Improving UV Curing in Organosolv Lignin-Containing Photopolymers for Stereolithography by Reduction and Acylation

Abstract

Despite recent successes in incorporating lignin into photoactive resins, lignin photo-properties can be detrimental to its application in UV-curable photopolymers, especially in specialized engineered resins for use in stereolithography printing. We report on chemical modification techniques employed to reduce UV absorption by lignin and the resulting mechanical, thermal, and cure properties of these modified lignin materials. Lignin was modified using reduction and acylation reactions and incorporated into a 3D printable resin formulation. UV–Vis absorption at the 3D printing range of 405 nm was reduced in all modified lignins compared to the unmodified sample by 25% to ≥ 60%. Resins made with the modified lignins showed an increase in stiffness and strength with lower thermal stability. Studying these techniques is an important step in developing lignin for use in UV-curing applications and further the effort to valorize lignin towards commercial use.

Lignin as a High-Value Bioaditive in 3D-DLP Printable Acrylic Resins and Polyaniline Conductive Composite

“…For lignin contents ≤2 wt.% the critical exposure ( E c ) to induce polymerization remains actually unchanged, whereas it doubles its value for 3 wt.% lignin. Notwithstanding, the E c values are in the same range or lower compared to those reported for commercial nonconductive resins [ 25 , 28 , 36 ]. The D p of LG1 (58 µm) lies within the low range of commercial resins without conductive fillers tested by Bennet et al (53–568 µm), whereas D p values decreased around 31% for 2 and 3 wt.% lignin contents [ 36 ].…”

“…The viscosity values of all liquid formulations as a function of shear rate and Lignin amount at room temperature are depicted in Figure S1 , whereas the viscosities at 1 s −1 are compiled in Table 1 . It is obvious that the higher the lignin content, the greater the viscosity of the formulations at 1 s −1 , since the presence of lignin limits the mobility of the polymer chains [ 25 , 35 ]. Increased lignin content (0–4 wt.…”

“…This is an expected behavior, partly due to the absorption of UV light, which competes with the light adsorption of the photoinitiator. The role of lignin UV blocker is due to the presence of UV-active functional groups such as C=O and aromatic rings [ 7 , 25 ]. The decrease in curing kinetics observed for lignin composites could also be related to the reported role of the phenolic groups of lignin as free radical scavengers and antioxidants [ 42 , 43 , 44 ].…”

“…In this context, future electronic devices could provide great benefits from the synergistic combination of AM techniques and green chemistry, delivering a wider range of 3D printed polymer composites with improved electrochemical performance and enhanced physicochemical properties. Nowadays, although lignin has been employed in a variety of 3D printing applications, its use in vat polymerization is still scarce [ 7 , 25 ].…”

Characterizations of Polymer Gears Fabricated by Differential Pressure Vacuum Casting and Fused Deposition Modeling

“…The polymer gear has some distinct advantages compared to the metal gear, including low weight, quietness of operation, and no need for external lubrication [ 1 ], and has been widely used in the automotive industry and consumer electronics. Additive manufacturing (AM) [ 2 , 3 ] has been defined as the process of building physical models by joining materials layer upon layer using computer numerical control data. The application of AM processes has increased in fabricating physical models across various industries because of its capability in manufacturing functional parts with complex geometries.…”