Nanocomposite-forming solutions based on cassava starch and laponite: Viscoelastic and rheological characterization Germán Ayala Valencia a,⇑ , Izabel Cristina Freitas Moraes a , Loic Hugues Gilles Hilliou b , Rodrigo Vinicius Lourenço a , Paulo José do Amaral Sobral a,⇑ a Department of Food Engineering, Faculty of Animal Science and Food Engineering, University of São Paulo, Pirassununga, SP, Brazil b IPC/I3N, Department of Polymer Engineering, University of Minho, Campus de Azurém, Portugal article info Article history: Received 13 February 2015 Received in revised form 1 June 2015 Accepted 3 June 2015 Available online 4 June 2015 Keywords: Biodegradable films Nanoclay Nanoparticles Newtonian behavior Non-Newtonian behavior Thermal transition abstract Nanocomposites-forming solutions (NFS) based on cassava starch and laponite were prepared and next characterized by means of dynamic oscillatory and steady shear rheological tests to evaluate their ability to be processed by knife coating. The effects of speed (rpm) and homogenization time on the laponite dis- persion characteristics were first analyzed. Laponite dispersions were affected by both process parame- ters. High speed (rpm), i.e. 20,000 or 23,000 rpm for 30 min or prolonged homogenization time (10,000 rpm 6 speed agitation 6 23,000 rpm, for 60 min) led to high f-potential values, with laponite particles size <80 nm. With addition of laponite nanoparticles to cassava starch dispersion, an evident transition in NFS from liquid-like viscous to solid-like elastic behavior was observed. Rheological results indicated that laponite nanoparticles induced new interactions with starch chains allowing to obtain a network structure typical of a semi-rigid gel which shows some spread ability. Ó 2015 Published by Elsevier Ltd. 1. Introduction Nanomaterials are characterized by having at least one dimen- sion of its particles in nanometric dimension, i.e. between 1 and 100 nm (Aouada et al., 2011). When the particle size is equivalent to the dimension of a molecule, the atomic and molecular interac- tions can have a significant influence on the macroscopic proper- ties of that material (Aouada et al., 2011; Jorge et al., 2014). Thus, this behavior is associated with the specifics size of nanoma- terials such as their high surface to volume ratio (Hassanabadi and Rodrigue, 2012). Among nanomaterials, there are some thin and flexible materi- als based on biopolymers charged with nanoparticles. This is a con- sequence of an approach to improve the mechanical and barrier properties of conventional polymer and biopolymers based films, then producing composites in nanoscale or nanocomposites (Tang and Alavi, 2012; Jorge et al., 2014). Nanocomposites should exhibit a notable enhancement in rigidity and resistance, reduced water vapor and gas permeability, and lower flammability (Tang and Alavi, 2012). In the biopolymer films technology for food applications, the montmorillonite is the nanoparticle most used in studies on devel- opment of films nanocomposites. It has been used to load films based on gelatin (Flaker et al., 2015), zein (Park et al., 2012), starch (Cyras et al., 2008), chitosan (Kasirga et al., 2012), among others. A nanoparticle not so much studied in biopolymer based film is the laponite. Laponite or hydrous sodium lithium magnesium silicate (Na + 0.7 [(Si 8 Mg 5.5 Li 0.3 )O 20 (OH) 4 ] 0.7 ) is a synthetic hectorite clay with particle disk-shape with a thickness of 1 nm, and a diameter of approximately of 25 nm (Nicolai and Cocard, 2000; Cummins, 2007). Laponite disk have an octahedral configuration with Mg 2+ ions in the octahedral sites and also Li + ions in minor amount and Na + ions in the interlayer domain (Perotti et al., 2011). In water, laponite disk hydrates and swells to form clear colloidal dispersions with high stability due to its negative surface charge density of 0.014 e-/Å 2 (Nicolai and Cocard, 2000; Herrera et al., 2004). Laponite has been broadly used in agriculture, construction, personal care, surface coatings and polymer industry (Kumar et al., 2008). Shibayama et al. (2004) reported that the laponite addition in hydrogels based of N-isopropylacrylamide led a notable high strength and elongation at break in excess of 1000%. Similar results were reported by Haraguchi et al. (2005) and Haraguchi and Li (2006) for hydrogels reinforced with laponite. Most recently, Chung et al. (2010), Aouada et al. (2011), Tang and Alavi (2012) and Perotti et al. (2014) demonstrated that laponite can improve the http://dx.doi.org/10.1016/j.jfoodeng.2015.06.006 0260-8774/Ó 2015 Published by Elsevier Ltd. ⇑ Corresponding authors. E-mail addresses: gayalav1230@gmail.com (G.A. Valencia), pjsobral@usp.br (P.J.d.A. Sobral). Journal of Food Engineering 166 (2015) 174–181 Contents lists available at ScienceDirect Journal of Food Engineering journal homepage: www.elsevier.com/locate/jfoodeng