Characterization of nanofibrillated cellulose samples using x-ray scattering, microtomography, transmission and scanning electron microscopy

Transcription

1 Characterization of nanofibrillated cellulose samples using x-ray scattering, microtomography, transmission and scanning electron microscopy Kirsi Leppänen Department of Physics University of Helsinki

2 Our group: University of Helsinki: X-ray scattering, microtomography, TEM Prof. Ritva Serimaa Marko Peura Aki Kallonen Jessica Lucenius Paavo Penttilä VTT: samples, SEM Jenni Sievänen Asko Sneck 2

3 Introduction and aims Nanofibrillated cellulose (NFC) is an interesting material offering numerous application possibilities In this study, the structure of NFC was characterized in different forms (as powder, foam, suspension) at various length scales from nano- to micrometer scale 3

4 Methods Characterization methods covered the size range from the micrometer structure to the nanometer level structure μct µct TEM SAXS WAXS 1 µm 1 nm 4

5 Samples NFC was studied in different forms: dry powders NFC-water/alcohol suspensions sheets made of pure NFC and with calcite fillers Sheets were made using vacuum filtration and with and without ethanol rinsing Commercial NFC: Arbocel MF40, NFC (J. Rettenmaier & Söhne GmbH), Celish KY-100G (Daicel Chemical Industries ltd.) Non-commercial NFC made from birch pulp using Masuko grinder 5

6 X-ray microtomography CMOS flat panel detector (Hamamatsu) Set-up at the University of Helsinki: µct device nanotom by Phoenix X-ray Systems + Services GmbH Resolution just below μm computer controlled sample stage nanofocus x-ray tube 6

7 X-ray microtomography results on NFC sheets Non-rinsed NFC sheet Porosity: 7±3 % EtOH-rinsed NFC sheet Porosity: 17±3 % Used NFC: The length of the scale bar is 100 µm SAXS 7

8 SEM results Details of the surface of the NFC film Used NFC: Masuko grinded 8

9 TEM reveals the structure of fibrils down to 5 nm TEM is suitable for NFC-water suspensions Samples were imaged using cryo-tem at Aalto University Individual fibrils of size of down to about 20 nm were detected grid 1 µm 100 nm 9

10 Characterization using x-ray scattering X-rays offer a non-destructive way to determine the structure Wavelength of the x-rays (1.5 Å) is about the same as the inter-atomic distance in solids The structures can be studied even in the nanometer scale Methods: wide- and small-angle x-ray scattering (WAXS, SAXS) 10

11 SAXS reveals the structure in the range of nm SAXS intensity arises from the nanoscale porosity of the samples Ethanol-rinsed sheets vs. non-rinsed sheets: Non-rinsed sheet: no scattering = no nanoscale pores Set-up at the University of Helsinki 11

12 Specific surface of NFC effected by solvents Using SAXS the samples can be measured in different solvents Specific surface: dry NFC powder: 6.4 m²/g NFC in water: 660 m²/g NFC in ethanol: 180 m²/g 12

13 WAXS reveals the nanostructure of the fibrils Dimensions of cellulose crystallites: Width: nm Length: nm Crystallinity (= fraction of crystalline cellulose among the whole sample): 42-56% WAXS pattern of Arbocel MF40 powder 13

14 A case study: NFC + filler sheets Calcite PCC fillers 3 samples: 90%, 80% and 50% fillers Studied by µct, SAXS and SEM More information on the samples: poster Flexible fillernanocellulose structures by K. Torvinen and J. Sievänen 14

15 X-ray microtomography and SAXS on high-filler sheets In the length scale of 1-40 nm the pore structures were similar At µm range differences could be detected between 50% and 80/90% samples 15

16 SEM revealed the scale between µct and SAXS Surface and cross-section images of NFC/filler sheets 50% fillers 80% fillers The length of the scale bar is 1 µm 16

17 Summary The properties of NFC samples arise from the structure, which is different at different length scales Thus the characterization methods have to cover the size range from atomistic to macroscopic level A combination of methods is needed from nm to µm: x-ray scattering, TEM, SEM, microtomography 17

18 Acknowledgements Pentti Jääskeläinen, Antti Nykänen (Aalto, TEM) Hans-Peter Hentze (VTT, samples) Tiina Pöhler (VTT, SEM) Thank you for your attention! 18