Controlling the structure and density of PMMA bimodal nanocellular foam by blending different molecular weights

Abstract

The bimodal cellular structure of foam is known to provide unique physical properties. In addition, it may help reduce foam density. This study proposes a simple method of creating a bimodal microcellular/nanocellular structure by blending PMMAs of different molecular weights using CO2 as the blowing agent. Nanofoam, with its low relative density, is the right candidate for thermal insulation, but obtaining it is challenging. Introducing micron-sized bubbles into homogeneous nanocellular structures may be one way to reduce the foam density and potentially not affect some of the properties. Beyond the bimodal structure, a transition from an ultramicrocellular to a nanocellular structure and from a closed-cell to an open-cell structure was observed. These transitions may be related to the relaxation time and weight percentage of non-entangled PMMA content. Formation of the bimodal nanocellular or open-cell structure may be predicted by the viscoelastic properties such as the relaxation time.

Keywords

• Nanofoam
• PMMA blends
• Viscoelastic properties
• CO2 solid-state foaming
• Bimodal foam