3D Printing of Porous Thermosetting Polyimide Composite with Oil Impregnated

Thermosetting Polyimide (TSPI) has been widely utilized as an kind of engineering material due to the excellent heat resistance properties, e.g. high mechanical strength, nonflammability, and UV-irradiation resistant. Nevertheless, the manufacturing of porous TSPI or TSPI with complicated structures by the traditional manufacturing methods is still a highly challenging topic because of the unobservable melt point and the poor solubility in organic solvents. The emerging additive manufacturing, generally known as three-dimensional (3D) printing, could translate digital model into physical components based on the principle of layer-by-layer stacking, which fortunately, has the capability of realizing the fabrication of porous TSPI with complex structures by a convenience strategy. Herein, direct ink writing (DIW) 3D printing technique is employed. DIW requires ink with moderate rheological properties including shear-shinning, viscoelasticity and rapid thixotropic recovery, which is critical to achieve the distortion-free and accurate 3D objects. In this work, 3D printing of carbon fiber (CF) filled porous TSPI/CF composites were realized via the DIW strategy. The printable composite inks for the DIW 3D printing were prepared by using the phenylethynyl-terminated polyamide acid (PAA) solution as matrix, the sodium chloride (NaCl) and carbon fiber (CF) as not only the rheology modifier but the pore-forming template and the reinforcing filler, respectively. The results showed that both NaCl and CF improved the rheological behavior of the inks to make them good self-supporting inks to realize objects with various shapes and complicated structures by the DIW 3D printing at room temperature. Then, the printed objects were turned into the porous TSPI/CF composites by the thermal treatment followed by the etching of the NaCl. It was found that the post-treatment resulted in the dimension shrinkage, which however was low and isotropic. The pores in the TSPI/CF composites were found to be interconnected with the mean diameter of 358.8 nm and the porosity of 66.12%. In addition, it was observed that the increase of CF content resulted in the increased porosity, and the decreased average pore diameter. The resultant TSPI/CF composites were also found outstanding thermal properties, and the mechanical performances that were highly dependent on the printing path, which was similar to many others built by DIW 3D printing technique. Moreover, when the CF was increased, the tensile strength and compressive strength of the porous TSPI/CF composites were improved. This was attributed to the orientation of CF in the porous TSPI which was consistent with the printing path and therefore the CF can serve as the skeleton that could transfer stress in the whole porous TSPI. Importantly, the porous TSPI/CF composites possessed excellent oil-storage capacity properties with the oil content rate of >130% and oil retention of >95% taking PAO 10 as the example, which could be benefit from the numerous pores. As the result, the porous TSPI/CF composites demonstrated preferable tribological performance with the PAO 10 impregnated. Briefly, DIW 3D printing technique provided a facile strategy to fabricate 3D structures for thermoset polyimide with outstanding comprehensive performances. While despite of the imperfect parts built in the present case, the DIW 3D printing of PSPI composite is believed to be highly promising by combining the high-performance PSPI with the structures in high complexity.