The 21st Century COE Program
Center of Excellence for Research and Education on Complex Functional Mechanical Systems

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Nanocomposites Research at TUHH

Karl Schulte (Polymers & Composites Section, Technische Universität Hamburg-Harburg)

Nanoscale carbon tubes (CNTs) with a diameter of 5-20 nm, are a new class of material with the potential to reinforce polymers. The combination of CNT with polymer matrices can be considered as a step forward in polymer and composites technology. A fundamental understanding of the CNT/polymer interaction will further enhance the exchange of materials for high performance fibre-reinforced polymers.

An improvement of the mechanical properties of polymer nanocomposites, based on carbon nanotubes (CNTs) and epoxy resin, is addicted to a good dispersion and strong interactions between the matrix and the filler. For this reason various types of carbon nanotubes (single, double- and multi-walled (SWCNTs, DWCNTs and MWCNTs respectively), produced by CVD and arc-discharge method, were purified by treatment with oxidising inorganic acids. The surface modification of the oxidised nanotubes (o-CNTs) can be achieved by refluxing the tubes in poly-functional amines. The investigation of composites containing amino-functionalised nanotubes showed, that the epoxy matrix is strongly bonded to the nanotubes. Crack bridging and matrix disposals remaining on the CNTs surface could be observed. The mechanical properties like tensile strength, Young's modulus and fracture toughness of epoxy resins could be significantly increased with only low contents of carbon nanotubes.

Furthermore, their size in the nanometre range allows their application in polymeric matrices of fibre-reinforced composites, without disturbing the fibre arrangement. Ii will be shown, that nano-particle reinforced GFRPs, containing carbon black (CB) and CNTs, can successfully be manufactured by resin transfer moulding (RTM). Due to their small size, the CNTs will not filtered by the glass fibre bundles. The produced glass-fibre reinforced epoxy composites exhibit significantly improved matrix-dominated properties. The interlaminar shear strength of the laminates could be increased by 19% from 32 to 38 MPa with a carbon nanotube modified matrix, containing only 0.3 wt.-% of CNTs. However, they already exhibit an anisotropic electrical conductivity. The in-plane conductivity was observed to be one order of magnitude higher than out-of-plane.

Furthermore, the electrical properties of neat matrix systems can already be achieved with a volume content of nanotubes less than 0.04 wt.-cont. This gives rise to numerous prospective applications, which will be discussed. We will also introduce the first investigation on the thermal conductivity, which are by far not as promising as the results above.

Based on the experimental results reported, an outlook on the potential application of nanocomposites will be given.

1. F.H. Gojny, M.H.G. Wichmann, B. Fiedler, K. Schulte, Compos. Sci. Technol. 65, 2300 (2005).
2. M.H.G. Wichmann, M. Cascione, B. Fiedler, M. Quaresimin, K. Schulte, Compos. Interfaces; in press.
3. F.H. Gojny, M.H.G. Wichmann, B. Fiedler, K. Schulte, Composites Part A 36, 1525 (2005).
4. F.H. Gojny and K. Schulte, Composites Science and Technology 64, 2303 (2004).
5. C.A. Martin, J.K.W. Sandler, A.H. Windle, M.K. Schwarz, W. Bauhofer, K. Schulte, M.S.P. Shaffer, Polymer 46, 877 (2005).
6. F.H. Gojny, M.H.G. Wichmann, U. K?pke, B. Fiedler, K. Schulte, Compos. Sci. Technol. 64, 2363 (2004).
7. F.H. Gojny, M.H.G. Wichmann, B. Fiedler, I. Kinloch, W. Bauhofer, A.H. Windle, K. Schulte, Polymer 47, 2036 (2006).

Reuse and Recycling of Carbon Fibre Reinforced Polymer Waste

Leif Ole Meyer (Polymers & Composites Section, Technische Universität Hamburg-Harburg)

Carbon fibre reinforced polymers (CFRP's) were first applied in the early 1970's in aerospace parts. At this time carbon fibres had a price of ~300$/Kg and were produced in small quantities of only a few tons per year. Due to their outstanding mechanical properties they are today widely used in aircraft structures, sporting goods and engineering applications. The availability of carbon fibres is still limited with a world production capacity of 25,000 tons in 2005 while the industrial demand is much higher. Consequently the price for carbon fibres is still relatively high with 15-20 $/Kg.

A chance to increase availability and to provide cheaper fibres is recycling of CFRP-waste. This waste consists of end-of-life-parts and production waste (e.g. prepreg-cutoff) and is usually disposed by landfilling or incineration (costs for disposal ~200 $/to). As a consequence the valuable carbon fibres are lost. But besides economic reasons there are also ecological reasons for recycling of CFRP's. Additional, laws have been enacted in the past years that limit landfilling and incineration of organic material containing waste in many countries.

Different methods for recycling of CFRP's were described in literature. However, none of these has found its way into industrial application. In this presentation different methods to reuse or to recycle carbon fibres are shown and their practicality is evaluated.

Tissue Engineering of Articular Cartilage: Determination of the Biomechanical and Biochemical Properties. A New Bioreactor for the Cultivation of Cartilage

Eduard Ilinich^a, Helge Petzold^b, Eva Eisenbarth^b, Christiane Goepfert^c, Ralf Pörtner^c, Nobert Meenen^d, Michael Morlock^b, Karl Schulte^a
a Polymers & Composites Section, Technische Universität Hamburg-Harburg
^b Biomechanics Section, Technische Universität Hamburg-Harburg
^c Bioprocess & Biochemical Engineering Section, Technische Universität Hamburg-Harburg
^d University Medical Center Hamburg-Eppendorf, Germany

Injured hyaline cartilage has no self healing capacity. Untreated cartilage defects limit the freedom of movement of the patient and can cause arthritis. Tissue Engineering is a promising method to repair or replace of defects in articular cartilage. Since frequently the subchondral bone is also involved, it is desirable to use cartilage-carrier constructs [1]. Cells are explanted from native cartilage, cultured in vitro and stimulated to produce cartilage on a ceramic substrate. The cartilage-carrier constructs are designed to be implanted in defective cartilage areas of the knee. The aim of this study was to determinate the properties of the cultivated porcine cartilage and to develop a bioreactor for the cultivation of cartilage with realistic joint loading.

To investigate the biomechanical properties the thickness, Young's Modulus and Aggregat modulus were measured and the Poisson's ratio was calculated. For comparison of the biochemical properties the GAG/DNA proportion was measured. Additionally histological and SEM analyses were performed.

To improve the properties of in vitro cartilage, a new bioreactor concept was developed that incorporates shear and/or roll motion for a physiological range of loading. The bioreactor applies dynamic load to cartilage, similar to in vivo loading conditions within the knee joint. Furthermore, testing of the cartilage mechanical properties can also be done within the bioreactor without removing the cartilage-carrier-construct.

[1] Stephanie Nagel-Heyer et al., "Bioreactor cultivation of three-dimensional cartilage-carrier-constructs", Bioprocess Biosyst. Eng (2005) 27: 273-280.