Cellulose activation

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Cellulose activation
What and how:
 Opening of pores and altering of fibril aggregates and highly
ordered regions in cellulose fibres by:
 Mechanical treatments
 Degrading treatments
 Swelling treatments
Why:
 To enhance the accessibility and reactivity of cellulose to
chemicals (solvents and reagents)
 Dependent on the structure and morphology of the
cellulose fibres and solvent or reagent used

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Motivation
 Currently, the strategic target for the European forest industry is to find new viable
applications for wood fibres.
 The industrial interest is focused on novel added-value products based on regenerated
fibres.
 This is mainly due to the promising market trends especially in the textile industry
combined with the environmental considerations related to currently used fibre raw
materials, e.g. cotton.
 Current regenerated fibres produced by e.g. viscose and Lyocell processes involve the
use of harsh and toxic chemicals.
 Fubio cellulose aims to develop novel sustainable, both non-aqueous and aqueous based
solvent systems for dissolving pulps
Finnish Bioeconomy Cluster FIBIC Oy 29.8.2013

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Dissolution
Dissolving
grade pulp
Pre-treatment:
mech. + enz.
treatments
Regenerated
fibres
Clothes
Hygiene
products,
wipes
FuBio Cellulose
From cellulose to textiles
 The process development of novel sustainable solvent systems for cellulose is
connected with the opening up of the fibre structure

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Dissolving grade pulps
 Produced either by sulphite or prehydrolysis kraft process
 a high cellulose content and only traces of hemicelluloses and lignin
 Dissolving grade pulps used for:
 production of cellulose derivatives
 regenerated cellulose
 Requirements: good accesibility and reactivity of cellulose
 Challenges:
 The removal of the non-cellulosic compounds in pulping and bleaching cause,
the cellulose fibrils to aggregate and form tight structures in drying
decreased fibre reactivity the lost conformability and swelling capacity
cannot be recovered by rewetting the fibres

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Cellulose fibres
Egal Mlle Magali (2006): Structure and properties of cellulose/NaOH aqueous
solutions, gels and regenerated objects. Ecole Doctorale 364: Sciences
Fondamentales et Appliquées, Ecole des mines de Paris, France, p.30.
Simplifying :
 Wood is a complex natural
composite built up of fibres
that are glued together by
lignin
 fibres consist of fibrils that are
held together by lignin and
hemicellulose.
 fibrils are built up of bundles of
microfibrils

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Schematics
of cellulose
microfibril
behavior during
different
processing
steps
Pönni et al (2013): Accessibility of cellulose: Structural changes and their reversibility in aqueous media, Carbohydrate Polymers.
Volume 93, Issue 2 2013 424 - 429

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Mechanical
treatment
Enzyme
treatment
Dope Fibres
State-of-the-art Biocelsol process
 Scale: 500 g
 Mechanical shredding by Baker Perkins, 5 h, 20 %
 Enzyme treatment: commercial enzyme, pH 5, 3h, 5 %
Pulp
Disintegrated pulp Mechanically treated
pulp (5h)
 No major changes in the
visual appearance of fibres
due to 5 h mechanical
shredding by the Baker
Perkins machine

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What does the state-of-the-art treatment do?
Mech. treatment
Baker Perkins
(0- 5h)
Enzymatic
(2 dosages) vrs.
acid hydrolysis
Dissolution of
samples in
NaOH/ZnO
Pulp
 Analyses:
 dissolved sugars, pulp viscosity, molar mass distribution, pore size
distribution, WRV, solubility

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Enzyme aided modification of cellulose
Kvarnlöf 1997: Activation of dissolving pulps prior to viscose
preparation. Dissertation. Karlstad University.
 Aim: To drop the pulp viscosity
to a level where dissolution of
cellulose in selected solvent
system is possible
 Due to the compact structure
of cellulose the accessibility to
chemicals and enzymes is
restricted mechanical
treatment needed

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Dyes:
 Yellow; larger particles and higher affinity to cellulose
 Blue; smaller in size, stains all sites that are too small for the
yellow dye
 More yellow -> more open structure
Shredding
time
min
micropore
volume
g/g
total pore
volume
g/g
Accessible
surface area
m2/g
0 0.42 0.53 9
30 0.43 0.75 28
60 0.44 0.78 29
150 0.47 0.82 30
300 0.48 0.91 37
Simons staining Solute exclusion approach
Effect of shredding with Baker Perkins on fiber
structure

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Effects of shredding on the following
enzymatic hydrolysis step
• Shredding (0-300 min) as indicated in the figure
• Enzyme treatment: 2h, 50°C, pH 5

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Porosity development by hydrolysis
Shredding time
min
micropore
volume
g/g
total pore
volume
g/g
Accessible
surface area
m2/g
Disintegrated pulp 0.42 0.53 9
Shredded 5 hours 0.48 0.91 37
Shredded 5h + 2h E (0.25
mg/g)
0.61 1.05 38
Shredded 5h + 2h E (1 mg/g) 0.61 1.17 48
Treatment micropore
volume
g/g
total pore
volume
g/g
Accessible
surface area
m2/g
Disintegrated pulp 0.42 0.53 9
Acid hydrolysis
(viscosity ~250 ml/g) 0.36 0.43 6
Enzymatic hydrolysis
(viscosity ~250 ml/g) 0.62 0.86 21
Nomechanical
treatment
Acid vrs. enzymatic hydrolysis
Effect of enzyme dosage

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Effect of pre-treatments on solubility
29.8.2013
300 min
60 min
30 min
150 min
 Pulps shredded by Baker Perkins and then treated enzymatically
(1 mg/g) for 2h.
 Cellulose content in the solutions was 5.5 wt%.
Shredding time

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Development of novel sustainable aqueous
based dissolution systems
 The mechanical treatment should:
 Modify accessibility of cellulose for enzymatic (and/or chemical modification)
 Be techno-economically feasible
 The enzymatic treatment should:
 Drop pulp viscosity, without formation of low molecular weight material, low
polydispercity of Mw-distribution
 As a result of the combined mechanical and enzymatic treatments:
 Cellulose should be soluble in selected system (here in NaOH/ZnO) and result in a clear
solution without undissolved particles
 The properties of the regenerated fibres should be on targeted level
Mechanical
treatment
Enzyme
treatment
Dope FibresPulp

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Screening of new enzymes
accepted discarded discarded discarded
Shredding
Enzymatic
treatment
Pulp
Dissolution
into
NaOH/ZnO
Microscopy
images
Falling ball
viscosity and
alfa
If soluble

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Screening of potential mechanical treatments
 Testing of various mechanical equipment
 Equipment selected based on expected capability to cause internal (and
moderate external) fibrillation
 Conditions for the mechanical treatment selected based on prior to art
knowledge
Sprout Waldron disc refiner, Pearl mill PFI mill

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Screening of various ways to combine the
mechanical and enzymatic processing steps
Pulp than can be
dissolved in selected
solvent and results in
regenerated fibres with
target properties
Pulp
Enzymatic
treatment
Mechanical
treatment

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Conclusions
 The process development of novel sustainable solvent systems for cellulose is connected with
the opening up of the fibre structure
 Apparently, it is necessary to break internal bonds within the fibre wall so that fibres
swell and pores expand.
 In the studied system:
 Opening of the fibre matrix due to mechanical treatment seems to proceed in steps, it
seems that after a certain amount of stress some structures are broken down or
collapsed, resulting in further opening of the matrix.
 The surface area available to an enzyme increased from 9 to 37 m2/g in 5 hours of
shedding and was further increased substantially by the action of the enzyme.
 There seems to be limited amount of accessible sites with adequate pore size available
in the pulp for enzyme catalysis
 Increased porosity results in better solubility of the cellulose.
 The work carried out to develop novel sustainable aqueous based dissolution systems for
dissolving pulps has resulted in very promising results.

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Acknowledgements
 The work has been partially funded
by the Finnish Bioeconomy Cluster
(FIBIC) through the Future Biorefinery
(FuBio) programme.
 The technical assistance of Maija
Järventausta, Leena Nolvi, Mariitta
Svanberg and Nina Vihersola is
gratefully acknowledged.

Cellulose activation

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Cellulose activation