| 1. |
- Utsel, Simon, 1984-
(författare)
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Surface Modification of Cellulose-based Materials for Tailoring of Interfacial Interactions
- 2012
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Doktorsavhandling (övrigt vetenskapligt/konstnärligt)abstract
- The awareness of our need for a sustainable society has encouraged the search for renewable, high quality materials that can replace oil-based products. This, in combination with increased competition in the forest industry, has stimulated a lot of research into different types of wood-based materials where cellulose-rich fibers are combined with different types of polymers. There is hence a great need to develop efficient fiber modification techniques by which the fibers can be tailored to obtain specific properties. A significant change in properties can be achieved by modifying only the surface of fibers although only a relatively small amount of the total fiber material is modified. In this thesis, several surface modification techniques are presented as new tools to design the properties of different cellulose-based materials.In paper I, thermoresponsive nanocomposites have been assembled from specially designed thermoresponsive block copolymers and nanofibrillated cellulose. The block copolymers have one thermoresponsive block and one cationically charged block which can thus attach the polymer to an oppositely charged fiber/fibril surface. Multilayers were assembled with these block copolymers and nanofibrillated cellulose (NFC) utilizing the Layer-by-Layer (LbL) technique, resulting in thin films with a thermoresponsive behavior.In papers II and III, amphiphilic block copolymers with one less polar high molecular weight block and one cationic block were synthesized for use as a compatibilizer between fibers/fibrils and less polar polymer matrices in composites. The less polar block consisted of polystyrene (PS) in paper II and poly(ɛ-caprolactone) (PCL) in paper III. These polymers self-assemble into cationic micelles in water which can adsorb to oppositely charged surfaces, such as cellulose-based fibers/fibrils, in water under mild conditions and decrease the surface energy of the surface. Atomic force microscopy (AFM) was used to evaluate the adhesive properties of surfaces treated with these compatibilizers which clearly showed the formation of physical entanglements across the interfaces, which are essential for improved interfacial adhesion in the final composites. This modification technique could probably be utilized to make fiber-based composites with better mechanical properties. To be able to better compare this physical modification technique with a more traditional covalent grafting-from approach a method to measure attached amounts of grafted PCL onto cellulose model surfaces was developed in paper IV using a quartz crystal microbalance (QCM).In paper V, multilayers of poly(allylamine hydrochloride) (PAH) and hyaluronic acid (HA) were assembled using the LbL technique and surface structure, build-up and adhesive behavior of the multilayers were evaluated. AFM force measurements showed that a significant adhesion even at long separation distances between two surfaces treated with PAH/HA multilayers could be achieved due to extensive interdiffusion across the interface during contact, leading to significant disentanglement during separation. Fundamental parameters contributing to improved adhesion for this type of system have been evaluated and this knowledge could be used to improve cellulose-based fiber networks and possibly also other types of cellulose-based materials.In paper VI, click chemistry was used to covalently attach dendrons to cellulose surfaces and further modify them with mannose groups to obtain specific interactions with Concanavalin A. The protein interactions were studied at different protein concentrations with a QCM. The multivalent dendronized surface showed a 10-fold increase in sensitivity to the protein compared to a monovalent reference surface demonstrating greatly improved interfacial interactions. This approach could be used to improve interactions at different types of interfaces.
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| 2. |
- Bruce, Carl, et al.
(författare)
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A comparative study of covalent grafting and physical adsorption of PCL onto cellulose
- 2012
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Konferensbidrag (refereegranskat)abstract
- A growing concern for the environment has, in the past years, directed the research towards a bigger focus on new “greener” materials, such as cellulose-reinforced options. Cellulose is the most abundant organic raw material in the world and it is a versatile material. However, to be able to use it in applications where it is not inherently compatible, a modification is often necessary.1-3 One common method to achieve this modification is to graft polymers onto/from the cellulose chain. This can change the inherent properties of cellulose to attain new properties, such as dimensional stability and water repellency.3 In addition to this, it has been shown that polyectrolytes can be physiosorbed onto charged surfaces.4 Due to this, it is possible to physically modify cellulose by adsorbing a polymer through electrostatic interactions instead of attaching it with a covalent bond.5However, a more detailed investigation concerning differences of covalent and physical attachment of poly(ε-caprolactone) (PCL) onto cellulose, has to the author’s best knowledge not been performed. Therefore, this project aims to compare these two techniques. Covalently bonded PCL was grafted by surface-initiated ring opening polymerization (SI-ROP) from the cellulose. For the adsorption approach, a block copolymer consisting of PCL and a shorter segment of 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 cationically charged chain – a polyelectrolyte. This can then be used as an electrostatic linker allowing the PDMAEMA-PCL copolymer to be adsorbed onto the negatively charged cellulose model surface. Finally, differences between the two approaches are evaluated regarding for example surface coverage and grafting/physiosorption efficiency investigated with techniques such as atomic force microscopy (AFM).
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| 3. |
- 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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| 4. |
- 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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| 5. |
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| 6. |
- Bruce, Carl, et al.
(författare)
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Physical Tuning of Cellulose-Polymer Interactions Utilizing Cationic Block Copolymers Based on PCL and Quaternized PDMAEMA
- 2013
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Konferensbidrag (refereegranskat)abstract
- In this study, the aim was to prepare and evaluate a block copolymer that can be used as a compatabilizer in cellulose fiber-reinforced biocomposites. It as an amphiphilic block copolymer consisting of poly(ε-caprolactone) (PCL), made with ring-opening polymerization (ROP), and a shorter segment of poly(2-(dimethylamino)ethyl methacrylate) (PDMAEMA) that was synthesized with atom transfer radical polymerization (ATRP). The PDMAEMA-part was made in one single length, while the PCL-part was varied in three different lengths; in total were three block copolymers prepared. In the last step of the synthesis, the PDMAEMA-part was quaternized that turns it into a cationically charged chain – a polyelectrolyte. The block copolymers were then able to form cationic micelles in water, from where they can adsorb, under mild conditions, to anionic surfaces such as silicon oxide and cellulose-model surfaces. This provides the surface with a more hydrophobic character shown with contact angle measurements. Finally, with atomic force microscopy (AFM) force measurements, it was demonstrated that there is a clear entanglement behavior obtained between the block copolymers and a PCL surface at about 60 °C, which is of importance for the information regarding the adhesive interface in a future biocomposite.
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| 7. |
- 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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| 8. |
- 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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| 9. |
- Bruce, Carl, et al.
(författare)
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Preparation and evaluation of well-defined di- and triblock copolymers based on poly[2-(dimethylamino)ethyl methacrylate] and poly(ε-caprolactone)
- 2014
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Ingår i: ACS National Meeting.
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Konferensbidrag (refereegranskat)abstract
- In this work, di- and triblock copolymers based on poly(2-(dimethylamino)ethyl methacrylate) (PDMAEMA) and poly(ε-caprolactone) (PCL) have been prepared. The PDMAEMA length was kept constant for both di- and triblock copolymers, while in the diblock copolymers the PCL length was varied in three different lengths, yielding three separate block copolymers. For the triblock blockcopolymers, on the other hand, also the PCL blocks were of the same length yielding one ABA- and one BAB-type block copolymer. In the next step, the PDMAEMA-part was quaternized to yield polyelectrolytes with either one or two charged block(s). In the final step, difference in adsorption behavior onto a negatively charged cellulose surface and subsequent alteration of surface properties was investigated. Overall, the polymers were evaluated in solid state, in solution, in water dispersion, and on cellulose surfaces with techniques including differential scanning calorimetry, size exclusion chromatography, dynamic light scattering and quartz crystal microbalance.
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| 10. |
- Carlsson, Linn, et al.
(författare)
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Surface-initiated ring-opening polymerization from cellulose model surfaces monitored by a Quartz Crystal Microbalance
- 2012
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Ingår i: Soft Matter. - : Royal Society of Chemistry (RSC). - 1744-683X .- 1744-6848. ; 8:2, s. 512-517
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Tidskriftsartikel (refereegranskat)abstract
- Polymer surface-grafting is an excellent method to modify the properties of a surface. However, surface-initiated polymerization is still relatively poorly understood due to the lack of appropriate characterization methods and tools to monitor the polymerizations. Herein, we report the in situ, surface-initiated ring-opening polymerization (SI-ROP) investigated in real time by the Quartz Crystal Microbalance (QCM) technique. The polymerization was performed from a cellulose model surface and the polymerization was initiated directly from the available hydroxyl groups on the cellulose. The cyclic monomer 3-caprolactone and an organic catalyst, 1,5,7-triazabicyclo[4.4.0]dec-5-ene (TBD), were used, and the reaction was performed in bulk at room temperature. Since a free polymer was formed in bulk in parallel to the grafting from the surface, the reaction was performed in three cycles with rinsing steps in between to measure only the effect of the surface grafting. The change in frequency showed that the grafted amount of polymer increased after each cycle indicating that most of the chain ends remained active. After polymer grafting, the cellulose model surface showed a more hydrophobic character, and the surface roughness of the cellulose model surface was reduced. This study clearly shows that QCM is a viable method to monitor SI-ROP in situ from cellulose surfaces. We believe this is an important step towards a deeper understanding of how to tailor the interface between polymer-modified cellulose and a polymer matrix in biocomposites.
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