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Self-healing Materials

Self-healing Materials

By TA News Bureau 

Dutch scientists led by Dr Marianella Hernández of Novel Aerospace Materials Group of the Delft University of Technology have developed a revolutionary self-healing natural rubber process that extends the service life of the material. Besides reducing waste and maintenance costs, it has several advantages and characteristics. In an interview to Tyre Asia, she said materials with the ability to heal are capable of making the damage disappear  thereby extend  the service life of such materials leading to reduced waste and lower maintenance costs

Materials scientists have always focused on the design of materials which are robust and resistant to mechanical and chemical damage. The strategy has worked very well over the past years and has served to develop very strong materials. However, these materials can still fail and once damage occurs it will not disappear, limiting their service life.
Inspired by nature, self-healing materials are here to overcome this limitation. “Materials with the ability to heal are capable of making damage disappear in a more or less independent way thereby extending the service life of such materials, and thereof reducing waste,” explains Dr Marianella Hernández of Novel Aerospace Materials Group of the Delft University of Technology, Netherlands.
In an interview to Tyre Asia the polymer scientist, who authored over 40 peer-reviewed research papers, emphasised that lifetime extension by healing events would also reduce the overall costs in material use and maintenance.
At the Novel Aerospace Materials group of the university, which she joined after winning the prestigious Marie Curie Fellowship from the European Commission, she and her research team have been working for several years in the development of different self-healing strategies and evaluation protocols to develop new self-healing and/or healable materials for applications such as coatings and composites.
“As a result of our pioneering experience in the field, we recently developed a self-healing vulcanized rubber based on reversible disulfide bridges. The new self-healing rubber can be seen as a model material to develop more robust self-healing rubbers without affecting too much the current manufacturing processes,” she said.
Commenting on the design and preparation of self-healing polymers with long-term durability, she pointed to the fact that traditional materials generally accumulate damage and fail after a certain period of use.
Such damaged materials (plastics, rubbers) are typically discarded in landfills, or in some cases repaired with a manually applied patch. On the other hand, self-healing materials offer an alternative to the damage-and-discard cycle and represent an innovative way for extending the long-term durability of goods.
“The self-healing character makes sure that total failure only occurs after very long usage times,” she says.

Intelligent polymers

Dr Hernández’s research has opened new avenues to fabricate intelligent multifunctional polymers with versatile functions that will give a boost to natural rubber producers who are struggling to find better prices in the world market.
“There are not too many research work addressing the potential of self-healing concepts to restore several functions lost during macroscopic damage,” she points out.
“As functions you can think of polymer composites with electrical and thermal conductivity as well as the necessary mechanical integrity to make the polymer industrially interesting. All three functions should be restored after healing a macroscopic damage.”
As a follow up to this, her research group is currently focused on demonstrating that achieving these characteristics is possible in different kinds of polymeric materials such as conductive rubbers.
The implementation of self-healing concepts offers new opportunities in the type of materials that can be developed, Dr Hernández explained.
“We can for instance think of applications in which properties like elastic recovery, fatigue and abrasion resistance, water resistance and electrical conductivity given by carbon black or other conductive fillers play a key role.”

Uses in tyres

Dr Hernández said such rubber can be used in the development of tyres that would offer better safety, performance, rolling resistance and longer fatigue life.
“Research in this area is at the level of making a jump into the industrial sector. Yet, this will require direct industry-university collaborations to better implement healing concepts.”
She is currently involved in developing natural rubber compounds with self-healing properties, following the intrinsic self-healing approach based on reversible bonding and by the inclusion of conductive nanoparticles.
The rubber that her team has presented should be seen as a starting material model concept for future developments with a more clear industrial focus, she said.
“The fact that we are able to develop a vulcanized self-healing rubber is a big step towards final applications. This is absolutely a promising result for the tyre industry in which safety, performance and longer fatigue life are crucial factors.”
Looking at the emerging trends in this field, Dr Hernández has made several observations for the future. Different concepts to implement healing have been proposed but several are unlikely to ever reach a level interesting enough for the industry.
It is then crucial to know what are the limitations and possibilities of the different concepts. At the same time each type of damage and application will require a totally different approach, in other words one does not fit them all.
Her research group sees the fastest implementation in the following fields:
• Devices that are hard to be repaired since they are located in places difficult to access (high altitude buildings, underground, etc.) and their repair costs are high.
• Applications where large repairs result in a lot of inconvenience to society.
• Products which need to have a damage-free and protective surface over a long period of time.
• Applications that have to comply with high safety requirements.
However, the growth of this emerging field will definitely depend on a mindset change where material’s life expectancy is more relevant than the initial cost.
In some areas the change has already arrived in The Netherlands such as in the construction sector with concrete and asphalt.
Dr Hernández thinks that the new insight into the character of both the network structure and the cross-linking system by means of dielectric processes will be useful in controlling self-healing properties of all elastomeric self-healing systems to be developed in the future.

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