Natural and Synthetic Waxes E-Book

Ernst J. Krendlinger

• Herausgeber: Wiley-VCH GmbH
• Kategorie: Fachliteratur
• Sprache: Englisch

Seitenzahl: 1232

Veröffentlichungsjahr: 2022

Beschreibung

Natural and Synthetic Waxes

A compilation of all relevant information for the production and use of waxes in technical applications

Waxes are among the oldest organic substances used by mankind. Before all others, beeswax is known to have played a role in human history for thousands of years. But over time, many other wax species have been detected and exploited, and prepared for different utilizations. Today, we possess knowledge of a great variety of different types of waxes. Unfortunately, there still is no broadly accepted definition of a wax: for the relatively few wax chemists, waxes are usually defined by their physico-chemical properties more than by their chemical constitution. Waxes are not uniform but oligomeric and polymeric substances, not simply describable with a chemical formula.

The realm of waxes encompasses fully or partly natural, refined, partly or fully synthetic products, which can be extended by “wax-like” products which do not fulfil all definition criteria. Waxes are offered in different forms like pellets, granules, powders, or micropowders. Their number of technical applications runs into thousands. However, waxes in most cases are just adjuvants or additives, and with few exceptions like candles not known to a broader public. Only few publications over the last decades tried to present a more comprehensive overview of heir chemistry, chemical composition, their physical and analytical properties, their applications, and their sometimes astonishing history.

Based on personal experience and expertise, the authors intend to present an overview on the main classes of waxes, their origin, history, future, and potential fate. Economical aspects like market size and development, ecological impacts and challenges, and regulatory issues are also addressed.

Waxes are indispensable products in everyday life and in industry and technology, though mostly not even visible or distinguishable to experts. They deserve more than the role of a “poor cousin” in chemistry and technology.

Leseprobe

Natural and Synthetic Waxes

Origin, Production, Technology, and Applications

Ernst J. KrendlingerUwe H. Wolfmeier

Authors

Dr. Ernst J. Krendlinger

Dr. K

Wachs - INTELLIGENCE

Ulrichstraße 63

86316 Friedberg

Germany

Dr. Uwe H. Wolfmeier

Rosengäßchen 10c

89312 Günzburg

Germany

Cover Image: © istock, drasa

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Foreword

Waxes are chemical species used by millions of people every day. However, in most cases, they have no idea where they use waxes in their daily life. They may know them from shoe and car polish, candles, or as addition to outdoor clothing. The term “beeswax” is known to most people, and even in scientific literature, sometimes this is taken as a synonym for all waxes. The connotation of wax is ambiguous, however. In Psalm 68 of the Holy Bible, we read: “As wax melteth before the fire, so let the wicked perish at the presence of God.”

Wax is perishable, can be easily melted, burnt, degraded, or destroyed. But mankind has been collecting, harvesting, preparing, using, and applying waxes since the earliest times of human history, and still continues to do so. The ranking of waxes has been fluctuating between extremes like “as valuable as gold” and “cheap auxiliary materials.” Over centuries, the economic importance and social valuation changed considerably, with the highs and lows of production, applications, trade volume, and reputation with consumers.

So why did wax, unlike many other substances, never attract a greater number of scientists? Chemists seem to love clearly defined molecules, rather than complex mixtures of various components. Natural as well as synthetic waxes are not uniform products; their collection, mining, refining, or preparation can be as complex as their analytical determination. Among the thousands of professorships in organic chemistry, there is hardly anyone – probably none – fully dedicated to waxes. And only a limited number of review articles and textbooks are dedicated to the “whole world of waxes”: we may quote the early compilation prepared by H. Bennet in 1947, which covered commercial “natural and synthetic” waxes. In 1956, the first really comprehensive book on all kinds of waxes was published by Albin H. Warth (1885–1973), at that time the first “encyclopedia of waxes.”

In commemoration of this deserving author, we repeat his statement from 1956:

The literature on the subject of waxes is abundant, but widely scattered. A number of textbooks on the subject of oils, fats, and waxes do exist; these, however, devote but a few pages to waxes.

If you look at the modern textbooks today, even more than 60 years later, you realize that Warth could have written those lines today. Waxes, in chemical literature, play a niche role. Yes, there have been two other review papers on waxes: R. Bull's extensive work on waxes, published by the former Hoechst AG company – however, this “handbook” is aimed at experts and is difficult to get access to. In 2015, Krendlinger published an updated review in the Ullmann's Encyclopedia of Industrial Chemistry, still addressed to readers with some expertise in waxes but much less specific and more open to the general scientific community. Other books, papers, and reviews dealing with waxes usually focus on specific, not general, aspects of this class of materials.

In contrast to this “step‐motherly” interest of science in waxes, their technical, industrial, and commercial importance is still quite high. This interest led the authors to prepare a new book on waxes in the year 2018.

Their focus is a bit different from the aforementioned publications on waxes. Albin H. Warth's book aimed at “bringing together and collecting material,” and not so much at offering background information on the genesis of waxes, their role in everyday life, or their extreme variety in uses. Despite its merits, it is “out of date” in many aspects today.

That is why the aim of the authors, E. Krendlinger and U. Wolfmeier, is to present an updated overview about the fascinating world of waxes, their origin, their history, structure, use, and possible developments in the future. As a matter of fact, their selection is absolutely subjective, based on their experience in industry, in different companies, starting with learning about waxes in a plant site of the former German Hoechst AG, Gersthofen. In the twentieth century some experts called it the “Mecca of Waxes,” because of its broad expertise on all kinds of waxes, irrespective of whether they had ever been produced or marketed by Hoechst or its successors. The starting point had been montan wax, a story in itself (see the corresponding Chapter 10).

This book is divided into two parts: based on the extremely voluminous literature on waxes, we decided to split this publication into two volumes: beginning with natural waxes, to be followed at a later time by synthetic waxes – a somewhat arbitrary but reasonable determination.

Here are the standard works and publications that we have used as basic sources for our present book on waxes.

Selected Standard Works and Publications:

Warth, A.H. (1956).

The Chemistry and Technology of Waxes

, 2e. New York: Reinhold Publishing Co.

Bennett, H. (1944).

Commercial Waxes: Natural and Synthetic

. Brooklyn, NY: Chemical Publishing.

Kolattukudy, P.E. (1976).

Chemistry and Biochemistry of Natural Waxes

. Amsterdam/Oxford/New York: Elsevier Scientific Pub. Co.

Hamilton, R.J. (1995).

Waxes: Chemistry, Molecular Biology and Functions

. Oily Press Lipid Library Series, C. Leray (ed.) “Waxes”, Kirk-Othmer Encyclopedia of Chemical Technology. New Jersey, 2000/2006.

NIIR Board of Consultants & Engineers (2011).

The Complete Technology Book on Wax and Polishes (Reprint)

, Delhi, Asia Pacific Business Press Inc.

Büll, R. (1977).

Das grosse Buch vom Wachs. Geschichte Kultur Technik. Hoechster Beiträge zur Kenntnis der Wachse

. München, licensed edition [“The Great Book of Waxes”, printed only in German; probably the most comprehensive survey on all kinds of waxes, with the best overview on history of waxes; partially outdated].

Krendlinger, E., Wolfmeier, U., Schmidt, H., et al. Ullmann Encyclopedia of Industrial Chemistry: “Waxes”. Revised 26 November 2015.

Part INatural Waxes

1Introduction

1.1 General Survey of Waxes

Since I nor wax nor honey can bring home,

I quickly were dissolved from my hive,

To give some labourers room.

Source: William Shakespeare, “All's Well That Ends Well,” King of France, I,2.

Waxes, in the broadest sense of their definition, have been playing a great role in history, science, and technical application. So, first we would like to address some of the most relevant kinds and uses of waxes of in the past millennia, starting with the first known touch of humanity with these very special materials.

But before all, what are waxes? Probably you may think of beeswax, of candles, or of polish – all still relevant but representing only a very small selection out of dozens of kinds of waxes, and more than 2000 known uses of waxes. Indeed, until the early nineteenth century, “wax” was a synonym for beeswax only. With the advent of chemical analysis, beeswax was identified with several different components. Then more and more natural and later also synthetic substances with similar properties were classified as waxes – see below.

Nevertheless, it makes sense to first set the focus on beeswax and closely related substances, as beeswax may be regarded as the “queen of waxes” throughout human history.

1.2 Definitions of Waxes

Wax is a generic term for a range of natural or synthetic products. For convenience, the range can be roughly subdivided as follows:

Natural waxes: plant, animal, etc.

Modified natural waxes

Fully and partially synthetic waxes

Mineral hydrocarbon waxes

Petroleum waxes

Waxes today are usually defined by their characteristic properties (see also International Customs Tariff, Harmonized System HS 3404), and less so, or not, by their chemical composition.

Probably the most conclusive definition has been drawn up – in Europe – by the “Deutsche Gesellschaft für Fettwissenschaft” (DGF, German Association for Fat Science).

This was first established in 1957 and – slightly modified – confirmed in 1974 [1]. In the modified form, it entered the customs tariff of the European Union [2, 3].

According to this definition,

waxes should have a drop (or melting) point (mp) >40 °C;

their melt viscosity must not exceed 10 000 mPa s at 10 °C above the drop point;

they should be polishable under slight pressure and have a strongly temperature‐dependent consistency and solubility;

at 20 °C they must be kneadable or hard to brittle, coarse to finely crystalline, transparent to opaque, but not glassy, or highly viscous or liquid;

above 40 °C they should melt without decomposition;

above the

melting point

(

mp

) the viscosity should exhibit a strongly negative temperature dependence and the liquid should not tend to stringiness;

waxes should normally melt between c. 50 and 90 °C (in exceptional cases up to 200 °C);

waxes generally burn with a sooting flame after ignition;

waxes can form pastes or gels and are poor conductors of heat and electricity (i.e. they are thermal and electrical insulators).

All substances that differ in more than one point from these items are not 100% waxes if this quite strict definition is applied; however, there are borderline cases.

Other attempts to define waxes have been made and published by, e.g. the European Wax Federation (EWF: see their website):

solid at 30 °C, varying in consistency from soft and plastic to brittle and hard;

as solids as coarse to finely crystalline, transparent to opaque, but not glass‐like;

have relatively low viscosity slightly above the melting point;

melt above c. 40 °C without decomposition;

consistency and solubility are highly temperature dependent;

buffable under slight pressure;

burn with yellow flame and can form pastes or gels when dispersed in solvents;

exhibit low thermal and electrical conductivity.

With this broader definition, more substances have been classified as “wax” or at least “wax‐like.” From experience, we learnt that an exact definition of wax turned out to be unattainable, and some disputes are ongoing. We should accept that waxes cannot, in any case, be precisely separated from related species such as oils, fatty acids, or plastics.

An overview of the most relevant waxes is given below. It may demonstrate the broad variety of this fascinating organic material.

1.2.1 Natural Recent Waxes

Natural waxes have either vegetable or animal origin. The predominant, and perhaps the best known wax of animal origin is [4]

beeswax (EU Marketing Standard E 901: see EU regulation 2016/673, April 2016)

Important representatives of vegetable origin are

carnaúba (E 903; from carnaúba palm tree: Cera Carnaúba)

candelilla (Spanish: “little candle”; E 902); plant wax from candelilla scrub

sugarcane wax (from sugarcane grass).

1.2.2 Mineral Hydrocarbon Waxes

Mineral hydrocarbon waxes are mostly mined and their application importance is continuously declining. There are two main types:

Montan wax – manufactured by solvent extraction of Oligocene lignite;

Ozokerite (naturally occurring earth wax).

1.2.3 Petroleum Waxes

Petroleum waxes are hydrocarbons derived from petroleum. There are four main types:

slack wax – unextracted wax derived from dewaxing distillate lube oil streams

paraffin – deoiled slack wax consisting predominantly of straight chain alkanes

microcrystalline – branched and cyclic alkanes from deoiling residual bright stock lube oil stream

petrolatum – bright stock deoiled residual lube oil or blends of oils and waxes – petroleum jellies

Remark: Although petroleum waxes are based on natural resources, they are not covered in Part I of this volume dealing with natural waxes: in their structure, they are more similar to fully synthetic waxes.

1.2.4 Fully Synthetic Waxes

For about a hundred years, waxes can be produced synthetically. We distinguish between two main types:

Polyolefin waxes

Fischer–Tropsch wax.

1.3 Brief History of Waxes

Beeswax marks the beginning of the use of any kind of wax by humans. According to recent scientific research, bees – they obviously existed already in the early Cretaceous period – started to dust flowering plants about 110 millions of years ago, long before man entered the world. We dedicate a few pages to the history of the use and application of beeswax.

Only since about 10, 000 BC, at the beginning of the Holocene era, beeswax has been verifiably collected by humans from bees' hives [5]. It is assumed that the home of bees is the present Indian subcontinent. In addition, they were also located in a narrow zone from the east to the west – running from China through Tibet: the Himalayas, Afghanistan, Persia, the northern part of the Arab States, Syria, and Asia Minor. The Indo‐European peoples collected honey and wax from wild bees that lived in the natural caves of forest trees.

We credit the first evidence about beeswax – probably the only wax being used all the time before – to the Egyptians, some 7000 years before the present. So, to the best of our knowledge Ancient Egypt may be considered as the origin of beekeeping. The first written records in hieroglyphs originate from the Fifth Dynasty of the Old Kingdom (2494–2345 BC). Earthenware pots were provided as beehives.

As to the European proof of early use of waxes, we may refer to cave paintings in Spain dating from the Mesolithic period (10.000–5.000 BC). The painting of a female honey hunter harvesting honey and wax from a bee's nest in a tree was discovered in one of the Cuevas de la Araña (Bicorp, province of Valencia) [6]. The anonymous artist created the first documented encounter of a human being with a wild beehive, beautifully colored in red on a rock.

Whether the people of the Mesolithic period really used the wax and for what purpose it was used remain speculative as can be seen and interpreted from Figure 1.1. But what seems to be clear is that the painting shows a woman who dares to approach the beehive on the rock wall.

Figure 1.1 Woman gathering honey; watercolor copy by F. Benitez Mellado of a Mesolithic (c. 6000 BC) painting in the Cueva de la Arana, near Bicorp, Spain; in the Museum of Prehistory, Valencia, Spain.

Traceable evidence for the use of beeswax has recently been published by Jones et al. [7] for the fourth and fifth millennium BC.

It makes sense to go back to Old Egypt for a moment, because the application of wax became more and more sophisticated at that age, and this is undoubtedly proved by archeological findings, scientific research, and later, written documents.

1.3.1 Waxes Used by Ancient Egyptians

The word “wax” (beeswax) is called “mum” in Old Coptic, most certainly the latest stage of the Egyptian language. Since “mum” was a basic material for the mummification process, it may sound reasonable that the word “mummification” originally just meant “preserved in wax.”

The procedure of mummification was quite complex, long‐lasting, and thus expensive. Recent chemical analysis [8] provided an astonishingly broad variety of individual ingredients. The ancient Egyptians discovered already 6000–7000 years ago that beeswax exhibits an antibacterial effect: therefore, it was essential to safeguard the durability of mummies. The chemicals required for mummification were based on natural resources, however rare, exclusive, and expensive. That is why only the “upper class” – like members of the Pharaoh's court, High Priests, etc. – were subjected to mummification after death.

1.3.1.1 The Mummification Process

Here we step into some details of mummification, because some principles of the methods of wax refining and application that still exist were already being practiced at that time. Beeswax intended for use in the mummification process had to be bleached before use. The Egyptians did not have access to “modern” chemicals applicable as bleaching agents such as chromic acid, hydrogen peroxide, or mixtures of nitric acid and hydrochloric acid. In contrast to the present, they just made use of the influence of the sun and moon to serve this process.

Indeed, bleaching beeswax can be technically achieved just by sunlight. However, the Egyptians also considered the position of the moon, planets, and stars: they strictly adhered to astronomy and astrology. As a result, the mummification ceremony was restricted to very limited hours. Thus, the bleaching of wax – “mum” – was more of a ritual act than just manual work in Old Egypt. It meant a form of conjunction with the Egyptian Sun God Ra.

It is plausible that the Egyptians transformed the originally dark yellow to brown beeswax by bleaching into a highly refined substance, becoming bright at the end. They believed that this process could only be performed with the support of Divine power.

As we know, the “holy bleached wax” prevented a bacterial infection of the dried bodies of mummies for a long time – in many cases until the present. The Egyptians did not rely on the sun, moon, and stars alone when preparing waxes, not only for mummification but also for other uses: they had already gained some experience in several other chemical substances of natural origin. Cox [9] examined a wig from the British Museum, which dates from the fourteenth century BC. He noted that unbleached beeswax was mixed with a special resin. This mixture of wax and resin was probably used to make wigs handsome and looking more brilliant. So, waxes may have served among the first aids of coiffeurs!

Bleaching wax stood for progress in chemical knowledge, but Egyptians were already more capable: to produce beeswax dispersions: in chemistry, a dispersion means a system in which particles – formed by wax – are dispersed in a continuous phase of different composition, usually a liquid. This dispersion‐making technique is being widely used to date, for many different purposes such as paints, glues, sun creams, lotions, etc. For the Egyptians, however, preparing dispersions was a very laborious issue, as anything had to be performed manually, without the assistance of modern technology.

1.3.1.2 Punic Wax

What are “Punic waxes,” and why have they been important?

Punic wax – or cera punica – is a beeswax soap of paste‐like consistency. The term “Punic” is equivalent to “Carthagian,” and the Punics were also known as Carthagians.

[For the interested but nonhistorian reader: the Punic Wars, a series of three wars, were fought between Rome and Carthago from 264 to 146 BC; the famous Carthaginian general Hannibal crossed the Alps, won the famous battle of encirclement of Cannae, but in the end Carthago lost against the Romans and Hannibal lost his life.]

When wax is treated with a caustic soda, it results in a water‐soluble soap. Saponification is not always just an easy procedure, at least not for people living a long time ago.

The numerous recipes and instructions for the preparation and processing of Punic Wax are somewhat mysterious: faith and ritual ceremonies played a great role. Egyptians believed that only during certain full moon phases the sea water would contain higher concentrations of sodium chloride (NaCl) and other salts necessary for the production of Punic Wax.

[Surprisingly, the salt content of water can depend on the moon phases, e.g. in zones where river water meets sea water. This is due to the different water layers near the surface and at depth.]

In short, to achieve chemical saponification wax had to be bleached with the aid of the sun and the moon, in combination with proper planetary alignments, by cooking with mineral soda, and heating with potash and other unknown, secret ingredients.

Since beeswax darkens rapidly in melted form through oxidation, the process of bleaching and saponification had to be interrupted and repeated several times. This is the standard procedure for wax saponification to date: darkening of beeswax dispersions can be counteracted by interrupting the process, intermediate cooling, and addition of hydrogen peroxide (H2O2).

Exact formulations of Egyptian Punic Wax are unknown, because the priests in ancient Egypt kept their mysteries secret and took them to their graves. Neither the recipes nor the ingredients or procedures of the priests can be identified today; there are too many unknown variables.

The continual development of Punic wax into modified and, at the end, completely new products has taken several thousand years. By adding and mixing wax with rubber, mastics, isinglass, egg, fig milk, turpentine oil, olive oil, walnut oil, and others, the properties of the resulting product could be changed dramatically. Experts could adapt their formulations to many different purposes.

Punic wax, in its water‐soluble form, could be used, e.g. as the basis for cosmetic applications. Another famous application is called encaustic, the art or process of encaustic painting: this means decoration of, e.g. ceramics by burning in colors as an inlay, especially using colored clays or pigments mixed with hot (Punic) wax. To prepare color pastes, people had to crush and grind the available pigments into very small particles, directly before use. Among the pigments or colorants were purple, anchusa (red), azurite, melinum, orpiment, abianum, malachite, cinnabar, earthy, tree bark, papyrus ash (black), heavy metal oxides such as cadmium (yellow) and lead oxide (white), or cadmium selenide (red). Some of these pigments are highly toxic and certainly left users with serious illnesses.

The chemical base for the use of waxes for colorant preparations is their binding power for pigments. On reliefs, stelae, etc. crafted before 3000 BC, we can still identify the waxes using analytical chemistry and determine the exact age using the radiocarbon method [10, 11]. It appears quite remarkable that the chemical composition and structure of beeswax, with its major components aliphatic hydrocarbons, acids, and alcohols, remain nearly unchanged over time.

In ancient Egypt, beeswax was already used in 3000 BC as a binding agent for pigments. This is seen in reliefs and stelae from this period [6, 7]. And the beeswax, even after all this time, did not change its original structure. This shows that aliphatic hydrocarbons, aliphatic acids, and aliphatic alcohols in beeswaxes guaranteed an almost infinite shelf life.

This is probably one of the most impressive examples of how long a color, protected by perfectly purified beeswax (the Punic wax), can resist the external environmental influences without changing itself. Visitors to the Egyptian “Valley of the Kings” are usually overwhelmed by the brilliance of colors of thousands of years of age.

1.3.1.3 Nefertiti

Nefertiti, Egyptian “Nfr.t‐jy.tj,” originally pronounced approximately “Nafteta” (in German: Nofretete) (c. 1370 to c. 1330 BC) [12], was an Egyptian queen and the Great Royal Wife (chief consort) of Akhenaten (German: Echnaton), an Egyptian Pharaoh (Figure 1.2).

Figure 1.2 Fund journal card from the bust of Nefertiti – Egyptian Museum, Berlin.

In January 1925, Prof. Rathgen realized that the pupil of the limestone bust of Nefertiti is a black disk of wax (beeswax with carbon black).

By using Punic wax as a base for the makeup of the bust of Nefertiti, which is exhibited in the Egyptian Museum of Berlin, the Egyptians preserved this beautiful image forever. The pigments for paintings were bonded in Punic wax, and subsequently, the bust was covered with an additional layer of Punic wax. Tulloch [13], when investigating the bust, found out that the makeup of the bust of Nefertiti was a mixture of beeswax with natural gum and resins. Stierlin [14] describes his first impression of the bust in his excavation diary with the note: “Colors as just launched. Work is quite excellent. Describe useless view. […] Every other word is superfluous.”

To be honest, there is still some doubt if the Nefertiti bust is a fake, a forgery [16]. Wax, which can be examined for its age using the C14 method, could help eliminate doubts.

Around 1920, the chemist Friedrich Rathgen had already drawn a sample, which survived in an old bag in the museum until its age was finally determined. Experts concluded that the material is probably more than 3300 years old. One may or may not find this proof convincing.

However, the material for analysis was not taken directly from the eye of the bust, where the wax had most probably been applied: this would be impossible today for reasons of conservation.

For the ancient Egyptians, Punic wax was not only processed locally but also traded and exported. Phoenician traders distributed this precious product over the entire Mediterranean region. All know‐how of manufacture was kept as a secret. In the famous Edfu Temple of Horus [a Falcon deity; temple built in 237 BC] numerous recipes for cosmetics can still be deciphered, engraved on the walls in hieroglyphs (Figure 1.3).

[Anyone deeply interested in the medical and cosmetic treatments in ancient Egypt is referred to the so‐called “Ebers Papyrus,” written in hieroglyphics [17]. It is currently kept in the library of the University of Leipzig in Germany.]

Figure 1.3 Case presentation “Tumor against the deity Xenus.”

Source: Public domain, https://commons.wikimedia.org/w/index.php?curid=1504673.

1.3.2 Greeks, Romans, and Waxes

1.3.2.1 Bronze Casting

The Greeks and (later) the Romans are known to have adopted many cultural achievements from other people. No wonder that they especially admired Egyptian arts and techniques. Among other items, they further developed the refinement and use of beeswax.

With respect to the head of a Greek bronze statue from the fifth century BC, Farnsworth [15] describes another substantial advance in the use of beeswax. After mixing with quicklime (unslaked calcium carbonate), the mixture was converted into a hard cement‐like mass. This could be processed and used as a casting mold.

1.3.2.2 Wax Tablets in Ancient Times

When today's people hear about “tablet” they think of “tablet computers.” However, “tablets” are much older (Figure 1.4).

Wax tablets have been found in various forms, ranging from a single slab of wood with waxen surface to a 10 or more‐paged book.