Waxes: Colloidal properties and systems

Abstract

AbstractColloidal systems formed by waxes with nonpolar organic solvents, in particular white spirit are discussed. The four principal wax/solvent systems, which are semisolid at room temperature, are termed paste, optimum paste, gel, and mixture‐mass. In their customary use, the terms paste and gel have slightly different meanings. Wax paste represents a crystalline, two‐phase system, a solid space lattice structure of paraffin wax crystals (mechanically not very strong), the interstices of which are filled with saturated paraffin wax solution (called free solution, because it can be separated by mechanical pressure). It is characterized by opacity, poor solvent binding, and low solvent absorption (i.e., low mass hardness). During solvent evaporation, which is of a high rate, it exhibits blooming, creeping, and drying‐up phenomena (subsiding from top to bottom in the evaporation vessel); the residue is a carpet of wax crystals. The paraffin wax possesses no swelling capacity. Wax gel may be regarded almost a one‐phase system, consisting of particles of colloidal dimensions. There is no (rigid) structure and no free solution. (Genuine ozokerite and high‐grade microcrystalline wax, both refined, are insoluble in white spirit at room temperature, but exhibit limited swelling.) The gel may be described as a multitude of swollen particles of microcrystalline wax or of most minute droplets of solvent isolated by films of wax. The gel has translucency, excellent solvent binding, and low solvent absorption (due to the lack of a rigid structure). On evaporation, which proceeds at a very high rate, it exhibits shrinking (top‐to‐bottom and towards the mass‐center), lack of blooming, and creeping; the residue is a nonporous, shrunken wax slab (taking the shape of the evaporation vessel). The mixture‐mass system consisting of two or more phases can be considered a random accumulation of comparatively coarse particles of carnauba (or another ester) wax held together by mechanical support; the comparatively wide interstices contain waxless solvent. The waxes concerned are little soluble to completely insoluble in white spirit at room temperature; there is no swelling. As in the case of a paste, a mixture‐mass contains a free liquid phase. It is characterized by pronounced opacity, as a rule very poor solvent binding, and absorption. Evaporation proceeds at a high rate often without blooming and, as a rule, without creeping. It exhibits the drying‐out phenomenon (solvent loss by almost constant outer volume); the residue is spongelike and friable. Optimum paste is virtually a one‐phase system of the border region crystalline/colloidal and results from a mixture of paraffin wax with an optimum amount of microcrystalline wax or ozokerite resulting in optimum solvent retention. It is characterized by moderate opacity, excellent solvent binding, and somewhat increased solvent absorption. On evaporation, the rate of solvent loss is extremely low (i.e. there is optimum solvent retention); drying‐up is very much slowed down. There is neither blooming nor creeping, and the evaporation residue is a dense wax slab, showing the contours of the evaporation vessel; there is no shrinking. The theory of retention is also discussed.