WAX AND THE COSMETIC CHEMIST particular purpose or function, and the use of suitable methods for analysis and technological evaluation as well as theoretical aspects of wax chemistry and physics. THE CONCEPT OF WAX During the past thirty years a considerable number of new types of synthetically produced waxes and related materials has been introduced necessitating a new approach to chemistry, technology and analytical evaluation of waxes. As a result the old-established concept and definition of the term "wax" have become more and more a hindrance to scientific and technological development and have, therefore, to be replaced. Until recently, sole emphasis was laid on the chemical composition of a commodity called wax, irrespective of whether it concerned a liquid, a semi- solid or a solid. Accordingly, sperm oil, for instance, was considered a wax, but paraffin wax, to give an example, a non-wax. These views have drastically changed, since it has been realised that the nature of wax, both scientifically and in its technological implications, can only be explained by a peculiar physical structure which is solely responsible for the great majority of industrial uses of waxes. Thus the somewhat wilfully introduced fat-chemical definition of wax can no longer be regarded as adequate or useful and has to be replaced by another one, based on con- sistency and applicability. In other words, certain specific, technological properties have become the definitive characteristics of "wax." From a chemical point of view waxes have only one feature in common, the chain-character of their building stones. The physical requirements concern optimum length of the chains and absence of cross-linkages between them. The optimum length of a chain depends largely on its chemical nature and structure in particular, the degree of polarity and branching. Elaborat- ing the physical nature of wax, it must be stated that waxes should no longer be regarded as mechanical mixtures of a number of chemical com- pounds, but as characteristic physical systems. It must be added that the latter depend to some extent, as already indicated above, on the type of wax concerned. The three main variables--length of chain, polarity and branch- ing--govern nature and properties of a particular substance. Chains below optimum length favour the formation of semi-solid, more or less fat-like masses, whilst much longer chains may lead to thermoplastics. A high degree of branching, particularly of relatively short chains, will, as a rule, represent oily or fatty materials, and in the case of very long chains, glasses. Location, length or size and nature of the side chains or branches are also of influence on the resulting structure and thus its properties. All waxes possess a certain degree of crystallinity, depending on the particular type. The crystallinity itself is related to the degree and nature of branching, in conjunction with the length and polarity of the chains. As 131

JOURNAL OF THE SOCIETY OF COSMETIC CHEMISTS far as equimolecular compounds• particularly alkanes, are concerned, melting-point and specific gravity decrease with increasing branching (of the same type). Polarity may lead to the formation of hydrogen and/or dipole bonds resulting in double or multiple molecules with correspondingly increased melting-points. Cross-linkages impede the "freedom" of the molecules (i.e., the mobility of the chains) and affect the crystallinity under certain conditions plastics may result. A high degree of two- or tri-dimensional cross-linking leads to masses which do no longer melt, but only soften. Reverting to the formation of systems, the degree of crystallinity will also depend on the width of chain- length-distribution and on the nature and the percentage of molecules of other types present. It is assumed that the "freedom" of the molecules is the principal requirement for a substance to produce gloss on slight buffing. The subject of specific systems characterisi. ng the different types of waxes is a rather complex one which, hitherto, has been almost completely ignored. Much has to be learned before it will be possible to make detailed statements nevertheless some general remarks can be offered as a guidance. Molecules of the same type but of different chain-length may form solid solutions (mixed crystals) as long as they fit the dominating crystal-unit without too much distortion, whereby substitutional or interstitional mixed-crystals will be formed. The conditions prevailing in the presence of molecules of different types are somewhat similar, but are also governed by the effects of polarity. Another important type of basic system is represented by eutectic mixtures. No doubt the actual systems represented by waxes are much more complicated. WAXES AS CHAIN-COMPOUNDS Another ne•v approach to waxes is based on the nature of the chains forming their building stones. The chains present in waxes can be grouped under four main and eight sub-headings--namely: 1. Non-polar, homogeneous chains: la. Straight chains (e.g. unbranched alkanes in paraffin waxes, microcrystalline waxes, etc.). 2a. Branched chains (e.g. alkanes carrying side-chains and/or naph- thenic or aromatic side-rings in microcrystalline waxes and/or ozokerites, to some extent also in paraffin waxes). 2. Polar, homogeneous chains: 2a. Straight chains (e.g., free fatty acids and free fatty alcohols in ester waxes free amines in aliphatic amides). 132