Three‐dimensional printing of high‐performance polyimide by direct ink writing of hydrogel precursor

Abstract

Three‐dimensional (3D) printing of all‐aromatic polyimides (PIs) is attracting extensive attention due to the advantages of excellent comprehensive performances and complex structures. It still remains challenges because of some drawbacks, such as poor solubility and infusibility, and the environmental unfriendly preparation. Here, polyamide acid salt (PAAS) hydrogels were prepared by the reaction of polyamide acid (PAA) with organic amines in water. PAAS hydrogels had remarkable rheological properties, which made it applied in direct ink writing 3D printing. The printed objects were finally converted into high‐performances PI objects with prominent mechanical properties and thermal stability. Not only so, the advantages also include simple preparation, less organic solvent, low thermal imidization temperature (250°C), controllable macrostructure and porous microstructure, and the present 3D printed PI by PAAS was expected to significantly promote the application potentials. In this study, thermal conductivity (100°C) of the PI objects after structure design and 3D printing was reduced from 0.102 W m−1 K−1 to 0.061 W m−1 K−1, and density was reduced from 0.4562 g cm−3 to 0.2731 g cm−3.

Preparation of polyimide aerogels by freeze‐extraction and chemical imidization for 3D printing

“…As the previous report, PAA (10.00 g) and DMAE (6.99 g) were dissolved in water (73.01 g) and mixed well by ball milling, followed by degassing under vacuum and standing 1 h, the 10 wt% PAAS hydrogel was prepared. 25 Afterward, the mixture was transferred to cube molds (which made of polytetrafluoroethylene) by spoon and stored at À20 C. Samples containing 5, 15, and 20 wt% PAAS were prepared by adjusting the amount of PAA and DMAE, respectively.…”

“…Our previous work pointed out that the excellent rheological properties of PAAS hydrogels are necessary requirements for DIW printing, but their thermally reversible behavior prevents the thermal imidization process. 25 In addition, the shape of PAAS hydrogel needs to be fixed by freeze-drying, and then thermally imidized. However, in this study, the freezeextraction and chemical imidization method is able to realize the imidization process and maintain the printed shape at the same time.…”

3D Printing of Thermal Insulating Polyimide/Cellulose Nanocrystal Composite Aerogels with Low Dimensional Shrinkage

“…Our results indicate that CNCs can be used as renewable fillers to 3D print PI/CNC composite aerogels with enhanced mechanical strength. Although our PAAS/CNC ink was printed under room temperature, several previous works preheated the inks to reduce the viscosity of the ink, facilitate material extrusion, and extend the printable time [21,23,51]. The printing speed and resolution may be further improved by selecting a suitable heating parameter.…”

“…In contrast to PI, the printing of PI aerogels has only been sporadically studied. It may be achieved by the freeze-drying of PAAS hydrogels [23] or using polymer microspheres as pore-forming agents and rheological modifiers for DIW [24].…”

Vertical Alignment of Liquid Crystal on Sustainable 2,4-Di-tert-butylphenoxymethyl-Substituted Polystyrene Films

“…Polyimide (PI), which has excellent thermal and chemical stability, has a side chain such as a long alkyl group and has been used to implement vertical alignment of LC molecules [ 35 , 36 , 37 ]. However, it is difficult to produce flexible plastic products because the post-baking and washing temperatures required for preparing the alignment layer from the PI derivative are too high [ 38 , 39 ]. Recently, a vertically aligned LC layer using a polystyrene (PS) derivative synthesized through a polymer substitution reaction has attracted much attention in the electro-optical field including flexible displays due to its advantages of excellent optical transparency and low-temperature processability [ 40 , 41 ].…”