A Guide to Silane Solution Mineral and Filler Treatments

Sep 7 2012

Mineral fillers are increasingly being used as important additives and modifiers for organic polymers. A mineral's surface can be made more compatible and dispersible in polymers or a reinforcing additive by the alkoxysilanes.

The use of silane-modified minerals in organic rubber has become increasingly important. In general, the minerals with aluminum and silicon hydroxyl groups on their surfaces are receptive to alkoxySilanes bonding. The treatment of a mineral surface by an organosilane is depicted in Figure 1.

Figure 1. Treatment of a mineral surface by an organosilane

Benefits of Silane Treatment

Silane treatment can improve processing, performance, and durability of mineral-modified products by:

Improving adhesion between the mineral and the polymer
Improving wet-out of the mineral by the polymer
Improving dispersion of the mineral in the polymer
Improving electrical properties
Increasing mechanical properties
Reducing the viscosity of the filler/polymer mix

Figure 2. Example of transforming a mineral filler from hydrophilic to hydrophobic with a phenyl-functional silane

Silane Treatment Effectiveness

Silane coupling agents have been effectively used in filled polymer systems with silica (both fumed and precipitated), glass beads, quartz, sand, talc, mica, clay, and wollastonite. Other metal hydroxyl groups, such as magnesium hydroxide, iron oxide, copper oxide, and tin oxide, may be reactive to a lesser extent, but often benefit from silane treatment. Traditionally, silane coupling agents give poor bonding to carbon black, graphite, and calcium carbonate.

Applying Silanes to Fillers

Minerals are treated with either neat silane or a solution of silane in water and/or alcohol. With a neat silane, the adsorbed water on the filler surface is often sufficient to hydrolyze the alkoxysilane and simultaneously bond the silane to the filler surface. It is important that the filler be coated uniformly through the use of intensive mixing, such as with a Henschel mixer. Commercial processes are continuous, often in heated chambers, followed by further heat treatment to remove byproducts of alcohol and water and to complete the bonding of the silane to the surface.

Treatment Level

The loading level of silane on the filler surface is a function of the surface area of the filler. While it was previously thought that one monolayer of silane should be sufficient, experimentation has shown that several layers of silane give optimal results. For example, typical fillers with average particle sizes of 1 to 5 microns often give best results when treated with about 1% silane (based on weight of the filler). The optimal level of silane treatment should be determined experimentally.

Silane Choice

The choice of which silane to use in a particular application is determined by the nature of the desired benefit. All alkoxysilanes will bond to a receptive filler or mineral surface. If the silane treatment is designed to provide surface hydrophobicity, then a silane with a hydrophobic group, such as butyl, octyl, fluorocarbon, or phenyl, should be chosen. If the silane treatment is designed to provide compatibility of the mineral in a polymer matrix, then the nature of the organic group on the silane should be similar to the chemical structure of the polymer (i.e., an octyl or longer-chain alkyl group will help provide compatibility and dispersibility of the mineral in a polyolefin matrix). If the silane treatment is to bond a filler to a polymer matrix, then an organo-reactive silane should be chosen that would bond chemically to reactive sites present in the polymer.

About Xiameter

In 2000, Dow Corning was facing an increasing number of competitors around the world that were getting into the standard silicones business. At the same time, for a growing customer segment called “price-seekers” who needed little or no service attached to the products, price had become the driving force.

Dow Corning needed to defend their position as a provider of innovative silicon-based materials and solutions (which, for the most part, came bundled and priced together). Dow Corning knew that they needed to find a better way to meet customers’ needs exactly.

It was time for a game-changing strategy – one that would simultaneously:

Meet customer needs for efficient, cost-effective silicone products
Empower Dow Corning to continue to innovate and grow the silicones market overall

Dow Corning decided the best way to take advantage of the potential in the mature market segment, without detracting from the value of the Dow Corning offering, would be to create a separate brand. This brand would offer a clearly defined value proposition and set of products via a web-enabled platform to provide competitive pricing.

The product set would be a wide range of standard silicone products generally thought of as “commodities” by customers. These standard products would be – and still are – manufactured by Dow Corning.

The tone would be “no frills” – just straightforward business terms and conditions, high-quality products, a reliable supply, and market-driven prices. Short. Sweet. To the point.

Defining success (2002-2009)

With the launch of the XIAMETER® brand in March 2002, Dow Corning revolutionized the way they do business. Specialty silicone products, service and solutions continued as part of the business under the Dow Corning® brand. The XIAMETER brand met the needs of “price-seekers” who purchased standard silicone products via www.xiameter.com.

The global drive to find greater efficiencies in business through a web-enabled business model worked in their favor. It helped Dow Corning maximize productivity and reduced human error, while keeping costs competitive for customers. Rather than cannibalizing the Dow Corning brand as some feared, the XIAMETER® brand made it stronger. The two brands worked in harmony, helping increase Dow Corning’s financial results dramatically during this period.

Between 2002 and 2009, the XIAMETER® brand was a web-enabled business with clear business rules, offering commonly used standard silicones at transparent, market-driven prices. However, those business rules only allowed for large-volume orders. There was no technical service. Lead times ran 7-20 days. And only 400 standard silicone products were available through www.xiameter.com.

Expanding the model (2009-present)

In 2009, Dow Corning expanded the XIAMETER® business model – for the same reason we launched it in the first place – to meet customer needs based on smart customer segmentation analysis. Xiameter saw a need for all customers – not just large-volume buyers – to be able to purchase standard silicone products at market-based prices. Based on the success of the original Xiameter model, company leaders were confident expanding the model would work – both for customers and Dow Corning. And it did!

The XIAMETER® business model, which was expanded in June 2009 and expanded again in 2011, now offers thousands of standard silicone products. Plus, the model is no longer for large-volume customers only. There are more volume-quantity options. With the Xiameter transparent price tiers, customers can choose the pricing most appropriate for them based on the volumes they need. They can purchase multiple items within a product family and receive greater discounts. They can lock in price and volume commitments through an online supply agreement. They also can choose credit terms that work best for them, which can be varied each time they order. Plus, customers who need smaller quantities, shorter lead times or more flexible ordering options can have them – by purchasing XIAMETER® brand products through local distributors.

With today’s XIAMETER® brand, customers can get all the standard silicones they need in the way that works best for them. Whatever they want. Wherever and however they want it. In a world of traffic jams, on-hold music and long supermarket lines, we think it’s a great option.