Characterisation methods of nanocellulose materials Assessment of behaviour using surface sensitive methods

Transcription

1 Characterisation methods of nanocellulose materials Assessment of behaviour using surface sensitive methods Dr. Tekla Tammelin Principal Scientist at VTT Technical Research Centre of Finland Docent in Bioproduct Technology at Aalto University Ongoing modification of cellulose nanofibers and their potential applications CostAction FP1205, October 15-16, 2014

2 2 Objective of the Study To obtain deeper understanding on the surface behaviour of cellulosic nanofibrils with respect to formation of functional structures using surface sensitive methods Surface chemical composition by XPS Indirect information on surface reactivity by following the relative abundance of C-C bonds, following the success of surface modifications Atomic force microscopy (AFM) Changes in fibrillar fine structure Contact angle - Direct information on wetting behaviour which can be linked to available -OH groups Quartz crystal microbalance with dissipation monitoring (QCM-D) equipped with humidity module water vapour uptake ability of cellulosic nanofibrils and changes in viscoelastic properties of the CNF thin films

3 23/10/ CASE I Surface modification of individual nanofibrils

4 4 Solvent impact on CNF surface chemistry and fine structure Behaviour of individual fibrils in DMA in toluene The effect of solvent on media driven aggregation tendency H 2 O MeOH DMA H 2 O MeOH Toluene Changes in fine structure by AFM Surface chemical composition by XPS indirect information on surface reactivity and medium dependent conformation Water contact angle direct information on the surface adaptation, accessibility and surface passivation Johansson, L.-S., Tammelin, T., Campbell, J. M., Setälä, H., Österberg, M.Soft Matter 2011, 7,

5 5 Understanding the nature of CNF surface by XPS How to maximize the available surface for derivatizations Determination of different carbon bonds Relative abundance of C-C bonds CNF surface is extremely reactive!! Minimizing the surface free energy when adapting towards hydrophobic media passivated surfaces

6 6 Changes in wetting NFC behavior Water contact angle direct information on the surface adaptation, accessibility and surface passivation Orientation of the hydrophilic and hydrophobic planes of the cellulose molecules The behavior demonstrated by several researchers hydrophilic plane hydrophobic plane Holmberg et al. J. Colloid Interface Sci., 1997, 186, 369; Yamane et al. Polym. J., 2006, 38, 819; Tammelin et al. Cellulose, 2006, 13,519, Suchy et al. Biomacromolecules, 2010, 11,515.

7 7 Silylations of NFC 500 nm The effect of solvent H 2 O MeOH DMA H 2 O MeOH Toluene Degree of surface substitution by XPS Changes in fine structure by AFM Andresen et al., Cellulose, 2006, 13, 665.

8 8 Nanofibrillar structure retained in cellulose compatible solvent Nanocellulose reactivity XPS indicates increase in silica content Increase in the relative abundance of C-C and C-Si bonds Degree of surface substitution can be calculated AFM results confirm the successful surface modification the maintained nanofibrillar structure The same derivatisation procedure: DMA-exchanged NFC DS=1.0 ± 0.2 Toluene-exchanged NFC DS = 0.02 ± 0.01 Surface chemistry of fibers and NFC: Relative abundance of C-C bonds indicates that NFC surface is extremely reactive and is easily passivated in hydrophobic media. In NFC compatible solvent the reaction efficiency is higher and the nanoscale structure is retained

9 9 AFM height image AFM phase image Unmodified NFC AFM images suggest the maintained nanofibrillar structure evenly distributed chemical modification on the fibril surface Silylated NFC 5 5 μm images

10 23/10/ CASE II Surface modification of CNF films

11 11 Chemical modification directly on CNF film surface APTES-modified (3-Aminopropyl)trimethoxysilane UV/O 3 activation Rinsing Contact angle (degrees) DMA (T, N 2 ) Untreated film UV/O 3 treated film (measured after 15 min) UV/O 3 treated film (measured after one week) Time (seconds) Air drying Tammelin, Tekla, Hippi, Ulla, Salminen Arto. Method for the preparation of NFC films on supports. PCT Int. Appl. (2013), WO A Arola, S., Tammelin, T., Setälä, H., Tullila, A. and Linder, M. Immobilization Stabilization of Proteins on Nanofibrillated Cellulose Derivatives and Their Bioactive Film Formation. Biomacromolecules, 2012, 13, Österberg, M.*, Peresin, M. S., Johansson, L.-S. and Tammelin, T.*, Clean and reactive nanostructured cellulose surface. Cellulose, 2013, 20, Peresin, M.S., Vartiainen, J., Kammiovirta, K., Heikkinen, H., Johansson, L-S., Österberg, M. and Tammelin, T. Surface modification on nanofibrillated cellulose films surface. Manuscript under preparation

12 12 Effect of activation of the CNF film surface on chemical functionalization Activated aminated Aminated NFC N 1s Si 2p

13 13 Surface modified nanocellulose films as barrier materials Nanocellulosic materials have an inherent tendency to form films upon drying Good oxygen barrier materials especially in dry conditions Sensitive towards moisture and water Oxygen permeability of surface modified nanocellulose film Oxygen permeability of APTES-modified 0.03 ml mm m -2 day -1 atm -1 at RH~50% 0.17 ml mm m -2 day -1 atm -1 at RH~80%. Tammelin, T. and Vartiainen, J., NFC Films and Barriers. In: Handbook of Green Materials; Processing Technologies, Properties and Applications. Vol 3. Self- and directed assembling of Bionanomaterials. Oksman, K., (Ed.). M.S. Peresin, J. Vartiainen, V. Kunnari, T. Kaljunen, T. Tammelin and P. Qvintus, in the 4th International Conference on Pulping, Papermaking and Biotechnology (ICPPB'12) (Nanjing, China, 2012), pp M

14 23/10/ CASE III Water vapour uptake ability of CNF

15 15 Water vapour uptake by Quartz Crystal Microbalance with Dissipation (QCM-D) Change in frequency, Δf change in mass on the crystal Due to the film swelling and water vapour penetration the mass detected by the crystal increases the frequency response decreases m = C f n -1 Change in dissipation ΔD The damping of the oscillation depends on the viscoelastic properties of the model film solvent bound in the film structure generates softer and more mobile layer Rodahl, K.; Höök, F.; Krozer, A.; Brzezinski, P.; Kasemo, B. Rev. Sci. Instrum. 1995, 66, Höök, F.; Rodahl, M.; Brzezinski, P.; Kasemo, B. Langmuir 1998,14, 7290.

16 16 CNF surfaces for QCM-D water vapour uptake studies fluid-flow/ evaporation substrate High surface xylan CNF Low surface xylan CNF ω Aqueous CNF dispersions were spin coated on the QCM-D sensor surface constant areal mass Mild heat treatment to ensure the adhesion Constant areal mass: ~15 mg/m 2 - individual fibrils ~170 mg/m²- CNF network Ahola, S. et al., Biomacromolecules, 2008, 9, 1273, Tammelin, T. and Vartiainen, J. Nanocellulose films and barriers. In Handbook of Green Materials, Vol 3. Self- and directed assembling of Bionanomaterials, K. Oksman, A. P. Mathew, A. Bismarck, O. Rojas, M. Sain (Eds), World Scientific Publishing Co. Pte. Ltd.Singapore, 2014, p Tenhunen et al. Reactive and Functional Polymers, 2014, DOI: /j.reactfunctpolym ,

17 17 Areal mass and thickness of the CNF Film Thickness determination by QCM-D m h = C f = n m Sauerbrey ρ Assumed Frequency change measured in air before and after cellulose layer deposition Sauerbrey equation is valid to estimate the mass change (areal mass) Assuming the density values of the film (1200 kg m -3 ), the thickness can be calculated Peresin, S., Kammiovirta, K., Setälä, H. and Tammelin, T.*, Structural features and water interactions of etherified xylan thin films. J Polym Environ., 2012, 20,

18 18 Water vapour uptake ability of CNF investigated by bulk and surface sensitive methods ~15 mg/m 2 - individual fibrils ΔD < rigid CNF layer. Tenhunen et al. Reactive and Functional Polymers, 2014, DOI: /j.reactfunctpolym ,

19 19 Water vapour uptake ability of CNF network f 0 = 5 MHz, n = 3, f 3 /n RH75%: the mass uptake of the fibrils is approximately 17 mg/m 2 calculated using Sauerbrey equation CNF film swells to some extent already at low humid conditions Swelling of the layer is even more pronounced at high relative humid conditions (>RH 50%) changes in structural properties (softening and thickening) when the film interacts water molecules. Material properties are significantly altered in the presence of water molecules Plain CNF films are poor water vapor barriers alike other hydrophilic natural polymer films Tammelin, T. and Vartiainen, J. Nanocellulose films and barriers. In Handbook of Green Materials, Vol 3. Self- and directed assembling of Bionanomaterials, K. Oksman, A. P. Mathew, A. Bismarck, O. Rojas, M. Sain (Eds), World Scientific Publishing Co. Pte. Ltd.Singapore, 2014, p

20 20 Conclusions Information gained by surface sensitive methods can effectively link the material behaviour at interfaces to the macroscale physical properties Changes in surface chemistry on the outermost surface of nanocellulosic materials due to medium driven surface adaptation and passivation are experimentally evidenced Previously observed changes in cellulose surface wetting behavior can be explained When the CNF surfaces remains clean and the fibrils are not aggregated, the hydroxyl groups on the fibril surface are fully accessible for further chemical reactions Controlling the reactivity and accesibility of CNF surface Significant improvement on properties of surface modified CNF films after activation Full performance of CNF when considering the formation of 2D and 3D structures

21 21 Acknowledgements Dr. Maria Soledad Peresin, M. Sc. Tiia-Maria Tenhunen, Dr. Leena-Sisko Johansson, Prof. Monika Österberg, Dr. Harri Setälä, M. Sc. Jaakko Pere, M.Sc. Pia Qvintus Kari Kammiovirta, Vuokko Liukkonen (VTT), Ritva Kivelä and Anu Anttila (Aalto) for the excellent laboratory assistance The work carried out within the Finnish Centre for Nanocellulosic Technologies (FCNT)

22 22 Thank You for Listening