Rheological Behaviour of Highly Filled Materials for Injection Moulding and Additive Manufacturing: Effect of Particle Material and Loading  
[PERSON]  
1 Faculty of Mechanical Engineering, University of Ljubljana, 1000 Ljubljana, Slovenia; [EMAIL_ADDRESS]  
[PERSON]  
2 Institute of Polymer Processing, Montanuniversitat Leoben, 8700 Leoben, Austria; [EMAIL_ADDRESS]  
[PERSON]  
3 Industrial Liaison, Montanuniversitat Leoben, 8700 Leoben, Austria; [EMAIL_ADDRESS]  
[PERSON]  
4 Faculty of Mechanical Engineering, University of Maribor, 2000 Maribor, Slovenia; [EMAIL_ADDRESS]  
[PERSON]  
5 Polymer Competence Center Leoben GmbH, 8700 Leoben, Austria; [EMAIL_ADDRESS]  
[PERSON]  
1 Faculty of Mechanical Engineering, University of Ljubljana, 1000 Ljubljana, Slovenia; [EMAIL_ADDRESS]  
Footnote 17: email: {j.slemenik.perse@named as Shape, Debind, and Sinter (SDS) processes [10]. Feedstock materials used in SDS processes have a complex multimaterial formulation since they meet several specific requirements for each of the stages of the process. The binder system usually consists of the main binder component, a backbone, and additives. The main binder component usually provides flowability and is removed first during debinding. The backbone supplies shape retention during debinding and is removed last. Additives help to improve various properties of the particle dispersion in the main binder component or prevent binder degradation. In the SDS processes, it is always beneficial to have the highest amount of filler particles to minimise geometrical distortions and shrinkage during sintering [16]. However, a high number of particles in the compound can lead to several problems during processing in the molten state. Moreover, it is challenging to obtain a homogeneous dispersion of the particles in the polymeric binder since some voids in the feedstock could appear due to deficiency of the polymer to cover each of the individual particles [16, 17]. The success of the shaping step of the SDS process depends on the rheological properties of the feedstock material. The introduction of fillers into the polymer, especially at high concentrations, can have a substantial effect on rheological properties. Several review papers are describing the behaviour of highly filled materials, such as review paper prepared by [PERSON] [18], a review oriented on experimental properties of filled thermoplastic melts by [PERSON] and [PERSON] [19], and more recently, a review focusing on powder injection moulding and rheological properties of feedstock [20] and an extensive review of highly filled polymers by [PERSON] et al. [21]. The rheology of highly filled polymers is influenced by many interrelated factors such as polymeric binder and its composition, particle loading, particle shape, and size distribution and surface chemistry of the particles. In general, higher powder loadings lead to higher viscosities and dynamic rheological moduli (i.e., G' and G\") [1, 16, 17, 22, 23]. At a certain particle loading level, a particle-particle network is established that promotes highly non-Newtonian behaviour. At low shear rates, the network prevents the flow of material; however, at the specific limit, the particle network breaks and material starts to flow (apparent yield behaviour). This flow is highly affected by the particles [24, 25]. The network also dictates the dynamic behaviour of materials as it limits the frequency dependence of dynamic properties [24] and at small loads result in solid-like material behaviour [25]. The rheological properties of highly filled materials depend on the selected binder and its composition as well. In our earlier work [1] we have investigated the viscosity of highly filled materials using different binder compositions and powder loadings.