Mechanical, thermal and dynamic mechanical properties of PCL/clay films

LEANDRO N. LUDUEÑA; ANALÍA VAZQUEZ; VERA A. ALVAREZ

Roma, Italia

Conferencia; 4th Annual Conference on Nanostructured Polymers and Nanocomposites - NANOFUN-POLY 4; 2008

European Centre of Nanostructured Polymers; Interuniversity Consortium for Materials Science and Technology (INSTM); UdR of Perugia-Italy

Due to environmental concerns, biodegradable polymers, such as Polycaprolactone (PCL), are receiving growing attention. Their performance can be enhanced by the dispersion of nanometer-size particles.    Morphology and mechanical properties of PCL/modified-clay nanocomposites prepared by casting and intensive mixing were studied. Casting (laboratory-scale technique), was selected because the solvent may act as exfoliation agent. Intensive mixing was chosen because of its industrial application.  X-ray diffractograms revealed an intercalated-exfoliated mixed structure for both techniques. For casting, the morphology and mechanical properties were influenced by the solvent and preparation conditions. For intensive mixing, shear forces produced higher clay dispersion and the mechanical properties were superior. In both cases, the highest modulus was achieved for 5wt.% of reinforcement. An effective-filler-parameters model was used to compare the relative dispersion of clay.    Using the best technique, the isothermal crystallization process of different modified montmorillonites at several clay contents were studied. Bulk-crystallization measurements were carried out in a Perkin-Elmer 7 DSC and modelled with the Avrami´s equation. The induction time was lowered and the global crystallization rate was increased by clay incorporation, even more when the clay was well dispersed in the polymer matrix. Krikorian et. al. obtained similar results with Polylactic acid(PLLA)/clay nanocomposites. Several clay contents were analyzed but it did not significantly affect the crystallization process. The spherulitic growth was observed by optical microscopy with polarized light. The secondary nucleation theory of polymer crystal growth was used to model the spherulitic growth rate. The results were in accordance with the bulk crystallization process.            Creep behaviour of the same materials was studied with a Perkin-Elmer DMA-7. The effect of clay content on deformation along time at different temperatures was modelled using different models: power-law, Kelvin-Voigt model and time-temperature superposition. Both, experimental curves and models demonstrated that the incorporation of the clay produces a significant improvement on the creep resistance with respect to the neat matrix. This improvement was even more important for higher clay content and high polymer/clay compatibility. Similar trend was obtained by Perez et. al. with PCL-starch/clay nanocomposites.