CelluForce (Canada)

Cellulose nanocrystals (CNCs) are used as a stabilizing agent in water-based zirconia suspensions at high concentration. The effects of CNC and NaCl concentrations were studied on the stability, adsorption, zeta potential, size, and rheology of slurries. We characterized samples and visualized CNCs at the surface of solid particles by scanning electron microscopy. The results confirm that the adsorption capacity of CNC on the surface of zirconia particles increases as salt concentration increases and causes an increase in the viscoelastic properties and a denser structure on the surface of adsorbent. The presence of counter-ions from the added electrolyte shortens the range of electrostatic repulsion between CNC particles through screening its electrical double layer resulting in more adsorption of adsorbate on the zirconia surface and, thus, provides stabilization.

While the improvement of water-based adhesives with renewable additives is important as industry shifts toward more sustainable practices, a complete understanding of how the compatibility between additives and polymers affects adhesive performance is currently lacking. To elucidate these links, cellulose nanocrystals (CNCs) were first functionalized via surface-initiated atom-transfer radical polymerization with the hydrophobic polymers poly(butyl acrylate) (PBA) and poly(methyl methacrylate) (PMMA) to facilitate their incorporation into latex-based pressure-sensitive adhesives (PSAs). Next, PBA latexes were synthesized using seeded semibatch emulsion polymerization with unmodified or polymer-grafted CNCs added in situ at a loading of 0.5 or 1 phm (parts per hundred parts of monomer). Viscosity and electron microscopy suggested that the polymer-grafted CNCs were incorporated inside or on the latex particles. PSAs containing any CNC type had one or more improved properties (compared to the no-CNC "base case"); CNCs with a low degree of polymerization (DP) grafts exhibited improved tack (up to 2.5-fold higher) and peel strength (up to 6-fold higher) relative to PSAs with unmodified CNCs. The best performing PSA contained the low DP PMMA-grafted CNCs, which is attributed to the higher glass transition temperature and the higher wettability of the PMMA grafts compared to PBA, and the more uniform dispersion of polymer-grafted CNCs throughout the PSA film. In contrast, PSAs containing CNCs with high DP grafts resulted in reduced tack and peel strength (compared to low DP grafts) due to enhanced CNC aggregation. Unfortunately, all PSAs containing polymer-grafted CNCs exhibited inferior shear strength relative to PSAs with unmodified CNCs (and comparable shear strength to the no-CNC "base case"). Collectively, these results provide guidelines for future optimization of more sustainable latex-based PSAs.

Emulsion polymerized latex-based pressure-sensitive adhesives (PSAs) are more environmentally benign because they are synthesized in water but often underperform compared to their solution polymerized counterparts. Studies have shown a simultaneous improvement in the tack, and peel and shear strength of various acrylic PSAs upon the addition of cellulose nanocrystals (CNCs). This work uses atomic force microscopy (AFM) to examine the role of CNCs in (i) the coalescence of hydrophobic 2-ethyl hexyl acrylate/n-butyl acrylate/methyl methacrylate (EHA/BA/MMA) latex films and (ii) as adhesion modifiers over multiple length scales. Thin films with varying solids content and CNC loading were prepared by spin coating. AFM revealed that CNCs lowered the solids content threshold for latex particle coalescence during film formation. This improved the cohesive strength of the films, which was directly reflected in the increased shear strength of the EHA/BA/MMA PSAs with increasing CNC loading. Colloidal probe AFM indicated that the nano-adhesion of thicker continuous latex films increased with CNC loading when measured over small contact areas where the effect of surface roughness was negligible. Conversely, the beneficial effects of the CNCs on macroscopic PSA tack and peel strength were outweighed by the effects of increased surface roughness with increasing CNC loading over larger surface areas. This highlights that CNCs can improve both cohesive and adhesive PSA properties; however, the effects are most pronounced when the CNCs interact favourably with the latex polymer and are uniformly dispersed throughout the adhesive film. This article is part of the theme issue 'Bio-derived and bioinspired sustainable advanced materials for emerging technologies (part 1)'.

The flow behavior of nanocrystalline cellulose (CNC) hydrogels in the presence of a monovalent electrolyte (NaCl) as a function of CNC and salt concentration is explored using a variety of linear and nonlinear rheological tests. We have first observed an apparent “slip yield stress” at small wall shear stress values that is mainly due to the onset of solidlike slippage of the hydrogels before their true yielding and deformation. This flow regime and the “slip yield stress” can be eliminated using a sandpaper of an optimum grit size. At higher wall shear stress values, two yielding points for the CNC/salt network are seen in strain sweep tests due to network disruption and cluster deformation that depend on the concentration of both CNC (1–5 wt. %) and electrolyte (0–100 mM). The first yield stress is due to yielding and flow of clusters, while the second one is due to breakage of clusters to small flocs and individual fibers. These yielding stresses were obtained by a variety of tests including strain amplitude sweep, creep, and steady shear, and their values are compared confirming their existence. Rheo-SALS (small angle light scattering) measurements confirmed structural changes as the scattering patterns change from isotropic to highly anisotropic with an increase of deformation and rate of deformation. Moreover, confocal laser scanning microscopy and polarized microscopy images confirm the gradual breakup of clusters to smaller ones and eventually to nearly individual fibers with an increase in the applied shear strain and rate.

A high-performance semiconductorzinc oxide (ZnO) on melamine formaldehyde-coatedcellulose nanocrystals (MFCNCs) was synthesized and evaluated forits application in smart cosmetics. These ZnO@MFCNC hybrid nanostructureswere evaluated for their in vitro sun protection factor performanceand photocatalytic activity under simulated UV and solar radiation.The photodegradation kinetics of a model pigment (methylene blue)was fitted to the Langmuir–Hinshelwood model. A 4-fold increasein the photocatalytic activity of ZnO@MFCNCs was observed when comparedto pure ZnO. This is associated with (i) increased specific surfacearea provided by the MFCNC template, (ii) confined surface energyand controlled growth of ZnO nanoparticles, and (iii) entrapment ofphotoinduced charge carriers in the pores of the core–shellMFCNC rod, followed by fast promotion of interfacial e-charge transferto the surface of the catalyst. The present study demonstrates howan increase in photocatalytic activity can be engineered without theintroduction of structural defects or band gap tailoring of the semiconductor.The aqueous-based ZnO@MFCNC hybrid system displayed attractive UV-absorptionand photocatalytic characteristics, offering the conversion of thisrenewable and sustainable technology into intelligent cosmetic formulations.

This paper reports on the synthesis of β-cyclodextrin-modified CNC@Fe3O4@SiO2 superparamagnetic nanorods for the removal of two model compounds: procaine hydrochloride and imipramine hydrochloride. During the synthetic process, sustainable natural materials and low-cost chemicals were used, and mild reaction conditions were adopted. TEM and SEM images indicated good dispersion of Fe3O4 nanoparticles with uniform silica coating on CNCs. The thickness of the silica coating was controlled by manipulating the amounts of precursor solution used. TGA data confirmed that the silica coating significantly enhanced the thermal stability of CNCs. The onset decomposition temperature of CNC@Fe3O4@SiO2 hybrids increased by 60 °C compared to pure CNCs. XRD, EDS, and FT-IR analyses confirmed the structure of CNC@Fe3O4@SiO2 and the successful grafting of β-cyclodextrin. The CNC@Fe3O4@SiO2@β-CD hybrids displayed good adsorption toward the model pharmaceutical residues: procaine hydrochloride and imipramine hydrochloride.

All in order: The self-assembly of nanocrystalline cellulose (NCC) with hydrogel precursors leads to nanocomposites with long-range chiral nematic order. The combination of chiral structure and hydrogel swelling behavior gives rise to iridescence that rapidly responds to various stimuli. As a service to our authors and readers, this journal provides supporting information supplied by the authors. Such materials are peer reviewed and may be re-organized for online delivery, but are not copy-edited or typeset. Technical support issues arising from supporting information (other than missing files) should be addressed to the authors. Please note: The publisher is not responsible for the content or functionality of any supporting information supplied by the authors. Any queries (other than missing content) should be directed to the corresponding author for the article.