The production of glass – one of the oldest materials of mankind – is transforming into the 21st century. A new approach to glassmaking treats material such as plastic, allowing scientists to inject vaccine bottles, meandering channels for laboratory chemistry and other complex shapes.
“It’s a really exciting paper,” says André Studart, a materials scientist at ETH Zurich. “This is a great way to shape glass into complex and interesting geometries.”
Glass was first produced in Egypt and eastern Mesopotamia around 3500 BC. Then, as now, the material was made by melting silica or silica at about 2000 ° C, and then using various techniques to shape it. Modern glassmaking techniques can easily produce certain shapes, such as flat window panes and rounded bottles, but they cannot mass-produce the intricate designs needed for modern biomedical instruments.
In 2017, researchers led by Frederik Kotz, a microsystems engineer at the Albert Ludwig University in Freiburg, tried to change that. They redesigned the 3D printer to forge glass, not print plastic or metals.
Scientists have created a printing powder by mixing silicon dioxide nanoparticles with a polymer that can be cured by ultraviolet (UV) light. After printing the desired shapes, the polymer was cured with UV light to retain the shape. The mixture was then fired in an oven to burn the polymer and melt the silica particles into a continuous glass structure.
The approach succeeded, allowing the making of shapes such as small pretzels and replicas of the castle gates. The business aroused the interest of companies that wanted to make minute lenses and other complex transparent optical components for telecommunications equipment. But the process was slow, exposing components one by one, instead of a completely industrial approach that could mass-produce parts, as is done with plastics.
To speed things up, Kotz and his colleagues have now expanded their approach to nanocomposites to injection molding, a process used to mass-produce plastic parts such as toys and car bumpers per tonne. The researchers started again with small particles of silicon dioxide. The silica was then mixed with two polymers, polyethylene glycol (PEG) and polyvinyl butyral (PVB). The mixture created a dry powder of toothpaste consistency. The team inserted the paste into an extruder that pressed it into a preformed disc-shaped or tiny gear.
Outside the mold, the parts retain their shape because countless weak attractive bonds are formed between adjacent silica particles, called van der Waals interactions. But the parts are still fragile.
To harden them, the researchers washed the PEG with water. The remaining material was then fired in two stages: first at 600 ° C to burn the PVB and second at 1300 ° C to join the silica particles into the final piece.
“What you end up with is high-purity silicon glass” in any shape you want, says Kotz. Glass parts also have the optical and chemical characteristics needed for commercial telecommunications devices and chemical reactors, he and his colleagues in Science.
This is useful, Studart says, because its transparency, chemical inertness and stability at high temperatures make it ideal for diagnostics, drug packaging, and even bumpy surfaces that improve the efficiency of solar cells. “I think [the method] it will encourage a lot of new ideas. “
Studart says this new approach to mass-producing glass parts still faces a bottleneck: PEG rinsing must be done slowly throughout the day to ensure the glass parts don’t crack. Accelerate that, he says, and glass injection molding could become just as popular as plastic.