Reactivity of cellulose
in pulp fibres
Tapani Vuorinen
Designing Cellulose for the Future II Seminar
18-19 May 2016, Helsinki
Acknowledgements
•  CLIC Innovation Ltd’s ACel Program
•  Cofunded by Kemira and Metsä Fibre
•  Collaboration with Raili Pönni, Saija Väisänen, Pegah Khanjani,
Ville Lovikka and Thad Maloney
•  Academy of Finland funding
•  ”Study of wood ultrastructure with microscopic and spectroscopic
techniques, and computational analysis”
•  Collaboration with Carlo Bertinetto, Mehedi Reza and Janne
Ruokolainen
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Motivation
•  Lignocellulose is the most abundant class of renewable
carbon resource/biomass on the earth
•  The bulk of lignocellulose is made of ‘fibres’
•  Chemical ’pulping’ is an advanced commercial fractionation
method for lignocellulose biomass to form
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Delignified pulp fibres = cellulose and hemicelluloses
Lignin rich aqueous liquid
•  The reactivity of cellulose is of paramount importance in
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Dissolution of cellulose for textile fibre production
Derivatizing cellulose for polymer production
Hydrolyzing cellulose for liquid fuel production
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Conclusions
•  The reactivity of cellulose can be quantified with several
absolute measures
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Amount of hydroxyl groups accessible to water
Amount of rapidly reacting primary hydroxyl groups
•  Part of the chemical reactivity of cellulose can be explained
by its fundamental structural features
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Extent of interfibril aggregation
Elementary fibril dimensions
Fraction of amorphous cellulose
•  Dissolution of cellulose is partly limited by orientation and
aggregation of the fibrils in the cell wall
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Reactivity of pulps by proton exchange
•  Reaction: Cellulose-O1H + 2H2O
Cellulose-O2H + 1H2O
•  Principle: The sample is treated with deuterium oxide (2H2O)
vapor and the increase in mass is monitored which gives the
quantity of ’accessible’ hydroxyl groups (mol/kg)
•  The amount of accessible hydroxyl groups:
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Theoretical maximum
Commercial chemical pulps
Effect of drying
Effect of 2 M NaOH treatment
18 mmol/g (100 %)
10-12 mmol/g (55-65 %)
-1 mmol/g (-5 %)
+2 mmol/g (+10 %)
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Reactivity of pulps by fast oxidation
•  Reaction: Cell-CH2OH + 4.TEMPO+
Cell-CO2H + 4.TEMPO
•  Principle: The sample is diluted with a pH buffer and the fast
consumption of the oxidant is measured which gives the
quantity of easily oxidizable sugar units (mol/kg)
•  The amount of easily oxidizable sugar units:
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Theoretical maximum
Never dried chemical pulps
Effect of drying
Bacterial cellulose
6 mmol/g (100 %)
0.8 mmol/g (13 %)
-0.2 mmol/g (-3 %)
0.25 mmol/g (4 %)
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Oxidation kinetics of pulp with TEMPO+
Oxidation of maltose
Reaction completed
in ca. 1 min!
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Indirect measures of reactivity of pulps
•  WRV – Water Retention Value
•  The amount of water retained by wet pulp under standard
centrifugal force (ml/g)
•  FSP – Fibre Saturation Point
•  The pore volume of wet pulp inaccessible to large water soluble
polymers (ml/g)
•  BET nitrogen adsorption
•  Surface area of dry* pulp that can adsorb nitrogen gas (m2/g)
*The collapse of the cell wall pore structure during water removal can be
minimized by critical point drying.
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Indirect measures of reactivity of pulps
•  EMC – Equilibrium Moisture Content
•  The amount of water retained by pulp in equilibrium with RH 95 %
air (%)
•  IVOMD – In vitro Organic Matter Digestibility
•  Gravimetric yield loss of organic matter during a two-stage
treatment that imitates bovine digestion system (g/kg)
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Direct vs. indirect measures of reactivity
Effect of alkali
treatments on pulp
Pönni et al., Cellulose 21 (2014) 1217
In vitro organic matter
digestibility of timothy
hay clones
Collaboration with Dr. Anne Jokela,
University of Oulu
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Indirect vs. direct measures of
reactivity
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Interpretation of the quantitative results
•  The test for accessible hydroxyl groups (deuterium exchange
coupled with DVS) probably measures the overall content of
amorphous cellulose and cellulose on fibril surfaces
•  The chemical reactivity test with TEMPO+ possibly quantifies
the amount of amorphous cellulose
•  The equilibrium moisture content correlates with the open
open surface area that can adsorb more water than the fibril
aggregates
•  It looks like the H/D exchange can take place even when the
fibrils are aggregated with each other
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Organization of cellulose fibrils –
A physical barrier for swelling and dissolution?
S1 layer
S1-2 transition layer
Mehedi Reza, Dissertation (2016).
Wire rope
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To be continued
next time!
Thanks for your patience!