Crystallinity and Water Vapor Permeability of n-Alkane, Alcohol, Aldehyde, and Fatty Acid Constituents of Natural Waxes

Natural waxes are valuable industrial products consisting of complex chemical mixtures. To probe the structure–function role of select constituents, model n-alkanes, alcohols, aldehydes, and fatty acids of C_18–19, C_22–23, and C_26–27 carbon chain lengths were synthesized and analyzed via calorimetry and X-ray powder diffraction. Pure compounds and binary mixtures crystallized into monoclinic (M), triclinic (T), and orthorhombic (O) lattices or combinations thereof. The C₂₆ aldehyde formed an O lattice and exhibited one solid–solid phase transition similar to n-alkanes. The water vapor permeability (WVP) of model systems cast as films was determined. For pure compounds, WVP decreased in the following order: fatty acid > even n-alkane > odd n-alkane > alcohol > aldehyde. Increasing carbon chain length, which translates to increasing unit cell volume, decreased WVP. Binary mixtures generally exhibited a more complex relationship with WVP. These findings may be applicable to the agricultural postharvest, pharmaceutical, and paperboard coating industries.