| 1. |
- Träger, Andrea
(author)
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Strategies for Molecular Engineering of Macroscopic Adhesion and Integrity Focusing on Cellulose Based Materials
- 2019
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Doctoral thesis (other academic/artistic)abstract
- Many aspects of modern human life pose a strain on the delicate ecosystems around us. One example is marine litter – mainly various plastic items – which accumulate in the marine environment, where they cause problems for the fauna, such as ingestion and entanglement.The widely used plastics offer many advantages for packaging, such as low cost and easy processing into many shapes. However, in addition to their low biodegradability leading to their persistence and accumulation in nature, they are largely manufactured from petroleum,a non‐renewable resource. Clearly, it would be highly desirable to exchange the petroleum‐based materials for biodegradable ones from renewable resources. Cellulose, as the most abundant biopolymer, is one choice. There are however challenges in terms of replacing currently used plastics with cellulosic materials. One is the low ductility and formability of cellulose. Various efforts are undertaken to increase the formability of cellulose. One approach to increase the renewable fraction within a material is to utilise the intrinsic stiffness and strength of cellulose to increase the structural integrity of a composite. To fully optimise these types of materials, a fundamental understanding of the interaction across interfaces within the material is essential. The main objective in this thesis was to elucidate strategies to measure, to tune and to control the interaction across interfaces. Specific polymers were designed and synthesised which could be used to modify surfaces to achieve a wet adhesion as high as that of mussel foot protein. Many properties of the joint were tuneable by varying length and structure of the polymer and amount of polymer deposited on the surfaces. A method to accurately evaluate interfacial adhesion between a chemically modified cellulose material and another surface was successfully developed, using nanometre smooth cellulose probes exhibiting bulk material properties. Two composite materials containing cellulose as reinforcing element were successfully prepared,utilising different strategies to control and enhance the interaction between the composite constituents. Together, these findings contribute to the knowledge of how to evaluate and control the interaction across an interface.
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| 2. |
- Mousa, Maryam
(author)
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Exploring bio-based and biodegradable polymers: free-radical polymerization, hydrolysis and applications
- 2024
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Doctoral thesis (other academic/artistic)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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| 3. |
- Alexakis, Alexandros Efraim, et al.
(author)
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2-Methoxy-4-Vinylphenol as a Biobased Monomer Precursor for Thermoplastics and Thermoset Polymers
- 2023
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In: Polymers. - : MDPI AG. - 2073-4360. ; 15:9
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Journal article (peer-reviewed)abstract
- To address the increasing demand for biobased materials, lignin-derived ferulic acid (FA) is a promising candidate. In this study, an FA-derived styrene-like monomer, referred to as 2-methoxy-4-vinylphenol (MVP), was used as the platform to prepare functional monomers for radical polymerizations. Hydrophobic biobased monomers derived from MVP were polymerized via solution and emulsion polymerization resulting in homo- and copolymers with a wide range of thermal properties, thus showcasing their potential in thermoplastic applications. Moreover, divinylbenzene (DVB)-like monomers were prepared from MVP by varying the aliphatic chain length between the MVP units. These biobased monomers were thermally crosslinked with thiol-bearing reagents to produce thermosets with different crosslinking densities in order to demonstrate their thermosetting applications. The results of this study expand the scope of MVP-derived monomers that can be used in free-radical polymerizations toward the preparation of new biobased and functional materials from lignin.
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| 4. |
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| 5. |
- Alexakis, Alexandros Efraim, et al.
(author)
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Bimodal nanolatexes prepared via polymerization-induced self-assembly : losing control in a controlled manner
- 2023
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In: Polymer Chemistry. - : Royal Society of Chemistry (RSC). - 1759-9954 .- 1759-9962. ; 14:19, s. 2308-2316
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Journal article (peer-reviewed)abstract
- The combination of reversible addition-fragmentation chain-transfer (RAFT) polymerization with polymerization-induced self-assembly (PISA) is known to yield monodisperse nanolatexes. Interestingly, based on the results of the current study, reproducible bimodal nanolatexes were shown to be the result of chain extension of protonated poly(2-dimethylaminoethyl methacrylate) (PDMAEMA) with methyl methacrylate (MMA) in water when aiming for a longer hydrophobic block, for which we provide the first imaging data to our knowledge. The bimodality was found to be induced by the hydrophilic Z-group of the RAFT agent, which has been reported in the literature to be the cause of bimodal molecular weight distributions in RAFT-mediated PISA in emulsion polymerization. Moreover, the advantages of such reproducible bimodal size distribution nanolatexes in coating applications were investigated briefly, underlining the possibilities of their one-pot synthesis. It was found that when bimodal nanolatexes are adsorbed onto cellulose filter paper, the contact angle against water is higher compared to chemically similar monomodal nanolatexes. Also, the morphological arrangement was found to be dependent on the drying protocol. This study aims to expand our understanding on bimodality and the identification of parameters that could promote it on demand to target high-end applications.
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| 6. |
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| 7. |
- Alexakis, Alexandros Efraim, et al.
(author)
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Modification of cellulose through physisorption of cationic bio-based nanolatexes - comparing emulsion polymerization and RAFT-mediated polymerization-induced self-assembly
- 2021
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In: Green Chemistry. - : Royal Society of Chemistry (RSC). - 1463-9262 .- 1463-9270. ; 23:5, s. 2113-2122
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Journal article (peer-reviewed)abstract
- The polymerization of a bio-based terpene-derived monomer, sobrerol methacrylate (SobMA), was evaluated in the design of polymeric nanoparticles (nanolatexes). Their synthesis was accomplished by using emulsion polymerization, either by free-radical polymerization in the presence of a cationic surfactant or a cationic macroRAFT agent by employing RAFT-mediated polymerization-induced self-assembly (PISA). By tuning the length of the hydrophobic polymer, it was possible to control the nanoparticle size between 70 and 110 nm. The average size of the latexes in both wet and dry state were investigated by microscopy imaging and dynamic light scattering (DLS). Additionally, SobMA was successfully copolymerized with butyl methacrylate (BMA) targeting soft-core nanolatexes. The comparison of the kinetic profile of the cationically stabilized nanolatexes highlighted the differences of both processes. The SobMA-based nanolatexes yielded high T-g similar to 120 degrees C, while the copolymer sample exhibited a lower T-g similar to 50 degrees C, as assessed by Differential Scanning Calorimetry (DSC). Thereafter, the nanolatexes were adsorbed onto cellulose (filter paper), where they were annealed at elevated temperatures to result in polymeric coatings. Their morphologies were analysed by Field Emission Scanning Electron Microscopy (FE-SEM) and compared to a commercial sulfate polystyrene latex (PS latex). By microscopic investigation the film formation mechanism could be unravelled. Water contact angle (CA) measurements verified the transition from a hydrophilic to a hydrophobic surface after film formation had occured. The obtained results are promising for the toolbox of bio-based building blocks, focused on sobrerol-based monomers, to be used in emulsion polymerizations either for tailored PISA-latexes or facile conventional latex formation, in order to replace methyl methacrylate or other high T-g-monomers.
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| 8. |
- 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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| 9. |
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| 10. |
- Alexakis, Alexandros Efraim, 1994-
(author)
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Nanolatexes: a versatile toolbox for cellulose modification
- 2023
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Doctoral thesis (other academic/artistic)abstract
- Cellulosic materials are widely used in our everyday lives, ranging from paperand packaging to biomedical applications. However, in most applications, cellulose must coexist with hydrophobic polymers which can be challenging due to its hydrophilic character. This has encouraged the exploration of chemical and physical modifications of cellulose.The projects included in this thesis focus on the physical modification of cellulosic materials with tailor-made, highly versatile colloidal nanoparticles synthesized in water, called nanolatexes. Their synthesis is based on the combination of the reversible addition-fragmentation chain transfer (RAFT) polymerization with polymerization-induced self-assembly (PISA). The bridging of these techniques results in the formation of amphiphilic diblock copolymers which self-assemble in water forming a variety of morphologies. Spheres, worms and vesicles with pH-responsive shell polymers were prepared to investigate the parameters that tune these morphological transitions. Less investigated parameters such as the chemical composition of the RAFT agent were studied which resulted in the formation of bimodal nanolatexes with opal-like characteristics in a reproducible manner. A fundamental investigation of the parameters that govern the adsorption of cationically charged nanolatexes onto silica and regenerated TEMPO-oxidized cellulose model surfaces was also performed. The combination of gravimetric and a reflectometric techniques revealed the complexity of that model surface. Both the size and the charge density of the nanolatexes were found to influence their adsorption. The information gained from this study was implemented in the preparation of cellulose nanofibril (CNF)-nanocomposites with low contents of nanolatexes. It was found that when the nanolatex content was below 1 wt% the mechanical profile of the CNF-nanocomposites was improved. Finally, wood-based components were used to replace fossil-based monomers in nanolatexes. They were readily adsorbed onto cellulose filter papers and annealed, thus demonstrating their film formation capacity. Nanolatexes comprised of a wood-based shell polymer have a promising high-end application profile, as showcased by their interactions with Cu(II) ions, where nanolatexes prevented the formation of Cu(II) ion aggregates. The results summarized in this thesis add to the understanding on physical modification of cellulose and are envisaged to further promote the utilization of wood-based monomers in the production of the polymers for high-end applications.
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| 11. |
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| 12. |
- Asem, Heba
(author)
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Design of Functional Polymeric Nanoparticles for Biomedical Applications
- 2020
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Doctoral thesis (other academic/artistic)abstract
- Most of the devastating diseases such as cancer are relatively incurable and have high risks of relapse. Therefore, persistent endeavors have been devoted to improve patient survival rate and quality of life. Drug delivery systems (DDS) based on polymeric nanoparticles (PNPs) have been demonstrated to increase the therapeutic index (efficacy/toxicity ratio) of chemotherapeutic agents. This thesis focuses on designing non-toxic and multifunctional biodegradable PNPs from preformed polymers for bioimaging and drug delivery applications. Multifunctional poly(lactide-co-glycolide) (PLGA) NPs were simultaneously loaded with imaging probes, superparamagnetic iron oxide nanoparticles (SPION) and manganese-doped zinc sulfide (Mn:ZnS) quantum dots (QDs), as well as an anti-cancer drug, busulfan (Bu), during the particle formation. The NPs were utilized to enhance magnetic resonance imaging (MRI) in vivo and controlled drug release in vitro (Paper I). Poly(ε-caprolactone) (PCL) was copolymerized with poly(ethylene glycol) (PEG) to achieve stealth property for in vivo purposes. Aluminum phthalocyanine, a photosensitizer and an anti-cancer drug, was encapsulated in the PEG-b-PCL NPs for photodynamic therapy during particle formation. The biodistribution of the prepared nanophotosensitizer showed targeted drug delivery toward lungs, liver and spleen as monitored by the intrinsic fluorescence of the photosensitizer (Paper II). The PEG-b-PCL NPs were loaded with SPION or surface functionalized with VivoTag 680XL fluorochrome and utilized for in vivo multimodal imaging, MRI and fluorescence imaging (Paper III). This thesis also presents stable and engineered PNPs obtained using reversible addition-fragmentation chain transfer (RAFT) mediated polymerization-induced self-assembly (PISA). Hydrophobic agents, nile red (NR) dye or doxorubicin (DOX) drug, were encapsulated in poly(N-[3- (dimethylamino) propyl] methacrylamide)-b-poly(methyl methacrylate) (PDMAPMA-b-PMMA) NPs via one-pot RAFT-mediated PISA in water (Paper IV). The PDMAPMA-b-PMMA NPs showed very monodisperse spheres and core-shell nanostructures. Stable and non-toxic poly(acrylic acid)-b-poly(butyl acrylate) (PAA-b-PBA) NPs, synthesized via RAFTmediated PISA in water, were surface engineered by allyl-functional groups prior to bio-conjugation for targeted drug delivery (Paper V). The engineered NPs retained their colloidal stability and size post-allyl functionalization. DOX was efficiently (90 %) encapsulated in the PAA-bPBA NPs during NPs formation. A controlled release pattern of DOX from PAA-b-PBA NPs was observed over 7 days.
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| 13. |
- Asem, Heba, 1987-, et al.
(author)
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Functional nano-carriers for drug delivery by surface engineering of polymeric nanoparticles post-PISA
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Other publication (other academic/artistic)abstract
- Engineered polymeric nanoparticles (NPs) have been comprehensively explored as potential platforms for diagnosis and targeted therapy for several diseases including cancer. Herein, we designed functional poly(acrylic acid)-b-poly(butyl acrylate) (PAA-b-PBA) NPs using reversible addition-fragmentation chain-transfer (RAFT)-mediated emulsion polymerization via polymerization-induced self-assembly (PISA). The hydrophilic PAA-macroRAFT, forming a stabilizing shell (i.e. corona), was chain-extended using the hydrophobic monomer n-butyl acrylate (n-BA), resulting in stable, monodisperse and reproducible PAA-b-PBA NPs, typically having a diameter of 130 nm. Two approaches of surface engineering of the PAA-b-PBA NPs post-PISA were explored; a two-step and a one-step approach. In the two-step approach, the hydrophilic NP-shell corona was modified with allyl-groups under mild conditions using allylamine in water which resulted in stable allyl-functional NPs (allyl-NPs) suitable for further bio-conjugation. Their versatility was investigated by the subsequent conjugation of a thiol-functional fluorescent dye (BODIPY-SH) to the allyl-groups using click chemistry, in order to mimic the attachment of a thiol-functional target ligand. The average size and size distribution of the corresponding NPs did not change after BODIPY-conjugation. Neither the NPs nor allyl-NPs showed significant cytotoxicity towards RAW264.7 or MCF-7 cell lines, which indicates their desirable safety profile. A one-step approach to concurrently conjugate allyl-groups and a fluorescent dye (FITC) to the preformed PAA-b-PBA NPs was investigated. The cellular uptake of the FITC-NPs using J774A cells in vitro was found to be time- and concentration-dependent. The anti-cancer drug, doxorubicin, was efficiently (90%) encapsulated into the PAA-b-PBA NPs during NP formation. After a small burst release during the first two hours, a controlled release pattern over 7 days was observed. The present investigation demonstrates a potential method to functionalize polymeric NPs post-PISA to produce targeted drug delivery carriers.
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| 14. |
- Brännström, Sara, et al.
(author)
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Enzymatically Synthesized Vinyl Ether-Disulfide Monomer Enablingan Orthogonal Combination of Free Radical and Cationic Chemistry toward Sustainable Functional Networks
- 2019
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In: Biomacromolecules. - : American Chemical Society (ACS). - 1525-7797 .- 1526-4602. ; 20:3, s. 1308-1316
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Journal article (peer-reviewed)abstract
- This work demonstrates a versatile and environmentally friendly route for the development of new orthogonal monomers that can be used for postfunctionalizable polymer networks. A monomer containing both vinyl ether (VE) and cyclic disulfide moieties was synthesized via enzyme catalysis under benign reaction conditions. The bifunctional monomer could be polymerized to form macromolecues with differing architectures by the use of either cationic or radical photo polymerization. When cationic polymerization was performed, a linear polymer was obtained with pendant disulfide units in the side chain, whereas in the presence of radical initiator, the VE reacted with the disulfide to yield a branched structure. The monomer was thereafter used to design networks that could be postfunctionalized; the monomer was cross-linked with cationic initiation together with a difunctional VE oligomer and after cross-linking the unreacted disulfides were coupled to RhodamineVE by radical UV-initiation.
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| 15. |
- Brännström, Sara, 1991-
(author)
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Exploring bio-based monomers for UV-curable polymer networks
- 2019
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Doctoral thesis (other academic/artistic)abstract
- Increased environmental awareness and concern has led to a high demand for sustainable, bio-based materials. Consequently, there is a need for research and development of new bio-based polymeric materials that can be synthesized via routes eliminating excessively toxic reactants and by-products. The work presented in this thesis has focused on the utilization of catalysis, mainly enzymatic, and photopolymerization in order to create efficient synthesis of polymeric networks from bio-based monomers.Polyesters from bio-based monomers have been polymerized in bulk and thereafter crosslinked by UV initiation to yield polymer networks with tunable properties. The synthesis was also studied more in detail by varying the different types of catalysts and comparing their effect on the polymer products. Polyesters are a promising class of polymers that can be made from bio-based resources due to the wide range of available bio-based carboxylic acids and alcohols that can be combined to yield many polymers with different properties. However, the synthesis of polyesters is rather time-consuming in order to reach high conversions.As a more efficient alternative, short chain esters monomers and oligomers that have vinyl ether (VE) functionalities were developed. These VE-esters can be synthesized partly from bio-based resources, such as acids, fatty acids and diols, and their synthesis is efficient with enzymatic catalysis. The VE functionality provides a reactive group which can be polymerized rapidly with cationic polymerization. In general, the vinyl ether-esters can be synthesized in less than one hour and crosslinked within a few minutes, which is significantly faster than traditional polyester-synthesis and crosslinking. The enzymatic synthesis of vinyl ether esters also provided a method for developing monomers with orthogonal functionality which was explored by developing functionalizable materials with a variety of macromolecular architectures.
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| 16. |
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| 17. |
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| 18. |
- Eliasson, Adrian, et al.
(author)
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Highly Ductile Cellulose-Rich Papers Obtained by Ultrasonication-Assisted Incorporation of Low Molecular Weight Plasticizers
- 2023
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In: ACS Sustainable Chemistry and Engineering. - : American Chemical Society (ACS). - 2168-0485. ; 11:24, s. 8836-8846
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Journal article (peer-reviewed)abstract
- Ultrasonication was used as a mean toincorporate glycerolor urea, yielding paper films with a ductility of up to 35%. Fiber-based materials are attractive sustainable alternativestofossil-based plastics, however, the lack of ductility (i.e., brittleness)limits their applicability in complex shapes as are often utilizedfor plastics. In this study, we hypothesize that it is possible toenhance the ductility of a cellulose-rich material by the incorporationof low molecular weight plasticizers (glycerol, urea, citric acid,and tannic acid). However, no significant effects could be observedafter swelling in the presence of plasticizers. To enhance any potentialeffect, it was decided to employ ultrasonication to mechanically disintegratethe fiber and aid the sorption of plasticizer prior to formation ofsheets from the treated fibers. Glycerol or urea in combination withultrasonication resulted in both internal and external fibrillationof the fibers, and it could be observed that the resulting fines createa film at the surface of the fibers in the formed sheets. Tensiletesting shows that this gives rise to a 100% increase in ductilitycompared to sheets from untreated fibers. The use of citric or tannicacid has the opposite effect, reducing ductility to a third of thatof the reference sheet. This is suggested to be due to the formationof covalent cross-links in the treated fibers, which also leads todifferent internal and external fibrillation mechanisms, as observedby scanning electron microscopy. The exceptionally high improvementof the strain-at-break for sheets from the glycerol- and urea-treatedfibers suggests that low molecular weight plasticizers affect theinternal properties of the fiber wall as well as the interactionsbetween the fine material forming in-between the fibers. The findingsfrom the current study suggest that the proposed approach to obtainductile cellulose-rich materials holds promise for the future, butit is also clear that more in-depth research is required to obtaina mechanistic understanding and release the full potential.
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| 19. |
- Engström, Joakim, et al.
(author)
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Core–Shell Nanoparticle Interface and Wetting Properties
- 2020
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In: Advanced Functional Materials. - : Wiley. - 1616-301X .- 1616-3028. ; 30:15
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Journal article (peer-reviewed)abstract
- Latex colloids are among the most promising materials for broad thin film applications due to their facile surface functionalization. Yet, the effect of these colloids on chemical film and wetting properties cannot be easily evaluated. At the nanoscale, core–shell particles can deform and coalesce during thermal annealing, yielding fine-tuned physical properties. Two different core–shell systems (soft and rigid) with identical shells but with chemically different core polymers and core sizes are investigated. The core–shell nanoparticles (NPs) are probed during thermal annealing in order to investigate their behavior as a function of nanostructure size and rigidity. X-ray scattering allows to follow the re-arrangement of the NPs and the structural evolution in situ during annealing. Evaluation by real-space imaging techniques reveals a disappearance of the structural integrity and a loss of NP boundaries. The possibility to fine-tune the wettability by tuning the core–shell NPs morphology in thin films provides a facile template methodology for repellent surfaces.
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| 20. |
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| 21. |
- Engström, Joakim, et al.
(author)
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Investigating the adsorption of anisotropic diblock copolymer worms onto planar silica and nanocellulose surfaces using a quartz crystal microbalance
- 2021
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In: Polymer Chemistry. - : Royal Society of Chemistry (RSC). - 1759-9954 .- 1759-9962. ; 12:42, s. 6088-6100
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Journal article (peer-reviewed)abstract
- Electrostatic adsorption of cationic polyelectrolytes onto anionic cellulosic substrates is an attractive route for facile surface modification of biorenewable materials. Recently, attention has focused on adsorbing cationic spherical diblock copolymer nanoparticles onto model cellulose and/or nanocellulosic substrates. Herein, we investigate physical adsorption of highly anisotropic copolymer worms bearing either anionic or cationic charge onto planar silica, cellulose nanocrystal (CNC) or cellulose nanofibril (CNF) surfaces using quartz crystal microbalance with dissipation monitoring. Electrostatic interactions dominate in the case of anionic silica and CNC surfaces because the adsorbed mass of cationic worms was greater than that of anionic worms. However, either anionic or cationic worms could be adsorbed onto in situ generated CNF substrates, suggesting that additional interactions were involved: hydrogen bonding, van der Waals forces, and possibly covalent bond formation. Scanning electron and atomic force microscopy studies of the dried planar substrates after adsorption experiments confirmed the presence of adsorbed copolymer worms. Finally, composite worm/CNF films exhibited restricted swelling behavior when immersed in water compared to reference CNF films, suggesting that the worms reinforce CNF films by acting as a physical crosslinker. This study is the first investigation of the physical adsorption of highly anisotropic diblock copolymer worms onto cellulosic surfaces.
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| 22. |
- Engström, Joakim, et al.
(author)
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Nanoparticle rearrangement under stress in networks of cellulose nanofibrils using in situ SAXS during tensile testing
- 2020
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In: Nanoscale. - : Royal Society of Chemistry (RSC). - 2040-3364 .- 2040-3372. ; 12:11, s. 6462-6471
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Journal article (peer-reviewed)abstract
- This study aims to describe and evaluate the mechanism for increased strain-at-break of composites made of cellulose nanofibrils (CNFs) reinforced with nanoscopic latex particles (<200 nm) stabilized by a cationic polyelectrolyte as corona. The applied latex nanoparticles (NPs), synthesized by polymerization-induced self-assembly (PISA), are composed of a neutral core polymer, either poly(butyl methacrylate) (PBMA) or poly(methyl methacrylate) (PMMA). At room temperature, PBMA is close to its glass transition (T-g), while PMMA is below its Tg. Nanocomposites with 75 wt% CNFs and 25 wt% NPs were analyzed using in situ small angle X-ray scattering during tensile testing, monitoring the structural evolution of the NPs under strain. The scattering of the spherical PMMA NPs, which do not coalesce like the PBMA NPs, shows changes to the organization of the NPs in the CNF-network. The observations are corroborated by cross-sectional transmission and scanning electron microscopy. No distinct change from spherical to ellipsoidal shape is evidenced for the PMMA NP cores during tensile strain. Changes in anisotropic scattering produced by the three-dimensional NP structure appear to be very different between nanocomposites loaded with PMMA or PBMA NPs, contrasting commonly described two-dimensional CNF networks. The discrete PMMA NPs can reorganize within the CNF-NP double network under strain, resulting in maintained strength and increased strain-at-break. Increasing the humidity (20, 50 and 80% RH) during in situ measurements further emphasizes this effect in the PMMA composite, relative to the PBMA composite and CNF reference films. The onset of deformation occurs at strain values beyond the fracture of the more brittle films, indicating the effect of secondary nanoscale interaction available only for the PMMA composite, extending the plastic deformation and increasing the ductility. These results provide key insights into the deformation mechanism occurring during tensile testing in the CNF composites loaded with PMMA NPs.
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| 23. |
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| 24. |
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| 25. |
- Farhat, Wissam, et al.
(author)
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Lactone monomers obtained by enzyme catalysis and their use in reversible thermoresponsive networks
- 2020
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In: Journal of Applied Polymer Science. - : John Wiley and Sons Inc.. - 0021-8995 .- 1097-4628. ; 137:18
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Journal article (peer-reviewed)abstract
- Enzyme-catalyzed transformations have a great potential in both the pharmaceutical and chemical industry to achieve complex and (stereo)selective synthesis under mild reaction conditions. Still, the implementation of biocatalysis in the prerequisite upgrading of inert synthons into activated monomers for polymer applications has not yet been fully realized. In this contribution, we show that scaled-up synthesis of bicyclic norcamphor lactone using an engineered Baeyer–Villiger monooxygenase (BVMO) is feasible to reach complete conversion of the corresponding ketone in 24 h in shake-flask. The lactone monomer obtained by enzyme catalysis was copolymerized with ε-caprolactone via ring-opening polymerization to study the impact of the additional ring on material properties. Moreover, four-arm star-like, homo and block copolymers were designed from ε-caprolactone, ε-decalactone, and norcamphor lactone and characterized for their structural and thermal properties. These newly explored macromolecules were functionalized with furan rings using the enzyme Candida antarctica lipase B which allowed the formation of thermolabile networks via the pericyclic reaction with bismaleimide by means of Diels–Alder chemistry. The bonding/debonding state of these star-like based materials can be tuned by a suitable selection of thermal treatment. The temperature-dependent reversibility was assessed by thermal analysis and solubility test. Our results presented here shed light on the high potential of the use of chemoenzymatic approaches in the synthesis of new functional materials with tuned physiochemical properties.
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