Sustainable manufacturing drives the growing interest in self-healing polymers. A property usually associated with living beings, self-healing could greatly enhance device lifetime and maintenance costs. This capability has previously been restricted to fragile gels or required high temperatures. A new strategy that combines both high durability and room-temperature self-healing into a polymer is needed.
In their communication in Advanced Materials, Sung Yeon Hwang, Dongyeop Oh, and Jeyoung Park from the Korea Research Institute of Chemical Technology, and their co-workers report a tough, transparent, self-healing thermoplastic urethane. Asymmetric alicyclic structures within the polymer can undergo self-healing by aromatic disulfide metathesis, restoring 75% of the initial mechanical properties within only 2 hours.
The researchers synthesize four different thermoplastic polyurethanes with polytetramethylene ether glycol (PTMEG) as the soft component by varying the diisocyanate, embedding the self-healing bis(4-hydroxyphenyl)disulfide component in the hard segments.
Of the four polymers, only the combination of isophorone diisocyanate (IP) and bis(4-hydroxyphenyl)disulfide (SS) achieved full scratch recovery at room temperature. A detailed investigation indicates that a loose packing of the IP moieties results in a favorable disulfide metathesis at room temperature. A split circular film of the material healed within 2 hours at room temperature and could withstand 5 kg after 6 hours.
In contrast to IP-SS, films containing other diisocyanates require 80 °C for self-healing. Tensile tests of an IP-SS polyurethane film at a drawing rate of 100 mm min–1 yield a record-high tensile strength and toughness of 6.8 MPa and 26.9 MJ m–3.
Printing silver electrodes onto the film creates a sensor for scratch detection. A connected LED turns off after scratching due to an increase in resistance, but emission is restored after just 25 min at room temperature.
Professor Dongyeop Oh states, “Finally, we showed our material is applicable as a scratch sensor. Thus, we believe our material has great potential in the wearable devices industry.”
To find out more about this remarkably durable self-healing polymer, please visit the Advanced Materials homepage.