The Grantville Gazette Volumn VI Page 24

  Appendix 1 lists the descriptive information that is available for each of the known rubber sources. I am not going to quote the actual text, since it is readily available in libraries or on the internet.

  However, I think it fair to warn you that the plant life of the rainforest is very diverse, and it is possible to be deceived by a closely related species that is a poor producer. For example, in Brazil, the leading rubber tree, Hevea brasiliensis, may be confused with Hevea spruceana (just to complicate matters further, there are interspecies crosses in the coastal regions), and in West Africa, those seeking Funtumia elastica may be misled into tapping Funtumia africana (the False Rubber Tree).(Polhamus, 36, 65; Christy, 78-9)

  * * *

  The Aztecs of Mexico and the Maya of the Yucatan and Central America used Castilla rubber for footgear, headgear, game balls, and incense (Shidrowitz, 2-5, 372-3). Because the rubber of this tree was used and even traded by the indios of Latin America, we don't actually need to be able to describe the tree in order to locate it. Chances are that if our agents go to the local markets in the correct general area, the Indians will know something about it.

  * * *

  Another special case is presented by the Indian Rubber Tree, Ficus elastica. This is one plant we don't have to journey far to find; it is a popular house plant, and I would be astounded if there were no specimens in Grantville.

  The story of how Francois Fresnau found the Hevea brasiliensis tree in French Guiana is an interesting one, because the techniques he used could be adapted to finding any rubber tree whose latex production is already known to the natives. Fresnau was quite fortunate to succeed—albeit after a fourteen year search—because H. brasiliensis is rare in Guiana. (There is another rubber tree that is more common there, called Hevea guianensis, which was identified in 1764). Although he was a military engineer, assigned to the fort of Cayenne, he had been asked to keep his eyes open for exotic plants that might be of interest to the Royal Gardens. Fresnau was especially anxious to find Guianese specimens of the elastic resin-producing Syringe Tree of Portuguese Brazil. However, the natives he bribed with "gewgaws" and gin all told him, "Nimati" ("I don't know").

  Then, by chance, Fresnau returned from a fishing trip on a boat crewed by Naurague Indians from Mayacare in Brazil. He showed them rubber articles, and they immediately realized which tree Fresnau was seeking. Because of his commitments, Fresnau could not travel to Mayacare, but he was resourceful enough to persuade them to make him clay models of the fruit and leaves of the Syringe Tree. He paid the Naurague for their troubles with liquor, salt and other presents.

  Fresnau showed the clay models to native hunters and French colonial officials in various parts of Guiana and was told that the trees he sought were to be found on the banks of the Matarani River. He brought his Naurague Indians to the site, and they confirmed that the trees were of the correct species. (Schidrowitz, 14-22)

  Rubber Collection Technology

  There are two basic techniques of gathering rubber. First of all, we can make a small wound in the bark of the tree, and collect the latex that flows out, without killing off the tree. This is called tapping.

  Secondly, we can cut down the rubber tree, or chop up the rubber shrub, vine or weed, and extract all of its rubber content. This may result in a large, quick return, but it is obviously wasteful (especially if the rubber source is a tree with a long maturation period).

  Appendix 2 lists the standard collection technologies for each of the rubber sources that were singled out previously as hot prospects, as well as for a few borderline cases. It also gives the expected productivity on a per tree and per acre basis. If land is cheap, and labor expensive, then it may be more important to determine the productivity per tapper.

  Rubber Tapping

  At least 95% of all of the rubber produced today comes from the latex tubes of the Para Rubber Tree, Hevea brasiliensis. There is good reason for this. Latex can be repeatedly extracted from Hevea without killing the tree, the latex has a high rubber content, and the rubber itself is of excellent quality. A single tap produces only 56 grams of latex, but the tree can endure 150 tappings in a single year (EA).

  The original method of gathering Hevea latex was both inefficient and destructive. The tree was nicked repeatedly, and latex bled from the injured areas (Dean, 10). EA says that the tapping that "inevitably resulted had led to the death" of the tapped tree.

  Thanks to the work of Henry Ridley in Malaya in 1890-1910, it was recognized that it was better, from the point of view of long-term productivity, to make a single cut, position a cup underneath, and return later to collect the latex. It was also desirable to allow the tree to "rest" periodically. Finally, the cuts must be made with care to avoid the cambium layer. If the latter is penetrated, the trees will toughen their trunks, which will make further tapping more onerous.

  If we want our collectors to follow these improved practices—which are described and illustrated in several of the encyclopedias—we will have to go with them to the trees and show them the proper technique. Moreover, if we want to make sure that they adhere to our instructions, we will have to make inspections from time to time.

  * * *

  In 1911, when the Encyclopedia Britannica, 11th ed. (EB11) was published, several different Para Rubber tapping methods were in use, and it was not yet known which would prove to be the best. The oldest was the V-system, in which V's were cut on the base of the tree, and a collection cup placed at the vertex of each. The width of each V was not more than one-quarter of the circumference of the tree. The V-system can be seen on two of the trees in the photo of Fig. 12.

  The V-system had already been largely replaced by the herringbone system, which is depicted in Fig. 2. In essence, there is a central collection channel which leads down to a single collection cup. This main channel is fed by alternating tributaries, diagonals cut at a 45 degree angle.

  The third method mentioned in the EB11 is the spiral system, which was then considered to be experimental. It involves making a series of spiral cuts, but the text does not elaborate on where the cuts start and end, how wide they are, how far apart they are spaced, and so forth. We can only judge this from the end result, which can be seen on three of the trees in the photo of Fig. 12. This shows spiral bands of cut bark, separated from each other by an unmarred region which is perhaps one-half to one-third the width of the cut bands. If I understand the system correctly, the cuts will ultimately be extended into this region, too, until the entire lower trunk has been sliced.

  The cuts were, whichever the system used, made by means of "small knives and prickers," rather than machetes. In other words, by 1911 it was already recognized that the cuts should be no deeper than the latex-bearing layer.

  The modern Hevea tapping method is a derivative of the spiral system; there is a diagram in the World Book Encyclopedia (WBE). The tapping of a virgin trunk begins with a single diagonal cut, starting four feet above the ground. It is angled downward, at what looks like a 30 degree angle (this is confirmed by the modern EB), and reaches halfway around the trunk. For the next tap, a parallel groove is cut just below the one before it. As this process continues, a "tapping panel," a diagonal band of scored bark, is created. (The cup is hung at the base of the fresh cut.) After three or four years, the tapping panel reaches the ground, and a new panel is started on the other side of the trunk. By the time this panel is completed, the originally tapped side has healed. For photos of tapping panels, see the modern EB and Collier's Encyclopedia (CE).

  According to CE, the tapping should begin early in the morning. The WBE mentions that some plantations tap a tree every other day ("1T1R"), while others tap it for 15 consecutive days and then let the tree rest for 15 consecutive days ("15T15R"). CE says that the 15T15R method produces provides much greater amounts of latex than the other.

  The Encyclopedia Americana (EA) entry provides more information about the cut itself. It is one twenty-fifth of an inch wide, and only one-quarter to one-half
inch deep. However, EA suggests a cut that is only one-third, not one-half, the circumference of the trunk; hence, this approach contemplates carving three successive tapping panels into the trunk. In addition, the tapping panels contemplated by EA are only six inches high. (One tapping panel is thus the result of 150 tapping cuts, which presumably occurred over 300 calendar days.)

  * * *

  The only encyclopedia to provide any information concerning the standard methods of tapping the other rubber trees is EB11, and it must be remembered that the methods it advocates may not be optimal. For collecting the Castilla elastica latex, the EB11 recommends a simple spiral cut at a 45 degree angle. The Funtumia elastica latex was collected using the "herringbone" system. Pernambuco or Mangabeira Rubber (Hancornia speciosa) was obtained by making eight shallow, oblique cuts around the trunk, then allowing the latex to drip into cups.

  * * *

  The problem with the Ceara rubber tree (Manihot glaziovii) is that the latex flows very slowly. Hence, the latex allowed to coagulate on the tree, and the coagulate is then pulled off in strings. Some of the latex will drip down, and large leaves are laid down in advance to collect it. (EB11)

  * * *

  Tapping methods will affect labor efficiency. For Hevea, just one cut is made per tree per day; a plantation worker can tap 250-400 trees in a day. In contrast, a Castilla must be hacked repeatedly, because the latex-bearing cells are not connected; as a result, the same worker could tap only 20 or 50 Castilla trees daily. (Polhamus 264; Treadwell, 32)

  Rubber Harvesting

  In some cases, the latex cannot be tapped; the plant must be harvested and the latex recovered from the dead plant material.

  If the plant can produce a rubber crop every year, then the main objection to this procedure is the labor cost involved in harvesting. The harvesting of milkweed and goldenrod are discussed below, in their own sections, while guayule and Russian dandelion are relegated to Appendices.

  Latex is produced by several different African (and Asian) species of vines. To extract the rubber, the vine must be cut down, and unfortunately, when the price of rubber was high, this encouraged over-exploitation. The EB11 notes that the southern Sudan was "nearly entirely denuded." In consequence, the authorities in the French Sudan, the Congo, and in German Africa adopted regulations which limited when and how the vines could be tapped, and also required replanting. As the EB11 notes, these edicts can only be enforced "at considerable expense."

  Library research in Grantville will reveal some information on how to extract the guayule rubber. EA says that 3- to 5- year old shrubs are shredded. The recommended collecting technique is to mow off just the top, so that the same plant can be harvested repeatedly. The latex is leached out of the plant material with hot water.

  CE, on the other hand, says that the rubber is found in all parts except the leaves. It suggests that the collected plant material be "cured" (that is, left outside to ferment), chopped up, and macerated in water, after which the rubber is skimmed off the surface.

  Latex Processing

  The latex of the Para Rubber Tree is said to be about 41% rubber and 55% water (EB11); CE says 27%/70% and 36%/60%, respectively, for four and ten year old trees.

  Hevea latex can be stabilized by the addition of ammonia or sodium sulfite (CE), and then concentrated (much like separating cream from milk) for shipping. Rubber gloves and toy balloons are made by dipping molds into latex and then allowing the acquired layer to dry. This is usually done several times, to increase the thickness of the rubber, and then the dipped article is removed from the mold. However, most latex is coagulated into rubber at or near the collection site, and only later shaped into a final product.

  The Hevea latex is unstable; the rubber will gradually separate from the water, a process called "coagulation." This can be expedited by addition of an acid, since Hevea latex is alkaline. Crude Hevea plantation rubber was typically 94.6% rubber, 2.66% resin, 1.75% protein, 0.14% ash, and 0.85% water.

  Grantville's only source of information concerning the handling of latex from other rubber trees is the EB11.

  Castilla latex has the advantage that the rubber can be separated from the water by centrifugation. However, the standard processing method is to strain the "milk" through a wire sieve, add an alkaline plant juice (the Castilla latex is acidic) to cause coagulation, flatten out the coagulum to remove water bubbles, and then let the material dry for a few weeks.

  In Africa, there was the curious practice of letting the Funtumia latex sit for half a month, covered with palm leaves, in a hollowed-out tree trunk. The trunk absorbs the water component, leaving the rubber behind. Another approach is to dilute the latex with water, and then heat it to coagulate the rubber. The Africans also employ plant-derived coagulating agents, but the bare reference to "Bauhinia leaves" is not likely to be of much use to us.

  Perhaps the most important characteristic of Funtumia latex is not mentioned by the Grantville sources; it is very stable (Polhamus, 264). The same is true, to a lesser degree, of Castilla latex (102) and Ficus latex (264).

  * * *

  A number of natural latexes have a high resin content, and, if the resin is not removed, the rubber will be considered inferior. In 1911, solvent extraction of the resin was considered commercially impracticable, but that of course is very dependent on the price of the solvent as well as on the price difference between high resin and low resin rubber. EB11 shows that Ceara, Castilla and Ficus rubbers have average resin contents of 10.04%, 12.42%, and 11.8%, respectively.

  Guayule rubber has a substantially higher resin content. According to CE, it is 20-25% for rubber extracted from the wild shrub, and about 16% in the case of the cultivated varieties. EA gives the resin content as 13-18%. It acknowledges that solvents have been used commercially to extract the resin, but does not provide particulars. The EB11 entry for "resin" says that it is "mostly soluble in alcohol, essential oils, ether and hot fatty oils." Curiously, CE states that the resin content is actually advantageous "as an aid to processing" when guayule rubber is blended with Hevea rubber.

  Rubber Processing

  A general problem with natural rubbers is the presence, inadvertent or deliberate, of gross impurities (dirt, chips of wood, leaf material, etc.) Such defects can be mitigated by filtering the latex (see above) and by washing the rubber.

  The rubber initially conforms to the shape of the collecting cup and is called a biscuit. The spongy mass of rubber is washed (with hot or cold water) as it is passed between grooved rollers (EB11, Fig. 8), producing ribbed sheet. CE suggests use of a series of rollers, with progressively finer corrugations. It was then hung to dry. If a smokehouse is used, the product is called smoked sheet. Or it can be dried without resort to smoking, producing crepe rubber. The rubber can be softened with heat and compressed into blocks.

  Additional shaping may be carried out in factories. After softening (if necessary), the rubber may be calendered (rolled), molded or extruded. By suitable incorporation of air, sponge and foam rubber can be formed. (WBE)

  The rubber is warmed or masticated to soften it. The masticating machine (EB11, fig. 8) kneads the rubber, and, as this is happening, any desired additional ingredients (e.g., sulfur, carbon black, fillers, anti-aging compounds, colors, and oils), are mixed in. The rubber can then be softened further by heat and pressed into molds. One type of masticator, the rubber mill, has two rollers rotating inward, but at slightly different speeds. A more advanced masticator, the Banbury mixer, has rotating blades. (EA)

  The last step in the preparation of commercial rubber is vulcanization, since the vulcanized rubber cannot be further shaped. Without this treatment, rubber is an unsatisfactory material; it is brittle when cold and sticky or gooey when hot. Goodyear overcame these problems with his vulcanization process. In vulcanized rubber, the polyisoprene chains are cross-linked by disulfide bonds. Several methods of achieving vulcanization are described in EB11. In one, the rubber is immersed in molten sulfur for an hour or
so at 140 deg. C. In another, the rubber is placed in a lead chamber with chloride of sulfur. In a third, it is cooked with a solution of calcium polysulfide at 140 deg. C. The use of excess sulfur or heat results in a hard, inelastic rubber (ebonite).

  The Microsoft Encarta CD, which is probably available in Grantville, mentions that vulcanization can be accelerated with aniline and thiocarbanilide.

  Rubberized cloth can be prepared by dissolving the rubber in one of its solvents ("carbon bisulphide, benzol and mineral naphtha, carbon tetrachloride, and chloroform") and then using the solution to coat the fabric. The original MacIntosh process used naphtha.

  The Logistics of Rubber Collection

  Most rubber plants require a tropical climate. Once these plants have been located, we have four choices. First, we can simply trade with the natives for it. Second, we can go out into the hinterland and collect the latex from wild plants ourselves. Third, we can establish local rubber plantations. Finally, we can collect the seed (or other propagatable plant materials) and cultivate the plant elsewhere. This could be at a different tropical location (presumably, one more advantageous to USE), or in greenhouses back home.

  All of the high-ranking rubber sources listed at the beginning of this essay have been cultivated, at least on an experimental basis. Most have also been transplanted, at least for trial purposes, to another part of the world, e.g., Hevea, Castilla and Manihot to Asia and Africa, Funtumia to Trinidad (Christy, 237) and Asia (EB11), Guayule to the Soviet Union, and the Russian dandelion to the USA.

  However, because Hevea is the most important source of natural rubber, it behooves us to take a closer look at why plantations in Asia and Africa have supplanted the collection of wild rubber in Brazil.