1. Structure of cellulose coagulated from different EmimAc-DMSO solutions
Artur hedlund

2. Swerea IVF: Biobased Fibers
Cellulose and other biopolymers
Wet-spinning
Solution blown
Functionalized fibers
Recycling of fibers

3. Understanding cellulose coagulation
What happens during coagulation?
Which factors are important to achieve certain structures and macro properties?
Focused on: EmimAc- DMSO mixtures, coagulated in H2O, EtOH and 2PrOH
Previously determined critical amounts of coagulant required for coagulation, also measured mass transport
Now investigated: The structures formed
Micro Properties:
Crystallinity
Cristallite dimensions
Porosity
Macromolecular orientation
Solution Composition
Coagulation Liquid Properties
Solution
Solution with precipitated skin
Immersion into coagulation liquid
Fiber
Macro Properties:
Strength
Stiffness
Toughness
Moisture retention
Fibrillation
Precipitation

4. Solutions used in the experiment
Subset of solution set from previous study of coagulation values CVsa
Remember the notation used (WtEmimAc:WtDMSO)
2PrOH and H2O used as coagulant for enlarged points (with respective CVs marked)
EtOH used for 14,3wt%cellulose (99:1)
(50:50) EmimAc:DMSO
Coagulant KV
H2O 11,1
2PrOH 16,7
(99:1) EmimAc:DMSO
Coagulant KV
H2O 25,7
2PrOH 38
Coagulant KV
H2O 13,8
2PrOH 24,9
EtOH 21,9
Coagulant KV
H2O 5,4
2PrOH 8,2
a Hedlund Artur, Tobias Köhnke and Hans Theliander. Coagulation of EmimAc-cellulose solutions: dissolution-precipitation disparity and effects of non-solvents and cosolvent. Nordic_Pulp_Paper_Res._J. 2015_30(1):_32-42.

5. Method Membrane coating plunger tip ~0.3g, 0.3mm thick.
Solvent exchange
Retention values measured
Specific surface area BET, MASS-NMR, SEM
H2O/EtOH
2PrOH
Butanone
Cyclo-Hexane
BET-measurement,
SEM, MASS-NMR
& Dry weight

6. Structures resulting from phase separation
SEM images of solvent exchanged (2PrOH-Butanone-cyclohexane) coagulates
25wt%cellulose (99:1)
14,3wt%cellulose (99:1)
5wt%cellulose (99:1)
14,3wt%cellulose (50:50)
2PrOH
H2O
Heterogenous structures of fibrillar cellulose with open pores
SSA m2/g
Assuming cylindrical fibrils: r=2/(ρ*SSA) gives: r ~ 3,6 to 4,6nm

7. Retention values: how much liquid does the microfibrillar network hold?
RVs depend on volume coagulated
Larger swelling in water but
Mostly due to density
Note the effect of H2O on alcohol coagulated material
H2O/EtOH
2PrOH
Butanone
Cyclo-Hexane

8. Different cellulose concentrations and DMSO
5wt% cellulose: ”collapses” in water
DMSO in solvent generates a denser gel
25wt% cellulose: as dense as expected

9. Specific surface area & Crystallinity
Very low crystallinity in alcohols
Thinner crystallites, but thicker fibrils in alcohols
Ccell ↑: CI↓, SSA↑ (i.e. r↓)
r=2/(ρ*SSA)

10. Conclusions Fibrillar network
Retention values depend mainly on the volume when coagulated
Water causes the structures to shrink, even after it has been coagulated
Higher cellulose concentration, gives higher SSA (finer fibrils) and lower crystallinity (smaller crystallites)
Alcohol coagulation give smaller SSAs i.e. courser fibrils, but lower crystallinity i.e. finer crystallites, compared to water

11. Thanks to: Södra skogsägarna Foundation for Research for funding & to
You
for the kind attention
Scientific Work for Industrial Use

12. Considerations based on structures
25wt%cellulose (99:1)
14,3wt%cellulose (99:1)
5wt%cellulose (99:1)
14,3wt%cellulose (50:50)
2PrOH
H2O
Polymer concentrated in fibrils, fast diffusion in between them
Convective flow could play a significant role. Kozeny-Carman may be applied: (μ=1mPas, D=10-5 cm2/s, ε=0,86, SSA=330, K”=6) predicts mass flows of equal size from diffusion and convection for ∆P=0,02MPa (obtainable in a cellulose hydrogel e.g. assuming E=1MPa and 2% strain)

13. Specific Surface Areas and fibril dimensions
Coagulated in EtOH or 2PrOH: ~300m2/g independently of the cellulose- or DMSO concentrations
Coagulated in H2O: ~330m2/g independently of the cellulose- or DMSO concentrations, except for 25wt% cellulose (375m2/g)
Assuming cylindrical fibrils: r=2/(ρ*SSA) gives: r ~ 3,6 to 4,6nm
Kozeny-Carman may be applied: and (μ=1mPas, D=10-5 cm2/s, ε=0,86, SSA=330, K”=6) predicts mass flows of equal size from diffusion and convection for ∆P=0,02MPa (obtainable in a cellulose hydrogel e.g. assuming E=1MPa and 2% strain)
I.e. there may certainly be significant hydrostatic pressure in the coagulating solution

14. interpretation
Surface is not crystalline

15. Swelling during coagulation
∆m=Qcoagulant-QEmimAc-QDMSO
Short times ∆m>0
Connected to the coagulation
Cm=∆C 2*(D*t/π)1/2
Long times generally ∆m~0 (or <0)
Corresponds to the washing stage
Cm =A+B*e(-t*b)

16. Mean Concentrations as function of time
∆m=Qcoagulant-QEmimAc-QDMSO
Values relative to initial solution weight
Short times ∆m>0
Cm=∆C 2*(D*t/π)1/2
Long times generally ∆m~0 (or <0)
Corresponds to the washing stage
Cm =A+B*e(-t*b)

17. Quantifying diffusion at short times
Cm=∆C *2*(D*t/π)1/2
“Effective” diffusion coefficients can be determined, assuming the infinite slab model and constant D
The coagulated depth:d=a*t1/2
Corresponds to the volume coagulated
I.e. the volume having had the most mass exchange with coagulation liquid

18. fig.4
fig.5

19. a, b, c,
d, e,
a, b,