Difference between revisions of "Wax"
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Wax refer to a class of hydrocarbons that are plastic (malleable) at normal ambient temperatures. Characteristically, they melt above 45 °C (113 °F) to give a low viscosity liquid. Waxes are insoluble in water but soluble in petroleum based solvent.
Waxes are secreted by many plants or animals, such as beeswax and carnauba (a plant epicuticular wax). Most industrial waxes are components of fossil fuels or are synthesized from petroleum-derived compounds, such as paraffin. Earwax is an oily substance found in the human ear. Many materials such as silicone wax exhibit similar properties, and are also described as wax or waxy.Contents
Classification of waxes
A wax is a type of hydrocarbon that typically contains long-chain alkanes often containing ester, carboxylic acid, or alcohol groups. The structure and molecular weight of the hydrocarbon chain and the relative concentration of the functional groups determine the hardness of the wax. Natural waxes especially are mixtures of several kinds of waxes whereas petroleum-derived waxes tend to be more homogeneous. Waxes can be classified according to their sources.
Natural waxes
Plant waxes
Especially in warm climates, plants secrete waxes as a way to control evaporation and hydration.[1] The most important is Carnauba wax, a hard wax with many applications. Other more specialized vegetable waxes include candelilla wax, ouricury wax, sugarcane wax, retamo wax, jojoba oil. The epicuticular waxes of plants are mixtures of substituted long-chain aliphatic hydrocarbons, containing alkanes, fatty acids, primary and secondary alcohols, diols, ketones, aldehydes.[2]
Animal waxes
The best known animal wax is beeswax but other insects secrete waxes and wool contains much wax. Beeswax is a substance secreted by bees and used in constructing their honeycombs. With a melting point 62 -65 °C, beeswax is primarily composed of esters with only a few percent of paraffin waxes.
Petroleum derived waxes
Paraffin waxes are hydrocarbons, mixtures of alkanes usually in a homologous series of chain lengths. These materials represent a significant fraction of petroleum. They are refined by vacuum distillation. Paraffin waxes are mixtures of saturated of n- and isoalkanes, naphthenes, and alkyl- and naphthene-substituted aromatic compounds. The degree of branching has an important influence on the properties. Million tons of paraffin waxes are produced annually. They are used as adhesives, in foods (chewing gum cheese wrapping), cosmetic, as coatings.
Montan wax
Montan wax is a fossilized wax extracted from coal and lignite. It is very hard, reflecting the high concentration of saturated fatty acids and alcohols, not esters that characterize softer waxes. Although dark brown and smelly, they can be purified and bleached to give commercially useful products.
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Waxes are obtained by cracking polyethylene by heating for a few minutes at 400 °C. The products have formulas of about (CH2)nH2, where n is about 50 or 100. As of 1995, about 200 million kilograms/y were consumed.[citation needed]
Uses of wax
Waxes are mainly consumed industrially as components of complex formulations, often for coatings.[1] The main use of polyethylene and polypropylene waxes is in the formulation of colourants for plastics. Waxes confer matting effects and wear resistence to paints. Polyethyelene waxes are incorporated into inks in the form of dispersions to decrease friction. They are employed as release agents. They are also used as slip agents, e.g. in furniture, and corrosion resistence.
Candles
Waxes and hard fats such as tallow have long been use to make candles, used for lighting and decoration in a number of religious traditions, including Christianity and Hinduism, as well as various neo-pagan religions such as Wicca. The Emperor Constantine is reported to have called for the use of candles during an Easter service in the 4th century AD. Candles continue to be used today by Christians[3] in worship as symbols of the light of Christ. In the Roman Catholic Church, beeswax candles are used, since a colony of bees is a celibate sisterhood with a single mother.[4] Candles of wax or tallow took the place of lamps used in various Jewish rituals such as the Sabbath lights; in the Havdalah ceremony; and the Hanukkah lights. A synagogue had to be well lit, and pious folk used to donate candles for the purpose. On the basis of the verse: 'The soul of man is a candle of the Lord' a special candle which burns twenty-four hours is kindled on the anniversary of the death of a near relative (Yahrzeit) and often two lighted candles are placed at the head of the corpse awaiting burial.[5]. Candles have also played a role in pagan religions and in modern humanist festivals. Virtually all rituals in Wicca include the lighting of altar candles, where two main candles are often used to represent the God and the Goddess; and the lighting of candles is a central theme at the Wiccan holiday of Brigid or Imbolc, which is also known as Candlemas or the Feast of the Waxing Light. Wax candles were also used in secular life for lighting, signals in warfare, safety in travel and for time keeping, and are still in popular use today to provide soft lighting for meals and other social activities.
Other uses
Waxes are used to make wax paper, impregnating and coating paper and card to waterproof it or make it resistant to staining, or to modify its surface properties. Waxes are also used in shoe polishes, wood polishes, and automotive polishes, as mold release agents in mold making, as a coating for many cheeses, and to waterproof leather and fabric. Wax has been used since antiquity as a temporary, removable model in lost-wax casting of gold, silver and other materials.
Wax with colorful pigments added has been used as a medium in encaustic painting, and is used today in the manufacture of crayons and colored pencils. Carbon paper, used for making duplicate typewritten documents was coated with carbon black suspended in wax, typically montan wax, but has largely been superseded by photocopiers and computer printers. In another context, lipstick and mascara are blends of various fats and waxes colored with pigments, and both beeswax and lanolin are used in other cosmetics. Also, the sports of surfing, skiing, snowboarding and skateboarding often use wax to enhance the performance. Beeswax or coloured synthetic wax is used to decorate Easter eggs in Ukraine and the Czech Republic. Paraffin wax is used in making chocolate covered bon-bons. Wax is also used in wax bullets, which are used as simulation aids.
Wax types
Animal waxes
- Beeswax - produced by honey bees
- Chinese wax - produced by the scale insect Ceroplastes ceriferus
- Earwax - found in the human ear.
- Lanolin (wool wax) - from the sebaceous glands of sheep
- Shellac wax - from the lac insect Kerria lacca
- Spermaceti - from the head cavities and blubber of the sperm whale
Vegetable waxes
- Bayberry wax - from the surface wax of the fruits of the bayberry shrub, Myrica faya
- Candelilla wax - from the Mexican shrubs Euphorbia cerifera and Euphorbia antisyphilitica
- Carnauba wax - from the leaves of the Carnauba palm, Copernica cerifera
- Castor wax - catalytically hydrogenated castor oil
- Esparto wax - a byproduct of making paper from esparto grass, (Macrochloa tenacissima)
- Japan wax - a vegetable triglyceride (not a true wax), from the berries of Rhus and Toxicodendron species
- Jojoba oil - a replacement for spermaceti, jojoba is pressed from the seeds of the jojoba bush, Simmondsia chinensis
- Ouricury wax - from the Brazilian feather palm, Syagrus coronata.
- Rice bran wax - obtained from rice bran (Oryza sativa)
- Soy wax - from soybean oil
Mineral waxes
- Ceresin waxes
- Montan wax - extracted from lignite and brown coal
- Ozocerite - found in lignite beds
- Peat waxes
Petroleum waxes
- Paraffin wax - made of long-chain alkane hydrocarbons
- Microcrystalline wax - with very fine crystalline structure
- Petroleum jelly
Synthetic waxes
- Polyethylene waxes - based on polyethylene
- Fischer-Tropsch waxes
- Chemically modified waxes - usually esterified or saponified
- substituted amide waxes
- polymerized α-olefins
See also
References
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zh:蜡- ↑ 1.0 1.1 Uwe Wolfmeier,Hans Schmidt, Franz-Leo Heinrichs, Georg Michalczyk, Wolfgang Payer,Wolfram Dietsche, Klaus Boehlke, Gerd Hohner, Josef Wildgruber "Waxes" in Ullmann's Encyclopedia of Industrial Chemistry, Wiley-VCH, Weinheim, 2002. doi:10.1002/14356007.a28_103.
- ↑ EA Baker (1982) Chemistry and morphology of plant epicuticular waxes. In The Plant Cuticle. Ed. DF Cutler, KL Alvin, CE Price. Academic Press. ISBN 0 12 199920 3
- ↑ The Hive and the Honey Bee, ed. Dadant & sons, revised 1975, p. 540
- ↑ Butler, C.G. (1954) The world of the honeybee. Collins, New Naturalist series, No. 29
- ↑ Jacobs, Louis (1995) "The Jewish Religion - a Companion" Oxford University Press
