8/10/2019 Self healing polymer technology http://slidepdf.com/reader/full/self-healing-polymer-technology 1/23 1 | Page ACKNOWLEDGEMENT To put an effort like this requires the determination and help of many people around me and I would not be doing justice to their efforts by not mentioning each helping hand in person. I express my heartful gratitude to Prof. H G. Phakatkar, Head of Department and other staff members of the Mechanical Engineering Department for their kind co-operation. I feel privileged to acknowledge with deep sense of gratitude to my guide PROF. M.V. Walame for his valuable suggestion and guidance throughout my course of studies and help render to me for the completion of the report. I would like to give sincere thanks to the Central Library Cell and Reference Library Cell and Information Access Centre for their kind co-operation throughout my work. Last but not the least I would like to thank my parents and my friends. It would have not been possible to complete the report without their moral support, valuable comments and suggestions which motivated me towards work. Shinde Atul K. TE-V_01
This document is posted to help you gain knowledge. Please leave a comment to let me know what you think about it! Share it to your friends and learn new things together.
Heating induced healing of polymers depends on inter diffusion of chains and formation
of entanglements. Crack healing happens only at or above the glass transition
temperature. In order to reduce the effective glass transition temperature polymer is
treated external agent for e.g. PMMA is treated with methanol and ethanol reducing the
glass transition temperature to a range of 40~60°C, and found that there were two
distinctive stages for crack healing: the first one corresponding to the progressive healing
due to wetting, while the second related to diffusion enhancement of the quality of
healing behavior.
Healing of epoxy, for instance, has to proceed above the glass transition temperature.
Then, the molecules at the cracking surfaces would interdiffuse and the residualfunctional groups react with each other. A 50% recovery of impact strength can thus be
obtained.
1.2. Self-healing based on Chemical Interactions
Cracks and strength decay might be caused by structural changes of atoms or molecules,
like chain scission. Therefore, inverse reaction, i.e. recombination of the broken
molecules, should be one of the repairing strategies. Such method does not focus on
cracks healing but on „nanoscopic‟ deterioration. Examples are polycarbonate (PC)
synthesized by ester exchange method and poly-phenylene ether (PPE) in which the
repairing agent was regenerated by oxygen. The above example shows that PPE might be
probably designed as a self-repairing material by means of the reversible reaction. The
deterioration is expected to be minimized if the recovery rate is the same as the
deterioration rate.
Another method is using thermally reversible crosslinking behavior has been known for
quite a while. Wudl et al . combined this with the concept of „self -healing‟ in making
healable polymers. They synthesized highly cross-linked polymeric materials with
multifuran and multi-maleimide via Diels-Alder (DA) reaction. At temperatures above
120°C, the „intermonomer‟ linkages disconnect but then reconnect upon cooling (i.e. DA
reaction). This process is fully reversible and can be used to restore fractured parts of the
through which cells and growth factors migrate as healing ensues. Owing to the vascular
nature of this supply system, minor damage to the same area can be healed repeatedly.
Figure 4. Schematic diagram of repair concept using 3D network
2.2. Self-healing in terms of healant loaded microcapsules
Figure 5. Self-Healing Coating
The principle of this approach resembles the aforesaid pipelines but the containers forstoring healing agent are replaced by fragile microcapsules. As soon as cracks destroys
the capsules, the healing agent would be released into the crack planes due to capillary
effect and cure crack under initiation of the latent hardener.
Although all types of these materials have their own self-healing mechanism, we start
from describing some common features. Virtually all materials with long degradation
time deteriorate through development of microcracks (fatigue). A sharp apex of each
crack works as a knife cutting the materials with ease. This results in larger cracks, and
consequently, mechanical degradation. Example of such material would be plastics used
for construction, artificial bones, dental cement, etc. To heal such materials, one needs to
seal those microcracks before their further growing. The other type of degradation and
the healing mechanism is important for materials that can degrade sufficiently fast.
Example of such materials can be various coatings, armor, all surfaces that can suffer
sudden impact or collision with a projectile. In such a case, not only cracks, but even
holes should be sealed and healed. Definitely there are materials of dual purposes, which
would degrade through both of the above mechanisms.
To classify self-healing materials, one can consider four different classes:
plastics/polymers, paints/coatings, metals, and ceramics/concrete. We will discuss each
of these classes below.
1. Plastics/polymers
Polymers/plastics are attractive from mechanical and chemical points of view. Many
plastic materials are strong and resistant to breaking. However, once fractured, the
material deteriorates irreversibly. Even under normal wearing, plastics used to developsmall cracks that also grow irreversibly. This leads to degradation of their mechanical
properties and decreasing life time of such materials. This is where self-healing is needed
the most. The working principle of self-healing mechanism is based on having small
capsules filled with healing glue. These capsules are mixed within the polymer body. The
Efforts to create autonomic, or self-healing, materials have become a fast-growing line of
research, in large part due to advancements made by Beckman Institute researchers.
In 2001, Beckman faculty members Nancy Sottos, Jeff Moore, and ScottWhite published
a paper in Nature magazine detailing their breakthrough work that demonstrated for the
first time self-healing in an engineered materials system. The paper drew worldwide
attention in newspapers, journals, and websites and earned a front page story in the
Washington Post.
Inspired by biological processes in which damage triggers an autonomic healing
response, their work has used encapsulated microcapsules and microvascular networks as
methods for generating self-healing in a polymer material and, in a recent research line,
in electrical energy storage systems, including batteries. Since the Nature paper first
appeared in 2001, numerous advances have been made by Beckman researchers,
including developing methods that are more practical and cost-effective than the original
approach, developing systems that are able to repair multiple cracks, and the introduction
of mechanochemical approaches to self-healing. Potential applications could includematerials that self-repair damage on coatings such as those applied to airplane fuselages
or bridges, and batteries for electrical vehicles.
Nancy Sottos, JeffMoore, and ScottWhite have developed microvascular composites that
improved the microcapsule concept (in which the healing agent was consumed) through
an interconnected delivery network of microchannels that provide for multiple self-
Polymer composite circuit boards and electronic components can suffer frommechanical and electrical failures if microcracks progress unabated. This self-
healing technology would help to prevent such failures.
VI. Civil construction
Calcium for self-healing concrete is cheap. Self-healing coatings on structural
steel components in, for example, bridges can be very popular. Again, here the
healing mechanism is not in recovery mechanics of the coating but rather in protection against rust. This helps sustaining mechanical integrity of the coated
steel constructions.
VII. Paints, Coatings, and Adhesives
Used in a wide variety of products, paints, coatings, and adhesives are subject to
scratches, cracks, and deterioration. This self-healing technology would repair this
damage, maintaining protection from environmental conditions and/or a longerlasting seal.
Achievements in the field of self-healing polymers and polymer composites are far fromsatisfactory, but the new opportunities that were found during research and development
have demonstrated it is a challenging job to either invent new polymers with inherent
crack repair capability or integrate existing materials with novel healing system. But this
provide aspect for future development and application possibility of polymeric materials.
Also, the extended service life of components made from these intelligent materials
would contribute to reduce waste disposal. It is undoubtedly important for building up a
sustainable society.
Comparatively extrinsic self-healing techniques might be easier for large-scale usage for
the moment but from a long-term point of view, synthesis of brand new polymers
accompanied by intrinsic self-healing function through molecular design and automatic