Gutta-percha

Gutta-percha is a tree of the genus Palaquium in the family Sapotaceae, which is primarily used to create a high-quality latex of the same name. The material is rigid, naturally biologically inert, resilient, electrically nonconductive, and thermoplastic, most commonly sourced from Palaquium gutta; it is a polymer of isoprene which forms a rubber-like elastomer.

The word "gutta-percha" comes from the plant's name in Malay: getah translates as 'sticky gum' and pertja (perca) is the name of a less-sought-after gutta tree. The western term therefore is likely a derivative amalgamation of the original native names.

Description

Palaquium gutta trees are 5–30 metres (20–100 ft) tall and up to 1 m (3 ft) in trunk diameter. The leaves are evergreen, alternate or spirally arranged, simple, entire, 8–25 cm (3–10 in) long, glossy green above, and often yellow or glaucous below. The flowers are produced in small clusters along the stems, each flower with a white corolla with four to seven (mostly six) acute lobes. The fruit is an ovoid 3–7 cm (1–3 in) berry, containing one to four seeds; in many species, the fruit is edible.

In Australia, gutta-percha is a common name specifically used for the euphorbiaceous tree Excoecaria parvifolia, which yields an aromatic, heavy, dark-brown timber.

Characteristics

Raw gutta-percha is brown to grey-brown and, due to the harvesting methods, typically contains some sand, small pieces of wood and bark as impurities. It is fibrous, flaky, almost woody and easy to cut – unlike rubber – and pliable but not elastic, somewhat greasy with a leathery odor. After cleaning, it becomes plastic. It consists of about 50–75% gutta (polyterpenes), about 10–48% resins (Fluavil, Alban, Albanan), salts, nitrogen compounds and triterpenes; lupeol, esterified amyrins. Bassic acid is found in some Palaquium species. It is then de-resinified with solvents and cleaned and bleached; it is then white, solid, crystalline and almost odorless.

Pure gutta-percha is chemically similar to natural rubber, but unlike natural rubber, it is composed of trans -configured 1,4- polyisoprene rather than cis -configured polyisoprene, with a much lower molar mass due to the fact that the molecule contains far fewer repeating units. It is biocompatible and inert, as well as optically anisotropic, i.e., birefringent, and chemically much more resistant to aggressive media than rubber. It can also be vulcanized, but this is usually not done. Its thermoplastic behavior (softening temperature 70–90 °C) allows for shaping without vulcanization.

At room temperature, it is harder and less elastic, but becomes soft and malleable at approximately 48–60 °C. The degree of polymerization (the number of monomer units in a macromolecule) is approximately 1500, while that of natural rubber is 8000–30,000. 

At room temperature, solid gutta-percha oxidizes quickly and becomes brittle; therefore, it must be stored under water or sealed airtight. 

Similar products include balata from the balata tree (Manilkara bidentata) and chicle, which is obtained from various Manilkara species. Guayule rubber from the guayule tree (Parthenium argentatum) is also used on a larger scale; here, the polyisoprenes are cis -configured.

Chemistry

Chemically, gutta-percha is a polyterpene, a polymer of isoprene, or polyisoprene, specifically (trans-1,4-polyisoprene). The cis structure of polyisoprene is the common latex elastomer. While latex rubbers are amorphous in molecular structure, gutta-percha (the trans structure) crystallizes, leading to a more rigid material. It exists in alpha and beta forms, with the alpha form being brittle at room temperature.

Forms

Gutta-percha can occur in three forms: two ordered (crystalline) alpha and beta, and one disordered (amorphous) form. The crystalline alpha and beta forms differ in a different repeating unit in the polymer chain— beta one monomer, alpha two monomers—as well as in the single-bond configuration. The two forms have different crystallographic structures, the variations of which are reflected in volume changes induced in gutta-percha by heating and cooling.

Most commercial gutta-percha exists in the beta form. The alpha form occurs in raw latex. When the natural alpha form is heated above 65°C, it becomes amorphous and melts. If this amorphous material is cooled extremely slowly (0.5°C per hour), the alpha form recrystallizes. On the other hand, if the amorphous melt is routinely cooled, the beta form recrystallizes. Most commercial gutta-percha, including dental gutta-percha, exists in this form. Now, when the beta form is reheated, the polymer becomes amorphous at 56°C, 9°C lower than the melting point for the alpha form. It is therefore obvious that the factor determining the melting point of alpha and beta gutta-percha is the cooling rate, which in turn controls the extent and character of crystallinity in the solidified material. The beta form transforms into the alpha form at 42–49 °C, which then becomes amorphous again at 53–56 °C. 

Uses

Gutta-percha was widely used in the travel industry, thanks to Maison Moynat, which began using this insulating material in the manufacture and lining of its trunks in 1854. Other trunk makers later began using the sap to waterproof their products. It has been used for the manufacture of everyday objects such as lockets, photo frames, ambrotype or daguerreotype boxes, gramophone records. It was used to make bottles to store hydrofluoric acid (HF), an acid used to etch glass by chemical attack. It was also used in gunsmithing to make revolver stocks in the late 19th and early 20th centuries.

In the mid-19th century, gutta-percha was used to make furniture, notably by the Gutta Percha Company, established in 1847. Several of these ornate, revival-style pieces were shown at the 1851 Great Exhibition in Hyde Park, London. The company also made a range of utensils.

The "guttie" golf ball (which had a solid gutta-percha core) revolutionized the game. Gutta-percha was used to make "mourning" jewelry, because it was dark in color and could be easily molded into beads or other shapes. Pistol hand grips and rifle shoulder pads were also made from gutta-percha, since it was hard and durable, though it fell into disuse when synthetic plastics such as Bakelite became available.

Gutta-percha was used in canes and walking sticks. In 1856, United States Representative Preston Brooks used a cane made of gutta-percha as a weapon in his attack on Senator Charles Sumner. In the 1860s, gutta-percha was used to reinforce the soles of football players' boots before it was banned by The Football Association in the first codified set of rules in 1863. Gutta-percha was briefly used in bookbinding until the advent of vulcanization. The wood of many species is also valuable.

Historic

Long before gutta-percha was introduced into the Western world, it was used in a less-processed form by the natives of the Malaysian archipelago for making knife handles, walking sticks, and other purposes. The first European to study this material was John Tradescant, who collected it in the far east in 1656. He named this material "Mazer wood". William Montgomerie, a medical officer in imperial service, introduced gutta-percha into practical use in the West. He was the first to appreciate the potential of this material in medicine, and he was awarded the gold medal by the Royal Society of Arts, London in 1843.

Scientifically classified in 1843, it was found to be a useful natural thermoplastic. In 1851, 30,000 long cwt (1,500 t) of gutta-percha was imported into Britain. During the second half of the 19th century, gutta-percha was used for many domestic and industrial purposes, and it became a household word. Gutta-percha was particularly important for the manufacture of underwater telegraph cables. Compared to rubber, it does not degrade in seawater, is not damaged by marine life, and maintains good electrical insulation. These properties, along with its mouldability and flexibility made it ideal for the purpose, with no other material to match it in the 19th century. The use in electrical cables generated a huge demand which led to unsustainable harvesting and collapse of supply.

Dentistry

In dentistry, gutta-percha is primarily used in root canal treatments. The "gutta-percha points" used to fill the canals contain a high percentage of gutta-percha, along with a number of other components. The same bioinertness that made it suitable for marine cables also means it does not readily react within the human body. It is used in a variety of surgical devices and during root canal therapy. It is the predominant material used to obturate, or fill, the empty space inside the root of a tooth after it has undergone endodontic therapy. Its physical and chemical properties, including its inertness and biocompatibility, melting point, ductility, and malleability, make it important in endodontics, e.g., as gutta-percha points. Zinc oxide is added to reduce brittleness and improve plasticity. 

Barium sulfate is added to provide radiopacity so that its presence and location can be verified in dental X-ray images. Gutta-percha is also sometimes used for temporary fillings, for example, to bridge the time between preparation and the insertion of an inlay. Compared to synthetic temporary materials, it has the advantage of being removable in one piece.

Art

Gutta is also used in silk cloth painting as a release agent to create contours. In this contour technique, known as the gutta technique, the fabric is not colored where the release agent was applied. A colorless line or area remains.

Electroplating

In the second half of the 19th century, electroplating methods were used to copy historical metalwork in small editions or to transfer small sculptures by artists into metal. Impressions made with heated, elastic gutta-percha could be easily taken even from fully round objects or heavily undercut reliefs. Made electrically conductive with graphite powder, the resulting forms could be electroplated into metal. 

Gutta-percha latex is biologically inert, resilient, and is a good electrical insulator with a high dielectric strength. Michael Faraday discovered its value as an insulator soon after the introduction of the material to Britain in 1843. Allowing this fluid to evaporate and coagulate in the sun produced a latex which could be made flexible again with hot water, but which did not become brittle, unlike rubber prior to the discovery of vulcanization.

By 1845, telegraph wires insulated with gutta-percha were being manufactured in the UK. It served as the insulating material for early undersea telegraph cables, including the first transatlantic telegraph cable. The material was a major constituent of Chatterton's compound used as an insulating sealant for telegraph and other electrical cables.

The dielectric constant of dried gutta-percha ranges from 2.56 to 3.01. Resistivity of dried gutta-percha ranges from 25×1014 to 370×1014 Ω⋅cm. Since about 1940, polyethylene has supplanted gutta-percha as an electrical insulator.

Sport

In the past, golf balls were also a typical application for this material. Such balls were also called gutties, gutties, or brambles. However, gutta-percha was already being replaced by the cheaper and more suitable rubber in the second half of the 19th century. 

Everyday objects

Gutta-percha buckets were widely used in the chemical industry before more modern materials became available. Gutta-percha buckets were particularly used in dynamite factories to transport small batches of blasting oil and are frequently seen in older illustrations. Gutta-percha was also used as an ingredient in chewing gum. A gutta-percha walking stick was used as a weapon in the Brooks-Sumner affair.

Aircraft construction

At the beginning of the 20th century, gutta-percha was also used to produce tensioning materials for the wings and outer skin of aircraft, the so-called “aeroplane materials”.

Electrical cable insulation

Because of its good insulating properties, polyterpene was used to sheathe electrical cables from the mid-19th century onwards. Material tests in 1846 and the invention of the extrusion press by Werner Siemens led to the founding of the Telegraph Construction Company of Siemens & Halske in 1847. Such cables made intercontinental telegraphy possible, particularly through the laying of submarine cables. Gutta-percha has since been completely replaced by various types of plastics as an insulating material for electrical cables.

Substitutes

Gutta-percha remained an industrial staple well into the 20th century, when it was gradually replaced with superior synthetic materials, such as Bakelite.

A similar and cheaper natural material called balatá was often used in gutta-percha's place. The two materials are almost identical, and balatá is often called gutta-balatá.

Sourced from Wikipedia