Ethylene vinyl acetate as a binder for additive manufacturing of tricalcium phosphate bio-ceramics

Abstract

Tricalcium phosphate (TCP) ceramic scaffolds were made by the fused filament fabrication (FFF) using different grades of Ethylene Vinyl Acetate (EVA) as a thermoplastic binder. Stearic acid was studied as a processing aid. A wide range of rheological properties, shaping and debinding behavior could be observed with feedstocks made with different EVA grades. The addition of stearic acid affects flexibility of the solid filaments, the viscosity of feedstocks, and causes a pronounced yield stress behavior. These effects are strongly dependent on the molecular weight of the EVA and influence the printing process and shape stability during the debinding process. EVA binder system works well for thin and small parts, made with nozzle sizes below 0.4 mm, whereas samples made by thicker nozzle size form defects during debinding process. TCP scaffold structures with fin struts of 0.27 mm and partition wall thickness of 0.25 mm and a layer thickness of 0.20 mm could be successfully shaped, debinded and sintered. Excellent fusion between the different layers was achieved, since no defects at the interface could be detected.

Influence of the Infill Orientation on the Properties of Zirconia Parts Produced by Fused Filament Fabrication

“…The fused filament fabrication (FFF) of ceramics, also known as Fused Deposition of Ceramics (FDC) [ 8 , 9 , 10 ], is a MEX process based on the selective extrusion through a nozzle of feedstock in the shape of filament. The feedstock is a multicomponent polymer system highly filled with powder of the desired ceramic material [ 9 , 11 , 12 , 13 ]. Once the so-called green parts are shaped by FFF, the polymer components are removed in the debinding stage by a catalytic reaction [ 14 ], dissolution in a solvent [ 12 , 15 , 16 ] and/or thermal decomposition [ 9 , 17 , 18 , 19 ].…”

Modification of Interfacial Interactions in Ceramic-Polymer Nanocomposites by Grafting: Morphology and Properties for Powder Injection Molding and Additive Manufacturing

“…To improve the adhesion between the polymer and the ceramic, one approach includes the coating of the nanoparticles with a coupling agent such as silane [13] or with a fatty acid such as stearic or oleic acid [6,7,10], which can also be incorporated as a surfactant [8,19]. Fatty acids and stearic acid have been extensively used in PIM and FFF as they improve the dispersion of the particles and reduce the viscosity of the composites [6][7][8]10,19]. Nonetheless, these low molecular weight polymers are very unstable and degrade if processed at high temperatures or long times [7].…”

Manufacturing complex Al2O3ceramic structures using consumer-grade fused deposition modelling printers

“…The feedstock was developed on the basis of the experience obtained in previous studies (Gorjan et al, 2018). An alumina powder loading of 50 Vol.-per cent was chosen.…”

“…Furthermore, in the case of debinding in air, reactions with oxygen occur and the binder is transformed into a hard brown resin on the surface (Gorjan et al, 2012). This leads to the formation of a dense skin on the surface, which hinders the transport of gaseous species, and consequently, leads to a pressure build-up, which can cause cracking and bloating (Gorjan et al, 2018;Zorzi et al, 2002). The formation of such a dense skin depends on the diffusion of oxygen into the samples.…”

“…Further scaffold structures, some with functional materials, were manufactured by other researchers (Ho et al, 2002;Houmard et al, 2013;Jang et al, 2014). The effect of stearic acid on the stability of the 3D printed scaffold structures during thermal treatment was investigated by Gorjan et al They used different grades of ethylene vinyl acetate (EVA), together with tricalcium phosphate and stearic acid, to manufacture bioceramic scaffold structures (Gorjan et al, 2018). Another functional material was used by Rangarajan et al (1998), who investigated the homogeneity of simple structures created by using the FDC method.…”