I am working with a PLA with unknown trade name.
Is it possible that the PLA contains chain extenders( I mean its Mw has been increased by some kind of chain extenders, so they continue to react during processing)?
Dear Catherine
Salam
Did you try to know about your PLA chains end groups?
If you can determine this option maybe you can explain the reason of the molecular weight increasing better
cheers
Dear Mohammad,
Thank you for your answer. Which method do you recommend?
Dear Catherine you can search about the usual methods for determination of polymer end groups. Unfortunately, I didn't remember the methods, but I know when you use a polyester in a harsh processing the molecular weight probably decreased because the ester bonds are not stable in the harsh conditions.
So I guess maybe if your polymer chains have an active end group such as: Acidic or alcoholic end group probably they could have a condensation reaction and maybe they are cross-linked with each other
If you suspect that you can always try some form of end group titration. I would doubt if NMR would be helpful. FTIR might be another option.
I performed some tests, it seems it is due to unreacted chain extenders!
Dear Catherine,
According to the opinion of other RG colleagues, the increase of molecular weights of PLA could be firstly explained by the presence of reactive CEs able to react with PLA end-groups to generate esters or ethers of increased both weight-average molecular weight and viscosity.
Please consider the technical sheet of Ingeo™ Biopolymer 4044D NatureWorks a PLA reactive extrusion grade.
Among the CEs stated for PLA, it is worth pointing out the good results obtained by the utilization of styrene-acrylic multifunctional-epoxide oligomeric CEs such as Joncryl® products. These additives are commercialized by BASF with different characteristic features (glass transition temperature, molecular weight, epoxide concentration, etc.).
It was reported that addition of CE at an appropriate loading had a profound effect not only on the control of polymer degradation, but also on the increase of molecular weights and consequently, of the polymer viscosity (you can consider the papers of N. Najafi et al. (doi:10.1016/j.polymdegradstab.2012.01.016) or other scientists- for more information).
Finally, I believe that it is a key point to have maximum information from supplier about the PLA used in our studies.
Good luck in your research works,
Marius
http://www.natureworksllc.com/~/media/Technical_Resources/Technical_Data_Sheets/TechnicalDataSheet_4044D_films_pdf.pdf?la=en
http://onlinelibrary.wiley.com/doi/10.1002/app.42480/abstract
- If you are working with an unknown PLA grade you have to perform the characterization of that by yourself, and then do a comparison with present articles. by this way you are able to unfold the plot. FTIR, optical purity and GPC and so on can help you. Anyway, your question seems like a profound position because as far as I conserned PLA is extreamly sesitive polymer and this dam is its Ashills' heel. it meams by perfoming any melting process, a plothera of chain scissions are expected to be happen, so Mw have downward trend.
Dear Pejman,
Thanks a lot for your answer. You can find the GPC results and more discussions on this matter in another question I asked after this one (with the same title!).
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