| 21. |
- Bruce, Carl, et al.
(författare)
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A comparative study of covalent grafting and physical adsorption of PCL onto cellulose
- 2011
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Konferensbidrag (refereegranskat)abstract
- 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.3Additionally, 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.References(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.
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| 22. |
- Bruce, Carl, et al.
(författare)
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Comparative study of covalent grafting and physical adsorption of PCL onto cellulose
- 2012
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Konferensbidrag (refereegranskat)abstract
- In this work, an investigation concerning differences between covalent and physical attachment of poly(ε-caprolactone) (PCL) to a nanocellulose modell surface was conducted. For the covalent attachment, ring-opening polymerization (ROP) was performed using the “grafting-from” approach, building the polymer from the surface. For the physical attachment, a block copolymer consisting of PCL and poly(di(methylamino)ethyl methacrylate) (PDMAEMA) was made combining ROP and atom transfer radical polymerization (ATRP). The PDMAEMA-part was then quaternized, which resulted in a charged chain – a polyelectrolyte. The charges allow for the PDMAEMA-PCL copolymer to be adsorbed onto the nanocellulose modell surface. The length of the PDMAEMA-part was kept constant (DP=20), and the length of PCL was varied (DP=150, 300, 600) for both the covalently attached polymer and for the copolymer. Finally, differences between the two approaches were evaluated regarding for example surface coverage and grafting/physiosorption efficiency investigated with techniques such as atomic force microscopy.
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| 23. |
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| 24. |
- Bruce, Carl, et al.
(författare)
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Preparation and evaluation of a block copolymer compatibilizer for biocomposite applications
- 2012
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Konferensbidrag (refereegranskat)abstract
- In this study, the concept of using a free polymer as a compatibilzer in biocomposite applications has been evaluated with focus on the polymer poly(ɛ-caprolactone) (PCL), commonly used in conventional grafting onto/from cellulose. A block copolymer consisting of PCL and a shorter segment of poly(di(methylamino)ethyl methacrylate) (PDMAEMA) was made combining ring-opening polymerization (ROP) and atom transfer radical polymerization (ATRP). The length of the PDMAEMA-part was kept constant, and the PCL-part was varied in three different lengths, yielding three separate block copolymers. As a final step, the PDMAEMA-part was quaternized, which resulted in cationically charged chains –polyelectrolytes. The charged part could then be used as an electrostatic linker allowing the PDMAEMA-PCL copolymer to be adsorbed onto negatively charged cellulose model surfaces. Finally, these cellulose model surfaces were evaluated regarding for example amount of polymer adsorbed and hydrophobic character, investigated with techniques such as quartz crystal microbalance (QCM) and contact angle measurements.
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| 25. |
- Bruce, Carl, et al.
(författare)
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Preparation and evaluation of a block copolymer compatibilizer for biocomposite applications
- 2012
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Konferensbidrag (refereegranskat)abstract
- In this study, a comparison between covalent grafting and physical adsorption of PCL onto a nanocellulose model surface was conducted. For the covalent attachment, surface-initiated ring-opening polymerization (SI-ROP) was performed. For the physical attachment, a charged block copolymer consisting of PCL and quaternized PDMAEMA was synthesized by ROP and ATRP, and adsorbed to the cellulose. Finally, differences in between the two substrates were investigated with techniques such as AFM.
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| 26. |
- Carrick, Christopher, et al.
(författare)
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Hollow cellulose capsules from CO2 saturated cellulose solutions - Their preparation and characterization
- 2013
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Ingår i: RSC Advances. - : Royal Society of Chemistry (RSC). - 2046-2069. ; 3:7, s. 2462-2469
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Tidskriftsartikel (refereegranskat)abstract
- A new material consisting of mm-sized hollow cellulose spheres, for biomedical applications or for the preparation of low weight porous materials has been prepared by a unique solution precipitation (SP) method. The technique is based on three separate steps. In the first step, high molecular mass, non-modified cellulose is dissolved in a suitable solvent. This cellulose solution is then saturated with a suitable gas (CO2 or N2 in the present work) and finally this gas-saturated solution is drop-wise added to a water reservoir. In this step, the cellulose is precipitated and a gas bubble is nucleated in the center of the cellulose sphere. When stored in water, the hollow center is filled with water, indicating that the capsule wall is porous in nature. This was also supported by BET-area measurements as well as by high resolution SEM-images of broken capsule walls. The internal void volume of a capsule was about 5 μl and the wall volume was about 8 μl. It was also established that the properties of the cellulose capsules, i.e. wall and void volume, the specific surface area, the average pore size of the capsule wall, the wall density, and the compressive load capacity could be tuned by the choice of cellulose concentration in the solution before precipitation. The capsule wall volume and void volume were also affected by the choice of gas, the gas pressure and the gas dissolution time during the gas saturation step. The response of the cellulose wall of the prepared capsules to changes in pH and ion concentration in the surrounding solution was also investigated. The swelling-shrinking behavior was further investigated by introducing more charges to the capsule wall, via carboxymethylation of the cellulose. This was achieved by using carboxymethylated cellulose which increased the swelling-shrinking effect. The results show a typical polyelectrolyte gel behavior of the capsule wall and the wet modulus of the cellulose wall was determined to be between 0.09-0.2 MPa depending on the charge of the cellulose in the capsule wall. Furthermore, the freeze dried cellulose spheres had a modulus of 1.9-7.4 MPa, depending on the cellulose concentration during the preparation of the spheres. These cellulose capsules are suitable both for the preparation of porous materials, where these larger spheres are joined together in 3D-shaped materials, and for controlled release where the interior of the capsules is filled with active substances and these substances are released by controlling the pores in the capsule walls.
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| 27. |
- Carrick, Christopher, et al.
(författare)
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Immunoselective cellulose nanospheres : a versatile platform for nanotheranostics
- 2014
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Ingår i: ACS Macro Letters. - : American Chemical Society (ACS). - 2161-1653. ; 3:11, s. 1117-1120
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Tidskriftsartikel (refereegranskat)abstract
- This paper describes a novel route for the preparation and functionalization of perfectly spherical cellulose nanospheres (CNSs), ranging from 100 to 400 nrn with a typical diameter of 160-170 nrn,for use in theranostics. The method of preparation enables both surface and interior bulk functionalization, and this presumably also makes the CNSs suitable for use in end-use applications other than theranostics. Surface functionalization was here demonstrated by antibody conjugation with an antibody specific toward the epidermal growth factor receptor (EGFR) protein, i.e., facilitating interaction with cancer cells having the EGFR. Besides showing specificity, the CNS-antibody conjugates showed a very low nonspecific binding. The CNSs could easily be bulk functionalized by embedding gold nanoparticles in the cellulose sphere matrix during CNS preparation to provide imaging contrast for diagnostic purposes.
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| 28. |
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| 29. |
- Carrick, Christopher, et al.
(författare)
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Lightweight, Highly Compressible, Noncrystalline Cellulose Capsules
- 2014
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Ingår i: Langmuir. - : American Chemical Society (ACS). - 0743-7463 .- 1520-5827. ; 30:26, s. 7635-7644
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Tidskriftsartikel (refereegranskat)abstract
- We demonstrate how to prepare extraordinarily deformable, gas-filled, spherical capsules from nonmodified cellulose. These capsules have a low nominal density, ranging from 7.6 to 14.2 kg/m(3), and can be deformed elastically to 70% deformation at 50% relative humidity. No compressive strain-at-break could be detected for these dry cellulose capsules, since they did not rupture even when compressed into a disk with pockets of highly compressed air. A quantitative constitutive model for the large deformation compression of these capsules is derived, including their high-frequency mechanical response and their low-frequency force relaxation, where the latter is governed by the gas barrier properties of the dry capsule. Mechanical testing corroborated these models with good accuracy. Force relaxation measurements at a constant compression rendered an estimate for the gas permeability of air through the capsule wall, calculated to 0.4 mL mu m/m(2) days kPa at 50% relative humidity. These properties taken together open up a large application area for the capsules, and they could most likely be used for applications in compressible, lightweight materials and also constitute excellent model materials for adsorption and adhesion studies.
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| 30. |
- Carrick, Christopher, et al.
(författare)
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Native and functionalized micrometre-sized cellulose capsules prepared by microfluidic flow focusing
- 2014
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Ingår i: RSC Advances. - : Royal Society of Chemistry (RSC). - 2046-2069. ; 4:37, s. 19061-19067
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Tidskriftsartikel (refereegranskat)abstract
- Cellulose capsules with average outer and inner radii of approximately 44 mu m and 29 mm respectively were prepared from cellulose dissolved in a mixture of lithium chloride and dimethylacetamide using a microfluidic flow focusing device (MFFD). The MFFD had three inlets where octane oil in a cellulose solution in silicone oil was used to produce a double emulsion containing a cellulose capsule. This technique enables the formation of capsules with a narrow size distribution which can be beneficial for drug delivery or controlled release capsules. In this respect, cellulose is a highly interesting material since it is known to cause no autoimmune reactions when used in contact with human tissue. Furthermore, by controlling the chemical properties of the cellulose, it is possible to trigger a swelling of the capsules and consequentially the release of an encapsulated substance, e. g. a model drug, when the capsule becomes exposed to an external stimulus. To demonstrate this, capsules were functionalized by carboxymethylation to be pH- responsive and to expand approximately 10% when subjected to a change in pH from 3 to 10. The diffusion constant of a model drug, a 4 kDa fluorescently labelled dextran, through the native capsule wall was estimated to be 6.5 X 10(-14) m(2) s(-1) by fitting fluorescence intensity data to Fick's second law.
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