Effect of Cellulose Nanofibers’ Structure and Incorporation Route in Waterborne Polyurethane–Urea Based Nanocomposite Inks

Abstract

In order to continue the development of inks valid for cold extrusion 3D printing, waterborne, polyurethane–urea (WBPUU) based inks with cellulose nanofibers (CNF), as a rheological modulator, were prepared by two incorporation methods, ex situ and in situ, in which the CNF were added after and during the synthesis process, respectively. Moreover, in order to improve the affinity of the reinforcement with the matrix, modified CNF was also employed. In the ex situ preparation, interactions between CNFs and water prevail over interactions between CNFs and WBPUU nanoparticles, resulting in strong gel-like structures. On the other hand, in situ addition allows the proximity of WBPUU particles and CNF, favoring interactions between both components and allowing the formation of chemical bonds. The fewer amount of CNF/water interactions present in the in situ formulations translates into weaker gel-like structures, with poorer rheological behavior for inks for 3D printing. Stronger gel-like behavior translated into 3D-printed parts with higher precision. However, the direct interactions present between the cellulose and the polyurethane–urea molecules in the in situ preparations, and more so in materials reinforced with carboxylated CNF, result in stronger mechanical properties of the final 3D parts.

Cellulose nanofiber‐incorporated high‐solid siloxane acrylic latex by mini‐emulsion polymerization for hydrophobic coating and wood adhesive

“…In this case, the viscosity of all the siloxane acrylic/CNF nanocomposite latexes were in the range of 214–362 cP. Since the viscosity in polymer latex originates form the interaction between polymer particles and water molecules, such interaction was supposed to be screened by the CNF 38 . Moreover, the lowering of viscosity in nanocomposites might be due to the shear‐thinning during the viscosity analysis 39 .…”

“…Since the viscosity in polymer latex originates form the interaction between polymer particles and water molecules, such interaction was supposed to be screened by the CNF. 38 Moreover, the lowering of viscosity in nanocomposites might be due to the shear-thinning during the viscosity analysis. 39 Therefore, the ex-situ prepared latex at 0.5 wt% CNF showed much lower viscosity (214 cP) compared to the in-situ latex (362 cP) of same CNF concentration.…”

Waterborne Polyurethane-Urea-Based Composite Inks for 3D Printing with Enhanced Properties

“…When inks with poor rheological properties are printed, crushing of the cell wall can take place due to their inability to hold the weight of the top layers . However, this was not the case for the printed composite inks, where, though, elongated pores were observed, there was no trouble in supporting the top layers since no signs of wall crushing could be observed in the micrographies.…”

Impact of physico‐chemical properties of nanocellulose on rheology of aqueous suspensions and its utility in multiple fields: A review

“…Tables 3 and 4 illustrate the work done in the last 2–3 years and clearly highlight the value of NC's distinctive rheological qualities for a wide range of applications. [ 84,120–149 ] Some of the top‐notch characteristics that specifically define the distinctive rheological features of NC suspensions and their ability to act as rheology modifiers in diverse applications include their large water retention/holding potential, remarkable shear thinning behavior, their capabilities to align at high shear rates, thickening impact, and their capacity to form thixotropic frameworks that excellent restoration phenomena. The literature review carried out in the present section makes clear the emerging and cutting‐edge applications of NCs as rheology modulators in the coating [ 117 ] and paint industries [ 118 ] as well as a rheology modulator for cement, [ 119 ] composites, [ 118,120–122 ] electronic devices, [ 122–125 ] cosmetics, foods, [ 117,126–130 ] drilling fluids, [ 122,131 ] and so forth.…”

“…The superior mechanical, shear thinning, and bio-compatible/non-cytotoxic qualities of NC have also piqued researchers' attention in developing 3D bio-printing materials for creating viable living human organs/tissues. [125,128,[132][133][134][135][136][137][138][139] From the tables, it can be concluded that both CNFs and CNCs have remarkable potential as rheology modifiers/modulators in multiple fields; however, the rapid expansion of such applications at the industrial level is constrained by issues related to their complicated structure and the consistency of production in regards to various features of NC that dramatically influence their rheological behavior.…”