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Novel bionanocomposites: processing,
properties and potential applications
K. Oksman*
1,2
, A. P. Mathew
1
and M. Sain
1,2
The demand for environmental sustainability has resulted in a great interest in finding new
materials that are biodegradable and environmentally friendly. Therefore, materials derived from
natural resources are now being extensively studied. Preparation of novel biocomposites based
on nanocelluloses has drawn specific attention. It is expected that cellulose nanocomposites will
open new areas for applications in medicine, packaging, electronics, the automotive sector,
construction and other areas. This article presents a new research field of bionanocomposites
where different types of nanocelluloses are used as reinforcements in biopolymers. Isolation of
cellulose nanofibres and nanowhiskers from different sources, and processing technologies for
the composites, are described and discussed. The main difficulty when producing cellulose
based nanocomposites is to disperse the reinforcement in the polymer matrix without degradation
of the biopolymer or the reinforcing phase. This can be addressed by improving the interaction
(compatibility) between nanofibres and the matrix and by using suitable processing methods. The
study of alignment of the nanocelluloses by using magnetic field is discussed and the
nanocomposites’ mechanical properties, based on the findings from different studies, are
presented. Finally, some examples of future nanocomposites are discussed.
Keywords: Nanocellulose, Nanocomposites, Isolation process, Dispersion, Manufacturing process, Mechanical properties, Nanostructure
Introduction
The use of nanocelluloses as reinforcements in biode-
gradable polymers is a relatively new field in nanotech-
nology and has attracted significant attention during the
last decade.
1–4
In spite of various challenges in this
research area, nanoreinforcements derived from renew-
able resources and cellulose nanocomposites have been
studied by researchers since the late twentieth century.
5–
13
This research area is in its infancy and much
interdisciplinary research will be required to scale it up
to a commercial level. The major challenges of nano-
composite research are the efficient separation of
nanoreinforcements from natural resources, compatibi-
lisation of the nanoreinforcements within the matrix
polymer, development of suitable methods for proces-
sing these novel biomaterials, as well as the energy
consumption factor and the cost factor involved with
novel biomaterials.
14–23
Several terms are used for the nanocelluloses in the
literature; for example, cellulose nanowhiskers, nano-
crystals, microfibrillated celluloses and nanofibres, to
name a few. These are of great interest due to their
renewable nature, good mechanical properties and large
specific surface area.
1,3–23
The theoretical elastic mod-
ulus of cellulose nanowhiskers (crystals) has been calcu-
lated to be 167?5 GPa, by Tashiro and Kobayashi.
5
Use
of these as reinforcement in biopolymers such as starch,
cellulose acetate butyrate, polylactic acid (PLA), poly-
urethane or polyvinyl alcohol (PVA) will lead to the
development of new biodegradable and environmentally
friendly nanocomposites.
15–21
This new family of composites is expected to result in
remarkable improvement of material properties when
compared with the pristine matrix polymers or conven-
tional micro- and macrocomposite materials. Such
improvements can include higher modulus and strength,
decrease in gas permeability, increase in heat distortion
temperature and also an increase in the biodegradability
of biodegradable polymers.
3
Researchers in Grenoble, France, (Dufresne and co-
workers) showed that cellulose whiskers have a great
potential to act as reinforcement for polymers, but these
studies were mainly based on hydrosoluble polymer
systems in which the polymers’ mechanical properties
were very low.
4,6,7,15
Later on, researchers in Kyoto, Japan, (Yano and co-
workers) showed that when cellulose nanofibre mats
were impregnated by thermoset polymers such as
phenolics, the nanocomposites reached very high
mechanical properties.
22,23
Drawbacks in these types of
composites are that if a thermoset polymer is used as
1
Division of Manufacturing and Design of Wood and Bionanocomposites,
Lulea˚ University of Technology, SE-97187, Lulea˚ , Sweden
2
Faculty of Forestry, University of Toronto, 33 Willcocks Street, Toronto,
ON M5S 3B3, Canada
*Corresponding author, email kristiina.oksman@ltu.se
396
ßInstitute of Materials, Minerals and Mining 2009
Published by Maney on behalf of the Institute
Received 28 September 2009; accepted 28 September 2009
DOI 10.1179/146580109X12540995045723 Plastics, Rubber and Composites 2009 VOL 38 NO 9/10
binder, the composites will be expensive because the
nanofibre content is very high (80–90 wt-%) and that
they are limited in the flat shapes.
Studies have also been conducted on different surface
modifications, PEG grafting, partial silylation or use of
surfactants or other additives to obtain stable colloidal
dispersion of nanowhiskers capable of interacting with
biopolymer matrices.
10,24
Our task in nanocomposites research has been to
pursue cellulose nanocomposite processing by solvent
casting method, partial dissolution as well as twin screw
extrusion in an attempt to identify efficient and
compatible bionanocomposite systems and take them
to an industrially viable level. The studies on nanocom-
posite structure and properties have enabled the
optimisation of the process as well as the perfor-
mance.
16–21,25–33
Depending on the extent of separation
of cellulose nanowhiskers (CNWs) in the dispersion
medium and the interaction of cellulose nanowhiskers
with the polymer matrix, different types of bionano-
composites, with aggregated structure, partially dis-
persed nanostructure or fully dispersed nanostructure
can be achieved. The present studies of partially
dissolved nanocomposites also showed that cellulose
nanocomposites with very high mechanical properties
can be achieved.
Ultimately, all these studies are aimed at producing
bionanocomposites with good mechanical properties,
barrier properties, thermal stability and transparency
and at the same time developing an energy efficient and
cost effective processing methodology. The authors have
processed some promising nanocomposites, orientation
of whiskers using magnetic field, using twin screw
extrusion, solvent casting, crosslinking and by partially
dissolving cellulose nanofibres.
16–21,25–33
We believe that
these studies will help in producing industrially viable
bionanocomposites, for which applications will be found
in packaging, the automotive sector, electronics and
medical devices.
Processing of nanocelluloses
Generally, two different types of nanoreinforcements
can be produced from cellulose: nanofibres (sometimes
called microfibrils or microfibres) and whiskers (also
called nanocrystals). Nanofibres contain both amor-
phous and crystalline regions of cellulose and unlike
whiskers they have the ability to create entangled
networks. Whiskers, on the other hand, are described
as isolated monocrystalline regions of cellulose and they
are believed to have a modulus equivalent to the
theoretical modulus of cellulose (167?5 GPa) due to
their near perfect crystalline structure.
5
The cellulose
nanowhiskers have equally good mechanical properties
as layered silicates (170 GPa).
34
Cellulose nanowhiskers
Cellulose nanowhiskers (CNWs) are prepared by H
2
SO
4
as well as HCL hydrolysis and have been described
elsewhere in detail.
9,14
The schematic picture of the
isolation process is shown in the Fig. 1. Basically, any
cellulose based material can be used as a starting
material to produce nanowhiskers; for example, saw-
dust, different straws, vegetables or paper fibres, but we
have mainly used microcrystalline cellulose (MCC)
because of its high purity. Acid hydrolysis (HCl/
H
2
SO
4
), followed by neutralisation techniques and
concentration are carried out to produce nanowhiskers
from commercially available MCC. It can also be seen
that HCl hydrolysed nanowhiskers are more thermally
stable than H
2
SO
4
hydrolysed nanowhiskers but that the
whiskers produced by HCl are not as well separated as
whiskers from H
2
SO
4
, depending on the lack of negative
charging on the nanowhisker surfaces. Cellulose nano-
whiskers in Fig. 2, show well dispersed whiskers in
nanometre scale. The separated cellulose whiskers are
usually characterised using different microscopy tech-
nologies.
11
Optical microscope, field emission scanning
electron microscope (FESEM), atomic force microscope
and transmission electron microscope can be used, but
the easiest way to assure that nanosized whiskers have
been separated is to study the flow birefringence of the
whiskers, because these nanowhiskers act as liquid
crystals showing a birefringence when viewed through
cross-polarised light. Figure 3 shows the birefringence of
cellulose nanowhiskers after acid hydrolysis.
Cellulose nanofibres
The processing of cellulose nanofibres has attracted
considerable interest and there are several different ways
to prepare cellulose nanofibres. The most common
isolation method is a mechanical refining using ultrafine
grinding followed by high pressure homogenisation,
schematically represented in Fig. 4. The raw materials
are first swollen in water. The swollen fibres are then
dispersed using a blender to get a homogeneous fibre
1 Isolation process of cellulose nanowhiskers from microcrystalline cellulose
Oksman et al. Novel bionanocomposites
Plastics, Rubber and Composites 2009 VOL 38 NO 9/10 397
suspension, and then diluted with water to a 1 wt-%
suspension.
The first step in the fibrillation is the refining step,
where an ultrafine grinder (Cerendiptor MKCA 6-3,
Masuko, Japan) is used. The grinder consists of two
discs, one rotating and one static, with an adjustable gap
between them. The cellulose fibre suspensions were
passed through the ultrafine grinder 5, 25 and 50 times.
2 Cellulose nanowhiskers, isolated by acid hydrolysis
(photo I. Kvien)
3 Flow birefringence of cellulose nanowhiskers in water
(photo L. Petersson)
4 Mechanical isolation of cellulose nanofibres
Oksman et al. Novel bionanocomposites
398 Plastics, Rubber and Composites 2009 VOL 38 NO 9/10
Further fibrillation is done using a high pressure
homogeniser (Model 2000, APV, Denmark). The
ground cellulose fibres were passed through a valve at
high pressure and exposed to a pressure drop when
leaving the valve, resulting in high shear force. Large
fibres were removed before the homogenising step to
avoid blocking of the equipment by passing the
suspension through a sieve with 250 mm mesh. The
pressure was adjusted to 500 bar and the suspensions
were passed through the equipment until no further
fibrillation was observed. Figure 5 shows how the
grinding and homogenising processes affect the fibre
size and structure and Fig 6 shows a more detailed
view of the isolated nanocellulose fibres after
homogenisation.
Degree of fibrillation was studied using an optical
microscope and by measuring the mechanical properties
of fibre networks. The mechanical properties of the
networks are expected to give indirect information about
the degree of fibrillation. The stress at break and the
relative Emodulus were calculated and the results are
shown in Fig. 7. The results show that that the wood
fibre network (starting material) had a maximum stress
of 1?3 MPa, which increased to y50 MPa after the
grinding process and further to y80 MPa after the
homogenising process. The Emodulus of the fibre
network was initially 0?1 GPa and increased to 2 GPa
after the grinding and to 2?6 GPa after the homogenisa-
tion. It was therefore concluded that a steady state in
stress and Emodulus was reached after 50 grinding
passes and no statistically significant improvement was
observed with further grinding, whereas during homo-
genisation, a steady state was reached after five passes.
This trend in mechanical properties also reflects the
progress in fibrillation observed using microscopy.
Composites manufacturing process and
properties
The commonly used manufacturing methods for cellu-
lose nanocomposites are solvent casting, impregnation
of a fibre network or nanopaper with a polymer and
melt compounding. Solvent casting and fibre network
impregnation are easy ways to produce test samples
because no specific equipment is needed. However, melt
compounding needs to be done using a specific extruder.
The solvent casting of nanocomposites means that the
matrix polymer has to be dissolved and that the
nanocelluloses need to be dispersed in the same solvent.
Therefore, this method is usually used when water
soluble polymers are used, but the authors have also
tested polymers that are not water soluble. The
challenge using non-water soluble polymers is the
dispersion of nanocelluloses in the solvents, which mean
that the water needs to be removed without drying or
agglomerating the nanocelluloses.
31,32
The impregnation of nanofibre paper/network of films
has some limitations; the used polymer needs to be in the
dissolved stage or have a low viscosity. Also, the shape is
limited to films or flat products.
The third method is compounding extrusion, where
the nanocelluloses are mixed with a polymer melt.
Compounding is the most promising processing method
of industrial production. This is due to the possibility of
scaling up the process and the fact that the produced
nanocomposites can be easily injection moulded or
compression moulded to different shapes.
Examples of nanocomposites produced by solvent
casting, modified impregnation and melt compounding
are described more in detail.
Solvent casting
The aim of this study was to produce unidirectional
oriented nanocomposites, showing the capability of
CNWs to align in the direction of magnetic field. The
resultant nanocomposites properties were studied in the
parallel and transverse direction with respect to orienta-
tion of whiskers.
25
It has been reported that cellulose whiskers in
suspension can be oriented by superconducting magnets,
shearing forces and by an electric field. The magnetic
orientation of a whisker with its long axis perpendicular
5 Isolation of nanocellulose awoodfibresasstarting
material and after b50 grinding steps and cfive homo-
genising steps
Oksman et al. Novel bionanocomposites
Plastics, Rubber and Composites 2009 VOL 38 NO 9/10 399
to the field is due to the negative diamagnetic anisotropy
of cellulose.
35–37
Figure 8 shows the preparation method used to
develop an aligned nanocomposite.
25
Polyvinyl alcohol
was dissolved in water (10 wt-%) at 80uC for 4 h and
CNWs were added and formed a suspension of 0?2 wt-%
CNW in PVA and water. The nanocomposites were
prepared by solvent casting the suspension of PVA and
CNW in aqueous medium in a homogeneous magnetic
field with magnetic flux density of y7 T. The resultant
transparent nanocomposite films had a CNW content of
2 wt-%. The structure of the nanocomposite was studied
by field emission scanning electron microscopy
(FESEM) and the mechanical performance was studied
using a dynamic mechanical thermal analyser.
The FESEM analysis of the nanocomposites was done
after etching the surface with ionised argon gas and it is
shown in Fig. 9. The micrograph shows cellulose
nanowhiskers aligned in the direction perpendicular to
the magnetic field.
The dynamic mechanical properties of the nanocom-
posites were studied in the parallel and transverse
direction, shown in Fig. 10. The results showed that
the storage modulus below the Tg(at25uC) was
remarkably higher (2 GPa) in the transverse direction
(whiskers in parallel direction) than the parallel direc-
tion of the magnetic field (whiskers in perpendicular
direction). This improvement is significant and can be
considered as a direct impact of orientation of nano-
whiskers in the PVA matrix.
This study gave an indication that cellulose nano-
whiskers can be aligned by using a magnetic field and
that the nanowhiskers have an excellence reinforcing
capability when aligned.
Modified impregnation
The aim of this work was to develop all-cellulose
nanocomposites using wood based cellulose nanofibrils
as the raw material. These were partially dissolved and
compression moulded to flat films. The nanofibrils for
this study were produced as described earlier in the
section on ‘Cellulose Nanowhiskers’. In this process, the
matrix phase is generated during the process by partial
dissolution of the nanofibrils using an ionic liquid. The
nanofibrils that remain unaffected by ionic liquid act as
the reinforcing phase. These nanocomposites are inter-
esting materials for biomedical applications, as they are
based solely on cellulose and the used ionic liquid 1-
butyl-3-methylimidazolium chloride ([C
4
mim]Cl) is
recyclable, efficient, without VOC emission and has
low toxicity.
26,38
Nanocomposite processing was carried out as follows:
cellulose nanofibre dispersions were diluted to 1 wt-%
and vacuum filtered through a filter press. The water was
allowed to drain out completely and obtained nanofibre
networks were dried in a hot press at 100uC. The
nanocellulose fibre networks of y1 g were impregnated
with 15 mL ionic liquid in a Petri dish. The Petri dish
and network were placed in an oven set at 80uC for
effective dissolution times of 60, 90 and 120 min.
Thereafter, the samples were taken out of the oven
and subsequently immersed in two different precipita-
tion baths, after which they were thoroughly rinsed to
6 Atomic force microscopy image, detailed view of isolated nanocellulose fibres with fibre thickness measurement
atensile strength; bEmodulus
7 Mechanical properties of nanocellulose fibre networks
showing indirect number of needed processing
Oksman et al. Novel bionanocomposites
400 Plastics, Rubber and Composites 2009 VOL 38 NO 9/10
remove residual solvent. The excess of water was then
wiped off the specimens with a paper towel, and the
samples were dried in a hot press at 60uC.
The prepared nanocomposite microstructures
(Fig. 11) show nanocellulose fibre network before
dissolution and after 60, 90 and 120 min of dissolution.
The nanofibrils were visible in all the materials,
indicating that some fractions of the nanofibrils are
unaffected. It was found that in all the samples the
cellulose dissolution was mostly on the surface and
limited dissolution of nanofibrils has occurred in the
bulk. The microscopy of the composites showed that
the extent of dissolution increased over time and the
composites showed skin core morphology, as can be
seen from Fig. 11c.
The mechanical properties of the nanocellulose fibre
network and the composites are shown in Table 1. It can
be seen that the tensile strength and Emodulus are high
for the nanocellulose network and a trend to further
increase after dissolution with ionic liquid can also be
seen.
Short term creep of the materials was studied using a
dynamic mechanical analyser, at 37uC and with a
constant load of 10 MPa. The aim was to simulate the
body conditions, regarding temperature and stress. The
results of this creep study are seen in Fig. 12 and show
that the creep decreased as the dissolution time
increased. The pure nanocellulose network, NF-0,
without dissolution, showed the highest creep, while
the nanocomposites with 120 min dissolution time, NF-
120, showed a negative deformation or shrinkage. NF-
90 composites showed the most stable creep response
and indicated that partial dissolution resulted in
improved performance under an applied stress.
This study gave an indication that nanocellulose
based fibre networks and partially dissolved composites
have good mechanical properties and low toxicity and
are biomaterials for potential medical applications.
Melt compounding
The main challenge in melt compounding of nanocom-
posites is to achieve well dispersed nanoreinforcements
in the polymer matrix. The focus of this work was to
develop a new processing technique for larger scale
production of cellulose nanocomposites. The mechanical
properties of materials were studied to get an idea of
how the incorporation of cellulose whiskers will affect
the composite’s modulus, strength and elongation to
break. This study was the first attempt to prepare
8 Processing of aligned nanowhiskers in PVA matrix
9 Image (SEM) of ion etched surface of PVA nanocompo-
site showing highly oriented structure (SEM image
Ingvild Kvien)
10 Dynamic mechanical thermal analysis of PVA nano-
composites with aligned whiskers
10
Table 1 Mechanical properties of nanocellulose network
and nanocomposites.
Properties NF-0 NF-60 NF-90 NF-120
Strength, MPa 106¡5 101¡4 112¡6 118¡7
Modulus, GPa 6.6¡0.55
.7¡0.78
.2¡0.86
.8¡0.6
Strain, % 7¡26¡15¡17¡2
Oksman et al. Novel bionanocomposites
Plastics, Rubber and Composites 2009 VOL 38 NO 9/10 401
cellulose nanocomposites by melt extrusion technique
using a commercially available grade of MCC in a
biodegradable polyester matrix.
16
Poly lactic acid (PLA), Nature Works 4031 D,
supplied by Cargill Dow LLC, Minneapolis, MN,
USA, was used as matrix and cellulose nanowhiskers
were used as reinforcement.
16
N,N-dimethyl acetamide (DMAc) and lithium chlor-
ide (LiCl) were used as dispersion and pumping medium
and polyethylene glycol (PEG1500) was used as a
processing aid to reduce the viscosity of the system.
Maleic anhydride (MA) grated PLA was prepared in the
authors’ lab and was used as a processing aid and
coupling agent.
PLA–CNW nanocomposites were compounded using
a co-rotating twin screw extruder (Coperion Werner &
Pfleiderer ZSK 25 WLE) with a gravimetric feeding
system for dry materials (K-Tron) and a peristaltic
pump (Heidolph) for dispersed whiskers. Figure 13
shows a schematic picture of the compounding process.
The compounding was carried out in the temperature
range of 170–200uC. Polylactic acid polymer was fed
into the main inlet and the dispersed whiskers were
pumped into the melt polymer using a peristaltic pump.
The liquid phase was removed by atmospheric venting
and by vacuum venting. The speed of the main feeder
and the pump were adjusted to have 5 wt-% CNW in the
final composition. Both PLA–MA and PEG were
premixed with PLA and fed into the main inlet. The
final compositions were: 10 wt-% PLA–MA coupling
agent, 15 wt-% PEG plasticiser and 5 wt-% CNW. The
amount of DMAc/LiCl was 20 wt-% and it was removed
by the venting system during the extrusion. The codes
for the tested material combinations were PLA
DMAC
as
reference material, the composite with coupling agent
PLA
DMAC
/PLA–MA10/CNW5 and composite with
plasticiser and coupling agent PLA
DMAC
/PEG15/PLA–
MA10/CNW5.
The melt compounding of cellulose nanocomposites
presents several challenges. The major difficulties are to
11 Scanning electron microscopy of ananopaper (NF-0) and nanocomposites obtained after b60 min (NF-60), c90 min
(NF-90) and d120 min (NF-120) of dissolution
12 Short term creep performance of nanocellulose and
nanocomposites at 37uC and with constant load of
10 MPa
Oksman et al. Novel bionanocomposites
402 Plastics, Rubber and Composites 2009 VOL 38 NO 9/10
feed the CNW into the extruder and achieve uniform
dispersed whiskers in the polymers matrix. The CNWs
have a very high surface area and have a tendency to
aggregate when dried. That can be avoided by feeding
them in a suitable medium where the CNW are
dispersible, compatible with the polymer matrix and
do not cause any degradation at high temperatures. In
this study we have tested DMAc/LiCl as pumping
medium. DMAc/LiCl was chosen because it is shown to
act as an isolation agent for CNW and a medium in
which CNW can be dispersed.
The visual examination of the compounded materials
showed that PLA
DMAc
showed a slightly brown colour
compared to pure PLA. This colour change may be due
to some degradation that takes place due to the DMAc/
LiCl.
The mechanical properties of composites are shown in
Table 2 and Fig. 14. The properties are compared with
reference PLA, which were subjected to same process as
the studied nanocomposites.
Both nanocomposites showed better mechanical
properties and the composite with partly dispersed
cellulose nanowhiskers PLA
DMAc
/MA–PLA10/CNW5
showed an increase in elongation to break around
800%. The ductility of this material was clearly much
better than the others. The strength improved, but the E
modulus decreased slightly for this composite. The E
modulus for composite without PEG improved by about
35%, the strength about 90% and elongation to break
about 35%. It is obvious that the addition of CNW had
a positive effect for this composite and the effect was
most visible on the composite strength. It is difficult to
explain why CNW together with PEG were affecting the
elongation to break and ductility to this large extent, but
similar results have been obtained in another cellulose
nanocomposite system.
30
Petersson and Oksman
reported an increase in all mechanical properties
including elongation to break when cellulose acetate
butyrate was used as matrix.
30
The reason for this
behaviour might be the combination of nanosized
whiskers dispersed in a low molecular weight polymer
and the brittle matrix. It is also possible that PEG
interacts with cellulose whiskers, covers them, and
thereby improves the dispersion of the CNW. This
might result in improved toughness but will lower the
reinforcing effect of CNW. Generally, the addition of
CNW had a positive effect on the mechanical properties
of the composites.
The first study on compounding of cellulose nano-
composites gave an indication that nanocomposites can
be prepared using a conventional compounding extruder
and that the liquid feeding of the nanocelluloses into the
extruder is possible. The results showed that cellulose
nanowhiskers have a reinforcing capacity for polymer.
Furthermore, it is important to find a suitable proces-
sing/feeding medium that does not degrade the polymer
or the whiskers during this high temperature process.
Present and future products for cellulose
nanocomposites
The demand for environmental sustainability is an
important driving force behind the development of
new materials that are biodegradable and environmen-
tally friendly. It is expected that cellulose based
nanocomposites will open new areas for, among others,
medical, packaging, electronics, automotive and con-
struction applications.
Medical applications
Nanocelluloses have inherent properties such as low
toxicity, biocompatibility and biodegradability, together
with excellent mechanical properties and thermal
stability. These features make cellulose based nanocom-
posites an interesting candidate in biomedical applica-
tions such as artificial implants, wound dressing
products, drug delivery, medical devices, etc.
Nanocellulose, particularly bacterial cellulose, is a
natural biomaterial for the development of medical
applications thanks to its biostability and biocompat-
ibility. Examples of present medical applications
includes wound dressing, temporary skin for burn
injuries, and connective tissue replacement.
39
When
13 Schematic of compounding process of PLA–nanocel-
lulose composites
14 Typical tensile strength of tested PLA and PLA
nanocomposites
Table 2 Mechanical properties of matrix and nanocomposites
16
Properties PLA
DMAc
PLA
DMAc
/MA–PLA10/CNW5 PLA
DMAc
/MA–PLA10/PEG15–CNW5
Strength, MPa 41 78 49
Modulus, GPa 2.93
.92
.6
Strain, % 1.92
.717
.8
Oksman et al. Novel bionanocomposites
Plastics, Rubber and Composites 2009 VOL 38 NO 9/10 403
applied around wounds, new tissue and blood vessels
can grow around and into the nanocellulose without
causing inflammation. Therefore, it can be used as cuffs
for blood vessels and nerves, and made into artificial
vessels for vessel reconstruction.
40
In addition, the
synthesised bacterial cellulose tubes are widely used in
providing realistic training for microsurgery.
41
Because of its hydrophilic nature, nanocellulose is
used to produce hydrogel, a composite made with
polymers like PVA. The hydrogels have been found to
be suitable materials for controlled release drug delivery
and tissue scaffolds.
42
The authors’ earlier study of in
situ crosslinked cellulose nanowhiskers with a hydro-
philic matrix resulted in a hydrogel capable of taking up
moisture as high as 900% of its original weight. These
materials are potential applications for burn healing or
controlled release of drugs.
33
All-cellulose nanocomposites prepared from cellulose
nanofibres showed potential for use as artificial liga-
ments and tendons, owing to their excellent mechanical
properties at body temperature, non-toxicity and
biocompatibility. Figure 15 shows the comparison of
the prepared nanocomposites with the mechanical
properties of natural tendon and ligament.
43
As seen
in the Fig. 15, prepared nanofibre networks as well as the
nanocomposites, owing to their mechanical properties,
can compete with natural ligaments and tendon in body
conditions (temperature and high humidity). The pre-
pared cellulose nanofibre networks showed excellent
mechanical properties, being better than natural tendon
and ligament, while the all-cellulose nanocomposite was
in the range of tendon and better that the ligament.
Automotive applications
Thanks to its excellent reinforcing ability, the incorpora-
tion of cellulose into plastic materials is one of the most
studied and most interesting areas of study in composite
development. Cellulose in its various sizes and forms has
received positive recognition in building strong yet
lightweight materials. Cellulose nanofibres are as strong
as steel and are used as an alternative to fibreglass. With
5–10% of nanofibre loading, the tensile strength of the
overall composite can increase by twofold to threefold.
1
Also, cellulose nanofibres have proven to be optically
transparent, as larger diameter fibrils have been
excluded and distribution has been improved. When
combined with optical polymers like acrylic and epoxy
resins, the resulting composites can transmit up to 80%
of visible light and can reduce the coefficient of thermal
expansion compared to the pure polymer.
44
The
nanocomposites can be either flexible or rigid, depend-
ing on the selection of matrices, and the latter would be
suitable for glass replacement. Today, many motor
companies have invested in the potential of these
nanofibres in producing partially biodegradable car
panels, door modules and various load bearing parts.
Their rheological ability in attracting water is also
utilised to avoid phase separation and improve the
texture of paints and interior fabric coatings.
Conclusions
The major challenges of nanocomposite research are the
efficient separation of nanoreinforcements from natural
resources, compatibilisation of the nanoreinforcements
with the matrix polymer, development of suitable
methods for processing of these novel biomaterials, the
energy consumption factor and the cost factor involved
with novel biomaterials.
These nanomaterials are still in the research phase but
are expected to be implemented in industrial applica-
tions in the near future. Many research groups are
working on the isolation and chemical modification of
nanocelluloses and the development of novel composite
materials.
This paper introduces the reader to the research topic
of biobased nanocomposites and provides information
about the isolation process of nanocellulose as well as
nanocomposite processing methods and properties.
Nanocomposites, which are described more in detail,
are solvent cast nanocomposites in which cellulose
nanowhiskers were aligned in a polymer matrix using
magnetic field, all-cellulose composites in which nano-
cellulose network was partially dissolved using an ionic
liquid, and melt compounded nanocomposites with
polylactic acid as matrix and nanowhiskers as reinforce-
ments. In all examples, the used nanocelluloses
show excellent reinforcing potential and are expected
to be used in medical, automotive and electronics
applications.
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