Using fillers to tune material properties of an ion-containing semi-crystalline poly(ethylene glycol) for fused filament fabrication additive manufacturing

The materials library for Fused Filament Fabrication (FFF) additive manufacturing processes has been primarily dominated by amorphous thermoplastic materials. Semi-crystalline polymers form tough plastics due to their strong intermolecular forces, which makes them well suited for applications requiring wear and chemical resistance, thermal stability, and structural loading. However, they are infrequently used in FFF because of large shrinkage that occurs due to recrystallization during cooling, which causes printed layers to warp. The authors have previously evaluated a semi-crystalline polymer series (sulfonated poly(ethylene glycol) (SPEG)) for FFF printability. The influence of divalent counter-ions in the SPEG series altered the material properties and crystallization to enable processing via FFF. The SPEG containing a calcium counterion resulted in the print quality due to the higher viscosity (105 Pa∙s) allowing the material to hold shape in the melt and high-nucleation and small spherulite size mitigating the layer warping. However, the dialysis used for the ion exchange in the polymer synthesis procedure proved challenging for mass manufacturing scale-up. To circumvent this limitation, the authors explore the incorporation of ionically charged filler materials in the SPEG with a sodium counter-ion, poly(PEG8k-co-NaSIP), to achieve the desired properties for FFF processing. Both ionic (calcium chloride and calcium carbonate) and non-ionic (silica and starch) filler particles were added to poly(PEG8k-co-NaSIP) and the resulting material properties and effect on FFF printability were measured. The calcium chloride filler changed the viscosity, crystallinity, spherulite growth, and spherulite size which improved the processing via FFF without requiring an ion exchange. This technique may be applicable to other ionic polymers in order to alter their material properties to enable FFF printing.