I attempted to fabricate a flexible substrate intended to be thermoplastic using PLA powder through the solution casting method. I referred to two sources for the procedure. In this process, 5 g of PLA powder (4032D, NatureWorks) was dissolved in 100 mL of chloroform. Based on the references, I applied two different stirring durations at the same speed (200 rpm): one for 1 hour and the other for 24 hours. Both solutions were stirred at room temperature.
However, the resulting films from both conditions turned out to be very brittle. The film from the 24-hour stirring was more uniform, while the one stirred for only 1 hour was extremely brittle and could not be peeled off from the petri dish.
Is there anything wrong with my method? The references I followed reported good transparency and improved ductility, which I was unable to replicate.
the reference:
Rhim, J. W., Mohanty, A. K., Singh, S. P., & Ng, P. K. W. (2006). Effect of the processing methods on the performance of polylactide films: Thermocompression versus solvent casting. Journal of Applied Polymer Science, 101(6), 3736-3742. https://doi.org/10.1002/app.23403
Li, M.-X.; Ren, Y.; Lee, D.; Choi, S.-W. Crystallization Behavior and Electrical Properties of Nanoparticle-Reinforced Poly(lactic Acid)-Based Films. Polymers 2022, 14, 177. https://doi.org/10.3390/polym14010177
The brittleness of your PLA films may stem from factors such as residual solvent, rapid evaporation, or the inherent properties of the PLA grade. Try annealing the films, using a slower evaporation process, or adding a plasticizer to enhance flexibility.
Abdelhak Maghchiche
Thank you for your previous suggestions. I plan to implement a slow evaporation process by using aluminum foil within a closed chamber, as recommended.
Previously, I attempted to incorporate PEG 400 at a concentration of 30% w/w (approximately 1.5 g) into the PLA solution. However, this concentration did not appear to significantly improve the film’s flexibility or reduce brittleness. As an alternative, I experimented with adding 10 mL of PEG 400, which resulted in a wax-like material rather than a flexible film. I would appreciate any recommendations regarding alternative plasticizers or more appropriate PEG concentrations for this system.
Additionally, I observe during the stirer both after 1h and 24h, there still undisolved PLA (theres a dust like material) ould the presence of undissolved PLA powder in the solution, potentially due to the use of technical grade rather than analytical grade chloroform, be contributing to the brittleness or poor film formation observed in my results?
I chose PEG as a plasticizer due to its reported thermal and flexibility-enhancing properties, as described in the following reference:
Yuniarto, K., Kurniawan, B., Welt, B. A., Foliatini, F., Hanafi, M., & Irawan, C. (2017). Morphological, Thermal and Oxygen Barrier Properties of Plasticized Polylactic Acid Film. Journal of Applied Packaging Research, 9(3), 1–9.
You can try these steps to ensure a flexible film:
- Add a plasticizer – Try ATBC, PEG400, or TEC based on PLA weight.
- Dry slowly at room temperature for 2–3 days in a covered but ventilated setup.
- Post-dry in a vacuum oven at 40–50°C for 24 h to remove residual solvent.
Hope this helps! All the best!
Akanksha Adaval
Thank you for the advice, i would try this setup
Akanksha Adaval; Abdelhak Maghchiche
Hello, thank you so much for all your help. I was finally able to make the film using pure PLA. It turns out the material I used before was not in good condition due to degradation. After switching to granule resin instead of the powder form, it worked much better. Also, I found that using slow evaporation with a covered but ventilated setup gave the best results
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