T H E ' J O U R N A L OF I N D U S T R I A L A N D ENGINEERING CHEMISTRY
858
Vol. 14, No. 9
Recent Advances in P u l p and Paper By Clarence J. West CHAIRMAN, COMMITTEE ON BIBLIOGRAPHY, T. A. P. P. I., 1701 MASSACHUSETTS AvE., WASHINGTON, D. C.
RAW'MATERIALS NE O F T H E most interesting questions in the pulp in-
IMPROVEMENTS I N PROCESSES
Rue has raised the question why a greater yield of pulp dustry to-day is the future source of its raw materials. should not be obtained in the chemical processes. Fifty-five The forests are rapidly disappearing and only a few of to 60 per cent of wood is true cellulose, yet less than 45 the more enterprising mills are taking any precautionary per cent of the wood is obtained as high-grade pulp; this repmeasures with regard to reforestation. It is true that paper resents a loss of about 25 per cent. The solution of the probcan be made from practically any fibrous lem will necessitate a fundamental rematerial known, but it is also true that, in search into the various processes of pulpthe majority of such raw materials, the ing wood. The further need of economical process is far from being satisfactory, as utilization of other woods than spruce, far as the yield of pulp is concerned. It hemlock, and balsam fir is also a pressing is not possible, in the United States a t problem. least, to prepare pulp from annual plants The Forest Products Laboratory has and similar materials, under conditions that suggested that one solution of these probmake the process econoinically feasible. lems may be obtained through a prelimiThe most promising raw materials, other nary impregnation of the wood before than wood, thus far studied are bamboo digestion. The initial results indicate an and cotton linters. The early difficulties appreciably shorter cooking time a t lower encountered in the treatment of bamboo temperatures. It is probable that the have now been overcome and one or two method will require a change in the usual methods are known to be quite successful. acid composition to take care of the inIndia appears to offer an inexhaustible creased speed of the chemical reaction. supply. dccording to Raitt, India, with The results will be increased yield, deits supply of bamboo, and the Savannah creased screenings, and stronger pulp. Angrasses, can produce pulp for the whole other innovation in digesting practice world. Raitt further estimates that the consists in fractional digestion, introduced cost of production of bamboopulp would not by Aitken in the cookLg of esparto. He C J. WEST exceed half that of the manufacture of wood proposes to remove members of the starch pulp. Many years ago the Department of Agriculture tried and pectose groups in the first treatment, using a 1.5 per cent to cultivate bamboo in the southern states, but their experi- sodium hydroxide solution, and then remove the ligneous maments were not very successful. It still remains to determine terial by a more drastic treatment with 14 per cent alkali. whether bamboo can be grown in this country. If so, this This method gives a cleaner and more easily washed stock, greater economy of bleach and reduction in costs of recovery. would offer one solution of the problem of raw materials. Cotton linter pulp has attracted much attention since the No mention has been made of comparative yields. The process of rag boiling has been studied by Grimm. It war. The great demand for cotton during the war period made it necessary that the cotton attached to the seed after is stated that the mechanical treatment to which the stock the usual ginning process (about 200 lbs. to the ton of seed) is subjected in the washer and in the hollander modifies the be removed as far as possible. At the conclusion of the war chemical constituents of the fibers very considerably. His the demand for this materia! dropped practically to zero, and conclusion is that the present proportion of chemicals and successful efforts were made to convert this into pulp for paper. rags is correct. This is the first time the commercial pracThe manufacturers claim that this pulp may be used to ad- tice has been checked by scientific studies in the laboratory. The possibility of using decayed pulp wood has been studvantage in place of old rags, and also in certain proportions in place of new rags. Because it is a new cotton fiber which has ied by Bates and by Sutermeister. Bates concludes that innot been worked or processed, it gives somewhat greater fected wood may be used for sulfite pulp production if decay bulk to paper for the same unit of weight. There is, natu- is limited to discoloration, and believes that chipper dust rally, still some question in the minds of certain paper manu- pulp might be satisfactorily blended with ordinary sulfite facturers as to how far this pulp will be successful, but it is pulp and so utilized. Sutermeister has found that by using felt that it can be mixed with other pulps even if it cannot be wood permeated with threads of dry rot but still quite hard and firm, the yield was considerably lower, the fiber weaker and used alone. Papyrus has been proved as a paper-making material but practically unbleachable. Stained wood had little effect the source of supply (Zululand and the Sudan, as well as upon any quality other than that of bleaching. Bleach other parts of Africa) would seem to make it unimportant as consumption in the case of stained pulp was about 15 per cent as compared with 10 per cent for an ordinary pulp. a raw material for American manufacturers. Processes have been developed for utilizing the Jack pine, ANALYTICAL METHODS which will make available large tracts of this hitherto littleMethods of control in the pulp mill continue to be a subused species. Very interesting developments are reported along the line of the use of southern pine waste. Some of ject of investigation. Various analytical methods for sulfite the claims of the promoters are questioned and only large- liquors have been proposed and reviewed. While the analysis of the raw acid seems to be a comparatively simple bne, scale operations can settle the question.
0
'_
Sept., 1922
THE JOURNAL OF INDUSTRIAL A N D ENGINEERING CHEMISTRY
the analysis of the liquor produced during the digestion of the wood is complicated by the presence of the decomposition products from the ligneous portions of the wood, and the analysis of the sulfite waste liquor seems an almost hopeless task. Another interesting field of research is in methods of differentiating the various pulps, sulfite, sulfate, soda, and mechanical. The whole procedure, from the preparation of standard samples of known pulps to the actual determination of the composition of unknown mixtures, is in need of standardization. Various stains have been proposed for this purpose but it seems a difficult matter to obtain a sufficiently marked differential staining of some of the pulps to enable even an approximately accurate determination. Lofton and Merritt have recently proposed the use of Malachite Green and Basic Fuchsin for determining the amounts of unbleached sulfite and ijulfate pulps in a mixture of the two. The sulfate fibers are stained a blue or blue-green while the sulfite fibers assume a purple or pink color. The need of standard methods is thoroughly recognized by the ‘rechnical Association of the Pulp and Paper Industry, which has a committee actively engaged in the preparation of a f;et of methods which it is hoped will prove so satisfactory that they will be adopted by the whole industry. BEATING The most important questions in the beating of paper pulp are methods of accelerating the process, thereby decreasing the caost and methods for the control of the process. It is believed that a possible improvement in the manner of beating consists in the use of higher concentrations of stock moving through the beater a t a higher rate of speed. This suggests that it is not the length of time which the stock is in contact with the water in the beater but the total distance that the stock travels that determines the degree of beating. The question of chemical hydration of pulp has been discussed by McKay. He claims that the process introduced by Meigs, Bassett and Slaughter will give an increase in strength of the finished sheet with no reduction in the paper-making qualities of the pulp, a decrease in beating time and a reduction in caustic, time of digestion, amount of bleach, and time required for bleaching with every grade of stock. One of the most interesting parts of McKay’s contribution is the fact that he has introduced the copper number and viscosity as means of controlling the degree of beating. Much more work is necessary before it can be said that these methods will or will not answer the problem of control. It does seem to be certain that the so-called slowness test does not. BLEACHING The bleaching of paper pulp, in the case of rags, may be readily carried out by the use of liquid chlorine. In this process no special equipment is necessary, for the liquid chlorine may be injected directly into the beater or washer where the bleaching is done. This avoids the handling of bleach drums and solutions and tends to cleanliness in the mill. The only danger is from the fumes of chlorinegas, and with properly designed control apparatus this should be very slight. The use of liquid chlorine is, it is believed, gradually displacing the electrolytic bleach in many paper mills. Because of the higher concentrations necessary, it is not possible to use liquid chlorine with chemical pulp as in the case of rags. It is first transformed into calcium hypochlorite solution, which solution is claimed to have quite different physical properties from that prepared from dry bleaching powder. Much of the success of this application depends upon the apparatus developed by the Wallace and Tiernan Company for controlling liquid chlorine. This makes possible the production of an absolutely uniform liquor. This
859
liquor has a lower alkalinity than that prepared from bleaching powder which, under some conditions a t least, is an advantage. Wolff has proposed a new form of bleaching tub which permits the circulation of pulp concentrations of 10 to 15 per cent; naturally this gives a greater efficiency of operation. An important advantage is the saving of steam in bleaching a t lower temperatures, while there is also less loss of fiber and cleaner pulp. Wells has studied the bleaching of soda and sulfate pulps, prepared from coniferous woods, by the action of bleaching powder solutions. He finds that the alkali-solubility of the pulps increases with the strength of bleaching liquor employed and that considerable degradation of the cellulose takes place before the color is removed, indicating the unsatisfactory nature of this type of bleach. He obtains slightly more satisfactory results with regard to color removal by carrying out the bleach treatment in two stages with an intermediate washing. The pentosan contents of the pulps were found to be unaffected by bleaching, but on the other hand their methoxyl contents were reduced by the treatment. SIZING Little advance has been made in the study of sizing materials. The most important study is that of Blasweiler on the use of water.glass (sodium silicate). He made a large number of tests with water glass alone and in combination with soaps, f&s, animal size, starch, casein, etc. He draws the following conclusions, which may or may not be warranted: good suction on the paper machines; no sticking a t the press rolls; rapid and complete setting of the suspended matter in backwater; greater strength and better rattle to the paper with a higher retention of clay or loadings; good color and dyeing results. Vail has also discussed, in various trade journals, the uses of water glass in the paper industry. One of the interesting questions of the present day is the difference between gum and wood rosin in the sizing of paper, and especially in the color imparted by the latter. That there is a difference even the manufacturers of wood rosin admit. We have still to discover the reason and to remedy it, if possible. Another question that is engaging the attention of some of the technical men of the industry is that of the real meaning of sizing quality of paper and a method of measuring it in terms of a definite, absolute unit. There are many tests for sizing quality. Recently the Valley Size Tester has appeared. This machine claims to give an accurate unit for sizing and to enable the manufacturer to keep his sizing constant during a run and from run to run. The test, however, is a relative one, and does not give us a fundamental unit for sizing quality. Such a unit is really necessary before a careful study of the factors influencing the sizing quality of paper can be made. The Paper Section of the Bureau of Standards is studying the general question of the testing of the sizing and it is hoped that they may be able to solve the problems involved. Much interest has been aroused in the announcement of the Englishman, Kaye, that the application of rubber latex to paper-making appears to improve the texture and the strength of the paper so treated. The paper possesses the property of folding without serious permanent cracking along the line of fold. It is also claimed to be more water-repellent than paper not treated with rubber. Many other claims are made, based in part on commercial tests. If these results are substantiated by other mills, it would seem that this was an important contribution to the industry. The Flintkote Company has reported a process for the emulsification of asphalt by means of a highly colloidal clay, so that it may be introduced into the paper-making process
