Hello, I've used 2,2,2-trifluoroethanol (TFE) as a solvent to dissolve PLA or PLGA for solvent casting on glass cover-slips (dip coating). I have prepared two solutions, 4% and 10%; however, I've found that using 4% solutions was unsuccessful as the resultant film was porous with spots of dissolved polymer (which might explain what you've found). the 10% solution was successful in making nice PLA films as checked under the microscope. I suggest you use this procedure to have a nice film of PLA on the petri dish as well. you can also use DCM (Methylene Chloride) instead of TFE, but beware that it might dissolve your petri dish (if it's plastic! ).

I suggest to dry your PLA before to be disolved in any solvent. Generally, the whitening in polymeric films (PMMA, PC, PS, etc.) that usually should transparent films, these can get some dull or opaque aspect. Also, you can try to dry your solvent incase that it absorbs humidity of the environment. Are you using a closed system (vacuum oven or bag) to evaporate the solvent?

Dear Pezhman, thank you to give a figure out of your process that you are following to produce your PLA. The reason to dry the PLA before the dissolution of it, is because PLA absorbs humity of the environment. The producers suggest to dry the PLA before to be processed by injection or extrusion systems, You can consult the data sheets of the PLA supplier in order to know the temperatura and the time for drying. Tomas Madera.

Could it be crystallising during the solvent evaporation process? This could account for the lack of transparency. If this is the case then re-melting the film then quench cooling quickly might help to minimise the amount of crystallinity.

Because solvent evaporates so fast, then leaving tiny air bubbles inside. It is not easy to get transparent film by this method.

The whitening could also be due to phase separation which could happen due to non-homogeneous drying of your film. So, one thing to try would be to further lower your PLA concentration in the final solution and dry it longer. Hope this helps

First of all you should specify if by solvent casting you indeed obtain a white powder or a white (opaque) film.

In the first case the result is likely due to low molar mass of the used polymer. Any alternative way of obtaining a film will fail due to this intrinsic feature of your material.

If what you get is an opaque film, while you want a transparent one, you must avoid formation of domains with different refractive index. They could be micro-voids resulting from formation of solid polymer cages containing inside more or less diluted solutions. In this case, rate of solvent removal can play a role. Most likely, however, the turbidity in your sample is originated by the crystallization of PLLA. Fortunately, this is a slowly crystallizing polymer. Therefore, you can take your opaque film, place it in an oven at ca. 200 °C and then cool it as fast as you can.

A nice transparent (amorphous and glassy) PLLA film will be the result.

Thank you so much dear researchers.

Professor Alfonso my problem was existence of white powder in my film that with your guidance it was improved. Thanks.