Year: 2019

We report our efforts toward 3D printing of polyether ether ketone (PEEK) at room temperature by direct-ink write technology. The room-temperature extrusion printing method was enabled by a unique formulation comprised of commercial PEEK powder, soluble epoxy-functionalized PEEK (ePEEK), and fenchone. This combination formed a Bingham plastic that could be extruded using a readily available direct-ink write printer. The initial green body specimens were strong enough to be manipulated manually after drying. After printing, thermal processing at 230 °C resulted in crosslinking of the ePEEK components to form a stabilizing network throughout the specimen, which helped to preclude distortion and cracking upon sintering. A final sintering stage was conducted at 380 °C. The final parts were found to have excellent thermal stability and solvent resistance. The Tg of the product specimens was found to be 158 °C, which is 13 °C higher than commercial PEEK as measured by DSC. Moreover, the thermal decomposition temperature was found to be 528 °C, which compares well against commercial molded PEEK samples. Chemical resistance in trifluoroacetic acid and 8 common organic solvents, including CH2Cl2 and toluene, were also investigated and no signs of degradation or weight changes were observed from parts submerged for 1 week in each solvent. Test specimens also displayed desirable mechanical properties, such as a Young’s modulus of 2.5 GPa, which corresponds to 63% of that of commercial PEEK (reported to be 4.0 GPa).

Additive manufacturing (AM) technologies are expanding the boundaries of materials science and providing an exciting forum for interdisciplinary research. The ability to fabricate arbitrarily complex objects has made AM technologies indispensable in personalized healthcare, soft electronics, and renewable energy. At the intersection of AM technologies and materials chemistry are stimuli-responsive polymers, which change their chemical and physical properties in response to specific environmental cues. The responsiveness of these “smart” polymers makes them suitable for AM and provides functionality to the additively manufactured objects. Furthermore, the type and degree of stimulus response of smart polymers can be regulated through precise synthetic design or via incorporation of additives. Herein, we review recently reported stimuli-responsive polymers used in AM, with a focus on the design and chemistry of the polymers. The materials are broadly classified by type of printing, and more specifically classified by type of stimulus response. Finally, we briefly consider existing challenges that stimuli-responsive materials in AM can address in the future.

Production of objects with varied mechanical properties is challenging for current manufacturing methods. Additive manufacturing could make these multimaterial objects possible, but methods able to achieve multimaterial control along all three axes of printing are limited. Here we report a multi-wavelength method of vat photopolymerization that provides chemoselective wavelength-control over material composition utilizing multimaterial actinic spatial control (MASC) during additive manufacturing. The multicomponent photoresins include acrylate- and epoxide-based monomers with corresponding radical and cationic initiators. Under long wavelength (visible) irradiation, preferential curing of acrylate components is observed. Under short wavelength (UV) irradiation, a combination of acrylate and epoxide components are incorporated. This enables production of multimaterial parts containing stiff epoxide networks contrasted against soft hydrogels and organogels. Variation in MASC formulation drastically changes the mechanical properties of printed samples. Samples printed using different MASC formulations have spatially-controlled chemical heterogeneity, mechanical anisotropy, and spatially-controlled swelling that facilitates 4D printing.