ORIGINAL PAPER Effect of Silica Nanoparticles on the Mechanical Performances of Poly(Lactic Acid) A. Dorigato • M. Sebastiani • A. Pegoretti • L. Fambri Published online: 7 April 2012 Ó Springer Science+Business Media, LLC 2012 Abstract Various kinds of fumed silica nanoparticles, different in terms of specific surface area and surface functionalization, were melt compounded with a poly(lac- tic acid) biodegradable matrix, with the aim to investigate the thermo-mechanical and optical properties of the resulting materials. Untreated nanoparticles at elevated surface area resulted to be 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. Also the fracture toughness and the creep stability were substantially enhanced by nanosilica addition, without impairing the original optical transparency of the matrix. Keywords Poly(lactic acid)  Silica  Nanocomposites  Mechanical properties  Fracture  Creep Introduction In the last decades an increasing attention was devoted to the problem of waste disposal, especially for packaging materials. For this reason, extended efforts were made for the development of new materials, combining environ- mental sustainability and biodegradability or composta- bility [1–3]. Among various biodegradable polymers, aliphatic polyesters, such as poly(glycolic acid) (PGA), poly(lactic acid) (PLA), poly(e-caprolactone) (PCL) and poly(3-hydroxybutyrate) (PHB), represent the most important family [4, 5]. In particular PLA, initially pro- posed by Kulkarni et al. [6] for surgical implants, has become the most promising polymer for various biomedi- cal and industrial applications, due to the good balance of performances and degradation kinetics in dependence on the composition [7]. Moreover, poly(lactic acid) can be synthesized either from oil or from renewable resources [8], it is fully biocompatible and it possesses higher ther- mal, mechanical and optical properties with respect to other biodegradable polyesters [9]. From a chemical point of view, PLA is a homopolymer or a copolymer of L-lactic acid and/or D-lactic acid monomers. The final properties of PLA are related to the enantiomeric composition [9, 10]. Poly(L-lactic acid) (P-L-LA) and poly(D-lactic acid) (P-D- LA) are enantiomerically pure polymers, obtained from the polymerization of L-lactic acid and D-lactic acid, respec- tively. Because of their high stereoregularity, these are semicrystalline polymers with a melting temperature of about 180 °C[11]. On the other hand, poly(D,L-lactic acid) (P-D,L-LA), formally synthesized from equimolar mixture of L-lactic acid and D-lactic acid enantiomers, is a com- pletely amorphous statistical copolymer with a glass tran- sition temperature of about 50–60 °C[12]. Both melting temperature and crystalline content progressively decrease as the percentage of D lactic acid in copolymers increases, as shown in the case of poly-L,DL-lactide 70/30 [13]. From a mechanical point of view, PLA polymers behave as glassy and quite brittle materials, exhibiting a tensile modulus in the range 2–4 GPa and tensile strength of 30–50 MPa with deformation at break between 1 and 7 % in dependence on molecular weight, enantiomeric purity and crystallinity content [14–16]. A. Dorigato (&)  M. Sebastiani  A. Pegoretti  L. Fambri Department of Materials Engineering and Industrial Technologies and INSTM Research Unit, University of Trento, Via Mesiano 77, 38123 Trento, Italy e-mail: andrea.dorigato@ing.unitn.it URL: http://www.ing.unitn.it 123 J Polym Environ (2012) 20:713–725 DOI 10.1007/s10924-012-0425-6