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ABSTRACT 076676 EFFECTS OF CHRYSOTILE ASBESTOS ADDITIONS TO CELLULOSIC PAPER Robert G. Woolery* The effects of incorporating a new, highly purified. grit-free chrysotile asbestos fiber in cellulose paper are discussed. Data are presented from both laboratory handsheet tests and paper mill trials on the effect of the fiber on both operational factors and on sheet properties. Effects discussed include retention of cellulose fines and fillers such as Ti02, freeness, drying rate, pitch control, bright ness and opacity, softness, strength, porosity, printability, and dye retention. Savings possibilities and other economic factors are also discussed. * Group Leader - Product Development and Technical Services Union Carbide Corporation Mining and Metals Division P. 0. Box 32U Tuxedo, New York IO9S7 076671 THE EFFECT OF CHRYSOTILE ASBESTOS ADDITIONS TO CELLULCSIC PAPER I. INTRODUCTION In the previous paper the properties of a highly refined chrysotile asbestos product were discussed. The three principal characteristics of this product that apply to paper applications are: 1. The surface charge - cationic 2. Particle shape - fibrous 3. Surface characteristics - (a) organic adsorption (b) chemical reactivity These properties differ sufficiently from those of the more conven tional paper additives to Indicate a promising potential for use in the paper industry. In addition, refined asbestos Is a material of low cost and is available in sufficient quantity to supply a consumer as large as the paper industry. Advances In processing techniques have insured a uniform product that can be supplied within quite rigid specifications. With respect to abrasiveness, radiometric determinations have shown that the purified asbestos Is considerably less abrasive than ordinary fillers or bleached sulfite pulp. The properties imparted to paper by addition of purified chrysotile asbestos, as well as paper-machine behavior, were determined by experimental work both in the laboratory and in full scale mill trials. These results are discussed in this paper. II. LABORATORY DATA The laboratory results, as reported herein, were obtained in our own laboratories at Tuxedo, New York, and through the efforts of Professors L. C. Jenness and A. J. Chase of the University of Maine, who have acted as our con sultants during this program. The tests were conducted principally in the laboratory Noble and Wood handsheet machine and, unless otherwise specified, used a bleached sulfite stock beaten to a Canadian Standard Freeness of 3CO + 10 ml. Handsheets were made at the standard basis weight of 60 grams per square meter and tested, wherever applicable, according to the TAFRI standard proced ures 016673 1. Effects on Retention - The effects of incorporating a highly defibrillated chrysotile fiber in cellulose paper were found to be unique among inorganic additives. Because of its electropositive surface charge, the self retention of the asbestos fiber is very high when compared with clay or titanium dioxide pigment. As shown in Figure 1, this improved retention is significant on a single pass retention system or in one where white water recirculation is employed. On the basis of single pass retention, the asbestos showed almost 80# retention compared with only 40$ for either clay or titanium dioxide. It can be postulated that any method of introducing a positively charged material into a paper furnish should tend to improve retention of all components. A summary of the relative surface charges of paper-making con stituents (as calculated from laboratory measurements of individual mobilities) were determined to be: f Bleached Sulfite Cellulose Titanium Dioxide (RA-50) Talc Purified Chrysotile Asbestos -14 -9 -19 None -15 +38 +45 PH 6.4 5.0 10 6 6.6 6.6 5.0 Accordingly, the chrysotile asbestos should coflocculate with any and all of the furnish constituents. That this Is so is shown when asbestos and TIOg pigment are agitated together to form what appears to be a fibrous titanium dioxide pigment. Titanium dioxide dispersed in water produces a milky liquor that tends to remain cloudy for long periods of time. When coflocculation is achieved, the water at the interstices of the floes is clear. Thus, all of the TiOa is being held by the asbestos. Electron micrographs of the combined product (Figure 2) show that the pigment is still in the dispersed state and is held by the asbestos. Most important is the fact that these floes are formed without agglomeration of the pigment. This should allow maximum effi ciency in obtaining its optical properties. The advantages of asbestos over conventional flocculants, either 076679 inorganic or organic, are two-fold: (l) retention without agglomeration, and (2) floe stability. Experience has shown that no degradation of the flee occurs even after repeated agitation. Once formed, these floes are stable even under prolonged high-shear agitation of a Waring Blendor. Laboratory studies have shown asbestos to be compatible with all types of organic and polymeric flocculants. In a furnish of high filler content, particularly, the combination of asbestos and coagulant is especially effective. Usually the net effect is greater than can be achieved by either alone. Data from laboratory tests run on handsheets to demonstrate the re tention properties of chrysotile fiber are shown in Figures 3 and 4. The con trol series for this evaluation were made with 4$ clay. Where asbestos was employed, it was substituted on a pound-for-pound basis for clay, so that at equivalent retention the ash and opacity values would be comparable. The level of Ti02 addition was then varied from no Ti02 to 10$ added based on the stoefe. It is apparent that the retention of the additives is greatly improved with as little as 2$ asbestos. Clay retention is also greatly affected. Because these data are based on single pass retention values, the values are quite low as can be seen in Figure h. Since this is probably the most difficult retention con dition, the effectiveness of the purified, fiber is clearly demonstrated. In another series of tests, run under similar conditions but with high levels of clay, the results were equally encouraging. The ash values for levels of clay additions ranging from 25$ to 50$ show that the retention of the filler is Increased with increasing asbestos additions up to 6$ asbestos (Figure 5). The effects of white water recirculation on the ash content of the sheet were also determined and are shown in Figure 6. Whereas the average ash retention only reached about 17$ with a one pass circuit, with recirculation the average retention was increased to 70$. There is also evidence that equili brium was reached in the recirculation system at 3$ asbestos whereas it required about 5$ for the single pass system. 2. Effects or. Opacity - Inasmuch as chrysotile asbestos has an index of refraction of 1.52 - 1.55 that is similar to that of kaolin, it could be expected to have equivalent opacifying power. On the basis of the amount added, asbestos-filled sheets showed higher opacities; however, as is shown in Figure J, the opacities are essentially identical at corresponding filler weights in the sheet, Ir. the series where asbestos was substituted for 2$ clay 076660 in a titanium dioxide filled sheet, the resulting opacities associated with the asbestos were invariably higher. In Figure 6, the average opacity in crease is from 2 to 3 points. This is attributed to the increased retention of all components through the cationic charge of the chrysotile asbestos. 3. Effects on Tear and Tensile - The comparative tear values for the addition of either clay or asbestos are similar. For both minerals, small quantities are beneficial whereas larger quantities prove to be detrimental. Figure 9 shows that small quantities (< 5$) of asbestos resulted in better tear factors. Above 5$ asbestos additions the tear factor decreases below that for clay-filled paper. This effect is probably due to the geometry of the fiber as well as to its smaller particle size. Asbestos is more efficient at disrupting the hydrogen bonding of the cellulose fiber than are non-fibrous minerals. An even better example of the geometry effect can be seen in Figure 10, where the tensile values are shown for corresponding filler content of the sheet. Onde 3# filler in the sheet is exceeded, the effect on tensile strength is influenced considerably more by the asbestos than by either clay or Ti02. k. Effects on Softness - While the strength of the sheet is reduced by asbestos content, a corresponding softening effect is also achieved. This relationship is shown in Figure 11. In a light-weight tissue sheet a 9# asbestos content resulted in doubling the softness values obtained on a Clark SoftnessStiffness tester. Various furnishes were investigated and all types appeared to respond in a manner similar to the light weight sulfite furnish. 5. Effects on Pulp Freeness - As might be expected from the use of a small sized, fibrous filler, the freeness of the furnish is affected. The degree to which the asbestos slows up the furnish drainage appears to be depend ent on the original freeness of the stock. For example, the data in Figure 12 show that the lower the freeness of the stock the less it is affected by asbestos. At the low levels of asbestos additional normally used in paper this has not been a problem in the mill. 6. Effects or. Porosity - With the incorporation of the highly refined asbestos the sheet porosity invariably has a tendency to decrease with increasing asbestos content as shown in Figure 13. The initial high increase in porosity values obtained by the addition of between zero and 2$ asbestos is attributed to the retention of fines. This effect normally'accompanies the addi tion of chrysotile asbestos. 07663 7. Effects on Printability - Normally, any time the porosity of the sheet is reduced and the formation of the sheet is improved, the printability is subsequently benefited. Printing evaluations by the Research In stitute for the American Newspaper Publishers' Association of samples obtained from the various mill trials verified these conclusions. Where sheet contain ing asbestos were compared to the control runs on the same grade, improvements in the following properties were noted: 1. Smoothness 2. Opacity 3. Ink Transfer h. Printability In most cases, improvements were noted for both the felt and wire sides. Usually the more significant improvements were observed on the wire side thus demonstrating an improvement in two-sidedness, 8. Effects of Stock Type - Some data have been obtained on fur nishes employing stocks other than a bleached sulfite stock. For the most part the data obtained were consistent with the results reported so far. The most notable exception was in a typical newsprint furnish of 80$ groundvood - 20fs bleached sulfite. Under these conditions, as much as 6$ asbestos in the sheet caused no appreciable reduction in the tensile strength. This probably can be attributed in part to the inherent weakness of the sheet and, in part, to the retention of the groundwood fines which contribute to the sheet strength. 9. Other Applications - Probably the largest single application for asbestos, in addition to those already described, is as a pitch controlling agent. Laboratory studies have been conducted on a wide variety of pulps, but because of the diversity of pitch problems, no universal data are obtainable. In the majority of the cases, however, asbestos has proven to be more effective than other commercially available products. The total reduction in pitch is generally only slightly lower than competitive products but the amount of asbes tos necessary to reach this level is usually significantly less. Considerable laboratory effort has also gone into the retention of beater-additive latices. Since most of the commercially available latices are anionic, they have proven to be compatible with the cationic chrysotile.Aa.^_It has been found advantageous to blend the asbestos with the cellulose first in order to put the asbestos on the cellulose in a dispersed state, Thus, when the latex 766S2 6. is added, it is deposited uniformly throughout the furnish and minimizes the tendency to form the latex agglomerates which are undesirable in the finished sheet. The overall asbestos retention is almost universally improved and the resulting physical properties have been found to be enhanced (particularly wet tensile and fold) to a higher degree than can be attributed to the improved latex retention. Studies in dye retention have shown that 2$ asbestos addition will generally improve the retention and greatly reduce the two-sideness. This is particularly true with acid and pigment dyes. It has also been possible to pre-dye the asbestos which in turn can be added directly to the furnish and results in a close control of color and shade. A rather unique application was also discovered in the field of con ductive paper. Its function in this area is to improve the sheet formation and to provide a more uniform distribution of the conductive media through oflocculation. Again, the asbestos addition levels required for this applica tion are found to be in the 2-3$ range. III. MILL TRIAL DATA Since the beginning of this program, something in excess of 200 mill trials have been conducted. In the majority of these trials the purified asbestos has performed as predicted from the laboratory studies. In addition, on machines where mineral additions are commonplace, no serious problems have developed due to the addition of asbestos. These trials have been conducted on a wide variety of paper grades as well as in paper board. A review of some of these trials demonstrates the versatility and advantages obtained with the chrysotile fiber. 1. Retention - In a machine trial on a ^0 lb. opaque printing paper, 3$ asbestos substituted for 3f clay resulted in a reduction of the TiOa requirement from l6p l'os/ton to 120 Ibs/ton and eliminated the glue previously used as a retention aid. This was accomplished without departing from the specifications of the sheet and without machine problems. A summary of these results is as follows: aw 076653 Condition 1 (control) 2 3 k # Clay k 1 1 1 # Asbestos 3 3 3 # Ti02 8.25 7.0 6.0 6.0 # Glue 0.25 0.25 0.25 Opacity 89.5 92.5 91. 91. In another trial, on a 37 lb bond paper, - 2# asbestos was used for a corresponding amount of clay. Titanium dioxide amounting to 2.5# of the furnish was also going intc> this sheet for opacity. A summary of these results follows: Condition Pre-trial 2# Asbestos Added Post Trial Opacity 82.5 83.5 82.0 PAPER ANALYSIS # Ti02 1.6^ 2.20 1.75 # Ash 12.0 13.9 12.2 # Ti02 Retention 65.5 88. 70. These data show an improvement in Ti02 retention from about 68# to 88# with a 2# asbestos addition. , In addition, the saveall effluent was monitored during both the control and trial periods. The average solids content during the pre-trial and post trial period was 2.3 pounds per 1000 gallons. During the trial the solids con tent was reduced to 1.5 lbs per 1000 gallons. Due to the improved efficiencyresulting from the asbestos, a 35# reduction in solids loss was realized. It is not unusual to expect saveall efficiencies improvement during these trials. In one trial, particular attention was paid to the saveall unit since it had been operating under a heavy load with a low efficiency. In this instance both the influent and effluent were monitored. A summary of these data follows: Saveall - (lbs solids/1000 gal.) Condition Influent Effluent Saveall Efficiency Pre-trial 17.9 k.36 During Trial (2* asbestos) 1.0 hr. 2.0 hr. 3.0 hr. 1^.3 13.2 11.0 1.15 0.90 0.71 Post Trial 21. k 6.00 Average: Without Asbestos With Asbestos 19.6k 12.83 5.18 0.92 1H 93*** Reduction in Solids resulting from the use of Asbestos 35* 82* 2. Softness - A natural application for the highly refined chrysotile fiber is in the tissue and towel grades. This mineral is unique as an inorganic softening agent. Numerous mill trials have demonstrated its ability to impart both softness and a velvety handfeel to both tissue and towels. A typical relationship between asbestos content and Handle-0-Meter values on a kO pound towel is shown in Figure Ik. The levels illustrated, up to 5* asbestos, are typical of the levels used for this purpose. For this grad.e a 5* asbestos addition reduced the Handle-0-Meter values from a control of 27 to 17. In a machine trial on a 13*25 lb tissue, k* asbestos was added to improve softness and handfeel. The furnish consisted of 25* Pine, 60* Hardwood and 15* Broke. The effects on Handle-0-Meter values were as follows: to 1 01 Condltion Control Trial * Average of 6 reels ** Average of 8 reels HANDLEMD 15 * Q #-# CD 22.5 * 11.5 * Not only was a s lgr. if leant improvement in softness realized, but the level of difference between machine direction and cross-machine direction was reduced by nearly 50*. This is probably due to the improved sheet formation. VQ In addition to these improvements the improved drying rate of the asbestosfilled tissue resulted in a lover steam requirement to the Yankee Dryer. By virtue of the inherent physical properties of chrysotile asbestos a vide variety of applications to the tissue and towel grades have been ex plored. Its largest single application at this time is as a tool to achieve quality in a wide variety of furnish components. In mills where the use of coarser and harsher cellulose stocks (or even waste paper) is limited, the incorporation of asbestos has permitted a higher percentage of these cheaper and coarser pulps without a loss in quality and at a significantly reduced furnish cost. For still another mill, where the drying chain controlled the machine speed, as much as JO to JO feet per minute increase in machine speed was achieved with a 2$ asbestos addition, a situation considerably more economical than the standard furnish at the slower rates. J. Pitch Control - The most universal application to date is id pitch control. In mills where this use has been investigated it has been found to be more effective than other commercially available products. Where asbestos is currently being used it has replaced talc, at the ratio of 2 lbs. of asbestos per 3 Its* of the competitive product. IV. CONCLUSION These studies have shown purified chrysotile asbestos to be unique as an inorganic additive to cellulosic paper. Unlike other paper components this material is cationically-charged and, as such, performs as a retention aid to flJ 1 constituents in the furnish. Its uniformity, small particle size and fibrous geometry contribute to the softness of the sheet and improve two-sided effects. The high surface area and its adsorption of organics aid In dye adsorption and printability. Its performance on the paper machine has been most satisfactory and, as a rule, has caused no problem in the subsequent processing of the paper. Where care has been used to employ a sufficient quantity of asbestos to be effective, yet not so much that the strength of the paper is degraded beyond reasonable limits, the results have been quite successful. Because of this versatility we believe that purified chrysotile asbestos will continue to grow in its present application to the paper industry and that new areas will develop where the unique properties of this material will be advantageous. ACKNWLEDCMENTS I am greatly indebted to Professors L.C.Jenness and A.J.Chase, of the University of Maine, for their collaboration, guidance, and laboratory data throughout all stages of this project. Thanks are also due to Messrs. B.L.Ingalls and G.L.Dickson, of the Union Carbide Corpora tion, Mining and Metals Division Research Center, for their assistance in obtaining the data that have been used in this paper; to Dr. S.Chvastiak for the electrophoretic mobility data; and to the many members of the laboratory staff who have helped through their advice and encourage ment. WHITE WATER RECIRCULATION 0766S7 0766SS FIGURE 2: Co-flocculation of purified chrysotile asbestos and titanium dioxide (electron photomicrograph,, m agnification2 15.900X). FILLER FILLER I- 5 LU liJ X co 24 cn < LU u CL LU 0766S0 24 68 PERCENT Ti02 ADDED FIGURE 3: Ash content vs. percent TiOg added, with and without asbestos. ------------------ 1---------------------r 60 \ FILLER = 4% Clay --------FILLER = 2% Clay 2% Asbestos \ 80 g/m2 \ 48% Ti02 RET. 076690 50 60 g/m2 45 % TiO, RET. PERCENT ASH RETENTION r- FIGURE 4: Effect of basis weight and percent Ti02 ' j:':------ - V*;i>h nnH with - PERCENT ASH 3 7 lb s /3 0 0 0 ft2 Basis Weight Sheet m- PERCENT ASBESTOS ADDED FIGURE 5: Effect of asbestos additions on ash content in highly filled handsheets. AVERAGE PERCENT OF FILLER RETAINED PERCENT ASBESTOS FIGURE 6: Average filler retention vs. asbestos additions. PERCENT OPACITY ii. PERCENT WEIGHT OF FILLER IN HANDSHEET FIGURE 7: Handsheet opacity vs. filler content. PERCENT OPACITY .I*. 076834 FIGURE 8: QpocWy gain vs. percent Ti02 added, with and without asbestos. n 076695 FIGURE 9: Tear factor vs. filler content. BREAKING LENGTH, METERS I*. r 076696 FIGURE 10: Handsheet tensile strength vs. filler content. CLARK SOFTNESS VALUES *r r 070697 FIGURE II: Handsheet softness vs. asbestos content. CANADIAN STANDARD FREENESS-ml 076693 FIGURE 12: Furnish freeness vs. asbestos content. PERCENT ASBESTOS ADDED FIGURE 13: Handsheet porosity vs. asbestos content. *r i* 076700 / FIGURE 14: Towel softness vs. asbestos content.