Storm Over Silicones

Slowly and quietly over the past decade, a cyclic methylsiloxane that was once an industry workhorse disappeared from the personal care market. Known as octamethylcyclotetrasiloxane, or D4 for short, it was a relatively inexpensive ingredient that gave skin creams a silky nongreasy feel and hair a luxurious bounce and shine.

Studies suggesting that D4 is potentially toxic and can wash off from hair and skin and build up in the marine environment led to its replacement by a related compound: decamethylcyclopentasiloxane, or D5. Consumers were none the wiser. D5 has many of the characteristics of D4. What’s more, ingredient labels didn’t change because formulators list D4 and D5 under the same generally accepted name, cyclomethicone.

But now regulators, especially in Canada, are raising concerns that D5 may also be bioaccumulative, and this time there is no quick and easy substitute. In response, the big silicone makers have banded together into advocacy groups to defend D5 and undertake studies intended to show it is not a bad actor. At the same time, competitors such as BASF and Dow Chemical are promoting substitutes, albeit none that can simply be used in place of D5.

Silicone makers emphasize the human safety of D5 at current use levels, which can range from a few percent by weight to as high as 85% in some hair glosses. Residual levels of D4 and D5 are also present in the derivatives made from them. Derivatives include polymers for personal care use, as well as sealants and elastomers. Only use of D4 and D5 in personal care and industrial water defoaming are under scrutiny at this time.

For both D4 and D5, there is “no risk to human health,” maintains Karluss Thomas, director of the Silicones Environmental, Health & Safety Council of North America, in Herndon, Va. SEHSC members include major silicone producers Wacker Chemie, Dow Corning, Shin-Etsu Chemical, Momentive Performance Materials, and Bluestar Silicones.

Competitors don’t raise safety or environmental issues when talking about substitute ingredients but instead simply point out that silicones have been used for decades and that the time is ripe for alternatives. “We’re giving formulators an opportunity to differentiate their products,” says Ulrich Issberner, global personal care marketing director for Cognis, which was recently acquired by BASF. The firm has even come out with a kind of cookbook that recommends starting formulations for personal care products without silicones.

At least one silicone maker is worried about potential regulations. In a recent filing with the U.S. Securities & Exchange Commission, Momentive said regulation of D4 and D5 “would likely reduce our sales.” The firm also added that “these reductions in sales could be material.”

In addition, the ruckus over D5 comes at an especially bad time for silicone ingredient providers. Regulatory scrutiny aside, cosmetic marketers are touting green ingredients and peddling plant-derived extracts and emollients as wholesome and good. Meanwhile, they cast aspersions by implication on synthetic ingredients such as silicones.

One cosmetics firm has even come out with a shampoo and a hair conditioner clearly marked as containing no silicone. L’Oréal’s “no silicone” Garnier Fructis Pure Clean shampoo and conditioner, recently introduced in the U.S., are advertised as 94% and 92% biodegradable, respectively. In addition, they are called “non-ecotoxic” and are packaged in polyethylene terephthalate bottles that include 50% postconsumer recycled plastics.

Calls and e-mails by C&EN to L’Oréal representatives to inquire about the firm’s objection to silicones went unanswered. However, a hint of the company’s attitude toward silicones can be gleaned from its “2008 Sustainable Development Report.”

There, the firm reported it had tracked “concerns” over the past few years regarding the “potential impact of a specific type of silicone on the environment: siloxanes.” Because of those concerns, the firm replaced D4 and has not included it in its products since 2002.

L’Oréal also said it is studying other siloxanes “so as to gain a better understanding of their potential impact.” Although the new L’Oréal products claim to have no silicones of any sort, the firm’s environmental report targets only the cyclic methylsiloxanes.

Regulators have raised no concerns about straight-chain polydimethylsiloxanes, which frequently appear on ingredient labels as dimethicone and are often used in lotions, shampoos, and bar soaps. Another major class of silicones is amine-functional silicone polymers, often labeled amodimethicone and frequently used in hair care products.

The Garnier no-silicone claim has annoyed some observers in the personal care industry. Consultant David C. Steinberg calls the posture “marketing balderdash.” He questions whether silicone in any form is ecotoxic and says the no-silicone claim used as a negative marketing tool is just another way to sell more shampoo and scare consumers over a safe class of ingredients.

Compared with L’Oréal, German personal care products maker Henkel is a bit more ambivalent about removing silicones. Erik Schulze zur Wiesche, a hair care development researcher at the firm, says Henkel is closely following silicone makers’ discussions with regulators over cyclic methylsiloxanes.

If regulators act, substitution of cyclic methylsiloxanes would pose challenges for Henkel, Schulze zur Wiesche says. Replacement ingredients would necessarily influence product performance and costs, he notes. And he is worried that consumers may not accept a hair care product that doesn’t impart the smooth feel and gloss that the cyclic methylsiloxanes provide.

Workhorses of many industries, D4 and D5 are building blocks for a variety of silicone fluids, resins, elastomers, and gels. Made by reacting silicon metal and methyl chloride, D4 and D5 are also used without further processing in personal care products.

According to consulting firm Kline & Co., D4, D5, and dodecamethylcyclohexa­siloxane, or D6, made up two-thirds of the 104 million lb of silicones used in the U.S. personal care market in 2009. D6 hasn’t received much regulatory attention; it is present at low levels in both D4 and D5.

The government of Canada raised concerns over D4 and D5 a few years ago as it began an assessment of chemicals used in commerce. The assessments caught the personal care industry’s attention not only because of the widespread use of D5 but also because even in purified D5, residual levels of D4 are present.

Thomas of SEHSC says Environment Canada’s review of the cyclic methylsiloxanes was based on computer models of the fate of these silicones in the environment that raised alarms about marine bioaccumulation. The models, however, contradict field studies SEHSC and its members have conducted over many years.

In the case of D4, the Canadian government agency appears convinced that the siloxane poses a hazard to marine organisms. It is proposing restrictions on D4 concentrations ranging from 1.35% by weight in makeup remover to 0.01% in hair dye and other cosmetics. These restrictions would apply to products made and sold in Canada.

For D5, the Canadian government has appointed a review board including scientific experts, industry representatives, and nongovernment interest groups to review the science. The board will come up with recommendations on the need, if any, for restrictions in personal care products.

In Europe, Michel De Poortere, secretary general for the European Silicones Center (known as CES), says the Environment Agency of England and Wales contacted him in 2004 with questions about methylsiloxanes and their potential persistence in the environment. “We are now in a constructive dialogue with the U.K. authorities looking at these potentially problematic substances,” he says. CES membership mirrors that of SEHSC.

The U.K. is acting as a reporter country to the broader European community on the substances. “But we are not at the stage where U.K. regulators are ready to take any action,” De Poortere says. The silicone industry is working hard to determine the fate of siloxanes in the environment, he says. Studies so far show that “the siloxanes used in personal care ultimately degrade and go back to silica.”

Several regulatory bodies have confirmed that, at current levels, D4 and D5 are used safely, De Poortere points out. Last June, for instance, the European Commission’s Scientific Committee on Consumer Safety concluded that D4 and D5 “do not pose a risk for human health when used in cosmetic products.” However, the committee advised European Commission authorities to “consider whether an environmental risk assessment associated with the use of [D4 and D5] in cosmetic products is required.”

Personal care product formulators are following the discussion with keen interest. Beta Montemayor, director of environmental sciences and regulations at the Canadian Cosmetic Toiletry & Fragrance Association (CCTFA), tells C&EN that removing D4 and D5 from cosmetic formulations “is not warranted at this time.” The cyclic methylsiloxanes are very important ingredients, he maintains, and “the science behind their environmental safety is strong and robust.”

Individual chemical makers are also closely following the debate. Silicone chemical companies, while defending their products’ safety, are making alternatives available. Firms that don’t manufacture silicones are pushing alternatives more aggressively but without calling the safety of silicones into question.

John Heitler, vice president of Shin-Etsu Silicones of America, says D5 “has been and always will be used in personal care products.” However, if customers are concerned about using methylsiloxanes, “we’re happy to work with them and offer replacements.” Among the alternatives are polydimethylsiloxane-based fluids, but no simple drop-in can take the place of methylsiloxanes, he says.

“We have replacements too,” says David A. Cohon, global marketing manager at Momentive Performance Materials. But as for an exact replacement, nothing Momentive has will do, he concedes. Wacker contends, along with other silicone makers, that cyclic methylsiloxanes are safe, but it is looking at reducing the cyclic residual levels in derivative products.

Anthony J. O’Lenick Jr., president of Siltech, says he foresees the day when “silicones used as solvents and carriers in personal care products will disappear.” O’Lenick’s firm manufactures organofunctional silicones, which can substitute for siloxanes.

Cyclic methylsiloxanes are used at high concentrations as an ingredient carrier for deodorants and antiperspirants, which account for half of the entire U.S. market for silicones in cosmetics, according to Kline & Co. As O’Lenick sees it, cyclic methylsiloxanes in antiperspirants “will be the first to go,” despite being prized for their light, non-oily feel.

O’Lenick argues that the cyclic methyl­siloxanes are not a “sustainable green” material. And he suggests that natural esters with an added touch of an organofunctional silicone will give the performance attributes consumers have come to expect of products such as shampoos, antiperspirants, and skin creams. “If a personal care product is a gourmet meal, silicones should be the salt and spice and not the meat and potatoes,” he contends.

Some firms are recommending formulations that do without silicones entirely. BASF, for instance, is promoting its Cetiol C5 emollient as an alternative to D5. According to marketing director Issberner, the esterified vegetable oil is not a drop-in replacement, but it can be formulated to make face, body, sun, and hair care products with the same feel as D5-containing products.

Another trick in BASF’s formulary is Lamesoft micronized wax dispersions with hair conditioning, shine, and strengthening properties. “We’re not saying silicones are bad or dangerous; we’re offering alternatives and choices,” Issberner says.

Oliver Thum, head of biotechnology research for Evonik Industries, says nothing has all the properties of D5. Still, Evonik offers esterified oils, such as Tegosoft AC, produced via an enzymatic process with all-natural raw materials that some customers might find an attractive substitute for D5. Evonik also sells organofunctional silicones.

A surprising source for silicone alternatives is Dow Chemical, half owner of silicone maker Dow Corning. The firm recently brought out EcoSmooth Silk Conditioning Polymers as such an alternative. As the first polyolefin in Dow’s personal care line, EcoSmooth is “a new beast no one has seen before,” says Lionel Genix, the firm’s global marketing director for personal care.

Like polydimethylsiloxanes, the new polymer minimizes hair breakage and allows a comb to glide easily through hair, Genix says. Still, he emphasizes that “this is not a silicone replacement, but an alternative to silicones. It’s an additional tool for formulators and implies no negative connotation for silicones.”

Explaining the “Eco” branding of the new polymer, Genix says Dow’s studies of polyolefins have determined that their environmental footprint is small. Environmental acceptability is “not just about natural products,” he points out.

And at least one firm is taking an entirely different approach to silicones. Air Products & Chemicals has come out with a cationic polymer that can enhance deposition of silicone on hair and skin so less is needed in a formulation and less goes down the drain. Solomon Lemma, global business manager, says Deposilk Q1 Polymer also performs as a conditioner and rheology stabilizer.

Although cosmetic makers can, if need be, replace cyclic methylsiloxanes, the jury is still out on whether and how regulators will act to restrict them. For now, many formulators are hanging tough. If governments restrict the use of D5 on the basis of science and a comprehensive risk assessment, “then we’ll consider formulating accordingly,” CCTFA’s Montemayor says. But “we believe no evidence supports that course of action,” he adds.

However, if efforts like those of Garnier to remove silicones from personal care products succeed in the marketplace, other firms may follow suit, regardless of the science. “You need to put science and proof first,” says Gillian Morris, director of chemicals and materials at Kline & Co., “but the personal care business is all about marketing and telling stories.”