lecture on intrinsically conducting polymers on textiles [en] · conducting polymers •...
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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).
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