating said third sample by the same method as step (b) in said Claim 1; treating said fourth sample by the same method as step (c) of Claim 1; there-after measuring the amount of anionic and cationic colloidal polymer reacted with said third and fourth samples, respectively, by subtracting the titrated amounts of the respective colloidal polymers from the total amount of the polymer initially added to the respective sample; and subtracting the amount of cationic polymers reacted with said third sample from the amount adsorbed by said first sample; and the amount of anionic polymer reacted with said fourth sample from the amount adsorbed by said second sample to find the corrected values of cationic and anionic surface charge on the suspended solids portion of the aqueous colloidal suspension.

5. The method of Claim 4 in which the cationic colloidal polymer is selected from the group consisting of methyl glycol chitosan and 1,5-dimethyl-1,5-diazaundecamethylene-polymethobromide, the anionic colloidal polymer is potassium polyvinyl sulfate; and the indicator dye is Toluidene Blue O.

6. A method of improving first pass retension and drainage in a papermaking process employing a furnish containing suspended colloidal particles and other additives by measuring the net surface charge potential of the suspended colloidal particles of the furnish at regular time intervals using the method of Claim 4 to find the most efficient value of anionic and cationic surface charge potential on said suspended solids to provide the most efficient first pass retention and drainage;
thereafter maintaining the furnish at such value by measuring the total anionic and cationic surface charge potential of the suspended colloidal particles of the furnish at regular time intervals to determine which additives to replenish in the furnish to maintain the surface charge potential at the most efficient value; and replenishing the required additive in measured amounts to maintain said value.

7. The method of Claim 4, in which the ratio between anionic and cationic surface charges is obtained according to the following formula:

in which "A" is the amount in milliliters of cationic collidal polymer titrant of known concentration necessary to neutralize v milliliters of the standard, known strength anionic colloidal polymer solution plus y milliliters of the aqueous portion of the first sample of the colloidal suspension;
"a" is the amount in milliliters of the same cationic colloidal polymer titrant required to neutralize z milliliters of the aqueous portion of the second sample of the colloidal suspension;
"C" is the milliliters of anionic colloidal polymer titrant of known concentration required to neutralize v milliliters of the standard, known strength cationic colloidal polymer solution plus y milliliters of the aqueous portion of the third sample of the colloidal suspension;
"c" is the milliliters of the same anionic colloidal polymer titrant required to neutralize z milliliters of the aqueous portion of the fourth sample of the colloidal suspen-sion; and "r" is the ratio of volume of the first sample divided by the second sample.