Paraffin wax (or petroleum wax) is a soft colorless solid derived from
petroleum,
coal, or
oil shale that consists of a mixture of
hydrocarbon molecules containing between 20 and 40 carbon atoms. It is solid at room temperature and
begins to melt above approximately 37 °C (99 °F),[2] and its boiling point is above 370 °C (698 °F).[2] Common applications for paraffin wax include
lubrication,
electrical insulation, and
candles;[3] dyed paraffin wax can be made into
crayons. It is distinct from
kerosene and other petroleum products that are sometimes called paraffin.[4]
Un-dyed, unscented paraffin candles are odorless and bluish-white. Paraffin wax was first created by
Carl Reichenbach in Germany in 1830 and marked a major advancement in candlemaking technology, as it burned more cleanly and reliably than
tallow candles and was cheaper to produce.[5]
In chemistry, paraffin is used synonymously with alkane, indicating hydrocarbons with the general formula CnH2n+2. The name is derived from
Latinparum ("very little") + affinis, meaning "lacking
affinity" or "lacking
reactivity", referring to paraffin's unreactive nature.[6]
Properties
Paraffin
wax is mostly found as a white, odorless, tasteless, waxy solid, with a typical melting point between about 46 and 68 °C (115 and 154 °F),[7] and a density of around 900 kg/m3.[8] It is insoluble in water, but soluble in
ether,
benzene, and certain
esters. Paraffin is unaffected by most common chemical
reagents but
burns readily.[9] Its heat of combustion is 42 MJ/kg.[10]
Paraffin wax is an excellent material for
storing heat, with a
specific heat capacity of 2.14–2.9 J⋅g−1⋅K−1 (
joules per
gram per
kelvin) and a
heat of fusion of 200–220 J⋅g−1.[14] Paraffin wax phase-change cooling coupled with retractable radiators was used to cool the electronics of the
Lunar Roving Vehicle during the crewed missions to the Moon in the early 1970s.[15] Wax expands considerably when it melts and so is used in
wax elementthermostats for industrial, domestic and, particularly, automobile purposes.[16][17]
If pure paraffin wax melted to the approximate flash point in a half open glass vessel which is then suddenly cooled down, then its vapors may autoignite as result of reaching
boiling liquid pressure.[18]
History
Paraffin wax was first created in 1830 by German chemist
Karl von Reichenbach when he attempted to develop a method to efficiently separate and refine waxy substances naturally occurring in petroleum. Paraffin represented a major advance in the candle-making industry because it burned cleanly and was cheaper to manufacture than other candle fuels. Paraffin wax initially suffered from a low melting point. This was remedied by adding
stearic acid. The production of paraffin wax enjoyed a boom in the early 20th century due to the growth of the oil and meatpacking industries, which created paraffin and stearic acid as byproducts.[5]
Manufacturing
The feedstock for paraffin is
slack wax, which is a mixture of oil and wax, a byproduct from the refining of lubricating oil.
The first step in making paraffin wax is to remove the oil (de-oiling or de-waxing) from the slack wax. The oil is separated by crystallization. Most commonly, the slack wax is heated, mixed with one or more
solvents such as a
ketone and then cooled. As it cools, wax crystallizes out of the solution, leaving only oil. This mixture is filtered into two streams: solid (wax plus some solvent) and liquid (oil and solvent). After the solvent is recovered by distillation, the resulting products are called "product wax" (or "press wax") and "foots oil". The lower the percentage of oil in the wax, the more refined it is considered (semi-refined versus fully refined).[19] The product wax may be further processed to remove colors and odors. The wax may finally be blended together to give certain desired properties such as melt point and penetration. Paraffin wax is sold in either liquid or solid form.[20][21][22]
Applications
In industrial applications, it is often useful to modify the crystal properties of the paraffin wax, typically by adding
branching to the existing carbon backbone chain. The modification is usually done with additives, such as
EVA copolymers,
microcrystalline wax, or forms of
polyethylene. The branched properties result in a modified paraffin with a higher viscosity, smaller crystalline structure, and modified functional properties. Pure paraffin wax is rarely used for carving original models for
casting metal and other materials in the
lost wax process, as it is relatively brittle at room temperature and presents the risks of chipping and breakage when worked. Soft and pliable waxes, like
beeswax, may be preferred for such sculpture, but "
investment casting waxes," often paraffin-based, are expressly formulated for the purpose.
In a histology or pathology laboratory, paraffin wax is used to impregnate tissue prior to sectioning thin samples. Water is removed from the tissue through ascending strengths of alcohol (75% to absolute), and then the alcohol is cleared in an organic solvent such as
xylene. The tissue is then placed in paraffin wax for several hours, then set in a mold with wax to cool and solidify. Sections are then cut on a
microtome.
Ink. Used as the basis for solid ink different color blocks of wax for thermal printers. The wax is melted and then sprayed on the paper producing images with a shiny surface
Forensic investigations: the nitrate test uses paraffin wax to detect nitrates and nitrites on the hand of a shooting suspect
Antiozonant agents: blends of paraffin and micro waxes are used in rubber compounds to prevent
cracking of the rubber; the admixture of wax migrates to the surface of the product and forms a protective layer. The layer can also act as a
release agent, helping the product separate from its
mould.[26]
Paraffin is effective in the treatment of
Osteoarthritis of the hand joints. Treatment consists of dip-wrapped paraffin bath therapy for 15 minutes until paraffin cooled for five days a weeks. The use of paraffin wax bath has been shown to decrease pain at rest and during ADLs (activities of daily living) compared to groups who did not receive wax therapy.[30]
Improvements in grip strength and pinch strength have been found in patients with Carpel Tunnel Syndrome, Osteoarthritis, spasticity, and post-traumatic stiffness for those who have used paraffin bath therapy along with traditional physical therapy in their recovery. It has been found that patients who have used paraffin bath therapy have yielded lower VAS and AUSCAN scores (pain scores) compared to those who did not.[31]
^
abFreund, Mihály; Mózes, Gyula (1982). Paraffin products: properties, technologies, applications. Translated by Jakab, E. Amsterdam, the Netherlands: Elsevier. p. 121.
ISBN978-0-444-99712-8.
^Nasser, William E (1999). "Waxes, Natural and Synthetic". In McKetta, John J (ed.). Encyclopedia of Chemical Processing and Design. Vol. 67. New York: Marcel Dekker. p. 17.
ISBN978-0-8247-2618-8. This can vary widely, even outside the quoted range, according to such factors as oil content and crystalline structure.
^Seager, Spencer L.; Slabaugh, Michael (19 January 2010). "Alkane reactions". Chemistry for Today: General, Organic, and Biochemistry. Belmont, California: Cengage. p. 364.
ISBN978-0-538-73332-8.
^"Electrical insulating materials". Kaye and Laby Tables of Physical and Chemical Constants. National Physical Laboratory. 1995. Archived from
the original on 27 September 2007. Retrieved 25 October 2013.
^"Specific Heat Capacity". Diracdelta.co.uk Science and Engineering Encyclopedia. Dirac Delta Consultants Ltd, Warwick, England. Archived from
the original on 4 August 2007. Retrieved 25 October 2013.
^Dean, W. G.; Karu, Z. S. (February 1993). "Space Station thermal storage/refrigeration system research and development". Final Report Lockheed Missiles and Space Co.
Bibcode:
1993lock.rept.....D.
^
abBodén, Roger.
"Paraffin Microactuator"(PDF). Materials Science Sensors and Actuators. University of Uppsala. Archived from
the original(PDF) on 8 February 2012. Retrieved 25 October 2013.