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- Telaretti Leggieri, Rosella
(author)
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Towards compatibilization of cellulose nanofibrils in polymer matrices : Polymer design for mediating the nanofibril–matrix interface
- 2023
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Doctoral thesis (other academic/artistic)abstract
- Magnifying the nanostructure of wood reveals the features of an extraordinary nanocomposite material. In this nanocomposite, long fibrils of semicrystalline cellulose, with a cross-section in the nanometer range and length up to several micrometers, are embedded in an amorphous matrix made of other polymeric components. Cellulose is the load-bearing skeleton responsible for the mechanical strength of plant tissues, while the matrix cements the fibrils together and provides flexibility. Ever since the first methods were developed for producing individualized cellulose nanofibrils (CNFs), materials scientists have explored the potential of these biobased nanomaterials as reinforcement for nanocomposite applications. In light of the quest for renewable alternatives to fossil-based materials, both for common use and high-value applications, wood nanocomponents offer important opportunities. However, dispersing CNFs within conventional polymer matrices entails challenges related to the hydrophilic–hydrophobic character of the nanofibril–matrix interface. In this context, the aim of this thesis is to evaluate strategies for compatibilizing CNFs in relatively hydrophobic polymer matrices. Three different nanocomposite applications were explored by incorporating low loadings of CNFs (0.5–6 wt%) in polymer matrices. The properties of the nanofibril–matrix interface were modified by two alternative approaches, both based on the adsorption of copolymers onto CNFs in water dispersion. In the first part of the work, a tailor-made random copolymer was adsorbed onto the CNF surface and used as a macroinitiator for the in situ polymerization of methacrylate monomers by aqueous atom transfer radical polymerization (ATRP). The second part focuses on the adsorption onto CNFs of amphiphilic block copolymers synthesized by ATRP to function as CNF–matrix compatibilizers. Synthetic and analytical aspects related to the design of well-defined structures were investigated, as well as fundamental parameters affecting their adsorption onto cellulose. The use of amphiphilic block copolymers as CNF–matrix compatibilizers was explored both while targeting the dispersion of CNFs in a thermosetting coating resin, and in a thermoplastic polymer matrix. The outcomes of this work highlight significant effects induced by surface-modified CNFs on the structural and mechanical properties of the studied nanocomposite materials.
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- Rahm, Martin, 1982-
(author)
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Green Propellants
- 2010
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Doctoral thesis (other academic/artistic)abstract
- To enable future environmentally friendly access to space by means of solid rocket propulsion a viable replacement to the hazardous ammonium perchlorate oxidizer is needed. Ammonium dinitramide (ADN) is one of few such compounds currently known. Unfortunately compatibility issues with many polymer binder systems and unexplained solid-state behavior have thus far hampered the development of ADN-based propellants. Chapters one, two and three offer a general introduction to the thesis, and into relevant aspects of quantum chemistry and polymer chemistry. Chapter four of this thesis presents extensive quantum chemical and spectroscopic studies that explain much of ADN’s anomalous reactivity, solid-state behavior and thermal stability. Polarization of surface dinitramide anions has been identified as the main reason for the decreased stability of solid ADN, and theoretical models have been developed to explain and predict the solid-state stability of general dinitramide salts. Experimental decomposition characteristics for ADN, such as activation energy and decomposition products, have been explained for different physical conditions. The reactivity of ADN towards many chemical groups is explained by ammonium-mediated conjugate addition reactions. It is predicted that ADN can be stabilized by changing the surface chemistry with additives, for example by using hydrogen bond donors, and by trapping radical intermediates using suitable amine-functionalities. Chapter five presents several conceptual green energetic materials (GEMs), including different pentazolate derivatives, which have been subjected to thorough theoretical studies. One of these, trinitramide (TNA), has been synthesized and characterized by vibrational and nuclear magnetic resonance spectroscopy. Finally, chapter six covers the synthesis of several polymeric materials based on polyoxetanes, which have been tested for compatibility with ADN. Successful formation of polymer matrices based on the ADN-compatible polyglycidyl azide polymer (GAP) has been demonstrated using a novel type of macromolecular curing agent. In light of these results further work towards ADN-propellants is strongly encouraged.
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| 4. |
- Porsch, Christian, et al.
(author)
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In Vitro Evaluation of Non-Protein Adsorbing Breast Cancer Theranostics Based on 19F-Polymer Containing Nanoparticles
- 2013
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In: Particle and Particle Systems Characterization. - : Wiley. - 0934-0866 .- 1521-4117. ; 30:4, s. 381-390
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Journal article (peer-reviewed)abstract
- Eight fluorinated nanoparticles (NPs) are synthesized, loaded with doxorubicin (DOX), and evaluated as theranostic delivery platforms to breast cancer cells. The multifunctional NPs are formed by self-assembly of either linear or star-shaped amphiphilic block copolymers, with fluorinated segments incorporated in the hydrophilic corona of the carrier. The sizes of the NPs confirm that small circular NPs are formed. The release kinetics data of the particles reveals clear hydrophobic core dependence, with longer sustained release from particles with larger hydrophobic cores, suggesting that the DOX release from these carriers can be tailored. Viability assays and flow cytometry evaluation of the ratios of apoptosis/necrosis indicate that the materials are non-toxic to breast cancer cells before DOX loading; however, they are very efficient, similar to free DOX, at killing cancer cells after drug encapsulation. Both flow cytometry and confocal microscopy confirm the cellular uptake of NPs and DOX-NPs into breast cancer cells, and in vitro 19F-MRI measurement shows that the fluorinated NPs have strong imaging signals, qualifying them as a potential in vivo contrast agent for 19F-MRI.
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| 5. |
- Porsch, Christian, et al.
(author)
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Toward Unimolecular Micelles with Tunable Dimensions Using Hyperbranched Dendritic-Linear Polymers
- 2014
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In: Biomacromolecules. - : American Chemical Society (ACS). - 1525-7797 .- 1526-4602. ; 15:6, s. 2235-2245
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Journal article (peer-reviewed)abstract
- A library of amphiphilic, hyperbranched dendritic-linear polymers (HBDLPs) are successfully synthesized, and evaluated as potential unimolecular micelles. Hyperbranched macroinitiators (HBMI), extended with poly(ethylene glycol) methacrylate (P(OEGMA)), are afforded via a combination of self-condensing vinyl (co)polymerization (SCV(C)P) and atom transfer radical polymerization (ATRP), providing a versatile two-step synthetic route. The HBDLP architecture and chain lengths are varied, and the effect on the nanoparticle (NP) stability and properties are evaluated. The HBDLPs form predominantly stable and spherical NPs, and the NP dimensions could be tailored by the HBDLP characteristics. The NPs formed are of high molecular weight, and their stability varies with the properties of the corresponding HBDLP. Too small dendritic segment, or too low degree of PEGylation, results to some extent in NP aggregation, while higher molecular weight HBDLPs, with a high amount of hydrophilic segments, appears to form discrete unimolecular micelles. The versatility of the platform is further demonstrated by the convenience of forming a HBDLP. with a more complex, linear copolymer extension instead of P(OEGMA).
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| 6. |
- Östmark, Emma, et al.
(author)
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Dendritic Structures Based on Bis(hydroxymethyl)propionic Acid as Platforms for Surface Reactions
- 2005
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In: Langmuir. - : American Chemical Society (ACS). - 0743-7463 .- 1520-5827. ; 21:10, s. 4512-4519
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Journal article (peer-reviewed)abstract
- In this paper we present results related to the self-assembly of different generations of disulfide-cored 2,2-bis(hydroxymethyl)propionic acid-based dendritic structures onto gold surfaces. These molecular architectures, ranging from generation 1 to generation 3, contain removable acetonide protecting groups at their periphery that are accessible for hydrolysis with subsequent formation of OH-terminated surface-attached dendrons. The deprotection has been investigated in detail as a versatile approach to accomplish reactive surface platforms. A special focus has been devoted to the comparison of the properties of the layers formed by hydrolysis of the acetonide moieties directly on the surface and in solution, prior to the layer formation.
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| 7. |
- Alexakis, Alexandros Efraim, et al.
(author)
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Modification of CNF‐Networks by the Addition of Small Amounts of Well‐Defined Rigid Cationic Nanolatexes
- 2022
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In: Macromolecular Chemistry and Physics. - : Wiley. - 1022-1352 .- 1521-3935. ; 224:1, s. 2200249-2200249
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Journal article (peer-reviewed)abstract
- Cellulose nanofibril (CNF)-networks are modified by the addition of small amounts (below 10 wt%) of well-defined cationic nanolatexes synthesized through reversible addition–fragmentation chain-transfer-mediated polymerization-induced self-assembly (PISA). Minute amounts of nanolatex inclusions lead to increased tensile and shear moduli, indicating that nanolatexes can act as bridging-points between CNFs. At higher nanolatex content, this stiffening effect is lost, likely due to interactions between nanolatexes leading to plasticization. The influence of nanolatex content and size on interparticle distance is discussed and is used as a tool to understand the effects observed in macroscopic properties. Upon annealing, the stiffening effect is lost due to the softening of the nanolatexes, indicating that the core–shell morphology is a prerequisite for this effect. These systems form a versatile platform to develop fundamental insights into complex condensed colloidal systems, to ultimately aid in the development of new sustainable material concepts.
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| 10. |
- Kaldéus, Tahani, et al.
(author)
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Molecular Engineering of the Cellulose-Poly(Caprolactone) Bio-Nanocomposite Interface by Reactive Amphiphilic Copolymer Nanoparticles
- 2019
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In: ACS Nano. - : American Chemical Society (ACS). - 1936-086X .- 1936-0851. ; 13:6, s. 6409-6420
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Journal article (peer-reviewed)abstract
- A molecularly engineered water-borne reactive compatibilizer is designed for tuning of the interface in melt-processed thermoplastic poly(caprolactone) (PCL)-cellulose nanocomposites. The mechanical properties of the nanocomposites are studied by tensile testing and dynamic mechanical analysis. The reactive compatibilizer is a statistical copolymer of 2-(dimethylamino)ethyl methacrylate and 2-hydroxy methacrylate, which is subsequently esterified and quaternized. Quaternized ammonium groups in the reactive compatibilizer electrostatically match the negative surface charge of cellulose nanofibrils (CNFs). This results in core-shell CNFs with a thin uniform coating of the compatibilizer. This promotes the dispersion of CNFs in the PCL matrix, as concluded from high-resolution scanning electron microscopy and atomic force microscopy. Moreover, the compatibilizer "shell" has methacrylate functionalities, which allow for radical reactions during processing and links covalently with PCL. Compared to the bio-nanocomposite reference, the reactive compatibilizer (<4 wt %) increased Young's modulus by about 80% and work to fracture 10 times. Doubling the amount of peroxide caused further improved mechanical properties, in support of effects from higher cross-link density at the interface. Further studies of interfacial design in specific nanocellulose-based composite materials are warranted since the detrimental effects from CNFs agglomeration may have been underestimated.
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