3D Printing of Lightweight Polyimide Honeycombs with the High Specific Strength and Temperature Resistance

Abstract

Lightweight structures are often used for applications requiring higher strength-to-weight ratios and lower densities, such as in aircraft, vehicles, and various engine components. Three-dimensional (3D) printing technology has been widely used for lightweight polymer structures because of the superior flexibility, personalized design, and ease of operation offered by it. However, synthesis of lightweight polymeric structures that possess both high specific strength and glass transfer temperature (T g ) remains an elusive goal, because 3D printed polymers with these properties are still very few in the market. For example, 3,3′,4,4'-biphenyl tetracarboxylic dianhydride (BPDA) and p-phenylenediamine (PDA)-type (UPILEX-S type) polyimides show exceptional thermal stability (T g up to ≈400 °C) and mechanical properties (tensile strength exceeding 500 MPa) and are the first choice if extremely high temperatures of 400 °C or even higher (depending on the duration) are required, which hampers their processing using existing 3D printing techniques. However, their processing using existing 3D printing techniques is hampered due to their thermal resistance. Herein, a 3D printing approach was demonstrated for generating complex lightweight BPDA-PDA polyimide geometries with unprecedented specific strength and thermal resistance. The simple aqueous polymerization reaction of BPDA with water-soluble PDA and triethylamine (TEA) afforded the poly(amic acid) ammonium salt (PAAS) hydrogels. These PAAS solutions showed clear shear thinning and thermo-reversibility, along with high G′ gel-state moduli, which ensured selfsupporting features and shape fidelity in the gel state. Postprinting thermal treatment transformed the PAAS precursor to BPDA− PDA polyimide (UPILEX-S type). The resulting layer-by-layer deposition onto lightweight polyimide honeycombs in the form of triangular, square, and hexagonal structures showed tailorable mechanical strength, exceptional compressive strength-to-weight ratio (highest up to 0.127 MPa (kg m −3 ) −1 ), and remarkable thermoresistance (T g approximately 380 °C). These high-performance 3D printed polyimide honeycombs and unique synthetic techniques with general structures are potentially useful in fields ranging from automotive to aerospace technologies.

Progress in Aromatic Polyimide Films for Electronic Applications: Preparation, Structure and Properties

“…Aromatic polyimide films have been widely used in many high-tech fields, including electrical insulation [ 15 , 16 , 17 , 18 , 19 , 20 ], electronic packaging [ 21 , 22 ], and aerospace [ 23 , 24 , 25 , 26 , 27 , 28 , 29 , 30 ], due to their excellent combination of thermal, mechanical, and electrical properties. Aromatic polyimide films can be made by casting the polyimide precursor solution–polyamic acid (PAA) on the substrate surface, and then thermally baking it to form a self-supporting gelled film.…”

Additive manufacturing of high‐performance engineering polymers: present and future

“…Others focused their efforts on noncovalently crosslinked PI systems such as DIW‐printable water‐swellable PAAs (Fig. 7(b)) described by Chen and co‐workers 22 . PAA hydrogen bond disruption with triethylamine neutralization produced sufficient ink viscosities for DIW extrusion and ensuing material solidification post‐extrusion.…”

“…3D‐printed PIs: (a) FFF of PI thermosetting filament 21 ; (b) PI honeycomb printed from water with DIW 22 ; (c) UV‐assisted DIW of fully aromatic PI part 26 ; (d) carbonaceous structure formed from the carbonization of a PI part printed through a VP process 27 …”

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.…”

“…The thermal imidization also induces a significant shrinkage of the printed object. Wang et al demonstrated that DIW with a rapid drying apparatus enabled 3D printing of PI from poly(amic acid) ammonium salt (PAAS) hydrogels [21]. Water-soluble PAAS inks can be prepared by mixing polyamic acids and triethylamine (TEA).…”