Characterization of cellulose nanofibrils (CNF)
Ali Naderi
Email: ali.naderi@innventia.com
Tel: +46-(0)768767321
Cellulose nanofibril (CNF)
 Length  several micrometers
 Width  100 nanometers
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Cellulose nanofibril
CNFs
– Broad size distribution
– Highly entangled
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Cellulose nanofibril
 CNFs
– Entangled state  vey difficult to separate the different constituents
– Properties are defined by all the different constituents
 Innventia’s characterization strategy
– Investigation of the overall properties
– Combination of different methods
 All methods have their strengths and weaknesses!
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Characterization: Why?
 Evaluation of the impact of different processing conditions on (selected)
properties of CNF
– Important for the development of CNF-related processes
 Quality control
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Characterization
 Requirements
– Easy to employ
 Simple methodology, affordable machinery, high reproducibility, “quick”
– Logical responses and trends in the results
– Good correlation with other methods of analysis
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Innventia’s current methods of analysis
 Rheology
– Higher rheological response (often) indicates higher degree of fibrillation
 Mechanical properties of CNF-film
– Higher strength indicates higher degree of fibrillation
 Centrifugation
– A higher concentration in the supernatant (often) indicates higher degree of fibrillation
 Barrier properties of CNF-films
– Highly fibrillated CNFs (often) have excellent barrier properties, compared to less fibrillated
systems
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Rheological studies
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Rheological investigations
 Established method in the industry
– Polymer industry
– Food industry
– …
 Highly sensitive
– Advantage
 Detection of small changes
– Challenge
 Development of rigorous sample handling- and measuring protocols
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 Rheometer
Imposes a specific deformation to the sample, and monitors the resulting deformation.
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Rheological test methods
 Controlled shear rate measurements
 Creep tests
 Relaxation tests
 Oscillatory Measurements
– Oscillatory strain sweep (increasing the applied strain at constant frequency)
– Oscillatory frequency sweep (the applied strain is kept constant while the frequency is increased)
 ….
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Controlled shear rate measurements
 What we do?
– Apply a deformation at a fixed speed = shear rate (𝛾)
 What we measure?
– Stress ()
Viscosity* () =

𝛾
* Apparent values!
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Oscillatory measurements
 What do we do
– Apply a oscillatory deformation strain/force
 What do we register
– The elastic response of the viscoelastic material (storage modulus, G’)
– The viscous response of the viscoelastic material (loss modulus, G’’)
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What do G’ and G’’ tell?
 When we have a flowing material like dilute polymer solutions: G’ < G’’
 When elastic properties dominates (e.g. nanocellulose gels): G’ > G’’
 Information that can be obtained:
– Increasing degree of delamination  increasing
𝐺′
𝐺 ′′
𝐺′
– Very strong gels: 𝐺 ′′  10
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Rheological studies at Innventia
 Sampling
 Sample handling
 Choosing the correct “geometry”
 Measuring
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Sampling
 The sample is collected straight from the homogenizer/microfluidizer, to avoid:
– Contamination
– Change of the dry content
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Sample handling
 Equilibration of samples  3 days
 Storage in fridge
 Equilibration of samples at room temperature  24 hours
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Geometry
 Measuring geometry
– Plate-cone
– Plate-plate
– Cup and bob
 Smooth surfaces
 Splined surfaces to minimize slip effects
– Used when
𝐺′
𝐺 ′′
≫1
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Measuring protocol
 Shaking the sample container or blending the content to “even out” the sample
 Employing equal amounts of sample in the measuring chamber (increases the reproducibility)
 Pre-shearing of the sample in the measuring chamber to “even out” the sample
 Covering the chamber with a “hood” to decrease water evaporation
 Equilibration of the sample before measuring
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Mechanical properties of CNF-film
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Mechanical properties of CNF-film
 Tensile strength measurements on sheets is an established method in the pulp &
paper industry
 Description:
– Dewatering of the CNF suspension through filtration
– Drying of the CNF-films in constrained form
– Analysis
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CNF-film preparation: General description
 Preparation of diluted CNF suspensions
– Dilution of concentrated CNF samples to 0.1% (w/w)
– Blending process: magnetic stirrer (750 rpm/min, 24 hours)
 Production of CNF-films through filtration
– Degassing of the 0.1% (w/w) samples by applying vacuum
– Careful addition of the sample (along a glass rod) into the filtration unit
– Application of vacuum to remove the excess water
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CNF-film preparation: General description
 The filter-membrane and the film are dried in constrained form
 50 C/ 7 hours
a)
c)
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b)
Tensile strength measurements
Width: 6 mm
Length: 45 mm
Distance between the grips: 30 mm
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Centrifugation
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Centrifugation
 Basis
– Centrifugation of highly diluted (<< 1% (w/w)) CNF systems
 Easier separation of particles*
– Smaller particles can better resist the centrifugal forces (compared to larger particles)
* Naderi et al. 2014) Cellulose, 21(4), 2357-2368.
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Protocol
  0.02% (w/w) CNF samples are prepared (magnetic stirrer, 750 rpm/24 h)
 Centrifugation: 1000g for 15 minutes
 The suspension concentrations before (cbc) and after (cac) the centrifugation treatment are
used to estimate the fraction of nano-sized cellulosic materials (cNS (w/w) %) in the dry
content of the suspension:
cNS % (w/w) =
cac
cbc
x 100
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Barrier properties

OTR (oxygen transmission rate) is the steady state rate at which oxygen gas permeates through a film at
specified conditions of temperature and relative humidity. Standard test conditions: 23°C 50% RH or 23C
and 80% RH.
Courtesy of Göran Flodberg (Innventia)
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Comparison of the properties of different CNFs
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CNF systems
 Carboxymethylated CNF (CNFCarb)
– Charge density:  30 eq/g
 Enzymatically pre-treated CNF (CNFEnz)
– Charge density:  600 eq/g
 CMC*-grafted CNF (CNFCMC)
– Charge density:  170 eq/g
* Carboxymethyl cellulose
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Rheology
 Nr of homogenization passes in the CNF manufacturing process: 1 or 5
1500
1000
Viscosity (Pa.s)
Dry content: 1.9-2.0% (w/w)a)
CNF
1pass
Gen1
1 pass
Enz
Gen1
5 pass
CNF
5 pass
Enz
Gen2 1 pass
CNF
Carb 1 pass
Gen2
5 pass
CNFCarb
5 pass
Gen4 1 pass
CNFCMC
1 pass
8 Gen4
5 pass
CNFCMC 5 pass
500
 Highest viscosity for CNFCarb
 Little change in viscosity of CNFEnz
– The CNF is difficult to fibrillate!
0
0
1
Dry content % (w/w)
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2
Apparent fraction of nano-sized material (cNS)
cNS (%)
1.9% (w/w) Gen1, 1 pass
3
1.9% (w/w) Gen1, 5 pass
5
2.0% (w/w) Gen2, 1 pass
31
2.0% (w/w) Gen4, 1 pass
10
2.0% (w/w) Gen4, 5 pass
24
 Highest cNS for CNFCarb
 Increasing nr of passes leads to little change in the cNS of CNFEnz
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Tensile strength measurements on CNF films
Tensile strength index (TSI)
(kNm/kg)
1.9% (w/w)
CNFEnz, 1 pass
1.9% (w/w)
CNFEnz, 5 pass
2.0% (w/w)
CNFCarb, 1 pass
2.0% (w/w)

TSI of CNFEnz is little affected by EC

Highest TSI for CNFCarb

CNFCMC, 1 pass
2.0% (w/w)
CNFCMC, 5 pass
TSI of CNFCMC increases with EC
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102  5
107  6
166  16
114  6
164  12
Barrier properties: Oxygen permeability (OP)
 Poor barrier properties for CNFCMC
 Better barrier properties for CNFEnz than CNFCarb, at 50% RH?!
 Similar properties for CNFEnz and CNFCarb at 80% RH
OP** (23 C/50% RH)
OP** (23 C/80% RH)
(cm3μmm−2d−1kPa−1)
1.9% (w/w) CNFEnz, 1 pass
0.04  0.008
(cm3μmm−2d−1kPa−1)
15.0  2.1
2.0% (w/w) CNFCarb, 1 pass
0.17  0.03
12.6  2.2
2.0% (w/w) CNFCMC, 1 pass
70  3
-*
* Not measured
** OTR normalized with the film-thickness
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CNFs
Exciting properties/Exciting applications
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 Stiffness comparable to Kevlar*
 Strength comparable to glass fibre**
* Sakurada et al. (1962) J. Poly. Sci. 57, 651-660
** Saito et al. (2012) Biomacromolecules 14, 248-253
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Spinning of CNF threads
Patented technology (by Innventia and KTH)
Karl Håkansson (2014) Nature Communications, 5
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Exciting properties
 Nano-sized material
– Dry strength additive in pulp and paper applications
 Stronger paper and cardboard products
Innventia AB (unpublished results)
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CNF
 Network formation (percolation) at vey low concentrations (< 1% (w/w))
Rheological modifiers
Composite applications
1000
Viscosity (Pa.s)
100
10
1
0,1
0,01
0,001
0,01
0,1
1
10
100
1000
Amount of CNF in a polymer-composite
-1
Shear rate (s )
Boufi et al. (2013) Macromol. Mater. Eng. 299(5)
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 Low thermal expansion coefficient*
– Electronics
* Fukuzumi et al. (2009) Biomacromolecules 10 (1), 165-165
** Siro et al. (2011) J. Appl. Poly. Sci. 119 (5), 2652-2660
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CNF-film**
 Excellent barrier properties
– Dense films (same density as crystalline cellulose  1.5 g/cm3)
 Packaging applications
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 High surface area ( 300 m2/g) and high strength
– Foams and aerogels
Expanded polystyrene
> 90 (vol)% porosity
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NFC AEROGEL DEVICE
Hamedi et al., Angew. Chem. 2013
Supercapacitor of
crosslinked NFC aerogel
coated with PEI and SWCNT,
(PEI/SWCNT)5
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Innventia’s CNF: potential applications
 NFCCarb
– Transparent films
– Rheological modifiers
– Barrier applications
– Threads
– Foams
– Conducting materials
 NFCEnz
– Barrier applications
– Dry strength additive
 NFCCMC
– Dry strength addtive
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Thank you for your attention!
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