U. S. DEPARTMENT OF AGRICULTURE • FOREST SERVICE • FOREST PRODUCTS LABORATORY • MADlSON, WIS. In Cooperation with the University of Wisconsin

U. S. FOREST SERVICE RESEARCH NOTE FPL-0156 MARCH 1967

A REVIEW OF METHODS FOR ESTIMATING HARMFUL PITCH IN WOODPULPS Summary

This report describes the development of and procedures for two basic methods, mechanical agita­ tion and air flotation, for measuring the amount of harmful pitch in woodpulps under standardized condi­ tions. The procedure for the air-flotation method as adapted at the Forest Products Laboratory and the p r o c e d u r e for an impeller-agitation method are included. Translations are appended for the air- flotation method and the propeller-agitation technique with ultraviolet spectrometry. A REVIEW OF METHODS FOR ESTIMATING HARMFUL PITCH IN WOODPULPS

By F. A. SIMMONDS, Chemist 1 Forest Products Laboratory, Forest Service U.S. Department of Agriculture

Introduction

Pitch particles in woodpulp that become problems in papermaking are termed "harmful." They adhere to the papermaking machinery, including the wire and the press or dryer rolls. These pitch particles can cause the sheet to tear dur­ ing formation, and they can cause specks or even holes in the sheet.

Two basic methods have been developed for measuring under standardized conditions the amount of harmful pitch in woodpulp. One is by mechanical agita­ tion, and the other, by air flotation. At the Forest Products Laboratory a method based on air flotation has been applied and test results are included in this review of methods, as is an impeller-agitation procedure used by the Kimberly- Clark Corporation, Neenah, Wis.

In a 1960 review of his extensive studies and those of others on the problems 2 of pitch in papermaking, Back (1) said: "The use of unstored wood and of mixed softwood and hardwood species in the pulpmill, the increasing speed of paper machines, the efficient closing of mill white water systems, and the rising quality requirements on the pulp and paper produced all tend to accentuate the impact of pitch troubles."

The trend toward use of sulfite types of high-yield pulps probably will further accentuate pitch troubles. It is clearly important, then, to estimate (1) if the pitch in a given pulp is likely to cause trouble by being deposited at various points in the papermaking system and (2) to estimate the relative quantity of pitch involved.

1 Maintained at Madison, Wis., in cooperation with the University of Wisconsin.

2 Underlined numbers in parentheses refer to Literature Cited at the end of this report.

FPL-0156 Method Background

For many years it has been known that a measure of troublesome pitch in the original pulp cannot be made by extraction with solvents, such as ether or alco­ hol benzene.

In a review of research on pitch troubles conducted at the Finnish Pulp and Paper Research Institute during the past 15 years, Kahila (2) classified pitch according to its distribution in pulp. He noted a dispersible form of pitch on the outside of fibers that is easily detached in a colloid form when pulp is agitated and an emulsifiable form in larger sized particles. He also noted pitch in wood rays that is not emulsifiable in water unless the rays have been crushed by mechanical processing, and pitch inside the tracheids that is not easily emulsifi­ able. The amount of this harmful pitch is only about 0.1 percent of the pulp and varies slightly.

Kahila states it has been generally assumed that the amount of pitch deposited on copper or steel surfaces is essentially dependent on the amount of dispersible and emulsifiable pitch. Within the limits of his data, the regression of deposit- able pitch, y, on the dispersible pitch, x, was y = 384x + 29. Deposited pitch was determined in a steel vessel at pH 8, in hard water (256 parts per million), at 40° C. His data limits were: dispersible pitch 0 to 0.42 percent (3).

He also developed a method for measuring dispersible pitch. Air-dry pulp, about 8 grams calculated on the moisture-free basis, is agitated for 5 minutes in 300 milliliters of distilled water using a conventional propeller with a maxi­ mum speed of 1,000 revolutions per minute. The suspension is then filtered on a 75-millimeter Büchner funnel, but without a filter paper. The filtering procedure is repeated. The pulp pad is then dried and extracted with ethyl ether in accord­ ance with Testing Method A4071 of the Finnish Pulp and Paper Research Institute. The amount of dispersible pitch is the difference between the amounts of ether extracts of the original and the treated pulp.

Measurement of depositable pitch is predominantly made by stirring a pulp and water mixture with an impeller under standardized conditions and collecting and weighing the material adhering to the stirrer and walls of the container- vessel. The container-vessel is either cylindrical or square; either stainless steel or copper is used for the stirrer and the vessel.

In general, good reproducibility is claimed for this method. Cleanliness of the surfaces before each run is, however, critical. The complete removal of the deposited pitch is far more exacting than might appear. Our experience with this method has not been encouraging.

FPL-0156 -2- Another method of measurement is by flotation. Although unpublished and undocumented it has been suggested that “pulpmill pitch problems... are prob­ ably caused by a process of aeration of the stock rather than by a simple mechanical deposition as is often assumed.”

Gavelin (4) advanced a flotation theory but said, however, it could explain but few of the problems encountered with harmful pitch. This pitch occurs as particles adhering to the fiber surfaces as Kahila was later to confirm (3).

Gavelin based his theory on the affinity between pitch and gas bubbles, which, he mentioned, was well known among papermakers. He then proceeded to demon­ strate the deposition of pitch induced by carbon dioxide released from bicarbon­ ate in process water. At the Hallsta Paper Mill, where he was then employed, if 800 gallons of water per minute entered the white-water system at 100° F., 32 gallons of carbon dioxide had to leave it simultaneously. In addition, at that temperature, 25 gallons of dissolved gases would be released.

Ströle and Teves (5) used a flotation method and two other methods to deter­ mine the effectiveness of dispersing agents in preventing deposition of pitch. Their method was based on introducing purified air into a low-consistency pulp suspension with a resulting deposition of pitch.

Later, Ogait (6) used a flotation method, which he had developed, although it was presumably based on the work of Ströle and Teves (5). Ogait sought a method rapid enough for mill-control testing. A vibrator method, one of the three used by Ströle and Teves (5), met this requirement, but it was not satisfactory for bleached pulp. Hence, he selected the flotation method. According to Ogait, the rapidity of the method results from the pitch being measured spectrometrically. At the Forest Products Laboratory, however, the pitch has been determined gravimetrically. A translation of the portion of Ogait’s paper dealing with the method is given in Appendix A.

Recently a publication by Mehnert (7) came to our attention. He reviewed the more significant, available methods and reported on his experiments with the flotation method of Ogait. Mehnert concluded that to obtain satisfactory results with the Ogait turbidimetric procedure, the calibration curve must be developed from the total resin solution of the pulp being tested instead of from a standard solution. For example, he found 4.7 milligrams of harmful resin per sample weight for each of the five pulps when using a “standard” solution for calibration. With the “total resin solution,” however, his values ranged from 2.5 to 4.7 milli­ grams, the average being 3 milligrams.

FPL-0156 -3- Mehnert adopted the propeller agitation technique and ultraviolet spectrometry and claimed a new and rapid method. Details of this procedure are given in Appendix B.

In its Routine Control Methods, the Technical Association of the Pulp and Paper Industry includes a gravimetric procedure (RC 324) for estimating depositable pitch (8).

Procedures Used at Forest Products Laboratory Based on Ogait Method

Apparatus

A schematic drawing of the apparatus is shown in figure 1.

Water Quality

Water used for the test should have a total hardness of 179 to 358 parts per million as calcium carbonate to effect a separation of the harmful pitch. We selected a total hardness of 254 parts per million as calcium carbonate. The total volume of pulp and water used in the pitch determination tube (fig. 1) is 3,400 milliliters. Hence, as a part of this total value, one adds 104 milliliters of a 1 percent calcium chloride solution and 52 milliliters of a 1 percent solution of sodium bicarbonate. We have confirmed the importance of Ogait's specifica­ tion for water quality.

Weight of Sample

A sample weight of pulp, 6.8 grams (moisture-free basis), was used, although this may vary from 5 to 8 grams.

Temperature

The temperature maintained during the test was 60° C., but this is arbitrary. A lower temperature would lengthen the time required for deposition, and a higher temperature would shorten it. It is advantageous to preheat an adequate volume of water. With the Forest Products Laboratory apparatus, the dial on the voltage regulator was set at 65.

FPL-0156 -4- Figure I.--Schematic drawing of apparatus for determining depositable pitch in woodpulps by a flotation method.

M 132 308 Aeration

A constant pressure on the compressed air supply is necessary as is a suitable filter to prevent any oil getting into the sample. Oil will precipitate with the resin. Rate of flow is not critical, but it is important to have a good dispersion of air. In using this apparatus, the control pressure valve is regulated to show a 13 to 15 setting on the pressure gage. The air bubbles will be fairly large.

Manipulations

Place the sample in a 500-milliliter beaker, add 300 milliliters of the preheated water, and stir to uniformity of suspension with a counter rotary mixer.

Close the drain hose on the pitch determination tube, pour the remainder of the preheated water into the tube, and open the air-control pressure valve to a gage reading of 13 to 15.

Pour the pulp slurry into the tube and, if necessary, add water to bring the level to the 3,400-milliliter mark on the tube.

Connect the heating element, have dial on the regulator set at 65.

Place a frosted-glass insert into position in top of the tube, and adjust the depth of the insert with the rubber band that is around the insert to prevent it from falling into the tube. The air may have to be adjusted slightly, also. The depth of the insert is determined when the slurry in the tube bubbles up 1 to 2 inches into the insert.

After 30 minutes of operation in this position, replace the insert with a clean one, and repeat this procedure until there is no visible evidence of any further pitch deposition on the inside walls of the insert tube.

Wash the pitch contained on the insert into a 500-milliliter beaker using a small amount of hydrochloric acid (10 percent by volume), a squeeze bottle of distilled water, and a rubber policeman.

After the last deposition on the insert has been washed into the beaker, filter the solution in the beaker through a Büchner funnel, about 3 inches (8 centi­ meters) diameter, using a “fast” filter paper.

FPL-0156 -6- Tear up the filter paper with its contents into a 250-milliliter Erlenmeyer flask containing about 100 milliliters of ethyl alcohol, insert a reflux condenser, place under an exhaust hood, and boil approximately5 minutes over a low flame, keeping watch for fires.

Clean the Büchner funnel with alcohol.

Filter the boiled solution twice with different filter papers; wash paper and filter with hot alcohol. (A conical filter may be used, but suction should not be applied.)

Discard filter papers and their contents and pour the filtered solution into a small beaker that has been preweighed, ovendry, on an analytical balance to 0.1 milligram

Place the beaker on a hotplate and evaporate the liquid. Remove the beaker from the hotplate the moment bubbling stops. The residue must not be burned. Dry the beaker and contents to constant weight at 105° C.

Determine the weight of pitch and divide its weight by 6.8 (the amount of pulp) to determine the percent of harmful resin.

Clean the pitch determination tube with Alconox, water, and a brush while the air is on. Drain, and add a very dilute solution of sulfuric acid while the air is still on to clean the fritted-glass air disperser.

Test Results Test results are-given in table 1.

Impeller-Agitation Procedure Used at the Kimberly-Clark Corporation 3

Equipment Required: 1. A laboratory-sized variable speed-stirrer with a stainless steel stirrer shaft 12 inches long and fitted with two adjustable stainless steel 3-blade propellers, each two inches in diameter.

3 Acknowledgment is gratefully made to the Kimberly-Clark Corporation, Neenah, Wis., for permission to include this procedure.

FPL-0156 -7- Table 1. --Depositable pitch in several sulfite types of pulps 1

1 Procedure conducted at Forest Products Laboratory based on flotation method of Ogait. 2 Determinations of pitch content were made in duplicate. 3 Permanganate number. 4 0.6 percent heartwood 5 7.4 percent heartwood. 6 7 percent heartwood.

FPL-0156 -8- 2. One 3,000-milliliter stainless steel container. 3. Ringstand type of support for stirrer and a variable-grip column clamp for holding 3-liter stainless steel container in position on base support. 4. Spatula with 3/4-inch blade. 5. Erlenmeyer flasks, 250 milliliter. 6. Glass-stoppered Erlenmeyer flasks, 50 milliliter. 7. Glass funnels with 65- to 70-millimeter top diameter. 8. No. 4 Whatman filter paper, diameter 12.5 centimeter. 9. Celite 263 (a diatomite mineral filler) supplied by Johns-Manville Products Corporation. 10. Ivory soap, granular form. 11. Methyl alcohol-benzene solution (330 milliliters methyl alcohol--670 milli­ liters cp benzene per liter).

Preparation of 3-liter stainless steel container and propeller for deposition test.--Before making a pitch deposition, scrub the 3-liter stainless steel con­ tainer and propeller clean with a moist wad of clean cheesecloth and about 0.5-gram each of Celite 263 and granular Ivory soap. This amount need not be weighed but can be applied to the container with a 3/4-inch wide spatula. Moisten the wad of cheesecloth with sufficient water to make a heavy suds with the Celite and soap. After scrubbing, rinse the container and propeller with ordinary tap water and finally with distilled water. Clean the container and the propeller in this manner before each test.

Caution: Never use any other soap, soap powder, detergent or cleanser other than Celite 263 and Ivory soap to scrub and clean the steel container and propeller. Such cleansers have been found to effect the final test results.

Procedure for Determining Pitch Deposition

The pitch deposition test is made at a 2.91 percent consistency, using the equivalent of 60 grams ovendry pulp and 2,000 milliliters of distilled water at 100° F.

FPL-0156 -9- First determine the consistency of the pulp to be used in the deposition test.

Using the consistency of the pulp, calculate the amount of wet or air-dry pulp to use and adjust the amount of water needed, taking into consideration the amount of water in the pulp.

Example: Ovendry consistency of pulp to be used = 30.0 percent. Weight of wet pulp required to be equivalent to 60 grams 60 ovendry pulp = = 200 grams. 0.30 200 - 60 = 140 grams water in wet pulp. 2,000 - 140 = 1,860 milliliters of distilled water to add to get the 2.91 percent consistency required for the deposition test.

After the required amount of wet pulp and water to add has been determined, place the pulp into the 3-liter stainless steel container and add the required amount of distilled water. Fasten the double stainless steel propeller in the chuck of the mixer, lower it into the pulp and water in the container, and agitate for a moment to insure a uniform mixture. Then stop the mixer and raise the propeller out of the pulp slurry and examine to be sure no pulp has wrapped around the propeller shaft. This can happen especially when dry pulps are tested. Again lower the propeller into the pulp slurry so that it is 1/2 inch from the bottom and 2 inches from the side of the container. (The distance from the bottom of the container can be predetermined and a mark made on the rod of the base support to which mark the mixer can be lowered.)

Start the mixer and adjust the speed of the mixer by means of the rheostat so that the pulp turns over in the stainless steel container so that the pulp does not hang to the sides of the container but rolls evenly toward the propeller at all times. Excessive speed must not be used.

Allow the pulp slurry to agitate for exactly 2 hours. Then remove the 3-liter stainless steel container and its contents from the mixer. Empty the pulp slurry from the container and rinse both the container and the propeller with cold water and dry by a jet of clean compressed air, using an ordinary heavy walled rubber tubing to direct the air into the container and onto the propeller.

Remove the pitch adhering to the sides and bottom of the container and on the propeller with 150 to 200 milliliters of 1:2 methyl alcohol-benzene solution in 50-milliliter portions using a glass rod with a rubber policeman to scrub off the pitch from the propeller and from within the container.

FPL-0156 -10- Filter each portion of the solvent used into a dry 250-milliliter Erlenmeyer flask through a No. 4 Whatman filter paper. After all the required solvent has been filtered into the Erlenmeyer flask, use an additional 20 milliliters of the methyl alcohol-benzene solvent to rinse the No. 4 Whatman filter paper receiv­ ing the rinse in the Erlenmeyer flask.

Caution: The methyl alcohol-benzene solution gives off toxic fumes and must be made up and used in a well- ventilated fume hood.

After the filter paper has been rinsed with the small portion of methyl alcohol-benzene, evaporate the solvent in the 250-milliliter Erlenmeyer flask to about 10 to 15 milliliters in a boiling hot water bath in a well-ventilated fume hood. Remove the Erlenmeyer flask from the water bath, and wipe the outside surface dry with clean, dry cheesecloth. Transfer the alcohol-benzene remain­ ing in the 250-milliliter Erlenmeyer flask into a weighed 50-milliliter glass- stoppered flask. Rinse the 250-milliliter Erlenmeyer flask with two 5-milliliter portions of alcohol-benzene solution and add to the weighed flask.

Evaporate the solvent in the 50-milliliter flask to dryness in a boiling hot water bath. Remove the flask from the water bath and wipe the outside dry, and clean with clean, dry cheesecloth.

Dry the flask for 1 hour at 105° C., cool in a desiccator, and weigh on an analytical balance. The pitch deposition test is reported as milligrams pitch per 100 grams ovendry pulp.

Example:

Weight of ovendry pulp used = 60 grams. Weight of Erlenmeyer flask and pitch = 62.7451 grams. Weight of Erlenmeyer flask = 62.7401 grams. Weight of deposited pitch = 0.0050 gram. 0.0050 gram = 5.0 milligrams. 5.0 Then: x 100 = 8.3 milligrams per 100 grams 60 ovendry pulp.

FPL-0156 -11- Literature Cited

1. Back, Ernst 1960. Resin in conifer pulpwood and fundamentals of pitch control in paper making. Svensk Papperstidn. 63( 22): 793- 802.

2. Kahila, Seppo K. 1964. Pitch troubles caused by unbleached spruce sulfite pulp. Paper and Timber 46(11): 615-624.

3. 1962. Pitch troubles caused by sulfite pulp VI. The influence of the dispers­ ible pitch content of unbleached sulfite pulp upon the quantity of pitch deposited on a steel surface. Paper and Timber 44(3): 103-106.

4. Gavelin, Gunnar 1950. Carbon dioxide and pitch troubles in paper mills. Pulp Paper Mag. Can. 51(4): 87-89.

5. Ströle, Ulrich, and Teves, Dieter 1956. Combating pitch t r o u b 1 e s with dispersing agents. Das Papier 10(13/14): 264-270.

6. Ogait, Alfred von 1961. A rapid method for the determination of harmful resins in coniferous pulps. Das Papier 15(1): 10-16.

7. Mehnert, E. 1963. Spectrophotometric determination of "harmful rosin." Zellstoff und Papier 12(7): 194-196.

8. Technical Association of the Pulp and Paper Industry 1966. RC 324 Determination of depositable material in pulp and the evaluation of chemical deposit control agents. Tappi 49(2): 144A­ 145A.

FPL-0156 -12- APPENDIX A

Excerpt from:

A RAPID METHOD FOR THE DETERMINATION OF ‘‘HARMFUL

RESINS” (PITCH) IN CONIFEROUS PULPS1

Alfred von Ogait

Das Papier 15:10-16 (Jan. 1961)

Apparatus

Separation of the harmful resins is effected by flotation. This process occurs in a tube of heat-resistant glass being 6.5 to 7.0 centimeters (about 2-3/4 inches) in diameter, 85 to 90 centimeters (3 feet) long with a wall thickness of 0.2 centi­ meter(1/12 inch). The tube carries on top one of several ground-in glass attach­ ments. These attachments are 10 to 12 centimeters (4-1/2 inches) long and can be exchanged during the course of the determination. The apparatus can thus hold 3 to 3-1/2 liters (about 1 gallon).

The lower end of the tube is closed with a rubber stopper having 2 bores. A dispersion tube with fritted disk is inserted through one of the bores for the dis­ tribution of air. It has the fineness number of 17 CG3 (G2 gives air bubbles too big, G4 has too high a resistance). A drain for emptying the tube at the end of the test goes through the other bore.

The suspension in the dispersion must be heated. The compressed air must be carefully freed from any oil that precipitates together with the resins and thus gives higher readings. Therefore, the air is passed through a glass tube of, say, 30 centimeters (1 foot) in length and 4 to 5 centimeters (1-1/2 to 2 inches) in diameter not too loosely filled with cotton wool.

1 TransIation by H. Erfurt, of Germany, formerly of the Hammermill Paper Co., Erie, Pa.

FPL-0156 -13- Procedure

The glass tube is filled with the suspension so that its level reaches about halfway up into the ground-in glass attachment on top during airing. As soon as one gets the impression that the resin separation, which occurs on the inner wall of the attachment just above the surface of the liquid, is mainly finished, the air supply is shut off and the attachment is replaced. Then the air is again turned on. After some time this second attachment is replaced by a third. Only traces or no resin will deposit in the third attachment. Thus, the method strives at a quantitative and directly controllable gathering of the harmful resins that is very easily facilitated by the interchangeable attachments.

The resin precipitates, being contaminated by traces of calcium carbonate and microfibers, are separated from these contaminants with diluted hydro­ chloric acid and are collected in a beaker. After removal of these contaminations, the harmful resin is determined by the turbidity method to be described.

Effect of Certain Variables on Quantity

of Resins Deposited

Water Quality

The quality of the water in the pulp suspension has an important bearing on the separation of the harmful resins. The experiments have indicated that, under the working conditions to be described, a rapid and maximum separation of the harmful resins is obtained when the water contains 0.2- to 0.4-gram calcium chloride (water-free) and, as a buffer, 0.15-gram sodium bicarbonate per liter.

Such a solution corresponds to a total hardness of 10° to 20° and a bicarbon­ ate hardness of 5°. Analogous to water of such a hardness is the behavior of the solution in that a constant pH of 8.0 to 8.5 is obtained in both cases throughout the time of flotation at a temperature of 60° C. Also, the quantity of harmful resins was the same.

Resin is not deposited if salts are completely absent. A pulp sample contain­ ing considerable amounts of harmful resins was completely freed of calcium salts by repeated treatment with cold diluted hydrochloric acid and washing with distilled water.

FPL-0156 -14- The pulp was then put into the apparatus and water of a pH of 8.0 to 8.5 (adjusted with sodium bicarbonate) was added. No trace of resin separation was noticed. However, after adding calcium chloride solution the separation started immediately. Pulp that had not been treated with hydrochloric acid before the resin determination and thus contained certain amounts of calcium salts showed some resin deposits even with distilled water.

Amount of Pulp

A suitable amount of pulp for one determination is 5 to 8 grams. The turbidity method is capable of determining small quantities of harmful resin with sufficient accuracy. When larger pulp samples are used, the small air bubbles in the tube tend to combine to form bigger bubbles because of the increased resistance of the suspension. This has an adverse effect on the flotation process.

The following tabulation shows that the results are largely independent of the amount of pulp used, within the limits of reproducibility.

Weight of Pulp Percent HarmfuI Resin Grams Pulp I Pulp II

8.0 0.16 0.08 6.0 .16 .06 4.0 .15 .06 2.0 .14 .06

Temperature and Time

With increasing temperature, rate of resin deposition increases. Our experi­ ments indicated that a temperature of 60° C. is required for a quantitative separation within 2 hours, and several hours are needed at Bower temperatures. A temperature of 60° C. was therefore chosen.

Method of Turbidity

For the determination of the quantities of harmful resins, first the resins must be separated from calcium carbonate and microfibers. For this purpose, the precipitate is washed off the glass attachments with diluted hydrochloric acid into a beaker. The carbonate decomposes, and the solution is filtered with vacuum and washed until neutral reaction.

FPL-0156 -15- Dissolving the resin from the remaining fibers can be done in two ways. In one method the dry suction filter is cooked with a small amount of alcohol (e.g, 10 milliliters), using a condenser, for some minutes. The solution is then filtered and diluted with water containing some hydrochloric acid to a certain volume. The resin then precipitates in a fine turbidity the intensity of which is a measure for the resin quantity. More practical, however, is the method utilizing the fact that resin dissolves quantitatively in a cooking solution of tetrasodium pyrophosphate, The solution is slightly opalescent, and the resin precipitates again after addition of hydro­ chloric acid. Special experiments have shown that both methods give satisfactory reproducible and agreeing results. We prefer the less complicated tetrasodium pyrophosphate method. The intensity of the turbidities is determined by measuring their light absorp­ tion with a colorimeter, and the quantity of harmful resins is read from a cali­ bration curve. At the beginning, we were using as standard a solution of harmful resins in alcohol. Since the makeup of this solution is troublesome, we later changed to easily procured and, in addition, chemically well-defined substances which assured a good reproducibility of the turbidities. After numerous experiments, a 50:50 mixture of sylvic acid and oleic acid, 1.26 grams which are dissolved in 1-liter dioxane, was adopted. One milliliter of this solution gives the same turbidity as 1 milligram harm­ ful resin. We preferred dioxane because of its low volatility and especially because an esterification of the acids may occur in alcoholic solutions during storage for a longer time which affects the turbidity data. A calibration curve was obtained with this solution (milligrams resin in 100 milliliters as a function of percent of light absorption). To determine the effect on the turbidity method of possible variations in the composition of harmful resin connected with the raw material used in the cook­ ing and bleaching processes, a number of experiments have been conducted. For this purpose, the hard resins of a large number of bleached and unbleached coniferous wood pulps as well as spruce and pine wood pulps 2 were determined

2The separation of harmful resins from wood (as groundwood) directly in the flotation apparatus is practically impossible because the fibers are in flotation during aeration preventing the deposit of the harmful resins. Therefore, the following procedure was adopted: The chips were extracted with acetone in a soxhlet apparatus. The resin solu­ tion was then, under vigorous shaking, drop by drop given into an aqueous solution of defibered filter paper. The liquid was removed by suction, and the residue washed. The harmful resins were then separated from the fibers in the flotation apparatus. After removal with hydrochloric acid and washing to neutralization, the resin residue was dis­ solved in aIcohoI (which, of course, did not contain any denaturants that would cause turbidity upon dilution with wafer). A part of the solution was boiled down, dried at 105° C., weighed, and finally dissolved again to obtain a solution of 1.0-milligram resin per milliliter. The turbidity method was applied, and the results compared with these of the standard solution, FPL-0156 -16- directly and compared using alcoholic solutions of 1 milligram per milliliter. A practically complete agreement was found so that the method of turbidity appears to be applicable to coniferous woodpulp in general. It is being investi­ gated how far this holds true for hardwoods.

Reproducibility of Results

The deviations in parallel tests need not exceed ± 10 percent, provided this procedure is carefully followed. The accuracy obtained is critically affected by the kind of colorimeter used or, in other words, by the accuracy with which the turbidity test can be made. This degree of reproducibility is entirely adequate as it is of no interest in the evaluation of a pulp whether it contains a 10 percent higher or lower amount of harmful resin.

Analysis of Results

During the study of a great number of domestic as well as foreign pulps according to our method we found data for harmful resin of up to 0.25 percent of the pulp weight. Data above 0.20 percent and below 0.05 percent were only occasionally found. These values refer to unrefined pulps. It was therefore of interest to study how much harmful resin can be additionally produced during beating.

A number of pulps being characteristic in this respect were beaten in a jokro-mill of 80° to 85° Schopper Riegler (SR) (= 200° to 150° SR freeness). The results were:

FPL-0156 -17- A comparison of the total resin content of the pulps with their harmful resin shows that there is no relationship. This agrees with the observation that the total resin content is not a criterion for the behavior of the pulp in following operations.

It can be further seen that the amount of harmful resins increases more or less during beating because the resin that is originally enclosed in the ray cells becomes partly free and increases the total amount of harmful resin present. This increase during beating is greater for a larger amount of harmful resin in the unbeaten pulp.

This proportionality of harmful resin before and after beating seems, there­ fore, to be a relative measure for the harmfulness of the total amount of resin present in the pulp. According to these results, the harmful resin content of an unbeaten pulp should be more realistic for its classification as to possible pitch troubles than to the total resin content.

When the data in the tabulation are compared from this viewpoint, the results for the two extreme pulps A and B are particularly striking. Both have about the same total resin contents, yet the harmful resin content of B is only about one-fourth that of A, and even after prolonged beating does B contain less harm­ ful resins than A unbeaten. It is obvious, therefore, that B will cause consider­ ably less pitch troubles than A. This could have been expected from the ages and conditions of the two pulps since B was cooked from wood stored for 2 years, and A was made from fresh wood. Amounts of harmful resins in pulps C and D are between these two extremes.

This classification of pulps according to their content of harmful resins is, however, not of universal value because the degree of pitch troubles arising during the processing of the pulp does not depend only on the total resin content but also to a large extent on the operating conditions of the paper machine.

Several factors favoring the resin separation are of importance here, such as the intensity of the mechanical treatment of the suspension, the amount of air entering the suspension that controls and favors flotation processes, and the higher temperatures of the water.

The most important role, however, is played by the pH of the suspension as has been discussed. Adjusting the pH to 4.5 to 5.5 by controlled addition of alum will generally avoid pitch troubles completely even if pulps with unfavorable resin contents are used. However, negligence of this factor, particularly when the pH is in a higher range such as 6 to 7 will create difficulties, sometimes

FPL-0156 -18- even with pulps of low resin contents. The pH of 4.5 to 5.5 can have additional benefits as it prevents picking at the presses and improves water removal in the wet end so that even a slightly higher production may be possible.

Procedural Details

Apparatus for Flotation

The same as has been described.

Solutions

1 percent solution of calcium chloride (water free) 1 percent solution of sodium bicarbonate These solutions are required only if no suitable water is available (see the following). 1 percent solution of tetrasodium pyrophosphate (water free) 10 percent (by volume) hydrochloric acid (1 volume cone hydrochloric acid + gram-volume water) Standard solutions for the turbidity tests contain 1.26 grams of a 50:50 mix­ ture of pure sylvic acid and oleic acid dissolved in 1,000 milliliters dioxane. Since small quantities of liquid oleic acid are difficult to weigh accurately, the following method is recommended: Weigh 6.3 grams of oleic acid and 6.3 grams sylvic acid. Dissolve both substances in 100-milliliters dioxane (volumetric flask), take 10 milliliters of this solution and fill up with dioxane to 1,000 milli­ liters. The standard solution has to be stored in a dark room.

Procedure

Enough water of the required quality for the expected number of tests must be provided. The water should have a hardness of 10° to 20° (out of this at least 5° bicarbonate hardness), water of greater hardness is diluted with distilled water. Or use distilled water and add 30 milliliters of the 1 percent calcium chloride solution and 15 milliliters of the 1 percent sodium bicarbonate solution per liter.

Six to eight grams (absolute dry basis) of pulp are completely agitated (using mixer) in about 500 milliliters of this water, and the suspension is poured into the flotation tube. The air supply is opened and more water, pre­ heated to 60° to 70° C., is added so that the ground-in attachment is not quite half filled.

FPL-0156 -19- The quantity of air introduced should be enough to whirl the suspension well (about 2 to 3 liters of air per minute). The temperature of the suspension is kept at about 60° C. with the heating equipment controlled by the contact ther­ mometer. The pH adjusts itself 8.0 to 8.5 because of carbonic acid losses due to aeration and heating (phenolphthalein becomes slightly red). The air supply should be held constant to avoid washoff of the deposited harmful resins by the rising surface level of the liquid.

Pulps containing larger amounts of harmful resins give deposits on the wall of the attachment just above the surface level after several minutes. Sometimes, especially with unbleached pulps, longer fibers are also deposited that may affect the separation of the harmful resins. Because this difficulty is in most cases due to inadequate washing of the pulp, it can be avoided by washing the pulp before treatment.

After about 30 to 60 minutes of aeration, the air supply is closed, the attach­ ment removed, replaced by another, and the aeration started again. After another 30 to 60 minutes the whole procedure is repeated. The change of the attachment is made to control the complete deposit of the resins because, as mentioned, the desired result is a quantitative separation. After flotation, the attachment is removed and treated together with the other two, as will be des­ cribed. In preparation for the next test, the tube is drained and washed with water.

The three attachments are treated one after the other with 50 to 100 milliliters of the diluted hydrochloric acid in a beaker (e.g. 600 milliliters, wide form). The deposit has to be quantitatively transferred into the beaker using a glass rod with rubber tubing and washing with distilled water. The mixture of resins and microfibers is filtered after a little while and after some shaking through a filter on a Büchner funnel, which should be as small as possible, and washed with distilled water until neutral.

As preparation for the turbidity measurement, the filter with the resin-fiber mixture is boiled into about 50 milliliters of the 1 percent tetrasodium pyro­ phosphate for about 5 minutes. The resin goes in solution. This is done in the same beaker used before for the separation of the calcium carbonate in order to include traces of resin that may adhere to the wall.

The filter is then washed with distilled water and rejected. The slightly opalescent solution of harmful resin is then separated from the fibers by filter­ ing through a coarse filter paper on a small Büchner funnel, using suction, and the solution of harmful resins is washed with water so that the total volume is about 100 to 400 milliliters.

FPE-0156 -20- For the turbidity test 10 milliliters diluted hydrochloric acid is added to the cooled resin solution, filled up to 150 milliliters, and after about 15 minutes the light absorption is determined with light electric colorimeters. The full turbidity does not occur before this time. Also, having the solution standing for a longer time (more than half an hour) has to be avoided because flocculation of resin may result in lower readings. Should the solution contain more than 5 milli­ grams per 100 milliliters, the solution has to be diluted with distilled water until it contains 3 to 5 milligrams per 100 milliliters. Too high a dilution must be avoided as far as possible because this would needlessly increase the volume and effect the accuracy of the test unfavorably.

The resin content of the solution is determined, as described, from the calibra­ tion curve that, of course, must be determined for each colorimeter separately. For this purpose, 1, 2, 3, 4, and 5 milliliters of the standard solutions are added to 50 milliliters of the tetrasodium pyrophosphate solution, 10 milliliters of the diluted hydrochloric acid are added, and the total filled up to 100 milliliters.

After 15 minutes the light absorption is measured. It can be recommended to check the colorimeter with the standard solution before each determination. If an appropriate colorimeter is not on hand, a rough estimation of the amount of harmful resins can be made by comparing the solution to be tested with the solutions described made from the standard solution.

The calculation is done according to the formula:

RH = harmful resin in the pulp in percent r = harmful resin in 100 milliliters of the testedsolution in milligrams h V = volume of the tested solution in milliliters W = weight of sample, absolute dry

FPL-0156 -21- APPENDIX B

Excerpt from:

1 SPECTROPHOTOMETRIC DETERMINATION OF “HARMFUL ROSIN”

E. Mehnert

Part 1. Zellstoff und Papier 12(7): 194-196 (July 1963)

Experimental Part (Pp. 195-196)

Eight grams of air-dry pulp are stirred with a copper propeller for 2 hours in a 500-milliliter cylinder at a consistency of 3.5 percent using distilled water at 40° C. The propeller speed is 400 revolutions per minute. Its diameter is 5.5 centimeters and the propeller is of the ship-propeller design.

The following conditions are specified:

(1) The propeller must be treated before each determination for 10 hours with 2.5 percent hydrochloric acid and washed with distilled water.

(2) The temperature must be held constant during the agitation.

(3) The speed of stirring must be constant.

(4) The agitator must be in the same position for each determination. This may be accomplished by putting a mark on the shaft of the agitator.

After having stirred for exactly 2 hours, the agitator is removed from the suspension and rinsed with distilled water. It is dried by rotation in air for 10 hours.

A 100-milliliter beaker is fitted with some glass wool and approximately 12 milliliters of 96 percent ethanol is added. The container is heated in a water

1 Translated by Charlotte Hiller of the Forest Products Laboratory.

FPL-0156 -22- bath, and the agitator washed thoroughly with warm alcohol; that is, the entire surface of the agitator and shaft is washed with the aid of tweezers and glass wool. The washing is repeated three times, and each time the washing fluid is filtered through fritted glass into a 50-milliliter measuring flask; the flask is filled to the mark, and then 6 to 7 milliliters of the solution are taken to deter­ mine absorptivity at 240 millimicrons.

The calibration curve will give the amount of harmful resins. The calibration solution used is a solution of the entire resin of the respective pulp in alcohol. The determination can be made easily in 2-1/2 hours, exclusive of the prepara­ tion of the calibration curve, For a careful determination the error is ± 1 percent.

The results of some parallel determinations showing the precision of the method are given in the following tabulation:

The harmful resin contents of pulps 1 and 3 were also determined according to Ogait’s method. Even though it was evident that the pulp contained larger amounts of harmful resin, it was found that there was only an insignificant difference between pulps 1 and 3 on the basis of Ogait’s method. In pulp 1, 0.11 percent was found, and in pulp 3, 0.12 percent harmful resin.

If, however, one uses as calibration curve a solution of the entire resin in the respective pulp, then one finds for pulp 1, 0.07 percent and for pulp 3, 0.12 per­ cent harmful resin. Ogait’s flotation method cannot be compared with the separation method because the conditions for separation are different. However, if one obtains with the separation method such different contents of harmful resin as are given in the table for pulps 1 and 3, then it should not be possible to find approximately the same values for both pulps. The values describe the true conditions only when one uses as calibration solution a solution of the entire resin in the respective pulp.

FPL-0156 -23- 1.5-26