Plastics and other polymer composites owe at least some of their ubiquity to the ease with which they’re manufactured. At the industrial scale, a stock of pellets is melted and then injected into a mold, where it cools and solidifies into a desired shape. The process is quick, cost-effective, and highly reproducible.
Glass, however, isn’t made using injection molding. Its raw materials—sand, soda ash, and limestone—must be heated to 1500–2000 °C and then formed with a float-glass process to make sheets or with a glass-blowing technique to make curved objects. But University of Freiburg PhD student Markus Mader, postdoc Frederik Kotz, their adviser Bastian Rapp, and their colleagues have now identified an alternative way to make glass. The strategy uses the standard injection-molding technique for plastics and may potentially be more economical than the energy-intensive standard process for glass.
As a proof of concept, the researchers made glass microlenses. Despite the superior optical properties of glass, microlenses for various optical applications are mass-produced with transparent plastic because of the cost efficiencies. To try to replicate injection molding with glass, the researchers mixed silica powder with a plastic binder matrix to create an injection-moldable composite that they then manufactured into their desired shapes. Previous efforts with glass composites and injection molding produced only white and opaque borosilicate glasses, which have a low melting point and limited applications.
But adding a debinding step to the process removed the plastics from the glass in the nanocomposite material. The lenses were immersed in water for several hours, and the researchers heated the mixture to 130 °C to get rid of any residual binder matrix. In the last step of the process, the material was heated to 1300 °C and sintered, which compacted the glass to its final shape and left it highly transparent.
The new glass-making process may be suitable for industrial applications. The picture above shows about 200 glass components, which were generated in about 18 minutes (the scale bar is 1 cm). The pictures below show a lens and some complex shapes formed from 3D-printed molds (scale bars are 1 cm). Some of the authors of the paper, including Kotz and Rapp, have already made some steps toward commercialization: They are part of the Glassomer company, which has patented the technology and already offers glass-production services. (M. Mader et al., Science 372, 182, 2021.)