INDUSTRIAL UTILIZATION O F CARBOHYDRATES
Industrial Cellulose Research As in the past, continued development of new uses of cellulose will come from a sound program of industrial research WENDELL W . M O Y E R Crown Zcllerbach
V^ELLULOSE
is a
uniquely
appropriate
object to study under the lens of the instrument known as industrial research. Counting the products which depend upon their cellulosic content for the properties that make them useful, such as lumber, plywood, building and insulating boards, carton board, fiber cordage and textiles, along with products derived from purified cellulosic materials, cellulose exceeds in quantity and distribution any other substance used by man. Cellulose is the most abundant of natural products because it was developed by nature as the chief structural element for the physical support of all higher plants. It originates as a product of the photosynthesis process of plants and hence the supply is one that "grows"—not an accumulated resource. Cellulose utilization can be traced to the beginning of civilization, and the tremendous scientific advances of the 20th century have merely increased the consumption by diversifying the end uses. Before concentrating on the object of cellulose and its place in the industrial scene, it is desirable to consider the scope and limitations of industrial research. We are not going to see anything about cellulose that is beyond the resolving power of the instrument at our disposal. The position that cellulose occupies in our affairs has been attained by sound principles of industrial research, and it is certain that no spectacular achievements will be realized in the future that run counter to sound practices. Natural products that are accessible to many people are always the target for promotions by the unscrupulous and by the well-intentioned but uninformed. Disregarding all dishonest efforts, the causes of failure of projects aimed at the utilization of natural products, such as cellulosic materials, should be reviewed if we are to draw any conclusions on where we are, and where we are going, and why. Industrial research is generally considered to be the application of natural laws and fundamental knowledge to the production of things that people need and want. What they want has a lot more psychological drive behind it than what they need. People will buy what they 510
Corp, Cartas, Wash.
"VVTENDELL W- MOYER, director of re-
^V search at Crown Zellerbach Corp., was born in Iowa and roved far a n d wide in pursuit of an education. H i s stint as research associate at Princeton University wound up a 13-year academic period which began at Findlay College in Iowa and included periods at University of Illinois, Munich, Germany, a n d Harvard University. H e joined t h e Solvay Process Co. as project leader in 1933 and in 1937 moved to A. E. Staley Mfg. Co. as director of research. He has published a dozen papers and has 20 patents to his credit.
want and pay a profit to those who produce for them. In many cases value is measured purely by utility; and in others, factors such as appearance, convenience, and emotional appeals are of equal or greater importance. W e are comparing hemp rope with rayon, or kraft paper with cellophane. Will People Buy It? This paper does not purport to b e a treatise on applied psychology, but the psychological evaluation is the first step to be taken in any industrial research project aimed at the development of a new product. Is the product something that people desire more than comparable products that are available? Will people buy the product at prices that will likely afford a profit? These questions appear so elementary that often they are passed over completely at a heavy penalty later of disillusionment and expense. Correct intuitive evaluation of the psychological factors is covered by the term "common sense." Large research organizations do not rely on intuition or common sense; they make thorough market surveys. The lack of a psychological evaluation, made objectively, is a minor error compared to the damage that is done by a nonobjective evaluation, influenced by fhe personal interests of individuals and groups. The insidiousness of à biased evaluation is that the compulsion toward it is usually in the subconscious mind. In the desire to utilize a certain raw material, subjective factors creep in and wishful thinking takes the place of sound logic. This astigmatism of the mental vision is C H E M I C A L
responsible for a host of mishaps. It causes one to overestimate the desirable properties of a new product a n d underestimate the deficiencies, while at the same time miraculously reversing the process when examining existing products that will be competitive. It causes one to inaugurate projects that run counter to a clearly-evident technological trend. I t causes one to interpret local conditions on a national scale, and to assume that an abnormal period of demand is a continuing economic condition. It causes one to ignore or underestimate the importance of many nontechnical problems upon which a successful industrial development depends. It causes one to overlook the consequences of success, that t h e pioneer of a useful new product invites competition which might prevail by virtue of cheaper raw materials or an improved process. To a scientist, whether pursuing fundamental discoveries in a university laboratory or working for an industrial organization as a livelihood, there is a great spiritual satisfaction in creative effort. Below this, research is a competitive struggle. The pure scientists compete for honor and renown, the industrial scientists compete with nature and other groups to_ obtain for the companies that employ them a greater share of the money the ultimate consumer has to spend. In the last analysis, industrial research is a new type of competitive enterprise that has been employed by industry to ensure profits. Fortunately, the competition with nature results in new wealth which gives the consumer more money to buy the end-products of research. A N D
ENGINEERING
NEWS
INDUSTRIAL CELLULOSE RESEARCH Industrial research is the most powerful instrument t h a t has been devised by t h e h u m a n r a c e for t h e creation of wealth. Its successful use depends upon an objective evaluation of t h e problems which it is pressed t o undertake and a most respectful attention to t h e competitive scientific a n d economic elements that are in force in o u r free enterprise system of economy. Cellulose materials h a v e no natural exemption to t h e rules of good industrial research b e cause t h e y g r o w on every farm a n d forest land. I n fact, as may be surmised, t h e w i d e s p r e a d abundance of cellulose and its manifold uses make it a particularly susceptible object of misdirected research efforts. A definition of cellulose in the industrial field is i n o r d e r here even t h o u g h it m a y serve o n l y as an excuse t o misuse t h e w o r d . Cellulose is used generically t o characterize t h e various products derived from v e g e table m a t t e r w h i c h contain p r e d o m i n a n t l y the ideal set b y chemists, a-cellulose. a-Cellulose is a polysaccharide built u p of straight chains of glucopyranose rings joined f r o m t h e first to the fourth carbon atom b y beta-linkages. F u r t h e r m o r e t h e degree of polymerization must b e such t h a t the molecules are insoluble in d i l u t e alkalies a n d acids, and have an o r g a n i z a tion t h a t gives a typical x-ray d i a g r a m . T h e degree of polymerization of a-cellulose is not a fixed quantity but, like starch, varies from plant species to species. T h e cellulose of industry contains t h e a l p h a species i n various degrees of purity, t h e tolerance to impurities d e p e n d i n g u p o n t h e end-uses. a-Cellulose does not occur in p u r e form in n a t u r e . Vegetable matter may contain from a small amount to almost 9 8 % in t h e b e s t cotton lint fibers. T h e majority of plant m a t e r i a l s contain from 30 to 5 0 % . Associated w i t h natural cellulose are a group of polysaccharides k n o w n as h e m i celluloses which have m a n y properties similar t o a-cellulose but are of m u c h lower molecular weight and contain sugars other t h a n glucose in their structure, as well as u r o n i c acid residues. Another class of c a r b o h y d r a t e s commonly associated with cellulose comprise the pentosans, a n d in particular, xylan. The chief n o n c a r b o hydrate c o m p a n i o n of cellulose is lignin. T h e relationship between lignin a n d cellulose is so close t h a t many of the processes used for purifying cellulosic materials m a y be properly called delignification processes. Among t h e minor impurities are g u m s , pectins, fats, waxes, sugars, resins, a n d lignans.
T h e organization of cellulose into a fibrous s h a p e is t h e u n i q u e characteristic that makes cellulose so widely useful in industry. Cotton a n d linen textiles owe their existence to t h e natural fiber occurring in t h e seed hairs of cotton a n d the bast fibers of flax. Paper is m a d e b y a mat-forming process on isolated fibers from wood a n d other sources. M a n y of t h e natural cellulosic fibers of industry consist of unseparated fiber b u n d l e s , or filaments, rather than individual fibers t h a t have been reformed. Among these are the bast, fibrovascular, and leaf fibers of plants such as jute, h e m p , a n d sisal w h i c h a r e used for rope, cordage, and bagging. E c o n o m i c s vs. Chemistry An o r g a n i c chemist might evaluate cellulose as a chemical r a w material on t h e basis of t h e desired degree of polymerization a n d freedom from impurities, a n d h e n c e d r a w t h e conclusion t h a t economics w o u l d dictate the source of supply. T o a large extent this, is true, b u t again t h e kind of fiber a n d t h e way it is preX^ared play very important roles. Every plant species produces a different t y p e of fiber. T h e variations are in length, thickness, smoothness, shape, a n d organization of t h e cellulose molecules. Since chemical reactions with cellulose involve a heterogeneous p h a s e , the speed of. reaction and t h e control will d e p e n d upon t h e accessibility of the cellulose molecules to the reactants. A thick, highly oriented or crystalline fiber cannot be a t t a c k e d as readily as a t h i n fiber h a v i n g less orientation and more amorphous areas. The presence of fiber bundles not broken down d u r i n g prior processing or formed b y matting are particularly deleterious. T h e im-
portance of t h e physical condition of t h e cellulose fibers is illustrated particularly by the nitration reaction which is very rapid. Fiber bundles are u n d e m i t r a t e d a n d the individual fibers are overnitrated. Not to digress from the general n a t u r e of this discussion, t h e problems of industrial research on cellulose c a n be divided into five broad divisions: 1. 2. 3. 4. 5.
Supply problems Purification problems Application problems Chemical problems F u n d a m e n t a l problems
In commenting briefly on each of these types of problems, it is well to k e e p in m i n d t h e competitive nature of industrial research which was mentioned above. T h e m a n y sources of cellulose compete with each other for their place in t h e e c o n o m i c , sun, a n d cellulose, irrespective of source, must compete with other r a w materials for the consumers' dollars. Supply problems concern all phases of obtaining plant raw materials for cellulose in its existing uses and for new uses. Some of these problems do not involve chemical research and seem aloof from the activities of a laboratory o r pilot plant, b u t they are problems to b e considered to ensure industrial success later. T o explain the factors behind the status of current cellulosic sources such as wood, cotton, h e m p , straw, for example, it is perhaps easier to start with a n analysis of a hypothetical problem: Can plant species " Z " be utilized to produce a grade of commercial cellulose? I n a preliminary survey a n u m b e r of questions must b e raised a n d answered w i t h a fair degree of accuracy. Does species " Z " h a v e any other economic values such as oil-bearing seeds, t a n n i n ,
Small digesters for experimental p u l p i n g of w o o d and fibrous materials
Its Unusual Properties T h e u n u s u a l properties t h a t distinguish cellulose from other c a r b o h y d r a t e s a n d m a k e it so useful can be t r a c e d to t h e linearity a n d h i g h degree of polymerization of t h e molecules. The beta linkage minimizes curling and spiraling a n d p e r mits the molecules to line u p with a h i g h degree o f orientation to form, in a h i g h p e r c e n t a g e of cases, a fibrous s t r u c t u r e . V O L U M E
3 0, N O .
6
»
•
FEBRUARY
11,
1952
511
INDUSTRIAL UTILIZATION O F CARBOHYDRATES
/ Angiosperm wood fibers, cottonwood ( l O O x )
Gymnosperm wood fibers, Douglas fir ( 100 X )
or alkaloids that can be realized? What i n the availability and cost of cellulose is the cellulose content? W h e r e is it from established sources. Gymnosperm located? What are the associated noncellu- wood is an excellent example. Although lose materials? Are the impurities o f such wood contains only from 40 to 5 0 % cellunature that they would interfere with lose, it provides the most favorable anphysical and chemical purification proc- swers to many of the questions posed for esses? What is the yield p e r a c r e per other plants and agricultural residues. As annum? What is the value of the land to a result, in the early days of pulping wood, be used for growing "Z"? W h a t is the logging practices were wasteful and no was given to growing probability that another crop c a n be consideration grown more profitably? How e a n the another crop. T h e unprecendented decrop be harvested—any special equipment mand for wood pulp, primarily because it required? Is harvesting a seasonal o r year- was c h e a p , depleted forest reserves at an round proposition? What is the cost of alarming rate and focused attention to collecting and delivering to a processing the advantages of wood that had previplant? Are there any unusual storage ously been taken for granted. problems? This is not a compre-hensive At t h e present time in the Pacific Northlist, but the wrong answei to any- of the west, and increasingly so in the South, above questions can spell failure even trees are {armed as an agricultural crop, though all the other factors are favorable. the farmers being professional foresters. Yields are increased by scientific logging, Agricultural Residues thinning, replanting, and seeding. The crop The list is not so long when t h e raw is protected against insect pests by spraymaterial under consideration is the by- ing, and from fire hazard by watchers, product of crops grown for other values, well-built fire-roads, and clean-up of logsuch as corn stocks, sugar cane bagasse, ging debris. Experiments in hydridization wheat straw, and many others. However, are b e i n g made to increase growth rate lessening the number of factors d o e s not and improve fiber quality. The pulp mills greatly alter t h e severity of the problem are being geared to areas of land which because the ones that remain are extremely will supply sufficient logs to keep the mills critical. Here is the problem of what is running at capacity forever. termed "agricultural residues" as sources Economics Key to Supply of cellulose. These residues comprise a stupendous potential source of cellulose, If t h e supply problems connected with almost untapped, because of economic the evaluation of a source of cellulose can barriers that can't b e breached u n d e r pres- be solved economically, there is great ent conditions. The cotton plant rproduces reason to be encouraged about the evenfar more cellulose in the roots, sta.lks, and tual success of t h e project. T h e next step leaves than in the form of seed h a i r s , yet in t h e procedure, the isolation of the celonly the latter has commercial v a l u e . lulose in a form suitable for some indusAlso in active competition w i t h new trial application, is on a more objective sources of supply, are the improvements plane because information can be devel512
CHEMICAL
oped by experimental methods. All the problems in this area are designated purification problems. The first one is the removal of dirt and extraneous substances from the plant material. Only for the coarsest uses can an appreciable amount of inorganic or darkcolored organic dirt be tolerated in cellulose fibers. For example, the carbon particles from a fire-charred log can ruin a large batch of paper-making pulp. T h e best place to remove dirt is at the beginning, not after the plant has been reduced to fibers. The next step is to determine, with due regard to the contemplated end use, how much of the undesired portions of the plant material can or should b e removed by physical means before using any pulping or chemical process. By way of illustration, bagasse is composed of about 50r/c of pith that should b e removed by a physical process before attempting to pulp the fibrous stalks; the cost of pulping chemical to solubilize the pith exceeds that of the preliminary mechanical processing. The required type and degree of purification depend entirely upon t h e field of utilization of the cellulose, and it has been assumed that this has been understood in t h e discussion of supply problems. T h e application field may be divided into three areas: the first includes uses which require only the elimination of the nonfibrous portions of the plant to leave the fibrous part in which the cellulose remains b o u n d with t h e hemicelluloses, pentosans, and lignins, for use in such products as wall and insulating boards. The second comprises the separation of cellulose fiber filaments as, say, in the preparation of ramie fiber; and the third comprises the reduction of AND
ENGINEERING
NEWS
INDUSTRIAL CELLULOSE RESEARCH cellulose to individual fibers as in the p u l p ing of wood. Superimposed on all three classes may b e bleaching problems. The reduction of the plant raw material to individual fibers is commonly called pulping. T h e selection of a suitable p u l p ing process again brings in economic factors. The geographical location of the pulping mill and its proximity to chemical supplies and a d e q u a t e water, as well as disposal of mill effluents, must be carefully analyzed. As indicated under supply, the nature of the noncellulosic material is also a controlling factor. It is safe to say that any p l a n t material can be pulped by the kraft process b u t the properties of the pulp, the location, cost, and many other considerations m a y count against kraft pulping. T h e sulfite process also has limitations; some woods cannot be p u l p e d by the sulfite process because of high resin content or the presence of extractive chemicals t h a t react with the lignin more readily than does the sulfurous acid. The development of a suitable pulping process with t h e experience available at the present time becomes chiefly a matter of industrious experimentation. T h e bleaching of cellulose material to lighten the color and remove residual impurities involve t h e use of chlorine, hypochlorites, chlorine dioxide, hydrogen peroxides, alkalies, a n d combinations of these. The ancient method of bleaching in sunlight is hardly applicable in modem industry. The problem of bleaching a new cellulose material is, again, chiefly o n e of experimentation w i t h various known processes. The degree of purity of cellulose fibers ties in closely w i t h t h e third division: application p r o b l e m s . T h e end use of the cellulose depends upon the quantity and nature of residual impurities in the fibers. The paper industry provides an example of one that requires an impure fiber. A pure a-cellulose fiber would yield a weak sheet that would have limited utility. A certain small percentage of hemicelluloses and pentosans is necessary to obtain strength due to fiber-to-fiber bonding. On the other h a n d , too high a content of hemicelluloses p r o d u c e s a glassine type of sheet of limited application. The evaluation of a cellulose fiber or pulp for one of t h e established applications such as textiles, p a p e r or chemical conversion is a highly specialized undertaking that should n o t be attempted by thosu who have n o more than an academic knowledge of the science a n d art of the field. Lack of appreciation of this fact has been and will continue to b e the cause of wasted money and disappointment. Each of t h e thousand-and-one different grades of p a p e r n o w manufactured h a v e rather specific fiber requirements w h i c h must b e recognized in order to obtain the desired properties such as tensile strength, mullen, tear, formation, fold, stiffness, absorbency; opacity, transparency, density, and smoothness. There is a tremendous amount of k n o w - h o w in the choice of a VOLUME
3 O,
NO.
Ö .
suitable fiber furnish for a particular grade. T h e type of p u l p i n g process required, t h e length and shape of t h e fibers, the crystallinity of the fiber, the degree of hydration, and cutting by beating and jordaning, to mention only a few, are all significant. Some grades of p a p e r can be ^ d e from any- fiber furnish, but whether or not said p a p e r will compete with an existing commercial grade is a matter for expert opinion. It is ridiculous to attempt to make newsprint, for example, from a fiber that produces a rattly, transparent sheet that permits ink to show through. T h e cellulose textile industry imposes likewise a scries of limitations on the properties of t h e fibers it can use to advantage. For t h e production of regenerated cellulose products, the a-cellulose content must b e higher, say above 9 0 % , and impurities, particularly the pentosan content, much lower than for the best paper-making p u l p . A natural cellulose product of unusually high pentosan content would not likely b e a suitable r a w material to be pulped for viscose or cellophane. For the production of cellulose derivatives, in general, it could be said that the purification process should he extended as far as possible to yield a-cellulose. T h e chemical problems involved in the utilization of cellulose comprise all those concerned with the preparation of chemical derivatives such as the intermediate xanthates in the viscose process, esters, ethers a n d acctals, swelling and m e c e r i z a tion, hydrolysis, oxidation, in short, all the operations in which cellulose is treated as an organic compound or as a polysaccharide. These specialized problems will not he discussed here because this field is essentially that of industrial organic chemical research. If one can produce a-cellulose of the proper degree of polymerization a n d in accessible physical form, it can be used for chemical purposes. T h e last division comprises what should be called fundamental problems. Fundamental research which seeks n e w laws and principles is an integral part of a sound industrial research program, although managements lrequeiitly prefer to designate all work done in an industrial laboratory as applied because it sounds more practical. Actually, the record shows that the big things originate in research t h a t is indistinguishable in procedure at its beginnings from investigations in any university laboratory. M a n y Problems Await
Solution
An impressive list of fundamental cellulose problems u n d e r investigation or waiting for study could be compiled. Among these the following should b e mentioned: 1. Studies on t h e nature of the binding forces between cellulose and t h e associated carbohydrates in natural materials. Present pulping processes are so harsh t h a t production of fibers is a t t e n d e d by loss of valuable a-cellulose as well as loss of desirable strength properties. 2. Further studies on the fine structure
» FEBRUARY
11,
1952
of cellulose. Not all of t h e behavior of cellulose fits well with t h e concept of linear chains differing only in degree of polymerization. 3 . Investigation of t h e hydrolytic breakdown of cellulose in steps to the ultimate sugar glucose. 4. Physical chemical studies of the modification of fibers by surface treatments, including fiber-to-fiber b o n d i n g and absorption of chemicals on surface. 5. Investigation of t h e influence of fiber crystallinity o n the behavior of the fibers. 6. Studies on t h e distribution of substituents of cellulose derivatives a m o n g the 2-, 3 - and 6- positions of t h e glucopyranose units. 7. A study of means for increasing the elasticity of filaments m a d e from natural and regenerated cellulose. I n conclusion, it is proper to indulge in the interesting b u t inexact science of prophecy in a n attempt to look into t h e future of cellulose. Scientific method permits the extrapolation of t r e n d curves, and a prophet can insure t h e accuracy of some of h i s predictions b y making m a n y of them couched in ambiguous terms. Since the following predictions are few in n u m b e r , the accuracy will d e p e n d u p o n t h e extrapolation technique. 1. An a b r u p t shifting u p w a r d in t h e utilization of cellulose will be t h e outgrowth of a new fundamental discovery by research o n cellulose. An a b r u p t d o w n trend will result from a fundamental discovery made by research o n competitive materials. 2. The long-term trend in the utilization of cellulosic fibers, natural a n d regenerated is u p w a r d . 3. The long-term trend in the utilization of cellulose in the form of derivatives is downward and will b e reversed only by a heroic discovery that will reduce the production costs. 4. Cellulose nitrate is an exception to the above prediction. Its value in peace, and particularly in war, will increase. 5. Combinations of cellulose with synthetic polymers will find greater and greater fields of application. 6. The hydrolysis of cellulose to glucose and simple oligosaccharides will become a d o m i n a n t economic factor. T h e logical solution to the p r o b l e m of agricultural and forest residues is to convert t h e m to nutritional products to feed an expanding population. 7. Cellulosic byproducts will find increased utilization as r a w materials for the production of simple aliphatic chemicals through chemical engineering and biological processes. 8. Looking far into t h e future, w e can see that cellulose, the most a b u n d a n t of all photosynthetic products, will b e c o m e one of man's most useful r a w materials. The supply is replenished by growth while materials stored from past ages are continuously d e p l e t e d . 513
