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length causes some variability in performance and in • High shear rates produce low viscosity that
a composite’s shelf-life. In addition, the International permits faster mixing prior to application, improves FEBRUARY
Agency for Research on Cancer (IARC) found leveling during the application of high-viscosity 2019
that particle lengths greater than 5 microns have mixtures, and improves workability (pumping,
evidence of carcinogenicity. 3 spraying, spreading, feathering, etc.).

How attapulgite works Returning to “at rest”, or rebuilding of the lattice
Attapulgite bristles have weak electrical charges, structure, is very fast. Mixtures quickly return to their
positive on the ends and negative along the original higher viscosity after mixing or after being
shaft. When well dispersed in liquids, the charged applied, resulting in:
particles “at rest” are in close proximity and form • Improved flow and leveling of paints, adhesives,
weak electrical bonds, end-to-face, creating a sealants, etc.;
three-dimensional lattice network. This structure • Reduced settling and sag;
entraps liquids and keeps insoluble particles • Reduced overspray and spattering; and
both separated and suspended. Under shear the • Reduced permeability and shrinkage.
weak lattice structure dissociates, resulting in
lower viscosity and markedly improved mixing, It is important to reiterate that this cycle of lattice
pumping and workability. When the system returns formation and reformation can be repeated
to “at rest”, the rate of ‘thixotropic recovery’ – or indefinitely without fade. This is the behavioral
rebuilding of the lattice structure – is exceptionally attribute of high-quality, U.S. gel grade, attapulgite
fast with an immediate return to a stable structure products that keeps coatings and other composites
(Figure 2). Since attapulgite mineral does not swell, stable and allows consistent, optimum performance
there is no post-thickening or creep viscosity. It is over their intended shelf-life.
not a dispersant but further aids the separation of
liquids and particles and keeps them suspended. Features and performance
The key features in selecting an attapulgite product
are gel quality and fineness of residue. Products
suitable to coatings, adhesives, sealants and many
other fine applications require a very low +325
mesh residue, typically less than 1%. This is not
only critical for the end-use applications but also
reflects the degree of separation of attapulgite’s
naturally bundled and compressed particles by the
manufacturing process. With greater separation,
the attapulgite particles disperse easier and more
completely permitting optimal performance.

Exceptional performance and economies
Figure 2: Attapulgite lattice network when dispersed in a liquid.
High-quality U.S. gel grade attapulgite products are
the most economical low-shear rheology modifiers
Unlike most other thixotropes, this shear-thinning can in their class and provide consistent performance
be repeated endlessly without loss of performance.
over diverse liquid systems. Their dosage in most
applications is similar to not-in-kind products, about
Particle network and performance 0.1 to 2.0% by weight, and yet their cost per pound
The thixotropic effect, coupled with suspension is usually far less than half.
and rapid recovery, provides benefits beyond just
rheology modification. Most coatings require a mix of different rheology
modifiers to provide a fuller rheological profile to meet
The lattice network “at rest” provides a uniform and the demands of in-can stability (Stormer viscosity) and
stable mix with all components well dispersed. This paint application (ICI viscosity). Paint manufacturers
better ensures the mixture can perform optimally as have found that U.S. attapulgite products add key
well as maintain consistent quality throughout shelf- rheology benefits while wholly or partially replacing
life. Benefits are: more expensive additives, such as associative
• Syneresis Control; thickeners (alkali-swellable acrylics), urethane-based
• Freeze-Thaw Stability; and rheology modifiers, and cellulosic thickeners.
• Pigment Suspension (reduced pigment float & Attapulgite products have distinct advantages over
flooding and improved tint strength).
other commonly used thickening and suspending
agents. They do not fade under repeated shear and
Under motion, the particles align with the direction are chemically inert and non-swelling. Additionally,
of flow and stay dispersed among the particulate attapulgite products are easier to use as they do not
solids, keeping them separated. This optimal require a higher pH, special solvent or modifier to
dispersion provides lower viscosity and markedly activate them. They are ideal for low-pH paints. In
improved flow, pumping, spraying and workability. solvent-based systems with less than 10% water, a
• Low shear rates maintain high viscosity, which surfactant is often needed.
minimizes sag and flow after application, controls
the penetration rate of adhesives and stains, Hydroxyethyl cellulose (HEC) is a popular co-
and prevents adhesive squeeze-out during high thickener for emulsion coating systems. Key benefits
pressure laminating. of HEC include syneresis control, freeze-thaw

Journal of Surface Coatings Australia 15