Nathan Grishkewich

Functionalization of cellulose nanocrystals for advanced applications

Replacing the widespread use of petroleum-derived non-biodegradable materials with green and sustainable materials is a pressing challenge that is gaining increasing attention by the scientific community. One such system is cellulose nanocrystal (CNC) derived from acid hydrolysis of cellulosic materials, such as plants, tunicates and agriculture biomass. The utilization of colloidal CNCs can aid in the reduction of carbon dioxide that is responsible for global warming and climate change. CNCs are excellent candidates for the design and development of functional nanomaterials in many applications due to several attractive features, such as high surface area, hydroxyl groups for functionalization, colloidal stability, low toxicity, chirality and mechanical strength. Several large scale manufacturing facilities have been commissioned to produce CNCs of up to 1000kg/day, and this has generated increasing interests in both academic and industrial laboratories. In this feature article, we will describe the recent development of functionalized cellulose nanocrystals for several important applications in ours and other laboratories. We will highlight some challenges and offer perspectives on the potentials of these sustainable nanomaterials.

Continuous flow adsorption of methylene blue by cellulose nanocrystal-alginate hydrogel beads in fixed bed columns

The adsorption behavior of methylene blue by cellulose nanocrystal-alginate (CNC-ALG) hydrogel beads in a fixed bed column was studied by varying the initial dye concentrations, bed depths and flow rates. An unusual phenomenon was observed in the early phase of the adsorption, and the phenomenon was elucidated by varying other critical design parameters, such as the flow direction, diameter of column and composition of adsorbent. The swelling and shrinkage of hydrogel beads during the adsorption was responsible for the anomalous concentration versus time profile of the adsorption process. The maximum adsorption capacity of the column was 255.5mg/g, which is in agreement with the batch study determined from the Langmuir adsorption isotherm. A comprehensive understanding on the adsorption mechanism of CNC-ALG hydrogel beads during the early stages of adsorption was derived from this study.

Synthesis and characterization of pH-responsive and fluorescent poly (amidoamine) dendrimer-grafted cellulose nanocrystals

Poly (amidoamine) (PAMAM) dendrimers have found promising applications in biomedicine and in the encapsulation of inorganic nanoparticles. G6 PAMAM dendrimer-grafted cellulose nanocrystals (CNC-PAMAM) were prepared via a simple carbodiimide-mediated amidation process and they displayed pH-responsive and fluorescent characteristics as confirmed by zeta potential, transmittance, isothermal titration calorimetry (ITC), and fluorescence spectroscopy. Stable aqueous dispersions of CNC-PAMAM were obtained at pH⩽4 and pH⩾10, driven by electrostatic repulsion from positive charge and negative charge respectively. However, large aggregates were formed at pH values from 5 to 9 due to electrostatic attraction. In addition, strong blue fluorescent emission was observed, and the fluorescent behaviour of CNC-PAMAM was influenced by the formation of aggregates. The pH-responsive and fluorescent properties of CNC-PAMAM may be suitable for their applications in pH-responsive nanodevices, fluorescent-based pH sensors, optical markers, and nanoreactors for the encapsulation of inorganic nanoparticles.

Swelling and shear viscosity of stimuli-responsive colloidal systems

In this review, we describe the recent progress in the synthesis of responsive micro/nanogels and their swelling properties, with specific focus on the shear viscosity and the scaling relationship of stimuli-responsive micro/nanogel systems. We highlight the recent progress in the scaling models that provide important information on the swelling and rheological properties of responsive micro/nanogels, which are especially relevant in the applications of these soft nanostructures. Future perspectives on the applications of soft nanostructures are outlined and discussed.

Cellulose nanocrystal-poly(oligo(ethylene glycol) methacrylate) brushes with tunable LCSTs.

This paper reports on the synthesis of poly(oligoethylene glycol) methyl ether acrylate (POEGMA) grafted cellulose nanocrystals (CNCs) via surface initiated atom transfer radical polymerization (ATRP). An ATRP initiator (α-Bromoisobutyryl bromide) was covalently bonded to the surface of CNCs, followed by copolymerizing di(ethylene glycol) methyl ether methacrylate (MEO2MA) and oligoethylene glycol methyl ether methacrylate (OEGMA300) monomers from the surface using Cu(I)Br/2,2-dipyridal. Multiple POEGMA-g-CNC systems with varying MEO2MA/OEGMA300 content were synthesized, and they displayed a range of lower critical solution temperatures (LCSTs) in aqueous medium. μDSC endotherms and microstructural analysis indicated the collapse of POEGMA chains, followed by the aggregation of nanoparticles above their LCSTs. Cloud point measurements demonstrated a hysteresis in the heating and cooling of the POEGMA-g-CNC systems. It was found that the LCST of the nanoparticles could be tuned to between 23.8 to 63.8°C by adjusting the OEGMA300 content of the POEGMA brushes.

Cellulose nanomaterials: promising sustainable nanomaterials for application in water/wastewater treatment processes

In recent years, sustainable nanomaterials, such as cellulose nanocrystals (CNCs) and cellulose nanofibrils (CNFs), jointly referred to as cellulose nanomaterials (CNs), have been explored for application in water/wastewater treatment processes. Unique properties of CNs coupled with the global quest to develop low carbon footprint alternatives as aids for water treatment processes have been the driving force for the increasing interest among researchers worldwide. There are several reviews that describe the chemistry and modification of CNs; however, a comprehensive review on the potential application of CNs in water/wastewater treatment processes is scarce. Thus, this review provides a detailed overview of pristine, surface-functionalized CNs and CN-incorporated nanocomposites for applications in various water/wastewater treatment processes, such as sorption, membrane filtration, and flocculation. The latest advances and developments on other processes using CNs, such as catalytic degradation and disinfection, are also discussed. The mechanism responsible for the performance of CN-based systems in all these water treatment processes is also elucidated. The key challenges and knowledge gaps that limit the practical application of CNs in water treatment processes are examined, which offer appropriate perspectives to researchers working in this field.

Cross-linked Pluronic-g-Polyacrylic acid microgel system for the controlled release of doxorubicin in pharmaceutical formulations

&NA; The binding of doxorubicin (DOX) to cross‐linked Pluronic F127‐g‐PAA‐EGDMA and L92‐g‐PAA‐EGDMA microgels at different alpha (&agr;) and salt concentrations was investigated using isothermal titration calorimetric (ITC), optical and scanning electron microscopic techniques (SEM). We seek to elucidate the mechanisms of interaction and the release of DOX from cross‐linked microgels composed of Pluronic and poly(acrylic acid). The ITC results indicated a high binding affinity of DOX to the microgel, which is a function of salt concentrations due to the impact of electrostatic shielding on the DOX‐binding process. Applying the polyelectrolyte theory allows the decoupling of the Gibbs free energy of binding that describes the role of non‐electrostatic interaction of DOX and the microgel. The presence of DOX within the microgel resulted in the collapse of the microgel due to charge shielding, &pgr;–&pgr; interactions and self‐association of polymer‐bound DOX molecules. The diffusion of DOX through the microgel is controlled by the dissociation of COO−/DOX+ coupling pairs. Graphical abstract Figure. No caption available. HighlightspH responsive microgels were developed to encapsulate doxorubicin.Mechanism on the encapsulation and release was elucidated.The release of DOX can be controlled by pH.