Cellulose nanofiber is in a water solution and PLA is sensitive to the temperature and water. Any suggestions?
This is really a difficult task but crucial point for the preparation of PLLA based nanocomposites. From my prevous experience, I would suggest to modify the nanocellulose surface by low amount plasticizer (try to avoid using hydrophilic plasticizer like PEG). After being confirmed that fibers are modified, you can melt mix them with PLA. It can improve the dispersion of fibers but can also reduce the modulus of PLA. If possible carry out the melt mixing of well dried components (both PLLA and modified fibers) in Nitrogen environment to avoid moisture. Mixing time nad temperature can be reduced using this idea. It may work. good luck.
How about trying to melt them under vacuum? Low pressure will help melting at lower tempeature.
Li, this would be a good idea. Did you try it? time of heating is important here. once it melts it should be cooled down at room temperature. Can you make a comparison between the TGA of sample melted in vaccum and in air? I am curious to know this.
Another thing, I met Prof. McKenna last year in a conference in Italy. I took the award of the best from his hand. I hope he remembers me.
Hi Li, I would think it is difficult to vacuum for a relatively big lab scale environment, isn't it? People use this technique for degassing during TSE compounding although.
Usually we can do it in vacuum oven, but if you are running an extruder, abosulutely that is difficult.
First of all you definitely you should dry the nanofibers (is better if you functionalize them before drying to avoid the hidrogen bonds formation during druing process of nanofibers) beacuse the water can cause bubbles into your nanocomposite which acts as breaking point. To avoid the problem you have raised im using the solvent casting method, but my personal guess is that you should firs make some TGA to your PLA to see which is the degradation temperature of your PLA (consider making some TGA at constant temperatures during some time to see the degradation of PLA at certain temperature during some time). keep on mind that one of the hypothesis of the thermal degradation of the PLA is that small quantities of water could depolymerize the PLA.
Finally my suggestion is to make some mechanical testing of PLA after proccesing in some conditions and see which conditions could you use to minimize the degradation of PLA
Hi Jon Trifol, Thank you for your suggestion. As far as I know, even surface treatment can hardly preserve the the nanosturcture of the fibers, do you have reference?
To Ailton Gomes, Thank you for your suggestion. Do you have reference related to your suggetion?
i havent go very deep into the functionalization of nanofibers, so I dont know so much and i dont have lot of references about this topic, but probably yes. A good way to see the effect os this parameter might be to make a -maybe 1% w/w - disolution of never dried functionalized nanofibers, keep them at vigorous stirring during at least 48 hours and compare the two disolutions.
hi.
There are a good method to producing MFC/PLA for minimize thermal degrading. this will be done at water area but without melt compounding. did you try it?
To Pezhman Heidarian, Can you please tell a bit more? "at water area without melt compounding", what does it mean? how do you make sure the dispersion? and we don't need water in the end.
I have seen some work in which after acetilation of MFC, the reinforcement can be dried better with a minor agglomeration. See: Slides of Tingaut EMPA. Sustaincomp Final Conference, 2012 from http://www.sustaincomp.eu/
Alternatively you can also accept that degradation happens, add a chain extender to mitigate MW loss and also put the vacuum in the extruder to remove volatiles and avoid bubbles in the final material.
You can try a acidic solution/LA solution, which can prohibit the hydrosis of PLA.
Shuai Zhao, Acidic PLA solution or acidic solution of ...? Could you please tell more about this? Is there any reference I can look into?
I have not been working with PLA but with PPC (polypropylene carbonate) which has similar issues in processing
Dear colleague,
Before to reflect about the different surface treatments of the nanofiller, please consider that is very important to minimize by drying the water content of both, PLA and cellulose nanofibers (CNF), to avoid polymer degradation. Furthermore, to have successfully results in correlation to your objectives, there is also the possibility to previously purify your CNF and to choose a PLA with lower melting point and adequately viscosity. I believe that we can try to tune the processing conditions (shear, time of mixing, etc.)…
Maybe this paper can give you some ideas: D.M. Fox et al. / Polymer Degradation and Stability 98 (2013) 590-596. Good luck in your work,
Marius
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