Potential of Natural Halloysites to improve the Insulation Behavior and the Mechanical Properties of Cellular Polymers

• Applicant: Professor Dr.-Ing. Holger Ruckdäschel
• Subject Area: Polymeric and Biogenic Materials and Derived Composites ; Plastics Engineering ; Polymer Materials
• Term: since 2023
• Project identifier: Deutsche Forschungsgemeinschaft (DFG) - Project number 524820165

Polymer foams have become an indispensable part of our daily lives due to their light weight and attractive properties such as thermal insulation, dimensional stability at high temperatures and chemical resistance. In view of their special properties, the use of polymer foams in numerous applications (e.g. thermal insulation in buildings or sandwich constructions in wind power) is indispensable. Insulating materials with reduced thermal conductivity play an important role in reducing global energy consumption and carbon dioxide emissions. Reducing foam density and cell size are known strategies for improving insulation performance. To achieve this, foam nanoadditives (e.g., carbon-based nanoadditives such as graphene as well as clay mineral-based nanoadditives such as Halloysite (HNTs)) are mainly used as foam nucleating agents. HNTs increase the number of nucleation sites in the polymer matrix to obtain foams with optimized morphology. Natural HNTs have gained attractiveness as foam nucleating agents due to their advantages such as high natural occurrence, low price, nontoxicity and ease of processing compared to carbon-based nanoadditives. Their unique nanotubular porous shape with sharp edges, high aspect ratio and improved mechanical properties lead to foams with low density and fine morphology, improved insulation and mechanical properties at very low HNT concentrations (< 1 wt%). Therefore, in this study, we focus on the potential of HNTs as a foam nanoadditive to improve the performance of an insulating foam, namely polystyrene (PS), and a core material, namely recycled polyethylene terephthalate (rPET), for sandwich composite structures. To our knowledge, no scientific study has addressed the effects of HNTs on the morphology and properties of PS and rPET foams. Laboratory-scale autoclave foams followed by continuous foaming processes are used to produce HNT-based insulating and core materials. The main objective of this research project is to understand the influence of the aspect ratio and concentration of HNTs on the nucleation and morphology of amorphous PS and semi-crystalline rPET foams. The influence of HNTs on the three different heat transport mechanisms will also be studied more intensively as a function of concentration and geometry. In particular, the reduction of thermal radiation will be considered here. In addition, the influence of HNT type and concentrations on the crystallization behavior, kinetics, and crystallite size of rPET and the resulting foam morphology will be investigated. The correlations between foamability, processing type and parameters, cell and nucleation efficiency, foam morphology, density, and insulation and mechanical properties of HNT-based foams will be determined.

• DFG Programme: Research Grants