New horizons for nanocellulose technology

09:00-09:05 Welcome by the Royal Society

09:05-09:45 Development of Advanced Lignocellulosic Bioproducts from Multiphase Systems

Professor Orlando Rojas, Department of Bioproducts and Biosystems, Aalto University, Finland

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09:45-10:30 Hybrid Superlattice Structures From Nanocellulose and Inorganic Materials

Dr Docent Tekla Tammelin, VTT Technical Research Centre, Finland

Abstract

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.

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10:30-11:00 Coffee break

11:00-11:45 Order and Gelation of Cellulose Nanocrystal Suspensions

Professor Derek Gray, McGill University, Canada

Abstract

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.

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11:45-12:30 Cellulose Nanocrystals in Pickering Emulsions and Polymer Systems

Dr Wadood Y. Hamad, FPInnovations and University of British Columbia, Canada

Abstract

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.

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13:30-14:15 Cellulose Nanomaterials as Green Nanoreinforcements for Polymer Nanocomposites

Professor Alain Dufresne, INP Pagora, Grenoble Institute of Technology, France

Abstract

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.

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14:15-15:00 Optimizing Cellulose Nanocrystal Surface Chemistry to Enhance Colloidal and Thermal Stability

Professor Emily Cranston, Department of Chemical Engineering, McMaster University, Canada

Abstract

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

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15:00-15:30 Tea break

15:30-16:15 Watching Paper Dry: Making Photonic Structures form Cellulose Nanocrystals

Professor Mark MacLachlan, Department of Chemistry, University of British Columbia, Canada

Abstract

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.

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16:15-17:00 Better together: Synergy in Nanocellulose Blends

Professor Alexander Bismarck, University of Vienna and Department of Chemical Engineering, Imperial College London, UK

Abstract

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.

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09:00-09:45 Folding of Xylan onto Cellulose Fibrils in Plant Cell Walls Revealed by Solid-state NMR

Professor Paul Dupree, Department of Biochemistry, University of Cambridge, UK

Abstract

Exploitation of plant lignocellulosic biomass is hampered by our ignorance of the molecular basis for its properties such as strength and digestibility. Xylan, the most prevalent non-cellulosic polysaccharide, binds to cellulose microfibrils. The nature of this interaction remains unclear, despite its importance. Here it is shown that the majority of xylan, which forms a 3-fold helical screw in solution, flattens into a 2-fold helical screw ribbon to bind intimately to cellulose microfibrils in the cell wall. 13C solid-state magic angle spinning NMR spectroscopy, supported by in silico predictions of chemical shifts, shows both 2- and 3-fold screw xylan conformations are present in fresh Arabidopsis stems. The 2-fold screw xylan is spatially close to cellulose, and has similar rigidity to the cellulose microfibrils, but reverts to the 3-fold screw conformation in the cellulose-deficient irx3 mutant. The discovery that induced polysaccharide conformation underlies cell wall assembly provides new principles to understand biomass properties. The cell wall structure suggests strategies for improved extraction of nanocellulose from wood.

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09:45-10:30 Structure of Native Cellulose Microfibrils, the Starting Point for Nanocellulose Production

Dr Michael C Jarvis, School of Chemistry, Glasgow University and IBioIC, Strathclyde University, Glasgow

Abstract

There is an emerging consensus that higher plants synthesise cellulose microfibrils that initially comprise 18 chains. However the mean number of chains per microfibril in situ is usually greater than 18, sometimes much greater. Microfibrils from woody tissues of conifers, grasses and dicotyledonous plants, and from organs like cotton hairs, all differ in detailed structure and mean diameter. Diameters increase further when aggregated microfibrils are isolated. Because surface chains differ, the tensile properties of the cellulose may be augmented by increasing microfibril diameter.

Association of microfibrils with anionic polysaccharides in primary cell walls and mucilages leads to in vivo mechanisms of disaggregation that may be relevant to the preparation of nanofibrillar cellulose products. For the preparation of nanocrystalline celluloses, the key issue is the nature and axial spacing of disordered domains at which axial scission can be initiated. These disordered domains do not, as has often been suggested, take the form of large blocks occupying much of the length of the microfibril. They are more likely to be located at chain ends or at places where the microfibril has been mechanically damaged, but their structure and the reasons for their sensitivity to acid hydrolysis need better characterisation.

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10:30-11:00 Coffee break

11:00-11:45 Residual Wood Polymers Facilitate Compounding of Microfibrillated Cellulose with Non-polar Media

Professor Wolfgang Gindl-Altmutter, Institute of Wood Technology and Renewable Materials, BOKU-Vienna, Austria

Abstract

Microfibrillated cellulose is a fascinating material with an obvious potential for composite reinforcement due to its excellent mechanics together with high specific surface area. However, in order to utilise this potential, commercially viable solutions to important technological challenges have to be found. Notably, the distinct hydrophilicity of microfibrillated cellulose prevents efficient drying without loss in specific surface area, necessitating storage and processing in wet condition. This greatly hinders compounding with important technical polymers immiscible with water. Differently from cellulose, the chemistry of the major wood polymers lignin and hemicellulose is much more diverse in terms of functional groups. Specifically, the aromatic moieties present in lignin and acetyl groups in hemicellulose provide distinctly less polar surface-chemical functionality compared to hydroxyl groups, which dominate the surface chemical character of cellulose. Experimental evidence demonstrates that the surface-chemical functionalities of lignin and hemicellulose can be utilised to the benefit dispersion of microfibrillated cellulose in non-polar media and promote interfacial adhesion between fibrils and polymer matrices. It should be noted that lignin and hemicellulose do not provide hydrophobicity to a comparable extent as achievable by chemical modification of cellulose, but may be a cost-efficient alternative to modification in a number of specific cases.

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11:45-12:30 Molecular Interactions at Play in Nanocellulose Assembly

Dr Yoshiharu Nishiyama, CERMAV-CNRS, France

Abstract

Cellulose is often described as strong, stiff and difficult to process, in contrast to commodity plastics. Hydrogen bonding and hydrophobic interactions are often mentioned in the literature as the origin of these particular behaviors, but the description remains qualitative. How can we quantify in a simple way the contribution of different types of molecular interactions in the context of material properties and processing? The crystal structure analysis, molecular modeling including quantum mechanical approaches, thermodynamics data of analogue molecules give clues to the dissection of the different types of energy contribution. Hydroxyl groups of cellulose form hydrogen bond comparable to other simple alcohols. Trends of heat of vaporization of alkyl-alcohols and alkanes suggests a stabilization by such hydroxyl-group hydrogen bonding to be of the order of 24 kJ/mol, while London dispersion force contributes to about 0.41 kJ/mol/dalton. Simple arithmetic gives striking agreement with experimental enthalpy of sublimation of small sugars, where the major cohesive energy comes from hydrogen bonds. For cellulose, due to the reduced number of hydroxyl groups, London dispersion force would be the major component in intermolecular cohesion. The role of multipolar interactions and hydrophobic interactions will be also discussed.

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13:30-14:15 Understanding the Structure of the Plant Cellulose Synthase Complex and its Relationship to Cellulose Microfibril Structure

Professor Simon Turner, School of Biological Science, University of Manchester, UK

Abstract

In higher plants, cellulose is synthesised at the plasma membrane by a very large membrane-bound protein complex. This complex is driven through the plane of the plasma membrane while catalysing the formation of 18 to 24 individual cellulose chains that bind together to form a cellulose microfibril. The cellulose synthase complex requires three different, but related, types of catalytic subunits. The organisation of these catalytic subunits, known as CESA proteins within the cellulose synthase complex is critical for the formation of the cellulose microfibril produced. Analysis suggests that some of catalytic subunits are more important for the assembly of complex while others are more critical for producing a cellulose microfibril. While much of the focus has been on cellulose synthesis in higher plants, a wide variety of different types of cellulose synthase complexes exist within the plant kingdom. The availability of extensive genome sequence information suggests that it may now be timely to consider engineering plants to make different kinds of cellulose and to determine what effect this may have on the properties and utility of the cellulose produced.

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14:15-15:00 Wood nanotechnology based on porous nanocellulosic templates

Professor Lars Bergland, KTH Royal Institute of Technology, Sweden

Abstract

Wood modification is a large technical area including salt impregnation, coating and adhesive technologies as well polymer-impregnated wood. Inspired by recent progress in the area of nano-cellulose materials, we are extending these approaches to build a wood nanotechnology platform. In wood cell wall bulking methodologies, polymers with affinity to wood become located inside the cell wall. New methodologies make it possible to bring in other polymers, inorganic nanoparticles and carry out chemical functionalization in the cell wall (Burgert et al 2015). The property range for modified wood can then be extended through tailoring of the cell wall structure at molecular and nanoscale levels. Methods for increasing the pore space in the wood cell wall are discussed, and related to results in terms of morphology and specific surface area. Examples are provided, where the pore space is modified by the use of inorganic nanoparticles diffusing into the pores. This alters thermal degradation behavior, and improves fire retardancy. Additional modification approaches are discussed, including methods to prepare optically functional materials. Functions include combinations of load-bearing properties, diffused luminescence and lasing properties of wood. The implications for other functionalities will be discussed as well as the potential for large scale applications.

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15:00-15:30 Tea break

15:30-16:15 Bioinspired Self-assembled CNC Blends for Superior Mechanical Properties

Dr Jeffrey W. Gilman, National Institute of Standards and Technology (NIST), USA

Abstract

We report the fabrication of pristine, tough cholesteric cellulose nanocrystals (CNC) films with varying ratios of short (w-CNC) and long aspect ratio (t-CNC) CNCs using evaporation induced self-assembly (EISA). The effect of the addition of the long aspect ratio t-CNCs on the structure of the w-CNCs is studied using SEM, TEM imaging, UV-Vis-NIR chiral dichroism (CD) and reflectance spectra. We find that the helical pitch of the cholesteric films can be controlled in a non-linear fashion, between 700 and 220 nm, by tuning the t-CNC content. In agreement literature results, the neat w CNC films were found to be brittle, inflexible and difficult to handle. However, the addition of even a small percentage (1%) of t-CNCs was found to cause significant improvement in the films properties. The in-plane mechanical properties of these films were found to improve non-linearly with t-CNC content, with the modulus, tensile strength and strain to failure nearly doubling with 10 % of t-CNCs. Overall toughness enhancement of 8 times were seen. These films reflect some of the highest properties reported for pristine CNC-Bouligand films. We propose that these films as excellent starting materials for Bouligand nanocomposite fabrication through template filling, or one-step EISA processing.

16:15-17:00 Panel discussion: future directions

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