Foam processing and cellular structure of polylactide-based nanocomposites

Abstract Via a batch process in an autoclave, the foam processing of neat polylactide (PLA) and two different types of PLA-based nanocomposites (PLACNs) has been conducted using supercritical carbon dioxide (CO 2 ) as a foaming agent. The cellular structures obtained from various ranges of foaming temperature–CO 2 pressure were investigated by using scanning electron microscopy (SEM) and transmission electron microscopy (TEM). The incorporation with nano-clay induced heterogeneous nucleation because of a lower activation energy barrier compared with homogeneous nucleation as revealed by the characterization of the interfacial tension between bubble and matrix. The grown cells having diameter of ∼200 nm were localized along the dispersed nano-clay particles in the cell wall. The dispersed nano-clay particles acted as nucleating sites for cell formation and the cell growth occurs on the surfaces of the clays. The PLACNs provided excellent nanocomposite foams having high cell density from microcellular to nanocellular.

[1]  M. Okamoto,et al.  Direct Melt Intercalation of Polylactide Chains into Nano-Galleries: Interlayer Expansion and Nano-Composite Structure , 2006 .

[2]  R. G. Griskey,et al.  Diffusion and solution of gases into thermally softened or molten polymers: Part II. Relation of diffusivities and solubilities with temperature pressure and structural characteristics , 1969 .

[3]  V. Drits,et al.  X-Ray Diffraction by Disordered Lamellar Structures , 1990 .

[4]  V. Mathot.  Temperature dependence of some thermodynamic functions for amorphous and semi-crystalline polymers , 1984 .

[5]  S. Ray,et al.  Crystallization Behavior and Morphology of Biodegradable Polylactide/ Layered Silicate Nanocomposite , 2003 .

[6]  Jonathan S. Colton,et al.  The nucleation of microcellular thermoplastic foam with additives: Part I: Theoretical considerations , 1987 .

[7]  S. Ray,et al.  New polylactide/layered silicate nanocomposites. 3. High-performance biodegradable materials , 2003 .

[8]  T. Kotaka,et al.  Biaxial Flow-Induced Alignment of Silicate Layers in Polypropylene/Clay Nanocomposite Foam , 2001 .

[9]  N. Fletcher.  Size Effect in Heterogeneous Nucleation , 1958 .

[10]  L. J. Lee,et al.  Synthesis of polystyrene-carbon nanofibers nanocomposite foams , 2005 .

[11]  T. Chow.  Molecular Interpretation of the Glass Transition Temperature of Polymer-Diluent Systems , 1980 .

[12]  S. Ray,et al.  Well-controlled biodegradable nanocomposite foams: From microcellular to nanocellular , 2003 .

[13]  T. Kotaka,et al.  Foam processing and cellular structure of polypropylene/clay nanocomposites , 2002 .

[14]  E. Beckman,et al.  Generation of microcellular polymeric foams using supercritical carbon dioxide. I: Effect of pressure and temperature on nucleation , 1994 .