Rubber & Chicle Photos

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Economic Plant Photographs #13

Chicle & Rubber-Producing Plants

Chicle From The Sapodilla Family (Sapotaceae)

Chicle or Naseberry (Manilkara zapota), a native tree of Central America and the West Indies. The fruit is also known as the sapodilla. The fleshy pulp is used to make sapodilla custard and ice cream. Chicle gum is extracted from the sap of the trunk and is used in some natural chewing gums to this day. It was once a major component of chewing gums, often mixed with latex from the jelutong tree (Dyera costulata), a Malaysian rain forest tree in the Apocynaceae. Large chicle trees were originally tapped by tree-climbing workers called chicleros. Although the rubbery latex is a polyterpene, it does not vulcanize into durable rubber. Vulcanization is the addition of sulfur to rubber to form cross-linking of the isoprene subunits with disulfide bonds, thus improving the elasticity of the latex and making it impervious to weather.

Chicle (Manilkara zapota), native tree of Central America and the West Indies.


An assortment of traditional American chewing gums. Some of the original brands of packaged stick gums and colorful gum balls were manufactured with chicle gum base. Most present-day sugar and artificially sweetened chewing gums are made from a synthetic gum base. According to Michael Redclift (Chewing Gum: The Fortunes of Taste, 2004), modern gum bases are made from vinyl resins or microcrystalline waxes, producing a synthetic rubberlike substance similar to that used for the cover of golf balls. These newer substances produce longer-lasting flavor, improve the texture, and reduce tackiness. According to www.wrigley.com, the Wrigley Company still uses natural rosin softeners in their gum base. In the United States, rosin is largely derived from southeastern pines, including longleaf pine (Pinus palustris) and slash pine (P. elliotti) grown in large plantations. Crude turpentine sap is distilled in order to separate the volatile essential oils called "spirits" from the nonvolatile diterpene residue called rosin. Rosin is used in the manufacture of varnishes and oil base paints, and for violin bows and baseball pitchers. Rosin also enhances the texture of the gum base used in some chewing gums.

  More About Rubber Latex & Chewing Gums  

Three classic chewing gums that are still available today (although they are no longer made with pure chicle gum base). The original packaging did not include bar codes on the side.

Old-Fashioned Gum & Candies Available From Cousin's Candy Shops
Visit Cousin's Candy Web Site: Cousin's Candy Web Shop

Some commercial chewing gums are made from a natural chicle gum base.


Rubber From The Sunflower Family (Asteraceae)

A native shrub in the sunflower family (Asteraceae) called guayule (Parthenium argentatum) contains a latex sap with polyterpenes similar to those found in Hevea rubber. It is native to Mexico and the southwestern United States. Guayule is a potentially good source of natural rubber, and has been grown on large plantations in arid desert regions.

Guayule (Parthenium argentatum), a small shrub native to Mexico and the southwestern United States. The latex sap contains polyterpenes very similar to those found in the primary rubber-producing tree of the Amazon basin (Hevea brasiliensis). Guayule belongs to the sunflower family (Asteraceae), while Hevea belongs to the euphorbia family (Euphorbiaceae). Both guayule and Hevea latexes are composed of up to 6,000 isoprene subunits. When they are cross-linked with disulfide bonds during the vulcanization process, the rubber product becomes very elastic and weather resistant. Although synthetic butadiene polymers are commonly used in tires, natural rubber is also incorporated into the tires to provide more resilience. Because of the great demand for natural rubber to this day, guayule is considered by some authorities to be a good alternative source of the valuable latex.


Rubber From The Euphorbia Family (Euphorbiaceae)

Rubber and chicle are polyterpenes composed of thousands of C5H8 isoprene subunits. They are found in the milky latex sap produced inside special cells called laticifers or laticiferous tubules in the secondary phloem. Laticifers are single cells or strings of cells that form tubes, canals or networks in various plant organs. Plant families which produce copious amounts of milky latex include the euphorbia family (Euphorbiaceae), milkweed family (Asclepiadaceae), mulberry family (Moraceae), and the dogbane family (Apocynaceae). The main source of natural rubber comes from the para rubber tree Hevea brasiliensis (Euphorbiaceae), a rain forest tree native to the Amazon Basin. Ninety percent of all natural rubber comes from the latex sap of this species. Another New World source of natural rubber in the euphorbia family is the ceara rubber tree (Manihot glaziovii). The ceara rubber tree belongs to the same genus as cassava (Manihot esculenta), the source of tapioca and the staff of life for millions of people living in tropical countries where cereals and potatoes will not grow.

Tapping latex-rich phloem of para rubber tree (Hevea brasiliensis) in Thailand.
The milky latex runs out of deep cuts in the bark into the shells of coconut seeds.

Trifoliate leaves of para rubber tree (Hevea brasiliensis).

In his fascinating article "Are Vascular Plants Inside-Out Lichens" Ecology 69 (1): 17-23, 1988, Peter Atsatt of the University of California, Irvine discusses several types of cells and tissues in vascular plants which resemble fungal hyphae, including pollen tubes, vascular (xylem) tissue, laticifers, and haustoria. Pollen tubes not only resemble the growth of fungal hyphae, but in Pinus, cycads, and Ginkgo they are branched and actually absorb nutrients from the "host's" megasporangium. The latex-producing laticifers found in many members of the Euphorbiaceae, Asclepiadaceae and other dicotyledonous families are very similar to fungal hyphae. Nonarticulated laticifers are elongate, multinucleate cellular tubes that grow throughout the plant body of these families. These laticiferous tubules are the source of the milky latex that is used to make natural chewing gums and rubber.

The trunk and leaf of the ceara rubber tree (Manihot glaziovii), a little-known source of natural rubber latex prior to the 1900s. Like another economically important species in the genus Manihot called cassava (M. esculenta), the leaf is palmately compound.


Rubber From The Mulberry Family (Moraceae)

There are a number of other plant families with rubber-producing species. One of the most famous is the rubber tree (Ficus elastica), commonly grown as an indoor ornamental and outdoors in coastal southern California. The genus Ficus is a member of the mulberry family. It contains about 1,000 species distributed throughout tropical rain forests of the world, all with a milky latex sap. Every species of fig has its own species of pollinator wasp, in one of nature's most complex interrelationships between a plant and an animal.

Trees of the Mulberry Family

Fig & Fig Wasp Hyperlinks:

The Calimyrna Fig & Its Pollinator Wasp
Creeping Fig: One Source Of Grass Jelly
The Amazing Fig & Fig Wasp Relationship
Sexuality and Political Correctness In Figs
A Summary Of The Ficus carica Life Cycle
Pollination Patterns In Dioecious Fig Species
Cauliflory In Tropical Species Of Figs (Ficus)
Strangler Figs & Banyans: Remarkable Trees
A Petrified Fig Syconium From The Cretaceous
The Evolution Of Dioecious Fig (Ficus) Species
Gall Controversy--Do Fig Wasps Induce Galls?
Nonpollinator Fig Wasps With Long Ovipositors
Figs Of The Holy Land (Their Role In Religions)
  Sex Determination In Common Fig (Ficus carica)  


Rubber From Gutta-Percha (Sapotaceae)

There are a number of other plant families with rubber-producing species. One of the most interesting latex products comes from the gutta-percha tree (pronounced GUT-a PUR-cha in Webster's Dictionary). Gutta-percha (Palaquium gutta) is tall tree native to rain forests of eastern Asia. It belongs to the sapodilla family (Sapotaceae), along with the chicle or naseberry tree (discussed above). After it is collected from girdled trees, the gutta-percha latex is allowed to coagulate into globs. It is then washed, purified, and molded into bricks for shipping.

Because the latex of gutta-percha contains fewer branched polyterpene chains than Hevea rubber, it is not as elastic. In addition, the polyterpene molecules of gutta-percha have a trans structure, while those of Hevea rubber have a cis structure. This molecular configuration makes gutta-percha more stable, but reduces its elasticity.

An Explanation Of Cis & Tran Isomers

Two polymers of butene. In the cis configuration, both methyl groups (CH3) occur on the same side of the main axis. In the trans configuration, the methyl groups occur on opposite sides of the main axis. The trans configuration is more stable. When polyunsaturated vegetable oils are partially hydrogenated to improve their texture, trans fatty acids are produced. Trans fatty acids tend to raise the level of low density liporoteins (bad LDLs) and lower the level of high density lipoproteins (good HDLs). These changes in blood lipids (cholesterol levels) may increase the risk of heart disease (athersclerosis) in some people. Dieticians generally recommend the use of mono-unsaturated, unhydrogenated oils such as canola or olive oil whenever possible, and the avoidance of trans fatty acids found in french fries, donuts, chips, cookies and crackers.

    See The Chemistry Of Plant Oils    
See Olive Fruits (Olea europea)

Gutta percha rubber is an excellent nonconductor and insulator, and is resistant to seawater. It was used in the past for rubber strands in the core of golf balls and to coat undersea cables. In 1850 the first submarine telegraph cables were laid, and by the end of the nineteenth century over 250, 000 miles of telegraph cable was in use, all insulated with gutta-percha. Today, gutta-percha insulation has largely been replaced by synthetic polymers, such as polyethylene.

Another interesting property of warm gutta-percha is its resistance to shrinkage while cooling. This property was exploited by die sinkers (people who cut and shape dies) to test their dies before making metallic medals. Medals made from gutta-percha are sometimes seen in antique fairs. In the USA and elsewhere, the name gutta-percha is also used to describe a variety dark-colored Victorian molded materials.

One of the most interesting uses for gutta-percha is in dentistry. Slender strands of gutta-percha are commonly used in endodontics as a filling to replace the reamed out nerve core during root canals. The stable, natural properties of gutta-percha make it one of the best materials for this procedure.

Slender strands of gutta-percha are inserted into the root canals after the nerve tissue has been removed. The openings are then sealed with a filling material and the tooth is capped with a crown.


More About Rubber Latex & Chewing Gum

In 1839, Charles Goodyear accidentally spilled a mixture of rubber latex and sulfur on a hot stove and discovered that when it cooled, the rubber lost its stickiness and retained its elasticity. The process was named vulcanization after Vulcan, the Roman god of fire. Vulcanization produces cross-linkages (disulfide bonds) between the thousands of isoprene subunits in the rubber latex, improving the elasticity and durability of the rubber. Although synthetic butadiene and styrene polymers are commonly used in the manufacture of tires, natural rubber is still incorporated into the tires to provide more resilience. This is particularly true in radial tires and high impact airplane tires. Because of the great demand for natural Hevea rubber to this day, guayule is considered by some authorities to be a good alternative source of the valuable latex.

Chicle, the milky latex of the sapodilla tree (Manilkara zapota), was once thought to be a good source of natural rubber. In 1866, Antonio Lopez de Santa Anna brought a sample of chicle to New York. There he met Thomas Adams, a man he hoped could produce rubber from chicle. [Santa Anna was a former Mexican president and the famous general who led the Mexican troops in the battle of the Alamo in 1836.] Santa Anna arranged to have two tons of the chicle latex sent to Adams for experimentation. Adams tried unsuccessfully to vulcanize the chicle, but he could not produce a usable elastic product. He had two tons of chicle with no use for it. Then he remembered a comment by Santa Anna that people in Mexico chewed the chicle latex. Adams came up with the idea of sweetening and flavoring the chicle to make chewing gum. At that time, most of the chewing gum was made from sweetened paraffin, so this seemed like a viable alternative to waxy paraffin. Adam's idea marked the beginning of the chewing gum industry and Adams® brand chewing gums which are still sold to this day. One reference referred to chewing gums as a "social nuisance particularly peculiar to the United States," but Adam's discovery produced one of life's simple pleasures. Although natural chicle is still used, most of today's chewing gums are made from a synthetic vinyl gum base.

Although Thomas Adams was certainly one of the early pioneers of chewing gums, it was William Wrigley Jr. who established an international market for the chewing gum industry. In fact, his name became synonymous with chewing gum throughout the twentieth century. He introduced a number of brands and flavors to the industry and became one of the ten wealthiest men in the United States. Some of his acquired assets included the Chicago Cubs baseball team (with a stadium named after him) and Catalina Island off the coast of California. By establishing factories abroad, he stretched his empire to 37 countries. According to Michael Redclift (2004), his factories produced 280 million sticks of gum a week. Chewing gum had truly become part of the American way of life.


Other Natural Polysaccharide Gums and Terpene Resins

Many different species of plants in a variety of families produce sticky saps composed of gums and resins. These chemicals presumably seal off wounds and help to protect the plant from bacterial and fungal infections. The resinous sap of conifers, such as pines (Pinus), also inhibits the boring larvae of bark beetles. True gums are an entirely different class of chemicals from the chicle gum used in chewing gums. True plant gums are polysaccharides composed of many sugar subunits linked together. Unlike chicle gum, true gums are soluble in water. In fact, water-soluble plant gums are commonly used as thickening agents and emulsifiers, such as guar gum and gum tragacanth. Guar gum comes from the powdered seeds of Cyamopsis tetragonolubus, a herbaceous perennial legume from Africa. It is used in ice creams to prevent the formation of ice crystals by absorbing water. Another natural gum called algin is also used in ice creams and many other products. Algin is obtained from macroscopic brown algae (called kelps) that grow along the coast of southern California, including giant bladder kelp (Macrocystis pyrifera). Gum tragacanth is considered one of the world's best natural plant gums. It come from the sap of several species of spiny, shrubby, Middle Eastern locoweeds of the genus Astragalus, including A. gummifer. It was largely imported from the Zagros Mountains of Iran, when the United States was on better diplomatic terms with that nation. Locust bean gum, a thickening agent in ice creams and salad dressings, comes from the ground seeds of the carob tree (Ceratonia siliqua). Another valuable plant gum is gum arabic, obtained from the spiny, shrubby Acacia senegal of northeastern Africa. In addition to its use in foods, hand lotions and soaps, it is used in fine water colors, inks and confections. It also produces the water-soluble adhesive on postage stamps and the "lace curtain" on the sides of your beer glass. Plant gums also provide the soluble fiber in a healthy diet by absorbing water and adding bulk to the large intestine. Several dietary supplements contain the powdered husks of psyllium seeds from Plantago ovata (Plantaginaceae). Insoluble fiber comes from the indigestible cellulose cell walls of fruits and vegetables. Both types of fiber are beneficial in maintaining a healthy colon, particularly in older adults with diverticulosis. Eucalyptus "gums" are chemically very different from true carbohydrate gums. They are rich in tannins (kinotannic acid) and are similar to the phenolic compound called catechu. They are known in the trade as kinos or gum kinos and are used as tannins to convert animal hide into leather. One of the main Australian sources of kino is the common red gum (Eucalyptus camaldulensis), naturalized throughout San Diego County. Kino gums are also used medicinally as astringents to relieve throat irritation, dysentery and diarrhea.

Gum arabic, a natural thickening agent and emulsifier from the powdered sap of Acacia senegal. It is used in many products, from foods, cosmetics and pharmaceuticals, to sticky adhesives.

The milky, latex sap of chicle trees and rubber-producing plants, such as Hevea & guayule, belongs to another class of plant chemicals called terpenes which are composed of thousands of 5-carbon isoprene (C5H8) subunits. Sticky, plant resins are much smaller terpenes, composed of 5-carbon isoprene subunits joined together to form 20-carbon, nonvolatile diterpene molecules. In some species, such as the West Indian locust (Hymenaea courbaril), globs of resin become buried in the soil and gradually harden into copal which is used for incense and varnishes. It is often sold as amber, but it is still relatively soft and can be readily be pierced with a hot needle. Older globs of resins, from an ancestral species of Hymenaea (H. protera) that lived over 25 million years ago, have hardened and polymerized into New World amber. This very expensive, fossilized resin can be polished like beautiful gemstones. Oleoresins (such as pine pitch) also contain volatile 10-carbon (monoterpene) and 15-carbon (sesquiterpene) molecules, producing their "piney" aroma. Fragrant monoterpenes and sesquiterpenes also produce the characteristic odors of perfumes, herbs and spices. Resins are typically produced within canals or ducts found throughout the stems, leaves, flowers and fruits of many plant families. Resins are insoluble in water--have you ever tried to remove pine pitch from your fingers? Complex polyterpenes are composed of thousands of 5-carbon isoprene subunits joined together forming giant molecules with elastic properties, particularly when they have been vulcanized. They include chicle (used in chewing gum) and milky latexes used in the synthesis of vulcanized rubber.

The milky, latex sap of some plants, such as the opium poppy (Papaver somniferum), does not have the elastic properties of Hevea and guayule rubber. In addition, the "latex" in latex-based paints is chemically different from natural plant latex saps. Latex paints consists of synthetic plastic particles dispersed in water with a binding agent. When the water evaporates, the particles fuse, producing a rubbery, latexlike coating.

Mature seed capsule of the opium poppy (Papaver somniferum) with milky latex sap dripping from a recent cut. The latex sap contains a mixture of naturally-occurring narcotic alkaloids including morphine and codeine. Morphine is acetylated to produce diacetylmorphine--better known as heroin.

Wayne's Word Plant Chemistry #1
  Chemistry of Natural Plant Gums  
Chemistry of Natural Plant Resins

Images Of Natural Gums & Resins

Glistening globs of gum oozing from the branch of an apricot tree (Prunus armeniaca). Although it superficially resembles a terpene resin it is chemically very different. True gums are polysaccharides that will dissolve in hot water. Like resins they probably benefit the plant by sealing off wounds.

Left: Close-up view of the inflorescence of a female marijuana plant (Cannabis sativa). The threadlike structures are styles of pistillate (female) flowers. The granular appearance is due to numerous glandular hairs (trichomes), each with a blob of resin. Male plants generally lack the dense, glandular hairs. Right: Microscopic view of the inflorescence showing numerous gland-tipped hairs called trichomes, each with a tiny blob of resin at the tip. The resin contains a mixture of volatile mono and sesquiterpenes, along with several phenolic cannabinoids. The most potent psychoactive cannabinoid is delta-tetrahydrocannabinol (THC).

  See Resins & Gums in the Sap of Plants  
Natural Incense & Resins From Plants
See Article About Resins & Amber
See Article About Gum Tragacanth
See "Gums" Of Eucalyptus Trees
See Article About Psyllium Seeds
See Article About Plant Alkaloids

See Article About Gum Acacia

References

♦  Langenheim, J.H. 2003. Plant Resins: Chemistry, Evolution, Ecology
    and Ethnobotany.
Timber Press, Portland Oregon.

♦  Redclift, M. 2004. Chewing Gum: The Fortune of Taste.
    Routledge, New York, New York.


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