How smart polymers are healing patients and the planet

New classes of polymers don’t come along very often, so it was kind of a big deal when Ludwik Leibler and his team at the Laboratoire Matière Molle et Chimie at ESPCI ParisTech created vitrimers. By combining the properties of two different classes of materials, they invented a self-healing polymer that can switch from a solid to a pliable state simply by a temperature change. The ramifications are profound, including the capability to heal patients and, to some extent, the planet. The impact of vitrimers on myriad applications is one of the topics that Helen Lentzakis, PhD, will discuss during a Center Stage presentation—Get Smart with Smart Materials—at Expoplast, which comes to Montréal, QC, Canada, on Nov. 30 and Dec. 1.

Lentzakis is currently an application specialist at Group NanoXplore Inc. (Saint Laurent, QC), the largest Canadian producer of graphene, but she has special insights into vitrimers, as she pursued her post-graduate degree at ESPCI ParisTech, where the material was invented. “The work conducted by Leibler and his team received the European Inventor Award in the research category in 2015,” she notes. “The material combines the properties of thermoplastics and thermosets. The bond exchange reactions allow you to rearrange the material’s topology while the bonds remain essentially unchanged. It’s a thermoset network, and therefore has strong mechanical properties, but it can be recycled when processed at higher temperatures, when the bond exchange reactions are active,” explains Lentzakis.

The medical applications of the material, according to the researchers, include water-based nano gels that can “bridge” biological tissues. For example, vitrimers could bind together the sides of open wounds by serving as a type of organ glue in surgical procedures where stitches are unsuitable. The material also has environmental benefits.

The self-healing polymer has the potential to reduce plastic waste by prolonging the useful life of plastic-based products. The European Patent Office (EPO), which produces the European Inventor Awards program, cited the example of surfboards in its profile of Leibler. “Once set into a mold, conventional epoxy cannot be melted or dissolved. This rules out recycling, sending thousands of broken surf boards to landfills each year,” writes the EPO. “Meanwhile, current production of new surfboards, estimated at 750,000 per year, creates around 220,000 tons of CO₂. A ‘self-healing’ surfboard from vitrimer-infused epoxy could reduce production volumes by extending the life cycle of existing equipment significantly.”

"Terminator" polymer repairs itself

During her presentation, Lentzakis also will discuss the so-called “Terminator” polymer developed by scientists at the Centre for Electrochemical Technologies (CIDETEC) in San Sebastian, Spain. Considered to be the first self-healing polymer that can repair itself without human intervention, the thermoset elastomer “undergoes exchange reactions active at room temperature,” explains Lentzakis, who collaborated with the scientists while working on her post-graduate degree. “If you cut the rubber into two pieces, and join them together by applying light pressure, you will have 97% healing efficiency after two hours.” The formerly severed material is unbreakable when stretched manually, according to the researchers. Moreover, they add, “the fact that poly (urea-urethane)s with a similar chemical composition and mechanical properties are already used in a wide range of commercial products makes this system very attractive for a fast and easy implementation in real industrial applications." Indeed, self-healing technology based on dynamic bonds is currently being commercialized by chemicals company Arkema (Colombes, France). “Applications include conveyor belts, shock absorbers and paint,” says Lentzakis.

At Expoplast’s Center Stage, Lentzakis also will cover other smart materials, which she defines as materials that undergo significant, controlled change in response to environmental stimuli. These include thermoresponsive polymers, chromogenic materials, shape-memory polymers and phase-changing materials. “Smart materials provide solutions to complex problems, for example, by preventing food spoilage, protecting against excessive temperature changes, improving drug delivery and reducing waste,” she explains. She will also delve into the real-world applications and potential of graphene, which is her current professional focus at NanoXplore.

Graphene's path to commercialization

Two researchers at the University of Manchester first isolated graphene in 2004, for which they received the 2010 Nobel Prize in physics. It has been called a “wonder material” in recognition of its many properties—the material is ultra thin, light and flexible, yet 200 times stronger than steel, and is conductive yet serves as a perfect barrier that is impenetrable even to helium—but commercialization has been slow so far. “Yes, that has been challenging,” Lentzakis agrees, but she believes that NanoXplore has found a viable business model.

First, Nanoxplore’s production process makes large volumes of graphene at industrially useful pricing. This makes its benefits available to most plastic users. “We’re not just selling powder to customers,” she explains, “we’re moving down the supply chain.” The company offers graphene masterbatch, in which the material is well dispersed in the polymer matrix. NanoXplore has also begun producing parts via blow molding and injection molding technology. “You can add very low loadings of graphene, as little as one percent, and see beneficial results,” says Lentzakis, adding that graphene is starting to creep into real-world applications. She cites bicycle frames and—this being Canada, eh—hockey sticks.

“Sher-Wood has graphene-enhanced hockey sticks on the market,” says Lentzakis. The material improves tensile strength and thermal dissipation, and the more even thermal distribution imparted by the material prevents the formation of micro cracks, she explains. NanoXplore has partnered with companies to take that technology to the next level.

You might consider that to be a fairly pedestrian application for a “wonder material,” but tell that to St. Louis Blues defenseman Colton Parayko. He has cycled through around a dozen sticks in eight games, sometimes breaking two sticks in the same game. Now, there’s someone who could use a graphene-enhanced hockey stick.

Lentzakis will present Get Smart with Smart Materials on the Center Stage at Expoplast on Nov. 30 at 4:15 PM.