Advanced Materials through Assembly of Nanocelluloses.

TLDR: There is an emerging quest for lightweight materials with excellent mechanical properties and economic production, while still being sustainable and functionalizable, which could form the basis of the future bio economy for energy and material efficiency.

Abstract: There is an emerging quest for lightweight materials with excellent mechanical properties and economic production, while still being sustainable and functionalizable. They could form the basis of the future bioeconomy for energy and material efficiency. Cellulose has long been recognized as an abundant polymer. Modified celluloses were, in fact, among the first polymers used in technical applications; however, they were later replaced by petroleum-based synthetic polymers. Currently, there is a resurgence of interest to utilize renewable resources, where cellulose is foreseen to make again a major impact, this time in the development of advanced materials. This is because of its availability and properties, as well as economic and sustainable production. Among cellulose-based structures, cellulose nanofibrils and nanocrystals display nanoscale lateral dimensions and lengths ranging from nanometers to micrometers. Their excellent mechanical properties are, in part, due to their crystalline assembly via hydrogen bonds. Owing to their abundant surface hydroxyl groups, they can be easily modified with nanoparticles, (bio)polymers, inorganics, or nanocarbons to form functional fibers, films, bulk matter, and porous aerogels and foams. Here, some of the recent progress in the development of advanced materials within this rapidly growing field is reviewed.

Figures

Figure 3. a) Periodate oxidation and reductive amination of cellulose, and (b) TEM-image of n-butylamino-functionalized CNCs. Reproduced with permission.[21] Copyright 2014, American Chemical Society. c) Facilitated assembly of CNF at air/water interface via amphiphilic biomolecules and film transfer on a hydrophobic surface, d) AFM topography image of a self-assembled protein CNF film picked up from air/water interface, and e) AFM topography image of a self-assembled protein CNC film picked up from air/water interface. Reproduced with permission.[87] Copyright 2011, Royal Society of Chemistry.

Figure 19. Scaffolding cells and viruses on nanocelluloses. a) Hematoxylin and eosin staining of 6-week-old teratoma sections (5 mm) of human embryonic stem cells (WA07/WiCell), cultured in CNF hydrogel for 26 days. (A) Cartilage (1), bone (2), epithelial tissue (3), and pigmented cells (4). (B) Neuronal rosettes. (C) Pigmented cells. (D) Blood vessels (indicated by asterisks). (E, F) Muscle (indicated by arrows). (G) Cartilage. (H–J) Endodermal epithelia (indicated by arrows). Scale bars 100 mm. Reproduced with permission.[384] Copyright 2014, Liebert Inc. b) Attachment of the human adipose cells on CNF surgery thread surface. Especially on crosslinked CNF, they exhibit elongated cytoplasmic intermediate filaments (stained red with phalloidin). Nuclei were counterstained in blue. Scale bars 50 mm. Reproduced with permission.[64] Copyright 2016, Elsevier.

Figure 9. Atomic layer deposition (ALD) allows well defined oxide layers on CNF aerogels and optionally a concept for hollow tube aerogels by thermally degrading the CNF template. Reproduced with permission.[179] Copyright 2011, American Chemical Society.

Figure 14. Magnetic materials based on nanocelluloses. a) SEM micrographs of a flexible bacterial cellulose aerogel decorated with cobalt ferrite nanoparticles, allowing magnetic actuation. Reproduced with permission.[175] Copyright 2010, Nature Publishing Group. b)

Figure 8. Nanocellulose-directed self-assemblies. a) Scheme for a CNC-based brushes for a high density of supramolecular binding sites along the colloidal rod. b) Polyacrylic acid brush modified CNC, as resolved using AFM. Reproduced with permission.[76] Copyright 2011, American Chemical Society. c) Poly(acrylic acid)-decorated CNC-brushes direct selfassembly of nanostructures on CNCs in aqueous media, upon interpolyelectrolyte complexation of cationic-nonionic diblock copolymers. Reproduced with permission.[79] Copyright 2016, American Chemical Society. d) Chemical structure of cationic CNC-gPQDMAEMA. e) The cationic CNC-g-PQDMAEMA electrostatically bind to negatively charged viruses, like cowpea chlorotic mottle virus (CCMV), as shown by a TEM micrograph. Reproduced with permission.[78] Copyright 2014, Royal Society of Chemistry. f) Two-step surface modification of CNF followed by SI-ATRP of hydrophobic poly(n-

Figure 21. Tribology of nanocelluloses. a) Friction force as a function of load between the CMC-g-PEG-decorated CNF film and a cellulose sphere at pH 7.3. The slope of the solid lines represents the friction coefficients. Reproduced with permission.[448] Copyright 2013, Royal Society of Chemistry. b) Friction forces between a glass microsphere and a gold substrate (squares), a CNF film (circles), and a CNF film with HA attached (triangles) in PBS pH 7.4. Reproduced with permission.[450] Copyright 2015, Elsevier. c) Macroscopic friction coefficients of as-extracted quince mucilage as a function of sliding speed measured with pinon-disc with a 50 N normal load. The concentration of the mucilage was1 g L-1 (closed circles) and 5 g L-1 (open circles). Reproduced with permission.[452] Copyright 2014, Royal Society of Chemistry.

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Kontturi, Eero; Laaksonen, Päivi; Linder, Markus B.; Nonappa; Gröschel, André H.; Rojas,
Orlando J.; Ikkala, Olli
Advanced Materials through Assembly of Nanocelluloses
Published in:
Advanced Materials
DOI:
10.1002/adma.201703779
Published: 01/06/2018
Document Version
Peer reviewed version
Please cite the original version:
Kontturi, E., Laaksonen, P., Linder, M. B., Nonappa, Gröschel, A. H., Rojas, O. J., & Ikkala, O. (2018). Advanced
Materials through Assembly of Nanocelluloses. Advanced Materials, 30(24), [1703779].
https://doi.org/10.1002/adma.201703779

1
DOI: 10.1002/((please add manuscript number))
Article type: Review
Novel materials through assembly of nanocelluloses
Eero Kontturi, Päivi Laaksonen, Markus Linder, Nonappa, André H. Gröschel, Orlando J.
Rojas, Olli Ikkala*
Prof. E. Kontturi, Prof. P. Laaksonen, Prof. M. Linder, Dr. Nonappa, Prof. O. J. Rojas, Prof.
O. Ikkala
Department of Bioproducts and Biosystems, Aalto University, Espoo FI-00076, Finland
Dr. Nonappa, Prof. O. J. Rojas, Prof. O. Ikkala
Department of Applied Physics, Aalto University, Espoo FI-00076, Finland
Prof. A. Gröschel
University of Duisburg-Essen, Physical Chemistry and Centre for Nanointegration
(CENIDE), DE-45127 Essen, Germany
Prof. P. Laaksonen, Prof. M. Linder, Dr. Nonappa, Prof. O. J. Rojas, Prof. O. Ikkala
Center of Excellence Molecular Engineering of Biosynthetic Hybrid Materials Research,
Aalto University and VTT, Espoo, Finland
E-mail: olli.ikkala@aalto.fi
Keywords: Nanocellulose, cellulose nanofiber, nanofibrillated cellulose, cellulose
nanocrystal, functional
Abstract
There is an emerging quest for lightweight materials with excellent mechanical properties and
economic production, still being sustainable and functionalizable. They could form the basis
of the future bioeconomy for energy and material efficiency. Therein, cellulose has long been
recognized as an abundant polymer. Modified celluloses were, in fact, among the first
polymers used in technical applications, however, later replaced by petroleum-based synthetic
polymers. Currently, however, there is a resurgence in the interest to utilize renewable
resources, where cellulose is foreseen to make again a major impact, this time in the
development of advanced materials. This is because of its availability and properties as well
as, in the future, its economic and sustainable production. Among the cellulose-based
structures, cellulose nanofibrils and nanocrystals display nanoscale lateral dimensions and

2
lengths ranging from nanometers to micrometers. Their excellent mechanical properties are,
in part, due to their crystalline assembly via hydrogen bonds. Owing to their abundant surface
hydroxyl groups, they can be easily functionalized with nanoparticles, (bio)polymers,
inorganics or nanocarbons to form functional fibers, films, bulk matter and porous aerogels
and foams. Here, we review some of the recent progress in the development of advanced
materials within this rapidly growing field.
1. Introduction
Cellulose is the polysaccharide responsible for the structural scaffold of all cells in all
green plants. In wood and plant cell walls, cellulose resides in microfibrils with crystalline
and disordered domains. Within their crystals cellulose chains align in tightly packed
assemblies owing to inter- and intra-chain hydrogen bonding, facilitated by the abundant
hydroxyl groups of cellulose (Figure 1a). At the molecular level, this is closely related to the
rigidity of the polymer chain and the nature of the β-1,4 glycosidic bonds between the
repeating units. The resultant structures span different dimensions and hierarchies, as can be
observed in the cell walls of fibers in plants, including those in trees (Figure 1a).
Deconstruction of fibers from wood or other structures formed by plants can result in
cellulose nanofibrils (CNF) and/or cellulose nanocrystals (CNC).
[1–8]
The latter ones are high-
aspect “whiskers” that are produced from fibers and fibrils after removal of the disordered
cellulose domains by acid hydrolysis. Consequently, highly crystalline nano-objects are
obtained at different yields, depending on the conditions used (Figure 1b). Upon dispersion in
aqueous media, CNCs form characteristic chiral assemblies that, upon drying, reproduce such
structuring except for tighter packing in the absence of water and owing to strong hydrogen
bonding (see a scanning electron, SEM, micrograph of a cross section of such films in Figure
1c).

3
By contrast, the longer and less crystalline CNFs are most typically produced by
strong mechanical shearing of fibers, resulting in micro and nanofibrils with dimensions that
vary depending on the source, pre-treatment and specific process used for deconstruction
(Figure 1d). Therefore, characteristically CNFs form highly percolative structures in water,
with a high tendency to form hydrogels, even at low concentrations. They can display a strong
shear thinning behavior (Figure 1e), which is useful in applications where injectability is
needed.
In addition to plants, some bacteria are able to directly extrude cellulose microfibrils
without the hierarchical order found in plant cell walls. Such nanocellulose species are termed
bacterial cellulose (BC).
[4]
CNF, CNC, BC, as well as rod-like tunicates
[4]
are here generically
referred to as “nanocelluloses”. They possess different morphologies and sizes depending on
the sources and processes, and are excellently suited for the fabrication of advanced materials,
taking advantage of their remarkable physical, mechanical and chemical features. Associated
topics have become widely discussed in the scientific literature in the recent years, and full
coverage of all progress would be a grand challenge. This review focuses on self-assembled,
biomimetic, and directed assembled materials based on nanocelluloses, their interactions with
water, the possibilities for functionalization and fabrication of nano-objects, nanoparticles,
filaments, films and 3D structures, as well as tribology. Such systems facilitate a number of
functional properties and materials, for example, biomimetic toughening, plasmonics,
fluorescence, mechanosensing, actuation, motility, membranes, biosensors and bioactive
systems, flexible piezoelectric, magnetic, and conducting materials, among many others. Even
if we present the state of the art broadly, this review emphasizes the role of nanocelluloses
within such emerging advanced materials concepts, in the view of the present thematic issue
on Finnish research and related collaborations. Therefore, some of the main applications of
nanocelluloses will not be discussed here, such as fiber-reinforced composites, viscosity
modifiers, barrier properties for food packaging, electronics templating, and drug delivery,

4
some of which are already maturing towards technical applications. They have been recently
reviewed in a comprehensive manner.
[9]
Figure 1. Disintegration of wood and plant cell wall material to form nanocelluloses and
some of their most characteristic properties. a) Schematics to disintegrate cellulose
nanocrystals (CNC) and cellulose nanofibers (CNF) from wood and plant cell walls and
chemical formula of cellulose. Modified with permission.
[10]
Copyright 2004, Wiley-VCH. b)
Transmission electron micrograph of CNC nanorods. Reproduced with permission.
[11]
Copyright 2001, Wiley-VCH. c) CNCs typically form chiral assemblies, as shown in a
scanning electron micrograph. Reproduced with permission.
[12]
Copyright 2012, Springer. d)
By contrast, the longer CNFs typically form percolative structures, such as hydrogels.
Reproduced with permission.
[13]
Copyright 2007, American Chemical Society. e) They can be
strongly shear thinning, promoting injection. Reproduced with permission.
[14]
Copyright
2012, Elsevier.
2. Nanocelluloses as colloidal level structural units
2.1 Advanced preparation techniques, fundamental interactions, and modification
Sulfuric acid hydrolysis is overwhelmingly the most widely used preparation technique for
CNCs. It is executed within a fairly small reaction window that efficiently cleaves the
disordered segments in a native microfibril (Figure 1a, b), leaving behind just the crystallites
(i.e., CNCs) and simultaneously introducing sulfate esters on their surface to enhance the
colloidal stability.
[1,15,16]
CNFs, in turn, are generally isolated from the fiber matrix by high
mechanical shear coupled with suitable pretreatments.
[4,17]
A notable case of pretreatment is
the oxidation catalyzed by 2,2,6,6-tetramethylpiperidine-1-oxyl radical (TEMPO) which

Frequently asked questions

Q1. What have the authors contributed in "Novel materials through assembly of nanocelluloses" ?

A review of cellulose-based materials can be found in this paper, where the authors focus on self-assembled, biomimetic, and directed assembled materials based on nanocelluloses, their interactions with water, the possibilities for functionalization and fabrication of nano-objects, nanoparticles, filaments, films and 3D structures. 

Q2. What have the authors stated for future works in "Novel materials through assembly of nanocelluloses" ?

Finally, the celluloses are biologically compatible, which opens possibilities for biological scaffolding. On the other hand, the smaller fibrils in nanopapers pack more densely, thus leading to nanoscale porosity, allowing fundamentally different possibilities for functional membranes. The authors foresee that carefully engineered nanocelluloses and plant based materials could have major impact as components e. g. in sustainable energy sector, high tech clothing, and 3D printed materials. But perhaps the most exciting application potential of nanopapers is related to flexible devices, [ 8 ] which can directly benefit from the tunable optical properties, smooth surface, and smaller thermal expansion coefficient than many synthetic polymers. 

Q3. What is the exciting application potential of nanopapers?

But perhaps the most exciting application potential of nanopapers is related to flexible devices,[8] which can directly benefit from the tunable optical properties, smooth surface, and smaller thermal expansion coefficient than many synthetic polymers. 

Q4. What is the effect of the addition of CNCs on the thermal stability of the system?

The thermal stability of the system was observed to increase with the addition of CNCs owing to a strong interaction of the lignin−PVA matrix with the dispersed CNCs, mainly via hydrogen bonding. 

Q5. What are the main reasons why CNCs have been subjected to more sophisticated modification techniques than?

Good dispersion properties are among the major reasons why CNCs have been subjected to targeted self-assembly and more sophisticated modification techniques more than CNFs which tend to gel already at low concentrations. 

Q6. Why is it important to use CBMs to drive self-assembly and?

Due to their well-defined structures and supramolecular interactions, it is logical toexplore how proteins can be used to drive self-assembly and interactions of nanocellulose. 

Q7. What is the role of amorphous polymer chains in the degradation of CNFs?

Subsequent grafting of polymer chains may cause swelling of the amorphous domains during brush growth in turn destabilizing the CNF backbone followed by CNF degradation into small fragments. 

Q8. What is the importance of polymer grafting on nanocellulose surfaces?

Polymer grafting on nanocellulose surfaces has also received significant attention,[70–75] being particularly important for guiding self-assembly and tuning the compatibility of nanocelluloses with other materials. 

Q9. What are the main reasons why the authors think nanocelluloses could be used in the future?

The authors foresee that carefully engineered nanocelluloses and plant based materials could have major impact as components e.g. in sustainable energy sector, high tech clothing, and 3D printed materials. 

Q10. What are the potential applications of nanopapers?

Among the potential applications, the authors foresee that nanopaper device substrates for flexible transparent devices are particularly promising. 

Q11. Why is the use of materials properties of proteins in combination with cellulose motivated?

The use of materials properties of proteins in combination with cellulose is motivated by the interface compatibility or due to exploring the promising mechanical properties of proteins. 

Q12. How much was the reduction in tensile strength of PVA mats?

As they were conditioned from low (10% RH) to high relative humidity (70% RH), the reduction in tensile strength of neat polyvinyl alcohol (PVA) fiber mats was found to be about 80%,from 1.5 to 0.4 MPa. 

Q13. What is the way to combine functions of structural proteins?

An attractive approach is to combine functions of structural proteins such as resilin within a scaffold of nanocellulose in order to achieve an elastic interconnection between the cellulose components. 

Q14. What surface chemical modification techniques have been applied to non-polar matrices?

In the case of incorporation of hydrophilic nanocelluloses to non-polar matrices, several surface chemical modification techniques have been applied. 

Q15. What is the effect of lipophilic groups on the nanocellulose surface?

More recently, aprotic systems have been applied to directly attach hydrophobic polymers by adsorption on nanocellulose surfaces.[85]Amphiphilic CNC were achieved by introducing lipophilic groups to the reducing endof the cellulose nanocrystal via consequent regioselective periodate oxidation and reductive amination (Figure 3a).[21] 

Q16. What is the effect of asymmetric thiolation on the CNC rods?

Due to asymmetric thiolation and significant coulombic repulsion, the endtethered CNC rods, which are preferentially oriented upright in aqueous media, are reminiscent of biological cilia like structures (Figure 7d). 

Q17. What is the role of polycationic brushes in the development of breast cancer cells?

Other polycationic brushes such as poly(N-(2-aminoethylmethacrylamide) and poly(2-aminoethylmethacrylate) have been investigated for their cytotoxicity in mouse cells and human breast cancer cells. 

Q18. What is the effect of crosslinking on the wet strength of chitosan?

in the case of neutral chitosan at high pH, crosslinking is effective in increasing significantly the wet strength, Figure 5a.[101] 

Q19. What is the problem with re-dispersion of CNCs in water?

Under high mechanical forces and suitable surface charges, dried CNCs can be re-dispersed in water but this not self-evident in every case and can often be incomplete.[39]