Assessing the reactivity of cellulosicpulps by dynamic vapor sorptionanalysisSaija Väisänen, Raili Pönni,Tapani Vuorinen5.6.2015

Cellulose: a versatile raw material

Understanding cellulose reactivity enhances thedevelopment of new products

• Amount of accessible OH-groups in cellulose influences thereactivity of cellulose during different chemical and enzymatictreatments

• DVS combined with D2O exchange is a direct method to assessthe amount of accessible OH-groups

Dynamic Vapor Sorption (DVS)

• Sorption rate measurement

• Measured variable: mass changeof sample (balance accuracy: 0,1 µg)

• Changed variable: relative humidity(RH%)

• Solvent: water, D2O, organic solvent

DVS combined with D2O exchange

• Hydrogens in accessible OH-groups are replaced by deuterium inthe sample by applying 95% RH of D2O vapour

• Deuterium heavier than hydrogen -> replacement can bemonitored by weight gain

D2O

Cellulose microfibrilOHOD

Determination of accessible OH groups is based onincrease in weigth

The atomic mass difference betweendeuterium (2H) and protium (1H) is 1 g/mol

Accessible OH groups (mol/kg)

A = × 1000

-> Accurate measurement of the drymasses is important!

Measurement sequence

1) Predrying at RH 0% until the change inmass < 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 inmass < 0,0005 %/min for 10 min (~ 7 h)

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)

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

,fina

l

Time (min)

NDK NDK_CPD DK DD NDD_CPD NDD Avicel

0 100 200 300 400 500 6000

5

10

15

20EM

C%

Time (min)

NDK NDK_CPD DK NDD NDD_CPD DD Avicel

Equilibrium moisture content vs time

Calculated accessibility values (mol/kg)

A = × 1000

Equilibrium moisture contents

Equilibrium moisture contents vs water retentionvalues

Summary

• We have applied a method to assess the reactivity of cellulosein 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

Acknowledgments

A special thank you to Mr Ville Lovikka for preparing the critical pointdried samples