FIBIC ACel Programme Seminar: Use of Solvent Exchange and Critical Point Drying in Assessing the Reactivity of Cellulosic Pulps

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Use of Solvent Exchange and Critical Point

Drying in Assessing the Reactivity of

Cellulosic Pulps

Thad Maloney, Ville Lovikka

Aalto University

Finnish Bioeconomy Cluster FIBIC Oy 5.6.15

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Cell Wall Pore Structure and Reactivity

• The relationship between fiber pore structure and reactivity depends on the reaction

system.

• Reactants must access in regions of cell wall through pores

• Pulps with higher swelling have larger pores, more accessible surface area and are

often more “reactive”.

Finnish Bioeconomy Cluster FIBIC Oy

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Measuring Cell Wall Pore Structure

• The cell wall is porous in the wet state and non-porous in the dry state

• Some pore analysis methods can be used with wet fibers

• Several interesting pore analysis methods require dry material

This requires that we prepare dry fibers with intact pores


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Preparing Dry Fibers With Intact Pores

• When pulp fibers are dried the pores collapse and the fibers hornify


BKSW, WRV (mL/g) 1.52 1.21 after drying/rewetting

• The hornification can be prevented by dehydrating in a solvent

BKSW, WRV (mL/g) 1.52 1.49 after dehydration with acetone

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Removing the Solvent and Preventing the Pore

Collapse


CO2

evaporation

Acetone/CO2

exchange

CO2 phase diagram

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Pore Categories

Micropore Mesopore Macropore


IUPAC: D2nm 2nmD50nm D50 nm

Thad: D3.2 3.2nmD50nm D50 nm

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Watersaturated

fibers

intermediatesolvent

Exchange to

CO2

Critical pointevaporation

Micropores(thermoporosimetry)

Microscopy(SEM, ESEM)

Macropores(Hg Intrusion)

Mesopores(N2 sorption)

Analysis of Dry, Porous Fibers

Water Sorption Isotherm(DVS)

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N2 Isotherms for Never-dried and

Previously-dried Dissolving Pulp


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Pore Size Distribution for

Dissolving Pulps, N2 Sorption


macropores

mesopores

micropores

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Dynamic Vapor Sorption Never Dried,

BKSW,

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What do the Pores Look Like?

Compare Birch Kraft and Birch Dissolving Pulps, Never Dried


12Finnish Bioeconomy Cluster FIBIC Oy 4.6.2015

Never-Dried Kraft Hardwood

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ND Kraft HW



ND Kraft HW


ND Kraft HW


Never-dried Dissolving Pulp, Hardwood

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ND Diss. HW



ND Diss. HW


ND Diss. HW

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Dried Diss. HW, no critical point drying


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The Opportunity


FIBIC ACel Programme Seminar: Use of Solvent Exchange and Critical Point Drying in Assessing the Reactivity of Cellulosic Pulps

Science