Synthesis and Characterization of Biodegradable Nanocomposites

V.P.CYRAS; L. B. MANFREDI; A. VÁZQUEZ

Buenos Aires, Argentina

Simposio; 15th International Symposium on Metastable, Amorphous and Nanostructured Materials (ISMANAM 2008); 2008

Development of polymer/clay nanocomposites is one of the latest revolutionary steps of the polymer technology. Preparation of blends or nanocomposites using low percentages of inorganic fillers are among the routes to improve some of the properties of biodegradable polymers such as barrier, thermal and oxidative, when compared with traditional composites. Montmorillonite (MMT) is among the most commonly used layered silicates because it is environmentally friendly and readily available in large quantities with relatively low cost [1]. Therefore, the aim of this work is to improve the properties of biodegradable polymers by the addition of small amounts of a natural montmorillonite. Nanocomposites based on two different biodegradable polymers were synthetized and characterized and the influence of the addition of the clay Cloisite®Na+ (2 and 5 % w/w) in their properties were studied. The behaviour of the two polymers were compared and the diferences arised were analysed in terms of the chemical composition and dispersion of the montmorillonite. The biodegradable polymers used were glycerol–plasticized starch and poly(hydroxybutyrate) (PHB). Both of them can be new start renewables resources based replacement to commodities polymers. However, they posees disadvantages that limit their applications. Starch is a semicrystalline polymer with poor mechanical resistance and strength as well as it absorbs high quantity of water. PHB insted do not absorb water but it is fragile and expensive. From the characterization of the starch based composites it was observed an increment in the interlayer distance of the clay in the nanocomposites providing evidence that the clay nanolayer formed an intercalated structure without reach a complete exfoliation. In addition an improvement in the thermal resistance of the starch with the addition of clay as well as a reduction in the maximun and in the rate of water absorption was observed. On other hand, the clay was not well dispersed in the nanocomposites with PHB matrix. Additionaly, the thermal resistance was slightly improved and the polarity diminished with the addition of clay. The starch composites behavior was attributed to the structure formed between the hydrophilic molecules of starch and the MMT. The formation of a tortuous path-way by the presence of clay influences the water-uptake. The composites showed a higher hydrophilic character than the starch due to the high polarity of the MMT added. Inversely, the PHB is an hydrophobic polymer and the Na-montmorillonite is hydrophilic with a high surface area. This could be the reason for the difficult in the dispersion of the clay in the polymer. Thermogravimetric results also indicated that the clay acts as heat barrier enhancing the overall thermal stability of both systems.