John,

You need to think about the chemistry of the process. The carbonisation process requires that the nitrile side groups polymerise into a ladder polymer. Furthermore the puckered cyclised polymer needs to be aromatised to achieve a planar strucure, which acts as a nuclei for the graphitisation process. Thus an essential component of CF formation is

1. Drawing of the polymer to bring the isotactic side groups into juxtaposition for plymerisation (cyclisation)- I suspect that the electrospun fibres have a limited spin-draw ratio. And therefore have limited thermal stability.

2. Oxygen is required to oxidise the cyclised polymer into one with aromatic planar segments-vacuum clearly would give a poor thermal stability.

3. Since the PAN is atactic there is only a limited number of side groups which can be brought into a reaction volume so maintenance of the degree of draw during oxidation and carbonistion is essential. Typical number of cyclised AN groups in a cyclised sequence is only about 5- 15 so stabilisation is essential.

I recommend you read the chapter on Carbon fibres by W. Watt in Strong fibres, by Watt and Perov, 1985.

Dear John,

first of all...which kind of PAN fibre do you use? The type of PAN is important for the following process parameter windows.

Normally if you perfom the stabilization step at air and the fibre is sufficient stabilized you directly can carbonize in nitrogen. The vacuum step you don't need.

The carbonization temperatur you need to get a sufficient properties of the carbon fibre should be in between 1200 and 1500 °C.

How does the fibre, carbonized at 800°C look like? ....is it brittle?

With best regards

Michael

I agree with Michael. Vacuum is not needed at all.

What is your purpose, depending on the purpose process may be different.

yes , no need of vacuum. You can carbonized it under nitrogen from 800 to 1500 °C.

Thanks for your input, appreciate them.

I'm using PAN with MW150000 dissolved in DMF for electrospinning. In another trial with higher flow rate where there's no total lost, the fiber is brittle which makes processing a bit difficult. Is this normal?

Since you said vacuum is not needed, does that mean I have to purge the tube with nitrogen gas throughout the entire heating stage in a closed system or open system?

Thanks!

Brittleness of carbon fibre is normal and indicates that your stabilisation conditions should be improved. If the PAN after spinning is brittle that means your spinning process is not ideal.

To work with nitrogen, it is sufficient to purge the tube with nitrogen. The system can be open and closed. If it is open you have to check if no oxygen diffuses from the outside.

Have you measured the density of the PAN, the stabilized PAN and the carbonized carbon fibre? This value can give you information about the process step and the correctness of the reaction parameters.

Hi, vacuum is not normally used, b ut if you like play with conditions you may try. Please remember to stabilize your fibers and be sure nitogen you use is of high purity. If not it may contain oxygen that burns carbon matter. Jacek

Thanks! Indeed vacuum is not needed, just nitrogen is sufficient. Someone told me that the total sample lost I did last time under vacuum is due to the poor vacuum which continued to draw in outside air into the tube hence consumed my sample.

I used to think that combining vacuum and nitrogen will provide a better atmosphere in the tube but it's the other way around due to the poor vacuum system

Dear John

You have just to carbonise in nitogen fllow ( T=800 C is enough), you have not to use vaccum at all

John,

You need to think about the chemistry of the process. The carbonisation process requires that the nitrile side groups polymerise into a ladder polymer. Furthermore the puckered cyclised polymer needs to be aromatised to achieve a planar strucure, which acts as a nuclei for the graphitisation process. Thus an essential component of CF formation is

1. Drawing of the polymer to bring the isotactic side groups into juxtaposition for plymerisation (cyclisation)- I suspect that the electrospun fibres have a limited spin-draw ratio. And therefore have limited thermal stability.

2. Oxygen is required to oxidise the cyclised polymer into one with aromatic planar segments-vacuum clearly would give a poor thermal stability.

3. Since the PAN is atactic there is only a limited number of side groups which can be brought into a reaction volume so maintenance of the degree of draw during oxidation and carbonistion is essential. Typical number of cyclised AN groups in a cyclised sequence is only about 5- 15 so stabilisation is essential.

I recommend you read the chapter on Carbon fibres by W. Watt in Strong fibres, by Watt and Perov, 1985.

Dear John,...

are there any news from your side and your efforts to carbonize oxidized PAN-fibers. Have you optimized the conditions of the stabilization reaction in oxygen atmosphere to perform the carbonization step in a well manner..

With best regards

Michael

Few years ago we also tried to carbonize electrospun PAN fibers and to combine it with TEOS to obtain carbon/inorganic hybrid fibers. If we used textile grade PAN it became powder. We succeeded only if we used so-called carbon-precursor PAN which contains some % itaconate or other comonomer.