Waxes are a diverse class of that are lipophilic, malleability solids near ambient temperatures. They include higher alkanes and , typically with above about 40 °C (104 °F), melting to give low viscosity liquids. Waxes are Solubility in water but soluble in nonpolar organic solvents such as hexane, benzene and chloroform. Natural waxes of different types are produced by plants and animals and occur in petroleum.
Chemistry
Waxes are organic compounds that characteristically consist of long
aliphatic alkyl chains, although aromatic compounds may also be present. Natural waxes may contain unsaturated bonds and include various
such as
carboxylic acid,
primary alcohol and secondary alcohols,
ketones,
Aldehyde and fatty acid
. Synthetic waxes often consist of homologous series of long-chain aliphatic hydrocarbons (
or paraffins) that lack
.
[
]
Plant and animal waxes
Waxes are biosynthesis by both plants and animals. Those of animal origin typically consist of derived from a variety of fatty acids and carboxylic alcohols. In waxes of plant origin, characteristic mixtures of unesterified hydrocarbons may predominate over esters.[ The composition depends not only on species, but also on geographic location of the organism.
]
Animal waxes
The best-known animal wax is beeswax, used in constructing the of beehives, but other insects also secrete waxes. A major component of beeswax is myricyl palmitate which is an ester of triacontanol and palmitic acid. Its melting point is . Spermaceti occurs in large amounts in the head oil of the sperm whale. One of its main constituents is cetyl palmitate, another ester of a fatty acid and a fatty alcohol. Lanolin is a wax obtained from wool, consisting of esters of .[Wilhelm Riemenschneider1 and Hermann M. Bolt (2005). "Esters, Organic". Ullmann's Encyclopedia of Industrial Chemistry. Wiley-VCH, Weinheim. .]
Plant waxes
Plants secrete waxes into and on the surface of their plant cuticle as a way to control evaporation, wettability and hydration.[ The of plants are mixtures of substituted long-chain aliphatic hydrocarbons, containing alkanes, alkyl esters, fatty acids, primary and secondary alcohols, , ketones and aldehydes.][EA Baker (1982) Chemistry and morphology of plant epicuticular waxes. In The Plant Cuticle. Ed. DF Cutler, KL Alvin, CE Price. Academic Press. ] From the commercial perspective, the most important plant wax is carnauba wax, a hard wax obtained from the Brazilian palm Copernicia prunifera. Containing the ester myricyl cerotate, it has many applications, such as confectionery and other food coatings, car and furniture polish, floss coating, and surfboard wax. Other more specialized vegetable waxes include jojoba oil, candelilla wax and ouricury wax.
Modified plant and animal waxes
Plant and animal based waxes or oils can undergo selective chemical modifications to produce waxes with more desirable properties than are available in the unmodified starting material.
Petroleum derived waxes
Although many natural waxes contain esters, 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 n- and iso- Alkane, naphthenes, and Alkyl group- and naphthene-substituted aromatic compounds. A typical alkane paraffin wax chemical composition comprises hydrocarbons with the general formula C nH2 n+2, such as hentriacontane, C31H64. The degree of branching has an important influence on the properties. Microcrystalline wax is a lesser produced petroleum based wax that contains higher percentage of isoparaffinic (branched) hydrocarbons and naphthenic hydrocarbons.
Millions of tons of paraffin waxes are produced annually. They are used in foods (such as chewing gum and cheese wrapping), in candles and cosmetics, as non-stick and waterproofing coatings and in polishes.
Montan wax
Montan wax is a fossilized wax extracted from coal and lignite.
Polyethylene and related derivatives
, about 200 million kilograms of polyethylene waxes were consumed annually.[
]
Polyethylene waxes are manufactured by one of three methods:
-
The direct polymerization of ethylene, potentially including co-monomers;
-
The thermal degradation of high molecular weight polyethylene resin;
-
The recovery of low molecular weight fractions from high molecular weight resin production.
Each production technique generates products with slightly different properties. Key properties of low molecular weight polyethylene waxes are viscosity, density and melt point.
Polyethylene waxes produced by means of degradation or recovery from polyethylene resin streams contain very low molecular weight materials that must be removed to prevent volatilization and potential fire hazards during use. Polyethylene waxes manufactured by this method are usually stripped of low molecular weight fractions to yield a flash point >500 °F (>260 °C). Many polyethylene resin plants produce a low molecular weight stream often referred to as low polymer wax (LPW). LPW is unrefined and contains volatile oligomers, corrosive catalyst and may contain other foreign material and water. Refining of LPW to produce a polyethylene wax involves removal of oligomers and hazardous catalyst. Proper refining of LPW to produce polyethylene wax is especially important when being used in applications requiring FDA or other regulatory certification.
Uses
Waxes are mainly consumed industrially as components of complex formulations, often for coatings. The main use of polyethylene and polypropylene waxes is in the formulation of colourants for . Waxes confer matting effects (i.e., to confer non-glossy finishes) and wear resistance to paints. Polyethylene waxes are incorporated into inks in the form of dispersions to decrease friction. They are employed as , find use as slip agents in furniture, and confer corrosion resistance.[Uwe Wolfmeier, Mr. 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. .]
Candles
Waxes such as paraffin wax or beeswax, and hard fats such as tallow are used to make , used for lighting and decoration. Another fuel type used in candle manufacturing includes soy. Soy wax is made by the hydrogenation process using soybean oil.
Wood products
Waxes are used as finishes and coatings for wood products.
Other uses
Sealing wax was used to close important documents in the Middle Ages. were used as writing surfaces. There were different types of wax in the Middle Ages, namely four kinds of wax (Dubrovnik, Montenegro, Byzantine, and ), "ordinary" waxes from Spain, Poland, and Riga, unrefined waxes and colored waxes (red, white, and green).[The rational arts of living: Ruth and Clarence Kennedy Conference in the Renaissance, 1982, page 187, Studies in History, No 50, Alistair Cameron Crombie, Nancy G. Siraisi, Dept. of History of Smith College, 1987.]
Wax with colorful pigments added has been used as a medium in encaustic painting, and is used today in the manufacture of , Grease pencil and colored . Carbon paper, used for making duplicate typewriter documents was coated with carbon black suspended in wax, typically montan wax, but has largely been superseded by and . 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. Ski wax is used in skiing and snowboarding. Also, the sports of surfing and skateboarding
Some waxes are considered food-safe and are used to coat wooden cutting boards and other items that come into contact with food. Beeswax or coloured synthetic wax is used to decorate in Romania, Ukraine, Poland, Lithuania and the Czech Republic. Paraffin wax is used in making chocolate covered sweets.
Wax is also used in , which are used as simulation aids, and for Wax sculpture.
Specific examples
Animal waxes
Vegetable waxes
Mineral waxes
Petroleum waxes
-
Paraffin wax – made of long-chain alkane
-
Microcrystalline wax – with very fine crystalline structure
See also
-
Slip melting point
-
Wax acid
-
Wax argument, or the "ball of wax example", is a thought experiment originally articulated by Renė Descartes.
External links
