Page 16 - 201902 SCA February 2019 Volume 56 Number 1

The Australian Distributor for Active Minerals is
IMCD Australia Limited. For more information contact:
Technical ARTICLE Steven Whippy • +61 3 8544 3100 • cs@imcd.com.au

An easy, tried-and-true method to ensure

quality in coatings

by Jeffrey B. Carr, Director of Technical Sales and Marketing, Active Minerals International, LLC
This article is reproduced from Coatings World, October 2017.
Coatings are complex composites designed to have a stable shelf-life, apply easily to
a substrate, and provide lasting durability in varied environments. These performance
criteria require disparate materials to be finely dispersed and work cohesively, which
presents a major challenge as composites can be unstable and ultimately fail at points
of inconsistency.

To address this, the first thing a new paint chemist with particulate solids, when it’s well-dispersed in a
learns is that wetting agents are mandatory in liquid. High-quality gel-grade attapulgite products,
allowing mineral fillers to disperse properly. Without produced from deposits in the United States, proved
them, these inorganic particles generally reject their to be ideal low-shear rheology modifiers, syneresis
organic media, agglomerate and settle out. It would control agents and suspension stabilizers for a wide
be imprudent to forgo wetting agents. variety of water-based and organic liquid systems.
They are especially effective in mixtures containing
Another well-known, tried-and-true technique to high solids. Drilling muds, coatings, and tape joint
stabilize composites and improve their uniformity is to compounds were among the first applications. Later
use high-quality, gel-grade attapulgite mineral products. developments included suspension fertilizers, animal
They have been common in paint applications for feed suspensions, adhesives, sealants, inks, color
several decades as thixotropic thickeners for low-shear concentrates and asphalt coatings.
flow and leveling, sag resistance and other rheology
benefits. However, a seemingly forgotten higher value
is their function as excellent stabilizers due to their
unique colloidal lathe-shaped particles forming a
lattice structure. This keeps liquids and particles more
evenly dispersed and suspended, generating important
benefits well beyond rheological properties.
This article gives a brief history of attapulgite, a
description of its mechanism that sets it apart from
other thixotropic thickeners and stabilizers, and
discusses its performance benefits in coatings.

Chemistry and morphology
Attapulgite is a naturally occurring hydrous
magnesium aluminosilicate clay mineral with the Figure 1: Crude attapulgite mined by Active Minerals
formula (Mg,Al) Si O (OH)· (H O). The composition International LLC.
4 10
2
2
4
and structure of attapulgite were determined in Although this sedimentary clay is found on nearly
the early 1940s and 1950s. 1 It has a lathe or bristle every continent the quality varies greatly with two
morphology that is non-swelling and non-fibrous primary distinctions. First, the majority of deposits
(Figure 1) and is inert and stable under a wide and the quality within the deposits are not gel grade,
pH, temperature and chemical range. Attapulgite making them only suitable for sorbent applications,
particles are naturally colloidal with weak electrical like filtration or floor absorbents. The other variance
charges. They have a high aspect ratio of 100:1 or is particle length. United States gel grade attapulgite
higher and are in tightly compressed large bundles products have a consistent particle size of 2.5
that must be dried and separated.
microns long and 25 nanometers wide. Other
Commercial development soon followed to capture deposits have much longer and varied lengths 2 ,
the benefits of attapulgite’s unique ability to form an which makes their primary value of forming a lattice
electro-mechanical lattice structure that interacts structure inconsistent. This non-uniform bristle

Author Profile
Jeff Carr, for nearly two decades, has been a leader worldwide for attapulgite and other minerals and led
in sales, marketing and business management for a successful turnaround for one attapulgite producer.
the two largest global attapulgite producers. He has He currently serves at Active Minerals International
developed many new products and applications and can be reached at j.carr@activeminerals.com

14 Journal of Surface Coatings Australia • February 2019