Dynamic Mechanical and Thermal Properties of the Composites of Thermoplastic Starch and Lanthanum Hydroxide Nanoparticles Stephen S. Ochigbo, 1 * Adriaan S.Luyt, 1 Julia P. Mofokeng, 1 Z ˇ eljka Antic ´, 2 Miroslav D. Dramic ´anin, 2 Vladimir Djokovic ´ 2 1 Department of Chemistry, University of the Free State, Qwaqwa Campus, Phuthaditjhaba 9866, South Africa 2 Vinc ˇa Institute of Nuclear Sciences, University of Belgrade, 11001 Belgrade, Serbia *Present address: Department of Chemistry, Federal University of Technology, PMB 65, Minna Niger State, Nigeria Correspondence to: V. Djokovic ´ (E-mail: djokovic@vinca.rs) ABSTRACT: Nanostructured lanthanum (III)-oxide (La 2 O 3 ) particles were prepared by a polymer complex solution method and fur- ther used for the preparation of lanthanum hydroxide (La(OH) 3 ) nanoparticles. The La(OH) 3 nanopowder was mixed with glycerol- plasticized maize starch and the effect of the filler on the thermal, mechanical, and viscoelastic properties of the matrix was investi- gated. It was expected that this nanofiller, which shows an affinity toward OH groups, would strongly affect the physical properties of thermoplastic starch (TPS). The pure TPS and the TPS-La(OH) 3 nanocomposite films (with 1, 2, and 3 wt % filler) were conditioned at various relative humidities (RHs) (35, 57, 75, and 99% RH). After conditioning at 99% RH, the pure TPS films exhibited higher affinity toward water than the nanocomposites. Differential scanning calorimetric measurements showed that, due to retrogradation effects, the melting enthalpies of the films increased with increasing RH. Dynamic mechanical analysis revealed that the mechanical properties in the linear range strongly depend on both the humidity conditions and the concentration of the filler. The results also show that La(OH) 3 nanoparticles are good reinforcement for TPS films. V C 2012 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 127: 699–709, 2013 KEYWORDS: biopolymer; thermoplastic starch; nanocomposites; nanoparticles; dynamic mechanical analysis; differential scanning calorimetric; mechanical properties Received 12 December 2011; accepted 9 April 2012; published online 27 April 2012 DOI: 10.1002/app.37859 INTRODUCTION Polymers from renewable resources are becoming a subject of increasing interest in current macromolecular science and tech- nology. 1 Dwindling supplies of petroleum and its increasing price together with rising environmental concerns triggered a burst of research activity in this field. To date, various natural polymers have been investigated, but the polysaccharides, espe- cially cellulose, chitosan, and starch, are still the most studied systems. 1,2 Besides potentially useful physical properties of these materials, the investigations are also motivated by their shear abundance and low cost. Starch, a major form of stored carbo- hydrate in plants, is a renewable biodegradable polymer that appears as a mixture of two main components; amylose, essen- tially linear O-(1!4)-a-D-glucan, and amylopectin, a highly branched macromolecule consisting of O-(1!4)-a short D-glu- copyranose chains linked by O-a-(1!6) glycoside bonds. The physical properties of starches such as gelatinization, solubility, viscosity, and retrogradation strongly depend on the amylose- amylopectin ratio as well as the material conditioning. The amylose content in typical starches is usually in the range from 15 to 30%. In the last two decades, starch has attracted a lot of attention as a thermoplastic material. 3 The addition of polyol-type plasticiz- ers reduces the glass transition temperature of starch below its decomposition temperature and makes it more flexible. 4 How- ever, despite good mechanical properties, its high hydrophilicity is a major drawback for the successful application of thermo- plastic starch (TPS). Blending with some other polymers or introduction of micron-sized and nanosized fillers has been usually used to improve its thermomechanical properties and sensitivity to water. 5 Cellulose fibrils and whiskers are typical fillers used in the preparation of TPS microcomposites and nanocomposites. 6–13 The other approach suggested was the modification of TPS by solution or melt mixing with nano- clays. 14–24 Recently, nanostructured inorganic particles such as SiO 2 , 25 ZnO, 26 and Zr(OH) 4 27 were successfully used as fillers V C 2012 Wiley Periodicals, Inc. WWW.MATERIALSVIEWS.COM WILEYONLINELIBRARY.COM/APP J. APPL. POLYM. SCI. 2013, DOI: 10.1002/APP.37859 699