Data analysis and modeling of the caloric properties of wax esters

Physical properties of wax-based oleogels are linked to the chemical composition of the natural wax, the latter being a complex mixture of aliphatic compounds. In most natural waxes, long-chained aliphatic wax esters (WE) are the main constituents responsible for network formation and thus the oleogel properties. WE differ in total carbon number (CN) and position of the ester bond (ΔCN), affecting crystallographic and thermal properties.

Building on literature data and own data, in this contribution the comprehensive database on pure components and oleogels containing single WE or WE mixtures is discussed. The data considered includes melting point temperatures (T_SL), heats of fusion (Δh_m) and WAXS/SAXS data for both pure components and oleogels. For example, it appears that for the majority, Δh_m is independent of the position of the ester bond within a WE-chain even though T_SL systematically decreases with increasing ΔCN (difference in chain length alcohol/acid). Deviations from this rule will be discussed considering structural data (WAXS/SAXS). For the mixed oleogels, SAXS data provides interesting new insights: It is established that the orthogonal chain arrangement only occurs at ΔCN +2 or -4. The presented data for the CN36 (20-16) + CN38 (18-20) system reveals that surprisingly the orthogonal configuration can occur in mixtures of WE that individually crystallize with inclined chains. This emphasizes that chain length difference between the WE and the respective ester bond position strongly impact crystalline packing.

To complement the discussion on the systematic behavior of WE, the gathered data is used to assess validity of different models and correlations formulated for molecules containing aliphatic chains. For example, the configurational approach to model pure component TAG properties is evaluated for WE.

The findings provide crucial insights to thoroughly understand the complex solid phase mixing behavior of natural waxes and exploit their full potential as oleogelators.