The document discusses various strategies for self-healing polymers, including: - Hollow fiber repair mechanisms which use hollow glass fibers filled with healing agents like epoxy. - Microencapsulation techniques which encapsulate monomers inside microcapsules that rupture to release the monomer when damaged. - Reversible cross-links using mechanisms like Diels-Alder reactions that allow cross-links to break and reform. - Applications of self-healing polymers discussed include self-healing paints, composites for aircraft repair, and next-generation self-healing concrete using bacteria to precipitate calcium carbonate to heal cracks.

1. Self Healing Polymer
Jayanta Saha
M.Sc.
2015CHS1003
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The different strategies of designing self-healing materials are as follows:
• release of healing agent
• reversible cross-links
Self Healing Polymer
Self-healing materials are a class of smart materials that have the structurally
incorporated ability to repair damage caused by mechanical usage over time.
The inspiration comes from biological systems, which have the ability to heal
after being wounded.

3. Strategies of self healing materials
Hollow fiber repair mechanism.
Microencapsulated healing agent.
Micro vascular network.
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Hollow fiber repair mechanism

5. Hollow fiber repair mechanism
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Hollow glass fiber repair mechanism

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 When DCPD comes into contact with the Grubbs’
catalyst dispersed in the epoxy resin a ring opening
metathesis polymerization (ROMP) starts and a
highly cross-linked tough polycyclopendiene is
formed that seals the crack
Polymer Engineering and Science, 46, 1804–11
Hollow fiber repair mechanism

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MICROENCAPSULATION:
This area of interest is based upon a biological ‘bleeding’ approach to
repair,

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Microencapsulation self-healing involves
the use of a monomer, (DCPD), stored in
urea-formaldehyde microcapsules dispersed
within a polymer matrix.
MICROENCAPSULATION:

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MICROENCAPSULATION:
When the microcapsules are ruptured
by a crack, the monomer is comes into
contact with a dispersed particulate
catalyst, thus initiating polymerization
& repair.
M. Scheiner et al. / Polymer 83 (2016) 260e282

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Microvascular System
To overcome the difficulty of
short supply of a healing agent
in microcapsule-based self-
healing concept, another
approach similar to biological
vascular system of many plants
and animals are applied

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Microvascular System

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Reversible Cross-links
 Cross-linking is an irreversible process, which gives superior mechanical properties
 highly cross-linked materials have the disadvantage of brittleness and have the tendency to
crack.
 One approach to bring process ability to cross-linked polymers is the introduction of
reversible cross-links in polymeric systems
 However, reversible cross-linked system does not show self-repairing ability by its own. An
external trigger such as thermal, photo, or chemical activation is needed to achieve
reversibility, and thereby the self-healing ability.

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Diels–Alder (DA) and Retro-DA Reactions
Major classes of thermally reversible polymers are made using Diels–Alder (DA) reactions

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Diels–Alder (DA) and Retro-DA Reactions

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Ionomers
 Ionomers are a special class of polymeric materials that contain a hydrocarbon backbone and
pendent acid groups
 The ionic interactions present in ionomers usually involve electrostatic interactions between
anions, such as carboxylates and sulfonates, and metal cations from Group 1A, Group 2A, or
transitional metal cations

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In particular, the self-healing ability of poly(ethyleneco methacrylic acid) (EMAA)-based ionomers

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Supramolecular Polymers
Recently, low molar mass monomers are assembled together by reversible noncovalent
interactions to obtain polymer-like mechanical properties . As noncovalent interactions can be
reversibly broken and can be under thermodynamic equilibrium, this special class of
macromolecular materials, that is, the so-called supramolecular polymers show additional features
compared to usual polymers
Liu, Y.-L., Hsieh, C.-Y. and Chen,
Y.-W. (2006) Polymer, 47, 2581–86.

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Photographs showing thermally reversible cross-linking
behavior of PA-MI/TF polymers (PA-MI-1/TF polymers
have lowest cross-link density and PA-MI-10/TF polymers
have highest cross-link density). Polymer gel
of PA-MI-1/TF in N, N-dimethylacetamide
(DMAc): (a) 30 ◦C, (b), 160 ◦C and
cross-linked PA-MI-1/TFin DMAc: (c) 30 ◦C,
5 h, insoluble and (d) 120 ◦C, 2 h, soluble.
Cross-linked PA-MI-10/TF polymer in DMAc:
(e) 30 ◦C, 5 h insoluble, (f) 120 ◦C, 5 h partially soluble,
and (g) 160 ◦C, 5 h, soluble.

20. Applications
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self healing paint

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Next Generation Self-Healing Concrete:
♜Microbial Induced Calcium
Carbonate Precipitation (MICCP)
♜Urease: (CO(NH2)2)  NH4
+ + CO3
2–
♜Ca+ + cell  cell-Ca+
♜cell-Ca+ + CO3
2–  cell-CaCO
bacilli megaterium
bacillus subtilus

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The composite material is made
from hollow fibers filled with epoxy
resin. When a hole or crack
appears, the resin leaks out and
seals the break and returns it to 80
to 90 percent of its original
strength
Self-Repairing Aircraft

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When the concrete is mixed with bacteria (bacillus subtilus), the bacteria go into a dormant state, a lot like seeds. All the bacteria need is
exposure to the air to activate their functions. Any cracks that should occur provide the necessary exposure. When the cracks form, bacteria very
close proximity to the crack, starts precipitating calcite crystals. When a concrete structure is damaged and water starts to seep through the
cracks that appear in the concrete, the spores of the bacteria germinate on contact with the water and nutrients. Having been activated, the
bacteria start to feed on the calcium lactate nutrient. Such spores have extremely thick cell walls that enable them to remain intact for up to 200
years while waiting for a better environment to germinate. As the bacteria feeds oxygen is consumed and the soluble calcium lactate is
converted to insoluble limestone. The limestone solidifies on the cracked surface, thereby sealing it up. Oxygen is an essential element in the
process of corrosion of steel and when the bacterial activity has consumed it all it increases the durability of steel reinforced concrete
constructions. Tests all show that bacteria embedded concrete has lower water and chloride permeability and higher strength regain than the
surface application of bacteria. The last, but certainly not least, key component of the self-healing concrete formula is the bacteria themselves.
The most promising bacteria to use for self- healing purposes are alkaliphilic (alkali- resistant) spore-forming bacteria. The bacteria, from the
genus Bacillus, subtilus is adopted for present study. It is of great concern to the construction industry whether or not these bacteria are "smart"
enough to know when their task is complete because of safety concerns. Bacillus Subtilus which is a soil bacterium (isolated from JNTUH soil)
is harmless to humans as it is non-pathogenic microorganism.
Chemistry of the Process Microorganisms (cell surface charge is negative) draw cations including Ca2+ from the environment to deposit on the
cell surface. The following equations summarize the role of
bacterial cell as a nucleation site 14
Ca 2+ + Cell --------> Cell- Ca 2+
Cell- Ca 2+ +CO 32-----> Cell-CaCO

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The bacteria can thus act as a nucleation site which facilitates in the precipitation of calcite which can eventually plug the pores
and cracks in the concrete. This microbiologically induced calcium carbonate precipitation (MICCP) comprises of a series of
complex biochemical reactions. As part of metabolism, B.Subtilus produces urease, which catalyses urea to produce CO 2 and
ammonia, resulting in an increase of pH in the surroundings where ions Ca 2+ and CO 32- precipitate as CaCO 3 . These create
calcium carbonate crystals that further expand and grow as the bacteria devour the calcium lactate food. The crystals expand until
the entire gap is filled. In any place where standard concrete is currently being used, there is potential for the use of bacterial self-
healing concrete instead. The advantage of having self- healing properties is that the perpetual and expected cracking that occurs
in every concrete structure due to its brittle nature can be controlled, reduced, and repaired without a human work crew. Bacterial
self-healing concrete also prevents the exposure of the internal reinforcements. This form of self-healing concrete was created to
continuously heal any damage done on or in the concrete structure. It was made to extend the life span of a concrete structure of
any size, shape, or project and to add extra protection to the steel reinforcements from the elements. With this process, money can
be saved, structures will last far longer, and the concrete industry as a whole will be turning out a far more sustainable product,
effectively reducing its CO2 contribution.

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