Imagine a material that resembles rubber, but can be extended up to ten times its size when it comes into contact with water, and then regain its original shape when the water disappears.

These are tailor-made properties for use in seals in wastewater treatment plants, sewers, and tanks for example; i.e.: applications where performance is important. These are the properties exhibited by a special type of thermoplastic elastomer (TPE) with water adsorbing (hydrophilic) capabilities.

Here we are probably turning things upside down as TPE is normally regarded as a material that is highly resistant to water. Chemistry, however, is the science of possibilities, and within the family of recyclable polymers, we find many examples of products that can help maintain a sustainable society.

In this article you will learn more about TPE with hydrophilic properties, but also a type of TPE, which provides better quality of life for disabled people.

Expanding elastomers

Swedish company ELASTO, headquartered in Åmål, produces many different types of TPE. With the hydrophilic materials in the Dryflex WS-Series, the company offers products with good sealing properties based on elastomers that expand in aqueous solutions.

These properties are achieved by adding a “superabsorbent polymer” in the elastomer mixture. The temperature, salinity and acidity (pH 7-12), and the mixture of elastomers, determines how much the material expands. The series consists of materials that can be expanded from 2.5 increments up to 10 times its size. When the material is no longer in contact with water it regains its original size. The process of expansion and shrinkage can occur repeatedly.

Unlike clay-based sealant, which can erode and rupture, Dryflex WS retains its basic structure during the expansion process. The thermoplastic elastomers can be processed in conventional processes for plastics processing, e.g. injection molding and extrusion. The materials can be colored and are fully recoverable. Antimicrobial versions are also available. Seals for wastewater treatment plants, tunnels, sewers, tanks, windshields, headlights and electric cables are some of the uses of hydrophilic TPE.

In 2011, the Material Library in Stockholm chose Dryflex WS as one of the ‘20 most inspirational materials’ at a design workshop organized by the Sony Design Centre in London, in collaboration with Les Ateliers Design University in Paris.

Flexyfoot gives better quality of life

The TPE product Flexyfoot is shock-absorbing and slip-resistant and can replace the traditional rigid rubber foot on crutches and walking sticks – something that facilitates movement and enhances quality of life for disabled people.

Designer David Goodwin developed the Flexyfoot idea. His disabled sister and elderly mother complained that their crutches caused them troubles. They also thought that the rubber feet wore too quickly and were difficult to replace.

Goodwin, together with manufacturer Pentagon Plastics, developed ELASTO, a tailored-made Dryflex TPE material with improved wear characteristics.

The material structure of Dryflex TPE gives Flexyfoot a good grip on slippery and wet surfaces.

“It was important for us to develop a material that gives the best performance and feel for the user but that is also easy to work with in the production process,” says Mark Griffiths, the head of development at ELASTO’s UK facility. “Design and material choices for Flexyfoot gave us a combination of challenges. Together with Pentagon Plastics, we worked with the material’s flow properties to get an exact mold filling.”

Flexyfoot became number two in the prestigious “British Healthcare Trades Association’s Independent Living Design Awards 2010.” The awards are given to the principal technical health products in the UK, products that make it possible for elderly and disabled to live independent lives.

The article was published in May 2012