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ELECTROSPUN NANOFIBRES NEW POTENTIALS AND CHALLENGES
Karen DE CLERCK [email protected]
2
20 μm
Very small fibre diameters
(< 500 nm)
High specific surface area
Small pore size
High porosity
Nanofibrous nonwovens have unique
characteristics Nanofibres
1000x zoom Human hair
Nanofibres have various dedicated end-
applications
3
Filtration
Composites
(Bio)medical
Catalysis Protection
Sensors
Energy
Electrospinning allows for various material
morphologies
4
From nanofibers over nanobeads
From random to oriented structures
From solid to porous to hollow structures
5
Needle
Taylor cone
Voltage source
Collector
Polymer reservoir
Nonwoven
Polymer jet
High stability
High reproducibility
Fine fibres (nm-range)
Use of solvents
Nozzle-less
Collector
Polymer jet
Polymer reservoir Rotating
drum
Electrospinning technology @ UGent:
solvent electrospinning
Multi-nozzle
Principle of nozzle solvent electrospinning:
a simple yet complex process
6
Initiation:
Formation of the Taylor cone
Polymer solution
Pendant drop
Taylor cone
Charges induced
by electric field
Jet initiation Bending instability:
Formation of the nanofibres
by solvent evaporation,
jet stretching and splitting
The electrospinning process is governed by
a multitude of parameters
Polymer solution parameters
Solvent (type, mixture)
Polymer (concentration, MW)
Viscosity, surface tension, electrical properties
Processing conditions
Voltage
Distance
Flow rate
Needle, collector
Ambient parameters
Humidity
Temperature
Atmosphere 7
Stable process Reproducible nanofibres
Upscaling
Production of nanofibre
based media
- As rolled goods with or
without substrate
- With grammage between
0.05 - 100 g m-2
Semi-industrial multinozzle setup:
+100 nozzles, modular based prototype
Upscaling
Waterfiltration
Composites
Biomedical
applications
Optical monitoring: pH-
sensors
Waterfiltration
Composites
Biomedical
applications
Optical monitoring: pH-
sensors
11
The ECM, the structural and biomedical support for cells, has a nanofibrous structure
Biomedical applications
Nerves and nerve bundles
Extracellular matrix (ECM)
Ganglion cells
Electrospun nanofibres are the ideal candidate to
mimic the ECM in biomedical applications
12
Stem cell cultures on man-made
electrospun nanofibres
The ECM, the structural
and biomedical support
for cells, has a
nanofibrous structure
Drug delivery using nanofibres: several production
methods and materials available, making tailored
release possible
Waterfiltration
Composites
Biomedical
applications
Optical monitoring: pH-
sensors
pH sensors in water
First signal or warning
Application in wound dressings, protective clothing, ….
Various combinations of pH-indicators
and textile fibres are promising
16
pH-indicator cotton polyamide
Xylenol Blue √
Cresol Red √
Methyl Orange √ √
Ethyl Orange √ √
Congo Red √ √
Alizarin Red √ √
Methyl Red √
P-Rosolic Acid √
Bromocresol Purple √
Alizarin √ √
Nitrazine Yellow √
Bromothymol Blue √
Brilliant Yellow √ ** √
Neutral Red √ √
Phenol Red √
√
clear halochromic sensitivity
acceptable dyeing performance
**
Dyes applied through
conventional dyeing
technique
L. Van der Schueren, K. De Clerck; The use of pH-indicator dyes for pH-sensitive textile materials; Textile Research Journal, vol. 80, p. 590-603, 2010.
Production and analysis of nanofibres functionalised with a pH-sensitive dye
17
electrospinning
process
2μm
PA6
2μm
PA6/DR1-A
Colour change
with pH
Reversible
Quick response
time
pH 0
pH 1
Minimising dye
migration
Use of a complexing agent
Use of functionalised polymers
Faster
response time
Minimal dye
leaching
L. Van der Schueren et al, European Polymer Journal, vol. 46, 2229-2239, 2010. L. Van der Schueren et al, Carbohydrate Polymers, 91 (1), p. 284– 293, 2013. Steyaert I. et al, Polymer Chemistry, vol. 6, p. 2685–2694, 2015.
Halochromic nanofibres show potential for wound dressing applications and protective clothing or equipment
18
Waterfiltration
Composites
Biomedical
applications
Optical monitoring: pH-
sensors
High potential for water filtration
Same filter surface, high porosity, higher flux
High potential for water filtration
Nanofibre membrane Microfibre membrane Conventional membrane
20 000 l/m³.h.bar 2 000 l/m³.h.bar
Effluent microfiltration
Removal after filtration with
nanofibres:
• 69% turbidity
• 76% biological activity
• 44% humic acids
High-flux filtration technique for
effluent recuperation.
Secondary effluent is often discharged into surface waters, while there is
an increased interest in water reuse.
N. Daels et al, Electrospun nanofibre membranes functionalised with TiO2 nanoparticles: Evaluation of humic acid and bacterial removal from polluted water; Separation and purification Technology, vol. 149, p. 488-494, 2015.
Functionalisation of nanofibres
50 nm 300 nm
Post-functionalisation Inline functionalisation
0
1
2
3
4
5
6
7
log1
0 r
em
ova
l (C
FU/1
00
ml)
non-functionalised PA-6
5 omf% WSCP functionalised
Functionalisation with biocides/active
nanoparticles
Nanofibre
membrane
Pressure pump
Bacteria
Microfiltration
Functionalisation
Lab scale filtration set-up
N. Daels et al Potential of a functionalised nanofibre microfiltration membrane as an antibacterial water filter, Desalination, vol. 275, p. 285-290, 2011.
Waterfiltration
Composites
Biomedical
applications
Optical monitoring: pH-
sensors
“Delamination is the most
frequently encountered type
of damage occurring in
composites during service.” S.W. Tsai
Composites
Nanofibre properties allow for a uniform distribution of the polymer in the matrix, without viscosity increase
A whole range of polymers can be
electrospun into nanofibrous webs
Freedom to choose whatever properties you like, e.g. Young’s modulus
Polyamide
Polycaprolactone
Polyurethanes, rubbers, …
Matrix epoxy resin
strain
stre
ss
1.
Producing nanofibrous
webs
2.
Interleaving composite
laminates
3.
Testing for mechanical
properties
100% increase!
PCL nanofibres double the Mode I interlaminar fracture toughness
Van der Heijden et al. (2014). Interlaminar toughening of resin transfer moulded glass fibre epoxy laminates by polycaprolactone electrospun nanofibres. Composites Science and Technology, 104, 66–73.
Mode II interlaminar fracture toughness increases up to 200% upon addition of PA nanofibrous veils
Daelemans et al. (2015). Nanofibre bridging as a toughening mechanism in carbon/epoxy composite laminates interleaved with electrospun polyamide nanofibrous veils. Composites Science and Technology, 117, 244–256.
Energy taken up by the PA nanofibres
Nanofibres can bridge cracks and absorb energy
without nanofibres
with nanofibres
Waterfiltration
Composites
Biomedical
applications
Optical monitoring: pH-
sensors
THANK YOU
Karen DE CLERCK [email protected]
Thanks to: Lien Van der Schueren, Jozefien Geltmeyer, Iline Steyaert, Ella Schoolaert, Sander De Vrieze, Nele Daels, Bert De Schoenmaker, Sam Van der Heijden, Lode Daelemans, Timo Meireman Based on collaborations with: Richard Hoogenboom (UGent), Stijn Van Hulle (UGent), Wim Van Paepegem (UGent), Hubert Rahier (VUB)