2010_MRS_Berglund.pdf

See discussions, stats, and author profiles for this publication at: https://www.researchgate.net/publication/287695058
Research and developments on cellulose-based nanocomposites
Article · January 2010
CITATIONS
3
READS
282
3 authors:
Some of the authors of this publication are also working on these related projects:
New materials and technologies View project
F. Vilaseca
Universitat de Girona
91 PUBLICATIONS 3,357 CITATIONS
SEE PROFILE
Pere Mutjé
Universitat de Girona
SEE PROFILE
Ton Peijs
The University of Warwick
SEE PROFILE
All content following this page was uploaded by Ton Peijs on 06 April 2019.
The user has requested enhancement of the downloaded file.

Cellulose
Biocomposites—
From Bulk Moldings
to Nanostructured
Systems
Lars A. Berglund and Ton Peijs
as an inferior construction material to
manufactured materials such as steel or
advanced composites. Because of the struc-
tural complexity of natural materials, sim-
ply extracting microscale cellulose fibers
from these plants and mixing them into a
polymer resin will lead to loss of structural
organization. Instead, we can try to learn
from biological materials. For instance,
cellulose organization in improved hierar-
chical structures would improve the prop-
erties of manufactured biocomposites.
Materials scientists and engineers, there-
fore, need to progress beyond the presently
used high-volume–low-cost products,
which are based on coarsely microstruc-
tured biocomposites (cellulose microcom-
posites). The following examples illustrate
promising approaches that include the use
of oriented fibers, more pure cellulose
reinforcements, nanostructured biocom-
posites, and porous materials.
Cellulose Microcomposites
Wood-plastic composites (WPCs) are
mixtures of wood fiber, often waste wood
at high loadings (50–80 wt%), and synthetic
resin, mainly polyethylene (virgin or recy-
cled). They have been hugely successful in
North America—with annual sales growth
continuing at double-digit figures—in
decking, railing, siding, and other construc-
tion applications because of their low life-
cycle costs and the environmental benefits
they offer over chromated copper arsenate-
treated lumber.1,2 WPCs can be worked like
wood and yet processed like plastics, and
they offer greater durability and moisture
resistance than softwood. Decking has
been by far the biggest growth area for
WPCs in the United States, while in
Europe, the automotive industry is the
biggest user of WPCs for interior applica-
tions. Because of this, the most popular
resin for WPC in Europe is not polyethyl-
ene but virgin polypropylene, while UV-
stable poly(vinyl chloride) also is used for
the manufacturing of window frames.
Challenges in WPC technology have been
mainly centered around maximizing mix-
ing, while minimizing mechanical or ther-
mal damage to the wood fibers during
compounding3 and also overcoming diffi-
culties in obtaining good interfacial adhe-
sion.4 Swelling due to moisture absorption
by the wood fibers5,6 also raises concern
with respect to property degradation and
attack by micro-organisms.
Where wood flour or waste wood is
principally used as a cost-cutting alterna-
tive to mineral fillers in commodity
plastics such as polyethylene and
polypropylene resin or for the upgrading
of post-consumer recycled plastics, plant
fibers such as flax, hemp, jute, coconut
Introduction
Since the 1960s, innovations in modern
composite materials have dramatically
changed the materials landscape. New
high-performance composite materials,
featuring glass, carbon, or aramid fibers,
are now commonly used for applications
ranging from tennis rackets to large com-
mercial aircraft. However, the possibility
of depletion of oil reserves and global
environmental concern has resulted in a
renewed interest in bio-based materials in
general and cellulose-based composites in
particular. Cellulose is the most common
plant biopolymer, and the annual produc-
tion is estimated to be around 1011 tons.
This illustrates that not only are plants
renewable resources, but the amount of
fibrous cellulose produced is enormous.
The low density of cellulosic fibers
together with their superior mechanical
properties, environmental benefits, and
low cost have been the main drivers for
the use of these fibers as reinforcement for
plastics. Examples of materials and appli-
cations are presented in Figure 1.
Biological materials are generally syn-
thesized in water at low temperature and
pressure by energy-efficient processes.
Wood is arguably one of the most complex
structures of all materials. Many levels
of hierarchical structuring are present,
from annual rings at the millimeter scale
via microscale cells to nanoscale cell wall
structures. Still, wood often is regarded
Abstract
Cellulose biocomposites are widely used in industry as a low-cost engineering
material with plant fiber reinforcement. However, chemical and microstructural
heterogeneity causes low strength, low strain-to-failure, high moisture sensitivity, and
odor and discoloration problems. Efforts toward improved performance through fiber
orientation control, increased fiber lengths, and biopolymer use are reviewed. Interfacial
strength control and moisture sensitivity are remaining challenges. As an attractive
alternative reinforcement, high-quality cellulose nanofibers obtained by wood pulp fiber
disintegration can be prepared at low cost. These nanofibers have high length/diameter
ratios, diameters in the 5–15 nm range, and intrinsically superior physical properties.
Wood cellulose nanofibers are interesting as an alternative reinforcement to more
expensive nanoparticles, such as carbon nanotubes. Nanopaper and polymer matrix
nanocomposites based on cellulose nanofiber networks show high strength, high work-
of-fracture, low moisture adsorption, low thermal expansion, high thermal stability, high
thermal conductivity, exceptional barrier properties, and high optical transparency. The
favorable mechanical performance of bioinspired foams and low-density aerogels is
reviewed. Future applications of cellulose biocomposites will be extended from the high-
volume/low-cost end toward high-tech applications, where cellulose properties are fully
exploited in nanostructured materials.
MRS BULLETIN • VOLUME 35 • MARCH 2010 • www.mrs.org/bulletin 1
MRS_Mar10_Berglund:MRS_March10_Berglund 2/11/2010 5:28 PM Page 1

fibers, and kenaf have been evaluated as
environmentally friendly and low-cost
alternatives for glass fibers in engineering
composites.7–10 Plant fibers from annual
crops have a higher aspect ratio than
wood fibers and therefore are more effec-
tive as reinforcements for composites. The
hierarchical structure of the flax stem is
illustrated in Figure 2. Natural fibers have
a number of advantages over glass fibers.
They are renewable, low cost, lightweight,
biodegradable, and nonabrasive to pro-
cessing equipment. They also provide bet-
ter working conditions, have good
acoustic and thermal insulating proper-
ties, and can be incinerated with energy
recovery. However, as discussed later,
there are still unsolved issues with respect
to recyclability and moisture durability.
In the 1990s, the combination of inter-
esting mechanical and physical properties
(Table I) together with the introduction of
environmental legislation triggered activi-
ties in the area of natural fiber composites
(NFC) in the European automotive indus-
try. In a large research program, Daimler
AG led the way in introducing natural
fibers such as flax and hemp in a number
of automotive applications,10 and the cur-
rent Mercedes E-class contains as many as
50 parts based on natural fibers, with a
total weight of 32 kg. Natural fibers have a
strong potential in the automotive indus-
try, as they are 40% lighter than glass
fibers. However, until now, most of their
use has been limited to interior compo-
nents, and few applications are found in
more structural parts.
Polypropylene dominates as a matrix for
natural fibers, but thermosets such as phe-
nolics, polyurethanes, and polyesters also
are used. The majority of these composites
are manufactured using press molding
technologies on nonwoven mats.10–12 In
recent years, research efforts have shifted to
bio-based and biodegradable polymers,13,14
such as polylactic acid (PLA),15,16 polyhy-
droxybutyrate,17,18 and starch.19 Japanese
industries, in particular, have been actively
pursuing the idea of fully biodegradable
parts. Toyota introduced kenaf (a fibrous
African hibiscus) as a door trim base mate-
rial in 2000, first in combination with
polypropylene and, since 2003, in combina-
tion with PLA for the Toyota Raum spare
tire cover. PLA and kenaf are used for the
casings in electronic devices, such as in
NEC’s Eco Mobile phone. Bio-based ther-
mosetting resins also have been used,
including resins derived from soybean oil20
and cashew nut shells.21 The idea of bio-
derived resins is far from new; in 1938,
Henry Ford made his first fiber-reinforced
car body panel using a plastic matrix
derived from soybean products.
Although these bio-based composites, or
as they are often referred to “green compos-
ites,” may well be more environmentally
friendly than alternative polymer compos-
ites, their eco-friendly character should not
be taken for granted.22 For this, a compara-
tive life-cycle assessment study is essential.
However, in general, NFC composites are
2 MRS BULLETIN • VOLUME 35 • MARCH 2010 • www.mrs.org/bulletin
Cellulose Biocomposites—From Bulk Moldings to Nanostructured Systems
Figure 1. Examples of industrial biocomposite material forms and applications.
(a) Thermoplastic/natural fiber granules for injection molding; (b) section of a dashboard
panel; (c) fiber mats for press-molding; and (d) a door panel.
Figure 2. (a) Example of interpretation of hierarchical structure in flax stems;46 the symbol
∅ stands for diameter. (b–c) Cross-sections of flax stem and (d) a technical fiber bundle.
Scutching and hackling refer to different parts of the processing procedure where the
fibrous entities are disintegrated from the flax stem.
a b
c d
hackling
breaking
scutching
bast fiber
bundle
technical fiber
∅ 50–100 μm
elementary fiber,
plant cell
∅ 10–20 μm
meso fibril
∅ 0.1–0.3 μm
micro fibril
∅ 1–4 nm
flax stem
∅ 2–3 mm
a
b c d

likely to have environmental benefits over
glass-fiber-reinforced plastics (GRPs)
because23 (1) natural fiber production has
much lower environmental impact than
high-temperature processed glass fibers; (2)
NFCs require higher fiber loadings for
equivalent performance, reducing the
amount of polluting polymer; (3) light-
weight NFCs can improve fuel efficiency
and reduce emissions in the use phase of a
component, especially in automotive appli-
cations; and (4) end-of-life incineration of
natural fibers results in energy recovery. In
the case of transport applications, however,
life-cycle assessment studies have shown
that the advantages of natural fibers are
mainly related to their low weight, espe-
cially in stiffness-based designs, rather than
their bio-based origin.23,24
NFCs have no real benefits in terms of
mechanical recycling. In fact, natural
fibers contain amorphous polysaccharides
and lignin and, therefore, tend to degrade
near the processing temperature of most
thermoplastics.25 Thermal degradation
during processing not only limits the
number of polymers that can serve as a
matrix for cellulose fibers but gives partic-
ular concern with respect to reprocessing
or recycling. Potential problems with
mechanical recycling are highly signifi-
cant for the automotive industry in light
of the European Union Directive on end-
of-life vehicles,26 which states that vehicles
need to be subjected to 95% materials
recovery, of which 85% is by reuse or recy-
cling and 10% by energy recovery or ther-
mal recycling. Mono-material concepts
such as “all-polymer” or “self-reinforced
polymer” composites based on a single
polymer for fiber and matrix may prove
better candidates for mechanical recycling
schemes.27–30 However, natural fibers have
clear advantages over glass fibers with
respect to end-of-life disposal by incinera-
tion, especially when combined with ther-
mosets or recycled plastics that are close to
the end of their lifetimes.
Optimization of Microcomposite
Properties
In common with WPCs, challenges in
natural fiber composites have been related
to the thermal stability limitations of ligno-
cellulose fibers,25 difficulties in fiber feed-
ing, fiber dispersion and breakage during
compounding,31–33 moisture absorp-
tion,5,34,35 attack by bacteria and fungi,2
flame retardancy,36,37 and especially the
creation of a strong interfacial bond with
the polymer matrix.6,7,9,38–44 Natural fibers
can easily compete with glass in terms of
stiffness, especially on a weight basis
(Table I).6,12 However, tensile strength,6,12
compressive strength,45,46 and especially
the impact strength of NFC6,47 are rela-
tively low compared to GRPs. Initial opti-
mization studies for cellulose fibers mainly
focused on the optimization of the interfa-
cial bond strength with the polymer
matrix.6,12,39,41,42,44 These interfacial modifi-
cations often followed schemes similar to
those used to modify glass fibers, while
traditional methods such as sodium
hydroxide and heat treatments of cellulose
fibers have been used to clean fiber sur-
faces, reduce moisture absorption, and
increase the surface roughness.48 The main
problem with NFCs, however, is the
incompatibility between the hydrophilic
natural fibers and the often hydrophobic
thermoplastic matrices. Here, compatibi-
lizers or coupling agents are needed to
improve the adhesion between the fiber
and matrix. The compatibility and dis-
persability of the fiber and matrix can be
improved by common coupling agents
such as silane-based compounds.6,38,43
Other fiber modification methods include
acetylation49 or physical methods, such as
corona or plasma surface treatments.50
Fiber upgrading methods, as well as
improved interfacial coupling, have been
shown to improve the moisture resistance
of NFCs.34 However, because of the non-
continuous nature of natural fibers, the
application of these coatings and treat-
ments is often less cost-effective than for
glass fibers, where a silane coating is
applied directly after the spinning process.
Compatibilization routes based on modi-
fied matrices are often more suitable
for natural fibers. Maleated polyolefins
such as maleic anhydride-grafted poly-
propylene (PP-g-MA) are the most com-
monly used coupling agents.6,12,39,41,42,44
Such matrix modifications allow
interactions between the anhydride
groups of maleated coupling agents
and the hydroxyl groups of cellulose.
Compatibilization can lead to significant
improvements in properties, particularly
in terms of tensile and flexural strength
and also moisture resistance. However, a
stronger interface often leads to further
embrittlement of the NFC, since the inter-
face is “too strong,” and toughening by
fiber pullout is prevented. In any compos-
ite system, interfacial properties need to be
optimized rather than maximized, and this
is particularly true for NFCs, which often
suffer from a lack of toughness, a fact that
is often attributed to the interfacial interac-
tion being too strong. A typical natural
fiber used in most of today’s composites
has a tensile strength of only one fourth
that of glass.12 At similar fiber-matrix
adhesion levels, for example, as a result of
similar compatibilization schemes, frac-
ture processes in NFCs will involve fewer
energy-absorption mechanisms, such as
debonding and fiber pullout, than in
GRPs, leading to brittle fracture. Hence,
interfaces in NFCs need to be weaker than
in GRPs in order to obtain similar levels of
toughness. Moreover, unlike isotropic
glass fibers, natural fibers are highly
anisotropic,12,46 and after optimization of
the interface, internal adhesion within the
fiber bundle structure often becomes the
weakest link to initiate failure.12,51
Recently, a completely new route to
cellulose-based composites with good
interfacial adhesion was proposed by
Nishino et al.52–55 They focused on
approaches following self-reinforced poly-
mer concepts.27–30 During composite
preparation, the surface layer of the cellu-
lose fibers was partially dissolved to form
the matrix phase of “all-cellulose” com-
posites. The surface dissolution method
results not only in very high fiber volume
fractions, but also in a gradual interphase
or interfacial region, which minimizes
voids and stress concentrations. Because of
this, all-cellulose composites often outper-
form traditional NFCs.53,54
Next to interface-based optimization
routes for NFCs, new developments also
include the use of longer fibers such as in
long-fiber thermoplastics33,44 or textile com-
posites based on spun yarns.56–58 The latter
materials allow the introduction of fiber
orientation through the use of textile
preforms such as woven or non-crimp
multi-axial fabrics. The use of low twist
yarns, as in the case of the recently intro-
duced Biotex flax/PLAcommingled yarns,
is essential for improved fiber efficiency
compared to highly twisted yarns, as used
in conventional textile applications.56
Natural plant fibers such as flax are
composed of cellulose microfibrils with
Table I. Mechanical Properties of Flax and Glass Fibers.
Density Young’s Tensile Specific Specific
(g cm3) Modulus Strength Modulus Strength
(GPa) (MPa) (GPa/g cm3) (GPa/g cm3)
Glass 2.5 70 2400 28 950
Flax (technical fiber) 1.5 50 500–700 33 350–450
Flax (elementary fiber) 1.5 60 1200–1500 40 800–1000

diameters on the order of 5–15 nm.
However, so far most fibers used in com-
posite application are fiber bundles
(“technical fibers”). These fiber bundles
have a relatively low strength of around 600
MPa,12 while the actual fiber cell is much
stronger (up to 1500 MPa).59–62 Therefore,
even higher intrinsic strengths are foreseen
when nanofibers are used as reinforcement.
Cellulose Nanocomposites
In the previous microcomposite section,
limitations such as low strength, low
strain-to-failure, and moisture sensitivity
were discussed. In addition, odor and dis-
coloring problems often arise due to ther-
mal decomposition of hemicelluloses and
lignin during composites processing.
A promising way to address these short-
comings is through nanocelluloses of high
cellulose purity. The nanocellulose in dif-
ferent organisms is suitable for nanocom-
posites63 and is present in the form of
native cellulose microfibrils in plant cell
walls, including algae and tunicate sea ani-
mals; nanocellulose also is produced by
bacteria (i.e., Acetobacter xylinus). Cellulose
molecules are in extended chain conforma-
tion and form highly ordered fibrous crys-
tallites. Experimental data by Sakurada
et al.64 (x-ray diffraction measurements of
crystal displacement during tensile load-
ing of fibrous ramie plant cells) and
Sturcová et al.65 led to an estimated axial
cellulose crystal modulus of 130–140 GPa.
Molecular dynamics simulations provide
estimates in the range 130–200 GPa.66,67
A recent review on the topic is available.68
It is interesting to note that the modulus of
native cellulose is similar to the modulus
of aramid fibers. The advantage of cellu-
lose, however, is in its bio-based origin and
the potential to use it in nanofibrillar form.
Elastomer nanocomposites based on
discretely dispersed short aspect ratio
microcrystalline cellulose or nanocrystals
can show strongly improved properties69
due to a mechanism of improved rubbery
network characteristics.70 In the case of
discrete nanoparticle composites, the
degree of dispersion of particles in the
matrix is critical. Gousse et al. used silanes
to disperse nanocellulose in organic sol-
vents,71 which widens the possible range
of cellulose-polymer nanocomposite com-
binations. Another approach is to graft a
polymer such as polycaprolactone from
(“graft-from”) cellulose, as studied exper-
imentally72 and by molecular dynamics
simulations73 (see Figure 3). This surface
modification allows good dispersion of
cellulose in an organic solvent and also
can improve cellulose-matrix adhesion.
Despite the interest in discrete cellulose
nanoparticle reinforcement, nanostructured
Figure 3. Cross-sectional illustration of how molecules can be grafted to the cellulose
crystallite surface in order to improve molecular interaction with a surrounding polymer.
The edge dimensions of the cellulose crystal cross-section are 4.3 nm × 4.8 nm. Molecular
dynamics simulation models for caprolactone (CL)-grafted cellulose crystals.73 (a) Neat
cellulose and polymer matrix, (b) 50% CL substitution on the cellulose, and (c) 100% CL
substitution on the cellulose surface.
Modified Cellulose
Matrix
x
y
z
Cellulose
a b c
cellulose networks appear to offer a more
generally applicable reinforcement mecha-
nism. The network reinforcement concept
was elegantly demonstrated in pioneering
studies reported by Favier et al.74,75 The
addition of small amounts of cellulosic
tunicate whiskers resulted in dramatic
improvements in modulus above the glass
transition temperature, Tg, of an amor-
phous polymer matrix. The main reason
was the formation of a cellulose whisker
network with high load-carrying ability so
that the thermal softening of the matrix was
counteracted in the composite. This
inspired a large number of reports on cellu-
lose nanocomposites (low cellulose content)
by researchers in Grenoble, France.76
Wood Cellulose Nanofibers
Nanofibers are interesting reinforce-
ments but are often very costly. Wood
cellulose nanofibers have the potential to
be widely used due to the low cost associ-
ated with recently introduced economical
disintegration procedures. Turbak et al.77
first described microfibrillated cellulose
from wood pulp. Wood fibers cooked in a
chemical solution to yield a high cellulose
content were used as starting materials. As
these fibers were subjected to mechanical
homogenization (as used in the food
industry for tomato soup and orange
juice), the fiber cell wall disintegrated into
cellulose nanofibers. Nakagaito and Yano
used such nanofibers in composites.78
Enzymatic pretreatment was then devel-
oped in Sweden in order to reduce energy
requirements during nanofiber disintegra-
tion,79 although chemical pretreatments
utilized in Reference 80 are more efficient.
The lateral dimension of such enzyme-
treated nanofibers is around 15 nm and
probably corresponds to the cellulose
aggregate scale in the pulp fiber cell wall.81
Recently, 5-nm microfibrils were readily
disintegrated from wood pulp based on a
TEMPO-catalyzed oxidation pretreat-
ment,82 which is possible to combine with
a simple kitchen blender treatment.
Cellulose Nanopaper
After disintegration from wood fibers,
cellulose nanofibers are available as a
dilute (≈1%) water suspension. Such a
water suspension can be vacuum-filtered
or cast, and strong interfibril interaction is
obtained during gel drying so that a
porous wood cellulose nanopaper is
formed.78,83 The nanopaper is a fibrous
network analogous to conventional paper.
The main difference is that the nanopaper
is structured at the nanoscale rather than
at the microscale of conventional paper.
The fine structure and improved proper-
ties of the fibrous unit lead to interesting
mechanical properties (Figure 4), includ-
ing 250 MPa tensile strength and high
work-to-fracture. The high strain-to-failure
is most remarkable and is due to a
nanofiber slippage mechanism. Saito
et al.82 recently reported higher strength
(310 MPa), similar strain-to-failure, and
lower modulus in a nanopaper system.
For comparative purposes, typical strain-
to-failure data for conventional high-
strength microscale paper (craft liner

board) are 3–4%,84 rather than the 10%
achievable with nanopaper.
Toward High-Performance
Nanocomposites
As the potential of wood-based cellulose
nanocomposites is discussed, moisture
sensitivity is an issue. In the absence of
amorphous polysaccharides also present
in plant cell walls, highly crystalline cellu-
lose has very low moisture adsorption.85
This is supported by detailed cellulose-
moisture interaction studies by molecular
dynamics simulations,86 where it has been
shown that the interior of the crystal is
inaccessible to water. It is also possible to
chemically modify cellulose nanofibers
(i.e., by acetylation) in order to reduce
hygroscopicity.87 Since the disordered
cellulose regions adsorb more moisture,
those regions are most likely to be influ-
enced by acetylation.
The tensile strength, Young’s modulus,
and work-of-fracture of cellulose network
nanocomposites depend strongly on the
cellulose content. High-volume fraction
composites have been prepared by impreg-
nation of porous nanopaper structures
with monomers, followed by polymeriza-
tion to form a thermoset composite.78 These
materials showed high modulus and flex-
ural strength but were quite brittle, as was
also confirmed for a different thermoset.88
In brittle materials, flexural strength is con-
trolled by defect size and depends strongly
on specimen size and surface smoothness.
For applications where ductility and
toughness are required, more ductile poly-
mer matrices are of interest.
Wood cellulose nanofiber networks also
form if a starch/glycerol mixture contain-
ing suspended nanofibers is cast.89,90 If the
matrix is highly plasticized and nanofibers
are well-dispersed and of high content, the
resulting biocomposite shows an attractive
combination of strength, modulus, and
work-to-fracture.90 The reason is high dam-
age tolerance due to the fine nanopaper
structure in a highly ductile matrix. Again,
nanofiber slippage is an important defor-
mation mechanism, providing ductility.
An important goal for cellulose
nanocomposites is nanostructural control.
Recently, Zhou et al. introduced a hygro-
scopic cellulose derivative (hydroxyethyl
cellulose [HEC]) in the water-based
culture during bacterial cellulose biosyn-
thesis.91 The HEC was adsorbed by the cel-
lulose microfibrils so that each microfibril
in the suspension was coated by HEC.
Vigorous mechanical mixing was used,
and a stable suspension of well-dispersed
HEC-coated nanofibers was obtained.
The resulting nanocomposite film with
random-in-the-plane nanofiber orientation
Figure 4. Toughened cellulose nanopaper.83 (a) Fracture surface and (b) stress-strain
curve in tension. DP410-DP1100 are measures of increasing molar mass of the cellulose
(c) atomic force micrograph of a nanopaper surface with a width of 1.0 micrometer (image
courtesy of I. Mondragon). (d) Loading-unloading curves in tension.
SE
SE
SE WD
WD
WD 8.1mm
8.1mm
8.1mm x20k
x20k
x20k 2um
2um
2um
a
c d
b
250
200
150
100
Stress
(MPa)
50
0
0 2 4 6
Strain (%)
8 10 12
DP-410
DP-820
DP-580
DP-1100
0 1.00 μM
Data type
Z range
Phase
143.6 0
200
150
100
50
Stress
(MPa)
0
0 2 4
Strain (%)
6 8
Figure 5. Compartmentalized bacterial cellulose (BC) microfibrils with hydroxyethyl-
cellulose (HEC) coatings.91 (a) Transmission electron microscopy (TEM) image of a loose
bundle structure of HEC-containing ribbons. (b) TEM image of more compact pure BC
ribbon reference. (c) Sketches showing interpretation of structures in (a) and (b).
(d) Homogeneous water suspension of HEC-coated BC. (e) Precipitated inhomogeneous
BC water suspension used as a reference.
a
b
c d
e
showed a tensile strength of 350 MPa,
which is much higher than for the neat
bacterial cellulose film (Figure 5). This sug-
gests a new nanostructured concept for
cellulose composites. Each nanofiber is
compartmentalized by a thin matrix layer

coating, similar to many biological com-
posites, such as the wood cell wall.
The work by Yano demonstrates
additional interesting characteristics of
cellulose nanocomposite properties such
as optical transparency and low thermal
expansion.92 The reason is low in-plane
axial thermal expansion of cellulose crys-
tals67,93 combined with the random-in-the-
plane network structure. It suggests that
the in-plane hygroscopic expansion is also
extremely low. Pure cellulose is thermally
stable, with degradation typically com-
mencing at temperatures exceeding
300°C.94 Improved toughness due to
nanofiber slippage together with optical
transparency was also found for in situ
grown bacterial cellulose/poly(vinyl alco-
hol) composites.62 Recently, it was also
shown that thin films of wood cellulose
nanofibers can be both transparent and
have low oxygen permeability, and this
was utilized in PLA film coatings.95
Native Cellulose Biofoams
and Aerogels
Biofoams based only on biological poly-
mers are interesting as replacements
of petroleum-based polymer foams.
Cellulose nanofibers are small enough to
reinforce the cell walls in such foams.
Efforts to include microcrystalline
cellulose in starch foams processed by
industrial methods show limited success
in terms of property effects. In contrast,
freeze-dried starch biofoams show the
potential of cellulose nanofiber rein-
forcement96 (Figure 6). The energy
absorption, which is estimated as the
area under the stress-strain curve, is more
than doubled as 40 wt% of cellulose
nanofibers are added. This is highly
relevant in the context of packaging mate-
rials. The biofoam shows as good energy
absorption as expanded polystyrene,
even at ambient conditions. The hygro-
scopic starch biofoam cell wall is also
stabilized by cellulose at a moisture
content of about 10%.
Aerogels are a class of materials where
the liquid phase of a gel is removed with-
out substantial shrinkage. One limitation
of low-density aerogels is fragility.97
Freeze-drying of wood cellulose nanofiber
gels results in low-density aerogels with
considerable mechanical robustness.98
These aerogels also were functionalized
by a secondary modification step, with a
conducting polymer coating. Recently, cel-
lulose nanofibers coated with a 50-nm
conducting polymer layer were used to
form a nanopaper structure99 that was
successfully applied in a low-cost bat-
tery.100 These efforts and others such as
flexible displays illustrate an interesting
Figure 6. Bio-inspired starch/cellulose nanofiber biofoams.96 (a) Microcellular structure
where the scale bar is 300 microns; (b) compressive stress-strain curves showing strong
improvement in energy absorption (area under stress-strain curve) with microfibrillated
cellulose nanofiber (MFC) addition; (c) cell wall structure with nanofibrillar characteristics
visible; and (d) relative modulus as a function of relative humidity (RH) for reference
(0% MFC cellulose) and 40 wt% MFC cellulose-reinforced foam. MFC reinforces the cell
wall and improves the mechanical integrity of the foam during humid conditions.
31947
31947
31947 x100
x100
x100 300um
300um
300um
0.8
0 wt% MFC
10 wt%
40 wt%
70 wt%
0.6
0.4
Stress
(MPa)
0.2
0
0 10 20 30
Strain (%)
40 50 60 70
1
WD
WD
WD 9.4mm
9.4mm
9.4mm x1.5k
x1.5k
x1.5k
x1.5k 12um
12um
12um
1.1
1
0.9
0.8
0.7
0.6
0.5
Normalized
Storage
Modulus
(–)
0.4
20 30
0 wt% MFC
40 wt%
40 50
RH (%)
60 70 80
a b
c d
trend of industrial cellulose utilization
expanding to high-tech applications.
Outlook
The microstructured cellulose biocom-
posites in use today have been critically
examined. Substantially improved per-
formance requires biocomposite engineer-
ing, including fiber length and orientation
control, fiber-matrix interface optimiza-
tion, and reduced moisture adsorption,
which can be achieved through chemical
fiber modification. Chemical and
microstructural heterogeneity can be
reduced through the use of more highly
purified cellulosic fibers. In addition, the
all-cellulose composite concept described
is both scientifically and technically inter-
esting. For the future, cellulose nanofibers
from wood pulp fiber disintegration offer
great promise as low-cost nanofiber rein-
forcements. This is based on a consistent
raw material source with an established
industrial infrastructure. The nanopaper
and nanocomposites based on wood cel-
lulose nanofiber networks show high
strength, high work-of-fracture, low mois-
ture adsorption, low thermal expansion,
high thermal stability, high thermal con-
ductivity, high optical transparency, and
also exceptional barrier properties. More
sophisticated bioinspired composite
nanostructured systems of high strength
also have been introduced, where the
cellulose nanofiber is compartmentalized
by a thin coating of polymer matrix. The
development of technologies for
nanofiber orientation control would fur-
ther boost new applications, as this opens
up possibilities for the creation of hierar-
chical structures as in nature. Finally,
bioinspired foams and low-density aero-
gels have potential in high-technology
applications, although more widespread
use requires the development of new con-
cepts for large-scale manufacturing.
Acknowledgments
Financial support through SustainComp
(EU) and the centers Biomime, BiMaC
Innovation, and Wallenberg Wood Science
Centeraregratefullyacknowledged(L.A.B.).
References
1. C. Clemons, For. Prod. J. 52, 10 (2002).
2. R.M. Rowell, J. Polym. Environ. 15, 229 (2007).
3. A.K. Bledski, M. Letman, A. Viksne,
L. Rence, Composites Part A 36, 789 (2005).
4. J.Z. Lu, Q.L. Wu, H.S. McNabb, Wood Fiber
Sci. 32, 88 (2000).

5. A.K. Bledzki, O. Faruk, Compos. Sci. Technol.
64, 693 (2004).
6. A.K. Bledzki, J. Gassan, Prog. Polym. Sci. 24,
221 (1999).
7. D.N. Saheb, J.P. Jog, Adv. Polym. Technol. 18,
351 (1999).
8. T. Peijs, Mater. Technol. 15, 281 (2000).
9. M.J. John, S. Thomas, Carbohydr. Polym. 71,
343 (2008).
10. T. Schlosser, J. Knothe, Kunstoffe: Plast Eur.
87, 1148 (1997).
11. K.P. Mieck, R. Lutzkendorf, T. Reussmann,
Polym. Compos. 17, 873 (1996).
12. S.K. Garkhail, R.W.H. Heijenrath, T. Peijs,
Appl. Compos. Mater. 7, 351 (2000).
13. A.K. Mohanty, M. Misra, G. Hinrichsen,
Macromol. Mater. Eng. 276, 1 (2000).
14. K.G. Satyanarayana, G.G.C. Arizaga,
F. Wypych, Prog. Polym. Sci. 34, 982 (2009).
15. K. Oksman, M. Skrifvars, J.F. Selin, Compos.
Sci. Technol. 63, 1317 (2003).
16. T. Nishino, K. Nakamae, K. Hirao,
M. Kotera, Compos. Sci. Technol. 63, 1281 (2003).
17. E. Bodros, I. Pillin, N. Montrelay, C. Baley
Compos. Sci. Technol. 67, 462 (2007).
18. N.M. Barkoula, S.K. Garkhail, T. Peijs, Ind.
Crop. Prod. 31, 34 (2010).
19. L. Averous, N. Boquillon, Carbohydr. Polym.
56, 111 (2004).
20. A. O’Donnell, M.A. Dweib, R.P. Wool,
Compos. Sci. Technol. 64, 1135 (2004).
21. E.T.N. Bisanda, M.P. Ansell, J. Mater. Sci. 27,
1690 (1992).
22. T.U. Gerngross, S.C. Slater, Sci. Am. 283, 36
(2000).
23. L. Shen, M.K. Patel, J. Polym. Environ. 16,
154 (2008).
24. T. Corbiere-Nicollier, B. Gfeller-Laban,
L. Lundquist, Y. Leterrier, J.-A.E. Månson,
O. Jollieta, Resour. Conserv. Recycl. 33, 267 (2001).
25. J. George, E.T.J. Klompen, T. Peijs, Adv.
Compos. Lett. 10, 81 (2001).
26. K. Bellmann, A. Khare, Technovation 19, 721
(1999).
27. N. Cabrera, B. Alcock, J. Loos, T. Peijs, Proc.
Inst. Mech. Eng. Part L, J. Mater. Des. Appl. 218,
145 (2004).
28. B. Alcock, N.O. Cabrera, N.M. Barkoula,
A.B. Spoelstra, J. Loos, T. Peijs, Composites Part
A 38, 147 (2007).
T. Peijs, Compos. Sci. Technol. 66, 1724 (2006).
C.T. Reynolds, L.E. Govaert, T. Peijs, Compos.
Sci. Technol. 67, 2061 (2007).
31. A. Keller, Compos. Sci. Technol. 63, 1307 (2003).
32. M.J.A. van den Oever, M.H.B. Snijder,
J. Appl. Polym. Sci. 110, 1009 (2008).
33. N.M. Barkoula, S.K. Garkhail, T. Peijs,
J. Reinf. Plast. Compos. (September 16, 2009);
DOI: 10.1177/0731684409104465.
34. A. Stamboulis, C.A. Baillie, S.K. Garkhail,
H.G.H. van Melick, T. Peijs Appl. Compos. Mater.
7, 273 (2000).
35. A. Stamboulis, C.A. Baillie, T. Peijs,
Composites Part A 32, 1105 (2001).
36. T.D. Hapuarachchi, G. Ren, M. Fan, P.J.
Hogg, T. Peijs, Appl. Compos. Mater. 14, 251 (2007).
37. R. Kozlowski, M. Wladyka-Przybylak,
Polym. Adv. Technol. 19, 446 (2008).
38. K.P. Mieck, A. Nechwatal, C. Knobelsdorf,
Angew. Makromol. Chem. 224, 73 (1995).
39. K.P. Mieck, A. Nechwatal, C. Knobelsdorf,
Angew. Makromol. Chem. 225, 37 (1995).
40. T. Peijs, S. Garkhail, R. Heijenrath, M. van den
Oever, H. Bos, Macromol. Symp. 127, 193 (1998).
41. M.H.B. Snijder, H.L. Bos, Compos. Interfaces
7, 69 (2000).
42. J. George, M.S. Sreekala, S. Thomas, Polym.
Eng. Sci. 41, 1471 (2001).
43. A.K. Mohanty, M. Misra, L.T. Drzal,
Compos. Interfaces 8, 313 (2001).
44. A. Nechwatal, T. Reussmann, S. Bohm,
E. Richter, Adv. Eng. Mater. 7, 68 (2005).
45. R. Heijenrath, T. Peijs, Adv. Compos. Lett. 5,
81 (1996).
46. H.L. Bos, M.J.A. van den Oever, O.C.J.J.
Peters, J. Mater. Sci. 37, 1683 (2002).
47. M.J.A. van den Oever, H.L. Bos,
K. Molenveld, Angew. Makromol. Chem. 272, 71
(1999).
48. J. Gassan, A.K. Bledzki, Compos. Sci. Technol.
59, 1303 (1999).
49. V. Tserki, N.E. Zafeiropoulos, F. Simon,
C. Panayiotou, Composites Part A 36, 1110 (2005).
50. M.N. Belgacem, A. Gandini, Compos.
Interfaces 12, 41 (2005).
51. H.L. Bos, J. Mussig, M.J.A. van den Oever,
52. T. Nishino, N. Arimoto, Biomacromolecules 8,
2712 (2007).
53. C. Qin, N. Soykeabkaew, N. Xiuyuan,
T. Peijs, Carbohydr. Polym. 71, 458 (2008).
54. N. Soykeabkaew, N. Arimoto, T. Nishino,
T. Peijs, Compos. Sci. Technol. 68, 2201 (2008).
55. N. Soykeabkaew, C. Sian, S. Gea,
T. Nishino, T. Peijs, Cellulose 16, 435 (2009).
56. S. Goutianos, T. Peijs, Adv. Compos. Lett. 12,
237 (2003).
57. S. Goutianos, T. Peijs, B. Nystrom,
M. Skrifvars, Appl. Compos. Mater. 13, 199 (2006).
58. B. Madsen, P. Hoffmeyer, H. Lilholt,
59. M.J.A. van den Oever, H.L. Bos, Adv.
Compos. Lett. 7, 81 (1998).
60. J. Andersons, E. Sparnins, R. Joffe,
L. Wallström, Compos. Sci. Technol. 65, 693 (2005).
61. S. Garkhail, B. Wieland, J. George, N.
Soykeabkaew, T. Peijs, J. Mater. Sci. 44, 510 (2009).
62. S. Gea, E. Bilotti, C.T. Reynolds, N.
Soykeabkeaw, T. Peijs, Mater. Lett. (January
2010); DOI:10.1016/j.matlet.2010.01.042.
63. S.J. Eichhorn, A. Dufresne, M. Aranguren,
E. Marcovich, J.R. Capadona, S.J. Rowan, C.
Weder, W. Thielemans, J. Mater. Sci. (2009); DOI:
10.1007/s10853-009-3874-0.
64. I. Sakurada, Y. Nukushina, I. Ito, J. Polym.
Sci. 57, 651 (1962).
65. A. Sturcová, G.R. Davies, S.J. Eichhorn,
Biomacromolecules 6, 1055 (2005).
66. L.M.J. Kroon-Batenburg, J. Kroon, M.G.
Northolt, Polym. Commun. 27, 290 (1986).
67. M. Bergenstråhle, L.A. Berglund, K.J.
Mazeau, Phys. Chem. B 111, 9138 (2007).
68. Y. Nishiyama, J. Wood Sci. 55, 241 (2009).
69. Q.J. Wu, M. Henriksson, X. Liu, L.A.
Berglund, Biomacromolecules 8, 3687 (2007).
70. S.S. Sternstein, A.J. Zhu, Macromolecules 35,
7262 (2002).
71. C. Gousse, H. Chanzy, G. Excoffier, L.
Soubeyranda, E. Fleur, Polymer 43, 2645 (2002).
72. H. Lonnberg, L. Fogelstrom, M.A.S.A.
Samir, L. Berglund, E. Malmström, A. Hult, Eur.
Polym. J. 44, 2991 (2008).
73. M. Bergenstråhle, K. Mazeau, L.A.
Berglund, Eur. Polym. J. 44, 3662 (2008).
74. V. Favier, H. Chanzy, J.Y. Cavaille,
Macromolecules 28, 6365 (1995).
75. V. Favier, G.R. Canova, J.Y. Cavaille,
H. Chanzy, A. Dufresne, C. Gauthier, Polym.
Adv. Technol. 6, 351 (1995).
76. M.A.S.A. Samir, F. Alloin, A. Dufresne,
77. A.R. Turbak, F.W. Snyder, K.R. Sandberg,
J. Appl. Polym. Sci. 37, 813 (1983).
78. A.N. Nakagaito, H. Yano, Appl. Phys. A 80,
155 (2005).
79. M. Henriksson, G. Henriksson, L.A.
Berglund, T. Lindström, Eur. Polym. J. 43, 3434
(2007).
80. L. Wågberg, G. Decher, M. Norgren,
T. Lindström, M.Ankerfors, K.Axnas, Langmuir
24, 784 (2008).
81. E.L. Hult, T. Iversen, J. Sugiyama, Cellulose
10, 103 (2003).
82. T. Saito, M. Hirota, N. Tamura, S. Kimura,
H. Fukuzumi, L. Heux, A. Isogai,
83. M. Henriksson, L.A. Berglund, P. Isaksson,
T. Lindstrom, T. Nishino, Biomacromolecules 9,
1579 (2008).
84. J. Bodig, B.A. Jayne, Mechanics of Wood and
Wood Composites (Krieger Publishing, Florida,
1993), p. 525.
85. A. Mihranyan,A.P. Llagostera, R. Karmhag,
M. Strømmec, R. Ek, Int. J. Pharm. 269, 433
(2004).
86. M. Bergenstrahle, J. Wohlert, P.T. Larsson,
K. Mazeau, L.A. Berglund, J. Phys. Chem. B 112,
2590 (2008).
87. M. Nogi, K. Abe, K. Handa, F. Nakatsubo,
S. Ifuku, H. Yano, Appl. Phys. Lett. 89, 233123
(2006).
88. M. Henriksson, L.A. Berglund, J. Appl.
Polym. Sci. 106, 2817 (2007).
89. A. Dufresne, D. Dupeyre, M.R. Vignon,
J. Appl. Polym. Sci. 76, 2080 (2000).
90. A.J. Svagan, M.A.S.A. Samir, L.A.
Berglund, Biomacromolecules 8, 2556 (2007).
91. Q. Zhou, E. Malm, H. Nilsson, P.T. Larsson,
T. Iversen, L.A. Berglund, V. Bulone, Soft Matter
5, 4124 (2009).
92. M. Nogi, S. Ifuku, K. Abe, K. Handa, A.N.
Nakagaito, H. Yano, Appl. Phys. Lett. 88, 13
(2006).
93. R. Hori, M. Wada, Cellulose 12,
479 (2005).
94. M.J. Antal, G. Varhegyi, E. Jakab, Ind. Eng.
Chem. Res. 37, 1267 (1998).
95. H. Fukuzumi, T. Saito, T. Wata, Y.
Kumamoto, A. Isogai, Biomacromolecules 10, 162
(2009).
96. A.J. Svagan, M.A.S.A. Samir, L.A.
Berglund, Adv. Mater. 20, 1263 (2008).
97. A.C. Pierre, G.M. Pajonk, Chem. Rev. 102,
4243 (2002).
98. M. Pääkkö, J. Vapaavuori, R. Silvennoinen,
H. Kosonen, M. Ankerfors, T. Lindstrom,
L.A. Berglund, O. Ikkala, Soft Matter 4, 2492
(2008).
99. A. Mihranyan, L. Nyholm, A.E.G.
Bennett, M. Stromme, J. Phys. Chem. B 112,
12249 (2008).
100. G. Nystrom, A. Razaq, M. Stromme, L.
Nyholm, A. Mihranyan, Nano Lett. 9, 3635
(2009). ■
■
View publication stats

2010_MRS_Berglund.pdf

Empfohlen

Empfohlen

Weitere ähnliche Inhalte

Ähnlich wie 2010_MRS_Berglund.pdf

Ähnlich wie 2010_MRS_Berglund.pdf (20)

Kürzlich hochgeladen

Kürzlich hochgeladen (20)

2010_MRS_Berglund.pdf