Ask the Experts.
What is Wax?
The majority of wax products one sees on the market today are derived from petroleum. Waxes are a residual by-product of the production of lubricating oils. When first separated from petroleum, the lube oil fraction contains about 5-10% wax, depending on the source of the crude. Of course, in cold weather, a lubricating oil containing wax will solidify and prevent efficient engine lubrication. So the wax must be removed for the oil to work. One hundred years ago, wax was a nuisance and a by-product. Now, wax's many uses are better known, and the product is highly valued in its own right.
The chemical composition of waxes is complex, but normal alkanes (hydro carbon chains in lengths from 32 to 72 carbon atoms) are always present in high proportion. So, if we know something about the properties of normal alkanes, we can begin to form an idea of the properties of the commercial wax mixtures that are composed, predominantly, of these alkanes. We can form an idea of the "ideal" paraffin by assuming that the commercial grades that are produced are a mixture of "pure" alkanes, with the properties that appear in the following table.
Heptadecane to Tetracosane
These "ideal" paraffins are solid under normal room temperatures. Such pure paraffins can only be produced under laboratory conditions. All commercially sold products are (or aim to be) mixtures of these pure alkanes.
Heptadecane |
Octadecane |
Nonadecane |
Heneicosane |
Docosane |
Tricosane |
|||
C17H36 |
C18H38 |
C19H40 |
C20H42 |
C21H44 |
C22H46 |
C23H48 |
C24H50 |
|
[629-78-7] |
[593-45-3] |
[629-92-5] |
[112-95-8] |
[629-94-7] |
[629-97-0] |
[638-67-5] |
[646-31-1] |
|
Molar mass (g/mol) |
240.47 |
254.50 |
268.53 |
282.55 |
296.58 |
310.61 |
324.63 |
338.66 |
Melting point (Celcius) |
21 |
29 |
33 |
36.7 |
40.5 |
42 |
49 |
52 |
Boiling point (Celcius) |
302 |
317 |
330 |
342.7 |
356.5 |
224 at 2 kPa |
380 |
391.3 |
Density (g/ml) |
0.777 |
0.777 |
0.786 |
0.7886 |
0.792 |
0.778 |
0.797 |
0.797 |
Flash point (Celcius) |
148 |
165 |
168 |
Pentacosane to Triacontane
Pentacosane |
Hexacosane |
Heptacosane |
Octacosane |
Triacontane |
||
C25H52 |
C26H54 |
C27H56 |
C28H58 |
C29H60 |
C30H62 |
|
[629-99-2] |
[630-01-3] |
[593-49-7] |
[630-02-4] |
[630-03-5] |
[638-68-6] |
|
Molar mass (g/mol) |
352.69 |
366.71 |
380.74 |
394.77 |
408.80 |
422.82 |
Melting point (Celcius) |
54 |
56.4 |
59.5 |
64.5 |
63.7 |
65.8 |
Boiling point (Celcius) |
401.9 |
412.2 |
422 |
431.6 |
440.8 |
449.7 |
Density (g/ml) |
0.801 |
0.778 |
0.780 |
0.807 |
0.808 |
0.810 |
Hentriacontane to hexatriacontane
Dotriacontane |
Tritriacontane |
Tetratriacontane |
Pentatriacontane |
Hexatriacontane |
||
C31H64 |
C32H66 |
C33H68 |
C34H70 |
C35H72 |
C36H74 |
|
[630-04-6] |
[544-85-4] |
[630-05-7] |
[14167-59-0] |
[630-07-9] |
[630-06-8] |
|
Molar mass (g/mol) |
436.85 |
450.88 |
464.90 |
478.93 |
492.96 |
506.98 |
Melting point (Celcius) |
67.9 |
69 |
70 - 72 |
72.6 |
75 |
74 - 76 |
Boiling point (Celcius) |
458 |
467 |
474 |
285.4 at 0.4 kPa |
490 |
265 at 130 Pa |
Density (g/ml) |
0.781 at 68 C |
0.812 |
0.811 |
0.812 |
0.813 |
0.814 |
Heptatriacontane to Dotetracontane
Heptatriacontane |
Octatriacontane |
Nonatriacontane |
Tetracontane |
Hentetracontane |
Dotetracontane |
|
C37H76 |
C38H78 |
C39H80 |
C40H82 |
C41H84 |
C42H86 |
|
[7194-84-5] |
[7194-85-6] |
[7194-86-7] |
[4181-95-7] |
[7194-87-8] |
[7098-20-6] |
|
Molar mass (g/mol) |
520.99 |
535.03 |
549.05 |
563.08 |
577.11 |
591.13 |
Melting point (Celcius) |
77 |
79 |
78 |
84 |
83 |
86 |
Boiling point (Celcius) |
504.14 |
510.93 |
517.51 |
523.88 |
530.75 |
536.07 |
Density (g/ml) |
0.815 |
0.816 |
0.817 |
0.817 |
0.818 |
0.819 |
Tritetracontane to Octatetracontane
Triatetracontane |
Tetratetracontane |
Pentatetracontane |
Hexatetracontane |
Heptatetracontane |
Octatetracontane |
|
C43H88 |
C44H90 |
C45H92 |
C46H94 |
C47H96 |
C48H98 |
|
[7098-21-7] |
[7098-22-8] |
[7098-23-9] |
[7098-24-0] |
[7098-25-1] |
[7098-26-2] |
|
Molar mass (g/mol) |
605.15 |
619.18 |
633.21 |
647.23 |
661.26 |
675.29 |
Boiling point (Celcius) |
541.91 |
547.57 |
553.1 |
558.42 |
563.6 |
568.68 |
Density (g/ml) |
0.82 |
0.82 |
0.821 |
0.822 |
0.822 |
0.823 |
Nonatetracontane to Tetrapentacontane
Nonatetracontane |
Pentacontane |
Henpentacontane |
Dopentacontane |
Tripentacontane |
Tetrapentacontane |
|
C49H100 |
C50H102 |
C51H104 |
C52H106 |
C53H108 |
C54H110 |
|
[7098-27-3] |
[6596-40-3] |
[7667-76-7] |
[7719-79-1] |
[7719-80-4] |
[5856-66-6] |
|
Molar mass (g/mol) |
689.32 |
703.34 |
717.37 |
731.39 |
745.42 |
759.45 |
Boiling point (Celcius) |
573.6 |
578.4 |
583 |
587.6 |
592 |
596.38 |
Density (g/ml) |
0.823 |
0.824 |
0.824 |
0.825 |
0.825 |
0.826 |
Source: Wikipedia
Petroleum waxes are frequently described as "straight cut" or "blended". "Straight cut" waxes tend to have a distribution of alkanes such that the mode, median and mean of the Carbon lengths of the component alkanes are similar. Blended waxes are mixed in order to achieve some average (mean) properties that otherwise might not be obtainable from the available straight-cut production runs.
The non-Petroleum waxes are predominantly derived from insects, plants or animals.
Beeswax has been traded for over 2000 years, at least since Odysseus ordered his men to seal their ears with it, to protect them from the Siren's song. Yellow beeswax is secreted by bees; it can be bleached with oxidizing agents to become the white beeswax which is highly valued in the production of cosmetics and skin lotions. Bees wax does NOT have the inert chemical properties of the alkane waxes, since it is a complex mixture of C25-C31 hydrocarbons, esters, alcohols and carboxylic acids..
Carnauba wax derives from a palm tree which grows in Brazil. Carnauba wax is hard, with a high melting point. It can easily disperse pigments which make carnauba useful in printing inks. It is also used to gel organic solvents and oils as a component of solvent and paste formulations. Carnauba polishes to a high gloss, and is used to polish items such as leather products, candies, metal surfaces, etc.
Candelilla wax is harvested from a Mexican shrub found in Coahuila, Chihuahua, and Texas. Candelilla products can be found in cosmetics, food and pharmaceuticals.
Other vegetable-based waxes include Japan wax, Ouricury wax, Rice-bran wax, and Jojoba.
Montan wax is derived by solvent extraction of lignite. Production has been reduced, but it is still used in polishes and as a plastics lubricants.
Paraffins and Microcrystalline Waxes
There are two major classifications of petroleum waxes: paraffins, which form large, clearly defined crystalline structures; and micro-crystalline waxes, which have more branched chains and much smaller crystals of irregular shape. Microcrystalline waxes have a higher melting point, higher viscosity, and other distinguishing features, such as "tackiness".
Fully refined waxes have oil contents of less that 0;5% (in the USA standard, 0.75% in the Chinese). Semi -refined waxes have up to 1.5% oil. Scale waxes and slack waxes have even more oil, up to a common maximum of 35%. Paraffin waxes sold commercially are mixtures of "normal" (straight chained) and "iso" (or branched) alkanes. They are exempt from the presence of the esters, acids, etc. found in the animal and vegetable-based waxes. Hence they are much more suitable for industrial formulations where predictable outcomes are preferred. Both Paraffin and Microcrystalline waxes are largely inert (the name paraffin itself comes from the Latin, meaning "against affinities"). Micro-crystalline waxes contain a higher proportion of isomers while paraffins have a higher proportion of normal carbon chains.
Two important tests are used to analyze waxes and their structures: Gas Chromatography to determine the distribution of Carbon chains of given lengths and given branch structures; Differential Scanning Calorimetry to measure the waxes enthalpy and degree of purity.
Synthetic waxes now play important industrial roles. Polyethylene waxes have a molecular weight higher than micro crystalline waxes, but lower than polyethylenes themselves. Such waxes have predictable qualities and are sought after for particular industrial applications, all the more so since these synthetic properties can be varied according to the production process. Major applications include include hot-melt adhesives, especially when there is a need for high-temperature performance. Other uses include plastic additives, slipping agents for inks, plastics processing, paints and cosmetics and ointments.
Fischer-Tropsch (FT) wax, a polyethylene wax produced by the polymerization of carbon monoxide under high pressure is the technology used in natural Gas to Liquid (GTL) projects. The hydrocarbon product of FT reaction is distilled to separate the mix into fuels products and waxes with melting points ranging from about 45 to 106 Celcius. Currently FT waxes are commercially produced in large volumes in South Africa and Malaysia. Uses are similar to those for polyethylene waxes including hot-melt adhesives and additives for inks and coatings.
Chemically modified waxes: paraffinic, and polyethylene waxes may be modified to meet specific market needs. In most cases, the first step is air oxidation of the wax with or without catalysts. Alternatively, one can use carboxylic acid at high temperatures and pressures. Oxidized wax can then be saponified or esterified at the carboxyl sites. Oxidized wax lends itself to the manufacture of emulsions in water, using surfactants or simple soaps, Such emulsions are elements of many coating, polishing and lubricating applications.
Alpha-olefins (e.g. C > 20) have wax-like properties and are sold as synthetic waxes. The polymerization process yields highly branched materials with broad molecular weight distributions. Properties of the individual products are highly dependent on the olefin monomers and polymerization conditions. Melt points range from 54 - 74 Celcius. The unique structure makes these products very effective when used in additive amounts to modify the properties of paraffin wax, primarily for use in candles. The products can increase the hardness and opacity of the paraffin with minimal impact on cloud point or viscosity. Other uses include mold release for polyurethane foams, additives for casting wax, additives for leather treating, and lubrication in the manufacture of PVC piping.