1. Jean Buffiere COST FP1205 workshop 13.4.2016
Nanocellulose precipitated from supercritical water treatment… …and its use as a stabilizer for oil-in-water Pickering emulsions
Jean Buffiere
COST FP1205 workshop

2. Aalto University
School of Chemical Technology, Department of Forest Products Technology
Research Group in Biorefineries
Prof. Herbert Sixta
Research areas:
Nonconventional pulping (GVL, SEW, high yield)
Dissolution-regeneration in ionic liquids (Ioncell-F and Ioncell-P processes)
Hydrothermal treatment of cellulose and pulp (posthydrolysis, supercritical water treatment)

3. STSM at Empa, Switzerland
Swiss Federal Laboratory for Materials Science and Technology
Empa Dübendorf (Zürich): ~ 1000 employees
Laboratory for Applied Wood Materials
Head: Tanja Zimmermann
Cellulose Nanocomposites Group
Group Leader: Thomas Geiger
The laboratory’s NEST

4. Outline Supercritical water treatment Product fractions
Cellulose precipitate and microfluidized cellulose
Use of precipitate as emulsion stabilizer
Summary

5. Supercritical water P = 250 bar 0.06 Temperature, °C Pressure, bar
0.01
0.06
Temperature, °C
Pressure, bar
Vapor
Liquid
Solid
Critical point
Triple point
100 1
374
221
Supercritical water
Self-ionization constant Kw
10-30
10-26
10-22
10-18
10-14
10-10
Dielectric constant εr 20 40 60 80
100
120
Near-critical
Supercritical
Subcritical
Temperature, °C
200
300
400
500
600
Density, kg.m-3,
800
1000
1200 Tc
P = 250 bar

6. Supercritical water treatment
Cellulose suspension
Supercritical water
Reactor
Cooling water
Reaction products
Ø 3 mm
Temperature
Time
Hydrolysis & dissolution °C
Precipitate
Centrifuge
MCC in suspension
Filtration & Precipitation
20 °C s

7. 3 product fractions Residual fraction  unreacted cellulose
Precipitated fraction  low molecular weight cellulose
Liquid fraction  glucose, soluble cellulose oligomers and degradation products
Cellulose is rapidly hydrolyzed and dissolved
The hydrolysis products have a wide molar mass distribution
Jean Buffiere

8. Precipitate Cellulose II DP ≈ 20 Size-exclusion chromatography
Wide-angle x-ray scattering
The precipitate is composed of low molecular weight cellulose
The precipitate has a cellulose II structure

9. Precipitation phenomenon
Supercritical water
Similarities with dissolution in phosphoric acid
and precipitation in ethanol/water*
TEM
Single cellulose II crystals
DP (from image height) ≈ 15
AFM
*Helbert and Sugiyama, Cellulose (1998) 5,

10. Precipitate vs. microfluidized MCC
Microcrystalline cellulose (MCC)
Hydrothermal pathway
Mechanical pathway*
Microfluidizer
Work at Empa:
Morphological characterization
Potential applications Composites
Emulsions
Foams
Precipitate
Microfluidized MCC
*Bandera et al. 2014, Reactive and Functional Polymers 85 (2014)

11. Particles Precipitate Microfluidized MCC MCC TEM AFM
Both pathways produce nanocellulose particles
There are morphological differences between the two materials

12. Films and composites MCC Precipitate Microfluidized MCC
Self-standing films: HPC composites:
More precipitate
The precipitate dries into a very dense and brittle structure
The microfluidized MCC forms more porous arrangements

13. Emulsion polymerization - sizes
Without cellulose
With microfluidized MCC
With precipitate
Adding precipitate leads to smaller polystyrene beads than with microfluidized MCC

14. Emulsion polymerization - surfaces
Without cellulose
With microfluidized MCC
With precipitate
Cellulose particles can be found at the surface of some polystyrene beads

15. Oil-in-water Pickering emulsions
Precipitate Microfluidized MCC
Water % % % % % % %
Water % % % % % % %
Both materials can stabilize a 30wt.% oil-in-water emulsion
The emulsion is stable already after adding only 1wt.% for precipitate

16. Summary
Supercritical water can efficiently hydrolyze and dissolve cellulose
The cellulose chains with a DP around 20 precipitate into crystalline cellulose II structures
These precipitated structures have a “nano” ribbon-like morphology
The precipitate can be used to stabilize oil-in-water Pickering emulsions