Bacterial Cellulose as A Building Block for Novel Materials
Jonathan J. Blaker, Koonyang Lee, Anne Dellile, Julasak Juntaro and Alexander Bismarck)
Department of Chemical Engineering, Polymer & Composite Engineering (PaCE) Group, Imperial College London, South Kensington, London, UK
Considering the current environmental, societal and political issues especially in the way we use materials, a pressing need for innovative, sustainable and recyclable materials can be identified. Industry and consumers need to move to greener materials to divert (valuable) materials from waste streams. Materials made form renewable resources are attractive but should perform at the same level (or better) than conventional engineering materials we aim to replace. It will be shown how anisotropic nanometre sized bacterial derived cellulose can be utilised as a building block for new materials namely to produce hierarchical composites, true nanocomposites and renewable highly macroporous nano-composites. Bacterial cellulose offers many attractive properties, its fibrils have diameters between 10 nm to 100 nm with a high crystallinity (~90%) and Young’s modulus similar to glass fibres; it has a highly hydrophilic character due the many hydroxyl groups on the surface, which are useful sites for modification.
The production of cellulose by bacterial fermentation in static and agitated culture will be discussed. Starting from this, we will show that it is possible to produce composites, which combine nano- and micrometre sized reinforcements within a renewable polymeric matrix to obtain hierarchical composite structures. We present a novel route to tailor interfaces in natural fibre reinforced polymers by attaching bacterial cellulose to natural fibre surfaces. Bacterial cellulose was successfully coated on to the fibres by culturing cellulose-producing bacteria, Gluconacetobacter xylinus BPR 2001, in presence of natural fibres. This natural fibre modification method does not affect the fibre tensile properties significantly; however, it results in a massive improvement of the interfacial shear strength, a measure of practical adhesion, between the modified fibres and renewable polymer matrices as well as unidirectional natural fibre reinforced composites with improved tensile strength parallel as well as perpendicular to the fibres.
Besides using bacterial cellulose directly as a reinforcement for (nano)composites we will demonstrate that it can be used if suitably modified to stabilise very concentrated emulsions, which can be used as template to produce very high porosity macroporous cellulose nanocomposites. Emulsion templating has emerged as an effective route for the synthesis of porous polymers with a well-defined morphology since the latter is defined by the structure of the emulsion template. Pickering emulsions are emulsions that are solely stabilised by small particles. We prepared renewable nanocomposite foams from acrylated epoxidized soybean oil (AESO) and hydrophobised bacterial cellulose whiskers. The hydrophilicity of bacterial cellulose whiskers was tailored by esterification of some of the cellulose whisker hydroxyl groups with organic acids. We were able to produce very concentrated Pickering emulsions by combining small amounts of the modified bacterial cellulose (<1 vol.-%) with AESO and water. The photopolymerisation of the continuous monomer phase of the emulsion resulted in green highly porous bacterial cellulose nano-composite polyPickering foams with rather interesting physical and mechanical properties.
Denilson da Silva Perez, Institut Technologique FCBA, and Alain Dufresne, PAGORA Grenoble INP, Grenoble, France
Cellulose is not only the most available natural polymer on earth, but also one of the most interesting, naturally existing, supramolecular structures. From a quite simple chemical structure (two molecules of anhydroglucose composing a cellulobiose unit), an amazing 3D network formed by hydrogen bonds leads to a complex structure formed by nano-domains of crystalline structure co-existing with amorphous cellulose. This crystalline structure is responsible for its intrinsic strength and its relatively high chemical stability. The potentials of exploiting its supramolecular structure from a technological point of view, allied to its availability and renewability, place cellulose as an excellent candidate for the sustainable development of new high-performance and high added-value materials.
However, the main cellulose-based product, paper, is mass-produced and, quite often, single-use oriented (printing and writing or packaging). Cellulose micro- and nano-fibres seem to be one of the ways of better exploiting such potential than the usual cellulosic fibres. In this presentation, the production of micro/nano-fibres is described in two parts: the first part is devoted to the state of the art about the cellulose microfibrils existing in nature. The second part describes the different approaches used for isolate them as cellulose micro/nano-fibrillated or nanocristals (whiskers) as well as the main applications.
Different techniques have been developed in the last years for the production of micro- or nano-fibrillated cellulose. In most cases, chemical or enzymatic pre-treatments are needed in order to weaken the structure of the fibre walls before the isolation of the microfibres. The separation of cellulose microfibrils is performed by different equipments able to disintegrate the ultrastructure of the cell wall while preserving the integrity of the microfibrils. Different “homogenizers” have been used by different European R&D teams and will be commented and compared.
Cellulose nanocristals are different products composed only by the crystalline portion of the microfibrils. They are obtained by acidic hydrolysis using concentrated sulphuric acid and are formed by cellulosic elements measuring few hundreds of nanometers of length depending on the starting raw material.
Scale-up of these technologies for larger production is nowadays under study. The main challenges and difficulties to pass from science to technology will be pointed out and discussed during the presentation.
Mohini Sain, Director, Centre for Biocomposites and Biomaterials Processing, University of Toronto, Canada
Nanotechnology is the manipulation of cellulosic materials measuring 100 nm or less in at least one dimension. Natural fibers have well established their reputation as reinforcement to plastics. Nowadays, a great deal of attention has been paid to cellulosic nanofibrillar structures as components in nanocomposites because of their wide abundance, their renewable and environmentally benign nature, and their outstanding mechanical properties. However, it is difficult to liberate cellulosic nanofibrils efficiently from different source of materials, and the fibrils lack compatibility with a variety of plastic matrices. The water-swellable nature of cellulose, especially in its non-crystalline regions, also can be a concern. In addition, the strong inter- and intra-molecular hydrogen bonding can result in agglomeration or entanglement of the nanofibrils. Once these happen, many of the beneficial properties we are targeting will be lost. The good news is these challenges have been greatly addressed and significant progresses have been achieved. This allows the nanofibrils with their advantages to be used in a wide range of high-tech applications, such as, aerospace building materials, packaging materials, medical scaffolds, and optically transparent films. This presentation will discuss research advancement and commercialization activities of cellulose nanofibre derived from biological matter including bacterial nanocellulose, plant-based cellulose nanocrystals and cellulose nanofibres.
Brian O’Connor, Ph.D., FPInnovations-Paprican Division, Pointe Claire, Quebec, Canada
Jurisdictions worldwide are presently working on various frameworks to deal with the presence of nanomaterials in the market place. In Canada, new materials (including nanomaterials) are controlled under the New Substances Notification Regulations (NSNR) of the Canadian Environmental Protection Act. As part of the program, a risk assessment examining any potential adverse effects of the new substance on the environment or human health, must be conducted. The Canadian pulp and paper industry is presently exploring the use of nanocrystalline cellulose (NCC), prepared through the acid hydrolysis of cellulose in kraft pulp, as a novel additive for a number of different products and applications. While current pilot facilities have the capability of producing kilograms of NCC, full scale facilities are expected within the next few years that would have production capacities of >1 tonne per day. As this work progresses, a key industry mandate is to develop this technology in an environmentally sound manner. As such, environmental and human health assessment studies that are aligned with Canada’s NSNR have been initiated. Our test protocol involved an in-depth battery of acute and chronic whole organism tests as well as cell viability and cellular uptake investigations. To date, this ecotoxicological characterization of NCC has not revealed it to be a substance of environmental concern. Further testing is on-going to assess mammalian toxicity and to examine potential exposure scenarios.
Orlando J. Rojas 1,2), Janne Laine2) and Monika Österberg2)
1) North Carolina State University, Department of Forest Biomaterials, Raleigh, USA
2) Helsinki University of Technology, Department of Forest Products Technology, Finland
In the past decades nanotechnology has been greatly developed but it has been until very recently that the visibility of cellulose as a nano-structured material has emerged to the central stage of technical and scientific discussions. Cellulose is the most abundant biopolymer on earth that offers interesting options as replacement of non-renewables in high-performance applications. Unique attributes of cellulose-derived nanomaterials include their hydrophilicity, biocompatibility, stereoregularity, biodegradability, chemical stability, multichirality and the ability to form superstructures.
In this presentation we will discuss cellulose nanocrystals and nanofibrillar cellulose in the development of light-weight structural materials, composites and coatings. Also, a question to be addressed is whether these emerging nanomaterials present new safety and environmental risks. It would be expected that their utilization would contribute to alleviate (environment, pollution, health, etc.) impacts of current inorganic or mineral nanomaterials. A conclusion that will be drawn is that the biological activity and exposure (location, component, duration) of nanocellulose materials need to be evaluated. It is proposed that key areas as those proposed by NIOSH (Hazard identification, hazard characterization, exposure assessment, risk characterization and management) be addressed through national and international collaborations on cellulose nanotechnology. While large differences in the chemical composition and physical characteristics of nanocellulose are evident one possible scenario is to use, as a benchmark, the documented assessment and regulatory and policy issues applied to other nanomaterials. Given the unique characteristics of cellulose, it is expected that few concerns, if any, are to be developed. However, more important is the implications, to the environment, that the production of such cellulose nanostructures could have. Education and training on the following topics should be the focus of any regulatory effort: nature and extent of hazards and exposure, nature and extent of risk, limitations of controls and protection and health surveillance guidance and impact to the environment during use and disposal of materials used in the manufacture of nanocellulose.