| 1. |
- Bergenudd, Helena, 1978-
(författare)
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Understanding the mechanisms behind atom transfer radical polymerization : exploring the limit of control
- 2011
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Doktorsavhandling (övrigt vetenskapligt/konstnärligt)abstract
- Atom transfer radical polymerization (ATRP) is one of the most commonly employed techniques for controlled radical polymerization. ATRP has great potential for the development of new materials due to the ability to control molecular weight and polymer architecture. To fully utilize the potential of ATRP as polymerization technique, the mechanism and the dynamics of the ATRP equilibrium must be well understood. In this thesis, various aspects of the ATRP process are explored through both laboratory experiments and computer modeling. Solvent effects, the limit of control and the use of iron as the mediator have been investigated. It was shown for copper mediated ATRP that the redox properties of the mediator and the polymerization properties were significantly affected by the solvent. As expected, the apparent rate constant (kpapp) increased with increasing activity of the mediator, but an upper limit was reached, where after kpapp was practically independent of the mediator potential. The degree of control deteriorated as the limit was approached. In the simulations, which were based on the thermodynamic properties of the ATRP equilibrium, the same trend of increasing kpapp with increasing mediator activity was seen and a maximum was also reached. The simulation results could be used to describe the limit of control. The maximum equilibrium constant for controlled ATRP was correlated to the propagation rate constant, which enables the design of controlled ATRP systems. Using iron compounds instead of copper compounds as mediators in ATRP is attractive from environmental aspects. Two systems with iron were investigated. Firstly, iron/EDTA was investigated as mediator as its redox properties are within a suitable range for controlled ATRP. The polymerization of styrene was heterogeneous, where the rate limiting step is the adsorption of the dormant species to the mediator surface. The polymerizations were not controlled and it is possible that they had some cationic character. In the second iron system, the intention was to investigate how different ligands affect the properties of an ATRP system with iron. Due to competitive coordination of the solvent, DMF, the redox and polymerization properties were not significantly affected by the ligands. The differences between normal and reverse ATRP of MMA, such as the degree of control, were the result of different FeIII speciation in the two systems.
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| 2. |
- Carlsson, Daniel O
(författare)
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Structural and Electrochemical Properties of Functionalized Nanocellulose Materials and Their Biocompatibility
- 2014
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Doktorsavhandling (övrigt vetenskapligt/konstnärligt)abstract
- Nanocellulose has received considerable interest during the last decade because it is renewable and biodegradable, and has excellent mechanical properties, nanoscale dimensions and wide functionalization possibilities. It is considered to be a unique and versatile platform on which new functional materials can be based.This thesis focuses on nanocellulose from wood (NFC) and from Cladophora algae (CNC), functionalized with surface charges or coated with the conducting polymer polypyrrole (PPy), aiming to study the influence of synthesis processes on structural and electrochemical properties of such materials and assess their biocompatibility.The most important results of the work demonstrated that 1) CNC was oxidized to the same extent using electrochemical TEMPO-mediated oxidation as with conventional TEMPO processes, which may facilitate easier reuse of the reaction medium; 2) NFC and CNC films with or without surface charges were non-cytotoxic as assessed by indirect in vitro testing. Anionic TEMPO-CNC films promoted fibroblast adhesion and proliferation in direct in vitro cytocompatibility testing, possibly due to its aligned fibril structure; 3) Rinsing of PPy-coated nanocellulose fibrils, which after drying into free-standing porous composites are applicable for energy storage and electrochemically controlled ion extraction, significantly degraded the PPy coating, unless acidic rinsing was employed. Only minor degradation was observed during long-term ambient storage; 4) Variations in the drying method as well as type and amount of nanocellulose offered ways of tailoring the porosities of nanocellulose/PPy composites between 30% and 98%, with increments of ~10%. Supercritical CO2-drying generated composites with the largest specific surface area yet reported for nanocellulose/conducting polymer composites (246 m2/g). The electrochemical oxidation rate was found to be controlled by the composite porosity; 5) In blood compatibility assessments for potential hemodialysis applications, heparinization of CNC/PPy composites was required to obtain thrombogenic properties comparable to commercial hemodialysis membranes. The pro-inflammatory characteristics of non-heparinized and heparinized composites were, to some extent, superior to commercial membranes. The heparin coating did not affect the solute extraction capacity of the composite.The presented results are deemed to be useful for tuning the properties of systems based on the studied materials in e.g. energy storage, ion exchange and biomaterial applications.
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| 3. |
- Boujemaoui, Assya, 1983-
(författare)
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Surface Modification of Nanocellulose towards Composite Applications
- 2016
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Doktorsavhandling (övrigt vetenskapligt/konstnärligt)abstract
- Nanocelluloses have attracted great interest during recent decades owing to their renewability, abundancy and remarkable physical and mechanical properties. The aim of this work was to investigate new strategies for surface modification and functionalization of nanocelluloses and their subsequent incorporation in polymer-host matrices.Nanocomposites of cellulose nanofibrils (CNF) and polycaprolactone (PCL) were produced by employing CNF nanopaper (NP) as a template and surface-initiated ring-opening polymerization (SI-ROP) of ε-caprolactone (ε-CL). SI-ROP of ε-CL from filter paper (FP) was also carried out for comparison. A larger amount of PCL was grafted from NP than from FP. The grafted NP had stronger mechanical properties than neat PCL.Cellulose nanocrystal (CNC)-reinforced polyvinyl acetate (PVAc) nanocomposites were also investigated. CNC were modified via “SI-reversible addition-fragmentation chain transfer and macromolecular design via the interchange of xanthate” (SI-RAFT/MADIX) polymerization of vinyl acetate (VAc). The resulting nanocomposites exhibited improved mechanical performance than the unmodified CNC.It is generally agreed that covalent grafting is superior to physical adsorption for the modification of a reinforcing agent. However, this hypothesis has never been thoroughly investigated. CNC was modified either through covalent grafting or through physical adsorption of poly(butyl methacrylate) (PBMA). Both methods resulted in improved mechanical performance than that of pure PCL or PCL containing unmodified CNC. However, covalent grafting gave the best mechanical performance even at high relative humidity.Functionalized CNC (F-CNC) were obtained through a versatile methodology employing organic acids bearing a functional group were employed for the simultaneous acid hydrolysis and esterification of cellulose fibers. This provided a facile route for the preparation of F-CNC.
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| 4. |
- Jonsson, Magnus, 1973-
(författare)
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Thermally Expandable Microspheres Prepared via Suspension Polymerization - Synthesis, Characterization, and Application
- 2010
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Doktorsavhandling (övrigt vetenskapligt/konstnärligt)abstract
- Thermally expandable microspheres are polymeric core/shell particles in which a volatile hydrocarbon is encapsulated by a thermoplastic shell. When these microspheres are heated, they expand and increase their volume dramatically. This volume increase is retained upon cooling, leading to a density reduction from around 1100 kg m-3 to about 30 kg m-3. Since the development in the early 1970´s, microspheres have been used extensively by the industry as a foaming agent or light weight filler. In this thesis, microspheres with a poly(acrylonitrile-co-methacrylonitrile) shell have been synthesized through free radical suspension polymerization. The microspheres have been characterized with respect to particle morphology and expansion properties in order to deepen the understanding of the microspheres. It was found that the monomer feed ratio and the polymerization temperature are very important parameters with respect to the expansion properties. Excellent expansion could only be accomplished when polymerizing at 62 °C, with the acrylonitrile feed, fAN, being around 60 mol%, even though core/shell microspheres are formed over a much wider range of fAN. Furthermore, no expansion was achieved when polymerizing at 80 °C, even though no noticeable differences were found, compared to the corresponding sample polymerized at 62 °C. It was also shown that the expansion properties can be modified by replacing the encapsulated hydrocarbon by another hydrocarbon with a different boiling point. Not only is the boiling point important, the structure of the hydrocarbon is also important. Isooctane which is highly branched was found to give superior expansion compared to linear or cyclic hydrocarbons having a similar boiling point. Crosslinking of the polymer shell has proven to be very important for the expansion properties. Both the amount and the structure of the crosslinker are important parameters. Especially the maximum expansion can be improved by the crosslinking of the polymer shell. This originates in an increase in the shape persistence of the expanded microspheres at elevated temperatures. By the combination of crosslinkers that are incorporated separately into the polymer shell, the onset temperature of expansion can be increased significantly. Finally, the surface of microspheres has been modified by grafting poly(glycidyl methacrylate) from the surface by ARGET ATRP. Given that the reaction conditions are appropriate, such modifications can be performed with only limited effects on the expansion properties of the microspheres.
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| 5. |
- Mousa, Maryam
(författare)
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Exploring bio-based and biodegradable polymers: free-radical polymerization, hydrolysis and applications
- 2024
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Doktorsavhandling (övrigt vetenskapligt/konstnärligt)abstract
- Increasing concerns regarding the depletion of fossil-based resources and theaccumulation of plastic waste in the environment have resulted in extensiveresearch aimed at finding more sustainable alternatives to today’s plastics.In this work, bio-based and biodegradable polymers have been synthesizedusing free-radical polymerization in homogeneous and heterogeneoussystems. The polymers have been characterized with respect to chemicalstructure, thermal properties and degradation. This is a step towards thedevelopment of materials that are bio-based and biodegradable, ultimately toreduce the negative impact of plastic materials on the environment.It was found that bio-based α-methylene-γ-butyrolactone and α-methylene-γ-valerolactone (MeMBL) which exhibit similar chemical structures to fossilbasedmeth(acrylate) monomers, are capable of yielding polymers withsimilar or even superior properties compared to their fossil-basedcommodity counterparts. The differences in monomer reactivity affect thestructure of the copolymer which, in turn, influences the polymer properties,for instance, thermal behaviour (glass transition temperature). Theseproperties were later evaluated after the incorporation of MeMBL in thepolymeric shell of thermally expandable microspheres by free-radicalsuspension polymerization. Replacing fossil-based methyl methacrylate(MMA) with bio-based MeMBL resulted in partially bio-based thermallyexpandable microspheres (TEMs) where it was seen that the expansionproperties were affected as the expansion temperatures increased. It waseven possible to synthesize TEMs with a fully bio-based polymer shell with amuch higher expansion temperature window than TEMs with a fully fossilbasedpolymer shell.Free-radical ring-opening polymerization (rROP) has been used to synthesizedegradable polymers using cyclic ketene acetals (CKAs) which weresynthesized using a new more efficient synthesis route. Unlike traditionalring-opening polymerization, which results in linear polyesters, rROP of CKAsresults in branched polyesters. The degree of branching and introducing aside-group to the polymer chain influenced the polymer degradability wherethe presence of side-groups slowed the degradation significantly.The possibility to use these monomers in heterogeneous systems has beenevaluated by introducing CKA in the free-radical suspension polymerizationof microcapsules with a polymer shell from acrylonitrile (AN) and vinylacetate. However, their incorporation into the polymer backbone could notbe verified. This as the use of CKA in heterogeneous systems is challengingdue to their sensitivity towards hydrolysis and their low reactivity duringcopolymerization, especially toward acrylonitrile.
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| 6. |
- Nordqvist, Petra
(författare)
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Exploring the Wood Adhesive Performance of Wheat Gluten
- 2012
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Doktorsavhandling (övrigt vetenskapligt/konstnärligt)abstract
- The increasing environmental concern has reawakened an interest in materials based on renewable resources as replacement for petroleum-based materials. The main objective of this thesis was to explore plant proteins, more specifically wheat gluten, as a binder in wood adhesives intended for typical solid wood applications such as furniture and flooring. Alkaline and acidic dispersions of wheat gluten were used as wood adhesives to bond together beech wood substrates. Soy protein isolate was used as a reference. The tensile shear strengths of the substrates were measured for comparison of bond strength and resistance to cold water. AFM in colloidal probe mode was used to investigate nanoscale adhesion between cellulose and protein films. Wheat gluten was divided into the two protein classes; glutenins and gliadins, and their adhesive performance was compared with that of wheat gluten. Heat treatment and mild hydrolysis were investigated as means for improving bonding performance of wheat gluten. The treated wheat gluten samples were analysed by SE-HPLC and 13C-NMR to correlate molecular size distribution and structural changes with bonding performance. Soy protein isolate is superior to wheat gluten, especially in regards to water resistance. However, the bond strength of wheat gluten is improved when starved bond lines are avoided. The AFM analysis reveals higher interfacial adhesion between soy protein isolate and cellulose than between wheat gluten and cellulose. These results partly explain some of the differences in bonding performance between the plant proteins. Soy protein isolate contains more polar amino acid residues than wheat gluten and possibly interacts more strongly with cellulose. Furthermore, the bond performances of wheat gluten and glutenin are similar, while that of gliadin is inferior to the others, especially regarding water resistance. The extent of penetration of the dispersions into the wood material has a large impact on the results. The bonding performance of gliadin is similar to the others when over-penetration of the dispersion into the wood material is avoided. Moreover, the bond strength of the wheat gluten samples heated at 90°C was in general improved compared to that of wheat gluten. A small improvement was also obtained for some of the hydrolyzed wheat gluten samples (degree of hydrolysis: 0-0.6 %). The improvements in bonding performance for the heat treated samples are due to polymerization, while the improvements for the hydrolyzed samples are due to denaturation. The 13C-NMR analysis of the treated samples confirms some degree of denaturation.
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| 7. |
- Svensson, Anna
(författare)
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Nanocomposites made from nanoporous cellulose fibre
- 2012
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Licentiatavhandling (övrigt vetenskapligt/konstnärligt)abstract
- This thesis explores how to use the dry nanoporous structure of cellulosic fibres in new types of composite materials. A large effort was also given on how to correctly characterize the structure of fibres where the wet structure has been preserved also in the dry state.Delignified wood fibres have an open fibrillar structure in their water-swollen state. In the present work, this open fibrillar structure was preserved in the dry state by performing a liquid exchange procedure and the samples were thereafter carefully dried with Ar(g). The samples of never-dried TEMPO-oxidized dissolving pulp had a specific surface area of 130 m2/g in the dry state, as measured using the Brunauer, Emmet, and Teller (BET) Nitrogen gas adsorption method. This open structure was also revealed using field emission scanning electron microscopy (FE-SEM).The water-swollen and dry open structures were thoroughly characterized for various pulps. A new method for determining the pore size of water-swollen delignified cellulosic fibres is presented. By combining the results from solid state nuclear magnetic resonance NMR, measuring the specific surface area [m2/g] in the water-swollen state, with fibre saturation point (FSP), measuring the pore volume of fibres in water-swollen state [mass water/mass fibre], the average pore size can be determined without the need of assuming a certain pore geometry.The dry nanoporous structure was then used as a scaffold for in-situ polymerization, to demonstrate how the properties of the fibrils in the fibre wall can be exploited without the need to disintegrate the fibre wall. Both poly(methylmethacrylate) (PMMA) and poly(butylacrylate) (PBA) were successfully used as the polymeric matrix, and both nanocomposites (i.e., fibre/PMMA and fibre/PBA) had a fibre content of approximately 20 w%. The structure of the composites was characterized using SEM and Atomic Force Microscopy (AFM) operated in the phase imaging mode. The AFM results indicate that the cellulose aggregates and polymeric matrix were successfully mixed on a nanoscale, creating a nanocomposite of interpenetrating polymer molecules and cellulose fibrils, rather than a microcomposite, when using microscopic cellulose fibres. The water absorption capacity of the nanocomposites was reduced significantly, indicating that almost all nanopores in the fibre wall were successfully filled with matrix polymer. The mechanical properties were investigated, showing the importance of nanosized reinforcement compared to fibres of micrometer size.
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| 8. |
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| 9. |
- Mousa, Maryam, et al.
(författare)
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Suspension polymerization of microcapsules from cyclic ketene acetals in combination with acrylonitrile and vinyl acetate
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Annan publikation (övrigt vetenskapligt/konstnärligt)abstract
- Microcapsules were synthesized by free-radical suspension polymerization using the cyclic ketene acetals (CKAs), 2-Methylene-1,3-dioxepane (MDO) and 5,6-Benzo-2-methylene-1,3-dioxepane (BMDO) together with acrylonitrile and vinyl acetate to encapsulate a blowing agent. The core/shell polymers were characterized with respect to their chemical structure, thermal expansion and morphology. SEM analysis confirmed the core/shell morphology of the particles which also showed a great encapsulation of the blowing agent by GC analysis. The incorporation of CKAs was difficult to confirm with structural analysis using NMR as there are many overlapping2peaks, however, the presence of BMDO in the system contributed to lower conversion of VAc and to a decreased thermal stability of the particle shell. Optimization of the polymerization system and a better control of the CKAs sensitivity to water are needed for a successful incorporation of CKAs.
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| 10. |
- Mousa, Maryam, et al.
(författare)
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Thermally expandable microspheres based on fully or partially bio-based polymers
- 2024
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Ingår i: Journal of Applied Polymer Science. - : Wiley. - 0021-8995 .- 1097-4628.
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Tidskriftsartikel (refereegranskat)abstract
- Bio-based or partially bio-based thermally expandable microspheres were synthesized by suspension (co)polymerization of the bio-based monomer α-methylene-γ-valerolactone (MeMBL) together with acrylonitrile and/or methyl methacrylate to form expandable core/shell particles by encapsulating a hydrocarbon-based blowing agent. The core/shell polymers were characterized with respect to their chemical structure, thermal expansion and morphology. The obtained particles, thermally expandable microspheres (TEMs), showed an increasing onset expansion temperature with increasing content of MeMBL owing to the high glass transition temperature of PMeMBL. As a result, bio-based/partially bio-based TEMs are achieved with high thermal stability and expansion properties which can be tailored for various applications.
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