Amorphous Biopolymer Blends

Amorphous polymer blends present unique challenges to hoth the experimentalist and the theorist, and, from an experimental perspective, often demand more creativity in extracting useful metrics than crystalline materials. Amorphous macromolecules, and their mixtures, challenge our notions on thermodynamic equilibrium, and require a time-dependent perspective. However, amorphous blends play key roles not only in materials and composites science but also in biological and life sciences where the transient structure of proteins and enzymes, membranes, lipid arrays, and many other dynamic structures control function. Fundamental insights gained from investigating the unique aspects of synthetic amorphous blends directly relate to complex systems in the life sciences, and also provide new directions for materials science development. 

National Science Foundation, Interdisciplinary Globally-Leading Polymer Science and Engineering (2007) available via the Web at http // www.nsf.gov/mps/dmr/reports.jsp. 

) (2007) Physical Properties of Polymers Handbook, Springer Science, New York. 

9 Zhao, Land Choi, P. (2006) Mater. Manu Processes, 21, 135. 

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Chapter 3 provides a brief review of recent developments in areas of amorphous polymer blends. Differential mixing, chain dynamics, and glass transition properties for individual polymer components in miscible binary blends, as well as new methods to experimentally acquire such information, are considered. Miscible blend dynamics and length scales of mixing of amorphous polymer blends are discussed. Amorphous biopolymer blends involving polymers obtained from renewable feedstocks is also briefly reviewed. 

As a polyester, PHB can partake in many of the hydrogen-bonding type of specific interactions with other functional additives that lead to partial miscibility and compatibility. For example, the miscibility of polyesters with chlorinated polymers, polyamides, polycarbonates, cellulose derivatives and other functional polymers is well documented,and PHB is no exception to this general observation. However, these interactions are dominated by the tendency to self-crystallize with exclusion of the additive to the amorphous phase. For example, an 80/20 melt compounded and injection-moulded sample of PVC/PHB polyblend appears initially to be exceptionally tough with the PHB acting as a polymeric plasticizer. The presence of the PVC retards but does not stop crystallization of the PHB at room temperature and the material eventually becomes brittle. Under extreme circumstances, the PHB phase can actually achieve almost 100% crystallinity within the blend, as determined by X-ray analysis and DSC. Thus, plasticized formulations and polyblends involving PHB itself are limited to relatively low levels of additive because only the minor amorphous phase of the biopolymer is involved in the interaction. Even so, some plasticizers have been proposed for PHB. ... 

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