CONICET | Buscador de Institutos y Recursos Humanos

Because of waste accumulation at the end of the life cycle of traditional polymer products, the development of environmental friendly, degradable, polymeric materials has attracted extensive interest. Polycaprolactone (PCL) is a chemically synthesized polymer based on caprolactone units. It does not occur in nature but it is fully biodegradable (Kunioka et al., 2007). PCL can be processed using conventional plastics machinery (Ludueña et al., 2007) and their properties make them suitable for a number of potential applications. Special interest is focused on packaging applications which is the biggest industry of disposable polymer products but until now, the relative high price and the weak rigidity of the PCL have limited their large-scale production as a substitute of traditional polymers (Kim et al., 2007). In order to overcome the limitations of PCL, one of the cheapest environmental friendly and efficient options is to incorporate nanofillers, such us clays to produce nanocomposites. These hybrid materials can exhibit high improvements on the mechanical, barrier and thermal properties, and some others such as the flammability, water adsorption and creep resistance with the incorporation of small amounts of filler (usually less than 10wt.%) (Ludueña et al., 2011). The use of a non-polar polymer matrix such as PCL force to take advance of the cation exchange capacity of the natural clays to change the small cations located into the galleries by large hydrophobic organo-modifiers improving the polymer/clay compatibility and enlarging the clay interlayer distance. In this work, the effect of addition of different organo-modified clays on the behavior of PCL based nanocomposites prepared by melt intercalation was studied. Commercial organo-modified montmorillonites (Cloisite series purchased from Southern Clay Products) and laboratory modified bentonites were used. First, the neat bentonite was modified by the cation exchange reactions with ammonium (octadecyl ammonium chloride and dodecyl ammonium chloride) and phosphonium (tributyl octadecyl phosphomium bromide) quaternary salts. All the modifications were optimized, in terms of modifier concentration and exchange reaction conditions. Then, PCL based nanocomposites with 2.5, 5.0 and 7.5 wt.% of each clay, were prepared by melt-intercalation. This study contemplates morphological (X-Ray Diffractometry, XRD) and thermal aspects (Differential Scanning Calorimetry, DSC, and Thermogravimetrical Analysis, TGA) and mechanical properties (tensile tests) which are important properties for packaging applications. In previous works (Ludueña et al., 2011), we concluded that higher clay dispersion degree inside the PCL matrix is expected using clays with large interlayer distance, strong hydrophobicity and strong processing stability. In this work the opposite result was obtained. The clay with largest interlayer distance, strongest hydrophobicity and strongest processing stability (natural bentonite modified with tributyl hexadecyl phosphonium bromide, TBHP) showed the lowest clay dispersion degree inside PCL. This result suggested that not always a similar matrix/clay hydrophobocity degree is related with optimal matrix/clay compatibility. Poor PCL/TBHP mechanical properties in comparison with PCL/Cloisite nanocomposites were obtained which is in accordance with the morphological analysis. On the other hand, the thermal properties of PCL (crystallinity degree and melting temperature) were not substantially affected by clay incorporation of any clay. This work was performed under the project FSNano004: ?Development of modified nanoclays and innovative products from national clays?.