Holger Ruckdäschel

Foaming of Microstructured and Nanostructured Polymer Blends

Foaming of multiphase blend systems can be identified as a promising approach to satisfy the steadily growing demand for cellular materials with enhanced properties. However, combining the sophisticated fields of polymer blends and polymer foams not only offers great chances, but also poses a significant challenge, as the multiphase characteristics of blends and the complexity of foam processing need to be taken into account. Therefore, the foaming behavior of polymer blends is systematically analyzed, correlating the blend structure and the physical characteristics of reference systems to their foam processability and resulting foam morphology. The cellular materials are prepared via batch-foam processing, using carbon dioxide as a blowing agent. Starting with an immiscible poly(2,6-dimethyl-1,4-phenylene ether)/poly(styrene-co-acrylonitrile) blend, pathways to tailor the foaming behavior via controlling the micro- and nanostructure of such blends are developed; strategies aiming at reducing the cell size, enhancing the foam homogeneity, and improving the density reduction. As a result of adjusting the blend structure over multiple length scales, cooperative foaming of all blend phases and cell sizes down to several hundred nanometers can be achieved. In the light of the results presented, a general understanding of foaming multiphase blends is developed and guidelines for the selection of blend systems suitable for foaming can be deduced.

Foaming of Polymer Blends : Chance and Challenge

The foaming behaviour of polymer blends was systematically investigated using carbon dioxide as a blowing agent. Two batch-processing techniques were used to prepare specimens of different size. Various binary mixtures over a wide compositional range were selected as reference materials, in particular including immiscible (poly(2,6-dimethyl-1,4-phenylene ether)/poly(styrene-co-acrylonitrile) (PPE/SAN) blends. Moreover, the influence of a compatibilization with block copolymers was investigated for PPE/SAN blends. The resulting foam morphology was characterised by evaluating the density, the cell size distribution, the cell wall morphology and the compression behaviour. Besides the commonly accepted key criteria for foaming neat polymers, our study identified significant factors determining the foamability of blends such as the blend morphology, the rheological and the thermal properties. Interestingly, the compatibilization of these PPE/SAN blends by block copolymers was identified as a technique to establish micro- and submicrocellular foam morphologies with nanostructured cell walls. In view of these results, new pathways for the tailoring of cellular materials are derived.

On the friction and wear of carbon nanofiber–reinforced PEEK–based polymer composites

: In the context of establishing novel polymer nanocomposites for successful industrial use, this chapter is aimed at providing a fundamental overview of comprehensive research regarding carbon nanofiber (CNF)-reinforced poly(ether ether ketone) (PEEK) composites for demanding tribological applications. Following a summary overview describing the potential of nanoscale additives for tribological systems in general, the intrinsic structure–property relationships of CNFs are discussed in order to set the frame for the subsequent experimental results regarding their use in PEEK. As demonstrated, successful PEEK–nanofiber composites have been developed, showing a clear enhancement in mechanical properties while minimizing other detrimental effects commonly observed with such nanocomposites. These nanocomposites also reveal a significant beneficial effect on the wear behavior of PEEK under dry sliding conditions. In addition to relating the observed enhancements in the tribological performance to the underlying microstructures and properties of the nanocomposites, evidence for a further optimization of such systems by combining the nanoscale filler with conventional tribological additives and reinforcements such as carbon fibers is provided. Lastly, based on the promising results regarding the wear behavior of such hybrid systems, the performance of advanced nanocomposite hybrid materials for an intended industrial tribological application is introduced and discussed.

CHAPTER 8 - On the friction and wear of carbon nanofiber–reinforced PEEK–based polymer composites

Abstract In the context of establishing novel polymer nanocomposites for successful industrial use, this chapter is aimed at providing a fundamental overview of comprehensive research regarding carbon nanofiber (CNF)–reinforced poly(ether ether ketone) (PEEK) composites for demanding tribological applications. Following a summary overview describing the potential of nanoscale additives for tribological systems in general, the intrinsic structure–property relationships of the CNFs are discussed To set the frame for the subsequent experimental results regarding their use in PEEK. As demonstrated, successful PEEK–nanofiber composites have been developed, showing a clear enhancement in mechanical properties while minimizing other detrimental effects commonly observed with such nanocomposites. These nanocomposites also reveal a significant beneficial effect on the wear behavior of PEEK under dry sliding conditions. In addition to relating the observed enhancements in the tribological performance to the underlying microstructures and properties of the nanocomposites, evidence for a further optimization of such systems by combining the nanoscale filler with conventional tribological additives and reinforcements such as carbon fibers is provided. Lastly, based on the promising results regarding the wear behavior of such hybrid systems, the performance of advanced nanocomposite hybrid materials for an intended industrial tribological application is introduced and discussed.

Influence of Nanoscale Morphology on the Micro- and Macromechanical Behaviour of Polymers and Polymer Nanocomposites

There is enormous scientific and economic interest in the development and evaluation of polymer nanocomposites due to the fact that the properties of a material become increasingly insensitive to flaws at the nanoscale, enabling the exploitation of the unique physical and mechanical properties of very small objects in large-scale components. However, the successful industrial implementation of such novel materials poses unique challenges which are not only related to the small size of the reinforcements. Decades of intensive research have shown that polymer nanocomposites differ from their counterparts based on traditional reinforcements in many ways and a fundamental understanding of the structure-propertyrelationships of such novel materials is only slowly emerging. Although issues such as the intrinsic properties of the nanoscale constituent as well as the degree of dispersion and orientation of individual filler particles clearly appear to be important factors, molecular interactions between the filler and the matrix during processing can lead to pronounced variations in the matrix microstructure. These variations in themselves lead to pronounced changes in the micro- and macromechanical deformation behaviour of the nanocomposites. A detailed investigation of fatigue crack growth behaviour of such novel materials for example is essential in order to understand the fracture mechanical performance and the transition from a ductile to a brittle behaviour which is often observed experimentally, especially in the case of amorphous matrices. However, as the size of the filler particles approaches the molecular level, the novel interactions at the interface or even in the interphase can lead to significant changes in the micromechanical deformation behaviour. Significant work has been carried out regarding the fracture mechanical investigation of polymer blends with both micro- and nanoscale morphologies and much can be learned by comparing the results of polymer nanocomposites to these more established polymer blends.