Dynamic Nanocellulose Networks for Thermoset-like yet Recyclable Plastics with a High Melt Stiffness and Creep Resistance

New 3D Ink Formulation Comprising a Nanocellulose Aerogel Based on Electrostatic Repulsion and Sol-Gel Transition

New 3D printing aerogel materials are environmentally friendly and could be used in environmental protection and biomedical fields. There is significant research interest in 3D printing cellulose-based aerogels since cellulose materials are biocompatible and are abundant in nature. The gel-like nature of the cellulose water suspension is suitable for 3D printing; however, the complexity and resolution of the geometry of aerogels are quite limited, mainly due to the inks' low viscosity that fails to maintain the integrity of the shape after printing. To address this limitation, a carefully optimized formulation incorporating three key ingredients, i.e., nanofibrils (TEMPO-CNFs), 2,2,6,6-tetramethyl-1-piperidinyloxy modified cellulose nanocrystals (TEMPO-CNC), and sodium carboxymethyl cellulose (CMC), is utilized to enhance the viscosity and structural stability of the ink. This combination of cellulose derivatives utilizes the electrostatic repulsive forces between the negatively charged components to form a stable and uniformly distributed suspension of cellulose materials. Our ink formulations improve printability and shape retention during 3D printing and are optimal for DIW printing. We print by employing an all cellulose-based composite ink using a modified direct ink writing (DIW) 3D printing method, plus an in situ freezing stage to form a layer-by-layer structure, and then follow a freeze-drying process to obtain the well-aligned aerogels. We have investigated the rheological properties of the ink formulation by varying the concentration of these three cellulose materials. The obtained aerogels exhibit highly ordered microstructures in which the micropores are well-aligned along the freezing direction. This study demonstrates a strategy for overcoming the challenges of 3D printing cellulose-based aerogels by formulating a stable composite ink, optimizing its rheological properties, and employing a modified DIW printing process with in situ freezing, resulting in highly ordered, structurally robust aerogels with aligned microporous architectures.

Innovative Applications of Nanocellulose in 3D Printing: A Review

Cellulose nanofibrils (CNFs) and cellulose nanocrystals (CNCs) are nanoscale materials with unique mechanical properties and geometry that attract considerable interest in recent years for a wide range of applications. This review pays special attention to the recent progress of CNFs and CNCs assisted 3D printing in medicine, food, engineering, and architecture fields. Various types of CNFs and CNCs used for 3D printing are summarized. The addition of nanocellulose improves the printability and quality of printed objects in certain cases, leading to greater accuracy and durability. The created functional structures with specific properties have promising applications in various fields such as medicine and food preservation and viscosity enhancement. Finally, this work highlights the transformative potential of nanocellulose-assisted 3D printing to revolutionize a range of fields and the need for continued research and development to overcome current technical challenges.

Biobased Resin for Sustainable Stereolithography: 3D Printed Vegetable Oil Acrylate Reinforced with Ultra-Low Content of Nanocellulose for Fossil Resin Substitution

The use of biobased materials in additive manufacturing is a promising long-term strategy for advancing the polymer industry toward a circular economy and reducing the environmental impact. In commercial 3D printing formulations, there is still a scarcity of efficient biobased polymer resins. This research proposes vegetable oils as biobased components to formulate the stereolithography (SLA) resin. Application of nanocellulose filler, prepared from agricultural waste, remarkably improves the printed material's performance properties. The strong bonding of nanofibrillated celluloses' (NFCs') matrix helps develop a strong interface and produce a polymer nanocomposite with enhanced thermal properties and dynamical mechanical characteristics. The ultra-low NFC content of 0.1-1.0 wt% (0.07-0.71 vol%) was examined in printed samples, with the lowest concentration yielding some of the most promising results. The developed SLA resins showed good printability, and the printing accuracy was not decreased by adding NFC. At the same time, an increase in the resin viscosity with higher filler loading was observed. Resins maintained high transparency in the 500-700 nm spectral region. The glass transition temperature for the 0.71 vol% composition increased by 28°C when compared to the nonreinforced composition. The nanocomposite's stiffness has increased fivefold for the 0.71 vol% composition. The thermal stability of printed compositions was retained after cellulose incorporation, and thermal conductivity was increased by 11%. Strong interfacial interactions were observed between the cellulose and the polymer in the form of hydrogen bonding between hydroxyl and ester groups, which were confirmed by Fourier-transform infrared spectroscopy. This research demonstrates a great potential to use acrylated vegetable oils and nanocellulose fillers as a feedstock to produce high-performance resins for sustainable SLA 3D printing.

Relatively Independent Motion of a Continuous Nanocellulose Network in a Polymer Matrix

Nanocellulose has been studied extensively in polymer composites as it can be employed as biobased reinforcement for synthetic polymers. However, the challenge to optimize the reinforcing component to consume applied energy as much as possible remains. This is related to the reacting force in the test sample and its extensibility. Prolonging the fracture strain of the material is one of the most effective strategies for such a purpose. The investigation on nanocellulose movement in a polymer matrix could shed light on the nanocellulose reinforcing mechanism's fundamental understanding. In this work, a continuous nanocellulose network was used to prepare nanocellulose/polymer composites. Different from using noncontinuous nanofillers, e.g., cellulose nanofibers and nanocrystal, the regenerated cellulose gel network used in this work could move together with the polymer under an axial signal force, serving as an excellent model advantageous in investigating the movement of nanocellulose in the polymer matrix. The deformation of the nanocellulose in the matrix was able to be evaluated by tracking the fracture strain of the materials. A series of chemical cross-linked nanoporous cellulose hydrogels (CCNCGs) were prepared, and their fracture strain increased first and then decreased as the molar ratio of epichlorohydrin (ECH) to the anhydroglucose unit (AGU) of cellulose increased. Two polymer matrices, polycaprolactone (PCL) and polyurethane (PU), were selected to be polymerized in CCNCGs in situ. The fracture strain of CCNCG/PCL and CCNCG/PU nanocomposites in the tensile test showed the same tendency as neat CCNCGs in the hydrated state, regardless of the surrounding environment. The relatively independent motion of the nanocellulose network in the polymer matrix was clearly demonstrated. Possible mechanisms of the nanocellulose's independent motion in the polymer matrix were discussed, implying the potential of independent deformation of the continuous nanocellulose network in the polymer matrix.

Hierarchical ordering in light-triggered additive manufacturing

Herein, recent developments in the 3D printing of materials with structural hierarchy and their future prospects are reviewed. It is shown that increasing the extent of ordering, is essential to access novel properties and functionalities.

Enhanced thermomechanical property of a self-healing polymer via self-assembly of a reversibly cross-linkable block copolymer

Introduction of a self-healable block copolymer increases the mechanical property whilst maintaining self-healing efficiency.