Australian scientists have developed a new polymer-coating technology that will help keep aircraft windows clear and crack-free. Melbourne-based Commonwealth Scientific & Industrial Research Organisation, funded by the Australian federal government, has created a process for coating aircraft windows with a water-repellent polymer that is flexible enough to accommodate changes in window shape.
The technology was developed with Sydney, Australia-based aircraft-window refurbisher Aeroclear Pty. Ltd.
CSIRO scientist Hans Griesser said his team discovered that aircraft windows developed fine cracks, called crazing, due to stress caused by changes in the water content of acrylic aircraft windows.
"These cracks, which look like scratches, don't pose any threat to safety, but they mean a major expense for airline companies, because the windows have to be removed and polished at regular intervals," Griesser said. "Longer intervals between polishings would be of considerable economic benefit to airlines, and would help keep the costs of air travel down."
Geoff Thomas, managing director of Aeroclear, said the water content of aircraft windows varies with altitude.
"At sea level it is about 2 percent. As an aircraft climbs to its cruising altitude, the water in the plastic is forced out. As it descends, the window takes up water again," he said. "This frequent change in water content is enough to cause stress that cannot evenly dissipate, hence the window crazes.
"We thought the problem could be lessened by adding a coating that would reduce or eliminate the water transfer. It is extremely difficult to produce a transparent coating that completely eliminates water vapor transport because water molecules are so tiny. However, we recognized that even slowing down the transport would help reduce the stress crazing," Thomas said.
The CSIRO team developed a way to plasma-coat the window with a thin protective polymer, applied with precision so the thickness is uniform and adheres strongly to the window.
Aeroclear and CSIRO designed a plasma reactor to apply the coating to passenger windows. The process has been successful in trials and is covered by patents.
Griesser said the coating technology involved a liquid vapor monomer being fed into a processing chamber where it is turned into a siloxane polymer coating.
"It is very different from conventional polymer manufacturing processes," he said.