Bio-based Silicon Carbide Ceramics from Thermoset-Based Wood Polymer Composites
Global warming and the depletion of fossil fuels force a transition to renewable energies and resources. This also requires a reorientation in the field of material development. Silicon carbide (SiC) is one of the most important technical ceramics due to its high hardness, chemical resistance and thermal properties even at very high temperatures. The excellent properties are attended by high costs. For broader use, cost reduction in materials and processing is inevitable. Natural fiber based composites can be used as green-bodies for the preparation of bio-based SiC ceramics. The green-bodies are transformed to porous carbon templates by a carbonization process. In an additional liquid silicon infiltration step, these templates can be transformed to SiC ceramics. The usage of thermoset-based fiberboards as green-bodies is sufficient for planar geometries [1-2]. 3D structures are accessible only by complex processing. The use of thermoplastic-based WPC (wood polymer composites) is an interesting approach [3]. 3D green-bodies are prepared by extrusion or injection molding. The limited dimensional stability during carbonization and the low carbon yield restrict the application.
Wood K plus has developed a process for thermoset-based WPC [4], which can be used as precursor for SiC ceramics. The thermoset-based green bodies can be shaped using standard polymer processing techniques like extrusion, compression molding, injection molding or 3D printing. They are structurally stable enough for conversion to porous carbon templates without distortion.
In the current study the influence of various additives, processing and heat treatment parameters on the properties of the porous carbon templates and subsequent SiC ceramics was investigated (mechanical testing, porosity, density, microscopic image analysis, computed tomography).
The main impact factor on the quality of the porous carbon templates and subsequent SiC ceramics is the distribution of the constituents as well as the density distribution in the green bodies. Variations in the composition of WPC, especially the thermoplastic content, allow adjusting the porosity of the carbon templates formed after pyrolysis. From optimized WPC green-bodies SiC ceramics with SiC contents up to 90 vol% (95 m%) could be produced. However, for e.g. tuning electrical or tribological properties, ceramics with defined C contents can be prepared.
 
Acknowledgement
This work was conducted within the project BioC4HiTech funded through the program Production of the Future by the Austrian Research Promotion Agency (FFG).
 
References
[1] Siegel, S.: Keramische Leichtbauelemente auf Holzfaserbasis, Symposium „Werkstoffe aus nachwachsenden Rohstoffen“, Erfurt 06-07.09.2007
[2] Gahr, M.; et al.: SiC-Keramiken auf der Basis von Holzwerkstoffen; Verbundwerkstoffe, 14. Symposium Verbundwerkstoffe und Werkstoffverbunde, 02-04.07.2003 Wien, S. 383-388
[3] Schubert, M.; et al.: Technical Ceramics Derived from WPC, 9th WPC, Natural Fiber and other innovative Composites Congress and Exhibition, 19-20 June 2012, Stuttgart/Germany
[4] Kompetenzzentrum Holz GmbH: Method For Producing A Silicon Carbide Ceramic Body. Patent, WO 2018/213859 A1