(118a) Fabrication of Highly-Filled Composites By Spouted Bed Coating and Study of the Influence of Particle Shape on Mechanical Properties of the Materials (Invited)

Naturally occurring composite materials are usually ceramic-polymer composites with high filling degrees on hard constituent. In recent years structure and properties of biological composite materials as bones, teeth and nacre have been studied in detail. The studies showed that high filling degrees, strong interface among particles and polymer, hierarchical structure and plate-like shape of particles cause good mechanical properties of the materials. Due to good or sometimes excellent mechanical properties of the bio-composites, many attempts have been made to mimick the structure of the composites. But it turned over to be difficult to reconstruct this structural design. In this contribution we present a process route for the fabrication of highly-filled composite materials with different particle shape by using of the spouted bed coating process. And we show the study of the influence of particle shape on mechanical properties in such composites.

Spouted beds are used for many applications in solids process engineering. Typical application examples for the spouted beds are drying, mixing, thermal treatment, coating as well as granulation and chemical reactions. Usage of spouted beds offers also many advantages for the design of composite materials. In this investigation fine particles were firstly spouted and uniformly coated, so the optimal properties for further processing to bulk materials could be obtained. For the spouting and the coating a hybrid spouted bed with prismatic process chamber and a high conical-cylindrical relaxation zone was designed. The small process chamber has two horizontal adjustable gas inlets. Two air streams change the flow direction from horizontal to vertical by means of a central profile in the middle of the process chamber. With this design of the apparatus it was possible to treat fine particles using a dilute spouting regime and to avoid particle elutriation from the bed. The injection of the polymeric binder was carried out with a bottom-spray two-fluid nozzle, which allowed a uniform coating of particles using a polymer solution. The thickness of the polymer layer (amount of the matrix polymer in the final composite material) could be simply adjusted by the amount of polymer used in the process. The possibility to adjust the thickness of the polymer layer is very important to fabricate composites of desired filling degrees.

The next producing step after the coating process was assembling of particles to a composite material by means of warm pressing, if composites with spherical particles were fabricated. For the fabrication of composites with particles, which should have a high aspect ratio, the coated particles were first rolled and after that aligned in the pressing die and pressed. The pressed compacts were sawed in narrow beams, which were used to determine mechanical properties of composites. As mechanical properties modulus of elasticity, bending strength and fracture toughness were tested. The determination of modulus of elasticity and bending strength was carried out in four-point bending-tests. The determination of fracture toughness was performed in three-point bending tests.

In the current study copper particles were used as model material. The copper particles were chosen due to the relatively softness of the material copper and hence the possibility to change the shape of particles.

In this contribution the change of mechanical properties due to the change of particle shape will be showed. Electrical properties of composites with spherical particles were studied and will be presented too.

Acknowledgement: We gratefully acknowledge financial support from the German Research Foundation (DFG) via the collaborative research centre SFB986.