Glass Molding: A tidbit

Glassomer GmbH has created intricate shapes using injection molding. Photo: Glassomer.

A new approach to glassmaking treats the material like plastic, allowing scientists to injection mold vaccine vials, sinuous channels for carrying out lab chemistry, and other complex shapes.

Glass was first produced in Egypt and eastern Mesopotamia around 3500 B.C.E. Silicon dioxide (silica) is heated to about 2000°C, then shaped using a variety of techniques. Current mass production techniques can easily produce many shapes, including glass sheets and bottles, but less successfully reproduce more intricate designs.

Since 2017, Frederik Kotz, a microsystems engineer, group leader at the Laboratory of Process Technology at Albert Ludwig University of Freiburg and Chief Scientific Officer (CSO) at Glassomer, and associates have reworked a 3D printer to forge glass.

They create a printable powder by mixing silica nanoparticles with a polymer. After 3D-printing the desired shapes, they cure the mix with ultraviolet (UV) light. This ensures it holds its shape, until they fire the mix in an oven to burn off the polymer and fuse the silica particles into a continuous glass structure.

Unfortunately the procedure is slow, and unsuitable for mass production. Thus, the process has been modified to include injection molding. Silica is mixed with two polymers, polyethylene glycol (PEG) and polyvinyl butyral (PVB). This creates a dry powder that can be fed into an extruder that presses it into a preformed mold with the desired shape.

Once released from the mold, the fragile parts retain their shape because of weak attractive bonds, called van der Waals interactions, that form between neighbouring silica particles. Water is used to wash away the PEG. Then the remaining material is fired in two stages: First at 600°C to burn away the PVB, and then a second firing at 1300°C to fuse the silica particles into the final piece.

The final products are transparent, chemical inert, and stable, even at high temperatures. This makes them ideal for numerous products including telecommunications equipment, packaging for pharmaceuticals, and solar cells.

Mass producing glass parts still faces one bottleneck. The washing away of the PEG must be done slowly, over days, to ensure the glass parts don’t crack.

For further information see the Science article by Robert F. Service, and the Neptun Lab website.