Structure of cellulose coagulated from different EmimAc-DMSO solutions Artur hedlund artur.hedlund@swerea.se

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

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

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.

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

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 300-380m2/g Assuming cylindrical fibrils: r=2/(ρ*SSA) gives: r ~ 3,6 to 4,6nm

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

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

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)

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

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

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)

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

interpretation Surface is not crystalline

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)

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)

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

fig.4 fig.5

a, b, c, d, e, a, b,