Latex

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Extraction of latex from a tree, for use in rubber production Latex-production.jpg
Extraction of latex from a tree, for use in rubber production

Latex is a stable dispersion (emulsion) of polymer microparticles in water. [1] Latexes are found in nature, but synthetic latexes are common as well.

Contents

Latex as found in nature is a milky fluid found in 10% of all flowering plants (angiosperms). [2] It is a complex emulsion consisting of proteins, alkaloids, starches, sugars, oils, tannins, resins, and gums that coagulate on exposure to air. It is usually exuded after tissue injury. In most plants, latex is white, but some have yellow, orange, or scarlet latex. Since the 17th century, latex has been used as a term for the fluid substance in plants, deriving from the Latin word for "liquid." [3] It serves mainly as defense against herbivorous insects. [2] Latex is not to be confused with plant sap; it is a distinct substance, separately produced, and with separate functions.

The word latex is also used to refer to natural latex rubber, particularly non-vulcanized rubber. Such is the case in products like latex gloves, latex condoms and latex clothing.

Originally, the name given to latex by indigenous Equator tribes[ clarification needed ] who cultivated the rubber tree, Hevea brasiliensis , was "caoutchouc", from the words caa ('tear') and ochu ('tree'), because of the way it is collected. [4]

IUPAC definition.
Latex: Colloidal dispersion of polymer particles in a liquid. [5] [lower-alpha 1]
Synthetic latex: Latex obtained as a product of an emulsion, mini-emulsion, micro-emulsion, or dispersion polymerization. [5]

Biology

Articulated laticifers

The cells (laticifers) in which latex is found make up the laticiferous system, which can form in two very different ways. In many plants, the laticiferous system is formed from rows of cells laid down in the meristem of the stem or root. The cell walls between these cells are dissolved so that continuous tubes, called latex vessels, are formed. Since these vessels are made of many cells, they are known as articulated laticifers. This method of formation is found in the poppy family and in the rubber trees (Para rubber tree, members of the family Euphorbiaceae, members of the mulberry and fig family, such as the Panama rubber tree Castilla elastica ), and members of the family Asteraceae. For instance, Parthenium argentatum the guayule plant, is in the tribe Heliantheae; other latex-bearing Asteraceae with articulated laticifers include members of the Cichorieae, a clade whose members produce latex, some of them in commercially interesting amounts. This includes Taraxacum kok-saghyz , a species cultivated for latex production. [6]

Non-articulated laticifers

In the milkweed and spurge families, on the other hand, the laticiferous system is formed quite differently. Early in the development of the seedling, latex cells differentiate, and as the plant grows these latex cells grow into a branching system extending throughout the plant. In many euphorbs, the entire structure is made from a single cell – this type of system is known as a non-articulated laticifer, to distinguish it from the multi-cellular structures discussed above. In the mature plant, the entire laticiferous system is descended from a single cell or group of cells present in the embryo.

The laticiferous system is present in all parts of the mature plant, including roots, stems, leaves, and sometimes the fruits. It is particularly noticeable in the cortical tissues. Latex is usually exuded as a white liquid, but is some cases it can be clear, yellow or red, as in Cannabaceae. [2]

Productive species

Latex is produced by 20,000 flowering plant species from over 40 families. These include both dicots and monocots. Latex has been found in 14 percent of tropical plant species, as well as six percent of temperate plant species. [7] Several members of the fungal kingdom also produce latex upon injury, such as Lactarius deliciosus and other milk-caps. This suggests it is the product of convergent evolution and has been selected for on many separate occasions. [2]

Defense function

Rubber latex Latex being collected from a tapped rubber tree.jpg
Rubber latex

Latex functions to protect the plant from herbivores. The idea was first proposed in 1887 by Joseph F. James, who noted that latex

carries with it at the same time such disagreeable properties that it becomes a better protection to the plant from enemies than all the thorns, prickles, or hairs that could be provided. In this plant, so copious and so distasteful has the sap become that it serves a most important purpose in its economy. [8]

Evidence showing this defense function include the finding that slugs will eat leaves drained of their latex but not intact ones, that many insects sever the veins carrying latex before they feed, and that the latex of Asclepias humistrata (sandhill milkweed) kills by trapping 30% of newly hatched monarch butterfly caterpillars. [2]

Other evidence is that latex contains 50–1000× higher concentrations of defense substances than other plant tissues. These toxins include ones that are also toxic to the plant and consist of a diverse range of chemicals that are either poisonous or "antinutritive". Latex is actively moved to the area of injury; in the case of Cryptostegia grandiflora , this can be more than 70 cm. [2]

The clotting property of latex is functional in this defense since it limits wastage and its stickiness traps insects and their mouthparts. [2]

While there exist other explanations for the existence of latex including storage and movement of plant nutrients, waste, and maintenance of water balance that "[e]ssentially none of these functions remain credible and none have any empirical support". [2]

Applications

Opium poppy exuding fresh latex from a cut Opium pod cut to demonstrate fluid extraction1.jpg
Opium poppy exuding fresh latex from a cut

The latex of many species can be processed to produce many materials.

Personal and healthcare products

Natural rubber is the most important product obtained from latex; more than 12,000 plant species yield latex containing rubber, though in the vast majority of those species the rubber is not suitable for commercial use. [9] This latex is used to make many other products including mattresses, [10] [11] gloves, swim caps, condoms, catheters and balloons.[ citation needed ]

Opium and opiates

Dried latex from the opium poppy is called opium, the source of several useful analgesic alkaloids such as codeine, thebaine, and morphine, the latter two of which can then further be used in the synthesis and manufacture of other (typically stronger) opioids for medicinal use, and of heroin for the illegal drug trade. The opium poppy is also the source of medically useful non-analgesic alkaloids, such as papaverine and noscapine.[ citation needed ]

Clothing

Latex is used in many types of clothing. Worn on the body (or applied directly by painting), it tends to be skin-tight, producing a "second skin" effect.[ citation needed ]

Industrial and biological applications from synthetic latexes

Synthetic latexes are used in coatings (e.g., latex paint) and glues because they solidify by coalescence of the polymer particles as the water evaporates. These synthetic latexes therefore can form films without releasing potentially toxic organic solvents in the environment. Other uses include cement additives and to conceal information on scratchcards. Latex, usually styrene-based, is also used in immunoassays.[ citation needed ]

Allergic reactions

Some people only experience a mild allergy when exposed to latex, like eczema, contact dermatitis or developing a rash. [12]

Others have a serious latex allergy, and exposure to latex products such as latex gloves can cause anaphylactic shock. [13] Guayule latex has only 2% of the levels of protein found in Hevea latexes, and is being researched as a lower-allergen substitute. [14] Additionally, chemical processes may be employed to reduce the amount of antigenic protein in Hevea latex, yielding alternative materials such as Vytex Natural Rubber Latex which provide significantly reduced exposure to latex allergens.

About half of people with spina bifida are also allergic to natural latex rubber, as well as people who have had multiple surgeries, and people who have had prolonged exposure to natural latex. [15]

Environmental impact

Microbial degradation

Several species of the microbe genera Actinomycetes , Streptomyces , Nocardia , Micromonospora , and Actinoplanes are capable of consuming rubber latex. [16] However, the rate of biodegradation is slow, and the growth of bacteria utilizing rubber as a sole carbon source is also slow. [17]

See also

Related Research Articles

Natural rubber Polymer harvested from certain trees

Rubber is also called India rubber, latex, Amazonian rubber, caucho or caoutchouc, as initially produced, consists of polymers of the organic compound isoprene, with minor impurities of other organic compounds, plus water. Thailand and Indonesia are two of the leading rubber producers. Types of polyisoprene that are used as natural rubbers are classified as elastomers.

Neoprene Family of synthetic rubbers

Neoprene is a family of synthetic rubbers that are produced by polymerization of chloroprene. Neoprene exhibits good chemical stability and maintains flexibility over a wide temperature range. Neoprene is sold either as solid rubber or in latex form and is used in a wide variety of applications, such as laptop sleeves, orthopaedic braces, electrical insulation, liquid and sheet-applied elastomeric membranes or flashings, and automotive fan belts.

Emulsion polymerization is a type of radical polymerization that usually starts with an emulsion incorporating water, monomer, and surfactant. The most common type of emulsion polymerization is an oil-in-water emulsion, in which droplets of monomer are emulsified in a continuous phase of water. Water-soluble polymers, such as certain polyvinyl alcohols or hydroxyethyl celluloses, can also be used to act as emulsifiers/stabilizers. The name "emulsion polymerization" is a misnomer that arises from a historical misconception. Rather than occurring in emulsion droplets, polymerization takes place in the latex/colloid particles that form spontaneously in the first few minutes of the process. These latex particles are typically 100 nm in size, and are made of many individual polymer chains. The particles are prevented from coagulating with each other because each particle is surrounded by the surfactant ('soap'); the charge on the surfactant repels other particles electrostatically. When water-soluble polymers are used as stabilizers instead of soap, the repulsion between particles arises because these water-soluble polymers form a 'hairy layer' around a particle that repels other particles, because pushing particles together would involve compressing these chains.

Apocynaceae Dogbane and oleander family of flowering plants

Apocynaceae is a family of flowering plants that includes trees, shrubs, herbs, stem succulents, and vines, commonly known as the dogbane family, because some taxa were used as dog poison. Members of the family are native to the European, Asian, African, Australian, and American tropics or subtropics, with some temperate members. The former family Asclepiadaceae is considered a subfamily of Apocynaceae and contains 348 genera. A list of Apocynaceae genera may be found here.

<i>Hevea brasiliensis</i> Species of flowering plant in the spurge family Euphorbiaceae

Hevea brasiliensis, the Pará rubber tree, sharinga tree, seringueira, or, most commonly, the rubber tree or rubber plant, is a flowering plant belonging to the spurge family Euphorbiaceae. It is the most economically important member of the genus Hevea because the milky latex extracted from the tree is the primary source of natural rubber.

Latex allergy Medical condition

Latex allergy is a medical term encompassing a range of allergic reactions to the proteins present in natural rubber latex. Latex allergy generally develops after repeated exposure to products containing natural rubber latex. When latex-containing medical devices or supplies come in contact with mucous membranes, the membranes may absorb latex proteins. The immune system of some susceptible individuals produces antibodies that react immunologically with these antigenic proteins. As many items contain or are made from natural rubber, including shoe soles, pen grips, hot water bottles, elastic bands, rubber gloves, condoms, baby-bottle nipples, and balloons, there are many possible routes of exposure that may trigger a reaction. People with latex allergies may also have or develop allergic reactions to some fruits, such as bananas.

Styrene-butadiene Synthetic rubber polymer

Styrene-butadiene or styrene-butadiene rubber (SBR) describe families of synthetic rubbers derived from styrene and butadiene. These materials have good abrasion resistance and good aging stability when protected by additives. In 2012, more than 5.4 million tonnes of SBR were processed worldwide. About 50% of car tires are made from various types of SBR. The styrene/butadiene ratio influences the properties of the polymer: with high styrene content, the rubbers are harder and less rubbery. SBR is not to be confused with the thermoplastic elastomer, styrene-butadiene block copolymer, although being derived from the same monomers.

<i>Parthenium argentatum</i> Species of plant in the Asteraceae family native to the southwestern United States and Mexico.

Parthenium argentatumA. Gray, commonly known as the guayule, is a perennial woody shrub in the aster family, Asteraceae, that is native to the rangeland area of the Chihuahuan Desert; including the southwestern United States and northern Mexico. It was first documented by J.M. Bigelow in 1852 through the Mexican Boundary Survey and was first described by Asa Gray. Natural Rubber, ethanol, non-toxic adhesives, and other specialty chemicals can be extracted from guayule. An alternative source of latex that is hypoallergenic, unlike the normal Hevea rubber, can also be extracted. While Castilla elastica was the most widely used rubber source of Mesoamericans in pre-Columbian times, guayule was also used, though less frequently. The name "guayule" derives from the Nahuatl word ulli/olli, "rubber".

A synthetic rubber is any artificial elastomer. They are polymers synthesized from petroleum byproducts. About 32-million metric tons of rubbers are produced annually in the United States, and of that amount two thirds are synthetic. Global revenues generated with synthetic rubbers are likely to rise to approximately US$56 billion in 2020. Synthetic rubber, just like natural rubber, has many uses in the automotive industry for tires, door and window profiles, seals such as O-rings and gaskets, hoses, belts, matting, and flooring. They offer a different range of physical and chemical properties, so can improve the reliability of a given product or application. Synthetic rubbers are superior to natural rubbers in two major respects, thermal stability and resistance to oils and related compounds. They are more resistant to oxidizing agents for example, such as oxygen and ozone which can reduce the life of products like tires.

<i>Ficus elastica</i> Species of Asian fig known as the Indian rubber plant, the rubber bush and other names

Ficus elastica, the rubber fig, rubber bush, rubber tree, rubber plant, or Indian rubber bush, Indian rubber tree, is a species of plant in the fig genus, native to eastern parts of South Asia and southeast Asia. It has become naturalized in Sri Lanka, the West Indies, and the US State of Florida.

Latex is an aqueous dispersion of polymers that can be solidified into rubber.

Acrylic resin

An Acrylic resin is a thermoplastic or thermosetting plastic substance typically derived from acrylic acid, methacrylic acid and acrylate monomers such as butyl acrylate and or methacrlyate monomers such as methyl methacrylate. Thermoplastic acrylics designate a group of acrylic resins typically containing both a high molecular weight and a high glass transition temperature which exhibit lacquer dry capability. Acrylic resins designed for use in two component systems for crosslinking with isocyanate are referred to as polyols and are made with the monomers previously mentioned as well as hydroxy monomers such as hydroxy ethyl methacrylate. Acrylic resins are produced in different liquid carriers such as a hydrocarbon solvent or water in which case they are referred to as emulsions or dispersions and they are also provided in 100% solids bead form.

The Talalay process is a method of producing molded pieces of latex foam rubber. A liquid latex rubber base is introduced to a closed mold and is then vacuumed of air. The mold is then frozen to stabilize the cell structure. Carbon Dioxide gas is introduced and the mold is heated to cure the rubber. Leon, Joseph and Anselm Talalay developed the "Talalay" process at various commercial entities. B.F. Goodrich in Shelton, Connecticut, Dunlopillo in Pannal, Harrogate, UK, and Vita Talalay in Maastricht, Netherlands, made this process commercially practical in the late 1940s. The first Talalay production plants were built in England, Canada and the United States.

Euphorbiaceae Family of Eudicot flowering plants

The Euphorbiaceae, the spurge family, are a large family of flowering plants. In common English, they are sometimes called euphorbias, which is also the name of a genus in the family. Most spurges such as Euphorbia paralias are herbs, but some, especially in the tropics, are shrubs or trees, such as Hevea brasiliensis. Some, such as Euphorbia canariensis, are succulent and resemble cacti because of convergent evolution. This family occurs mainly in the tropics, with the majority of the species in the Indo-Malayan region and tropical America a strong second. A large variety occurs in tropical Africa, but they are not as abundant or varied as in the two other tropical regions. However, the Euphorbiaceae also have many species in nontropical areas such as the Mediterranean Basin, the Middle East, South Africa, and the Southern United States.

Vytex Natural Rubber Latex (NRL) is a brand of natural rubber latex produced and marketed by Vystar Corporation. Vytex NRL is an alternative material to petroleum-based synthetics and traditional, or Hevea, natural rubber latex. Protein test results show that Vytex NRL typically has 90% fewer antigenic proteins than Hevea natural rubber latex.

<i>Taraxacum kok-saghyz</i> Species of flowering plant

Taraxacum kok-saghyz, often abbreviated as TKS and commonly referred to as the Kazakh dandelion, rubber root, or Russian dandelion, is a species of dandelion native to Kazakhstan, Kirghizia and Uzbekistan, that is notable for its production of high quality rubber. T. kok-saghyz was discovered in Kazakhstan in 1932 by the Soviet Union in an effort to find a domestic source of rubber.

Pro-hevein

Pro-hevein is a wound-induced and a lectin-like protein from Hevea brasiliensis where it is involved in the coagulation of latex.

Yulex

Yulex Corporation applies crop science, bioprocessing and materials science for the production of agricultural-based biomaterials made from Guayule. The company’s materials are designed to replace traditional tropical- or petroleum-based rubber in consumer, industrial, and medical products, with the residual agricultural materials utilized as a feedstock for bioenergy.

David Spence was one of the pioneering rubber chemists. He helped the war effort during the Second World War by devising new ways of extracting natural rubbers from plants, and worked to improve the processing of the rubber. Over the course of his career, he worked to improve the dyeing processes for rubber products and the vulcanization of rubber, and in developing new accelerants for strengthening lower-quality natural rubber. In 1941, he became the first recipient of the Charles Goodyear Medal, awarded by the American Chemical Society.

Two roll rubber mill

The two roll rubber mill is a machine used to process natural rubber into various compounds. Two horizontally opposed stainless steel rolls rotate in opposite directions towards each other at different speeds to mix the rubber and ingredients used to create the rubber compounds.

References

Footnotes

  1. The polymer in the particles may be organic or inorganic. [5]

Notes

  1. Wang, Hui; Yang, Lijuan; Rempel, Garry L. (2013). "Homogeneous Hydrogenation Art of Nitrile Butadiene Rubber: A Review". Polymer Reviews. 53 (2): 192–239. doi:10.1080/15583724.2013.776586. S2CID   96720306.
  2. 1 2 3 4 5 6 7 8 Anurag A. Agrawal; d Kotaro Konno (2009). "Latex: a model for understanding mechanisms, ecology, and evolution of plant defense Against herbivory". Annual Review of Ecology, Evolution, and Systematics . 40: 311–331. doi:10.1146/annurev.ecolsys.110308.120307.
  3. Paul G. Mahlberg (1993). "Laticifers: an historical perspective". The Botanical Review . 59 (1): 1–23. doi:10.1007/bf02856611. JSTOR   4354199. S2CID   40056337.
  4. "Natural Materials - Coco-mat". Coco-mat. Archived from the original on 2017-06-18. Retrieved 2017-07-04.
  5. 1 2 Stanislaw Slomkowski; José V. Alemán; Robert G. Gilbert; Michael Hess; Kazuyuki Horie; Richard G. Jones; Przemyslaw Kubisa; Ingrid Meisel; Werner Mormann; Stanisław Penczek; Robert F. T. Stepto (2011). "Terminology of polymers and polymerization processes in dispersed systems (IUPAC Recommendations 2011)" (PDF). Pure and Applied Chemistry . 83 (12): 2229–2311. doi:10.1351/PAC-REC-10-06-03. S2CID   96812603. Archived (PDF) from the original on 2013-10-20.
  6. "Taraxacum kok-saghyz". Pfaf.org. Archived from the original on 2014-03-20. Retrieved 2013-03-21.
  7. Thomas M. Lewinsohn (1991). "The geographical distribution of plant latex". Chemoecology . 2 (1): 64–68. doi:10.1007/BF01240668. S2CID   44594197.
  8. Joseph F. James (1887). "The milkweeds". The American Naturalist . 21 (7): 605–615. doi: 10.1086/274519 . JSTOR   2451222.
  9. J. E. Bowers (1990). Natural Rubber-Producing Plants for the United States. Beltsville, MD: National Agricultural Library. pp.  1, 3. OCLC   28534889.
  10. Liman, Stacy. "Latex Mattresses: The Best Latex Mattress Guide" . Retrieved 17 August 2020.
  11. Yurkovich, Dror. "Dunlop latex vs. Talalay latex". Getha.
  12. "Latex Allergy | Causes, Symptoms & Treatment". ACAAI Public Website. Retrieved 2019-03-24.
  13. "Latex Allergy - Eco Terra" . Retrieved 2018-10-10.
  14. Anderson, Christopher D.; Daniels, Eric S. (8 May 2018). Emulsion Polymerisation and Latex Applications. iSmithers Rapra Publishing. ISBN   9781859573815 . Retrieved 8 May 2018 via Google Books.
  15. "Latex allergy - Symptoms and causes". mayoclinic.com. Archived from the original on 7 October 2013. Retrieved 8 May 2018.
  16. Helge B. Bode; Axel Zeeck; Kirsten Plückhahn; Dieter Jendrossek (September 2000). "Physiological and Chemical Investigations into Microbial Degradation of Synthetic Poly(cis-1,4-isoprene)". Applied and Environmental Microbiology. 66 (9): 3680–3685. doi:10.1128/aem.66.9.3680-3685.2000. PMC   92206 . PMID   10966376.
  17. Rose, K.; Steinbuchel, A. (2 June 2005). "Biodegradation of Natural Rubber and Related Compounds: Recent Insights into a Hardly Understood Catabolic Capability of Microorganisms". Applied and Environmental Microbiology. 71 (6): 2803–2812. doi:10.1128/AEM.71.6.2803-2812.2005. PMC   1151847 . PMID   15932971.