Development of Conductive Polymer Using Cotton Precursor

Development of Conductive Polymer Using Cotton Precursor
Author: Mainak Mitra
Department of jute and fibre technology 
Calcutta University

  1. Conductive polymers are organic polymers that conduct electricity. They can offer high electrical conductivity but do not show mechanical properties as other commercially used polymers do. The incorporation of metal into textiles dates to the roman era, when they were mainly used for decorative purpose. With the advancement of technology, metal/conductive textiles found extensive functional applications. These materials have electrical conductivity and radar reflecting properties, yet are weight and flexible. Various methods have been developed to coat fibres and textile materials by metals and these are follows 2,3.
  2. Coating metal powder with binders.
  3. Vacuum deposition.
  4. Sputter deposition.
  5. Electro less coating.
  6. Metalised fabrics and fibres find πdiverse application, in many areas. Some of the important uses are protective fabrics, radar responsive fabrics, static electricity control, electromagnetic interference shielding.
  7. Such coating technques are energy intensive and suffer from the common disadvantages of being successful mostly in synthetic fibres and lack of biodegradeabilty 4. So work on the conducting to impart shielding properties to textiles, metalizing fabrics is an approach suitable for industrial scale processes , where textile structures are covered with metal, mainly by chemical methods 5,6.
  8. Reports of incorporation of electrically conductive fillers, into synthetic resins during the moulding stage are also available in the literature 8,9.
  9. Intrinsically conducting polymers, such as polypyrrole(PPy) polyaniline, polythiophene(PTh) have recently been reported to be superior to conventional metal based conducting systemin respect of energy efficiency and processing ease 10.
  10. In view of above, we thought it would have interest that pyrrole or aniline can be polymerised in situ with in a fabric structure by empolying simple padding technique.
Literature Review:
Conducting Polymers :
Inherently conducting polymers (ICP) present a group of conjugated organic polymers viz, polyaniline (PAn), polypyrrole (PPy), polythiophene etc having high electronic conductivity 11. The conductivity of such polymers (those that possess an extended π- conjugation along the polymer backbone) is the result of several processes in polymers the valence electrons are bound in sp3 hybridized covalent bonds. Such “sigma-bonding electrons” have low mobility and do not contribute to the electrical conductivity of the material. However, in conjugated materials the situation is completely different. Conducting polymers have backbones of contiguous sp2 hybridized carbon centres. One valence electron on each centre resides in a pz orbital, which is orthogonal to the other three sigma-bonds. The electrons in these delocalized orbital have high mobilty when the material is “doped”, which removes some of these delocalized electrons. Thus the conjugated p-orbital’s form a one-dimentional electronic band and the electrons within this band become mobile when it is partially emptied. The presence of an extended π-conjugation in polymers, however, confers the required mobility to charges that arecreated on the polymer backbone (by the process of doping) and make them electrically conducting 12.

Electrical Conductivity:
Poly-acetylene can be doped by oxidation with a halogen (iodine) called p-doping or by reduction with an alkali metal (sodium) called n-doping. In oxidation “the iodine molecule attracts an electron from the polyacetylene chain and becomes iodine three” a negatively charged ion. The polyacetylene molecule, now positively charged, is termed a radical cation or “polaron”13. The electron is removed from the top of the valence band of polyacetylene creating a vacancy or hole. Although the hole created does not delocalised completely, an electron can be removed locally from one carbon atom and produce a radical cation. For example, the chain has one electron removed on the fifth carbon atom, the polaron then migrates down the chain.polyacetylene behaves in this same manner when doped. However, since the counter ion (iodine three) to the positive charges is not very mobile, a high concetration of counter ions is required so that the polaron can move in the field of close counter ions, explaining why excessive doping is needed 13. The most widely accepted view of conductivity in these systems involves charge transport along the polymer chains. Electrically conducting polymers are semiconductors with a filled valence band and an empty conduction band. These bands are separated by an energy gap 4. Their transport occurs via mobility along segments of conjugated polymer chain and hopping of charges from chain to chain. The number of these charges contained in a material and their relative mobility controls the bulk electrical conductivity 14-17. 
Electroconductive fiber
This mechanism reported for explaining electrical conductivity of polypyrrole is given below 18,19.

Methods and Preparation of Sample:
Metals and metal coated materials generally show very high EMI. The deposition of conducting polymers as thin films onto textiles was seen as a possible method to produce the flexible conducting materials. ICPs such as polyaniline, polypyrrole and polythiophene are insoluble in solvents and this limits their application to textiles. The report for the method of incorporating condutive polymers in textiles following in-situ polymerisation process is sancaty 20,21. Also very limited report on incorporation of such conductive polymer following coating technique is available in literature 22-25.

Literature review presented above points to the short coming and limitations of recently invented conductive polymers , to the limited availability of the methods of incorporation of such conductive polymer into textile structure 26-28. Literature review also suggests that there remains oppertunity to improve the overall situation regarding use of such advanced material in making a flexible textile structure keeping biodegradabilty and environmentally friendliness of such product in view.

Applications of Conductive Textile Materials:
  1. Textiles for clothing protective against high-frequency EMF.
  2. Less conductive textiles which carry away static charges from clothing or equipment (as in semiconductor industry)
  3. Shielding curtains and wall covers for protecting rooms in special buildings (military,banks etc.)29.
  4. Radar responsive fabrics by reflecting the electromagnetic radiation giving echo 30.
Plan of Work
The introductory part and survey of literure highlights important short comings of flexible fibrous conductive polymer in respect of non-bio-degradability, energy intensive manufacturing techniques etc. Literature riview also suggests that the possibility of insitu development of conductive polymer using a biodegradable precursor following a relatively inexpensive pad-dry-cure technique is wide indeed if not unlimited. Our work would be under taken keeping such scope and growing environmental demand from the discerning consumer in view. The plan of present work is therefore drawn accordingly as detailed below:

1) Development of in situ Polypyrrole in Cotton :

In this work pyrrole would be polymerised in presence of suitable dopant insitu with in cotton, following a pad dry cure technique. Role and effect of conducting polypyrrole, doping agents on conductivity of cotton would be assesed and investigated. Reaction parameters in respect of concetration of pyrrole, doping agent and temperature of curing would be examined and an optimum process condition will be achieved.

2) Characterization of pyrrole modified cotton :
Pyrrole modified cotton would be analysed for its conductivity under different application potential differences and the attenable changes in the textile related properties in relation to such modification of cotton by pyrrole in respect of strength extesibility, flexibility, fastness to washing & light and rubbing would be examined and assesed.

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  20. Hemant K Chitte, Nrendra V Bhat, Vasant E. Walunj, Ganesh N. Shinde Department of Physics, Dnyansadhana College, near Etarnity Mall, Thane, India 2 Bombay 1 Textile Research Association, Mumbai, India Department of Physics, Indhira Ghandhi College, Cidco Colony, New Naded, India Received May 3, 2011; revised June 1, 2011; accepted June 7, 2011.
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  26. Halina Aniolczyk, Joanna Koprowska Pawel Mamrot, Joanna Lichawaska.
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