This document summarizes a study that uses dynamic vapor sorption (DVS) combined with deuterium oxide exchange to directly measure the accessible hydroxyl groups in cellulose samples, which influences cellulose reactivity. Several pulp samples were analyzed using this method. The results showed a correlation between the accessibility of hydroxyl groups and water retention values for industrially dried pulps. Never-dried pulps had relatively low accessibility, possibly because drying during the measurements affected accessibility. Equilibrium moisture content also correlated with water retention values. Further studies are needed to fully understand how drying impacts accessibility measurements.

1. Assessing the reactivity of cellulosic
pulps by dynamic vapor sorption
analysis
Saija Väisänen, Raili Pönni,
Tapani Vuorinen
5.6.2015

2. Cellulose: a versatile raw material

3. Understanding cellulose reactivity enhances the
development of new products
• Amount of accessible OH-groups in cellulose influences the
reactivity of cellulose during different chemical and enzymatic
treatments
• DVS combined with D2O exchange is a direct method to assess
the amount of accessible OH-groups

4. Dynamic Vapor Sorption (DVS)
• Sorption rate measurement
• Measured variable: mass change
of sample (balance accuracy: 0,1 µg)
• Changed variable: relative humidity
(RH%)
• Solvent: water, D2O, organic solvent

5. DVS combined with D2O exchange
• Hydrogens in accessible OH-groups are replaced by deuterium in
the sample by applying 95% RH of D2O vapour
• Deuterium heavier than hydrogen -> replacement can be
monitored by weight gain
D2O
Cellulose microfibril
OH
OD

6. Determination of accessible OH groups is based on
increase in weigth
The atomic mass difference between
deuterium (2H) and protium (1H) is 1 g/mol
Accessible OH groups (mol/kg)
A = × 1000
-> Accurate measurement of the dry
masses is important!

7. Measurement sequence
1) Predrying at RH 0% until the change in
mass < 0,0005 %/min for 10 min (~ 7 h)
2) RH 95% for 600 min (10 h)
3) Final drying at RH 0% until the change in
mass < 0,0005 %/min for 10 min (~ 7 h)

8. Samples
• Industrially dried pulps
- Softwood kraft (DK)
- Hardwood dissolving (DD)
• Never dried hardwood pulps
- Kraft (NDK)
- Dissolving (NDD)
- Critical point dried kraft (NDK_CPD)
- Critical point dried dissolving (NDD_CPD)
• Avicel (commercial microcrystalline cellulose powder)

9. Relative mass vs time
0 200 400 600 800 1000 1200 1400 1600
1,0
1,1
1,2
2,5
2,6
m/m,final
Time (min)
NDK
NDK_CPD
DK
DD
NDD_CPD
NDD
Avicel

10. 0 100 200 300 400 500 600
0
5
10
15
20
EMC%
Time (min)
NDK
NDK_CPD
DK
NDD
NDD_CPD
DD
Avicel
Equilibrium moisture content vs time

11. Calculated accessibility values (mol/kg)
A = × 1000

12. Equilibrium moisture contents

13. Equilibrium moisture contents vs water retention
values

14. Summary
• We have applied a method to assess the reactivity of cellulose
in pulp fibers
- Based on DVS combined with D2O exchange
- Direct assessment of the absolute amount of accessible hydroxyl groups
• Correlation between accessibility and WRV for dried samples
• Accessibility of ND pulps was relatively low
-> Drying during measurements affects accessibility and/or samples don’t
dry enough during the measurements
-> EMC% correlates with WRV
-> Further studies needed

15. Acknowledgments
A special thank you to Mr Ville Lovikka for preparing the critical point
dried samples