Should your paraffin be polymer free?
Paraffin wax is a mixture of straight chain hydrocarbons. Most manufacturers are adding plastic polymer resins to their paraffin wax. This hardens the tissue. Polymers were added to paraffins many years ago in response to insufficient infiltration in open processors, due to xylenes and alcohols absorbing water from the atmosphere. Insufficient infiltration causes “mushy” tissues and plastic polymers harden the block.
Improvements in tissue processors have significantly reduced water contamination in xylenes and alcohols. Most modern processors provide reagent management capabilities to keep reagents pure.
Benefits of medite pure™ paraffin:
- Tissues cut like butter
- No need to mix paraffin when polymers sink to the bottom
- No white precipitate polymer clumps in your embedding center
- Polymer free paraffin is excellent for both infiltration and embedding
Translucent color makes small biopsies easy to embed
Definition of wax: Waxes are organic substances that are solid at room temperature but become free-flowing liquids at slightly higher temperatures.
The chemical composition of waxes is complex, but normal alkanes are always present in high proportion, and molecular weight profiles tend to be wide. The main commercial source of wax is crude petroleum, but not all crude oil refiners produce wax. “Mineral” wax can also be produced from lignite, plants, animals and even insects produce materials sold in commerce as “wax.”
Bees wax
has been traded for over 2000 years; references to “wax” before the 19th century typically meant beeswax. Yellow beeswax is secreted by bees to build honeycombs; the empty comb is melted in boiling water to recover the wax. Yellow beeswax can be bleached with oxidizing agents to white beeswax, a product favored in the cosmetic industry. The composition of beeswax varies widely with geography and the diet of the bees forming the combs, but typical components are C25-C31 hydrocarbons, esters of C30 -C32 alcohols with C16 acids and free C25 – C31 carboxylic acids.
Other Animal bases waxes
include lanolin from the wool of sheep, and ambergris, produced in the intestines of sperm whales. Another example of animal waxes that have been traded in the past is spermaceti, derived from the head oil of the sperm whale. Of course, the endangered status of the whale has stopped trading in this product and resulted in the development of synthetic substitutes. One of the most enduring qualities of the wax business has been the ability to improvise and develop substitutes in the face of supply disruptions.
Carnauba wax
is recovered from a variety of palm tree which grows almost exclusively in northeastern Brazil. Carnauba wax forms on the fronds of the trees and is recovered by cutting and drying the fronds, then mechanically removing the wax. Impurities are removed from the wax by melting and filtering or centrifuging. Carnauba wax is distinguished by its hardness and high melt point, combined with an ability to disperse pigments such as carbon black, properties 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.
Candellia wax
is harvested from shrubs grown in the Mexican states of Coahuila and Chihuahua and in Texas. The entire mature plant is uprooted and immersed in boiling water acidified with sulfuric acid; the wax floats to the surface for recovery. Principal markets for candelilla wax include cosmetics, food and pharmaceuticals.
Other vegtable based waxes
include Japan wax, produced on the berries of a small tree native to Japan and China; Ouricury wax, obtained from the fronds of another palm tree growing in Brazil; Rice-bran wax, extracted from crude rice bran; and Jojoba, obtained from the seeds of the jojoba plant grown in parts of Costa Rica, Israel, Mexico and the United States.
Montan wax
is derived by solvent extraction of lignite. The earliest production of montan wax on a commercial scale was in Germany during the latter half of the nineteenth century, and Germany continues to lead the world in production of montan wax; some montan wax is produced in the United States from the Ione lignite bed in California. The composition of montan wax varies geographically with production, but includes varying amounts of wax, resin and asphalt. The largest traditional use for Montan wax is in the formulation of carbon paper inks. The decrease in use of carbon paper resulted in montan wax being further refined for use in the formulation of polishes and as plastics lubricants. Montan wax is hard and brittle and has a high melt point; its properties are similar to those of natural plant waxes such as carnauba, which it can replace.
Other mineral waxes
include peat waxes, ozokerite and ceresin waxes. Peat waxes are similar to montan waxes in that they contain wax, resin and asphalt, but montan waxes contain 50% more wax in proportion to peat waxes. Ozokerite wax was a product of Poland, Austria and the former USSR where it was mined. True ozokerite is no longer produced but has been replaced with blends of petroleum-derived paraffin and micro-crystalline waxes designed to meet specific applications once filled by ozokerite. Ceresin wax originally was a refined and bleached ozokerite wax, but now is a paraffin wax of very narrow molecular weight distribution. Once again we see the adaptability of the wax business – as supplies of these limited minerals have declined, innovators have developed ways to replace the functionality of natural materials by modifying other waxes; this is a trend that continues today.
Most of the waxes described so far can be characterized by a higher degree of difficulty required to recover and purify them in significant quantity. Waxes derived from petroleum are much easier to recover, and offer a wide range of physical properties that can often be tailored by refining processes. Most producers offer two distinct types of petroleum waxes:paraffins distinguished by large, well formed crystals and microcrystalline , higher melting waxes with small, irregular crystals. Some producers also sell “intermediate” wax, the boiling range cut where the transition in crystal size and structure occurs. Petroleum wax producers also characterize wax by degree of refinement: fully refined paraffin has oil content generally less than .5%, and fully-refined micro-crystalline less than 1.5%; “slack wax” – precursors to the fully refined versions in either case would have oil content above 2 and as high as 35% by weight. Paraffin wax produced from petroleum is essentially a pure mixture of normal and iso-alkanes without the esters, acids, etc. found in the animal and vegetable-based waxes. microcrystalline wax contains substantial proportions of branched and cyclic saturated hydrocarbons in addition to normal alkanes.
Synthetic waxes have entered the wax market in the past 50 years. Polyethylene waxes are low molecular weight polyethylenes (less than 10,000 Mn) having wax-like properties made by either high-pressure or low-pressure (Zeigler-type catalyst) polymerization. All such waxes have the same basic structure, but the various production processes yield products with distinctly different properties, and these have a major impact on the use of products. Products from one manufacturer may satisfy one particular application, while product from a similar process will not work well at all. Major uses include hot-melt adhesives for applications requiring high-temperature performance, additives to improve the processing of plastics, and slip and rub additives for inks, paints and cosmetics.
FT wax is a polyethylene wax produced by the polymerization of carbon monoxide under high pressure; this is the technology used in the emerging 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 – 106ºC. Currently FT waxes are commercially produced in large volumes in South Africa and Malaysia, with over 20 k MT consumed in the US in ’02. Uses are similar to those for polyethylene waxes including hot-melt adhesives and additives for inks and coatings.
|
Product |
Source |
Melt Pt/Pen 25C |
Main Uses |
|
Beeswax |
Honeycombs |
64c 20dmm |
Cosmetics |
|
Carnuba |
Palm Tree |
84 2 |
Inks, Polishes |
|
Candelilla |
Bush |
70 3 |
Cosmetics, Foods |
|
Ceresin |
Lignite |
65 60 |
Cosmetics |
|
Japan Wax |
Bush |
50 30 |
Candles, Pencils |
|
Montan |
Lignite |
80 10 |
Carbon paper ink |
|
Ouricury |
Palm Tree |
85 2 |
Inks, Polishes |
|
Ozokerite |
Mined East Europe |
68-96 9-15 |
Cosmetics |
|
Petroleum — Paraffin |
Crude Oil |
46-68 10-20 |
Various |
|
Petroleum — microcrystalline |
Crude Oil |
60-93 2-10 |
Various |
|
Polyethylene |
Synthesis |
85-140 3 |
Various |
|
Fischer Tropsch waxes |
Synthesis |
54-72 10-41 |
Various |
Chemically modified waxes: Microcrystalline hydrocarbon and Polyethylene waxes may be modified to meet specific market needs, most often to match performance characteristics of animal or vegetable waxes. In most cases, the first step is air oxidation of the wax with or without catalysts An alternative approach is to react the wax with a carboxylic acid at high temperature. Oxidized wax can be further modified by saponification or esterification at the carboxyl sites. 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. Petroleum waxes modified in this way can compete in specific areas with vegetable and insect 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 – 74C. 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, and additive for leather treating.
Wax is truly a versatile product whose unique properties pave the way for a myriad of end uses. New uses for wax have been found time and again, and the wax market today is as vital as ever.
