Attagel® from BASF as a Rheology Modifier and Thixotropic Additive

What is Attagel®?

Derived from attapulgite clay, Attagel® from world leading chemical company, BASF, is a versatile inorganic thickening agent known for its unique rheological properties.

Chemical and mineral composition of Attagel®

Attapulgite is a naturally occurring crystalline hydrated magnesium alumino-silicate mineral with a three-dimensional chain structure (Figure 1). This gives attapulgite unique colloidal and sorptive properties that differ depending on how hydrated the grade is. Attapulgite can retain a lot of water within the structure which contributes to Attagel®’s thickening and gel formation properties.

Figure 1: Chemical structure of Attapulgite showing the three-dimensional chain structure that allows for the unique colloidal and sorptive properties.

Table 1: Typical Chemical Analysis of Attapulgite-based products.

Where does Attagel® come from?

BASF mines Attagel® in Quincy, Florida which is where Attapulgite was first mined in 1983. To produce Attagel®, the crude mineral is purified and manufactured through well-controlled heat treatment and particle-size processing. For the grades that offer rheology modification, low-temperature drying is used for a well-hydrated grade with specific residue and moisture specifications.

Figure 2: Attapulgite is a natural mineral that is mined, processed, ground and heat treated to create a consistently fine powder of Attagel®

Particle size and shape

Attagel® is a micronized powder of needle-shaped (acicular) attapulgite crystal particles that can form bundles (Figure 3). With a diameter of only 0.1 microns and length of 2 microns, attapulgite has very small sub-micron particles which offer the final Attagel® products a high fineness.

Figure 3: SEM of attapulgite showing the crystal needle-shaped particles.

How does Attagel® work as a rheology modifier?

The small sub-micron particles of attapulgite form bundles, which, when well-dispersed in a liquid system, form a colloidal network that can entrap liquid and smaller particles or suspend larger particles. This mode of action offers effective gelling and suspension that is indefinitely stable when undisturbed. The thixotropic properties can be seen when shear is applied to the system, as the colloidal structure is then broken down giving a thin and flowable product. This effect only lasts while the shear is applied and when returned to a state of rest, the network will reform and give the same thickening properties as before. This cycle can be repeated endlessly with no reduction in performance.

Uses of Attagel®

Attagel® grades can be used across multiple applications to provide smooth application, sag prevention, suspension of particles or in-can stability. See Table 2 below for the different benefits that various grades can offer within different applications.

Table 2: Attagel® 30, 40 and 50 from BASF can be used across many industries to provide thickening and rheology modification.

How is Attagel® used in the Coatings Industry?

Different grades of Attagel®

Attagel® 30, 40, and 50 are the main grades across the CASE applications of Coatings, Adhesives, Sealants and Elastomers as can be seen in Table 2 above. These differ primarily in the amount of residue and the fineness which also results in different oil absorptions. Attagel® 50 is the most premium product with the lowest residue (the particulate matter left behind on the sieve) and therefore the tightest particle distribution size with the most consistency. This is particularly important in applications where fineness, surface smoothness and sprayability are desired or critical to the end product.

Our team of technical sales managers are available to assist with more specific applications.

Table 3: Physical properties of the different Attagel® grades.

How does Attagel® improve the performance of coatings?

The unique attapulgite structure means Attagel® products are suitable in aqueous and solvent-borne systems and are compatible with most additives and chemical environments. This is a huge benefit over other commonly used thickening and suspending agents such as laponite or bentonite which are often limited by pH, temperature or the chemical environment of the product. It also offers more cost-effective thixotropy than other thickeners and rheology modifiers making it a popular choice to wholly or partially replace their expensive counterparts.

Figure 4: Creating a paint or coating that has good in-can stability, ie it doesn't separate or fall out in the can, is essential for a high quality product.

End-use Benefits of Attagel®

• Syneresis control
• Sag resistance
• Film build
• Levelling
• Spatter resistance
• Spreadability
• Feathering
• Tint strength
• Hiding

Storage Benefits of Attagel®

• Reduce liquid separation (syneresis)
• Do not swell
• Stable in multivalent inorganic pigments
• Stable over wide pH
• Stable over wide temperature range
• Insoluble in organic liquids
• Generally resist settling

Formulating with Attagel®

In order to establish the required colloidal network of Attagel® within a formulation, some care must be taken to correctly disperse the material using high shear dispersion. The specific point of addition will depend on the formulation type and more information below explains the differences between a water-based or solvent-bourne formulation, but in both instances, Attagel® should be added during or towards the end of the grind step. Quantity levels range depending on the required consistency, whether other thickeners or modifiers are being used and the other ingredients included within the formulation weight percentages of up to 2.5% could be expected for more challenging thickening.

Table 4: The suggested concentrations of Attagel® differ depending on the required effect and the application.

While high-speed mixing is recommended, slower-speed mixing can still work but will take longer to establish the network and achieve maximum viscosity. Under and overdispersion must also be carefully avoided as they can respectively cause post-thickening when the undispersed attapulgite naturally wet out over time or a complete scattering and separation of the particles that impede network establishment. Figure 2 shows the difference in establishing viscosity when using 1700 FPM and 3000 FPM respectively.

Figure 5: The Brookfield Viscosity of a formulation including Attagel® as the network is established at different mixing speeds.

Where high-speed mixing cannot take place, a high solid content that increases the shear rate or an Attagel® pregel can be used to take advantage of particle crowding to ensure dispersion.

Pregelling Attagel®

As higher solid content creates higher shear which in turn aids dispersion, using a high solid pregelled Attagel® removes the need for the high shear mixing on the manufacture batch. This is particularly useful if another element of the formulation responds badly to high-shear or if the formulation has a low solid content. Pregels are typically 15 to 20% material and can be made in parallel to other components in the formulation and dosed as required.

Figure 6: High-speed mixing is required to establish the Attagel network in order to bring about the optimal rheology benefits.

Attagel® Synergy with Cellulose

Cellulose is an alternative thickener that works predominantly through entanglement and is often used as it can offer more elasticity, in-can stability, and a nice smooth application feel. However, being organic, it can be more susceptible to microbial attack and when a lot is put in, spattering can occur from the elasticity breaking, it also doesn't offer shear thinning as alternatives. Combining it with Attagel® can achieve the best of both worlds with a smooth application without spattering and nice shear-thinning properties. The ratio of Attagel® to Cellulose should be around 3:1 or 4:1 by weight with Attagel® concentration between 6 and 12 g/l.

Summary and Contact Us

Attagel® from BASF is an inorganic attapulgite thickener that when properly dispersed at high speed causes a network within a coating formulation providing thixotropic properties. Attagel® is widely compatible across a range of pHs, temperatures and chemical environments and can be used in both solvent and waterborne applications making it a popular choice over its counterparts. If you would like more details on anything you have read here or would like to receive a sample, please contact us here or fill in a sample request form.