Hi, I am trying to create large (> 1 micron) aligned PCL fibres. Getting smaller fibres has not been a problem using various solvent systems. A lot of papers show that large fibres are achievable using just chloroform however I find that a waxy deposit builds up at the spinneret tip (think 'stalactite') and blockage quickly ensues. I find that lowering the flow rate to prevent this results in an unstable cone and poor quality fibres with bimodal distribution. Adding a small amount of DMF prevents this but results in much smaller fibres. Any advice with this would be gratefully appreciated. Thanks in advance.
Hi Thomas
There are a few options you can try:
If you are ok with fibers of ~2µm you can use CHCl3:MeOH 3:1, this allows constant spinning for a while.
Spin around 50% relative humidity and 23°C, use a large nozzle and flowrates ~2ml/h, this should also allow for spinning for a while.
The best solution to my experience is a gas shield (Larsen et al):
I’ve attached a movie showing an extreme case of nozzle clogging and the effect of a gas shield. This gas shield suppressed the evaporation of the spinning solvent; hence it allows to continuously –for hours- electrospin with highly volatile solvents like Dichloromethane, Chloroform etc.
It requires at the beginning some tweaking to get the correct air flow, through your gas shield module, but if you have this parameter, you can spin PCL in CHCl3 at any flowrate and at any given humidity and temperature.
Good luck
Marc
Use of Coaxial Gas Jackets to Stabilize Taylor Cones of Volatile Solutions and to Induce Particle‐to‐Fiber Transitions, G Larsen; R Spretz; R Velarde‐Ortiz
Advanced Materials. 2004. DOI: 10.1002/adma.200306021
Thank you for this Marc. Unfortunately I am unable to control the relative humidity (spinning is carried out in a fumehood in an open lab). I will try with the chloroform/methanol and maybe think about creating a rough gas shield in the future.
Thanks again
Tom
Those are excellent suggestions Marc. I am having a similar problem when doing some electrospinning. I will also try to give it a try to the gas shield.
Hi Thomas
I usually find it really helpful to just increase feeding rate in the case of aggregation. I think this mainly adjusts the dynamics between solvent evaporation and electrospinning process. Although, if the aggregation is caused by highly viscous solution(which seems this is not your case), the first choice would be to decrease the polymer solution concentration
good luck.
Thomas,
I had same issue. What I did was to decrease the size of tip gauge. In this case, solution doesn't have enough contact surface with air to evaporate and becomes solid at tip. (I guess you cannot do that because of your huge fibers)
However, If that didn't work for your case, the easiest way is to clean the tip by a napkin with insulated handle while spinning is working.
Dear Thomas
May I ask if you have the freedom of increasing your PCL concentration?
If that were the case then I would suggest sticking to a CHCl3/DMF solvent system but just increase your polymer concentration. I have found that a 1:1 ratio to DMF conveniently compensates for chloroform's shortcomings (having both a low dielectric and boiling point) and resulted in a stable cone with no solution build-up at the nozzle. I measured an average fiber diameter of ~2µm spinning from 18%(w/w) PCL (80kDa) and a 15G blunt needle (it's a big one). Distance 20cm, flow rate 2ml/h and voltage ~ 15kV (lab conditions: RH 45% and 22°C).
If you are bound by your current concentration - then I suggest acquiring a coaxial solvent jacket as suggested by Marc.
Dear Willem
Thank you for your advice. I am not bound by polymer concentration constraints (other than physical ones) so i will try increasing the concentration. I have had some success with 10% DMF but will try increasing this ratio also and also needle size. Your flow rate seems quite high, especially at that distance/voltage do you not get a lot of dripping?
Thanks again,
Tom
Dear Tom
That is great news; I'm glad for you.
I observed no dripping in this particular case; it might seem a little high but once you have the higher DMF ratio (higher dielectric constant result in greater pulling rate) you will see that you can spin at a higher flow rate (or same flow rate and lower voltage).
Give it a go - it might work for you.
Wian
you could get thicker nanofibers of PCL by chloroform/methanol 4:1 solvent and also by decreasing needle gauges and increasing polymer solution and flow rate
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