Electrospun nanofiber easily degrades and ages during heat treatment (i.e. annealing), but the annealing temperature is well below its melting temperature. Why? Has anyone encountered that situation?
I've encountered this situation when doing carbonization of electrospun PVA and PAN in air.
Which nanofiber you're referring to? If carbonization (I think carbonization is a more suitable term) is done in air, oxygen will consume your samples which makes it very brittle or sometimes even total lost of nanofibers after carbonization.
Thank you, John. This is electrospun PA66 in my situation, where PA66 was carbonizated when annealed at 220 ℃ for 2h in air and partial lost at 200 ℃ even for 10 min. Considering the results, I am wondering whether the degradation can be prevented when annealing in vacuum atmosphere, even at high temperature. What do you think?.
I'm not sure the thermal properties of PA66, but sometimes the heating rate plays an important role. Heating up to 220 C at 10 C/min and 1 C/min do affect the properties of my fibers.
If you're doing it in a vacuum system, make sure the vacuum is a really good one where there will be no leakage of air into your system, or you can simply flow in inert gases like N2 or Ar during your annealing.
This is another related question. You can refer Dr. Asmus Meyer-Plath answer to my question. https://www.researchgate.net/post/How_to_solve_a_problem_with_flexible_carbon_nanofibers_from_polyacrylonitrile_PAN
If I am not wrong, when u anneal the sample after electrospinning, the polymer degrades as you mention it rightly. It doesnt melt or evaporate. It breaks down into constituent smaller molecules that make up the polymer chain and the smaller molecules are lost to the environment.
And if you could tell me what are you expecting out of your electrospun fiber at the end of annealing process, may be i will be able to give you a better suggestion with respect to what is the right way to go about.
Application of vacuum during annealing increases the chances of losing more than usual amounts of polymer. The vacuum decreases the vapor pressure inside the chamber hence enhancing the evaporation of the polymer rather than actually reducing it.
Thank you for your answer, Tejabhiram. The annealing of electrospun Nylon-66 nanofibers taken in my case was to achieve enhanced mechanical properties. For mechanical properties of as-spun nanofibers are not optimal, attributing to the confined crystallization during electrospinning. But your answer does not seem to encourage me to do in that way. Can you give me more beneficial advices?
Hey Bo
The first thing that you should do is to get yourself a TGA graph for the Nylon 66. THis will give u an idea as to when is the polymer starting to degrade. May be a parallel DSC will give u temperature of crystallization also.
Now this said, once you find out the temperature at which the polymer starts to degrade,
1. heating of your sample should be done under that temperature rather than above it.
2. If this process does not yield favorable results, the next thing you should try is do the annealing in a pressurized argon atmosphere rather than a general oven or a muffle furnace.
3. If this is not possible or doesnt yield good results, the next thing you can try is to put your sample in an autoclave along with small amounts of water of someother non reactive species (with your polymer) and do the heating. This way high pressure can improvise the crystallinity of the sample.
Tell me what you think of these, meanwhile i consult some of my colleagues on the same issue
hey man
From what I, have understood in your conversations you are doing the heat treatment in order to increase the mechanical properties of your fibers am i right ?
If so as others have suggested you have to do the TGA test in order to find the glass transition temperature,melting point and degradation temperature . And upon knowing these temperatures you can do the treatment more wisely . But in some cases when we need more heat stability from materials we either cross-link them using cross-link agent or we add mineral particles to them such as silica particles in this case they can withstand a higher temperature .
Hi,Sepehr.
You idea sounds great. As for nanofibers, the mechanical properties can be enhanced by annealing, which sacrifices the quality of nanofibers unluckily. The contradiction confuses me a lot. Introduction of mineral particles into nanofibers may help a lot. Have you worked on electrospinning or other relevant nanofiber fabrications, Sepehr?
Yes i,ve been working on electrospinning for 3 years now and i have worked with different polymers and minerals , and what i told you was according to my experiene with polyvinyl pyrrolidone (pvp) which i was trying to fabricate a polymer/mineral nanofiber composite . So i,ll be glad to help you if you have any question ralated to nanofibers and their applications .
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