Submitted to: Thermochimica Acta
Publication Type: Peer reviewed journal
Publication Acceptance Date: 11/5/2001
Publication Date: 12/15/2003
Citation: Cao, X., Mohamed, A., Gordon, S.H., Willett, J.L., Sessa, D.J. DCS study of biodegradable poly(lactic acid) and poly(hydroxy ester ether) blends. Thermochimica Acta. 2003. v. 406. p. 115-127. Interpretive Summary: There is global interest in developing biodegradable plastics from renewable resources. We have recently been developing materials based on combinations of starch with two biodegradable plastics known as PLA and PHEE. In order to understand the properties of the starch-PLA-PHEE materials, we need information on the properties of PLA-PHEE blends in the absence of starch. We found that PLA-PHEE blends when originally processed have a complex, heterogeneous structure indicating little mixing on a microscopic level. After subjecting the blends to elevated temperatures, the blends became progressively more homogeneous, indicating more complete mixing. The knowledge gained from this study will be useful in the design and processing of starch-PLA-PHEE materials for further development. The unusual mixing behavior displayed by these materials will be of interest to other scientists and manufacturers who work with complex heterogeneous plastic materials.
Technical Abstract: DSC heating-cooling cycles (0-200 degrees C) were repeated on PLA/PHEE blends to study the miscibility of the two polymers. The initial DSC thermograms show two distinguishable Tgs corresponding to the respective neat polymers, accompanied by a crystallization and a melting peak result- ing from PLA's delta Hc/Tc and delta Hm/Tm. Subsequent DSC runs show that the thermogram profiles are dependent on the number of DSC cycles the blends are subjected to: as the number of DSC cycles increases, TgPLA and TgPHEE shift inward towards each other and eventually merge into a single Tg, while delta Hc and delta Hm increase to maximum values then decreases to zero. It is concluded that after repeated DSC runs, PLA and PHEE achieve mixing on a molecular level, i.e. PLA and PHEE are miscible. The number of DSC cycles needed to reach a single Tg, maximum delta H and zero delta H, are dependent on the blend's composition.