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Sustainable smart polymers change color and self-repair when damaged

Plastics, which are polymeric materials composed of long chains of small molecules called monomers, are widely used in everyday life and industry due to their lightweight, good strength and flexibility. However, with approximately 52 million tons of plastic waste generated annually, plastic pollution has become a major environmental concern.

To address this issue, research efforts have focused on developing sustainable polymeric materials. Unfortunately, most materials developed so far suffer from complex synthesis processes or difficulties in separating them from other polymers during waste disposal.

To overcome these limitations, a research team led by Dr. Tae Ann Kim of the Convergence Research Center for Solutions to Electromagnetic Interference in Future-mobility (SEIF) at Korea Institute of Science and Technology (KIST) has developed a new polymeric material with self-healing capabilities and high recyclability.

The findings are in the journal Advanced Functional Materials.

The team designed a unique pentagonal ring-structured molecule that can not only be freely converted between monomers and polymers but also facilitates dynamic covalent exchange reactions in response to heat, light, and mechanical forces. This molecule enables creating polymeric materials with a wide range of properties, as flexible as a rubber band or as rigid as a glass bottle.

The newly developed polymer is easy to manage, as it exhibits fluorescence at damaged sites, enabling real-time damage detection, and self-heals when exposed to heat and light. Upon disposal, this material can selectively depolymerize into its monomers, even when mixed with conventional plastics.

The recovered monomers can then be used to regenerate polymers that retain their original properties. These features present an innovative solution for enhancing both sustainability and recyclability of polymeric materials.

Beyond its recyclability, this material dynamically changes its thermal, mechanical, and optical properties in response to heat, light, and mechanical forces.

When used as a protective coating, it demonstrates outstanding performance, with a hardness of up to three times and an elastic modulus more than two times higher than conventional epoxy coatings. Additionally, exposure to ultraviolet light strengthens molecular interactions, enabling the material to fix specific shapes.

This shape memory capability opens up potential applications in smart clothing, wearable devices, and advanced robotics.

With its high mechanical strength, damage resistance, self-healing, damage detection, and selective recyclability, this polymeric material presents a promising solution to reduce economic costs associated with sorting and processing mixed plastic waste.

Furthermore, by replacing industrial coatings with this eco-friendly alternative, the maintenance costs of coating can be significantly reduced while mitigating environmental pollution.

Dr. Tae Ann Kim, a principal researcher of the Soft Materials Research Group, emphasized, "This research introduces a new approach to designing materials with autonomous functionalities, such as damage detection and self-healing, while overcoming the thermal and mechanical limitations of recyclable plastics derived from pentagonal ring monomers.

"We are striving to pioneer the market for eco-friendly functional coatings that require minimal maintenance and generate no waste."