Intrinsically conducting Intrinsically conducting polymers on textilespolymers on textiles

CNR-ISMAC, BiellaC.so Giuseppe Pella, 16 – 13900 Biella

www.bi.ismac.cnr.it

Alessio Varesano

Outline

Introduction Electrical conduction Measurements Conducting polymers

Deposition processes Textile substrates

Application and performances Fastness and stability

Conclusion

Introduction

Conductive textiles

The term “conductive textiles” is used for a broad range of products with widely differing specific (surface) conductivity.Beginning with antistatic finishing with rather low conductivity or the modification of fibres by means of the incorporation of conductive particlesin the spinning process, textiles may be modified with conductive metal coatings or the interweaving or stitching of metallic fibres, the latter being used, e.g., for signal transport in so-called “smart textiles”.A new approach to conductive textile materials is the use of intrinsically conductive polymers.

Conducting polymers• Intrinsically conducting polymers (ICPs) are π-conjugated organic polymers able

to conduct electricity.• In 1976, Alan MacDiarmid, Hideki Shirakawa and Alan Heeger discovered the

conditions to dope the ICPs over a full range from insulator to metal, in particular for polyacetylene (Nobel Prize in Chemistry in 2000).

• ICPs are the fourth generation of polymeric materials (“metallic polymers”).

• In research, ICPs opened the way to progress in understanding the fundamental chemistry and physics of π-bonded macromolecules.

• In industry, ICPs offered the promise of achieving a new generation of polymers: materials which exhibit the electrical and/or optical properties of metals or semiconductors and which retain the attractive properties and processing of polymers.

Polyacetylene

The discovery

“In 1976, […] we succeeded in synthesizing polyacetylene directly in the form of thin-film by a fortuitous error. After a series of experiments to reproduce the error, we noticed that we had used a concentration of the Ziegler-Natta catalyst nearly a thousand times greater than that usually used.”

H. Shirakawa, Synth. Met. 125 (2002) 3

List of some ICPs

A.J. Heeger, Synth. Met. 125 (2002) 23

Natural conjugated polymer

NH

OH OH

NH

OHOH

Melamin is the natural black pigmentation molecule synthesised by most plants and animals.

It is a natural conjugated polymer which absorbs UV light due to the conjugated backbone.

Energy gap (Band-gap)

small Eg(few eVs)

conductors(metals)

semiconductors insulators(plastics)

e-

overlapping

big Eg

Energy gap is the “energetic distance” between the highest energetic level of (non-conducting) valence electrons and the lowest energetic level of conducting electrons.

Conductingband (CB)

Valence band (VB)

HOMO(highest occupied molecular orbitals

LUMO(lowest unoccupied molecular orbitals

Energy gap (Eg)Fermi levelE

nerg

y

Electronic configurations

In insulating carbon-based polymers (i.e. saturated polymers such as polyethylene) all of the four valence electrons of carbon are used in covalent σ-bonds.

In conjugated polymers, the chemical bonding leads to one unpaired electron (the π-electron) per carbon atom: π-bonding (carbon orbitals in sp2pz configuration) leads to electron delocalisation along the backbone of the polymer chain.This electronic delocalisation provides the “highway” for mobility along the backbone chain.

A.J. Heeger, Synth. Met. 125 (2002) 23

polyethylene

polyacetylene

Doping

In ICPs control of the electrical conductivity over the full range from insulator to metal can be accomplished by doping (i.e. by the introduction of electrical charges in the backbone chain).Concurrent with the doping, the energy level is moved either by a redox reaction or a acid-base reaction.Charge neutrality is maintained by the introduction of counter-ions in the polymer matrix. So highly conducting polymers are salts.

Mobility

The electrical conductivity results from the existence of charge carriers and from the ability of those charges to move along the π-bonded structure.

H. Shirakawa, Synth. Met. 125 (2002) 3

Delocalisation

… …δ+ δ+

δ+ δ+ δ+ δ+ δ+ δ+ δ+δ+δ+ δ+ δ+ δ+ δ+

As an π-electron is delocalised over several monomer units, also a charge in thebackbone chain is delocalised.In polyacetylene, ~85% of the positive charge is delocalised over 15 C-H units to give a positive soliton.

A.G. MacDiarmid, Sinth. Met. 125 (2002) 11

Charged species

The charges are organised in typical species (soliton, polaron, bipolaron) which energy level is depending on the chemical structure of the hosting polymer.These charged species create conducting mid-gap electronic states which the energy level usually fall into the energy gap reducing the energy gap.So the charges enhance the conductivity in most doped ICPs.

Polaron(e+, spin ½)

A positive charge and a unpaired electron

Bipolaron(e2+, spin 0)

Two coupled positive charges

Mid-gap electronic states

The π-band is divided into π- and π*-bands. Since each band can hold only two electrons per atom (spin up and spin down), the π-band is full and the π*-band is empty. Because of the energy gap between π- and π*-bands, ICPs are typically semiconductors.

Because Eg depends on the molecular structure of the repeating unit, the energy gas can by designed at the molecular level.

VB

CB

π*-band

π-bandEg

VB

CB

Ene

rgy

Dopants

The neutral state of the ICPs is ensured by the introduction in the matrix of counter-ions (so-called dopants).The counter-ions stabilise the charged species in the backbone of ICPs.

Counter-anions (dopants)

Mechanisms of electrical conductivity

A: intra-chain transport;B: inter-chain hopping;C: inter-particle hopping

Charges not only have to move along the polymer chain (A: intra-chain-transport), but they have to pass from chain to chain in the same polymer cluster (B: inter-chain hopping), and from particle to particle (C: inter-particle hopping).

Polymer cluster (particle)

Polymer chain

Resistivity/Conductivity measures

Linear resistivity (ρL)

Length (L)

Resistance (R)

Filaments, yarns

( )L

RL =Ω cm/ρOne-dimensional object

Surface resistivity (ρs)

b) Concentric ring configuration (EN 1149-1):

Concentric ring probe

R1

R2

( )

=Ω

1

2ln

2square/

R

RRs

πρ

Fabrics, non-wovens,…

In order to differentiate between, surface resistivity and resistance, ρs is often expressed as Ω/square (or Ω/sq. or Ω/) which is not a valid unit from the dimensional analysis point of view, because “square” (or “sq.” or “”) is not a unit but, for instance, “cm/cm”.

( )L

DRs =Ω square/ρ

a) Parallel probes configuration:

Volume resistivity (ρv)

( )LWTR

v×=⋅Ω cmρ

W

T

L

Three-dimensional object

Conductivities (σ)In general, “conductivity” refers to “volume conductivity” (in S/cm).

The relationship between conductivity and resistivity is:

( )ρ

σ 1S 1 =Ω= −

therefore:

( )

( )

( )v

v

ss

LL

ρσ

ρσ

ρσ

1cm/S

1squareS

1cmS

=

=⋅

=⋅Linear:

Surface:

Volume:

ICPs suitable for textile

List of some ICPsNot all ICPs are suitable for textiles (for instance polyacetylene is the most conducting polymer, but it is highly instable).

Requirements for textile applications are:• Ability to deposit• Good conductivity• Easy processability and handling• Good stability and fastnesses• Availability• Low cost

Polypyrrole (PPy)

Introduction• Polypyrrole (PPy) (black coloured polymer) is one of the most used ICP because

of its relatively good stability. It can be easily produced by chemical oxidative polymerisation in aqueous solutions of the monomer.

• Mechanism of the chemical oxidative polymerisation of pyrrole:

(a) pyrrole

(b) cation radical pyrrole

(c) dication of bipyrrole

(d) neutral bipyrrole

(e) cation radical bipyrrole

disprotonationoxidation

oxidation

• Dispersions of PPy (nano)particles in solvents are commercially available, but the cost is high.

Doping agentOxidants: ferric chloride, FeCl3

ammonium persulfate, (NH4)2S2O8ferric sulfate, Fe2(SO4)3

Dopant: naftalendisulfonate, NDS

A. Varesano et al., Synth. Met. 159 (2009) 1082–1089

FeCl3

(NH4)2S2O8+NDS

Fe2(SO4)3+NDS

Energy dispersive x-ray (EDX) analysis

Cl

S

S

The peak of chlorine (at 2.62 keV) indicates that Cl− ions were incorporated into the polymer during polymerisation with FC.The presence of sulphur (at 2.31 keV) is mainly due to the presence of NDS embedded in the PPy during polymerisation, although it is possible that some SO4

= ions incorporated at the same time in the polymer matrix using both APS and FS.

SO3- Na+

Na+ -O3S

( )

( )-24

23

-24

282

-23

3SO 2Fe22Fe

2SO2OS

Cl3 FeFe

+→+

→+

+→+

+−+

−−

+−+

e

e

e

One-dimensional structures

Linear

Branched

D. Schmeißer et al. Synth. Met. 93 (1998) 43-58

Pyrrole polymerisation usually occurs in α-α’ positions leading a linear structure.

When bonds take place in other positions, linearity is lost.

Temperature has a great influence: low temperature (< 10°C) promotes α-α’ bonds.

Two-dimensional structures

Planar graphite-like Non-planar

D. Schmeiβer et al. Synth. Met. 93 (1998) 43-58

Nanowires

Helical(1) In presence ofpoly(t-butylacrylate)(2)

PPy produced by electrochemical oxidation in presence of additives

1) D. Schmeiβer et al., Synth. Met. 93 (1998) 43–582) C. Jerome et al., Synth. Met. 142 (2004) 207–2163) G. Lu et al., Polymer 47 (2006) 1778–1784

In presence ofpyrenesulfonic acid(3)

Polyaniline (PANI)

Introduction

“Solutions” of PANI (i.e. colloidal dispersions with particles size <1 µm) are commercially available in water (low conductivity) and xylene or toluene (high conductivity) with a relatively low cost (Panipol Ltd., Finland).

PANI is common within the group of conductive organic polymers because of aniline is a cheap chemical, but its handling is cumbersome and hazardous.

Dimerisation

Aniline radical cation

Propagation

Mechanism of oxidative polymerisation of aniline:

Unwanted side reactions are known to occur during polymerisation, and little is known about long-term stability of end product.

PANI bases

C.M.S. Izumi et al., Synth. Met. 156 (2006) 654

white-greyfully reduced (strong reducing agent)environmentally instable (oxidation)

red-purplefully oxidizedenvironmentally instable (hydrolytic degradation)

dark-blue (green when salt/protonated)half oxidisedenvironmental stable

PANI exists in three different base forms (oxidation states) and different colours:

Redox reactions of PANI

C. Aleman et al., Polymer 49 (2008) 5169

Pernigraniline base (PNB): fully oxidized

Emeraldine base (EB): half oxidized

Leucoemeraldine base (LB): fully reduced

Redox states depend on the degree of oxidation of the nitrogen atoms:

Benzoid segment Imine form

Amine formQuinoid segment

Conducting state of PANI

It can be obtained by:

• protonation of emeraldine base (EB)

or

• oxidation of leucoemeraldine base (LB).

C. Aleman et al., Polymer 49 (2008) 5169

Emeraldine salt (ES) is the most conducting state of PANI.

Planar structurePANI emeraldine salt (ES) has the most planar structure: low energy gap.

C. Aleman et al., Polymer 49 (2008) 5169

PANI-ES

PANI-LB

PANI-PNB

Poly(3,4-ethylenedioxythiophene) (PEDOT)

IntroductionPEDOT is a dark-blue to dark-grey polymer.The monomer (3,4-ethylenedioxythiophene) is easy to handle, and the polymer is highly conductive and very stable.Mostly, PEDOT is used for the fabrication of displays for electronics using fully polymerised PEDOT products (e.g. Baytron® by Bayer). PEDOT-PSS can be also prepared as a stable dispersion in water and n-propanol.PEDOT-applications for textiles are rather unknown, probably because of the high cost of the monomer.

D. Knittel, E. Schollmeyer, Synth. Met. 159 (2009) 1433–1437

Deposition processes

Processes

Process Use of solvents

Pre-formed ICPs

Not yet for textiles

Electrical performances

Electrochemical polymerisation (water) High

(Liquid-phase) Chemical polymerisation (water) High

Vapour-phase chemical polymerisation (X) Middle

Spray chemical polymerisation (X) Low

Coating X X High

Plasma polymerisation X ?

Photo-polymerisation X ?

Melt-mixing X (few data) Low ?

Wet spinning X X (few data) High ?

Electrospinning X (X) Low

Electrochemical polymerisation

Electrochemical polymerisation

If the substrate is not a conducting material (e.g. a fabric) it is usually previously coated with a conducting material (e.g. ITO or metal).However, the conducting fabric has an ohmic potential drop that it needs to be considered, otherwise the measured potentials will not be real.

Three electrode setup for electrochemical synthesis:- reference electrode;- working electrode (cathode, where polymerisation occurs);- counter electrode (anode);all submersed in a monomer and electrolyte solution.

N.K. Guimard et al., Prog. Polym. Sci. 32 (2007) 876ITO: indium doped tin oxide

Electrochemical polymerisation of PANI

For instance, PANI has been electrochemically polymerised on conducting textiles of polyester covered with PPy.

Steps:

1) Chemical deposition of PPy (to obtain a conductive fabric)

2) Electrochemical deposition of PANI

Potentiodynamic Potentiostatic

J. Molina et al., European Polymer Journal 45 (2009) 1302–1315

Potentiodynamic synthesis

Max

cu

rren

t d

ensi

ty

The current density (J) increases continuously, and in the last scan (70th) a maximum anodic current density of nearly 22 mA cm-2 is reached.

The electrode was introduced at -0.2 V and cycled from this potential to 1.1 V (at 50 mV s-1) for 70 scans.Figure shows the voltammogramsobtained in the potentiodynamicsynthesis of PANI.

J. Molina et al., European Polymer Journal 45 (2009) 1302–1315

Potentiostatic synthesis

The electrode is introduced at open circuit potential (OCP) and then the potential is risen to the synthesis potential of 1 V.The electrosynthesis elapses during the necessary time to achieve the desired electrical charge (i.e. 80 C cm-2).

In the first part of the synthesis the current density decreases.It is related to the charging of the double electric layer.

Current density increases: electropolymerisationof aniline took place and the electroactivearea of the electrode increases with the time.

As soon as the electrode potential is risen from OCP to

1 V, an increase of current density (J) happened.

J. Molina et al., European Polymer Journal 45 (2009) 1302–1315

Results

PET/PPy+PANI potentiostatically synthesised (80 C cm-2)

PET/PPy+PANI potentiodynamically synthesised (range 0.2 V–1.1 V)

Low adhesionHigh doping levelOver-oxidation occurs

Better adhesionLow doping level (low conductivity)

PANI micro-fibre structure

PANI globular structure

J. Molina et al., European Polymer Journal 45 (2009) 1302–1315

OveroxidationRedox potentials:

Py PPy 0.65 VChemical polymerisation: Fe3+ Fe2+ 0.77 VElectrochemical polymerisation: ~1 V

During overoxidation, PPy lost its electro-activity in parallel with the ejection of the dopants.

The redox (chemical or electrochemical) potential is one of the important factors that affects the synthesis of the PPy.Pyrrole could not be electro-polymerised when the potential was <0.7 V (only soluble oligomers are formed). On the other hand, high potential would have caused overoxidation.

Y. Kong et al., J. Appl. Polym. Sci. 115 (2010) 1952–1957

(Liquid-phase)Chemical polymerisation

Process

Solution of oxidant and dopant

Fabric

Solution of monomer

(and dopant)

Fabric

Monomer(pure)

In-situpolymerisation

(deposition) Exhaust polymerisation

bath

Coated fabric

Oxidant (solution)

(a)

(b)

An excess of oxidant (with respect the stoichiometric) is needed to reach high yield.Usually polymerisation is carried out at room temperature.Chemically coated fabric from solution results in the best conductivity among deposition processes.Moreover, the process is cheap and easy.

Weight uptakeP

AN

I con

tent

on

PE

T (

%)

Time (minutes)

potassium dichromate/aniline (mol ratio) = 0.5dopant (HCl) = 0.25 mol/L

The yield of PANI shows a decrease at higher temperatures.

This might be explained considering that the polymerisation of aniline is exothermic (∆H = -372 kJ/mol) and hydrolysis reaction of PANI is endothermic. Therefore, the hydrolysis may be dominant at high temperatures.

hydrolysis

polymerisation

S. Kutanis et al., Composites: Part A 38 (2007) 609–614

Results

Cross-section of PPy coated wool fibres (transmitted light microscopy) (1).

SEM picture of a broken PPy coated wool fibre (without metallization).

Optical fibre diameter analyser Optical fibre diameter analyser (2)(2)::before coating:before coating: 18.64 µm (SD 3.92 µm)after coating:after coating: 20.91 µm (SD 4.19 µm) coating thickness: 1.13 µm

(1) A. Varesano and C. Tonin, Textile Res. J. 78 (2008) 1110-1115.(2) A. Varesano, et al., Polym. Degr. Stab. 89 (2005) 125-132.

Production of industrial prototypes

KF1:KF1: 20 wt.% PPy coated wool80 wt.% untreated wool

KF2:KF2: 100 wt.% PPy coated wool

PPy deposition:PPy deposition: 1 kg of loose wool fibres were PPy coated.

Mechanical intersecting

Antistatic fabricAntistatic fabric Heating fabricHeating fabric

Spinning Linear resistivity: 4.8 kΩ cm-1Linear resistivity: 16.8 kΩ cm-1

Knitting

A. Varesano, et al., Polym. Degr. Stab. 89 (2005) 125-132.

Vapour-phase chemical polymerisation

Batch process

Fabric

Solution of oxidant and

dopant

ImpregnationDrying or squeezing

Oxidant-coated fabric

Monomer

Vapour-phase deposition

Humidity and temperature sensor

Coated fabric

Advantages: no contamination of the chemicals (solution of oxidant and dopant is re-usable, as well as not evaporated monomer).

Disadvantages:• Coated fabric contain large amount of oxidant residue;• Deposition can be not homogeneous;• Adhesion is poor;• Resulting conductivity is low.

Results (1)PPy-coated viscose by vapour-phase deposition with ferric chloride as oxidant.

L. Dall’Acqua et al., Synth. Met. 156 (2006) 379–386

Uncoated FeCl3 concentration: 9 g/l

18 g/l

Smooth surface, good adhesion

Rough surface, poor adhesion

Conductivity increases with increasing oxidant concentration in the impregnation step

Results (2)PPy-coated PA6 by vapour-phase deposition with ferric chloride as oxidant.

• Rough surface• Loosely attached• Not uniform deposition• Low conductivity (2.4 × 104 Ω cm−1)

SEM image TEM cross-section

C.F. Xiao et al., Polym Int 55 (2006) 101-107

Results (3)

G.A. Dell’Aquila, Politecnico di Torino (2006), Thesis

Wool fabric

Vapour-phase deposited PPy by FeCl3 on:

PET non-woven

Poor adhesion Oxidant residue

Poorly linkedPPy structure between fibres

Uneven depositionUncoated fibre

Continuous process (for yarns)

(1) first gas washing (containing pyrogallol solution), (2) second gas washing (containing concentrated sulphuric acid), (3) gas is saturated with monomer vapour, (4) glass pipes, (5) un-reacted monomer condenser, (6) conductivity measurement cell, (7) feeding bobbin, (8) wind-up bobbin.

S. H. Hosseini and A. Pairovi, Iranian Polymer J., 14 (2005) 934-940

Yarns were saturated with the oxidant in solution before vapour deposition.

ResultsPPy by vapour-phase deposition on silk yarnsOxidant: Ferric chloride

Rough surface, poor adhesionConductivity is ~10-4 S/cm (low)

S. H. Hosseini and A. Pairovi, Iranian Polymer J., 14 (2005) 934-940

PPy by vapour-phase deposition on cotton and wool yarns

Oxidant: Ferric chloride

Low penetration into the yarn cross-sectionPoor adhesion

Linear resistivity is ~4 kohm/cm(for both cotton and wool)

A. Kaynak et al., Synth. Met. 158 (2008) 1-5

PPy coated wool yarn

Light microscopy cross-section SEM image

PPy

Spray chemical polymerisation

Spray process

Result with 3 runs:• Even deposition• Weight increase: 6.2%• Surface resistivity: 2.9÷3.3 × 104 ohm/sq.

(antistatic properties)

In cooperation with a textile industry, we studied a spray chemical process to coat fabrics with PPy.

The process can be applied to fabrics and non-wovens with high wettability.

Steps:1) impregnation with concentrated oxidant solution;2) spraying of concentrated monomer solution;3) polymerisation (15 minutes);4) rinse in water and squeezing.

In order to obtain a uniform deposition and increasing conductivity the process have to be repeated.

Coating processes

Introduction

Coating processes can be divided into:

• Post-metering processes: the material is deposited onto the substrate in excess and then metered at the desired thickness.

• Pre-metering processes: the material is metered before the deposition onto the substrate at the desired thickness.

Post-metering processes are useful for coating from 0.02 to 0.2 mm, accuracy is poor, but productivity is high and cost is low.Pre-metering processes are more accurate and reproducible, thickness are in the range from 0.1 to 0.5 mm, costs are high.

Usually, curing is needed after coating process.

Post-metering (knife)

1. substrate2. material3. knife

Profiles of the knife:

• penetration of the coating in the substrate

Material must have high viscosity

Post-metering (dip-coating)

1. Squeezing rolls2. Substrate3. Impregnation bath (material)

Material must have low viscosity and good affinity towards the substrate

Squeezing force affects both metering and penetration of the coating.

Pre-metering (roll)

Roll: metering depends on the distance between the blade 2 and the roll 1.

Kiss-coater: metering depends on the contact between roll 1 and 2.

Results

ITIS “Q. Sella”, Biella – HITEX project

Pastes were PANI/p-toluenesulfonic acid and PANI/camphorsulfonic acid in p-chlorophenol.Application with knife on glass-fibre fabric.Curing under vacuum for 4 h at 60°C.(1)

S. Geetha et al., J. Comp. Mater. 39 (2005) 647

Patterned PANI deposition using water dispersion (Panipol W) on cotton fabric.

Nanoimprinting

The gravure printing unit and the nanoimprinting unit are used consecutively to act on the web in a single cycle. The gravure unit is used to coat a PP web by a continuous layer of PANI (6% dispersion in toluene).Next the coated web is patterned by the nanoimprinting unit.

In gravure printing the pattern is engraved on the printing cylinder as small pits. The cylinder is inked and the exceeding ink is removed using a blade before the ink is transferred to the substrate web.

In nanoimprinting a nano-patterned printing roll engraves a pattern into substrate web by using pressure.

5 µmT. Makela et al., Microelectronic Eng. 84 (2007) 877–879

GRAVURE NANOIMPRINTING

Plasma polymerisation

Plasma glow discarge

Iodine-doped PANI coating by plasma polymerisation.

Plasma glow discharges was generated by a wave generator and an RF amplifier at 13.5 MHz and around 12 W of power.The system pressure was 2–8 x 10-2 Torr.The average temperature was ~90°C between the electrodes.The monomer was supplied as vapour exhausted from the container with liquid aniline.The polymerisation reaction times were 60 to 300 min.

Thin film adhered to glass and metal surfaces.By IR analysis, aniline benzene rings become broken by the glow discharge energy.Conductivity is low and decreases as the reaction time increases, from 1010–1011 S/cm for 40% RH to 104–109 for 90% RH.

G.J. Cruz et al., Synth. Met. 88 (1997) 213–218

Photo-polymerisation

UV photo-polymerisation

Pyrrole (0.2 M) and sodium dodecyl sulphate (0.2 M) solution were spin-coated. The film exposed under UV (wavelength of 172 nm) lamp for 1–20 min. The power density was about 50 mW/cm2, the sample surface temperature did not rise above 85°C.

Q. Fang et al., Sens. Actuators A 99 (2002) 74–77

PPy/SDS film under UV-radiation of 20 minutes

Melt-mixing

Introduction

Melt-mixing consists of the dispersion of particles in a molten polymer matrix.In the case of electrically conducting particles, particles have to be close together in order to ensure the electrical conductivity.This is reach above a specific concentration (percolation threshold).Percolation threshold is the minimum value of particle concentration for electrical conductivity.

No percolation Percolation

Melt-mixing

Counter-rotating inter-meshing double-screw extruder

PANI/PP and PANI/PDPE

B. Kim et al., Synth. Met. 146 (2004) 167–174

The conductivity is low (10-9 S cm-1) and does not change increasing the charge (PANI) content:• there is no percolation.

Two phases exist (particles of PANI were not dispersed):• no compatibiliser was used;

PANI

PP

PANI emeraldine salt is blended with LDPE at 150°C a nd PP at 200°C.

PS/SBS/PANI blends

Matrix: Polystyrene (PS)ICP: PANI emeraldine baseDopants: Dodecylbenzene sulfonic and poly(styrene sulfonic acid)Compatibiliser: Poly(styrene-co-butadiene-co-styrene) (SBS)

Temperature profile: 160–190°C

Fractures shows a good dispersion and structure of PANI particles within PS using SBS (compatibiliser).

Conductivity of 10-6–10-2 S cm-1 suitable for antistatic applications.

C.R. Martins, M.-A. De Paoli, Eur. Polym. J. 41(2005) 2867–2873.

Wet-spinning

Principle

Polymer solution is pumped in the coagulation bath by means of a needle (spinneret).

Coagulation bath removes the solvent leaving a solid filament.

Wet-spun PPy fibres

J. Foroughi et al., Synth. Met. 158 (2008) 104–107

The incorporation of di-(2-ethylhexyl) sulfosuccinate (DEHS) dopant anion renders the PPy “soluble” in polar or non-polar solvents, and suitable for wet-spinning.

Colloidal suspensions of PPy/DEHS (with particle sizes <100 nm) was obtained in dichloroaceticacid.The coagulation bath contained 40% (w/w) dimethylformamide (DMF) in water at 20°C.

The average electrical conductivity of PPy fibres was measured to be ~3 S/cm (good), and stress at break in the range 20–25MPa at ~2% strain (poor mechanical properties).

Round section and smooth surface

Wet-spun PANI fibres

Coagulation bath was a solution of poly(sodium 4-styrenesulfonate) (PSS) in water.

PANI-EB powder was mixed with 2-acrylamido-2-methyl-1-propanesulfonic acid (AMPSA) and dissolved in dichloroacetic acid.

AMPSA

1.5% PSS 5% PSS 15% PSS

Very rough, irregular Rough, cylindrical Smooth, cylindrical

F. Zhang et al., Synth. Met. 156 (2006) 932–937

High electrical conductivity

Electrospinning

Electrospinning

Method 1 (two-step)

Polymer(matrix)

Oxidant

Solvent

Solution for electrospinning

Electrospun into nanofibres

Exposed to vapour of the monomer(Vapour-phase polymerisation)

monomer

PA6 Ferric chloride

Formic acid

Electrospinning

Pyrrole vapour-phase polymerisation

F. Granato et al., Macromol. Rapid Commun. 30 (2009) 453–458

Conductivity test

Results

Method 2 (blending)

Polymer(matrix)

Soluble ICP(dispersion)

Solvent

Solution for electrospinning

Electrospun into nanofibres

ResultsPoly(ethylen oxide) + PANI/camphorsulfonic acid in chloroform(1)

Poly(vinyl cinnamate) + PPy/dodecylbenzene sulfonic acid in chloroform(2)

(1) I.D. Norris et al., Synth. Met. 114 (2000) 109–114(2) T.S. Kang et al., Synth. Met. 153 (2005) 61–64

O

Textile substrates

Surface resistivityTextile materials generally show high electrical resistivity and are insulators.

R. Neelakandan et al., J. Ind. Textiles 39 (2009) 175

Materials Electrical resistivity

(ohm/square)

Cotton fabric 109

Polyester fabric 1012

Nylon fabric 1012

Wool fabric 1012

ICP-coated fabric 10 to 104

Metal-coated fabric ~0.1

Animal fibres

Wool

Cross-section by light microscopy of PPy-coated fibres

The polymerisation process occurred on the fibre surface.

uncoated

PPy-coated

The typical scaled structure of wool surface can be observed. The surface of wool fibre consists of cuticle cells overlapping to form a structure like tiles on a roof.

A remarkable round off of the cuticle scales and a smoothing of the edges due to the PPy coating.

Silk

uncoated PPy-coated

The polymerisation process occurred on the fibre surface.

Cross-section by light microscopy Fibre surface by SEM

I. Cucchi et al., Synth. Met. 159 (2009) 246–253

Thermal and Mechanical properties

Pure silk

PPy-coated silk

PPy-coated silk

Pure silk

DSC. The endothermic peak at above 300°C is thermal degradation of silk fibroin (β-sheet crystalline structure). Coating with PPy enhanced the thermal stability of silk, whose degradation peak shifted to higher temperature.TGA. The weight retention at 500°C increased from 3 5 % of the untreated sample to 50 % for the PPy-coated sample. Protective effect of the PPy layer against thermal degradation.

DSC

TGA

Untreated abd PPy coated silk fibers displayed closely similar values of the tensile parameters.The polymerisation process did not affect the overall tensile performance of silk fibers.

A. Boschi et al., Fibers Polym. 9 (2008) 698-707

Cellulose fibres

CottonCotton (and in general cellulose-based) fibres show a great chemical affinity for ICPs, in particular for PPy.

PPy layer (black)

lumen (black)

cellulose (white)

Cross-section by light microscopy

PPy-coated cotton fibres

SEM image of coated fibre surface

A. Varesano et al., Synth. Met. 159 (2009) 1082–1089

Mechanical properties

A. Varesano et al., Synth. Met. 159 (2009) 1082–1089

Oxidants: ferric chloride, FCammonium persulfate, APSferric sulfate, FS

Dopant: naftalendisulfonate, NDS

Mechanical tests according to EN ISO 13934-1

Mechanical properties were enhanced by the PPy treatment increasing tensile strength at break and elongation at break with respect of pure cotton fabric.On the other hand, mechanical properties of PPy coated fabrics are similar, not significant variations occur as a consequence of the polymerisation conditions.

Thermal properties

A. Varesano et al., Synth. Met. 159 (2009) 1082–1089

Oxidants: ferric chloride, FCammonium persulfate, APSferric sulfate, FS

Dopant: naftalendisulfonate, NDS

SEM analysis of carbonised samples revealed the PPy-coated cotton still maintain the fibrous shape, on the contrary of pure cotton fabric that produces a very little amount of char.

Thermogravimetry (TGA) under air

PPy altered the combustion process of cellulose.PPy-coated cotton fibres degrade at lower temperatures than pure cotton, but PPy increases the residual weights.

Differential scanning calorimetry (DSC) under air

Viscose

Liquid-phase deposition

Vapour-phase depositionwet dry

Partial penetration of PPy inside the fibre bulk(1)

No penetration of PPy, external PPy-coating(2)

Full penetration of PPy inside the fibre bulk(1)

(1) L. Dall’Acqua et al., Synth. Met. 156 (2006) 379–386(2) G. Battistella, Politecnico di Torino (2004), Thesis.

Thermal properties

PPy content increase

The thermal stability of viscose was strongly affected by the polymerisation process.

The temperature decomposition decreases (from 345 to ~250°C) as the PPy content increases.

PPy-coated viscose fabric by chemical liquid polymerisation (oxidant: FeCl3)

L. Dall’Acqua et al., Synth. Met. 146 (2004) 213–221

Mechanical propertiesViscose fibres degrade in acidic condition.

In vapour-phase, the impregnation with concentrated ferric chloride solution (pH ~1) lowers the mechanical properties.

(1) T. Bashir et al., Polym. Adv. Technol. DOI: 10.1002/pat.1748(2) L. Dall’Acqua et al., Synth. Met. 156 (2006) 379–386

FeCl3 concentration VPV: vapour-phaseVPL: liquid phase

Tenacity of viscose decreases with increasing FeCl3 concentration in the impregnation bath.(1)

On the contrary, in liquid phase coated viscose maintains its mechanical properties.(2)

Synthetic fibres

Light microscopy cross-sections

PET PA6

PAN

Generally in synthetic fibres the polyme-risation process of ICPs occurred only on the fibre surface.

F. Ferrero et al., J. Appl. Polymer Sci. 102 (2006) 4121.

Polyethylentereftalate (PET)

Uncoated PET Coated PET

Smooth surface Rough surface

A. Ibarzabal Ferrer, Politecnico di Torino (2007), Thesis.PET

PPy

Thermal properties

DSC under air

TG

PPy-coated PET fibres degrade at lower temperature under air (probably oxidation of PPy occurs at ~300°C), but t he coated material maintains its shape.

A. Varesano et al., e-Polymers 22 (2007) 1-14A. Varesano et al., J. Thermal Anal. Calorim. 94 (2008) 559–565

Bi-component PET fibres (1)

In this work, we used a non-woven produced with PET/PET core-shell fibres. The core has higher melting point than the shell.

The heating runs of DSC shows two peaks at 248 and 254°C related to the fusion of shell and core, respectively.We observed shifts of PET melting points toward higher temperatures (due to the development of two new peaks) with the increase of PPy content.PPy coating improves the resistance to heat of PET with an increase of the melting temperature. heating

shellcore

PP

y co

nten

t inc

reas

e

A. Varesano et al., e-Polymers 22 (2007) 1-14

TemperatureCompression

Thermal bonding

under N2

Bi-component PET fibres (2)In cooling, thermogram of the PET fibres shows a broad exothermic peak at 177 °C related to the PET crystallization. The formation of a single peak is due to the mixing of the two PET components (core and shell).The thermograms of the PPy-coated fibres show the increasing of PET crystallization temperatures (up to 204°C) with increasing the PPy amount. The PPy-coated fibres solidify at higher temperature (about 20 °C) with respect to pure PET.

cooling shoulder

PP

y co

nten

t inc

reas

e

It seems that the orientation of PET polymer chains in the PPy-coated fibres is preserved in the molten state.The incomplete mixing of the two PET components during melting is due to the presence of the protective shell of PPy.

A. Varesano et al., e-Polymers 22 (2007) 1-14

under N2

Polyacrylonitrile (PAN)

Y. Xia and Y. Lu, Polym. Compos. 31 (2010) 340–346

ICPs might have interactions with the –CN groups and ester groups (–COO) in PAN most likely play an important role during the polymerisation on the fibre surface due to their negative charges.2.1–5.2 x 10-1 S/cm

3.3–5.5 x 10-2 S/cm

1.4–3.5 x 10-2 S/cm

It can also be found that ICP-coated fibres all keep the mechanical properties as pristine PAN fibre.

PAN PPy/PAN

PANI/PAN PEDOT/PAN

Application and Performances

Applications of ICPs on textile

• Antistatic garments• Heating textiles• EMI shielding fabrics• Sensorised garments• Anti-bacterial fabrics• Flame-resistant textiles

Electrostatic fabrics

Electrostatic discharge (ESD)

• Textile materials generally have high surface resistivity (1010–1012

ohm/sq). Standard EN 1149-1 requires a surface resistivity <5 × 1010

ohm/sq for antistatic fabrics.• Excess of static charges can accumulate generating harmful discharges

(damage of electronic devices), sparks (risk of explosions) and attraction of powder.

• PPy-coated fibres have been used in blend with untreated fibres to produce fabrics for ESD protection able to drain the electrostatic charges.

20 wt. % PPy-coated wool80 wt. % uncoated wool

Surface resistivity: 10 kohm/sq.A. Varesano, et al., Polym. Degr. Stab. 89 (2005) 125.

Heating textiles

Equations

Ohm’s law: V = RI

Voltage: V (V); Resistance: R (Ω); Current density:I (A)

Electrical power: P = VI = RI2 = V2/R (W = V·A)

Power density: p = P/Area (W/m2)

Heating fabrics (1)

• For resistivity below 1 kohm/sq., ICP-coated textiles can generate heat by heating Joule effect when electrical power is supplied.

• Low powers (<15 mW/cm2) generates mid-temperatures (i.e. <7°C above environment temperature) suitable for heating garments and clothing (lining and padding).(1)

• Heating panels (non-clothing devices), which have been used for instance to heat buildings, need a power density per unit area of around 15 mW/cm2 or more.(2) Non-clothing

Clothing

(1) A. Varesano, et al., Polym. Degr. Stab. 89 (2005) 125.(2) R. Jolly, et al. J. Coated Fabrics 23 (1994) 228.

Heating fabrics (2)

5 cm

10 20 30 40 50 mW/cm2

Environment temperature: 20°C

Fabrics in contact with human body

Power:

PPy-coated cotton and PET fabrics

33°C

22°C

Thermal images of PPy-cotton fabric during heating

Heating fabrics (3)

S. Shang et al., Polym. Int. 59 (2010) 204–211

PPy-coated PET fabricTemperature is a function of surface resistivity: low-surface resistivity fabrics reach higher temperature

High-power heating fabrics

PPy-coated cotton fabric (reaching high weight uptake, 2h, 5°C)

amount of pyrrole = fabric weight

Applied voltage: 9 VSize (L x D): 9 cm x 5 cm

C80PPY sample has more than 200 times the power density of the C10PPY sample.The maximum value of power density found for C80PPY is 5 W/cm2, while for C100PPY sample is 10 W/cm2.

N.V. Bhat et al., J. Appl. Polym. Sci. 102 (2006) 4690–4695

Electromagnetic interference(EMI) shielding

AimThe use of electronic devices for communication, computation, and automation rapidly increases. As the operating frequency and theintegration of electronic devices increase, EMI has become a major problem, which reduces the lifetime and the efficiency of electronic devices and electrical products.Various EMI shielding techniques have been developed. For example, a functional EMI shielding material such as metal complex or multi-layered metal has been introduced. Conducting or magnetic material can be used for the EMI shielding material.The high EMI shielding efficiency (SE) of metals is due to its high reflectance. On the contrary, conducting polymers have an absorption dominant EMI shielding characteristic, moreover they have good processability and relatively low mass density.

Principle

PI PTPA

PRPI = PA + PR + PTwhere PI : incident power

PA: absorbed powerPR: reflected powerPT: transmitted power

EMI SE (dB) = 10 log PT / PI EMI shielding efficiency

Source Receiver

Shielding material

Resistivity vs. EMI SE

EMI shielding efficiency increases from 13 to 36 dB with the decrease of the resistivity due to the increase of the conductivity toward a metallic conductivity.EMI shielding efficiency by reflection (R) increases with the decrease of the resistivity (metal-like behaviour).

Chemically synthesised PPy/naphthalene sulfonic acid on PET fabricEMI SE values at frequency from 50 MHz to 1.5 GHz

M.S. Kim et al., Synth. Met. 126 (2002) 233–239

Thermal images

Irradiated uncoated fabric

Irradiated PPy-coated fabric

Temperature of the coated fabric increases (microwave absorption)

Frequency: 15–16GHz

Temperature of the absorbent foam slightly increases

Temperature of the absorbent foam increases

Temperature of the uncoated fabric does not change (transparent to microwave)

A. Kaynak et al., Synth. Met. 159 (2009) 1373–1380

Chemical polymerisation of PPy/pTSA on PA6

Multi-layer (1)

To increase performance, metal/ICP multi-layered coating were applied to fabrics.

Steps:

1) Chemical polymerisation: PPy/naphthalene sulfonic acid (NSA).

2) Electrochemical polymerisation: PPy/NSA+PPy/anthraquinonesulfonic acid (AQSA)

3) Metallisation: thermally evaporated silver layer under vacuum (Ag)

PETPPy/NSA

PPy/AQSAAg

Without Ag Partially coated with Ag (~37%) Totally coated with Ag

Y.K. Hong et al., Current Applied Phys. 1 (2001) 439–442

Multi-layer (2)The EMI SE of fabric increases as the area of Ag evaporation layer increases by a synergic effect.

The contribution of the reflection to total EMI SE increases in presence of the

metal layer, while the absorption contribution decreases.

Y.K. Hong et al., Current Applied Phys. 1 (2001) 439–442

Multi-layer (3)

PET fabric

PPy/NSA

PPy/AQSAAg

PE non-woven

Ag+Pd

80dB

70dB

55dB

25dB

C.Y. Lee et al., Synth. Met. 119 (2001) 429-430.

Sensors

Gas sensor

NH3

CO2

Sensitivity changes because of the formation of salt.

NH3

HCl

PPy/p-toluene sulfonic acid on PET

Sensitivity is stable(conductivity is reversible).

D. Kincal, Synth. Met. 92 (1998) 53-56

Strain sensors (1)Smart materials may be used for biomechanical monitoring, injury prevention, rehabilitation, sport technique studies and medical treatments.

Knee sleeve (CSIRO)

Strain sensors (2)PPy-coated nylon/Lycra (85% nylon and 15% Lycra) plain knitted fabric

(by chemical vapour-phase polymerisation)

The PPy-coated knitted fabric demonstrates high strain sensitivity (up to 50% extension).Resistance increases during stretching and decreases during relaxing.

J. Tsang et al., Polym. Int. 56 (2007) 827–833Dynamometer set-up

Strain sensors (3)

The initial increase in resistance is attributed to deformation of the coating on the fabric surface.The subsequent decrease in resistance is attributed to improving electrical contacts between the individual threads of the textile.

PANI-coated wool/nylon/Lycra fabric(1)

(90.5% wool, 8.0% nylon and 1.5% Lycra)

(1) J. Wu et al., Synth. Met. 159 (2009) 1135–1140(2) J. Wu et al., Synth. Met. 155 (2005) 698–701

PPy-coated nylon lycra fabric(2)

(95.0% nylon and 5% Lycra)

Antibacterial

Antibacterial fabricsPositive charges act against bacteria as Ag ions and ammonium quaternary salts.

Bacteria culture contacted for 1 h with control fabric

Bacteria culture contacted for 1 h with a PPy-coated fabric

Antibacterial test method: ASTM E 2149

Bacteria colony

Antibacterial efficancy: >99%

Fire resistance

Fire resistance

EN ISO 15025

(a) Untreated PET(b) PPy/PET(c) PPy(NDS)/PET

Untreated PET molten in ~3 s(an hole was produced)

PET/PPy was self-extinguishing (in <2 s) and no

hole was produced

Contact with a flame for 10 s

A. Varesano et al., J. Thermal Anal. Calorim. 94 (2008) 559–565

Fastness and Stability

Abrasion

Adhesion

The chemical bonding of the polypyrrole to the surface proteins of the wool is presumably in the form of hydrogen bonding between the lone pairs of electrons on the various N and O on the pyrrole rings of the polymer and the amino acids of the protein. It is also possible there is some N–S bonding between the sulfur in the cysteine amino acids and the pyrrole nitrogen.

J.H. Johnston et al., Curr. Appl. Physics 6 (2006) 587

Electrostatic interaction between a protonatedPPy chain and charged surface.IR analysis: a remarkable shift of the band at 1090 cm-1 towards a lower wavenumberindicates the Coulomb interaction between the positively charged nitrogen of the protonatedPPy chains and the negatively charged surfaces.

T. Pojanavaraphan, R. Magaraphan, Polymer 51 (2010) 1111–1123

Adhesion on cellulose fibres

viscose

cotton

200 1000 5000 10000Abrasion cycles

Excellent adhesion due to chemical affinity between PPy and cellulose.

Excellent adhesion!

PPy penetrates inside viscose fibres

Adhesion on synthetic fibres

PPy-coated PET non-woven(1)

(1) A. Ibarzabal Ferrer, Politecnico di Torino (2006), Thesis(2) S. Shang et al., Polym. Int. 59 (2010) 204–211

PPy-coated PET fabric(2)

Poor adhesion due to hydrophobic behaviour of synthetic fibres.

Poor adhesion!

Ethanol

Pre

-tre

ated

Tetrachloroethylene

Abrasion runs: 200 1000 2000

PPy on PA6

A. Varesano et al., Synth. Met. 160 (2010) 1683–1687

Untreated

Excellent adhesion!

Solvent pre-treatments (based on ethanol and C2Cl4) have been used to improve adhesion.

PEDOT on PET

PEDOT-coated PET fabric before (A) and after 20 000 abrasion cycles (B).

PEDOT shows a good adhesion on PET fibres probably because of chemical affinity.

D. Knittel, E. Schollmeyer, Synth. Met. 159 (2009) 1433–1437

Poor adhesion!

Abrasion cycles10 50 100 200

200 1000 5000 10000

Plasma pre-treatments with O2 or Ar

Untreated

Sample: Ox60/80

Excellent adhesion!

PPy on PET

Abrasion cycles

Aging

Room temperature aging

Long-term physical aging of semi-conducting polypyrrole yields changes of the dielectric loss spectra and to the value of the activation volume of inter-chain (or inter-grain) polaron hopping. The results are interpreted through the reduction of the size of the conductive grains, the division of polymer chains into smaller ones and the decrease of the density of counter-ions.

I. Sakellis et al., Synthetic Metals 160 (2010) 2228–2230

Oxidative aging of PPy

The electrophilic attack of ozone on doped polypyrrole may be directed at the early stages towards these bipolaronic ‘‘defects’’ followed then by a more common reaction pathway which follows the normal degradation reaction of pyrroles by oxigen and ozone.

F. Cataldo, M. Omastova, Polym Degr Stab 82 (2003) 487–495

Ageing of PANI

Crosslinking is probably the most important reaction which modifies the molecular structure of PANI during ageing.No external oxidant is needed; this type of reaction is inherent to PANI.

Disproportionation between two quinonoidunits; the quinonoid rings are converted to benzenoid rings.

If the protonated quinonoid units enter thereaction, an acid is liberated and the product is deprotonated.

I. Sedenkova et al., Polym. Degr. Stab. 93 (2008) 2147–2157

Effect of the oxygen

Air, 25°C

Vacuum PANI-coated PET fabric

S. Kutanis et al., Composites: Part A 38 (2007) 609–614

Effect of the temperature

A. Varesano et al., e-Polymers 22 (2007) 1-14

PPy-coated PET non-woven

The stability of the electrical properties was evaluated by measuring the increase of the resistance ratio R/R0 with the time at different conditions.

The temperature greatly influences PPy conductivity decay.Humidity have a small effect at high temperature.High temperature (80°C) leads to a significant increase in resistance, whereas the samples stored at low temperatures (20 and -28°C) exhibit small resistance increase.

Heating performances

S. Shang et al., Polym. Int. 59 (2010) 204–211

PPy-coated PET fabrics 45°CDC voltage: 24 V

34°C 29°C

26°C

E. Hakansson et al., Synth. Met. 144 (2004) 21–28

Systems that have lower electrical conductivity reach lower temperatures, therefore are less subject to degradation and have a better stability.Note that heating performances required for clothing applications is <200 W/m2.

Systems that possess high electrical conductivity can reach high temperatures, but the heating performances are not stable. The decrease in temperature (or power density) is due to an increase in the surface resistance with time attributed to the oxidative degradation of the conductive polymer which causes loss of conjugation of the PPy.

Washing

Washing fastness

Resistivity increase as log R/R0R: actual resistivityR0: initial resistivity

(a) domestic washing (ISO 105-C01)(b) organic solvents (ISO 105-X05)

(a)

(b)

A. Varesano, et al., Polym. Degr. Stab. 89 (2005) 125-132.

A. Varesano and C. Tonin, Textile Res. J. 78 (2008) 1110-1115.

Fastness to domestic washing is poor (high resistivity increase), while fastness to organic solvents is excellent (resistivity does not change).

Dedoping (1)

C

O

Au

Cl

S

Domestic washing removes Cl- ions

embedded in PPy as counter-anions

Loss of counter-anions destabilizes charged

species

Increase in resistivity

A. Varesano, et al., Polymer Degradation and Stability 89 (2005) 125-132.

wool

PPy/wool

PPy/wool after domestic washing

PPy/wool after dry washing

EDX (Energy dispersive X-ray) spectra

Dedoping (2)PPy/AQSA-coated PET fabrics were soaked with solutions at pH 1, 6 and 13 for 1 h and washed following ISO 105-C01.

X-ray photoelectron spectroscopy (XPS) results

Since AQSA molecules have a sulphur atom, the S/N ratio was used as an indication of the doping ratio.Treatments with higher pHs (i.e. 13) cause decreases of the doping level (Nδ+/N) as well as the release of part of the dopant. Both phenomena cause an increase in the surface resistivity of the fabric.On the contrary, PPy layer was stable in acid and neutral solutions.The sample after washing tests, showed the same doping level (Nδ+/N) than the original sample, but part of the AQSA was removed due to the vigorous agitation and the use of detergents that produce a decrease of the surface tension.

Nδ+: partially charged nitrogen atoms

J. Molina et al., Polym. Degr. Stab. 95 (2010) 2574-2583

Conclusions

Some issues have to be solved:

Stability of inherent conductivity have to be improved, in particular for high temperature applications;

Adhesion in some cases (e.g. synthetic fibres) have to be take into account;

Washing in water and in general contact with polar solvents must be avoided.

ICPs make possible to produce electro-conducting textile materials for wide range of applications (antistatic, heating, EMI shiending, sensors, flame resistancy, antibacterial).