Winter storms dumped record amounts of snow on the East Coast and other regions of the United States this year, forcing many people to navigate icy sidewalks and roads. However, treacherous travel by foot may soon be a thing of the past thanks to a team of researchers from the Toronto Rehabilitation Institute and the University of Toronto, Canada, who are working on a new rubber sole to help pedestrians get a better grip on slippery surfaces.
The material is made up of glass fibers embedded in rubber, and it could be used to make slip-resistant rubber soles for winter boots.
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Ice can be an especially hazardous surface when the temperature gets close to zero degrees Celsius and a thin layer of liquid water forms on top. Cleated footwear provides effective winter traction because the cleats dig into the still solid ice beneath the slippery layer of water, but because they are slippery on other surfaces, they can be dangerous if the wearer does not take them off before going indoors. In response to the need for better winter footwear, the research team developed a new method to manufacture rubber soles that dig into an icy surface on a smaller scale than cleats do.
“I think anyone who has slipped or fallen on ice can testify that it is a painful experience,” said Reza Rizvi from the Toronto Rehabilitation Institute. “Now imagine being frail or disabled – a slippery sidewalk or a driveway is all that it takes to trigger a life-changing fall. A serious fall on ice resulting in a hip fracture can be a death sentence for an older adult.”
Tilak Dutta, also from the Toronto Rehabilitation Institute, points out that falls are only part of the problem. “Equally important are the many older adults who feel trapped indoors for long stretches in the winter because of the fear of falling. The lack of activity and isolation have major negative impacts on health. We need to give older adults better footwear so they feel confident maintaining their outdoor activity levels in the winter.”
Versions of the new rubber sole are being tested in a self-contained lab that can be tilted to create sloped floors that are covered in ice and snow. The incline is increased until the volunteers who are testing the special shoes start to slip. The lab is also equipped with a padded wall and a safety harness so the volunteers don’t get hurt.
A Cross Between a Rubber Sole and Sandpaper
The material is made up of thermoplastic polyurethane, a rubbery plastic, embedded with tens of thousands of tiny glass fibers that protrude out of the rubber like microscopic studs and give the material the feel of fine sandpaper.
The material looks like regular rubber and will stretch and deform in similar ways. The material also performs just as well as regular rubber on hard, dry floors. On ice, however the rubber-glass fiber composite provides significantly better traction. The researchers hope that their work will prevent many slips and falls on winter ice.
Existing methods for fabricating the material require first extruding a rubber slab with glass fibers running parallel with the surface. The slab is then cut and reoriented so that the fibers stick out of the surface like tiny pins.
“The materials required for creating a high friction composite are not expensive, but the process of slicing and rearranging the rubber is not easily scalable,” Rizvi says. The team has been working on ways to automate the process so that the material can be cheaply mass-produced and be made to last longer. The prototype rubber sole quickly loses its non-slip qualities with use, so it will not be appropriate for commercial footwear for walkers and hikers until its robustness is improved.
So, what excites the research team the most? “I am most excited about taking my research and having it applied to a serious societal issue of winter safety,” Rizvi says.
“This work has the potential to have a real impact on the massive, expensive public health problem of winter falls, not to mention the dramatic improvement in quality of life for those living in northern climates,” Dutta adds.
This research is published in the journal Applied Physics Letters.
Top Image: Volunteers wearing the rubber soled shoes walk up and down an ice-covered inclined floor in the Challenging Environment Assessment Lab. (Photos courtesy of Reza Rizvi, Yue Li, and Sharon Ravindran/ Toronto Rehabilitation Institute)