New Approach to Elaborate Exfoliated Starch-Based Nanobiocomposites Frédéric Chivrac, † Eric Pollet, † Marc Schmutz, ‡ and Luc Avérous* ,† ECPM-LIPHT (UMR CNRS 7165), Université Louis Pasteur, 25 Rue Becquerel, F-67087 Strasbourg Cedex 2, France, and ICS (UPR CNRS 22), Université Louis Pasteur, 6 Rue Boussingault, F-67083 Strasbourg Cedex, France. Received November 16, 2007; Revised Manuscript Received January 10, 2008 The present paper reports the successful elaboration of exfoliated plasticized starch-based nanobiocomposites. This was made possible by using cationic starch as a new clay organomodifier to better match the polarity of the matrix and thus to facilitate the clay exfoliation process. To demonstrate the efficiency of this new approach, either natural (MMT-Na) or organomodified (OMMT-CS) montmorillonite were incorporated into the starch nanobiocomposites by a melt blending process. The morphological analyses (SAXD and TEM) showed that MMT- Na leads to the formation of intercalated nanobiocomposites. On the contrary, OMMT-CS allowed the elaboration of well-exfoliated nanobiocomposites. Tensile tests performed on the obtained nanobiocomposites showed that exfoliated nanobiocomposites display enhanced mechanical properties compared to those of the intercalated nanobiocomposites and neat matrix. These results clearly highlight the great interest in using OMMT-CS to obtain starch-based nanobiocomposites with improved properties. 1. Introduction The use of agro-based products to replace common nonde- gradable petroleum-based plastics becomes of great interest because of the diminishing fossil resources combined with the increasing environmental concern. 1 Starch, which is an inher- ently biodegradable and renewable material, is a promising solution to develop new environmentally friendly materials especially for packaging and disposable applications. Several authors have already demonstrated the possibility to transform native starch into thermoplastic resin like products under destructuring and plasticization conditions (water, polyols). 2,3 Nevertheless, the water sensitivity and the brittleness of these materials have to be overcome to obtain suitable “green” plastics. 1 The classical approach to answer to these weaknesses consists in the preparation of blends or composites. 4–6 A recent and innovating area of composites called nanobiocomposites, which is a combination of a biodegradable polymer matrix and a nanosized filler, could also be an innovating solution. 7 Indeed, depending on the geometry and the nature of the nanofiller, new and/or improved properties (gas barrier, mechanical stiffness, transparency, thermal stability, . . .) could be obtained. 8–11 The main reason for such improvement compared to conventional biocomposites is the large surface area resulting in high interactions between the polymer matrix and the nanofillers when theses nanoparticles are well dispersed. The most intensive researches are focused on layered silicates, and especially on montmorillonites (MMT), as the reinforcing phase due to their availability, versatility, and respectability toward the environment. 12 The isomorphic substitutions that take place inside these clay platelets generate a negative charge naturally counterbalanced by the presence of inorganic cations (Na + , Ca 2+ , . . .) into the interlayer spacing leading to a hydro- philic character. To promote the polymer/silicate compatibility, an ion-exchange reaction of these inorganic cations by organic surfactant is often carried out. Depending on the process conditions and on the polymer/nanofiller affinity, the layered silicates dispersed into the polymer matrix can be intercalated by macromolecules and/or exfoliated. 13 Intercalated structures show regularly alternating layered silicates and polymer chains compared to exfoliated structures in which the clay layers are individually delaminated and fully dispersed in the polymer matrix. Best performances are commonly observed with the exfoliated structures. 12,13 Many authors have already published on starch-based nanobiocomposites 14–19 without obtaining a high extent of exfoliation. Because both starch and natural sodium montmo- rillonite are hydrophilic, they assume that these compounds will have a high affinity, but according to the small-angle X-ray diffraction results presented, it seems that mainly glycerol is intercalated, resulting in a low extent of exfoliation. Other groups have begun to work on the organomodification of the clay platelets to have a better affinity with the plasticized starch matrix but did not obtained a well exfoliated state. 20–22 Thus, the aim of this study is the elaboration and the use of a new organomodified montmorillonite to reach the exfoliation state in starch-based nanobiocomposites. To achieve this objec- tive, the MMT is organomodified with cationic starch to match the matrix polarity. To demonstrate the interest of the MMT organomodification, two families of nanobiocomposites are elaborated: one with the organomodified MMT (OMMT-CS), and another one with the natural sodium MMT (MMT-Na). The obtained materials are compared in term of dispersion, and then the influence of the morphology on the melt viscosity and mechanical properties is investigated. 2. Experimental Section 2.1. Materials. Wheat starch (WS) was kindly supplied by Roquette (France). The amylose and amylopectin contents are, respectively, 23 and 77%. Residual protein content is less than 1%. The glycerol used * Corresponding author. E-mail: averousl@ecpm.u-strasbg.fr. Telephone: +33 (0)3 90 24 27 07. Fax: +33 (0)3 90 24 27 16. † ECPM-LIPHT (UMR CNRS 7165), Université Louis Pasteur. ‡ ICS (UPR CNRS 22), Université Louis Pasteur. Biomacromolecules XXXX, xxx, 000 A 10.1021/bm7012668 CCC: $37.00  XXXX American Chemical Society Published on Web 02/21/2008