On Gelation and Thickening of Oil

Gel is 1 by adding a small amount of curing agent or gelling agent to make the liquid lose fluidity and solidified. Molecules or particles of the curing agent or gelling agent form three-dimensional structures through chemical reactions or physical interactions, and promote gel formation by locking oil between these structures.

In addition, oil-based gels can be broadly divided into two categories:

①　by 12-hydroxy stearic acid, amino acid derivatives and other molecules or particles through interaction to form a three-dimensional high-order structure of the "organic gel"

②　The wax such as solid paraffin and vegetable wax is precipitated into the oil to form "oil wax gel" with crystalline physical cross-linking structure ". The hardness and rheological properties of the gels vary according to the higher order structural mechanisms formed by these gelling agents.

12-hydroxystearic acid is the 1 hydroxyl-containing saturated fatty acid derived from castor oil. It is heated and mixed with a non-polar solvent such as mobile paraffin and cooled to form a gel. The gelation mechanism is that the intermolecular hydrogen bond between the hydroxyl group and the carboxyl group is the driving force to form a helical fiber structure in the oil, thereby forming a high-order structure. A hard and slightly transparent gel is generated, but the hydrogen bond between the gelling agents is relatively weak in a polar solvent as compared with a non-polar solvent, and therefore, it is generally difficult to form a gel in the coexistence of a highly polar oil agent containing a hydroxyl group.

Among the amino acid derivatives, N-acyl amino acid derivatives are used as oil-based gelling agents. Amino acid gelling agents are characterized by their fine rope-like structure and small refractive index difference between gelling agents and oil agents, so oil-based gels with low turbidity can be prepared. The binder formed by the intermolecular hydrogen bond as the driving force will form a fibrous structure, and the oil will be wrapped in the intertwined gaps of the fibrous structure, thereby achieving gelation.

Oil solidification by waxes such as polyethylene wax and vegetable wax can form a gel that is harder than a gel composed of the above-described organic gel, and is used for solid cosmetics such as lipstick. The plate-like crystals precipitated into the oil form a card-house structure (a structure formed by the physical bite of wax components like a playing card tower) and lock the oil in the structure, thereby forming a hard gel. The hardness and high temperature stability of the oil wax gel will change due to the polarity of the oil, the viscosity, the combination of the wax and other factors.

In recent years, the demand for cosmetic products of plant origin has been increasing. By combining a plant-based wax with a relatively low melting point (candelilla wax) and a long-chain ester wax (behenyl behenate), a high-hardness plant-based oil wax gel can be prepared. This technology has been widely reported 6). The company's research also shows that the combination of high polarity oil can further improve the high temperature stability of the product.