Research On Direct Ink Writing 3D Printing Of Thermosetting Polyimide And Its Composites

Polyimide(PI)has been widely used in aerospace,microelectronics,and other fields,because of the high and low temperature resistance,low dielectric constant,high strength and outstanding stability.The traditional manufacturing methods of polyimide and its composites are mainly the casting membrane,compression molding and injection molding.When fabricating polyimide and its composite parts,the traditional manufacturing methods need additional molds fabricating,and subsequently machining will produce plenty of waste.It has disadvantages of complicated operation,long production cycle,low efficiency,and waste of resources.3D printing technology is a manufacturing method that converts digital models into actual structures,which can customize complex three-dimensional structures under the principle of layered manufacturing.It has the characteristics of simple operation,high molding accuracy,short production cycle,and conserving resources.The 3D printing technology is applied in the fabrication of polyimide and its composite parts not only simplifies the processing technology,but also has large advantages for the preparation of parts with complicated shape.The direct ink writing 3D printing technology has mild extrusion temperature and simple formulation for inks,which is suitable for the process and manufacturing for thermosetting polyimide(TSPI)and its composites.Therefore,in this paper,the main research goal is to develop a simple,and efficiency direct ink writing 3D printing technology for thermosetting polyimide and its composites with highly complicated shapes and outstanding heat resistance.The research content is mainly divided into three parts:(1)The preparation and properties of the solvent-assisted direct ink writing 3D printing thermosetting polyimide(TSPI).The influence of n-hexane,petroleum ether,cyclohexane and water served as auxiliary solvents on the formability and thermal properties for polyimide 3D printing was studied using phenylethynyl-terminated polyamide acid(PAA)solution with a high solid content serve as feedstock.The results indicated that not only the molding and fabricating of PAA ink was realized by the auxiliary effect of solvent,but also the outstanding heat resistance for TSPI was maintained.(2)The preparation and properties of the direct ink writing 3D printing thermoset polyimide/nano-silica(TSPI/Si O₂)composites.The TSPI/Si O₂composite structures were obtained via preparing,printing and thermal curing of PAA/Si O₂composite inks.The results showed that nano-Si O₂improved the rheological behavior for the composite inks.When the content of nano-Si O₂was 26.3%,the composite ink had self-supporting and printability.The printed parts exhibited a low dimensional shrinkage,which was possessed as isotropic shrinkage.Compared with the C-TSPI,C-TSPI/Si O₂-26.3%composite exhibited improved thermal properties.Compared the C-TSPI/Si O₂-26.3%composite film obtained by the casting method with the TSPI/Si O₂-26.3%-X composite film obtained by the printing with transverse direction method,there was no significant difference in the average tensile strength between them.But the mechanical properties for the TSPI/Si O₂-26.3%composite film prepared by printing were anisotropic.(3)The preparation and properties of the direct ink writing 3D printing porous thermosetting polyimide/carbon fiber(TSPI/CF)composites.The porous TSPI/CF composites were obtained by preparing,printing,thermal curing from the PAA/CF composite inks and the Na Cl etch.The results showed that both Na Cl and CF improved the rheological behavior of the composite inks by synergistic effect,and realized the self-supporting performance for PAA/CF inks.The printed porous composites had complicated shape,a low volume shrinkage and isotropic shrinkage.The orientation of CF in TSPI was consistent with the printing path.Due to CF served as a skeleton in TSPI,when the content of CF was increased,the porosity of the porous composite was increased and the average pore diameter was decreased.In addition,the tensile strength and compressive strength for the porous TSPI/CF composite was improved.When the content of CF was 12.1%,the porous TSPI/CF composite exhibited excellent oil storage,oil output behavior,and wet tribological properties under the condition of oil was served as lubricant.