I did some tensile tests for poly(lactide) and PLA/PEG (PLA filled with rubber like particles) at different temperatures. The glass transition temperature for PLA was 60 degree and crystallinity is 0%. The glass transition temperature for PLA/PEG was 40 degree and crystallinity is 15%. For the tensile tests at 50 degree, I had reasonable curves, the PLA/PEG showed lower yield stress and Young's modulus than those of neat PLA but a higher failure strain due to the addition of soft rubber particles. However, I do not know how to explain the mechanical responses of these two materials at 80 degree. At 80 degree, PLA show rubber like mechanical behavior (a flow stress near to 0 and a very limited strain hardening after a critical strain). However, PLA/PEG showed typical semi-crystalline polymer behavior where the yield stress and Young's modulus were higher than those of PLA at the same temperature. I do not know how to explain this. In addition, at 80 degree, PLA showed a quite large strain at break (larger than 1000%), PLA/PEG showed a lower strain at break about 450% at 80 degree. How to explain this difference in the strain at break?
You might even want to investigate the effect of rubber particles on shear load transfer. This might explain the lower breakage energy
The addition of PEG, depending on it Mol.wt does induces certain degree of crystalline. I would def try at-least 3 diff comb of PEG concentration and 3 combination of 3 diff mo.wt of PEG, both with NP to understand if PEG actually influences the mechanical properties or its a combination of PEG and NPs.
It is really interesting.
I also worked with PLA/PEG.
I agree with Ankur Shah that it is important the molecular weight of PEG. But, It also depend on the cold crystallization temperature and its rate.
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