0 1 2 3 4 5 6 7 0 20 40 60 ! o [J /g ] FeCl3 [%] 0 1 2 3 4 5 6 7 0,00 0,05 0,10 0,15 0,20 0,25 0,30
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Capillary breakup and electrospinning of PA6 solutions
containing FeCl : experimental findings and correlations
3
S. Formenti, R. Castagna, F. Briatico-Vangosa, C. Bertarelli
Politecnico di Milano, Dipartimento di Chimica Materiali e Ingegneria Chimica “G. Natta”
REFERENCES
One of the main issues in the electrospinning technology concerns the control of the resulting fibres morphology. The extensional rheological behaviour of the fluid plays a fundamental role to this respect: a high degree of elasticity of the polymer solutions limits or prevents instabilities and subsequent
formation of non-uniform structures [1].
We present the case of solutions of PA6 and iron(III) chloride hexahydrate (FeCl ) in formic acid, selected to 3
electrospun a template for the following in situ polymerization of pyrrole vapours. The presence of ionic salt, essential for pyrrole growth, may disturb or even prevent H-bonds formation between amide groups of PA6 backbones, and thus perturb solution viscoelasticity.
To identify the effect of FeCl on the system rheological behaviour and spinnability, a systematic characterization was 3 carried out at fixed PA6 concentration (15% wt/wt) and varying the salt content, aimed at correlating electrospun fiber morphology and the extensional rheological behaviour of the solutions.
The addition of the ionic salt to PA6 solutions:
increases the shear viscosity, likely due to the swelling of macromolecular coils because of FeCl steric hindrance;3 lowers solution elasticity due to hydrogen bond scission, induced by the formation of complexes between
the salt and the amide groups of PA6 backbones.
Morphology of electrospun fibres becomes significantly inhomogeneous in correspondence to the solution
characterized by Ec<1, confirming the importance of elasticity in jet stabilization. All other solutions with De>>1 (here De>6) give rise to the formation of uniform structures.
Steric hindrance of FeCl also causes fibres to be completely amorphous above a critical concentration.3
COMMENTS AND CONCLUSIONS
DISCUSSION AND CORRELATIONS
O N H N O N H N H O N N O N N H Fe Cl Cl Cl Fe Cl Cl Cl
Free surface flow
ADIMENSIONAL ANALISYS [4] t =R 3 rl s h l0 t =visc s t = lel tvisc Oh= tR l De= tR tel Ec= t visc De Oh =
EXTENSIONAL RHEOLOGY
ELECTROSPINNING
Capillary Breakup Extensional Rheometry - CaBER
[2]Assumptions: viscoelastic extensional behaviour
D (t)=Dmid 1 D G1 4s exp 1 t 3 lC 3 l [ms ] C %FeCl3 E E E D0 L0 Dmid(t) Dmid(t) Dmid(t) D1 t t=0 tbr h [P a.s ]* 0 ,S %FeCl3 * shear reometry 4 6 8 ADIMENSIONAL MAP De 0 0 1 2 4 6 8 10 Viscous dominated 6,5% 1 2 Oh Elastically dominated 5,6% 4,5% 0% 1% Ec=1 Spinnability Unspinnability Collector Syringe Polymer solution High voltage supply UNSPINNABILITY %FeCl3 Fibr e mean diamet er [ m m]
Effect of chain solvatation Effect of H-bond scission
CRYSTALLINITY
‘Self-controlled thinning’
Governed by: characteristic time scales
6,5% 5,5% 4% 0% 2,5% 0 10 20 30 40 0 50 100 150 200 250 T [° C ] t [min] 50 100 150 200 250 5,6% exo 4,5% 4% 3,5% 3% 2,5% 1,5% 0% AMORPHOUS SEMI CRYSTALLINE 1 W /g
