ELECTROSPUN NANOFIBRES NEW POTENTIALS AND CHALLENGES

Karen DE CLERCK karen.declerck@ugent.be

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 karen.declerck@ugent.be

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)