Cetyl palmitate, a typical wax ester.
Commercial honeycomb foundation, made by pressing beeswax between patterned metal rollers.
Waxes are a diverse class of organic compounds that are lipophilic, malleable solids near ambient temperatures. They include higher alkanes and lipids, typically with melting points above about 40 °C (104 °F), melting to give low viscosity liquids. Waxes are insoluble
in water but soluble in organic, nonpolar solvents. Natural waxes of
different types are produced by plants and animals and occur in petroleum.
Chemistry
Ceroline brand wax for floors and furniture, first half of 20th century. From the Museo del Objeto del Objeto collection
Waxes are organic compounds that characteristically consist of long alkyl chains. Natural waxes may contain unsaturated bonds and include various functional groups such as fatty acids, primary and secondary alcohols, ketones, aldehydes and fatty acid esters, and aromatic compounds may also be present. Synthetic waxes often consist of homologous series of long-chain aliphatic hydrocarbons (alkanes or paraffins) that lack functional groups.
Plant and animal waxes
Waxes are synthesized
by many plants and animals. Those of animal origin typically consist
of wax esters 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 honeycombs of honeybees, but other insects secrete waxes. A major component of the beeswax is myricyl palmitate which is an ester of triacontanol and palmitic acid. Its melting point is 62-65 °C. 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 sterols.
Plant waxes
Plants secrete waxes into and on the surface of their cuticles as a way to control evaporation, wettability and hydration. The epicuticular waxes of plants are mixtures of substituted long-chain aliphatic hydrocarbons, containing alkanes, alkyl esters, fatty acids, primary and secondary alcohols, diols, ketones, aldehydes.
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.
This approach has relied on green chemistry approaches including olefin
metathesis and enzymatic reactions and can be used to produce waxes
from inexpensive starting materials like vegetable oils.
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- alkanes,
naphthenes, and alkyl- and naphthene-substituted aromatic compounds. A
typical alkane paraffin wax chemical composition comprises hydrocarbons with the general formula CnH2n+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. It is very hard, reflecting the high concentration of saturated fatty acids and alcohols. Although dark brown and odorous, they can be purified and bleached to give commercially useful products.
As of 1995, about 200 million kilograms/y were consumed.
Polyethylene waxes are manufactured by one of three methods: 1-
direct polymerization of ethylene (may include co -monomers also); 2- thermal degradation of high molecular weight polyethylene resin; 3- 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 plastics. Waxes confer matting effects
and wear resistance to paints. Polyethylene waxes are incorporated into
inks in the form of dispersions to decrease friction. They are employed
as release agents, find use as slip agents in furniture, and confer corrosion resistance.
Candles
Wax candle.
Waxes such as paraffin wax or beeswax, and hard fats such as tallow are used to make candles, used for lighting and decoration.
Wax products
Waxes are used as finishes and coatings for wood products. Beeswax is frequently used as a lubricant on drawer slides where wood to wood contact occurs.
Other uses
A lava lamp is a novelty item that contains wax melted from below by a bulb. The wax rises and falls in decorative, molten blobs.
Sealing wax was used to close important documents in the Middle Ages. Wax tablets were used as writing surfaces. There were different types of wax in the Middle Ages, namely four kinds of wax (Ragusan, Montenegro, Byzantine, and Bulgarian), "ordinary" waxes from Spain, Poland, and Riga, unrefined waxes and colored waxes (red, white, and green). 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, china markers 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. Ski wax is used in skiing and snowboarding. Also, the sports of surfing and skateboarding often use wax to enhance the performance.
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 Easter eggs in Romania, Ukraine, Poland, Lithuania and the Czech Republic. Paraffin wax is used in making chocolate covered sweets.
Wax is also used in wax bullets, which are used as simulation aids.
Specific examples
Animal waxes
- Beeswax - produced by honey bees
- Chinese wax - produced by the scale insect Ceroplastes ceriferus
- 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, Copernicia 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 liquid wax ester, from the seed of 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
- Tallow Tree wax - from the seeds of the tallow tree Triadica sebifera.
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
