Plasticized polylactide/clay nanocomposites. I. The role of filler content and its surface organo-modification on the physico-chemical properties

摘要

Polylactide (PLA)-layered silicate nanocomposites plasticized with 20 wt % of poly(ethylene glycol) 1000 were prepared by melt blending. Three kinds of organo-modified montmorillonites-Cloisite (R) 20A, Cloisite (R) 25A, and Cloisite (R) 30B-were used as fillers at a concentration level varying from 1-10 wt %. Neat PLA and plasticized PLA with the same thermomechanical history were considered for comparison. Nanocomposites based on amorphous PLA were obtained via melt-quenching. The influence of both plasticization and nanoparticle filling on the physicochemical properties of the nanocomposites were investigated. Characterization of the systems was achieved by size exclusion chromatography (SEC), thermogravimetric analysis (TGA), thermally modulated differential scanning calorimetry (TMDSC), X-ray diffraction (XRD), and dynamic mechanical analysis (DMTA). SEC revealed a decrease of the molecular weight of the PLA matrix with the filler content. Thermal behavior on heating showed one cold crystallization process in the reference neat PLA sample, while two cold crystallization processes in plasticized PLA and plasticized nanocomposites. The thermal windows of these processes tend to increase with the filler content. The crystalline form of PLA developed upon heating was affected neither by the plasticization nor by the type and content of Cloisite used. It was found that the series of organo-modified montmorillonites with decreasing affinity to PLA is Cloisite (R) 30B, Cloisite (R) 20A, and Cloisite (R) 25A, respectively. The dynamic mechanical properties were sensitive to the sample composition. Generally, the storage modulus increased with the filler content. Glassy PEG, well dispersed within unfilled PLA matrix, exhibited also a reinforcing effect, since the storage modulus of this sample was higher than for unplasticized reference at temperature region below the glass transition of PEG. Moreover, loss modulus of all plasticized samples revealed an additional maximum ascribed to the glass transition of PEG-rich dispersed phase, indicating partial miscibility of organic components of the systems investigated. The magnitude of this mechanical loss was correlated with the filler content, and to some extent, also with the nanofiller ability to be intercalated by polymer components. (c) 2005 Wiley Periodicals, Inc.