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Understanding Thixotropic Materials

Oftentimes certain high-viscosity products such as pastes, putties, or encapsulants are referred to as ‘thixotropic.’  But what does that really mean?  A material is considered thixotropic when its viscosity decreases in response to an external force.  This force can take the form of shear (such as squeezing or spreading) or agitation (stirring or shaking).  An everyday example of a thixotropic substance is ketchup. On its own, ketchup appears very thick, yet it becomes easily pourable when shaken, squeezed, or spread.

Thixotropic materials exhibit an interesting property: they gradually return to their original state once the force is removed.  Technically, these materials recover to a viscosity close to their original level after a certain period of rest (typically between 80% and 100%).  This aspect of ‘recovery time’ can actually be a key performance property.  For instance:

High-Viscosity Pastes & Putties:  When formulating a high-viscosity paste or putty that needs to hang in place and resist sagging, a short recovery time is critical.  This ensures that the material remains in position once applied via force (e.g., spreading a thixotropic, peanut-butter-like adhesive paste).

Lower Viscosity Paints & Coatings:  In contrast, lower viscosity products may benefit from a longer recovery time.  This allows the product to self-level before thickening back to its original viscosity.  Think of certain self-leveling paints and coatings.

In a lab setting, a viscometer or rheometer is used to assess a material’s thixotropic behavior (also known as thixotropy), and our chemists can calculate a thixotropic index to quantify this property.

Thixotropic materials can be highly advantageous when chosen for the right applications.  Reach out to our technical team to learn more about Astro’s range of thixotropic products and how they might suit your needs.

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