US3119732A - Method of treating cellulosic fibers with a cationic protein dispersion - Google Patents

Description

Jim 1964' J. D. ROBERTSON ETAL 3,119,732

METHOD OF TREATING CELLULOSIC FIBERS WITH A CATIONIC PROTEIN DISPERSION Filed May 1, 1961 PULP SLUE RY (ANIONIC) PROTEIN AcIb 4 PROTEIN ACID (CATIoNIc) 4 ALLJM PuLD- PROTEIN MIXTURE pH 4.5To 5.5

PAPER MACHINE Juuus b. EoaEIzTsoN and CHARLES N. BETTIS INVENTORSZ Byiyi United States Patent Ofiiee 3,11%,732 Patented Jan. 28, 1954 3,119,732 METHOD OF TREATKNG CELLULOSIC FIBERS WETH A CATKONHC PRSTEIN DEYERSEQN Julius D. Robertson and Cixaries N. lBetts, Hartsviiie, 3.6., assignors to Sonoco Products Company, Hartsviile, S.C., a corporation of douth Carolina Filed May 1, 1961, Ser. No. 1%,499 7 Claims. (Cl. 162-174) This invention relates to a method of making paper and more particularly to a method of treating paper pulp which is to be subsequently formed into a paper web.

In the making of paper, it has been proposed to add various materials to the paper pulp prior to its being formed into a paper web so as to impart certain highly desirable improved properties to the paper such as increased strength and the like. It is well known that proteins make good bonding agents and various proteins have been added to paper pulp during the paper making process in order to promote fiber bonding and thereby obtain an improved paper product.

It has been recognized that the maximum fiber bonding obtainable with the use of a protein additive to the paper pulp has not been accomplished as various limitations have been present which make it difiicult to utilize the full fiber bonding potential of the protein. For instance, use has been made of soluble proteins such as animal glue but soluble proteins do not produce the substantial increase in fiber bonding which it is desired to obtain. Insoluble proteins such as casein have been used as alkaline dispersions for beater additives with subsequent precipitation by an acidic agent such as aluminum sulfate but here again fiber bonding to the desired degree has not been obtained with such a process and the resulting paper product was somewhat deficient in strength.

Accordingly, a primary object of this invention is to provide a new and novel method for treating cellulosic fibers utilized in a paper making process which produces a bond between the cellulosic fibers of considerably greater strength than has been possible heretofore.

Another object of this invention is to provide a new and novel method of treating paper pulp utilized in a paper making process which permits full utilization of the fiber bonding potential of proteins added to paper pulp.

A further object of this invention is to provide a new and novel method of treating cellulosic fibers utilized in a paper making process which results in a paper product of high strength and which at the same time material-1y reduces the pollution load of the paper making effiuent.

Other further objects of the invention hereof will be apparent from the following description of the methods and procedures utilized in the production of the end prodnot.

The accompanying drawing illustrates the process of the present invention in flow diagram form.

In general, the novel method of the invention is directed to a paper making process in which paper pulp is prepared in the conventional manner as a slurry or suspension of fibers in an anionic condition at a pH within the range of 5.0 to 8.0. Preferably the pH of the pulp slurry is within the range of 6.5 to 7.5. The 6.5 to 7.5 pH range of the paper pulp or cellulosic material slurry is a pH range at which pulp is generally produced in conventional paper making processes and the anionic condition of the paper pulp provides a negative electrical potential on the pulp particles or fibers. However, it should be understood that a pH above or below this 6.5 to 7.5 range is contemplated within the scope of the invention provided that the fibers are in an anionic condition.

In the description of the processes of this invention, the term cellulosic fibers is to be construed as defining either purified cellulose or cellulose of various degrees of lignification, ranging from ground wood to highly delignified chemical pulps. It should be understood that the methods of the invention may be used with outstanding results for the treatment of any cellulosic fibrous material within thse broad categories.

The novel method of the invention has as one of its objects the addition of a protein to cellulosic fibers or paper-pulp to enhance the fiber-to-fiber bonding. To this end, a protein is colloidally dispersed in water having a suitable mineral or organic acid added thereto so that the pH of the acid-aqueous protein dispersion is adjusted to a value below the iso-electric point of the protein. Preferably the pH of the colloidal protein dispersion is within the range of 1.5 to 2.5. Since the pH of the acid colloidal protein dispersion is substantially below the isoelectric point of the protein, the protein particles in the dispersion are cationically or positively charged.

The protein used in the practice of the method of the invention can be identified generally as being amphoteric which term, its well known, identifies proteins capable of forming a colloidal dispersion with an acid to give a positively charged or cationic protein dispersion. By way of example, proteins such as casein, Delta protein (a purified soybean protein), cotton seed protein, soybean protein and the like give highly satisfactory results when used as described in the practice of the invention.

The acid employed in the preparation of the colloidal protein dispersion may be any suitable mineral or organic acid such as hydrochloric acid, acetic acid or formic acid.

The desired amount of the cationic protein dispersion is then mixed with the pulp slurry. Preferably, the protein, in cationic dispersion, is added to the pulp slurry in 7 an amount substantially less in proportion to the pulp by weight. Generally, the protein will be !1 0% and preferably within the range of 0.1% to 5% of the weight of bone dry pulp. The positive charges on the protein particles of the cationic protein dispersion and the negative charges on the cellulosic fibers or pulp particles bring about a mutual discharge or neutralization of the electrical charges, incipient flocculation of the paper pulp slurry, and acceleration of the rate of drainage and dewatering. The protein material from the colloidal dispersion is deposited or precipitated on the cellulosic fibers. The resulting deposit of protein on the surface of the fibers presents a good interface for subsequent fiber-to-fiber bondmg.

The precipitation of the protein is then completed by adjusting the pH of the protein-fibers mixture to substantially the iso-electric point of the protein. Generally speaking, this iso-electric point will occur at a pH within the range of between 4.5 to 5.5 or more specifically 4.5 to 5.0. This adjustment of the pH may be accomplished in the conventional manner by the use of an acid or papermakers alum (aluminum sulfate).

For a better understanding of the present invention, representative examples were carried out and control paper handsheets for use in these examples were prepared as outlined below. These handsheets were used for comparison purposes in Examples I, II, III below. The examples given below illustrate the wide range and scope of the novel method of this invention.

Laboratory control paper handsheets were prepared by beating repulped newsprint to a Schopper Freeness of 359 cc. to provide a pulp slurry. Portions of the pulp slurry were separated and Weighed and used to produce handsheets having a caliper of 0.03 inch.

EXAMPLE I Laboratory handsheets for this example were made by first preparing an acid colloidal protein dispersion utilizing casein as the protein dispersed in a weak hydrochloric acid solution to bring the pH of the dispersion to a value of 2.0. This casein, in acid dispersion, was added to weighed portions of this pulp slurry in an amount equivalent to approximately 1% of the weight of the bone dry pulp. To the protein-pulp mixture was added 1.25% (bone dry pulp basis) papermakers alum to adjust the pH of the mixture to approximately 4.5. Handsheets made from this protein-treated pulp were compared with the control handsheets described above and the results are shown in Table I below. It will be noted in this example that substantial increases in Schopper Freeness and Ring Crush were obtained with the protein additive.

Table I Hanclshects Containing Protein Additive Control Handsliccts EXAMPLE II The protein additive employed in this example was a high viscosity soybean protein in a hydrochloric acid colloical dispersion at a pH of 2.0. This protein, in acid dispersion, was added in an amount equivalent to approximately 1% of the weight of the bone dry pulp. Papermakers alum in an amount of 1.25% (bone dry pulp basis) was then added to the pulp to complete the precipitation of the protein at a pH of 4.5. Handsheets were formed from this protein-pulp mixture and tests results performed thereon were compared with the tests results of the control handsheets as shown in Table II. It will be noted in this example that substantial increases in Schopper Freeness and Ring Crush were obtained with the protein additive.

Table II Handshccts Containing Protein Additive Control Handshccts M ow to lo EXAMPLE III The protein used in this example was Kasoy 200 D which is a soybean meal containing approximately 50% protein and is a commercially available product. The

Kasoy meal was prepared as an acid colloidal dispersion in the manner of the previous examples and added to the pulp in an amount equivalent to approximately 3% of the weight of the bone dry pulp. The precipitation of the protein was then complet d with papermalters alum added to the Kasoy 2G0 D-pulp mixture in an amount of 2% (bone dry pulp basis). Tests results on laboratory handsheets prepared from Kasoy 2G0 D-pulp mixture were obtained and were compared with the control handshcets of Examples I and II as shown in Table III below. Here again, substantial increases in Schopper Freeness and Ring Crush were obtained with the Kasey 200 D additive.

In the two following examples, actual commercial paper making production conditions were employed. Accordingly, paper was prepared on a paper machine under production conditions to produce a conventional paper which was used as a basis for comparison with other runs of paper treated in accordance with the invention.

EXAMPLE IV In this example, the protein additive was casein in a colloidal aqueous dispersion with hydrochloric acid. This casein, in acid dispersion, was added to a newsprint pulp slurry in an amount equivalent to 1% of the weight of the bone dry pulp. Then, 2% (bone dry pulp basis) by weight of papermalters alum was added to the pulpprotein mixture to adjust the pH to approximate 4.5 and complete the precipitation of the protein. The tests results on machine made paper prepared from the pulp slurry having a protein additive are compared with the machine made control paper without the additive and these comparative results are shown in Table IV below. No ditierence was noted in the Schopper Freeness tests results comparison but the Ring Crush results were improved by the addition of protein to the paper.

EXAMPLE V Example V was carried out in a manner similar to Example IV using a paper machine under production conditions to produce control paper and paper having added thereto a colloidal acid dispersion of Kasey 200 D (soybean meal) in an amount equivalent to 3% of the weight of the bone dry pulp. Test results performed on the paper made from a pulp slurry having the protein additive were compared with the machine made control paper and comparative tests results are shown in Table V below. It will be noted that paper with the protein additive showed a substantial increase in Schopper Freeness and in the 6" Ring rush as compared with the control paper without the protein additive demonstrating clearly the advantages gained by the novel method of the invention.

Table V Machine Machine Made Paper Made Paper Without With Kasoy Additive 200 D Additive Type of Machine Cylinder Cylinder Type of Pulp Newsprint Newsprint Number of Plies 6 6 Caliper of Paper (in). .025 O25 pH of pulp slurry 6. 5-7. 5 4. 5 Percent Kasoy 200 D added to pul 0 3. 0 Percent Paperrnakers alum added to pulp-Kasoy mixture 0 2.0 Schopper Frceness (ca)... 400 450 6 Ring Crush (lbs) 169 200 Five day Biochemical Oxygen Demand of paper machine effluent (parts per million) 718 460 As shown in Table V the Biochemical Oxygen Demand of the efiluent from the paper machine was determined and the control paper made without the protein additive showed a considerably higher Biochemical Oxygen Demand in parts per million as compared with the paper made with the protein (Kasoy 200 D) additive. This reduction in Biochemical Oxygen Demand resulting from the manufacture of paper in accordance with the teachings of the invention is of considerable importance in that stream pollution laws present severe restrictions on paper making activity where a further increase in the Biochemical Oxygen Demand of the paper machine effluent due to increased paper making capacity produces prohibited stream pollution results. This, of course, means a severe and costly restriction to business expansion. With the novel method of the invention, an increased retention of the finely divided pollution causing material in the pulp is obtained and the Biochemical 4 Oxygen Demand of the paper machine effluent is sharply reduced as indicated in Table V.

While there has been described what at present is considered to be preferred embodiment of the invention, it will be understood by those skilled in the art that various changes and modifications may be made therein without departing from the invention and, therefore, it is the aim of the appended claims to cover all such changes and modifications as fall Within the true spirit and scope of the invention.

Having thus described the invention, what is claimed 1. In a method of treating cellulosic fibers comprising the steps of, preparing an anionic aqueous suspension of cellulosic fibers, colloidally dispersing an amphoteric protein in an acid solution to produce a cationic protein dispersion, mixing said cationic protein dispersion with said cellulosic fibers with the amount of said protein substantially less in proportion to the cellulosic fibers by weight the improvement of, adjusting the pH of the protein-fiber mixture to substantially the iso-electric point of the protein to complete the precipitation of the protein on the fibers of the paper pulp, and forming a paper web from the resulting paper stock.

2. In a method of treating cellulosic fibers comprising the steps of, preparing an anionic aqueous suspension of cellulosic fibers, colloidally dispersing an amphoteric protein in an acid solution to produce a cationic protein dispersion, mixing said cationic protein dispersion with said cellulosic fibers, the improvement of limiting the amount of protein mixed in said mixing step to less than 10 of the weight of the cellulosic fibers in a bone dry state, adjusting the pH of the protein-fiber mixture to substantially the iso-electric point of the protein to complete the precipitation of the protein on the fibers of the paper pulp and forming a paper web from the resulting paper stock.

3. In a method of treating cellulosic fibers comprising the steps 10f, preparing an anionic aqueous suspension of cellulosic fibers, colloidally dispersing an amphoteric protein in an acid solution to produce a cationic protein dispersion, mixing said cationic protein dispersion with said cellulosic fibers, the improvement of limiting the amount of protein mixed in said mixing step to a range of between 0.1% to 5.0% of the weight of the cellulosic fibers in a bone dry state, adjusting the pH of the proteinfiber mixture to substantially the also-electric point of the protein to complete the precipitation of the protein on the fibers of the paper pulp and forming a paper web from the resulting paper stock.

4. In a method of treating cellulosic fibers comprising the steps of, preparing an anionic aqueous suspension of cellulosic fibers, colloidally dispersing an amphoteric protein in an acid solution in the presence of heat at a pH within the range of 1.5 to 2.5 to produce a cationic protein dispersion, mixing said cationic protein dispersion with said cellulosic fibers with the amount of said protein substantially less in proportion to the cellulosic fibers by weight the improvement of, adjusting the pH of the protein-fibers mixture to substantially the isoelectric point of the protein to complete the precipitation of the protein on the fibers of the paper pulp, and forming a paper Web from the resulting paper stock.

5. In a method of treating cellulosic fibers comprising the steps of, preparing an anionic aqueous suspension of cellulosic fibers, colloidally dispersing an amphoteric protein in an acid solution to produce a cationic protein dispersion, mixing said cationic protein dispersion with said cellulosic fibers with the amount of said protein substantially less in proportion to the cellulosic fibers by weight the improvement of, adjusting the pH of the protein-fibers mixture with an acidifying composition to a pH within the range of 4.5 to 5.5 to complete the precipitation of the protein on the fibers of the paper pulp, and forming a paper web from the resulting paper stock.

6. In a method of treating cellulosic fibers comprising the steps of, preparing an anionic aqueous suspension of cellulosic fibers at a pH within the range of 6.5 to 7.5, colloidally dispersing an amphoteric protein in an aqueous acid solution in the presence of heat at a pH within the range of 1.5 to 2.5 to produce a cationic protein dispersion, mixing said cationic protein dispersion with said cellulosic fibers in an amount within the range of 0.5% to 1.5% of the weight of the cellulosic fibers in a bone dry state, the improvement of, adding papermakers alum to the protein-fibers mixture to adjust the pH of the mixture to a pH within the range of 4.5 to 5.0 to complete the precipitation of the protein on the fibers of the paper pulp, and forming a paper web from the resulting paper stock.

7. In a method of treating cellulosic fibers comprising the steps of, preparing an anionic aqueous suspension of cellulosic fibers, colloidally dispersing a protein selected from the group consisting of casein, soybean protein and soybean meal in an acid solution to produce a cationic protein dispersion, mixing said cationic protein dispersion with said cellulosic fibers with the amount of said protein substantially less in proportion to the cellulosic fibers by weight the improvement of, adjusting the pH of the protein-fibers mixture to substantially the iso-electric point of the protein to complete the precipitation of the protein on the cellulosic fibers, and forming a paper web from the resulting paper stock.

References Cited in the file of this patent UNITED STATES PATENTS 1,622,496 Davidson et a1 Mar. 29, 1927 2,352,922 Thomas et al July 4, 1944 2,559,848 Caldwell July 10, 1951 FOREIGN PATENTS 573,467 Canada Apr. 7, 1959

Claims (1)

1. IN A METHOD OF TREATING CELLULOSIC FIBERS COMPRISING THE STEPS OF, PREPARING AN ANIONIC AQUEOUS SUSPENSION OF CELLULOSIC FIBERS, COLLOIDALLY DISPERSING AN AMPHOTERIC PROTEIN IN AN ACID SOLUTION TO PRODUCE A CATIONIC PROTEIN DISPERSION, MIXING SAID CATIONIC PROTEIN DISPERSION WITH SAID CELLULOSIC FIBERS WITH THE AMOUNT OF SAID PROTEIN SUBSTANTIALLY LESS IN PROPORTION TO THE CELLULOSIC FIBERS BY WEIGHT THE IMPROVEMENT OF, ADJUSTING THE PH OF THE PROTEIN-FIBER MIXTURE TO SUBSTANTIALLY THE ISO-ELECTRIC POINT OF THE PROTEIN TO COMPLETE THE PERCIPITATION OF THE PROTEIN

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