Characterization of polylactide/poly(ethylene glycol) blends via direct pyrolysis mass spectrometry

- Poly(lactic acid) and poly(ethylene glycol) blends were prepared and characterized.
- Chemical interactions during the mixing processes were identified.
- Chemical interactions caused not only rupture of the polymer chains but also crosslinking.

In this study, melt blended poly(lactic acid) and poly(ethylene glycol), (PLA)/PEG samples involving 10, 15 and 20 wt% PEG were prepared and characterized by direct pyrolysis mass spectrometry technique in addition to classical techniques such differential scanning calorimetry, thermogravimetric analyses and mechanical tests. The incorporation of PEG resulted in consistent and significant decrease in the tensile strength and modulus, and reduction in endothermic melting peak of PLA due to the plasticizing effect of PEG with the virgin PLA matrix. Both TGA and DP-MS analyses pointed out that the thermal decomposition of the blend occurred mainly in two steps. In addition, the pyrolysis mass spectrometry analyses indicated presence of chains generated by the interactions of ether linkages of PEG and COOH groups of PLA, present either as end groups or due to reactions with water, during the blending and/or pyrolysis process. As a consequence, decrease in the thermal stability of PEG chains was detected. Analyses of the blends prepared by solution mixing for variable periods confirmed that these interactions took place mainly during the blending process. In addition, increase in the thermal stabilities of both components for the blends prepared by stirring for prolonged times was detected and associated with generation of a crosslinked structure.