Mechanical blends prepared from granules [<600 µm]of poly(L-lactide) [PLA] and poly(methylmethacrylate) [PMMA] were annealed and quenched under various conditions of time and temperature to assess the degree and mechanisms of formation of a new intermediate amorphous phase first identified in extrusion experiments for this polymer system. The physical properties of these annealed and quenched blends were determined by modulated differential scanning calorimetry (DSC). Two isolated Tg's appeared in most of the blends, suggesting the immiscibility expected from solubility parameter calculations. However, at temperatures greater than 195oC and at durations of 12 h, blends with 35 to 50 percent weight of PLA—the co-continuous range—exhibited a third Tg which occurred at approximately 80oC, intermediate between the glass transition peaks of PLA and PMMA. The occurrence of this new phase suggests that PLA and PMMA may not be truly immiscible, but rather form an intermediate reaction phase, which we have termed PG80, under certain conditions. Subsequent to the initial study, which involved quiescent annealing and no shear, a modified version of this study was conducted in which particles and films were pressed at elevated temperatures to impart a combination of residence time at temperature with more intimate particle contact and a very modest level of shear. Results from both study segments will be presented and the effects of time, temperature, and shear on the formation of PG80 will be described.
Back to Polymeric Biomaterials Posters
Back to The 37th Middle Atlantic Regional Meeting (May 22-25, 2005)