Where would we be without glass? We buy pickles, red cabbage, and mustard in jars. We pour beer, sparkling wine, and spritzers from bottles. At Christmas, elegant glass perfume flacons find their way under the tree. According to the industry association FEVE, around 80 million glass bottles and jars enter the European market each year, filled with food, beverages, creams or other cosmetics. Millions more circulate as returnable bottles, traveling between customers and bottlers up to 25 times before eventually being recycled. Besides metal cans, glass is the only packaging material that can be recycled endlessly without losing quality—it can always be reshaped.
Decisive for purchase
Because it’s so ubiquitous, glass rarely gets the appreciation it deserves. Most of us focus on what’s inside, not on the container itself. But that container has a long list of duties. Bottles and jars need to offer a firm grip, even when condensation forms. They also need to be robust. They must withstand impacts without shattering, ensuring safety. Labels and prints must adhere reliably. For premium products, a flawless appearance is key. A champagne bottle shouldn’t show scratches; a €100 perfume flacon must look immaculate. “Glass manufacturers therefore need to deliver a perfect look and feel—it can make a real difference at the point of sale,” says Dr. Stefan Hilf, Head of Research & Development for the Smart Effects business line at Evonik’s Rheinfelden site.
»Perfect look and feel make a real difference at the point of sale«
Stefan Hilf Head of Research & Development at Evonik Smart Effects
Two layers for the final finish
To meet these demands, glass containers receive a special coating that is just a few nanometers thick, yet extremely robust. It makes the surface scratch-resistant, gives it a pleasant grip, and enhances its overall quality. For returnable bottles, it also prevents the material from becoming dull and worn too quickly.
For decades, the industry has relied on a tried and tested two-step process. First, bottles are sprayed with butyltin trichloride, which forms a smooth tin oxide layer on the hot glass. This layer fills microscopic cracks and acts as an adhesion promoter for the second step: a film of polyethylene wax, which links with tin oxide across the entire surface, providing grip, scratch resistance, and a smooth finish.
The method is globally established but problematic. Butyltin trichloride is corrosive and toxic to aquatic organisms. In addition, the substance degrades only slowly, meaning it can persist in the environment for a long time and accumulate in living organisms. Since only the harmless tin oxide layer remains on the glass after the reaction, the process is still suitable for the food industry. However, glass manufacturers are only allowed to apply the butyltin trichloride under strict safety precautions. That makes occupational safety costlier and the whole production process more complex. That’s why Evonik and French company TotalEnergies jointly developed an entirely new, nontoxic coating approach. It’s scheduled for market launch in late 2027, when TotalEnergies intends to deliver the new product—named Glasskote Base 1—to its customers in the glass industry.
Coating in one go
So far, glass bottles are coated with polyethylene in a two-step process. The new silane process eliminates the need for hot coating.
Tailor‑made silanes
This new coating is based on silanes—a completely different chemical class of substances than butyltin trichloride. Silanes consist of a silicon framework to which molecular appendages with various chemical functions, known as functional groups, can be attached. “This allows you to tailor surfaces with a wide range of effects,” says Stefan Hilf. Metals can be made resistant to corrosion; walls can be treated to repel water and prevent moisture and moss formation. “With this new silane coating, Evonik is now entering a new segment of the glass industry,” Hilf emphasizes.
It took a long time to reach this point. The team needed a solution that matched the performance of the long-established tin oxide-polyethylene system. Development began in 2019, when TotalEnergies’ US division approached Evonik. Having supplied the glass industry with lubricants and release agents for years, their teams were well aware of the challenges surrounding butyltin trichloride. “We reached out to several companies in the United States that had attempted to create an alternative—but none could meet the industry’s requirements,” says Manuel Keller, Sales Director at TotalEnergies Glass Lubricants Europe. “Evonik was the first partner with the technical understanding and chemistry expertise needed to tailor suitable materials for this use.”
The goal: A perfect film
The breakthrough came largely thanks to the experience of the Rheinfelden team—especially Eckhard Just, who has worked at Evonik in Rheinfelden since 1987. As a chemical engineering specialist, he knows how to give silanes the needed properties and how to handle them—because they can be somewhat capricious. Silanes are predominantly delivered to customers in liquid form. However, the molecules tend to crosslink with one another when exposed to moisture. They form viscous gels, precipitate out of the liquid as flakes, or even clump together. Developing a silane solution that remains stable over a long period of time and only forms a fine, even film on bottles at the very end of the glass production process requires experience. “It’s truly a challenge,” says Just. “If the liquid ends up clumping in the hoses or spray nozzles of the system, you have a huge problem.”
The team had to identify the right acid for processing the silanes, determine the correct pH and the ideal solids content in the aqueous solution, and perfectly adjust many other parameters. And of course, the right ingredients also mattered. Silanes are assembled from small individual silicon building blocks known as monomers. These monomers join together in pairs or trios to form larger molecules—the dimers or trimers. Whether a silane ultimately forms a thin uniform layer on the surface of a bottle depends, not least, on the mixing ratio of these oligomers.
»For high-quality champagne bottles, the layer still needs to become even more scratch resistant«
Fabian Zschocke Project Manager Glass Lubricants at TotalEnergies
Testing in real world conditions
Eventually, the team found the perfect recipe. Initial spray tests in the lab looked excellent. When Eckhard Just sprayed glass bottles with a spray gun, a thin, even film formed. Then it was time for the first practical trial at a large test facility in the USA. As soon as the bottles had cooled to between 130 and 100 degrees Celsius, the silane—polyethylene mixture was applied—and it formed a flawless film on the bottles.
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And the experts achieved something else as well; the silane and the polyethylene wax could be applied to the bottles in a single step. “That was a huge success,” says Hilf, Head of Research, “because it significantly simplifies the coating process compared to the conventional method.” Butyltin trichloride and polyethylene have to be applied separately at two different points in glass production, with butyltin trichloride coming first. It is deposited as a vapor onto the bottles while they are still hot. They pass through a chamber in which a fine mist of butyltin trichloride settles on them. After that, the bottles cool down on the conveyor belt to around 90 degrees Celsius. Only then can they be sprayed with the polyethylene wax.
»We will enter the market at the beginning of 2027«
Karsten Korth Technical Manager at Evonik
Everything in one go
Not so with the silane coating. Customers simply mix the silane solution with the polyethylene emulsion of their choice at the plant and then fill the mixture into the spraying system—and that’s it. In recent months, TotalEnergies has carried out additional production tests together with glass manufacturers. Their results are also promising. “With Glasskote Base 1, we produce surfaces that reach 80 to 90 percent of the quality of a butyltin trichloride coating,” says Fabian Zschocke, a project manager and glass production expert at TotalEnergies. “For beer bottles and food jars, that is more than sufficient. But for champagne bottles, for example, the layer still needs to become even more scratch resistant.” He is confident that the quality will continue to increase, as every plant still has the potential to be optimized. “No production facility is like any other,” Zschocke explains. “A new process first needs to be fine-tuned and run in.”
Dr. Karsten Korth, Technical Manager at Evonik in Rheinfelden, is confident that the new technology will match the conventional system. “We will enter the market at the beginning of 2027 and will continue optimizing together with TotalEnergies and the customers—either by adjusting the production facilities or by modifying the silane with further additives,” he says. “What is crucial is that glass manufacturers can switch to the new coating without making major changes to their production equipment.” Fabian Zschocke is currently working with glass manufacturers to further optimize the spray‑nozzle technology so that the bottles truly receive a uniform, perfect layer.
Benefits for glass manufacturers
For glass manufacturers, the new technology offers a major advantage: They hardly need to make any modifications to their production lines in order to apply the silane coating. In addition, Glasskote Base 1 facilitates the transition from gas-fired furnaces to electric furnaces. Like many other industries, glassmakers will have to comply with stricter limits on carbon dioxide emissions in the future. Until now, melting furnaces have been heated with natural gas, releasing large amounts of CO2.
In the future, they are to be powered by electricity. The conventional coating process creates problems here: When the tin oxide layer forms on the hot glass surface from the butyltin trichloride, hydrochloric acid is released. Up to now, this acid has been mixed with the exhaust gases from the gas furnaces and thereby heavily diluted. When electric furnaces are used, these exhaust gases are no longer available, and the concentration of hydrochloric acid in the air stream reaches critical levels. “For this reason, the authorities prohibited one of our customers from using monobutyltin trichloride,” Zschocke explains. “With Glasskote Base 1, the problem disappears.”
Beyond that, the shift to silanes offers yet another advantage, adds Evonik RD&I manager Hilf. Under the European Union’s new supply chain regulations, companies must ensure that not only they themselves, but also their suppliers comply with environmental protection standards. “This means it also becomes important for bottlers and the food industry whether the glass was produced in a more environmentally friendly way,” says Hilf.
Evonik and TotalEnergies have high expectations for the new technology. The further the performance of the silane improves in an industrial environment, the greater the interest among glass manufacturers is likely to become. One major strength is that, by eliminating the use of butyltin trichloride, it makes production safer and more sustainable in terms of occupational health and environmental protection. Glass is already an environmentally friendly material. Because it can be melted down endlessly, it offers an excellent basis for a true circular economy. And with the transition from gas to electric furnaces, its carbon footprint will shrink even further. The silanes are paving the way for such a future.
