morden self healing polymer technology

Modern Self-Healing Polymer Technology

A REPORT

Submitted by:

VIVEK A. RANA (140520724008)

In partial fulfillment for award of degree

Of

MASTERS OF ENGINEERING

In

(PLASTIC ENGINEERING)

3

rd Semester

Central Institute of Plastic Engineering and Technology,

Department Of Chemicals & Petrochemicals Ministry of Chemicals & Fertilizers

Govt. Of India

Plot No.630, Phase IV,G.I.D.C.,

Vatva Ahmedabad – 382445

Gujarat Technological University, Ahmedabad

2015

CENTRAL INSTITUTE OF PLASTIC ENGINEERING AND TECHNOLOGY

AHMEDABAD

PLASTIC ENGINEERING

2015

CERTIFICATE

Date:

This is to certify that the report entitled “Modern Self-Healing

Polymer Technology” has been carried out by Vivek A. Rana

(140520724008) Under my guidance in partial fulfillment of the

degree of Masters of Engineering Degree in Plastic Engineering

(3rd Semester) of Gujarat Technological University, Ahmedabad,

during the academic year 2015.

Dr. Rajeev Vaghmare Dr. S K Jain

Principal Chief Manager (Technical)

HLC/CIPET- Ahmedabad HLC/CIPET- Ahmedabad

Dr. Radheshyam Giri Mrs. Hetal shah Lecturer Lecturer

HLC/CIPET- Ahmedabad HLC/CIPET- Ahmedabad

Central Institute of Plastic Engineering and Technology,

Phase - 4, Plot No.630, Vatva G.I.D.C., Ahmedabad-382445

ACKNOWLADGEMENT

This report shall be incomplete if we do not heartfelt gratitude to those people from whom we

have got considerable support and encouragement during this semester, many people have

helped, provided direction, technical information and advice at all stages of semester and it’s our

pleasure to say thanks to all of them.

We would also deeply acknowledge Dr. Rajeev Vaghmare, Principal, HLC/CIPET-

Ahmedabad who gave us opportunity to make the report.

We are also deeply indebted to the lecturers of Plastic Engineering Department for their

motivational support and continuous flow of encouragement while working in the direction of

preparation of the seminar.

We are thankful to Dr. S K Jain, Dr. Radheshyam Giri and Mrs. Hetal shah for helping us

and providing more technical information about Modern Self-Healing Polymer Technology

and also encouraged us during the preparation of this report.

Lastly, our warm thanks to our professor staff and all our supportive well-wishers for all that we

will always be indebted to.

We are thankful to our friends for helping us out in difficult situations during our report

preparations and also our parents for supporting us throughout the semester. Above all we like to

thank Almighty for giving us strength to do the work on seminar and report.

VIVEK A. RANA (140520724008)

M.E. 3rd Semester

Plastic Engineering

CIPET Ahmedabad

Abstract

This abstract frames the complexity of the Self-healing Materials for polymer

research with a purpose & significance that any reader can understand. Polymers and

polymer composites are used in a variety of applications, which include transport

vehicles, sporting goods, civil engineering, electronics etc.., However, these materials are

susceptible to damage induced by mechanical, chemical, thermal, UV radiation, or a

combination of these factors. This could lead to the formation of microcracks deep within

the structure where detection and external intervention are difficult or impossible. The

presence of microcracks in the polymer matrix can affect properties of a polymer such as

tensile strength, fatigue life, compressive strength, impact strength etc.., Several

techniques have been developed and adopted by industries for repairing visible or

detectable damages on the polymeric structures. However these conventional repairing

methods are not effective for healing invisible microcracks within the structure during its

service life. In response, the concept of self-healing polymeric materials was proposed as

a means of healing invisible microcracks for extending the working life and safety of the

polymeric components. The development and characterization of self-healing synthetic

polymeric materials have been inspired by biological systems in which the damage

triggers an autonomic healing response. Polymeric materials may be broadly classified as

Thermoplastics, Thermosets and Elastomers. An attempt is made to draw together much

of work published in the literature and to understand the progress and prospects of

Modern Self-healing Polymeric Material.

List of Figures

Figure no

Figure description

Page no

1 Schematic diagram of repair concept for polymer matrix composites

using pre-embedded hollow tube 6

2

Schematic diagram of repair concept using pre-embedded hollow tubes 6

3

Self-healing concept using hollow fibers or tubes 7

4 Schematic drawing of the principle of self-healing epoxy based

laminates with epoxy loaded microcapsules and latent hardener 10

4a Schematic drawing of the principle of self-healing epoxy based

microcapsules 11

4b

Self-healing effect by microencapsulation method in Thermoset 12

5

Car painted with “Scratch Guard Coat” 15

INDEX

Acknowledgement……………………………………………………………………………………………..…………………….I

Abstract…………………………………………………………………………………………………………………….….………….II

List of figure……………………………………………………………………………………………………………..………….… III

Index…………………………………………………………………………………………………………………………….…..…… IV

Chapter No Description Page No.

1. Introduction 1

1.1 Types of self-healing materials and the healing mechanisms 1

1.1.1 Plastics/polymers 2

1.1.2 Paint 2

1.1.3 Metals 2

1.1.4 Ceramics/concrete 3

2. Classification of Self-healing Polymers 4

2.1 Intrinsic self-healing 4

2.1.1 Self-healing based on physical interactions 4

2.1.2 Self-healing based on chemical interactions 4

2.2 Extrinsic self-healing 5

2.2.1 Self-healing in terms of healant loaded pipelines 5

2.2.1.1. Hollow glass tubes and glass fibers 5

2.2.1.2 Three-dimensional microvascular networks 8

2.2.2 Self-healing in terms of healant loaded microcapsules 9

3. Applications 14

3.1 Low cost sensitive applications 14

3.1.1 Medical dental/ artificial body replacements 14

3.1.2 Aero/Space 14

3.1.3Military 15

3.2 High cost sensitive applications 15

3.2.1Car painting 15

3.2.2 Civil construction 16

4. Benefits, Problems and Challenges 17

4.1 Benefits 17

4.2 Problems and Challenging 17

Conclusion 18

References 19


CENTRAL INSTITUTE OF PLASTIC ENGINEERING AND TECHNOLOGY Page 1

Chapter 1: Introduction

Self-healing materials, where does it come from? Indeed, this is what everyone

saw at least several times. Wounds or skin cuts heal after some time. So, it has been

natural to try to create materials possessing such a wonderful property. One can list

thousands of possible applications for such materials in variety of different fields.

Increased reliability and lifetime can be critical in medicine, space missions, traffic,

military, construction, and so on. In principle, it is possible to “heal” (recover) different

properties. For now self-healing means mostly recovery of mechanical properties. Recent

news from Nissan about successful commercial release of “self-healing” car painting has

heated public interest in such type of materials. Common names for these materials are

self–healing, self– repairing, autonomic–healing, autonomic-repairing materials. Because

all these names mean the same thing in nature, we will use just one, self-healing. As

usual, these names are used for quite a broad variety of materials with very different

healing/repair mechanisms. Here we briefly overview this variety of materials and the

mechanisms of healing, possible applications, general technical challenges.

1.1 Types of self-healing materials and the healing mechanisms

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:

1. Plastics/polymers,

2. Paints/coatings,

3. Metals, and

4. Ceramics/concrete.

1.1.1 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 develop small 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.

It is worth noting that thermoplastic materials demonstrate interesting natural healing

property. Being heated, they can recover their mechanical integrity and properties. This can

be used to fix some impact damage even autonomically. For example, after collision with

such a plastic, there can be a dent/hole/scratch. However, as a part of the collision energy

transfers into heat. So the area of the damage can be melted and heal itself.

1.1.2 Paint

Apart from cosmetic reason, paint is typically serves to protect surfaces. Self-

healing protection coating for cars from Nissan is one of such examples. However, main

cause of wearing of paint coating is due to scratches, abrasion, and mechanical damage. It

implies a specific restriction to a possible healing mechanism. Specifically, recover of

mechanical recovery is not as important as recovery of protective property. This means,

for example, that the healing agent can seal or inhibit corrosion of the surface underneath

the crack rather than seal the crack itself. To fix scratches cosmetically, and up to some

extend protect coated surface, a rather viscous polymer can be used instead of glue.

1.1.3 Metals

Metals being superior materials in many respects, suffer from cracks, dents and

corrosion. Presently, the issue of corrosion is addressed by various coating. Self-healing



of metals is not as developed as that for plastics. So far this activity was mainly

computational, and focused on modeling of a possible design of such metals.

Electro conductivity of metals can be used in self-healing of both metals and ceramics.

1.1.4 Ceramics/concrete

There are at least three different directions in autonomic healing of structural materials.

The first one is the “classical” use of healing capsules. The second one is inhibiting

corrosion of inner reinforcement frame (like the frame in concrete). Combination of both

showed promises. An encapsulated healing compound was added to concrete. Both

corrosion mitigation (using a time-release corrosion inhibitor) and crack sealing studies

have demonstrated these materials to have the potential for increasing the life of

reinforced concrete Structures.



Chapter 2: Classification of Self-healing Polymers

According to the ways of healing, self-healing polymers and polymer composites

can be classified into two categories:

(i) Intrinsic ones that are able to heal cracks by the polymers themselves, and

(ii) Extrinsic in which healing agent has to be pre embedded.

2.1 Intrinsic self-healing

The so-called intrinsic self-healing polymers and polymer composites are based

on specific performance of the polymers and polymeric matrices that enables crack

healing under certain stimulation (mostly heating). Autonomic healing without external

intervention is not available in these materials for the time being. As viewed from the

predominant molecular mechanisms involved in the healing processes, the reported

achievements consist of two modes:

(i) Physical interactions, and

(ii) Chemical interactions.

2.1.1 Self-healing based on physical interactions

Compared to the case of thermosetting polymers, crack healing in thermoplastic

polymers received more attention at an earlier time. Wool and coworkers systematically

studied the theory involved. They pointed out that the healing process goes through five

phases:

(i) Surface rearrangement, which affects initial diffusion function and topological

feature;

(ii) Surface approach, related to healing patterns;

(iii) Wetting,

(iv) Diffusion, the main factor that controls recovery of mechanical properties, and

(v) Randomization, ensuring disappearance of cracking interface.

2.1.2 Self-healing based on chemical interactions

In fact, 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.



2.2 Extrinsic self-healing

In the case of extrinsic self-healing, the matrix resin itself is not a healable one.

Healing agent has to be encapsulated and embedded into the materials in advance. As

soon as the cracks destroy the fragile capsules, the healing agent would be released into

the crack planes due to capillary effect and heals the cracks.

In accordance with types of the containers, there are two modes of the repair

activity:

(i) Self-healing in terms of healant loaded pipelines, and

(ii) Self-healing in terms of healant loaded microcapsules.

Taking the advantages of crack triggered delivery of healing agent, manual intervention

(e.g. heating that used to be applied for intrinsic self-healing) might be no longer

necessary.

2.2.1 Self-healing in terms of healant loaded pipelines

2.2.1.1. Hollow glass tubes and glass fibers

The core issue of this technique lies in filling the brittle-walled vessels with

polymerizable medium, which should be fluid at least at the healing temperature.

Subsequent polymerization of the chemicals flowing to the damage area plays the role of

crack elimination. Dry first identified the potential applicability of hollow glass tubes.

Similar approach was adopted by Motuku et al. and Zhao et al. Because the hollow glass

capillaries have diameters (on millimeter scale) much larger than those of the reinforcing

fibers in composites, they have to act as initiation for composites failure. Instead, Bleay

et al. employed hollow glass fiber (with an external diameter of 15 μm and an internal

diameter of 5 μm) to minimize the detrimental effect associated with large diameter

fibers. Complete filling of healing agent into the tiny tubes was achieved by vacuum

assisted capillary action filling technique.

Accordingly, three types of healing system were developed (Figure 1)



Figure1. Schematic diagram of repair concept for polymer matrix composites using

pre-embedded hollow tubes

Figure 2. Schematic diagram of repair concept using pre-embedded hollow tubes



Figure. 3 Self-healing concept using hollow fibers or tubes

(i) Single-part adhesive All hollow pipettes contained only one kind of resin like epoxy particles

(that can be flowable upon heating and then cured by the residual hardener) or cyanoacrylate

(that can be consolidated under the induction of air).

(ii) Two-part adhesive. In general, epoxy and its curing agent were used in this case. They were

filled into neighboring hollow tubes, respectively.

(iii) Two-part adhesive. One component was incorporated into hollow tubes and the other in

microcapsules.

With the aid of the pre-embedded healing system in hollow pipettes, Motuku and

co-workers studied the healing ability of glass fiber/unsaturated polyester composites

subjected to low velocity impact. The species of healing agent, characteristic parameters

of the hollow pipes (amount, type of tubing materials and spatial distribution),

composites panel thickness, and impact energy level were found to be critical to the



healing efficiency. Meanwhile, Bleay et al. proved that the epoxy based composites

reinforced by hollow glass fibers containing solvent diluted two-part epoxy became

repairable as assessed by compression after impact test.

Recently, Trask et al. considered the placement of self-healing hollow glass fibers

layers within both glass fibre/epoxy and carbon fibre/ epoxy composite laminates to

mitigate damage and restore mechanical strength. The hollow fibers were be spoken with

diameters between 30 and 100 μm and a hollowness of approximately 50%. The study

revealed that after the laminates were subjected to quasi-static impact damage, a

significant fraction of flexural strength can be restored by the self repairing effect of a

healing resin stored within hollow fibers. For example, Pang et al. added UV fluorescent

dye to the healing resin within the hollow fibers so that bleeding of the repair substance

in the composites can be visualized.

2.2.1.2 Three-dimensional microvascular networks

In conventional extrinsic self-healing composites it is hard to perform repeated

healing, because rupture of the embedded healant-loaded containers would lead to

depletion of the healing agent after the first damage. To overcome this difficulty, Toohey

et al. proposed a self-healing system consisting of a three-dimensional microvascular

network capable of autonomously repairing repeated damage events. Their work

mimicked architecture of human skin. When a cut in the skin triggers blood flow from the

capillary network in the dermal layer to the wound site, a clot would rapidly form, which

serves as a matrix 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. The 3D microvascular networks were fabricated by deposition of fugitive ink (a

mixture of Vaseline/microcrystalline wax (60/40 by weight)) in terms of direct-write assembly

through a cylindrical nozzle. Then, the yielded multilayer scaffold was infiltrated with epoxy

resin. When the resin was consolidated, structural matrix was obtained. With the help of heating

and light vacuum, the fugitive ink was removed and 3D microvascular networks were created. By

inserting a syringe tip into an open channel at one end of the microvascular networks, fluidic

polymerizable healing agent was injected into the networks.

The healing chemistry of this method used ring opening metathesis

polymerization of dicyclopentadiene (DCPD) monomer by Grubbs’ catalyst,



benzylidenebis (tricyclohexylphosphine) dichlororuthenium, which was used successfully

in microencapsulated composites. In the crack plane, the healing agent interacted with the

catalyst particles in the composites to initiate polymerization, re bonding the crack faces

autonomously. After a sufficient time period, the cracks were healed and the structural

integrity of the coating was restored. As cracks reopened under subsequent loading, the

healing cycle was repeated.

By means of four-point bending configuration monitored with an acoustic-

emission sensor, the above approach proved to be feasible. The authors imagined

extending this approach further to integrate pumps, valves and internal reservoirs, as well

as to introduce new functionalities, including self diagnosis or self-cooling, through the

circulation of molecular signals, coolants or other species. To provide theoretical

understanding how to vascularize a self-healing composite material so that healing fluid

reaches all the crack sites that may occur randomly through the material, Bejana et al.

studied the network configuration that is capable of delivering fluid to all the cracks the

fastest.

2.2.2 Self-healing in terms of healant loadedmicrocapsules

The principle of this approach resembles the aforesaid pipelines but the containers

for storing healing agent are replaced by fragile microcapsules. Because the technique of

microencapsulation has been rapidly developed since its emergency in 1950s and mass

production of microcapsules can be easily industrialized, self-healing composites might

be thus used in practice accordingly. Jung et al. prepared self-healing polyester composite

with pre-embedded polyoxymethylene urea (PMU) microspheres. The crack repair agent

is mostly composed of styrene monomers and high molecular weight polystyrene. The

latter helps to lower the rate of diffusion of styrene or diethenyl benzene into polyester

matrix. The system of 23% polystyrene (Mn = 2.5·105), 76.99% styrene and a trace

amount of inhibitor proved to offer the optimum healing efficiency. Jung et al. also tried

to utilize epoxide monomer loaded PMU microcapsules for rebinding the cracked faces in

polyester matrix. Solidification of the epoxy resin (i.e. the repair action) was triggered by

the naturally occurring functional sites or embedded amine in the composites.

The features of this healing system lie in the following.

(i) When the healing agent is applied to epoxy based composites, the miscibility between



the crack adhesive and matrix is guaranteed because of identity of their species.

(ii) The latent hardener possesses long-term stability and is hardly affected by the

surrounding environment. Moreover, it can be well pre-dissolved in uncured composites’

matrix, leading to homogenous distribution of the reagent on the molecular scale. Thus

the epoxy released from the ruptured microcapsules might meet the latent hardener

everywhere (Figure 4 ). The two-component healant is able to take effect in the woven

glass fabric/epoxy composite laminates.

Figure 4. Schematic drawing of the principle of self-healing epoxy based laminates

with epoxy loaded microcapsules and latent hardener



Figure 4 a. Schematic drawing of the principle of self-healing epoxy based

microcapsules



Figure 4 b



Self-healing performance reached maximum levels only when sufficient healing

agent was available to entirely fill the crack. Based on these relationships, the size and

weight fraction of microcapsules can be rationally chosen to give optimal healing of a

predetermined crack size. By using this strategy, self-healing was demonstrated with

smaller microcapsules and with lower weight fractions of microcapsules.

It is believed that the nanocapsules will make selfhealing materials responsive to

damage initiated at a scale that is not currently possible and compatible with composites

where the reinforcement spacing requires smaller capsules for applications such as self-

healing thin films, coatings, and adhesives.

If the inclusion has higher modulus than the matrix, the approaching crack tends

to pass by the microcapsules; conversely, the crack could penetrate the microcapsules

when the matrix is stiffer. On the other hand, simulation experiments manifest that the

difference in fracture toughness of the microcapsules and matrix should be less than 0.11

MPa·m1/2. Otherwise, cracks would not pass through the microcapsules.

The other critical factors include

(i) Good adhesion between microencapsulated healing agent and the matrix,

(ii) Size and concentration of microencapsulated healing agent,

(iii) Rate and degree of polymerization of the released healing agent, and

(iv) Shell thickness and core content of the microencapsulated healing agent.

This system possesses some advantages, including

(i) The healing chemistry remains stable in humid or wet environments,

(ii) The chemistry is stable to an elevated temperature (>100°C), enabling healing in

higher-temperature thermoset systems,

(iii) The components are widely available and comparatively low in cost, and

(iv) The concept of phase separation of the healing agent simplifies processing, as the

healing agent can now be simply mixed into the polymer matrix.



Chapter 3: Applications

Applications of self-healing materials are expected to be very broad. In the future

it will have a massive impact on virtually all industries, from the automotive industry to

the energy sector. It will be able to extend product lifetimes, to increase safety, to reduce

maintenance cost. The major applications being developed today are in automobile,

building/construction, and aerospace industries. Because nowadays the self-healing

materials are in their baby stage of development, research interest and funding focus

mostly on the development of the materials rather than their applications. Below we

overview the existing and probable applications in which the self-healing is expected to

be the most valuable. It makes sense to divide all applications on low and high cost

sensitivity.

3.1 Low cost sensitive applications

In average, these applications will be developed first because self-healing can be

attainedthrough a fast development cycle, using rather cost consuming mechanisms and

materials.

3.1.1 Medical dental/ artificial body replacements

Nowadays an artificial bone replacement can last up to 10 -- 15 years.

Development of good biocompatible self-healing composite materials may extend this

time. Another application will be in dentistry. In making artificial teeth and tooth filling

materials, self-healing would benefit their functional lifetime. All such material would be

in big demand virtually independent of price.

3.1.2 Aero/Space

Extending lifetime of a satellite in orbit around Earth, say twice, would

approximately decrease the cost of the mission two times. Furthermore the increase of a

spacecraft lifetime will result in longer time missions to the destinations far away in the

Solar System, and maybe beyond. Having satellites made of lighter self-healing polymer

materials instead of metal, which is relatively heavy, is a very cost-effective solution. A



single space carrier will be able to deliver multiple satellites. And finally, safety of air-

and space crafts can be improved by using self-healing components.

3.1.3Military

Having armor, body protection that could heal itself even during the battle will be

beneficial for the Army. Air force and Navy can additionally benefit from fast self

disappearing holes in the skin of a jet or ship. A prototype of such material already exists.

Dupont’s Surlyn® show good properties to heal after ballistic damage.

3.2High cost sensitive applications

3.2.1Car painting

Cost here is one of the main issues. Self-healing should definitely be cheaper than

just repainting. One of the first commercial self-healing materials, “Scratch Guard Coat”

was released by Nisan in December of 2005. According to the press release, Scratch

Guard Coat contains a newly developed high elastic resin that helps prevent scratches

from affecting the inner layers of a car’s painted surface. With Scratch Guard Coat a car’s

scratched surface will return to its original state anywhere from one day to a week,

depending on temperature and the depth of the scratch. Moreover, the paint is

hydrophobic. While the composition and healing principle has not been resealed, the

New scratches One week later

Figure 5. Car painted with “Scratch Guard Coat”



healing mechanism is clearly within the mechanisms described above. Presumably it was

possible to create a similar paint a while ago. The real state-of-the-art of the Nissan paint

is its fairly low cost and long lifetime.

3.2.2 Civil construction

Tones of these materials are required. Self-healing capsules might solve some

problems. However, this action is unlikely to be within the range of reasonable cost. So

far a reasonable solution was using the chalk. 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. The working mechanism of the self-healing coating is the

release of healing/inhibiting corrosion compounds when microcapsules containing these

compounds are abraded.



Chapter 4: Benefits, Problems and Challenges

4.1 Benefits

– Improving product safety and reliability and to extend product lifetimes.

– Improved toughness

– Reduced waste disposal

– Building sustainable society

4.2 Problems and Challenging

Apart from problems and challenges related to high-cost, there are many

technological problems. It would be far beyond the scope of the present overview to

discuss these problems in detail. We will outline just main issues that are common.

Virtually any self-healing mechanism has the following steps. The healing agent has to be

delivered to the damaged region, after that the healing should be initiated, and finally, the

result of healing should be compatible with the surrounding materials.

Therefore, technical challenges can be ordered as follows:

1. Storage of healing agent inside the material for a long period of time. This is

especially difficult inside of polymeric materials, which intrinsically permeable on

molecular level.

2. Initiation of healing. The healing agent should start react either with the

surrounding material or with a special initiator. Such an initiator can be impregnated in

the surrounding material or should be mixed with the healing agent. All these create

additional problems of storage of the initiator, and mixing the initiator and the healing

agent.

3. Finally, the healing agent should be strongly bound to the material, and be

stable with respect to the surrounding environment. This indeed is typically the simplest

problem, which is however, restrictive to the type of the healing agent.

The main challenge of course is to find the solution of the above problems in the way that

can be scaled up to the mass production.



Conclusion

Achievements in the field of self-healing polymers and polymer composites are

far from satisfactory, 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.

Methods of incorporating self-healing capabilities in polymeric materials can now

effectively address numerous damage mechanisms at molecular and structural levels.

Activities in the field not only focus on mechanical and chemical approaches to

improving the durability of materials but also involves new damage detection technique

incorporated in-situ the material, although none of these are commercially viable at

present.

Besides the approaches described in the above text, ongoing attempts are

continuously presenting new concepts.

From a long-term point of view, synthesis of brand new polymers accompanied

by intrinsic self-healing function through molecular design would be a reasonable

solution. Working out the solutions would certainly push polymer sciences and

engineering forward.



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