Dear Lucas Rafael Carneiro da Silva ,

I would suggest, before relying on the thermal data obtained in the first heating cycle, to perform your experiments (if possible), by using different heating rates. Sometimes, some effects (like Tgs, or chemical reactions) can be "hidden" mainly due to the heating rate employed (either being to slow or too fast). If after performing these experiments, the results are still the same you are observing, then your polymer might be curing or something during the first heating cycle, thus forming some sort of crosslinked network that then, during the second heating cycle (or during the cooling cycle), does not show any of the expected effects you are looking to.

By the way, just to add some certainity to your experiments, I would analyze also by DSC the pure components (PLA, and Flour), just to understand a bit how they behave by themselves during the cycles.

Hope this helps!