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DR. S. SIVARAMA 201, Polymers & Advanced MaterialsLaboratory, National Chemical Laboratory,Pune-411 008, INDIATel : 0091 20 2589 2614Fax : 0091 20 2589 2615Email : [email protected]
BUILDING POROSITY IN POLYMERS : HOW AND WHY ?
International Conferences on Emerging Trends in Chemical Sciences, VIT University, Vellore
December 5, 2013
POROUS POLYMERS : WHY ?
An important class of organic materials with a diverse range of applications
� Biomedical prosthesis and implants
� Separation media (RO, MF, NF and PV, gas separation)
� Super-absorbing materials
� Selective ion transporters ( Proton, Lithium ion)
� Ion exchange resins
� Catalyst and enzyme supports
� Sensors
� Optoelectronic devices
� Insulators
Alveoli in the lungs
Skin
Dialysis MembranePolyacrylonitrile
Polystyrene foam cup
PolyurethaneFloor mop
Porous Carbon electrode
Zeolite 4A
POROUS MATERIALS ARE UBIQUITOUS !
BUILDING POROSITY IN POLYMERS : HOW ?
� Physical aggregation of pre-formed polymer particles into objects with specific shape and geometry
� Use of suspension / emulsion / HIPE polymerization with or without porogens
� Membrane casting a polymer solution containing a porogen followed by extraction of porogen
� Membrane casting a polymer solution with an inorganic metal salts capable of forming weak complexes with polymers followed by extraction of salt
� Use of hard ( e.g silica spheres) or soft template (porogen) followed by removal of the template
� Intrinsically micro-porous polymers through chemical synthesis
� Phase inversion using a solvent and a non-solvent
� Nanoporous membranes derived from self assembled block copolymers containing a sacrificial segment
Physical aggregation of pre-formed polymer particles
POROUS POLYETHYLENES
0%
20%
40%
60%
80%
100%
0 200 400 600 800 1000 1200
Particle size, D (microns)
No
. o
f p
art
icle
s l
arg
er
tha
n D
(%
)
450 microns
600 microns
700 microns
800 microns
S value= 0.12
S value= 0.13
S value= 0.08
S value= 0.14
CHARACTERISTICS:
• Particle size ~ 400-1000
microns (application specific)
• Particles of narrow size
distribution fused together
• Porosity ~ 40-55%
• Pore size ~ 100-150 microns
• Interconnected pores
POROUS POLYETHYLENE IMPLANTS
Porous polyethylene implants are used by surgeons for non-weight bearing, volume-filling applications in the maxillo-facial, cranial and ocular regions. They are used for reconstructive and cosmetic surgery – often in patients who have met with serious accidents or have required surgical intervention due to tumors.
Key features:
Biocompatible (no adverse reaction by the body), Bio-integration (cells/ tissues migrate into implant), Low weight and not fragile (unlike ceramics), Suturability, Limited shape-ability, Customized implants are possible to make.
POROUS POLYETHYLENE IMPLANTS – IN THE MARKET!
Sphere with suture tunnels Orbital floor plate Floor plate (part non-porous)
Malar implant
Mandibular implant
Chin implant
Orbital rim
Nasal augmentation sheet
Nasal dorsum
Start-up company
www.biopore.in
Pterional implant Mastoid
Use of metal complexing agents to create weak networks in polymers
POROUS POLY(ACRYLONITRILE) MEMBRANES
Membrane preparation
By phase inversion of a soluble complex of metal halides (salts of bivalent alkali metals) with poly(acrylonitrile) followed by washing the cast membrane with water
Total membrane thickness : 9 - 11 mil
Membrane Cross Section(SEM)
CHARACTERISTICS OF UF MEMBRANE
• Average water flux: 50 lmh at 0.5 bar
• 5 log reduction for viruses
• 7-9 log reduction for bacteria
• Molecular Weight Cut Off : ~ 60 k Dalton
• BSA rejection > 90 %
• Total membrane thickness : 9 - 11 mil
UF MEMBRANE TECHNOLOGY :FROM CONCEPT TO MARKET
• Discovery of a unique process to control membrane porosity
- Reject smallest known pathogenic species (virus);
- Still be able to operate at tap water pressure (0.4 bar)
• Prototype preparation, demonstration & performance evaluation
- Designed various easy to use prototypes
- Demonstration & rigorous performance evaluation
• Technology transfer
- Technology licensed to Membrane Filters India Ltd., Pune, a start up enterprise incubated at NCL
- Product in the market since 2007; Current sales turnover of the company ~ US$ 15 million
Typical Installations
School near Pune
Army Camp-A’’’’ Nagar
Lake
@
Pun
e
Bore well- Lucknow
School in Pune
Tsunami Affected Camp
Open Well
High Internal Phase Emulsion Polymerization ( HIPE)
HIGH INTERNAL PHASE EMULSION POLYMERIZATION ( HIPE)
POROUS HIPE POLYMERS
Beaded porous polymers polystyrene-DVB
polyurethane HIPE stationary phase for HPLC and GC
High internal phase emulsion (HIPE) monolith
Schematic diagram of HIPE polymerizationSchematic diagram of HIPE polymerization
Optical microscopy
Water phase
Oil phase
W/O emulsion Poly (HIPE)50 µm
SEM
P & G – CSIR confidential
ALL ACRYLIC HIPE POLYMERIZATION
Characterization
HC layer AY layer
EHAEHMAEGDMAEMULSIFIERS
EHAEGDMAEMULSIFIERS
LAYER 1 LAYER 2� Mixing control (Constant cell size
for kinetics )
� Temperature control (65ºC)
� Controlled time for polymerization
� Water: Oil ratio
Residual Monomer analysis
stabilityCell size Distribution(SEM)
MechanicalProperties
Yield stress, compression
Layer 1 and 2 combined
Layer 1
Water : oil ratio ⇒⇒⇒⇒ 27: 1
Layer 2
Water : oil ratio ⇒⇒⇒⇒ 24: 1
HEIRARCHIAL STRUCTURES WITH GRADED LAYER POROSITIES
FUNCTIONAL ABSORBING MATERIALS
Always, the world’s leader in feminine protection, is dedicated to helping women embrace womanhood positively—from the very beginning of puberty through their adult lives.The Always brand is behind some of the biggest innovations in feminine hygiene history, including the introduction of winged pads in 1985 and Ultra thin pads in 1990. Continuing its goal of improving women’s lives across the world, Always recently introduced Always Infinity, a pad made with a new-to-the-world material that enables women to have the magical combination of absorbency, amazing softness, and flexibility all in one pad.
Hierarchical structures withgraded layer porosities
Porous polymers : Selective ion transporters ( Proton, Lithium ion)
INTERNALS OF A FUEL CELL
� Conversion of chemical energy to into electrical energy first demonstrated over 150 year ago !W.R.Grove, Phil.Mag.Ser.314,127-130 (1839)
� However, in spite of the attractive system efficiencies and environmental benefits, it has proved difficult to develop the concept into commercially viable industrial products
Greatest unmet challenge : Lack of appropriate materials and scalable manufacturing technologies
Proton Conducting
Membrane
M K. Debe Nature, 486, 43-51 (2012)
COMPONENTS OF A FUEL CELL
� Produces electricity from the electrochemical oxidation of hydrogen
� A fuel cell stack comprises of identical repeating unit of cells, called Membrane Electrode Assembly (MEA)
� The MEA electrodes are attached to a solid polymer proton conducting membrane that conducts protons, not electrons
� Hydrogen is oxidized at the anode and oxygen is reduced at the cathode
� The entire assembly is compressed by bipolar plates that introduce gaseous reactants and coolants to the MEA
Polymer Materials
(Membrane Electrode Assembly)
Stack Engineering
BoP
Control Electronics
Carbon and Carbon
composites
(GDL and Bipolar Plates)
Electro-catalysts
(Anode and Cathode)
ATTRIBUTES OF A PROTON CONDUCTING MEMBRANE FOR FUEL CELL APPLICATIONS
� High proton conductivity
� Low electronic conductivity
� Low permeability to fuel
� Low electro-osmotic drag coefficient
� Good chemical stability
� Good mechanical property
Ideal membrane material is a compromise between
performance, durability and cost
POROUS POLYMERS FOR SELECTIVE TRANSPORT OF LITHIUM IONS
� Current material of choice : Polyolefins (PO)
� Polyolefins are hydrophobic and, hence, intrinsically less compatible with liquid electrolytes ; have low retention capacity to hold organic solvents with high dielectric constant
� PO separators have poor wettability characteristics in polar electrolytes, such as, ethylene carbonate (EC), propylene carbonate (PC), and γ-butyrolactone (GBL) owing to their low polarity.
� Polyolefins have a Tm ~ 150 to 160°
C ; Pores tend to collapse near Tm, causing shrinkages and shorting
� Polyolefins are also flammable
POROUS POLYMERS FOR SELECTIVE TRANSPORT OF LITHIUM IONS
Need : A new porous polymer material for selective transport of lithium ions
Desirable Features
� Retention of porosity at high temperature � Amorphous polymers to prevent shrinkage at high temperatures and provide high dimensional stability� High surface wettability for polar electrolytes; ability to form hydrogen bonds with electrolytes� Ability to bind Lithium ions for facilitated ionic conduction
HIGH TEMPERATURE PEM-FC
Improved carbon monoxide tolerance (~185oC, up to 3% CO in H2 can be tolerated)
Simple cooling system
100% single water vapour phase
Electro-osmotic drag of water = 0; conductivity not dependent on humidity levels
No need for humidification
Unique proton conduction mechanism by self ionization /self dehydration; proton hopping from N-H to phosphate anions
No “cathode flooding” problem
Reduced methanol crossover
Improved kinetics of reaction at both electrodes
Better heat utilization / recovery
Greater ease of integration of a reformer with fuel cell
IOCL, Delhi 110308
Most preferred material : Poly(benzimidazole)s (PBI) doped with phosphoric acid
Q.Li, J.O.Jensen, R.F.Savinell, N.J.Bjerrum, Prog. Polymer Sci., 34, 449 (2009)
POLYMERSTRUCTURE
• Ring substitution
electronic/ steric
• Co-monomers
flelxible / rigid
• Porosity
• Crosslinking
PROPERTY
• Molecular weight
• Tg / free volume
•Crystalline/amorphous
• Acid binding sites
• Water retention
•Tensile strength and
elongation
PERFORMANCE
• Chemical stability
• Thermal stability
• Proton conductivity
• Gas permeability
POROSITY
STRUCTURE – PROPERTY – PERFORMANCE MATRIX FOR FUEL CELL MEMBRANES
����ACID DOPED PBI BY SOL-GEL PROCESS(DENSE MEMBRANES)
~ 5 molecules of H3PO4 per repeat unit for PBI; 2 molecules of H3PO4
bonded to two nitrogen atoms of repeat units, the rest of the acid is unbonded “free acid”
Presence of free unbound acid necessary for proton conductivity
Inherent Viscosity : ~ 2 dl/ g
Tg = 425 – 436oC
No weight loss in air at 500oC
pKa = 5.5H.Vogl and C.S.Marvel, J.Polym.Sci.,50, 511 (1961)J.S.Wainright, J.T.Wang, D.Wang, R.F.Savinell and M.LittJ.Electrochem.Soc., 142, L121 (1995)
16-24 hours
Tensile strength(circles) and elongation at break(squares)as a
function of polymer IV
Proton conductivity of PA doped PBI by sol-gel process
Sol-gel
NafionConventionalPhosphoric acid doped PBI : single
phase transparent sol from which membranes can be cast by phase
inversion process
POROUS POLY(BENZIMIDAZOLE)S : PROOF OF CONCEPT
MeOH
Porogen : Dibutyl Phthalate
70 % DBP : 0.05 S/cm at 25°°°° CDense PBI : 0.0015 S/cm
Porogen, wt% Uptake, wt%
0 132
25 173
50 246
Doping with 11M Phosphoric Acid, Porogen: Dibutyl Phthalate
Dense PBI : 440 mol % PA per RUPorous PBI :1460 mol % PA per RU
(70% porogen)
25% wt solution
25°°°° C
SEM micrographs of fractured porous PBI membranes prepared from PBI / dibutyl phthalate films containing (a) 25 wt % DBP, (b) 50 wt % DBP, (c) 70 wt %
DBP, and (d) 80 wt % DBP.
Poorly controlled macropores
Intrinsically micro-porous polymers through chemical synthesis
THERMAL REARRANGEMENTS OF AROMATIC POLYIMIDES
Glassy polymers with excellent thermal and mechanical properties, resistance to chemicals and easy processibility
Workhorse materials for separation membranes, nmely, RO, MF, UF, PV and gas separation
Precursor poly(amic) acids can be imidized using heat (3000 C), chemical methods using acetic anhydride and a base or an azeotropic imidization at 1600 C
Thermal treatment of polyimides with an ortho functional group can lead to rigid aromatic polymers like poly benzoxazole, polybenzothiazole or polybenzimidazole
Thermally rearranged (TR) polyimides possess some novel topologies which result is unusual increase in fractional free volumes
THERMAL REARRANGEMENT OF OF ortho-HYDROXYPHENYL PHTHALIMIDES TO
BENZOXAZOLES
G.L.Tullos, J.M. Powers, S.J. Jeskey and L.J. Mathias, Macromolecules, 32, 3598 (1999)
THERMAL IMIDIZATION OF BPDA−HAB POLYAMIC ACID AND THERMAL CONVERSION
TO AROMATIC POLYBENZOXAZOLES
Reasons for insolubility not
explored; chemistry has remained unexploited !
3,3I –Dihydroxy-4,4I-diamino biphenyl
(HAB) +
3,3I ,4,4I –Biphenyl tetracarboxylic
dianhydride (BPDA)
TR POLYIMIDES : AN EASY ROUTE TO POLYMERS WITH INTRINSIC MICROPOROSITY
� Change of chain conformation: meta- and para-linked chains can be created
� Spatial relocation due to chain rearrangement in confinement, leading to generation of free volume elements
X : -O-, -NH-, -S-
THERMAL REARRANGEMENT OF ortho-HYDROXYPHENYL PHTHALIMIDES TO BENZOXAZOLES :
REEXAMINATION
POSSIBLE ORIGINS OF BIS-BENZOXAZOLES
Cause : Inadvertent moistureReaction generates water !
Under carefully purified and dryConditions of reactions, the formation of
Bis benzoxazoles can be completely avoided
THERMAL REARRANGEMET OF ortho--AMINOPHENYL PHTHALIMIDES
POLYBENZIMIDAZOLES VIA THERMAL
REARRANGEMENT
Key step : hydrolysis of Polypyrollone
1 M tetrabutylAmmonium hydroxide
solution at 100 C
PBI via TR of POLYIMIDES WITH ORTHO AMINO GROUPS
PBI synthesized TR of polyimides derived from 3,3I,4,4I-tetramino biphenyl (TAB) and 3,3I ,4,4I–biphenyl tetracarboxylic dianhydride (BPDA)
PBI produced exhibits the same solubility characteristics as obtained from TAB and isophthalic acids
PBI doped with phosphoric acid exhibits a conductivity of 0.3 – 0.35 S/cm at 1400 C
PBI obtained via TR of polyimides exhibits better acid uptake properties and is also able to sequester water
Detailed characterization is in progress
This approach provides an ability to access hetero-aromatic polymers of diverse structures and explore structure –property relationships
NH2
NH2
H2N
H2N
CO2H
HO2C
PPA, 180 oC
2 hour
N
N
N
N
N
N
N
N
350 oC
N
N
N
N
N
N
N
N
N
N
N
N
N
N
N
N
CYCLOPHANE AS BUILDING BOLCKS FOR INTRINSICALLY POROUS POLYMERS
Polymer properties under investigation
N
N
N
N
N
N
N
N
CH3
CH3
N
N
N
N
N
N
N
N
H3C
H3C
N
N
N
N
N
N
N
NH3C H3C
H3C
H3C
250 oC
liquid phase hydrogen donor
APPROACHES TO REVERSE THE CROSSLINKING REACTION
ANOTHER APPROACH TO CYCLOPHANE BEARING
POLYMERS
HT PEM FC : 20 CELL, TARGET 200 W WITH H2/AIR
Cathode sideAnode side
Thermocouples
Bud pins – Vcell
Vstack
Blower100-200 slpm
Cooling duct
Insulation
Pad heaters on all four sides
Inlet gas at RT
Gas out sent to Arbin for exhaust and pressure measurement
BENCHMARKING WITH COMPETITION
0.4
0.5
0.6
0.7
0.8
0.9
1
1.1
0 100 200 300 400 500 600 700 800 900
Vo
lta
ge
(V
)
Current density (mA/cm2)
Sartorius
CelTek P
Advent (TPS)
Daposy (DPS)
NCL (20 cells average data)
NCL (best from 20 cells data)
Stoichiometry� Competitor: H2/air ���� 1.35/2.5� Our MEA: H2/air ���� 3.5/2.5 @ 800
mA/cm2
Temperature: ~165°°°°C
POLYMER ELECTROLYTE FUEL CELLSA TEAM CSIR EFFORT
Developed knowhow for making all key material components
Performance of MEAs benchmarked against competitive materials.
Durability demonstrated at single cell and stack levels for 500 - 700 h.
Built up to 1 kW prototype PEFC plants including BOP.
SUMMARY
• Porous polymers are a versatile material platform for creating new properties in existing polymers
• They are relatively easy to prepare and tailored porosities with surface properties useful for a given application can be designed
• Diverse applications in health care, ultra-filtration and separation processes and energy related applications e.g. fuel cell membranes and as electrode material for batteries
NCL 210706
THANK YOU