Imagine an airplane healing itself when it endured a crack in its structure or else the tire of a vehicle healing itself to prevent wear. Could these be possible? Or are they just fantasies? For the scientists who are involved in the research of ‘self-healing polymers’, these are not just mere fantasies but are distant possibilities.
What is a polymer?
A Polymer is a large molecule which consists of repeating structural units (monomers), which are linked together through covalent bonds. These bonds will allow the polymers to acquire certain characteristics, which make them so unique, and useful for everyday life. Among the examples for polymers, commonly encountered plastics and biological elements such as proteins and nucleic acids could be highlighted.
The process of creating a polymer is known as ‘polymerization’ and in the presence of heat, chemicals and other elements, polymers can degrade as well. However, the microstructure or the way ‘monomers’ are arranged within the polymer will decide its degradability.
Why do polymers degrade?
As mentioned earlier, when there is a disruption to the microstructure of a polymer, degradation will take place. It mostly signifies the separation of covalent bonds between the ‘monomers’. Often, the initiating point of such degradation processes is the occurrence of ‘micro-cracks’. These cracks appear deep within the polymer and therefore would not be detectable early. However, as the crack extends or multiplies, there is a grave danger of a breakdown and a potential catastrophe, as in the case of the essential components in an airplane.
What are ‘self-healing’ polymers?
According to scientists, the researches related to self-healing polymers have picked up in the past decade and although it is still considered to be in an infant stage, vast strides have been made. Some of the polymers developed have the ability to ‘heal’ micro-cracks without any outside influence and are said to have an intrinsic capability of healing. Certain other polymers need to be treated from outside or should be subjected to certain stimulus in order to initiate the healing process. The ideas for ‘self-healing’ polymers have been derived through biological processes such as wound healing and scientists believe that they may not be far from developing polymers which could mimic the efficiency of healing, shown by these biological processes.
How do polymers heal themselves?
There are several technologies being studied in relation to correcting ‘micro-cracks’ associated with polymer degradation. An autonomous or intrinsic healing method is one such approach and in this method, the healing agent is delivered via microcapsules or hollow fibers which are activated when the macromolecules are subjected to deformation or cracking. In another method, molecular diffusion techniques are being used to create chemical or physical adhesive linkages under the influence of thermal or ultraviolet stimulus. These materials will have the specific characteristic of forming reversible bonds repeatedly in order to close the cracks throughout a lifetime. Apart from these, localized strengthening mechanisms activated by stresses have also been used to develop ‘self-healing’ polymers.
What is the use of having ‘self-healing’ polymers?
When material used for building essential components possesses the ability to ‘self-heal’, the lifetime of such components will rise and the maintenance cost will drop drastically. It will avoid many catastrophes that are experienced due to undetectable micro-cracks appearing in vital components. Furthermore, it will reduce the environmental pollution, as wastage would become minimal.
Reference:
Y. C. Yuan et al, Self healing in polymers and polymer composites : Concepts, realization and outlook: A review, eXPRESS Polymer Letters Vol.2, No.4 (2008) 238–250
‘Self-healing polymers and composites’ by T. C. Mauldin and M. R. Kessler, International Materials Reviews, Volume 55, Number 6, November 2010 , pp. 317–346.
