The Effect of Shearing in the Thermo-mechanical Properties of Candelilla Wax and Candelilla Wax-Tripalmitin Organogels

We investigated the shearing effect in the thermo-mechanical properties of candelilla wax (CW) and candelilla wax-tripalmitin (CW-TP) organogels developed using safflower oil as the liquid phase. A shear rate of 600 s(-1) was applied during cooling (1 A degrees C/min) of 3% CW and 3% CW-1% TP solutions, until reaching nucleation (i.e., 47 A degrees C) or metastable conditions (i.e., 52 A degrees C) then allowing the development of the organogel under quiescent conditions at 15 A degrees C. The thermal and rheological properties of these organogels were compared with the ones of organogels developed under static conditions. The X-ray results showed that under static conditions the CW crystallized in an orthorhombic (O-perpendicular to) subcell packing with a lateral stacking with a length (L) equivalent to the hydrocarbon chain's length. During organogelation of the 3% CW-1% TP solution, CW and TP co-crystallized in a O-perpendicular to subcell packing with TP in a 2L stacking organization. The application of shearing did not modify the molecular packing of the crystals or the melting properties of the organogels. However, the CW and CW-TP organogels developed with shearing showed the formation of larger crystals (i.e., fiber-like or plate-like) in comparison with the ones developed under static conditions. The presence of 1% TP increased the solid fat content, and thus the CW-TP organogels showed higher elasticity (G') than CW organogels. The organogels developed with the application of shearing until reaching metastable conditions (i.e., CW 52 A degrees C and CW-TP 52 A degrees C) had the highest G' and yield stress of all organogels investigated. In the same way, creep and recovery analyses showed that CW 52 A degrees C and CW-TP 52 A degrees C organogels had the highest resistance to deformation, lowest instantaneous recovery, and highest extended recovery of all organogels studied. We concluded that application of shear and the extent of its application as a function of supercooling determine crystal size and the proportion of transient to junction zones throughout the three-dimensional crystal network and, therefore, the organogels' rheological properties.