Propiedades térmicas, físicas y mecánicas de nanocompuestos de almidón termoplástico/bentonita modificada por extrusión reactiva para aplicaciones en envases y embalajes

ALVAREZ, VERA ALEJANDRA; GUARÁS, MARÍA PAULA; ROMINA OLLIER; LUDUEÑA, LEANDRO NICOLÁS

Buenos Aires

Workshop; Workshop ?NanoBioTecnología: Del laboratorio a la empresa; 2017

Conventional polymers derived from fossil fuels are not only non-renewable and finite resources, but also causeproblems in post-consumer processing, as they are largely inert to microbial attack. The use of polymers capableof being degraded by the action of microorganisms and/or enzymes without causing harmful effects is a strategyin waste management. Starch is a natural, abundant and versatile biopolymer obtained from renewable plant resourcessuch as maize, wheat and potato harvests. Moreover, starch is economically competitive with polymersderived from petroleum for manufacture of packaging materials. However, the structure of native starch must bemodified since its degradation temperature is lower than the melting temperature. For this reason, natural starchcannot be processed by traditional polymer processing methods without being previously modified. Formation ofthermoplastic 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 replacedby 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 potentiallyimproved mechanical and thermal properties [2]. These composites are prepared by addition of low amounts ofclay to the biopolymer matrix. The main challenge for preparing nanocomposites with enhanced properties is thenanoscale dispersion of clay in the polymer matrix. Bentonite is one of the most commonly used natural clay andhas 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 claydispersion, 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 claydispersion.The objective of this work was to prepare biodegradable TPS/organobentonite nanocomposites by melt intercalationusing 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 presenceof 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), waterabsorption, mechanical response and biodegradability of nanocomposites were studied and discussed in detail.