Metalworking fluid formulators and emulsifier suppliers are facing numerous challenges with regard to performance demands, regulatory issues and commercial pressures. According to Claude-Emmanuel Hdoire of Solvay, todays new generation of high-speed machine tools require much improved foam control. He told delegates at the STLE Annual Meeting in Dallas in May that emulsifiers used in metalworking fluids for these newer machines must provide ultra-low foam and enhanced defoaming, without the need to add a separate defoamer.
He also explained that the strong worldwide regulatory environment like the Globally Harmonized System (GHS) for substances and mixtures and specific local requirements like the European Biocidal Product Regulation, trigger more stringent classification and labeling for some emulsifiers. As a result, there is a need to develop emulsifiers with milder labeling, as well as biostable emulsifiers.
Finally, some raw materials are not available globally, and end users are demanding more cost-effective fluids. As a result, said Hdoire, new generations of emulsifiers should be based on commonly and globally available raw materials.
Emulsifier Landscape
According to a Kline & Co. study, the global metalworking fluid market will reach 2.5 million metric tons by 2017, a compound annual growth rate of 2.3 percent per year. Along with corrosion inhibitors, emulsifiers are the most widely used additives in metalworking fluids, representing 140,000 tons per year out of a global additive consumption of 600,000 t/y.
Emulsifiers are backbone additives for water-soluble metalworking fluids (soluble oils and semisynthetic fluids), Hdoire explained. They stabilize oil-in-water emulsions, and the choice of emulsifier controls the oil droplet size distribution. Some emulsifiers provide other valuable benefits.
Emulsifiers commonly used in metalworking formulations include both anionic and nonionic compounds. Emulsifier systems comprise elaborate blends of components to finely balance their benefits and limitations. The table on Page 20 lists the properties of commonly used emulsifiers
In general, nonionic emulsifiers provide good emulsion stability, low foam in both deionized and hard water, poor defoaming in DI water and acceptable defoaming in hard water. However, they provide no corrosion or staining inhibition and no antiwear performance.
Phosphate-esters, which are anionic emulsifiers, generally provide good emulsion stability, low foam in DI water and ultra-low foam in hard water due to soap formation, no defoaming in DI water and excellent defoaming in hard water. They also provide good corrosion and staining inhibition and good antiwear performance.
Whats Available?
Hdoire then described efforts to develop nonionic emulsifiers based on alkoxylated fatty alcohols to meet todays performance, regulatory and commercial requirements. The molecular structure of these compounds provides more favorable classification and labeling requirements, according to guidelines issued by the European Committee of Organic Surfactants and their Intermediates (CESIO), he indicated, noting that most surfactant manufacturers are CESIO members. In contrast, the base molecule for conventional surfactants must be labeled with the dead fish pictogram.
He reviewed the commercial availability of the various alkoxylated fatty alcohol feedstocks, including lauryl alcohol, cetyl oleyl alcohol and branched alcohols. (See the Table on Page 22.)
Lauryl alcohol is manufactured from palm kernel oil or synthetically from crude oil. It is commonly and widely available from more than 10 suppliers in Asia, more than 5 suppliers in Europe and about 5 suppliers in North America. Lauryl alcohol is used as the base feedstock for numerous types of surfactants used in home and personal care products.
Cetyl oleyl alcohol is manufactured from palm kernel oil, using a patented technology. There are only 3 suppliers in the world, with production sites in Asia and Europe.
Branched alcohols are manufactured synthetically from crude oil. They are the base feedstock for numerous types of surfactants (particularly for coatings).
In general, long-chain alcohol ethoxylates provide the best performance in metalworking fluids. And while cetyl oleyl 5 EO (where 5 EO indicates the degree of ethoxylation) provides more stable emulsions and better defoaming, it requires more stringent labeling.
Solvay researchers took a number of steps to optimize the performance of alkoxylated fatty alcohol feedstocks. The first was propylene oxide insertion into short-chain alcohol ethoxylates. This provides similar performance to cetyl oleyl alcohol ethoxylates in terms of emulsion stability, and enhanced performance in terms of foam control and defoaming, said Hdoire. The result is a new generation of emulsifiers with ultra-low foam and enhanced defoaming.
The next step was to optimize performance by varying the degree of propylene oxide insertion and then fine-tuning the degree of ethoxylation and propylene oxide insertion to avoid the dead fish label. The result is the development of new nonionic emulsifiers that optimize performance and economics, and allow milder labeling Hdoire concluded.