In the past years, a growing concern for the environment has forced the research to focus more on new “greener” materials. The most abundant organic raw material in the world is cellulose. This, in combination with the versatility of the material, makes it interesting as a green option in various applications. However, to be able to take advantage of all characteristics possessed by cellulose, i.e., use it in applications where it is not inherently compatible, modification is often necessary.1-3 One common method used for modifying cellulose is grafting of polymers onto/from the cellulose chain. This offers a way of changing the inherent properties of cellulose to attain new properties, such as dimensional stability and water repellency.3
Additionally, it has been shown that polyectrolytes can be physiosorbed onto charged surfaces.4 This has made it possible to physically modify cellulose by adsorbing a polymer through electrostatic interactions instead of attaching it with a covalent bond.5 However, a more detailed investigation concerning the differences, such as surface coverage and grafting/physiosorption efficiency, between a covalent and physical attachment of a polymer has to the author’s best knowledge earlier not been performed. Therefore, this project aims to compare these two techniques. A block copolymer consisting of poly(ε-caprolactone) (PCL) and poly(di(methylamino)ethyl methacrylate) (PDMAEMA) is made, see figure 1 for 1H-NMR-spectrum.
Figure 1. The 1H-NMR-spectrum of PCL-block-PDMAEMA (in CDCl3).
The PDMAEMA-part is then quaternized (figure 2), which results in a charged chain – a polyelectrolyte.
Figure 2.The quaternization of the PDMAEMA block to obtain cationic charges.
The charges allow for the PDMAEMA-PCL copolymer to be adsorbed onto a cellulose surface. Finally, to evaluate and compare the differences between the covalent and the physical surface modification, regarding for example surface coverage, grafting/physiosorption efficiency, adhesion and matrix compatibility, various characterization methods are employed: fourier transform infrared spectroscopy (FTIR), contact angle measurements (CA), micro adhesion measurement apparatus (MAMA), force measurements using atomic force microscopy (AFM) and macroscopic peel tests using dynamical mechanical analysis (DMA) or Instron.
Figure 3. A schematic drawing of covalent attachment and physical adsorption of PCL onto cellulose.
Further work after preparation of fibres may include such steps as making of fiber-reinforced composites, out of both chemically and physically modified fibres, where for example differences concerning mechanical properties would be investigated.
(1) Lönnberg, H.; Fogelström, L.; Berglund, L.; Malmström, E.; Hult, A. European Polymer Journal 2008, 44, 2991.
(2) Lönnberg, H.; Zhou, Q.; Brumer, H., 3rd; Teeri Tuula, T.; Malmström, E.; Hult, A. Biomacromolecules 2006, 7, 2178.
(3) Roy, D.; Semsarilar, M.; Guthrie, J. T.; Perrier, S. Chemical Society Reviews 2009, 38, 2046.
(4) Decher, G.; Hong, J. D. Berichte der Bunsen-Gesellschaft 1991, 95, 1430.
(5) Utsel, S.; Carlmark, A.; Pettersson, T.; Bergström, M.; Malmström, E.; Wågberg, L. Abstracts of Papers, 241st ACS National Meeting & Exposition, Anaheim, CA, United States, March 27-31, 2011 2011, CELL.
IAWS, International Academy of Wood Science, Stockholm, 31st August – 2nd September 2011