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 carboxylic acids and fatty 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.
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.
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 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 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.