## 1 Introduction
The role played by silica nanoparticles with different thermoplastic matrices and the consequent thermo-mechanical behavior of nanocomposites produced firstly by melt-compounding and then either by compression molding [23; 24; 25; 26; 27; 28; 29; 30] or by fiber spinning [31; 32] was extensively investigated by our group in the last years. It was demonstrated how nanosilica addition leads to a strong stiffening effect on the polymer matrices, without impairing their failure properties, improving also the dimensional and thermal degradation stability. For the production of PLA-silica nanocomposites, different approaches were studied for improving the quality of dispersion and the resulting properties. In situ polymerization of lactide in the presence of dispersed silica was studied by various authors, in order to optimize and control the filler distribution in the resulting nanocomposites [33; 34; 35]. To overcome the problem of nanosilica aggregation, various other methods were proposed to modify the silica particles with lactic acid oligomers, with a surfactant, with silane-coupling agents or other compatibilizers. [PERSON] et al. [36], [PERSON] et al. [37], and [PERSON] et al. [38] reported interesting improvements in the physical properties of PLA-silica nanocomposites after direct grafting of L-lactic acid oligomer onto the surface silanol groups of the silica nanoparticles. [PERSON] et al. [39] melt mixed poly(lactic acid)-based nanocomposites prepared by adding oleic acid-treated fumed silica nanoparticles. The flexibility of the PLA matrix was improved through the addition of limited amounts (i.e., less than 1 wt%) of organomodified nanoparticles. It is also interesting to note that many processing studies have been dedicated to solution casting [36; 40; 41; 42; 43; 44] and only few papers have dealt with direct melt-processing of PLA-silica nanocomposites [45; 46; 47; 48; 49]. In addition, the biodegradation of PLA-fumed silica nanocomposites has been studied by [PERSON] et al. [40], and a certain protection action of silica towards PLA degradation was observed. Enzymatic, in vitro, burial, and composting degradation was properly considered for practical potential applications and waste management [41; 49; 50; 51; 52]. Different authors started to use hydrophilic fumed silica nanoparticles, having a surface area of about 200 m\({}^{2}\).g\({}^{-1}\), as an additive in PLA compounds [37; 41; 45; 53; 54]. In a paper of [PERSON] et al., the thermal properties of poly(lactic acid)-fumed silica nanocomposites were also investigated through molecular dynamics (MD) simulations, and the increase of \(T_{g}\) observedin nanofilled samples was qualitatively consistent between the experimental result and the MD predictions [55]. In a previous work of our group, various kinds of fumed silica nanoparticles, differing for the surface area and the presence of a surface functionalization, were melt-compounded with a poly(lactic acid) biodegradable matrix to be utilized for industrial packaging applications, and the mechanical and optical properties of the resulting materials were investigated [46]. Untreated nanoparticles at an elevated surface area resulted as effective in increasing elastic modulus, because of the extended filler-matrix interaction, while the finer dispersion of silica aggregates at the nanoscale obtained with surface-treated nanoparticles led to noticeable improvements of the tensile properties at yield and at break, both under quasi-static and impact conditions. In addition, the fracture toughness and the creep stability were substantially enhanced by nanosilica addition, without impairing the original optical transparency of the matrix. In the above cited papers, it can be seen that the investigation of the thermo-mechanical properties of PLA-silica nanocomposites has been substantially limited to differential scanning calorimetry (DSC), thermogravimetric analysis (TGA), and monofrequency dynamical mechanical thermal analysis (DMTA).