self healing polymer

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Self Healing PolymerJayanta 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.

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Strategies of self healing materials

Hollow fiber repair mechanism.Microencapsulated healing agent.Micro vascular network.

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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


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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 ReactionsMajor 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 PolymersRecently, 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 polymershave highest cross-link density). Polymer gelof PA-MI-1/TF in N, N-dimethylacetamide(DMAc): (a) 30 ◦C, (b), 160 ◦C andcross-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.

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Applications

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self healing paint

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Next Generation Self-Healing Concrete:

♜Microbial Induced Calcium Carbonate Precipitat ion (MICCP)

♜Urease: (CO(NH2)2) NH4+ + CO3

2–

♜Ca+ + cell cell-Ca+

♜cell-Ca+ + CO32– cell-CaCO

bacilli megateriumbacillus 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 14Ca 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.