In this study, polymer nanocomposites based on poly(lactic acid) (PLA) and organically modified layered silicates (organoclay) were prepared by melt mixing in an internal mixer. The exfoliation of organoclay could be attributed to the interaction between the organoclay and PLA molecules and shearing force during mixing. The exfoliated organoclay layers acted as nucleating agents at low content and as the organoclay content increased they became physical hindrance to the chain mobility of PLA. The thermal dynamic mechanical moduli of nanocomposites were also improved by the exfoliation of organoclay; however, the improvement was reduced at high organoclay content. The dynamic rheological studies show that the nanocomposites have higher viscosity and more pronounced elastic properties than pure PLA. Both storage and loss moduli increased with silicate loading at all frequencies and showed nonterminal behavior at low frequencies. The nanocomposites and PLA were then foamed by using the mixture of CO 2 and N 2 as blowing agent in a batch foaming process. Compared with PLA foam, the nanocomposite foams exhibited reduced cell size and increased cell density at very low organoclay content. With the increase of organoclay content, the cell size was decreased and both cell density and foam density were increased.

Summary: In order to produce modified poly(lactic acid) (PLA) resins for applications requiring high melt viscosity and elasticity (e.g., low‐density foaming, thermoforming), a commercial PLA product has been reactively modified in melt by sequentially adding 1,4‐butanediol and 1,4‐butane diisocyanate as low‐molecular‐weight chain extenders. By varying amounts of the two chain extenders associated to the end group contents of PLA, three resulted samples were obtained. They were then structurally characterized by FTIR spectroscopy and molecular structure analysis. Their thermal, dynamic mechanical thermal properties and melt viscoelastic properties were investigated and compared along with unmodified PLA. The results indicated that chemical modification may be characterized as chain scission, extension, crosslinking, or any combination of the three depending on the chain extender amounts. The increase of PLA molecular weight could be obtained by properly controlling amounts of two chain extenders. The samples with increased molecular weights showed enhanced melt viscosity and elasticity. Such property improvements promised a successful application for modified PLA in a batch foam processing by producing foams with reduced cell size, increased cell density and lowered bulk foam density in comparison with plain PLA foam.

Nanocomposites based on biodegradable polycaprolactone (PCL) and organically modified layered silicates (organoclay) were prepared by melt mixing. Their structures and properties were characterized by wide‐angle X‐ray diffraction, thermal analysis, and rheological measurements. The exfoliation of the organoclay was achieved via a melt mixing process in an internal mixer and showed a dependence on the type of organic modifier, the organoclay contents, and the processing temperature. The addition of the organoclay to PCL increased the crystallization temperature of PCL, but a high content of the organoclay could show an inverse effect. The PCL/organoclay nanocomposites showed a significant enhancement in their mechanical properties and thermal stability due to the exfoliation of the organoclay. The nanocomposites showed a much higher complex viscosity than the neat PCL and significant shear‐thinning behavior in the low frequency range. The shear storage modulus and loss modulus of the nanocomposites also exhibited less frequency dependence than the pure PCL in the low frequency range, and this was caused by the strong interactions between the organoclay layers and PCL molecules and by the good dispersion of exfoliated organoclay platelets in the PCL. © 2003 Wiley Periodicals, Inc. J Polym Sci Part B: Polym Phys 41: 670–678, 2003

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The aim of this work was to explore the feasibility of preparing thermoplastic films from commercial zein by film blowing technology. Zein, a cereal protein extracted from maize, was plasticized directly in the extruder, without the time-consuming and expensive solubilization step, usually utilized in literature for this material. Four different batches of zein were investigated, for it has been observed that properties such as the film-forming ability of natural polymers strongly depend on several factors such as sources, extraction, and drying conditions. Thermal, rheological, and macromolecular structural characteristics were evaluated for the different materials to establish a correlation among molecular structure, rheological behavior in uniaxial elongation, and film blowing processability. Results indicate that the best films were made by using thermoplasticized zein characterized with a pronounced strain hardening and a large content of a-helices.

The foaming process of poly(ϵ‐caprolactone) (PCL) with carbon dioxide and nitrogen has been investigated in this work from a theoretical and experimental point of view. CO2 and N2 showed very different behavior, as foaming agents for PCL. This was due to the different transport, chemical, and physical properties of the polymer/gas mixture that led to different foam morphology in terms of density, cell number density, and cell size. The lowest density (0.03 g/cm3) was obtained with CO2, but the highest number of cells with N2 (although with a higher density, (0.2 g/cm3). Foam with a low‐density microcellular structure, was obtained when a mixture of the two gases was employed. POLYM. ENG. SCI., 45:432–441, 2005. © 2005 Society of Plastics Engineers