CONICET | Buscador de Institutos y Recursos Humanos

Conventional polymers derived from fossil fuels are not only non-renewable and finite resources, but also cause problems in post-consumer processing, as they are largely inert to microbial attack. The use of polymers capable of being degraded by the action of microorganisms and/or enzymes without causing harmful effects is a strategy in waste management. Starch is a natural, abundant and versatile biopolymer obtained from renewable plant resources such as maize, wheat and potato harvests. Moreover, starch is economically competitive with polymers derived from petroleum for manufacture of packaging materials. However, the structure of native starch must be modified since its degradation temperature is lower than the melting temperature. For this reason, natural starch cannot be processed by traditional polymer processing methods without being previously modified. Formation of thermoplastic starch (TPS) requires disruption of the crystalline regions of starch granules by processing them inthe presence of a specific amount of plasticizer, under certain extrusion conditions [1].Neat TPS is not suitable for use as packaging material due to its poor mechanical properties and high hydrophilicity. Different methods can be implemented in order to improve its competitiveness with a high cost/efficiency ratio. On the one hand, various physico-chemical modification methods of TPS have been developed in order to improvethese aspects. Derivatization of starch is a type of chemical modification by which the hydroxyl groups are replaced by other groups with the desired functionality. On the other hand, nano-reinforcements can be incorporatedinto the mixtures. In this way, biopolymer-clay nanocomposites are a new class of materials with potentially improved mechanical and thermal properties [2]. These composites are prepared by addition of low amounts of clay to the biopolymer matrix. The main challenge for preparing nanocomposites with enhanced properties is the nanoscale dispersion of clay in the polymer matrix. Bentonite is one of the most commonly used natural clay and has been successfully applied in numerous nanocomposite systems. However, many starch-clay nanocompositessuffer from poor dispersion, which is a key factor for obtaining high performance materials. To improve the clay dispersion, organic cations such as alkylammonium cations can be used to exchange with the sodium ions residingin the interlayer of pristine clay [3]. The more the modifier is compatible with starch, the more it facilitates clay dispersion.The objective of this work was to prepare biodegradable TPS/organobentonite nanocomposites by melt intercalation using reactive extrusion technique. For this purpose, pristine bentonite was firstly exchanged with benzalkoniumchloride. The resulting organobentonite was used as nano-reinforcement of the thermoplastic starch matrix.The derivatization of starch was performed with maleic anhydride and once modified it was processed in the presence of a plasticizer in a twin screw extruder. The effect of clay modification on the morphology (X-ray diffractometry, XRD), thermal properties (differential scanning calorimetry, DSC, and thermogravimetry, TGA), water absorption, mechanical response and biodegradability of nanocomposites were studied and discussed in detail.