Enhancement of the Gel Hardness of Candelilla Wax through the Addition of Long-chain Ester Wax Behenyl Behenate

Abstract

Candelilla wax (CW) is used as an oil-gelling agent in cosmetic sticks. However, its hardness is inadequate compared to those of hydrocarbon waxes such as paraffin. In this study, behenyl behenate (BB), an additive plant-derived wax ester with a high melting point, was shown to improve the oil-gel hardness of CW. Although the gel with BB alone had a relatively low gel hardness, when BB was mixed with CW at a ratio of 70:30 (CW:BB), the gel hardness significantly increased to four times that of the CW gel. The hardness of the CW and BB mixtures was higher than that of paraffin wax, which is used to solidify cosmetic oils. An increase in gel hardness was not observed when additives with chemical structures similar to those of BB, such as stearyl stearate (which has a lower molecular weight than BB) and behenic acid or behenyl alcohol (which are components of BB), were blended. Scanning electron microscopy indicated the presence of many spherical clusters comprising fine crystallites in the CW gel. This morphology was in contrast to that of paraffin wax gel, in which only plate crystals were observed. It was concluded that this heterogeneous structure led to the low gel hardness of CW. When BB was added to CW, the spherical clusters disappeared, and the internal structure changed to a homogeneous card-house structure composed of plate crystals.