Surface Modification of Minerals

A Third Component to Consider

Minerals are widely used in plastics, paints, coatings, elastomers and adhesives, plus a great many other applications. The mineral particles are one component in the formulation and they are dispersed within the second component, for example a polymer resin. It is not widely appreciated that there is a third component to consider and that is the interface between the mineral surface and the surrounding material. Tailoring that interface is vital for optimal performance, and dispersants or coupling agents are additives that allow just that. What are dispersants and coupling agents? When should we pick one over the other? These and other common questions will be addressed.

Dispersion & Dispersants

Achieving proper dispersion is key to commercially successful products. So, what is dispersion and how do we measure it? Dispersion simply means that each particle is separated from the others. If I buy filler particles that are 2 microns average size, I do not want them to be clumped together and act as if they were 10, 50 or 100 micron sized particles. Clumps of agglomerated particles cause low impact resistance because they act as crack initiation sites and they lower elongation to break for the same reason. There are other less obvious caused by agglomerates, such as increased surface roughness, higher abrasion and lower gloss.

Dispersion can be improved either by increasing the mixing energy, or by decreasing the attractive forces between the particles. Increased mixing energy means added electricity cost when processing, whereas the attractive forces between the particles can be lowered by using a small amount of inexpensive dispersant. That makes dispersants cost-effective. If we take polypropylene, polyethylene or PVC filled with 20 percent by weight calcium carbonate, we would typically need just 0.2% stearic acid dispersant. Even at that low addition level, each particle is coated in a monolayer of dispersant which acts like a coating of lubricious wax.

The exact type and amount of dispersant to use varies from formulation to formulation and Arctic Minerals have expertise in finding you the optimal solution to suit your needs. A screening method allows fast, accurate results. We also have decades of experience producing commercial products with a variety of minerals and coatings.

Coating minerals with dispersants allows:

  • Higher filler loading levels
  • Reduced viscosity
  • Lower energy costs
  • Higher gloss
  • Better impact resistance
  • Greater elongation to break
  • Prevents unwanted adsorption of antioxidants and other additives by the filler

Coupling & Coupling Agents

Dispersants are bound to the mineral but not bonded to the surrounding material, so they actually reduce adhesion, just as though we had applied a thin layer of wax. In some instances though, we want to increase the bonding, i.e. coupling, and that is where coupling agents come into their own. By “gluing” the mineral filler particles to the surrounding substance, the material as a whole becomes stronger, because when we apply a load, the load is now carried by the mineral as well. In fact, the best way to tell whether a coupling agent has worked is to measure the yield strength of the final material and look for an improvement. Coupling agents are also used to ensure that bonding, and therefore strength, is maintained even at higher temperatures or under conditions of high humidity.

As you can tell from the description, coupling agents are a type of glue or adhesive and just like glues, there are many types depending on the materials to be adhered. Arctic Minerals has experience selecting the correct chemistry for each mineral and each material from epoxies, through silicones to polyesters, polyamides, acrylics and so on. Until recently, the use commercial use of coupling agents such as organosilanes was inhibited because the treatment process was costly. A process breakthrough has allowed Arctic Minerals to offer exceptionally affordable application of coupling agents using a high volume continuous process. That combined with extensive QC procedures has attracted an overwhelmingly positive response leading to substantial new business.

Normally, the customer is limited to one or two standard coupling agents pre-applied to the mineral. This means there is no way to ensure the best results and no way to differentiate your product from that of your competitors. At Arctic, we have the widest array of organosilane, titanate and stearate options, as well as other more exotic offerings. You get the treatment you need, and something your competition cannot replicate.

Conclusion

Arctic Minerals provide state-of-the-art surface treatments for virtually any mineral or pigment. Treatments can be applied in conjunction with toll processing, or if you prefer, we can apply the treatment to filler supplied by you, with no change in particle size. We have the ability to supply from two US-based facilities, which is essential for some global customers e.g. in the automotive industry, who demand auxiliary supply options.

Surface treatment of minerals is a well-established field. However, recent advancements at Arctic Minerals have provided companies the opportunity to make better products at lower cost. A rapid screening method allows us to identify the ideal treatment type and amount, whereas the state-of-the-art continuous treatment process provides lower cost and higher consistency than ever before. Want to get a step ahead of your competition? Then contact Arctic Minerals today!