We Now Grow Our Own Rubber (Jul, 1931)
We Now Grow Our Own Rubber
Mexico’s Wild Weed, Guayule, Raised on 5,600 Acres in California, Yields Precious Latex
By STERLING GLEASON
ACROSS the level surface of a sun- baked valley in central California, tractors drag strange, clanking machines down long, parallel rows of a grayish-green shrub that looks, at first sight, like sagebrush.
In a near-by mill, giant crusher rolls grind dried bushes to a pulp, while steaming, high-pressure hydraulic chambers spew forth myriad tiny cellular particles the size of a grain of wheat.
In the yard outside, men load freight cars with rectangular pine boxes filled with a spongy, porous material, whose acrid smell is strangely familiar. It is rubberâ€” produced commercially on American soil for the first time in history.
Mechanized American efficiency now promises to produce the crude rubber of industry at a cost that can successfully compete with the product of the labor of coolies who are virtually slaves.
On a 5,600-acre tract near Salinas, Calif., “guayule,” a shrub imported from the highlands of Mexico, is being grown on a huge scale. When ground to a pulp in machines much like those of a large ore mill, this queer plant yields from thirteen to twenty percent of its own weight in pure raw rubber.
The California rubber project represents the triumph of scientists who for years have been searching the world over for a rubber-producing plant that could be grown in the temperate zone. Great automatic machines are now flinging forth a challenge to the rubber plantations of the tropics, where for years man has bled the hevea tree of its sticky sap. This tree, from which almost all of the world’s supply of rubber is derived, grows only in a narrow section near the equator.
ALTHOUGH plants and trees bearing Â¦ special tubes filled with the milky “latex,” or sticky sap which becomes rubber, have long been known to exist in North America, few gave promise of practical commercial value.
Only when it was discovered that in northern Mexico and southern Texas an immense tract 130,000 square miles in extent is covered with a native weed whose juices contain the precious latex, did American-grown rubber begin to influence the markets of the world.
The strange desert shrub that secrets tiny cells of rubber in its bark and wood first came to the attention of science when American mining engineers in central Mexico found peon children chewing guayule twigs for material to make crude rubber balls. Starting with a bit of bark or the wood of the plants, and spitting out the splinters as they chewed, the children would get tiny balls of rubber.
This simple trick had come down to them from ancestors during the centuries. Companions of Cortez, on his second voyage to America, found natives of southern Mexico playing a game much like modern tennis, with balls “so elastic that when they touch the ground, even when lightly thrown, they spring into the air with the most incredible leaps”â€”astounding to the Spaniards, who knew nothing of rubber. In the guayule bush, the rubber is contained in cells in all parts of the bush except the leaves, entirely surrounded by cellulose. In the rubber tree it is in the sap. Nature seems to have intended it to perform entirely different functions in the two plants. In the rubber tree, it forms a sticky residue when sap flows out of a cut or wound and thus protects it, keeps insects out, prevents decay, and helps the wound heal. But in the guayule bush, the rubber is evidently stored up as reserve food. In the goldenrod, and other plants which have been found to contain rubber, it is located mainly in the leaves, and its function is unknown.
BRIDGING the gap between the wild weed known to the Indians of Mexico three centuries ago and the modern domesticated shrub, raised on American farms like sugar beets or potatoes, lies a strange story of patient search closely paralleling the amazing work of Luther Burbank.
Guayule rubber first came to the United States when samples were sent from Durango, Mexico, to the Centennial Exposition at Philadelphia in 1876, but it was eighteen years before the first commercial guayule rubber was produced in Mexico. It was sticky and soft, vulcanized poorly, and had a low tensile strength. Rubber experts scoffed at this product of a weed. Heavily laden with unwanted resinous compounds, it could never compete with the pure latex that oozes from the hevea tree.
Yet the need for more rubber became acute as the automobile chugged its way from the inventor’s workshop into American lite. The immense Mexican tracts of guayule were looked upon as a source from which rubber might be obtained.
In its laboratory, the Diamond Rubber Company, of Akron, made first-class rubber from guayule but the cost was too high to be of practical value.
Meanwhile, factories were set up in Mexico, where various companies spent hundreds of thousands of dollars in attempts at commercial manufactureâ€”and “went broke.” As many as thirteen different enterprises tried their hand at guayule extraction, but could not make ends meet, although they produced as much as 150.000.000 pounds of rubber in a single year, and decimated the immense guayule fields of our southern neighbor.
THE shrinking supply of wild guayule made it evident that a cultivated variety would have to be developed if a steady production was to be obtained. In 1907, the Continental Rubber Company began to cultivate the guayule on its Cedros range in Mexico; but when the guns of revolution boomed, laboratory work stopped.
Large quantities of seed were then brought to central California, where tracts of land were set aside near Salinas as a nursery laboratory for research purposes. Here began a long series of experiments directed by Dr. W. B. McCallum.
At once he exploded two popular fallacies regarding the guayule: First, that it would not reproduce itself from seed; and, second, that the wild plant, when grown commercially in the field, would not produce rubber.
As the seed had been taken from plants on the range, it was inferior, and contained much chaff. As the prophets had predicted, it would not germinate. As an alternative, Dr. McCallum tried planting cuttings from the shrub, but with scant success. Out of many thousands of cuttings set out, fewer than one hundred grew, and those that did take root were lacking in vigor and vitality.
Chemists and botanists went into consultation. After countless experiments, they learned to treat the seeds by chemical and other means, so that at least ninety-six out of every hundred would germinate.
Once the seeds had sprouted, the guayule grew rapidly. Accustomed to shift for itself in its barren native habitat, the hardy shrub fell prey to blights and diseases when grown in the rich soil of the farm. Dr. McCallum had to learn how to get the soil into just the right physical condition to develop in the plant strong disease-resisting qualities.
At once he was harassed by another problem. By irrigation, he could hasten the growth of the guayule and bring a large spreading shrub to maturity in a short time; but as the luxuriance of growth increased, the rubber content fell off to the vanishing point. A four-year-old range shrub yielded about fifteen percent of its dry weight in rubber, but the irrigated plant gave only-four percent.
MANY range bushes five years old weighed only one pound, but contained a large amount of rubber. Dr. McCallum’s cultivated guayule weighed as much as twenty pounds, but contained almost no rubber.
But he was not to be baffled by the plant’s eccentricities. In 1913 and 1914 he set out, in southern California, over a million plants grown from mixed seed from Mexico. Later a much larger number of plants was grown in Arizona. These myriad shrubs were catalogued and card-indexed, classified, selected, and reclassified. Out of this enormous number of specimens, only ten strains were chosen as commercial producers.
Meanwhile, new difficulties arose. In the nursery, the young plants throve, but when transplanted to the field they refused to take root again.
More analysis, more research. Study by the botanists at length revealed that, while the young guayule has a long, deep tap-root, with almost no branches, it later develops a branching root system that enables it to take advantage of the short, infrequent showers of its native region. The plant secretes most of its rubber during the dry season, when it lies almost dormant, little being stored up during the growing period. By patient, intensive culture, Dr. McCallum finally developed a plant whose period of strong root development coincided with the transplanting season, so that this work could be done by machines, without injury to the roots.
In twenty years of research, Dr. McCallum has wrought marvelous changes in the wild Mexican shrub, completely domesticating it and at the same time raising its rubber content amazingly. Some specimens grown in the nursery have yielded as high as forty-five percent of their weight in pure rubber. The undesired resins, which Nature supplied to the guayule plant as a sort of dressing to heal its wounds, are reduced as much as forty percent by simple dessication of the plant before it is milled.
THE vulcanized rubber has a softness of texture not found in the rubber of the tropics, yet specimens have been obtained with a tensile strength of 4,000 pounds per square inch. The improved strain produces in two years as much rubber as was stored by the wild plant in four. Dr. McCallum is now learning how to harvest the shrub at the fourth year and to get the guayule’s big root system to resprout, making possible several repeat crops at two- or three-year intervals.
While he has been engaged in this revolutionary experimentation, chemists, peering through high-powered microscopes, analyzed the juices of the guayule bush and classified them as a “colloid” substanceâ€”that is, a suspension of countless minute particles, each a microscopic ball of rubber. From knowledge of the behavior of colloids, they predicted that these tiny bits of rubber could be squeezed together into large grains which could be separated from the woody fibers of the plant.
This discovery has provided a basis for the production of guayule rubber without the application of costly chemicals and complicated processes, and has helped to make possible the complete mechanization of rubber manufacture.
ON THE California guayule plantation where the Mexican weed is being cultivated on a huge scale, machines perform every operation from planting the tiny-shrubs, six rows at a time, to gathering the mature bushes, extracting their rubber content, and compressing the finished product into sheets and slabs for shipment.
Devices much like vacuum cleaners suck up seeds for planting in the twenty-five-acre nursery, where the guayule bushes are started under the supervision of experts. Tractor-drawn mulchers prepare the top soil, making ready for the mechanical seeder which next passes over the beds, scattering the minute grains, so small that 28,000 of them weigh less than an ounce.
When water is needed, overhead sprinklers cast a gentle spray over the seedling plots. By transplanting time, the tiny shrubs have large, strong roots. A mechanical cutter clips their tops. Next comes a machine that digs the plants up bodily. Another machine sorts and boxes them, 5,000 to the bunch.
When the guayule has reached an age of four years or more, power-driven plows strip the bushes bodily from the ground and stack them in piles. Mechanical beaters flail the dirt from the roots, and the plants are allowed to dry out. Then harvester machines pick them up, chop them to shreds, and blow the bits into trailing trucks.
In the mill, automatic elevators, endless distributing belts, and revolving screw conveyors carry the chopped guayule through a series of crusher rollers that gradually reduce it to a pulp. Water helps to break down the fibers of the wood. In great wooden tubs half the height of the factory building, the pulp is held until most of the waterlogged wood has settled to the bottom. Then it is run off into hydraulic chambers, where steam and pressure together waterlog the cork particles of bark, which sink to the bottom, while the rubber floats to the top.
SKIMMED off, scrubbed by rubber-coated lead pellets the size of golf balls, squeezed through wringers, and dried in vacuum chambers that remove all but one percent of the water, the minute rubber grains are ready to be blocked into slabs. A hot press, exerting a pressure of 2,000 pounds to the square inch, does the rest, and the finished rectangular cubes are packed into pine boxes for shipment.
The successful production of rubber on American soil may prevent another world monopoly such as that which a few years ago forced the price of rubber to almost prohibitive heights. At the present record low price of crude rubber, no operators can hope to make money; but officials of the American Rubber Producers, Inc., under whose direction the Salinas plant is run, expect to make a reasonable profit when a normal market exists.
If the deadly blight which is the scourge of the hevea tree should sweep through the tropical plantations as it has already done in Brazil, guayule rubber might avert a serious world-wide rubber famine.