New horizons for nanocellulose technology

Hybrid materials containing nanoscaled cellulosic constituents can be an attractive choice for example for thermoelectric energy harvesting, since it is possible to fabricate layered superlattice structures and inorganic multilayer structures by incorporating various grades of nanocellulosic materials. The aim of the presentation is to introduce approaches to construct both type of the structures (superlattice and inorganic multilayer structures) using various nanoscaled cellulosic materials such as cellulose nanocrystals (CNC), cellulose nanofibrils (CNF) and TEMPO-oxidized CNF with Earth-abundant inorganic components. Ultrathin cellulose layers have been prepared using spin coating or dip coating whereas inorganic layers have been constructed using atomic layer deposition (ALD) method. Superlattice structures with alternating layers of various nanocellulosic materials and ZnO showed that resistivity and thermal conductivity of such structures can be manipulated by the cellulosic thin layer nanoarchitecture. Inorganic multilayer structures consisting of stacks of SiO2/Al2O3 with individual layer thickness values of 3.7 nm and 2.6 nm for SiO2 and Al2O3, respectively. Such multilayer structure fabricated on self-standing films of cellulose nanofibrils (CNF) efficiently blocked the diffusion of the oxygen molecules through the CNF film structure. Moreover, simultaneously developed low temperature ALD processes for ZnO, SiO2 and Al2O3 enabled the coating of thermally sensitive biomaterials by inorganic thin films.

Cellulose nanocrystals (CNC) are polydisperse rod-shaped particles of crystalline cellulose I, typically prepared by sulfuric acid hydrolysis of natural cellulose fibres to give aqueous colloidal suspensions stabilized by sulfate half-ester groups. Sufficiently dilute suspensions are isotropic fluids, but as the concentration of CNC in water is increased, a critical concentration is reached where a spontaneously ordered phase is observed. The (equilibrium) phase separation of the ordered chiral nematic phase is in competition with a tendency of the CNC suspension to form a gel. Qualitatively, factors that reduce the stability of the CNC suspension favour the onset of gelation. The chiral nematic structure is preserved, at least partially, when the suspension dries. Solid chiral nematic films of cellulose are of interest for their optical and templating properties, but the preparation of the films requires improvement. The processes that govern the formation of solid chiral nematic films from CNC suspensions include phase separation, gelation and also the effects of shear on CNC orientation during evaporation. Some insight into these processes is provided by polarized light microscopy, which indicates that the relaxation of shear-induced orientation to give a chiral nematic structure may occur via an intermediate twist-bend state.

Cellulose nanocrystals (CNCs), obtained by strong sulphuric acid hydrolysis of cellulosic biomass, are surface-charged, nano-scaled particles capable of self-assembly. CNCs possess unique optical and electromagnetic properties originating from their ability to form chiral nematic organisation under the influence of the Earth’s magnet. Dr Hamad’s presentation will focus on the application of CNCs to stabilise Pickering emulsions, as well as functionalising CNC surfaces to render them suitable for applications in polymer nanocomposites and flexible electronics.

The effects of CNC concentration and type of oil phase on the properties of medium- and high-internal phase Pickering emulsions have been studies, and details of the stabilisation mechanism will be discussed. The maximum oil phase volume that can be stabilised by CNCs is 87% when the CNC concentration is 0.6 wt. % and slightly decreases to 83% when CNC concentration is increased to 1.2 wt. % or higher.

Dr Hamad will also present in situ polymerisation strategies, in the presence of CNCs, for controlling the crystallinity and plasticity in thermoplastic polymer, as well as methods for tailoring cross-linking density and toughness in thermoset resins. He will further explore use of CNCs, along with conjugated polymers, to develop flexible, organic, semiconducting materials.

Unexpected and attractive properties can be observed when decreasing the size of a material down to the nanoscale. Cellulose is no exception to the rule. In addition, the highly reactive surface of cellulose resulting from the high density of hydroxyl groups is exacerbated at this scale. Different forms of cellulose nanomaterials, resulting from a top-down deconstructing strategy (cellulose nanocrystals, cellulose nanofibrils) or bottom-up strategy (bacterial cellulose) are potentially useful for a large number of industrial applications. These include the paper and cardboard industry, use as reinforcing filler in polymer nanocomposites, basis for low-density foams, additive in adhesives and paints, as well as a wide variety of filtration, electronic, food, hygiene, cosmetic, and medical products. However, it is as a biobased reinforcing nanofiller that they have attracted significant interest during the last 20 years. Impressive mechanical properties can be obtained for these materials. They obviously depend on the type of nanomaterial used, but the crucial point is the processing technique. As for any nanoparticle, the main issue is related to their homogeneous dispersion within the polymeric matrix. An important challenge consists in the preparation of polymer nanocomposites using industrial melt processing techniques, avoiding the liquid medium methods.

Cellulose nanocrystals (CNCs) are rod shaped nanoparticles extracted from natural cellulose sources through a hydrolysis procedure which most commonly uses sulfuric acid. Recently, other acids have been used in the hydrolysis procedure to modify CNC properties. CNCs hydrolysed with phosphoric acid have been shown to have increased thermal stability; however, this new procedure has not been optimized. Phosphoric acid-hydrolyzed CNCs (P-CNCs) have low surface charge, causing them to aggregate in suspension and even more so after heat treatment. A design of experiments approach was completed to study the effects of hydrolysis parameters on P-CNC size, aspect ratio, crystallinity, thermal stability and colloidal stability. Additionally, hydrolyses were performed with both sulfuric and phosphoric acid to yield CNCs with a combination of charged surface groups. It was found that the hydrolysis conditions have significant effects on several CNC properties, most notably on colloidal stability and aspect ratio. This study proposes facile methods (and small tweaks to industrial production protocols) for controlling key properties which are crucial for high temperature/pressure applications of CNCs, such as oil and gas drilling and completion fluids.

Anticipated Paper Title: Design of Experiments Optimization of Cellulose Nanocrystals Produced through Phosphoric Acid Hydrolysis for Enhanced Colloidal and Thermal Stability

Cellulose nanocrystals (CNCs) obtained from paper or cotton are of great interest for many applications. In water, CNCs spontaneously form a chiral nematic lyotropic liquid crystalline phase, which can be preserved in dried films. The helicoidal structural organization of the CNCs in these films resembles the Bouligand structure of chitin found in crabs and other arthropods, and leads the films to be iridescent.
In 2010, Shopsowitz, Qi, Hamad, and MacLachlan reported that this liquid crystalline phase of CNCs can be used to template mesoporous silica with chiral nematic order, and they have since been able to transfer the supramolecular organization of CNCs to diverse other materials, including titania, polymers, and hydrogels. In this talk, Prof. MacLachlan will discuss his team’s recent progress to use CNCs as a template for the construction of new materials. He will discuss the use of hydrogels as a means to study the liquid crystallinity and to form spheres with chiral nematic order.

Cellulose nanopapers have gained significant attention in the recent years as large-scale reinforcement for high-loading cellulose composites, substrates for printed electronics and filter nanopapers for water treatment applications. The mechanical properties of nanopapers are of fundamental importance for all these applications. Cellulose nanopapers can simply be prepared by filtration of nanocellulose. It was already demonstrated that the mechanical properties of cellulose nanopapers can be tailored by the fineness of the fibrils used or by modifying nanocellulose fibrils for instance by polymer adsorption but nanocellulose blends remain underexplored. We show that the mechanical and physical properties of nanopapers can be tuned by creating hierarchical structures in nanopapers by blending various grades of nanocellulose, i.e. bacterial cellulose, cellulose nanofibrils extracted from bagasse by mechanical and chemical pre-treatments. We found that nanopapers made from blends of two or even more nanocellulose grades show synergistic effects resulting in improved stiffness, strength, ductility and toughness and physical properties.