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 13.4.2016
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)
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
Outline Supercritical water treatment Product fractions Cellulose precipitate and microfluidized cellulose Use of precipitate as emulsion stabilizer Summary
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
Supercritical water treatment Cellulose suspension Supercritical water Reactor Cooling water Reaction products Ø 3 mm Temperature Time Hydrolysis & dissolution 320-380 °C Precipitate Centrifuge MCC in suspension Filtration & Precipitation 20 °C 0.2-0.8 s
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 20.8.2015
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
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, 113-122
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) 134-141
Particles Precipitate Microfluidized MCC MCC TEM AFM Both pathways produce nanocellulose particles There are morphological differences between the two materials
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
Emulsion polymerization - sizes Without cellulose With microfluidized MCC With precipitate Adding precipitate leads to smaller polystyrene beads than with microfluidized MCC
Emulsion polymerization - surfaces Without cellulose With microfluidized MCC With precipitate Cellulose particles can be found at the surface of some polystyrene beads
Oil-in-water Pickering emulsions Precipitate Microfluidized MCC Water 0.01% 0.1% 0.5% 1% 2% 5% 10% Water 0.01% 0.1% 0.5% 1% 2% 5% 10% Both materials can stabilize a 30wt.% oil-in-water emulsion The emulsion is stable already after adding only 1wt.% for precipitate
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