Upgrading of the fracture properties of multi-layered PMMA-nanosilica materials by interface modification
Résumé
Hybrid copolymers of methyl methacrylate and methacryloyl grafted nanosilica (MMA-MGS) exhibit a higher modulus, but also a marked embrittlement, as compared to pure poly(methyl methacrylate) (PMMA). With the aim of overcoming this latter feature detrimental for industrial applications, multilayered materials based on these hybrids were prepared by inserting pure polymer layers between the nanohybrid layers. Insertion of thin and 'soft' layers of poly(ethyl acrylate) (PEA) between the nanohybrid layers leads to a marked toughening resulting from crack smoothing at each interface. However, this procedure is detrimental to the Young's modulus, except for extremely thin (ca. 1 μm) PEA layers. Alternatively, insertion of 100 μm thick 'hard' layers of PMMA also produces toughening, as the consequence of crack deviation at the layer interface. The latter procedure presents potential interest for applications because the Young's modulus of the assembly remains very close to that of the monolithic hybrid. The observed behavior of these assemblages is analyzed within the framework of fracture mechanics.