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Incorporating phosphate-based glass into polymer films increases the films’ elasticity and makes them less permeable to oxygen, reports a group led by David A. Schiraldi of Case Western Reserve University (Macromolecules, DOI: 10.1021/ma100391u). Those qualities are desirable for food-packaging and flexible-electronics applications. Phosphate glasses are fluidic at temperatures used to prepare melt-processable polymers, which allowed Schiraldi and colleagues to use a coextrusion process to create layers of a propylene-maleic anhydride graft copolymer alternating with copolymer layers containing phosphate glass dispersed as spherical droplets. In that form, the films’ O2 permeability dropped by as much as 30% compared with that of the polymer alone. But if the films were stretched and the droplets elongated, O2 permeability dropped by as much as three orders of magnitude. Transparency of the films, which is important for some applications, depended on the amount of phosphate glass included. Experimental clay composite films that are being developed for similar applications show somewhat better mechanical properties than the new films, but they are made with layer-by-layer techniques (C&EN, Jan. 11, page 34). The ability to make phosphate glass composite films by coextrusion would enable inexpensive large-scale manufacturing, comments University of Michigan materials scientist Nicholas A. Kotov.
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