Wax usually refers to a substance that is a plastic solid at ambient temperature and that, on being subjected to moderately elevated temperatures, becomes a low viscosity liquid. Because it is plastic, wax usually deforms under pressure without the application of heat. The chemical composition of waxes is complex; all of the products have relatively wide molecular weight profiles, with the functionality ranging from products which contain mainly normal alkanes to those which are mixtures of hydrocarbons and reactive functional species.
For centuries, the honeycomb of bees, ie, beeswax, was the material coin~ monly referred to as wax. Substances having typical wax characteristics have traditionally come from insects, eg, beeswax; from vegetables, eg, carnauba. and from animal,
eg, spermaceti, origins (1). Waxes from mineral and svnthe~ic Supplies have been developed both as substitutes for waxes from traditional Supplies and for new applications. Waxes from minerals and synthetic Supplies now surpass waxes from traditional Supplies in tonnage and commercial importance.
Waxes obtained from natural Supplies such as vegetables or insects are subject to weather conditions which may severely affect the stability of supply and price and, to a lesser extent, the consistency of the products. Waxes from minerals and synthetic Supplies are less susceptible to weather conditions, and thus have a more stable supply and price.
Insect and Animal Waxes
Beeswax. White [8012-89-3J and yellow [8006-40-4J beeswax has been known for over 2000 years, especially through its use in the fine arts (2). References to wax prior to the nineteenth century are probably to beeswax. Beeswax is secreted by bees and is used to construct the combs in which bees store their honey. The wax is harvested by removing the honey and melting the comb in boiling water; the melted product is then filtered and cast into cakes. The yellow beeswax cakes can be bleached with oxidizing agents to white beeswax, a product much favored in the cosmetic industry. Imports of beeswax into the United States for the years 1990-1995 are listed in Table 1. Historically, Brazil had long supplied the majority of beeswax to the United States, but now (ca 1997) other countries such as China, Thailand, and Canada supply the majority of the material imported into the
United States (3).
The composition of beeswax varies, depending on its geographic origin. The major components are esters of C30 and C32 alcohols with C16 acids, free C25 to C31 carboxylic acids, and C25 to C31 hydrocarbons (4). Beeswax typically has a melting point of 640C, a penetration (hardness) of 20 dmm at 250C and 76 dmm at 43.30C (ASTM D1321), a viscosity of 1470 mm2/s at 98.90C, an acid number of 20, and a saponification number of 84.
The U.S. Food and Drug Administration (FDA) has affirmed the status of beeswax as Generally Recognized as Safe (GRAS) (5) in Title 21 of the Code of Federal Regulations, Section 184.1973 (21 CFR 184.1973). The major use of beeswax is in the cosmetic industry, with smaller amounts used in pharmaceuticals and candle production.
Spermaceti. Spermaceti [8002-23-il is derived from the head oil of the perm whale. Owing to the present status of the sperm whale as an endangered species, however, the material is no longer an item of commerce and has been replaced by other natural and synthetic waxes.
Carnauba. The source of carnauba wax [8015-86-9] is the palm tree, whose wax-producing stands grow almost exclusively in the semiarid northeast section of Brazil. Camauba wax forms on the fronds of the palm, and is removed by cutting the fronds, drying, and mechanically removing the wax. Impurities are removed from the wax by melting and filtering or centrifuging. Wide fluctuations in price and availability have caused markets served by carnauba wax to seek replacements. Whereas there is no other single wax which combines all the properties of carnauba, suitable substitutes are available for most
applications. Imports of carnauba wax into the United States for the years 1990-1995 are listed in Table 1. Brazil supplies over 80% of the carnauba wax imported into the United States (3).
The major components of carnauba wax are aliphatic and aromatic esters of long-chain alcohols and acids, with smaller amounts of free fatty acids and alcohols, and resins. Carnauba wax is very hard, with a penetration of 2 dmm at 250C and only 3 dmm at 43.30C. Carnauba also has one of the higher melting points for the natural waxes at 840C, with a viscosity of 3960 mm2/s at 98.90C, an acid number of 8, and a saponification number of 80.
The hardness and high melting point, when combined with its ability to disperse pigments such as carbon black, allows Carnauba wax increasing use in the thermal printing inks. Carnauba is also widely used to gel organic solvents and oils, making the wax a valuable component of solvent and oil paste formulations. Carnauba polishes to a high gloss and thus is widely used as a polishing agent for items such as leather, candies, and pills. Other uses include cosmetics and investment casting applications (see COPPER ALLOYS, CAST COPPER ALLOYS). The FDA affirmed Carnauba as GRAS for certain food applications in 21 CFR 184.1978.
Candelilla. Candelilla wax [8006-44-8j is harvested from shrubs in the Mexican states of Coahuila and Chihuahua and, to a very small degree, in the Big Bend region of Texas in the United States (6). The entire mature plant is uprooted and immersed
in boiling water acidified with sulfuric acid. The wax floats to the surface and is filtered. Imports of candelilla wax into the United States for the years 1990-1995 are listed in Table 1. Mexico supplies over 90"( of the candelilla wax imported into the
United States (3).
The major components of candelilla wax are hydrocarbons, esters of long-chain alcohols and acids, long-chain alcohols, sterols, and neutral resins, and long-chain acids. Typically, candelilla wax has a melting point of 700C, a penetration of 3 dmm at 250C, an acid number of 14, and a saponification number of 55. Principal markets for candelilla include cosmetics, foods, and pharmaceuticals. The FDA affirmed Candelilla as GRAS for certain food applications in 21 CFR 184.1976.
Japan Wax. Japan wax [8001-39-6] is a fat and is derived from the berries of a small tree native to Japan and China cultivated for its wax. Japan wax is composed of triglycerides, primarily tripalmitin. Japan wax typically has a melting point of 530C, an acid number of 18, and a saponification number of 217. Principal markets include the formulation of candles, polishes, lubricants, and as an additive to thermoplastic resins. The product has some food-related applications.
Ouricury Wax. Ouricury wax [68917-70-4] is a brown wax obtained from the fronds of a palm tree which grows in Brazil. Ouricury is difficult to harvest, as it does not flake off the frond as does carnauba wax; rather, it must be scraped free. Ouricury is sometimes used as a replacement for carnauba in applications that do not require a light-colored wax.
Rice-Bran Wax. Rice-bran wax [8016-60-2] is extracted from crude rice-bran oil. It can be degummed, the fatty acid content reduced by solvent extraction, and bleached. The wax is primarily composed of esters of lignoceric acid ~43 wt %), behenic acid (16 wt %), and C22-C36 alcohols (28 wt %). Rice-bran wax may be used in some food applications under the regulations described in 21 CFR 172.890.
Jojoba. Jojoba oil [61789-91-1] is obtained from the seeds of the jojoba plant grown in semiarid regions of Costa Rica, Israel, Mexico, and the United States. The oil is made up of ca 80 wt % of esters of eicos- 1 1-enoic and docos- 13-enoic acids,
and eicos-11-en-1-ol, and docos-13-en-1-ol, ca 17 wt % of other liquid esters, with the balance being free alcohols, free acids, and steroids. Jojoba oil is used primarily in the formulation of cosmetics. Hydrogenated jojoba oil is a wax used in candles and other low volume specialty applications.
Castor Wax. Castor wax [8001-78-31 is catalytically hydrogenated castor bean oil. The wax has a melting point of 860C, acid number of 2, saponification number of 179, and an iodine number of 4. Castor wax is used primarily in the formulation of cosmetics. Derivatives of castor wax are used as surfactants and plastics additives.
Bayberry Wax. Bayberry wax [8038-77-5] is removed from the surface of the berry of the bayberry (myrtle) shrub by boiling the berries in water and skimming the wax from the surface of the water. The wax is green and made up primarily of lauric, myristic, and palmitic acid esters. The wax has a melting point of 45~C, an acid number of 15, a saponification number of 220, and an iodine number of 6. The wax has an aromatic odor and is used primarily in the manufacture of candles and other products where the distinctive odor is desirable.
Montan Wax. Montan wax [8002-53-7] is derived by solvent extraction of lignite (qv). The earliest production on a commercial scale was in Germany durmg the latter half of the nineteenth century, and Germany continues to supply the majority of the world's production of montan wax. Montan wax production at Amsdorf is part of a massive coal-mining operation from a continuous vein and raw material is expected to last for decades. Montan wax is also produced in the United States. Imports of montan wax into the United States for the years 1990-1995 are listed in Table 1. Germany supplies over 80% of the montan wax
imported into the United States (3).
The composition of montan wax depends on the material from which it is extracted, but all contain varying amounts of wax, resin, and asphalt. Black montan wax may be further processed to remove the resins and asphalt, ~ is known as refined montan wax. White montan wax has been reacted wj~ alcohols to form esters. The wax component of montan is a mixture of long. chain (C24-C30) esters (62-68 wt %), long-chain acids (22-26 wt %), and long. chain alcohols, ketones, and hydrocarbons (7-15 wt %). Crude montan wax fro~ Germany typically has a melting point of 800C, an acid number of 32, and a saponification number of 92.
The largest traditional use for montan waxes was as a component in on~ time hot-melt carbon-paper inks. With the decrease in the use of carbon-paper inks, uses for the refined grades have become predominant, mainly in the formulation of polishes and as plastics lubricants. The alcohol ester derivatives may be used as components of articles intended for use with foods as regulated by the FDA in 21 CFR 178.3770.
Peat Waxes. Peat waxes are much like montan waxes in that they contain three main components: a wax fraction, a resin fraction, and an asphalt fraction. The amount of asphalt in the total yield is influenced strongly by the solvent used in the extraction. Montan waxes contain ca 50 wt % more of the wax fraction than peat waxes, and correspondingly lower percentages of the resin and asphalt fractions. The wax fraction in peat wax is chemically similar to that of the wax fraction in montan wax.
Ozokerite and Ceresin Waxes. Ozokerite wax [OO1-75-O] was a product of Poland, Austria, and in the former USSR where it was mined. True ozokerite no longer seems to be an article of commerce, and has been replaced with blends of petroleum-derived paraffin and microcrystalline waxes. These blends are designed to meet the specific physical properties required by the application involved.
Ceresin wax [8001-75-0] originally was a refined and bleached ozokerite wax, but now is a paraffin wax of very narrow molecular weight distribution or blend of petroleum waxes.
Petroleum Waxes. Waxes derived from petroleum are hydrocarbons of three types: paraffin [64742-43-4] (clay-treated); semimicrocrystalline or intermediate; and microcrystalline [64742-42-31 (clay-treated). Semimicr~ crystalline waxes are not
generally marketed as such (7). Others include acid-treated, chemically neutralized, and hydrotreated; and paraffin and hydrocarbon waxes, untreated. The quality and quantity of the wax separated from the crude oil depends on the source of the crude oil and the degree of refining to which it has been subjected prior to wax separation. Petroleum waxes are produced in massive quantities throughout the world. Subject to the wax content in the crude, paraffin and, to a substantially lesser degree, microcrystalline wax are produced in almost all countries of the world that refine crude oil. Production capacity in the United
States and imports for the years 1990 to 1995 are listed in Table 2. Canada supplies over 50% of the petroleum wax imported into the United States (3).
A paraffin wax is a petroleum wax consisting principally of normal alkanes. Microcrystalline wax is a petroleum wax containing substantial proportions of branched and cyclic saturated hydrocarbons, in addition to normal alkanes.
Semimicrocrystalline wax contains more branched and cyclic compounds than paraffin wax, but less than microcrystalline. A classification system based on the refractive index of the wax and its congealing point as determined by ASTM D938 was developed (9).
Table 2. U.S. Production Capacity and Imports of Petroleum Wax
U.S Capacity, t
Value in U.S. $ per kg ($/kg).
Table 3. Typical Properties of Petroleum Waxes
flash point, closed cup, C
viscosity at 98.90C, mm-9/s
melting range, ~C
refractive index at 98.9~C
number average molecular weight
carbon atoms per molecule
ductilitylcrystallinity of solid wax
Friable to crystalline
Ductile-plastic to tough-brittle
Value is minimum.
Paraffin wax is macrocrystalline, brittle, and is composed of 40-90 wt % normal alkanes, with the remainder C18-C36 isoalkanes and cycloalkanes. Paraffin wax has little affinity for oil content: fully refined paraffin has less than 1 wt %; crude scale, 1-2 wt %, and slack [64742-61-61, above 2 wt %. Within these classes, the melting point of the wax determines the actual grade, with a range of about 46-71"C. Typical properties of petroleum waxes are listed in Table 3.
The separation of paraffin wax from crude oil occurs during distillation, as shown in Figure 1. The distillate is processed to remove oil to the degree desired through solvent extraction. It is then decolorized, usually by hydrogenation, but percolation
through bauxite is also used. Microcrystalline wax is produced either from the residual fraction of crude oil distillation or from crude oil tank bottoms 10). After deasphalting of the residual fraction, heavy lubricating oil is removed by solvent extraction. The
degree of solvent extraction is dictated by the economics of the lubrication oil market. The filtrate is crude petrolatum, a dark-colored, unctuous material containing oil and microcrystalline wax. Percentages of each may vary, but are usually about 40 wt % wax and 60 wt % oil. This material is then solvent-extracted for the wax. Because microcrystalline wax has great affinity for oil, the oil content of the wax is 1-4 wt %, depending on the grade of the wax. Unlike paraffin wax, oil is held tightly in the crystal lattice of the microcrystalline wax, and does not migrate to the surface. The microcrystalline waxes obtained from petrolatum's are generally known as plastic grades, with penetrations greater than 11 dmm at 25'C.
Crude oil contains high molecular weight fractions which are soluble at the high temperatures found in underground formations, but not very soluble at ambient conditions once the crude oil is produced. These high molecular weight fractions precipitate onto the walls and floors of storage tanks, and are known as crude oil tank bottoms. Crude oil tank bottoms are essentially crude Oil with very high wax contents and are processed as indicated in Figure 1. The microcrystalline waxes obtained from crude oil tank bottoms are generally known as hard grades, with penetrations less than 11 dmm at 250C.
The use of refined grades of petroleum waxes in some food applications is regulated by the FDA in 21 CFR 172.886 and 21 CFR 178.3710. The Bundesges undheitsamt (BGA) of Germany also has specifications for refined petroleum waxes used in food applications. Many other countries reference either the FDA or BGA specifications for their food regulations. Petroleum wax is widely used in chewing gum to modify the properties of the chewing gum base. The wide range of properties available help chewing gum base manufacturers formulate a broad variety of chewing gum, ranging from the traditional hard stick gum to the softer bubble gum. Petroleum wax can also be used as protective coatings for fruits, vegetables, and cheeses. Petroleum wax is outstanding as a cost-effective moisture and gas barrier, and food packaging applications are a major market for refined food-grade petroleum wax. Blends of paraffin and microcrystalline wax are used by themselves or in combination with other additives such as high molecular weight polyethylene and ethylene vinyl acetate copolymers to improve the performance of paper packaging such as paperboard boxes, paper containers, and flexible packaging.
Petroleum waxes are also widely used in other industrial applications. Paraffin waxes are added to rubber during compounding, and exude to the surface during curing, which helps protect the rubber from degradation resulting from ozone. Paraffin and other waxes can be added to plastics, especially poly(vinyl chloride) (PVC) as lubricants. Both paraffin and micro-crystalline waxes are widely used to help control the properties of hot-melt adhesives. Dispersions of microcrystalline are added to inks to improve slip and rub properties. Petroleum waxes are used in many consumer applications such Is cosmetics, polishes, and candles. Unrefined petroleum waxes are often used n fireplace logs.
Polyethylene Waxes. Low molecular weight (less than ca 10,000 Mn) polyethylenes [9002-88-41 having waxlike properties are made either by high pressure polymerization or low pressure (Zeigler-type catalysts) polymerization. All the products have the same basic structure, but the processes yield products h distinctly different properties. Some polyethylenes have fairly low densiowing to branching that occurs during the polymerization. Molecular weight distributions, expressed as the weight average molecular weight divided by the number average molecular weight, or polydispersity, also varies widely among the different processes, as does the range of molecular weights available. Annual production in the United States is estimated at 100,000-140,000 t.
Differences among the processes have a major impact on the use of the products. Products from a particular process or manufacturer may dominate one market, while products from a different process may be preferred in a different application. Major uses include hot-melt adhesives for applications requiring high temperature performance, additives to improve the
processing of plastics, slip and rub additives for inks and paints, and cosmetic applications.
Products used in food applications require regulatory approvals. Most polyethylenes are regulated by the FDA under the olefin polymer regulation, 21 CFR 177.1520. This regulation includes a maximum amount of hexane-soluble material with other requirements. The amount of material extracted by hexane is a function of molecular weight and branching. Polyethylenes in the 500-1200-molecular weight range are regulated by the FDA under the synthetic petroleum wax regulation, 21 CFR 172.888. In addition to molecular weight requirements, this regulation includes an absorbance test to verify the suitability of the product for
Some by-product polyethylene waxes have been recently introduced. The feedstock for these materials are mixtures of low molecular weight polyethylene fractions and solvent, generally hexane, produced in making polyethylene plastic resin. The solvent is stripped from the mixture, and the residual material offered as polyethylene wax. The products generally have a wider molecular weight distribution than the polyethylene waxes synthesized directly, and are offered to markets able to tolerate that characteristic. Some of the by-product polyethylene waxes are distilled under vacuum to obtain a narrower molecular weight distribution.
Several of the polymerization processes allow different functionality to be added to the backbone of the polymer, including copolymers of ethene, propene, hexene, vinyl acetate, and acrylic acid, with waxlike properties. Copolyniers of ethene with other olefins provide a method of extending the range of properties available. The addition of other olefins creates a branched polymer, which decreases the melting point and hardness, while increasing viscosity as compared to a linear polyethylene of the same molecular weight distribution. Longer branches created through the addition of hexene show a larger effect than those from propene. Copolymers with vinyl acetate and acrylic acid provide a method of introducing oxygen functionality. These products may be further reacted with metal salts to form ionomers.
In addition to copolymerization, polyethylenes terminated as ketones. alcohols, and carboxylic acids with molecular weights as high as 700 daltons are now available. The products offer the same chemical functionality as common fatty alcohols and acids,
but are higher melting and harder. Similar to the fatty alcohols and acids, derivatives such as ethoxylates, esters, and amides also are available as higher melting versions of the fatty derivatives.
Functional polyethylene waxes provide both the physical properties obtained by the high molecular weight polyethylene wax and the chemical properties of an oxidized product, or one derived from a fatty alcohol or acid. The functional groups improve adhesion to polar substrates, compatibility with polar materials, and dispersibility into water. Uses include additives for inks and coatings, pigment dispersions, plastics, cosmetics, toners, and adhesives.
Fischer-Tropsch Waxes. Polymethylene wax [8OO2-74-2] production is based on the Fischer-Tropsch synthesis, which is basically the polymerization of carbon monoxide under high pressure and over special catalysts to produce hydrocarbons (see FUELS, SYNTHETIC-LIQUID FUELS). Distillation is then used to separate the hydrocarbons into different products, including liquid fuels and waxes with melting points ranging from about 45-1060C. Currently the waxes are produced in large volumes in South Africa and Malaysia, with an estimated 12,000-14,000 t consumed in the United States in 1994. Uses are similar to those
for polyethylene waxes, including hot-melt adhesives and additives for inks and coatings.
Chemically Modified Waxes. Hydrocarbon waxes of the microcrystalline, polyethylene, and polymethylene classes are chemically modified to meet specific market needs. In the vast majority of cases, the first step is air oxidation of the wax with or
without catalysts (11). The product has an acid number usually no higher than 30 and a saponification number usually no lower than 25. An alternative step is the reaction of the wax with a polycarboxylic acid, eg, maleic, at high temperature (12). Through its carboxyl groups, the oxidized wax can be further modified in such reactions as saponification or esterification. Oxidized wax is easily emulsified in water through the use of surfactants or simple soaps, and is widely used in many coating and polish applications.
Substituted Amide Waxes. The product of fatty acid amidation has unique waxlike properties (13). Probably the most widely produced material is N,N'distearylethylenediamine [110-30-5], which has a melting point of ca 140'C, an acid number of ca 7, and a low melt viscosity. Because of its unusually high melting point and unique functionality, it is used in additive quantities to raise the apparent melting point of themoplastic resins and asphalts, as an internal-external lubricant in the compounding of a variety of thermoplastic resins, and as a processing aid for elastomers.
Polymerized a-Olefins. Some polymers of higher a-olefins, eg, C>20, have waxlike 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 a-olefin nionomers and polymerization conditions. Melting points for the products range rorn 540C to 740C, with number average molecular weights ca 2600-2800, and penetrations at 250C of 5-12 dmm. 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, without increasing the cloud point or viscosity. Other uses include mold release for polynrethane foams, additives for casting wax, and additives for
Most waxes are complex mixtures of molecules with different carbon lengths, structures, and functionality. Attempts to measure the exact chemical compositionl are extremely difficult, even for the vegetable waxes, which are based on a relatively few number of basic molecules. Products such as oxidized microcrys talline wax not only have a mixture of hydrocarbon lengths and types as starting materials, but also add complexity through the introduction of various types of carboxylic functionality onto
those hydrocarbons during the oxidation process.
Because of the difficulty in analysis of chemical composition, most of the routine test procedures on waxes are for the measurement of the physical proper-ties of the waxes and are used to compare the properties of waxes within a class. Some properties, such as acid number or saponification number, give insight into the chemical functionality of the product, and are widely used for products which contain carboxyl groups such as vegetable, montan, and oxidized waxes. Increasingly, instrumental methods such as gas chromatography (gc), gel permeation (also Imown as size exclusion) chromatography (gpc), refractive index (ri), differential scanning calorimetry (dsc), infrared spectroscopy (ir), and nuclear magnetic resonance (nmr) are being used to further characterize the products. Properties such as molecular weight distribution, degree of branching, degree of crystallinity, and functionality can be readily measured with these techniques.
Melting and Congealing Points. Selection of the proper melting point method depends upon the characteristics of the wax. Drop melting point (ASTM D127) is suitable for amorphous waxes, eg, microcrystallines, but is not reliable for higher viscosity synthetic waxes, for which ring-and-ball softening point (ASTM D36) should be used. Waxes whose time-temperature cooling curves exhibit plateaus, eg, paraffin wax, may be evaluated by ASTM D87. Open or closed capillary tubes are used to measure the melting point of many of the natural waxes. The congealing point (ASTM D938) is the temperature at which a melted wax ceases to flow, and is more consistent than melting points for some waxes.
Hardness (Penetration). The standard test for the hardness of waxes in industry is the penetration test (ASTM D1321). This test measures the depth in tenths of a millimeter that a needle of a certain configuration under a given weight penetrates the
surface of a wax at a given temperature. A series of penetrations measured at different temperatures, rather than at a single temperature, is preferred.
Color. On solidification of a wax and depending on factors such as the rate of cooling, the amount of occluded air, and surface finish, the color of solidified samples of the same wax may be different. For this reason, the color of most waxes is judged only while molten, although some commercial standards for certain waxes, eg, carnauba, are based on the color of the solid wax. The accurate measurement of color in light-colored, ie, amber to off-white to white, waxes is difficult but very important because of the additional processing costs required to achieve the light color. The two most widely used color standards providing numerical measurement are ASTM D1500, which is used to measure dark-brown to off-white color, and ASTM D156, which is used to measure off-white to pure white.
Oil Content. The production of petroleum waxes involves the removal of oil; therefore, the oil content (actually the percentage of oil and low molecular weight fractions) is one indication of the quality of the wax. Oil content is determined
(ASTM D721) as that percentage of the wax soluble in methyl ethyl ketone at -31.7 degrees C.
Viscosity. Although traditionally of little importance in the evaluation of vegetable and insect waxes, viscosity is an important test for mineral and synthetic waxes. One of the most frequently used tests, ASTM D88, is used to measure the time in seconds required for a specified quantity of wax at a specified temperature to flow by gravity through an orifice of specified dimensions. This viscosity is expressed in Saybolt Universal Seconds (SUS) at the temperature of the test. The SI unit for kinematic viscosity is mm2/s (=cSt).
Acid Number. The acid number (ASTM D1386) is the milligrams ofpotassium hydroxide necessary to neutralize one gram of wax, and indicates the amount of free carboxylic acid present. The test is widely used for vegetable and insect waxes, and
synthetic waxes containing carboxylic acid groups.
Saponification Number. The saponification number (ASTM D1387) is the milligrams of potassium hydroxide which react with one gram of wax under elevated temperatures, and indicates the amount of free carboxylic acid plus any ester materials
which may be saponified. Both the acid number and saponification numbers are generally provided to give an indication of the free carboxylic acid and ester content of vegetable and insect waxes, and synthetic waxes containing carboxylic acids and or esters.
Differential Scanning Calorimetry (dsc). The dsc has become widely used to characterize waxes. Under controlled heating and cooling rates, the amount of energy consumed or released is measured. Curves of heat flow vs temperature provide insight
into the thermal characteristics of a wax, including crystalline transitions such as solid-to-solid, solid-to-liquid, and liquid-to-solid. Common values obtained from the curves include the initial and ending temperatures for heat flow, and heat of fusion, expressed as joules per gram.
Gas Chromatography (gc). Gas chromatography has been used for many years, especially on the relatively simple structures of vegetable and insect waxes. Use of the gc for petroleum and synthetic waxes was limited by the maximum carbon number which could be eluted, and the number of isomers for each carbon number. Improvements in technology have allowed wider use of this technique, with columns and equipment available which can resolve carbon numbers up to C100. Good resolution can be obtained on products with generally only one type of structure, eg, paraffins with a high preponderance of primary alkanes. Products such as microcrystalline wax which contain several different branched isomers for each carbon number, plus some cyclic compounds, cannot be completely resolved, although useful information can still be obtained.
Gel Permeation Chromatography (gpc). The gpc (also known as size exclusion chromatography) is widely used to measure the molecular weight distribution for synthetic polyethylene waxes. Whereas gpc can not match the reesolution available in gc techniques, useful information regarding the molecular weight, and molecular weight distribution can be obtained for products with molecular weights too high for gas chromatography. The molecular weight is normally reported using the number average, Mn, or the weight average, Mw The ratio of the weight average to the number average is known as the polydispersity. Pd.
Infrared Spectroscopy (Ir). Infrared curves are used to identify the chemical functionality of waxes. Petroleum waxes with only hydrocarbon functionality show slight differences based on crystallinity, while vegetable and insect waxes contain hydrocarbons, carboxylic acids, alcohols, and esters. The ir curves are typically used in combination with other analytical methods such as dsc or gc/gpc to characterize waxes.
Nuclear Magnetic Resonance (nmr). The nmr analysis has been used in the polymer industry for some time to measure properties such as amount and type of branching, polymerized ethylene oxide content, and hydroxyl content. The same techniques are applicable to waxes, and are used for both characterization and quality control.
This information comes from the Kirk-Othmer Encyclopedia of Chemical Technology.
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