Synthesis and Characterization of PLA Nanocomposites Containing Nanosilica Modified with Different Organosilanes II: Effect of the Organosilanes on the Properties of Nanocomposites: Thermal Characterization Luca Basilissi, Giuseppe Di Silvestro, Hermes Farina, Marco Aldo Ortenzi Dipartimento di Chimica, Universit a degli Studi di Milano, Via Venezian 21, I-20133 Milano, Italy Correspondence to: L. Basilissi (E-mail: luca.basilissi@unimi.it) ABSTRACT: Thermal behavior of polylactic acid (PLA)/nanosilica nanocomposites prepared via bulk ring opening polymerization from lactide was investigated by differential scanning calorimetry and thermogravimetric analysis (TGA). Both unmodified nanosilica and modified by surface treatments with different amounts of two distinct silanes were used. Samples containing pure silica show enhanced crystallization processes; with silane-modified silica this effect is magnified, especially in the case of materials with high loadings of epoxy silane. Nonisothermal crystallization temperatures become higher and isothermal crystallization kinetics show a marked increase of Kinetic constant (K c ). TGA analyses show that, when pure nanosilica is present, nanocomposites have a thermal stability far greater than the one of standard PLA, starting their degradation at temperatures up to 70  C higher than the ones of pure PLA. When silanes are present, thermal stability lowers as silane content increases, but it is anyway higher than the one of the pure polymer. V C 2012 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 128: 3057–3063, 2013 KEYWORDS: biopolymers and renewable polymers; nanostructured polymers; thermogravimetric analysis (TGA); differential scanning calorimetry (DSC) Received 5 April 2012; accepted 22 August 2012; published online 14 September 2012 DOI: 10.1002/app.38504 INTRODUCTION Polylactic acid (PLA) is one of the most important commer- cially available, synthetic biodegradable polyester; however, brit- tleness 1 and low crystallization rate 2 limit its industrial applica- tions. Low crystallization rate makes the polymer hardy suitable for injection molding processes and requires high production cycle times; on the other hand, brittleness does not allow for the production of engineering materials with good mechanical properties (i.e., low Izod–Charpy values). The use of nanofillers represents a good strategy to modify the physical and mechani- cal properties of PLA. In particular, nanoscale fillers can improve thermal stability of PLA and affect crystallization prop- erties. Their effects on thermal behavior of PLA nanocomposites are described in literature, concerning the use of montmorillon- ite 3,4 or nanosilica 5 introduced both in compounding 6,7 or with in situ polymerization. 3,4 In recent years, organic–inorganic nanocomposites with well- defined structures and morphology have become a very interest- ing and promising class of materials because of their potential use in a wide range of conventional application fields; particu- larly, among silica-based organic–inorganic nanocomposites, 8,9 PLA/nanosilica composites obtained via compounding have been already reported. 10–12 In these nanocomposites, silica can improve both thermal and mechanical properties. The advan- tages that can be obtained because of the mineral largely depend on the degree of mixing; as compatibility and adhesion between silica and PLA are rather poor, direct mixing of silica nanopar- ticles with PLA often leads to the aggregation of mineral par- ticles and deterioration of mechanical properties. To overcome this drawback, it is necessary to modify the surface of silica par- ticles to make them more compatible with the organic phase. The most common method is the modification of the silica par- ticles with a surfactant or with silane-coupling agents; such modification, can greatly help to improve the thermal behavior and the mechanical properties and to reduce the brittleness, increasing melt viscosity and strength. 13–15 In the first part of this work, 16 PLA/nanosilica composites were prepared by in situ polymerization of L-lactide using both stand- ard silica nanoparticles and silica nanoparticles that were previously modified using different quantities of two commer- cially available silanes (an epoxy-terminated one and an V C 2012 Wiley Periodicals, Inc. WWW.MATERIALSVIEWS.COM WILEYONLINELIBRARY.COM/APP J. APPL. POLYM. SCI. 2013, DOI: 10.1002/APP.38504 3057