by EGON GLESINGER
To the public, plastics are as unpredictable a wonder as the lighted fagade of the jukebox, itself made of plastics. This reputation is not wholly the product of press-agentry. Familiar as the substance of fountain pens and kewpie dolls, they turn up in bomber noses and auto finishes, toothbrush bristles and parachutes. They look like and do the work of stone, clay, metal, rubber, glass, and textile fibers. What all these plastics have in common is increasingly difficult to see. The word “plastics” is so loaded with meaning that it has begun to lose all meaning. No longer adequate is the literal definition, from
No longer adequate is the literal definition, from the Greek root, that plastics are “materials that can be shaped or molded.” This is only part of the story. Plastics are materials that can be created by chemical process to perform specific functions. To be precise, the word “created” in this definition should be followed by the phrase “practically at will.” Increasingly, through plastics, modern engineering is being freed from the need to trim and adjust its designs to the limitations of materials.
Wood is a natural plastic structure. Its cellulose fibers are complex plastic structures that possess great strength and resistance to fatigue. By the natural plastic lignin, these fibers are firmly bonded together and their strength is compounded in the unidirectional pattern of the grain. No synthetic process has yet been able to reproduce the oriented strength and resilience of wood as it grows in the tree. It is unlikely, therefore, that wooden beams will ever be replaced by plastic ones. Moreover, even if it were possible to endow, say, a plastic railroad tie with all the qualities of the wooden tie, the cost of such substitution would be prohibitive.
Theoretically, all that is needed to convert wood into a true plastic material is some means to overcome the limitations of its shape and size as it grows in the tree. This has already been accomplished. The various processes that gave birth to the new family of lignocellulose plastics are, for wood, the equivalent of the operation by which we reduce metals to liquids and then cast or roll them into desired shapes. As distinguished from the plastics that emerge from wood pulp, wood sugar, and lignin hydrogenation, the lignocellulose plastics look like wood, retain all of the constituents of wood intact, and can perform wood’s natural function as a structural material. Meeting an extraordinary variety of architectural specifications at low cost, lignocellulose plastics will become one of the pillars supporting the new Age of Wood.
Lignocellulose plastics were produced and used on a large scale for some time before their real significance was understood. The plastics industry has only recently caught up with them. Long before wood itself became a plastic, however, wood was established as a major plastic raw material.
Celluloid, the first of all plastics, was made of wood. It was discovered by John Wesley Hyatt as the accidental and undesired result of his efforts to produce from wood pulp a substitute for ivory billiard balls. Cellulose is the base for 70 per cent of the high-grade plastics that sell at more than twenty cents a pound. From purified high-alpha cellulose come photographic film, cellophane, and the big family of cellulose acetate, nitrate, and ester plastics that go into many other products. And no list of plastics should omit rayon, even though its huge volume puts it in a class by itself. Plastics, of course, are made from an infinite variety of other materials, ranging from coal tar to the excrement of tropical insects. Yet, in one form or another, most of the products made from these plastics contain some wood.
Few people realize, for example, that 50 per cent of every such item as a steering wheel, telephone, or fountain pen is wood. Wood is the filler or base that reduces the cost of these products and extends the supply of the expensive synthetic resins used to make them. But, just as the cherries or the apples, rather than the dough, identify the pie, the resin gives the plastic its essential features and name.
Most wood-filled plastics are of the bakelite type, invented around 1910 by Leo Hendrick Baekeland. This group of plastics constitutes three fourths of all the plastics produced in the United States and holds first place in every other country where plastics are made. The resin used in these plastics is based on phenol formaldehyde or some other coal-tar synthetic. Usually supplied to the molds in the form of a dry powder, it becomes liquid when heated, flows like hot metal, and cools in the mold. With it flows its filler, wood flour. Obtained by grinding sawdust and screening it through a fine mesh, wood flour is cheap and readily available. Its crucial role in molded plastics is indicated by the fact that phenolic resins cost nearly fifty times as much as wood flour, which sells currently for about half a cent a pound.
Wood flour does no more than keep the price of plastics down. The most common complaint against wood flour plastics is that they are brittle and unable to stand much stress. It could not be otherwise, since all plastic resins are low-polymer materials, devoid of inherent strength; and grinding wood into flour destroys the fibers and the molecular chains that create its strength. Soybeans, cornstalks, and other materials tried as fillers show the same weakness, because all must be ground to make them flow, and the grinding destroys their strength. Ever since Henry Ford failed to make car bodies out of soybean plastics, science has concluded that wood flour and similar fillers are suited only for the production of gadgets requiring no particular strength.
The alternative, to which the Ford Company and others turned, is to approximate the structure of wood by using the fibers intact instead of grinding them to powder. Wood fibers are readily available in paper. All that is required is to smear or impregnate sheets of paper with synthetic-resin glue, stack them until the desired thickness is obtained, and then cook the stack under pressure in a mold. To cut the cost, pulp sheets instead of paper can be used in the inner layers of the sandwich. Table tops, switchboards, and automobile dashboards have been made this way for years. The surface of such paper plastics can be given a natural glossy finish, it is impervious to cigarette burns and hard liquor, and it can be cleaned with a damp cloth. But, because the fibers, already felted into paper, do not flow, as wood flour does, paper plastics do not lend themselves to the making of intricate shapes. Their strength, also, was limited until recently, because no one paid much attention to the quality of paper used.
The fairly obvious idea of increasing the strengt h of the plastic by increasing the strength of the paper got its first active attention in the light-metal crisis that threatened to tie up war production shortly after Pearl Harbor. Six months of research and experiment produced a number of specially designed, high-strength papers. Laminated and bonded with plastic, they have twice the strength and half the weight of aluminum. Papreg, as this new paper plastic is called, has a tensile strength of 36,000 pounds per square inch, compared to the 5000to 10,000-pound strength of ordinary lumber and the 30,000to 40,000-pound strength of mild steel.
Stronger than plywood, and more easily molded, Papreg found immediate application in aircraft construction and was widely used in wing tips, ailerons, fuselage assemblies, pontoons, and other non-stressed parts. To engineers it offers the possibility of achieving monocoque structures — that is, self-supporting, like an egg, requiring no bracing, and capable of being molded in one piece. Reconversion has brought Papreg into the manufacture of furniture, building panels, refrigerators, stoves, and, according to enthusiasts, automobiles and railway cars.
Light weight and high strength are not the only virtues of paper plastics. They resist, flame, moisture, and vermin. With these qualities well established, paper has become a structural material that may one day require more pulp for the field of paper plastics alone than for all its present uses. Papreg may then come to be regarded as one of the outstanding inventions of World War II.
In order to complete the picture, wood should logically contribute the resin as well as the fiber and filler of structural plastics. The word “resin,” after all, once designated the sap of certain trees, even though most plastic resins today come from coal tar and petroleum. The natural source in the tree for such resins is lignin. Scientists know that lignin constitutes from 20 to 30 per cent of all wood, but they have yet to determine its exact chemical structure and properties.
Without lignin, trees could never grow several hundred feet tall, stand up against storms, and support heavy loads of snow. Binding together parallel bundles of cellulose fibers, lignin acts as nature’s plastic and gives wood its stiffness, impact strength, and resilience. Its action might be compared to that of the cement that surrounds and binds the iron rods in reinforced concrete. Nature itself thus suggests that we take lignin and use it as a binder for making cellulose plastics. Unfortunately, this is more easily said than done. For the lignin commercially available today refuses to duplicate its performance in nature.
The Marathon Paper Company, which spent a million dollars in lignin research and pioneered in the manufacture of synthetic vanillin, has made some progress. Lignin is used as the resin or resin extender in some of the paper and wood-flour plastics produced by this company. A few other United States forest-product enterprises have had similar tentative successes. Certain pulp and wood-sugar mills in Italy, Germany, Switzerland, and Sweden, it is reported, are producing fair lignin plastics on an industrial scale. At present, however, lignin plastics are unattractively dark in color, and their stability, strength, and moisture resistance leave much to be desired. They are, furthermore, a trial to the molder because they do not flow well, are sticky, and tend to gum up the molds.
Chemists are certain that none of these defects are inherent in lignin as it is synthesized in the tree. The trouble starts with the processes by which lignin is at present dissolved out of its bond with the cellulose fibers. At this point, reason suggests that lignin be left where it is in the natural structure of wood and be put to work in its pristine, natural condition. This is the eminently successful theory of lignocellulose plastics.
Synthetic vanillin is a perfect example of the high-grade products and prices lignin might yield. Obtained by treating waste sulphite liquors with an alkali, vanillin sells for $3 a pound. Substantial profit within this price sweetens its flavor substantially — at least for the Marathon Paper Company, which manufactures it. One day’s operation by United States sulphite pulp mills produces enough waste-liquor lignin to cover the nation’s vanilla consumption for a full year. And since the remaining 2000 million human beings consume substantially less vanillin in toto than America’s 140 million sweet-tooths, vanillin can never be more than a drop from the waste-liquor bucket.
Though it still has a long way to go, lignin’s commercial career does not begin and end with vanillin. Wartime scarcity of other materials in Germany and Sweden, for example, brought about the use of considerable amounts of waste liquors in the manufacture of soap. The product did not make the grade as bath or toilet soap, but it was completely satisfactory for laundry use and helped these nations to reduce their consumption of fats and oils in soap to one third.
Excellent qualities as a tanning agent have found lignin another market in the leather industry. Penetrating the cosmetics industry, lignin is an ingredient in some hand lotions and scalp tonics. It serves also in several well-known bactericides and fire extinguishers.
Advantage is taken of lignin’s natural plastic properties by using it as a rubber extender, a road binder, and an admixture to phenolic resins. A concoction of lignin and concrete is the basis for a number of new building materials and panels.
A constituent of natural humus, the biggest single deficiency in agricultural soils, lignin shows great promise as a fertilizer. Enriched with elemental phosphorus and nitrogen, lignin promotes the formation of topsoil and thus might be used to extend farming to poor soils in heavily forested countries.
None of these applications express lignin’s great potential value as a chemical raw material. This remains the objective of the research now moving forward in almost all forest-product laboratories.
A major and hopeful line of attack is the development of a process for the hydrogenation of lignin. Hydrogenation is the addition of hydrogen atoms to carbon compounds. Achieved by high temperatures and huge pressures, it results in profound and diverse changes in the structure, appearance, and properties of the chemical raw materials treated. Best known is the hydrogenation of coal, which supplied more than half of Nazi Germany’s gasoline and lubricating oils during World War II. In the petroleum industry, hydrogenation is the essence of the various cracking processes used to extend the yield of gasolines from crude oil and to produce the superfuels of aviation.
Lignin hydrogenation has so far been conducted largely in the laboratory pressure bombs of the United States Forest Products Laboratory at Madison, Wisconsin. It has produced yellow liquids of high viscosity that look and smell exactly like the basic fractions of crude oil. Fractionation and other chemical treatments of these liquids yield, first of all, a host of mysterious substances of no known immediate use but apparently great promise: phenols, the parent material for most thermo-setting or heatresistant plastics; volatile as well as heavy lubricating oils; and finally, most important of all, the hydrocarbon mixture known as gasoline.
Gasoline and lubricating oils from lignin are still far away. How far away is best demonstrated by the fact that recent industrial development of lignin has taken an entirely different course. It has led to the rise of a large industry engaged in making a variety of lignocellulose products — known by their less scientific name of “wood plastics” — in which the natural association of lignin and cellulose is maintained, but modified to meet a wide range of material specifications.
Lignin is justly regarded as the key to the future of wood chemistry. As long as wood-chemical industries are unable to process lignin to commercial advantage, their position in relation to coal and oil industries will remain that of the country butcher competing with the Chicago meat packer who exploits everything but the squeal. With the handicap of lignin as a by-product nuisance, it is remarkable that the wood-chemical industries — more correctly, the cellulose-converting industries — have not gone to the wall long ago. It is even more remarkable that wood pulp is highly profitable, that wood-sugar alcohol is fully competitive, and that other products of wood chemistry are making steady progress. The fact that, to date, lignin is almost a dead loss, however, has seriously hampered wood chemistry and kept its total turnover at about 20 million tons a year.
One of the products of Thomas Alva Edison’s wonder shop, the first lignocellulose plastic, was created by Owen Mason, an assistant to the master. Motivated, like Edison himself, by purely practical considerations, Mason was looking not for a new plastic, and still less for a solution to the problem of lignin, but simply for an industrial use for the millions of tons of excellent wood that America’s sawmills consign to their waste burners. Only now, a quarter of a century later, is it becoming clear that Mason invented more than a fiberboard, that he invented a true plastic by an original chemical-engineering process.
The basis of Mason’s invention is a gun loaded with sawdust or chips from almost any kind of wood waste. With the gun muzzle sealed, the wastewood charge is subjected to a few seconds of high pressure. Sudden release of the pressure produces a violent internal explosion in the cell spaces of the wood, tearing the fibers apart and reactivating the lignin so that it can form a new bond with the fibers. The gun fiber stock, a brown fluffy mass, is then washed, screened, and spread on a board machine, where it is rolled, dried, and cut into panels from one inch to several inches thick.
The standard Masonite panel has about half the density of softwood lumber. Its open, fibrous structure makes it an excellent insulator against heat, sound, and electricity. It is held together, not by the interlocking of cellulose fibers as in paper, nor by the addition of some extraneous plastic material, but by wood’s own lignin, which fixes the fibers again in a remarkably strong, stable, and homogeneous bond.
Edison was too busy to devote much attention to his assistant’s discovery. It did not take Mason long, however, to find a crop of aggressive capitalists who saw the commercial possibilities of his gun-explosion process. A factory site was acquired at Laurel, Mississippi, a town surrounded by large sawmills, and in the spring of 1924 the Masonite Corporation went into production, with Mason vice-president in charge of research.
Insulating materials were available long before Masonite was made, but the new wood fiberboards were so much better and cheaper that they swept the market. In insulating homes against the extremes of humidity and temperature, in soundproofing movie theaters, in iceboxes, refrigerated railway cars, and telephone booths, Masonite found huge sales. But it was in making modern city buildings and skyscrapers inhabitable that Masonite and the art of insulation came into their own.
The bonanza struck by Masonite soon brought a group of eager enterprises into the field. With a little experiment they developed alternatives to the patented gun-explosion process and demonstrated that wood chips and sawdust were by no means the only materials for producing insulating board. Out of ordinary groundwood pulp, sugar cane, straw, and bagasse, they produced competitors as good and as profitable as Masonite. For a time, Celotex, Insulite, Treetex, and other brands of insulating material popped up like mushrooms, not only in the United States, but all over Europe as well. Some were sold not as panels but as fibrous fillers and wool-like sheets. To the public they offered the advantages of constantly falling prices and variety of choice to suit different conditions.
Masonite had touched off an important new industrial development, which opened up large new outlets for wood. The least enthusiastic member of the new industry, however, was the Masonite Corporation, which found itself selling a highly competitive product instead of the patented specialty it had banked on. At this point, its vice-president in charge of research began to report some interesting results from his continuing experiments. Gun fiber stock, he found, could be squeezed into a homogeneous, grainless, synthetic board with great hardness and water resistance. No one had ever succeeded in making a similar product before, and no wood fibers produced by any other process could be made to organize and harden into quite such a superior board, no matter how they were squeezed. Clearly the gun-explosion process produced a unique effect upon the wood fibers. With some more thought and a little theorizing, Mason and his associates concluded that they had stumbled upon something revolutionary, a brand-new kind of plastic — a lignocellulose plastic. On the strength of this discovery, the Masonite Corporation took out, between 1926 and 1928, four exceptionally broad and shrewdly worded basic patents.
Masonite shifted its center of gravity from insulating boards to the new structural material. Produced in a wide range of densities, some even tough enough for floors and furniture, dark-brown Masonite boards have become a feature of the American landscape. Again the corporation found itself mobbed by competitors. This time, however, it had a patent case, and it went on the warpath. Masonite’s competitors had more than lawyers to contend with. The unmatched excellence of its product and the pre-eminence of its name had equal effect in bringing them to terms. One by one, Celotex, Insulite, Johns-Manville, and all the other leading manufacturers of insulating materials signed a standard contract to confine themselves to manufacturing insulating panels, but selling synthetic hardboard for Masonite instead of making it.
Secure in its monopoly, Masonite expanded without fear. In fifteen years enough Masonite boards have been made to pave a four-foot sidewalk to the moon. In 1928 the factory at Laurel produced 150,000 square feet a day; its present capacity, with a plant that is one of the showplaces of United States industry, approaches 2 million square feet a day. With the local supply of sawmill waste insufficient, Masonite became a direct purchaser and consumer of pulp wood.
Continuing its aggressive research policy, Masonite has reinvested large portions of its considerable profits in further research, has built a splendid laboratory almost as big as its original factory, and maintains on its permanent payroll a staff of one hundred chemical engineers. Out of this investment in science has come not only constant increase in the quality and variety of its products, but some important insight into the reasons for Masonite’s success. For when he squeezed his fiber into boards, Mason did not really know what made them so hard, nor did he have the full answer when he died in 1935. The discovery, since his death, that the explosion in the Masonite gun reactivates the lignin and gives it power, when squeezed, to rebond the cellulose fibers has opened up a fundamental line of thought about the future of lignin.
Masonite engineers feel pretty certain that their explosion process embodies the long-sought formula for making lignin industrially useful. This claim is supported by the properties of Benaloid and Benalite, the two heaviest and densest Masonite products, named after Ben Alexander, the late founderpresident of the company. These materials have been used to make die stock for stamping metals, and played a vital part in accelerating wartime aircraft production by eliminating the long and costly process of laying up and cutting steel dies. Other new products include all-Masonite iceboxes and fluorescent-light reflectors, plus a string of articles in which hard Masonite has replaced metals by virtue of its weight, strength, durability, and economy. The latest Masonite products not only are competitive with the best-known technical plastics, but also show considerably greater strength, resilience, and electrical resistance. Since practically no extraneous binders are used, Masonite engineers conclude that these virtues come from the highly superior qualities of lignin, especially lignin reactivated by the Masonite gun.
The wood that comes out of the Masonite process shows substantial improvement, in certain major respects, over its quality in the natural state. Although it is composed of the same constituents as wood in the trees, Masonite is homogeneous, free of defects, independent of the size of the tree, and can be produced in any given density. At its peak specific gravity of 1.4, it is three times heavier than ordinary pine. Balsa, the lightest, and lignum vitae, the heaviest, give natural wood a weight range of from 7 to 88 pounds per cubic foot. Masonite ranges from 1 to 90 pounds per cubic foot. Its density is varied, according to specification, by variation in the time and pressure of the explosion cycle and change in the mixture of its constituent softwoods and hardwoods, all of which are grown within a hundred-mile radius of Laurel. Very heavy or very light natural woods, by contrast, can be collected only at great expense from tropical forests.
Recent research has carried Masonite a step forward along another line into the lignin territory. Reactivated lignin has been separated from the gun fiber, mixed with furfural, a chemical recovered from the wash liquors of the explosion process, and made into a compound that yields fully molded plastics. Much research remains to be done before this laboratory development becomes an industrial process. But if Masonite’s record means anything, there is good reason to expect that its researchers may have succeeded in prying native lignin loose from its natural bonds. That this is better than a hunch is indicated by the fact that Masonite’s hard-boiled management has placed major emphasis, in its post-war production and sales campaign, on lignocellulose plastics of high technical properties, molded into intricate shapes.
Into the public domain
Masonite will need such an advance to maintain its position, for the basic hardboard patents all expired during the war, and the gun-explosion process is now in the public domain. The Supreme Court has, furthermore, declared that the agreements between Masonite and its competitors violate the antitrust laws and has ordered them voided.
The consequences of these two events should be rapid and decisive. Masonite’s monopoly has limited the annual consumption of synthetic hardboards in the United States to 220,000 tons — less than 2 per cent of United States lumber consumption and equivalent to not quite 4 pounds per person, compared to 25 pounds or 20 square feet per person in Sweden. It has also maintained sales prices of $65 and more as against estimated production costs of $25 per thousand square feet. Reduction of that profit margin and resulting increased sales will take synthetic hardboards out of the technical-specialty class and make them a major structural material.
Preparation for the day when lignocellulose plastics at last move into the public domain of competition has meanwhile been going forward in government and private laboratories outside of Masonite’s walls of secrecy. The United States Forest Products Laboratory at Madison and others have developed commercially practical lignocellulose molding compounds that have already found industrial uses. These include a sizable item in the form of a competitor for hard rubber for use in storage-battery separators and cases.
An even more lively research ferment has been at work upon the problem of obtaining free lignin for use not only in lignocellulose compounds but also as an all-purpose plastic resin. A hydrofluoricacid process has been developed which may do for wood sugar what the holocelluloseketene pulping process did for the wood-pulp industry. The testtube product of the first experiments along this line is a white powder that shows the same lively reactivity exhibited by the ketene-derivative lignin.
Without question, the day is near when lignin will be available for use as a major raw material of industrial chemistry. When that day comes, lignin may increase the supply of plastics tremendously. World output of plastics at present comes to about a million tons, to which may be added another one and one-half million tons of fiber board, both insulating and hard. The existing pulp industry and a wood-sugar industry that processed half the forest waste of Europe and North America could easily generate an annual supply of 40 million tons of lignin. If we assume, in accord with industrial practice, that lignin resins would constitute 50 per cent, by weight, of lignin plastics, end-product tonnage climbs to 80 million. Add the output of plastics from other sources indicated by the ascending curve of the industry, and the grand total reaches 100 million tons.
From 2½ to 100 million tons of plastic is a big jump. Weight for weight, the 100-million-ton figure is equal to the present world output of lumber and amounts to about one third of the world consumption of metals. If we allow for the lighter weight of plastics, it easily matches the metals in actual volume.
To achieve this output, of course, we need a market equal in magnitude. The market, in turn, is a function of price. At two cents a pound, the generally assumed figure, lignin would knock the props from under the price structure of the plastics industry. It would undersell lumber, which starts at two cents in the rough and enters the market at six to ten cents a pound, and would easily outrun the light metals, which cost from eight, to thirty cents in the ingot. Allowing for the weight factor again, lignin would even be competitive with standard auto body sheet steel, at its present six cents a pound. The potential size of the market for lignin is indicated by the fact that the United States auto industry could consume 3½ million tons of lignin in plastic bodies alone.
The figures with which we have been playing indicate that world consumption of cheap plastics could place these twentieth-century materials on a tonnage basis equal to that of metals, wood, stone, and other survivors of earlier ages. It should also be remembered that plastics represent only one of two self-contained cycles that can make full chemical use of all the wood in the tree. The second is liquid motor fuel, which could lay equally unlimited demand upon the world supply of lignin. Supplementing each other, the two could set the forest industries operating at full blast and would permit an elastic adjustment of wood chemistry and forest utilization to world economic conditions. Via both cycles, lignin, the last missing link, will connect up the conveyor chains and pipelines that lead from the forests to the fuel tanks, aircraft plants, and house factories of tomorrow.