Hydroxypropylmethylcellulose (HPMC) is a compound that has become a staple raw material in many industries due to its multifunctional properties. It is commonly used as a food additive, a thickener in cosmetics, and even a medical ingredient in many medicines. A unique property of HPMC is its thixotropic behavior, which allows it to alter viscosity and flow properties under certain conditions. In addition, both high-viscosity and low-viscosity HPMC have this property, exhibiting thixotropy even below the gel temperature.
Thixotropy occurs in HPMC when a solution becomes shear-thinning when pressure is applied or stirred, resulting in a decrease in viscosity. This behavior can also be reversed; when the stress is removed and the solution is left to rest, the viscosity slowly returns to its higher state. This unique property makes HPMC a valuable component in many industries as it allows for smoother application and easier processing.
As a nonionic hydrocolloid, HPMC swells in water to form a gel. The degree of swelling and gelling depends on the molecular weight and concentration of the polymer, the pH and temperature of the solution. High viscosity HPMC typically has a high molecular weight and produces a high viscosity gel, while low viscosity HPMC has a low molecular weight and produces a less viscous gel. However, despite these differences in performance, both types of HPMCs exhibit thixotropy due to structural changes that occur at the molecular level.
The thixotropic behavior of HPMC is a result of the alignment of the polymer chains due to shear stress. When shear stress is applied to HPMC, the polymer chains align in the direction of the applied stress, resulting in the destruction of the three-dimensional network structure that existed in the absence of stress. Disruption of the network results in a decrease in solution viscosity. When the stress is removed, the polymer chains rearrange along their original orientation, rebuilding the network and restoring viscosity.
HPMC also exhibits thixotropy below the gelling temperature. The gel temperature is the temperature at which polymer chains cross-link to form a three-dimensional network, forming a gel. It depends on the concentration, molecular weight and pH of the solution of the polymer. The resulting gel has a high viscosity and does not change rapidly under pressure. However, below the gelation temperature, the HPMC solution remained liquid, but still exhibited thixotropic behavior due to the presence of a partially formed network structure. The network formed by these parts breaks down under pressure, resulting in a decrease in viscosity. This behavior is beneficial in many applications where solutions need to flow easily when stirred.
HPMC is a versatile chemical with several unique properties, one of which is its thixotropic behavior. Both high-viscosity and low-viscosity HPMCs have this property, exhibiting thixotropy even below the gel temperature. This characteristic makes HPMC a valuable component in many industries that require solutions that handle easy flow to ensure smooth application. Despite the differences in properties between high-viscosity and low-viscosity HPMCs, their thixotropic behavior occurs due to the alignment and disruption of the partially formed network structure. Due to its unique properties, researchers are constantly exploring various applications of HPMC, hoping to create new products and provide better solutions for consumers around the world.
Post time: Aug-23-2023