The addition of inorganic fillers in the nanometric scale to a polymer matrix is a common strategy to improve the mechanical behaviour of a cellular polymer . Moreover, the nanometric size of the fillers can be profited as nucleating agent for the production of micro and nanocellular polymers . Nanocellular polymers are characterized by cell sizes in the range of tens to hundreds of nanometers. They have aroused great interest due to their unique combination of properties, such as a very low thermal conductivity, cell sizes useful for ultrafiltration and their semi-transparent behaviour .
In this work, needle-like sepiolites are used as a nucleating agent to produce nanocellular PMMA with a bimodal cellular structure . Cellular materials with different sepiolite contents (from 1 to 5 wt%) and different relative densities (ranging 0.3 - 0.5) are produced by the gas dissolution foaming. Mechanical properties in compression and fracture toughness behaviour are analyzed.
The results show that the addition of sepiolites produces a significant improvement in the compression properties of the solid nanocomposites. The elastic modulus of the cellular materials is shown to increase at high densities when sepiolites are included, and the reinforcement is greater than that observed in the solids. Also, fracture toughness decreases with the amount of sepiolites in the solid nanocomposites. However, cellular materials with and without sepiolites behave similarly, so cellular nanocomposites show improved relative fracture toughness compared with the pure PMMA. All these improvements are attributed to a synergetic effect between the addition of the particles and the presence of a cellular structure, due to a combination of an improved dispersion induced by the foaming process and the location of the aggregates inside the microcellular pores, isolated from the solid phase.
1. Ibeh, C. C., Bubacz, M. Journal of Cellular Plastics 2008, 44, 493–515.
2. Costeux, S., Zhu, L. Polymer 2013, 54 (11), 2785–2795.
3. Notario, B., Pinto, J., Rodriguez-Perez, M. A. Progress in Polymer Science 2016, 78–79, 93–139.
4. Bernardo, V., Martin-de León, J., Laguna-Gutiérrez, E., Rodríguez-Pérez, M. Á. European Polymer Journal 2017, 96, 10–26.