The Influence of POSS Types in the Nucleation and Cell Morphology of Polystyrene Nanocellular Materials
| Title |
The Influence of POSS Types in the Nucleation and Cell Morphology of Polystyrene Nanocellular Materials |
| Publication year |
2018 |
| General note |
Nano S&T-2018 |
| Author |
Barreto, Carlos (Norner) |
| Source |
The 8th Annual World Congress of Nano Science &Technology (Nano S&T-2018), Postdam (Germany) |
| Abstract |
Nanocellular low density foams are high performance insulators. In addition to the low density requirement in the order of 20 kg/m3 is Knudsen's effect responsible for the significant drop of the thermal conductivity in the gas phase when the cellular material has characteristic cell sizes below 1000 nanometers. Expanded polystyrene (EPS), a low density microcellular particle foam, is one of the most inexpensive and efficient thermal insulators which is broadly used in various applications. The focus of the work was therefore driving the performance of particle PS foams to achieve the nanocellular morphology while maintaining the low density with strong focus on processing and foam nucleation. The foaming process was performed in a batch autoclave using CO2 as the foaming agent by instantaneous pressure release. Various nucleating agent types were screened being POSS the most promising type. Therefore, various POSS types of varying substituents were studied in order to understand the effect of the POSS side branches in the foam nucleation. The solubility of POSS in PS is limited by the side branches. Only soluble POSS types have a positive nucleating performance. On the other hand, it was seen that soluble POSS types do not result in a significant modification of the glass transition temperature of polystyrene but are strong rheological modifiers and have a marked impact in the cell size distribution. It is therefore hypothesized that the improvement mechanisms are linked to the modification of the melt strength of the polystyrene by POSS softened by CO2 active during the decompression step. |