Modification of Interfacial Interactions in Ceramic-Polymer Nanocomposites by Grafting: Morphology and Properties for Powder Injection Molding and Additive Manufacturing  
[PERSON]  
1 Polymer Processing, Montanuniversitaet Leoben, 8700 Leoben, Austria; [PERSON]]  
[PERSON]  
2 Laboratory of Advanced Fibers, Empa-Swiss Federal Laboratories for Materials Science and Technology, CH-9014 St. Gallen, Switzerland; [PERSON]ESS]  
[PERSON]  
3 Industrial Liaison Department, Montanuniversitaet Leoben, 8700 Leoben, Austria; [PERSON]  
[PERSON]  
4 Chemistry of Polymeric Materials, Montanuniversitaet Leoben, 8700 Leoben, Austria; [EMAIL_ADDRESS]  
[PERSON]  
1 Polymer Processing, Montanuniversitaet Leoben, 8700 Leoben, Austria; [PERSON]]  
[PERSON]  
1 Polymer Processing, Montanuniversitaet Leoben, 8700 Leoben, Austria; [PERSON]]  
Footnote 1: email: {dj.goonei.goonei. detrimental for the highly-filled composites used in PIM and FFF, since it leads to failure of the process by, for example, filaments with poor mechanical properties which cannot be processed in the FFF machines [11] or by inhomogeneity in the composition of parts with complex geometry in PIM [17; 18]. The interaction between the polymers and the ceramic filler is greatly influenced by the polarity of both types of material. In PIM and FFF, multicomponent polymeric blends are used. A major fraction of the polymer blend has low viscosity for PIM, while for FFF not only low viscosity but also flexibility is required. The second major component of the blend, known as the backbone, is in many cases a polyolefin such as polyethylene or polypropylene, which is removed in the last step before sintering and thus must have a high adhesion to the powder. However, polyolefins are non-polar, whereas the surface of the inorganic particles is characterized by a high polarity. Therefore, different strategies have been developed to improve the adhesion and the interfacial interaction between both types of materials. 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]. Moreover, short molecules such as the fatty acids do not have strong entanglements with the rest of the polymeric components, which result in poor mechanical properties [13]. Another strategy is the use of polymers grafted with a polar component such as maleic anhydride or acrylic acid, which can be incorporated as a backbone [12; 20] or as a compatibilizer [5; 21; 22; 23; 24; 25; 26; 27; 28]. The improvement of the adhesion to the filler with the use of grafted polymers results in a better dispersion of the filler [27; 28] and in an increase in the mechanical properties [5; 21; 22; 23; 24; 25; 26; 27; 28]. Despite these efforts, a systematic investigation of interfacial interactions is still necessary to understand their effects on the properties of the feedstocks. Here, we aim to address this subject by means of various experiments as well as atomistic insights from molecular dynamics simulations. In this study, we focus on the effects of interfacial interactions on feedstock properties by grafting of polyethylene with acrylic acid and modifying its adhesion to ceramic zirconia nanoparticles. The resulting composite morphology and properties for the processing by FFF and PIM are addressed. Molecular dynamic simulations are employed to calculate the binding energies between polyethylene with different grafting densities and zirconia.