Browsing by Subject "Polymermaterialkemi"

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  • Tavaststjerna, Miisa (Helsingin yliopisto, 2020)
    Further proof of the unique morphologies of water-soluble poly(2-isopropyl-2-oxazoline)-block-poly(DL-lactide) and poly(2-isopropyl-2-oxazoline)-block-poly(L-lactide) (PiPOx-b-PDLLA and PiPOx-b-PLLA) nanoparticles was obtained via Fluorescence Spectroscopy. Additionally, loading and release studies were carried out with hydrophobic curcumin molecules to outline the potential of the amphiphilic block copolymers in drug delivery applications. To study the morphology of the nanoparticles, absorption and emission spectra of pyrene were measured in water dispersions of the nanoparticles at several concentrations. The obtained I1/I3, I337/I333.5 and partitioning constant (Kv) values were compared to corresponding data from a control core/shell nanoparticle poly(ethylene glycol)-block-poly(DL-lactide) (PEG-b-PDLLA). Of the three different amphiphilic polymers, PEG-b-PDLLA showed the smallest and PiPOx-b-PDLLA the highest Kv value. This indicates, that PiPOx-b-PDLLA core is less hydrophobic and looser compared to the dense cores of PEG-b-PDLLA and PiPOx-b-PLLA, making it capable of encapsulating the greatest amount of pyrene. In the loading and release studies, the nanoparticles were loaded with curcumin and placed in dialysis against PBS Tween® 80 solution. Curcumin content of the samples was monitored over a week by measuring the emission spectra of curcumin. PiPOx-b-PDLLA showed greater potential as a drug delivery agent: It formed more stable nanoparticles, showed higher loading capacities, higher encapsulation efficiencies and slower release rates. Flash nanoprecipitation method (FNP) was also used to prepare the same nanoparticles with and without encapsulated curcumin. In addition to the encapsulation efficiencies, sizes of the nanoparticles were determined via dynamic light scattering (DLS). PiPOx-b-PLLA forms the smallest nanoparticles with lowest encapsulation efficiencies, thus agreeing well with the higher density of PLLA core. All three investigated amphiphilic copolymers formed stable nanoparticles in water at room temperature. On the contrary, stability of the nanoparticles was found to be poor in saline solutions at body temperature. Mixing PEG-b-PDLLA with PiPOx-b-PLA in a ratio of 20:80 w-% increased the stability of the nanoparticles in physiological conditions simultaneously uncovering the thermoresponsive character of the PiPOx-blocks. Turbidity measurements of PEG-b-PDLLA mixed with PiPOx-b-PDLLA in ratio of 20:80 w-% showed slight decrease in transmittance at the 30 °C, which corresponds to the cloud point of PiPOx-b-PDLLA in PBS solution. However, it remains unclear, whether the increased stability is due to the PEG-b-PDLLA mixing in the same micelles with PiPOx-b-PDLLA, thus hindering the aggregation of the nanoparticles upon the cloud point of the PiPOx-blocks.
  • Kontinen, Joona (Helsingin yliopisto, 2020)
    Tutkielman kirjallisuusosuudessa on käyty läpi erilaisia kaupallisia biopolymeerejä, niiden synteesiä, käyttöä ja biohajoamista. Tutkielman pääpaino on erilaisten materiaalien biohajoamisessa ja näiden materiaalien kaupallisessa käytössä. Biohajoamisen evaluointiin tarkoitettuja standardeja, tutkimusmenetelmiä ja hyväksyntäkriteerejä on esitelty laajasti. Tutkimusosuudessa on valmistettu PLA:n ja PBAT:n seoksesta puukomposiitti ja materiaalin termomekaaniset ominaisuudet on karakterisoitu. Tavoitteena oli luoda biohajoava materiaali, jonka ominaisuudet ovat sellaisia, että sen kaupallinen hyödyntäminen kertakäyttömuovin korvikkeena on järkevää. Materiaalin mekaaniset ominaisuudet karakterisoitiin lopputuotteen kestävyyden, ja sulaominaisuudet kaupallisen tuotannon mahdollistamisen takia. Termomekaanisia analyysejä tehtiin materiaalin säilyvyyden ja lämpöominaisuuksien karakterisoimiseksi. Työssä on tutkittu myös puhtaan PLA/puukomposiitin biohajoamista meriympäristössä. Tutkimuksen tuloksena saatiin luotua riittävällä nopeudella biohajoava puukomposiitti, jonka mekaaniset ominaisuudet ovat riittäviä korvaamaan erilaisia kertakäyttöisiä muovituotteita ja joka on prosesoitavissa nykyisillä ekstruusiolaitteistoilla.
  • Spönla, Elisa (Helsingin yliopisto, 2020)
    The aim of the thesis was to study enzymatic treatment as a way to modify paper grade pulp to be a suitable raw material for the future textile industry. Wood as a raw material is an environmentally friendly option for textile production but its sustainable exploitation is not easy. Currently, ionic liquids are assumed to enable a safe and sustainable process for the production of wood-based regenerated fibres. These processes commonly use dissolving pulp as their raw material but replacing dissolving pulp with a paper grade kraft pulp would decrease environmental impact and production expenses. In this work, molar mass distribution of softwood paper grade kraft pulp was selectively modified using enzymes. Enzymes were utilized instead of acids because of their favourable abilities to selectively modify targeted polymers and to increase fibre porosity. Enzymatic modifications of softwood kraft pulp were performed to decrease degree of polymerization of cellulose and lower the quantity of hemicellulose. Hydrolysis of cellulose was catalysed with endo-1,4-β-glucanase (endoglucanase) and hemicellulose was degraded using endo-1,4-β-mannanase and endo-1,4-β-xylanase. The treatments were carried out both at high (20%) and low (3%) pulp consistency to examine the synergistic effect of enzymatic and mechanical action arising in the high consistency treatment. Additionally, influence of different enzyme combinations on the pulp properties was studied. The modified pulp samples were characterized by determining intrinsic viscosity, molar mass distribution, yield loss, and its composition. The fibres were imaged with light microscopy. The degree of polymerization of the pulp cellulose was successfully decreased with a relatively small endoglucanase dose. The amount of hemicellulose was reduced by removing 11% of the total galactoglucomannan and 40% of the total arabinoglucuronoxylan. The high consistency treatments decreased intrinsic viscosity 1.9 times more on average than the low consistency treatments. The high consistency treatments were effective with low enzyme doses, easy to control, and reliably repeated. Therefore, enzymatic pulp treatment at high consistency seems to be a compatible way to modify paper grade kraft pulp to suitable raw material for textile production. Further studies related to pulp dissolution in ionic liquids, fibre spinning, and fibre regeneration should be concluded to confirm applicability of the modified fibres.
  • Chou, Hao-Wei (Helsingin yliopisto, 2019)
    Diblock copolymers, poly(lactide)-block-poly(2-isopropyl-2-oxazoline) (PiPOx-b-PLA) and n-octadecyl poly(2-isopropyl-2-oxazoline) (PiPOx-C18), were characterized using the steady-state fluorescence with two fluorescence probes, pyrene and (1,6-diphenyl-l,3,4-hexatriene) (DPH), to investigate the core structure of the particles formed by the polymers. The two enantiomers of PiPOx-b-PLA, which are PiPOx-PLLA and PiPOx-PDLLA, reflected very different features in terms of polarity of the micellar core and the partitioning equilibrium constants of pyrene (Kv). This suggests that the core of the particles formed by PiPOx-PDLLA has higher polarity due to high water content in the range of the polymer concentrations from 0.03 g/L to 3 g/L, and more pyrene molecules are bound to the particles. Furthermore, the core of the particles formed by PiPOx-PDLLA reveals rigidity lower than that of PiPOx-PLLA, which is supported by the low anisotropy value (r) of DPH. r did not change upon heating from 15 ⁰C to 65 ⁰C for the PiPOx-PLLA particles. A slight decrease of r occurred above 50 ⁰C for the PiPOx-PDLLA particle. The PiPOx-C18 micelles exhibit higher critical micellar concentration (CMC), smaller Kv, and softer core in comparison to the PiPOx-b-PLA micelles. These differences owe to the nature of the alkyl chain end. Loading and release of a hydrophobic drug, curcumin, to/from the PiPOx-PLLA and PiPOx-PDLLA micelles were investigated by means of the steady-state fluorescence. The release test was conducted using the dialysis bag method. The PiPOx-PDLLA particles encapsulated more curcumin with encapsulation efficiency (EE) value being 98% while the curcumin-to-polymer ratio was 1:20. Curcumin intake of the PiPOx-PLLA particles was lower under the same condition (EE = 56%). The PiPOx-PDLLA particles show excellent ability of trapping curcumin. PiPOx-PDLLA bear 70% of curcumin inside the dialysis bag after 50 h, whereas 40% of curcumin was discharged from dispersions of PiPOx-PLLA. Precipitation of curcumin was observed in presence of PiPOx-PLLA in 4 days. No curcumin precipitating from the PiPOx-PDLLA dispersion occurred and a decrease in the intensity of curcumin owed to the degradation of curcumin. Finally, all the phenomena observed are well illustrated by the hypothesis of the morphology of the particles formed by PiPOx-PLLA and PiPOx-PDLLA. The particle formed by PiPOx-PDLLA consists of a loose hydrophobic core with hydrated tails extending to the aqueous phase, whereas the core of PiPOx-PLLA particle is dense.
  • Srbova, Linda (Helsingin yliopisto, 2020)
    In this work, a series of biocompatible nanocomposite hydrogels was prepared by UV-initiated polymerization based on 2-hydroxyethyl methacrylate (HEMA), using ethylene glycol dimethacrylate (EGDMA) as a crosslinker and 2-hydroxymethyl-2-methylpropiophenone as a photoinitiatior, containing liquid crystals of cellulose nanocrystals (CNCs) doped with magnetic nanoparticles. The formation of liquid crystals was achieved thanks to the intrinsic property of CNCs to self-assemble above a critical aqueous concentration. By varying the preparation conditions, allowing different times for phase-separation between the nanoparticles and CNCs and exposing the polymerization mixture to small magnetic field, films with different size and orientation of CNC liquid crystal domains were synthesized. Subsequently, the hydrogel films were studied by dynamic mechanical analysis (DMA) to evaluate the effect of these parameters on the mechanical properties, specifically the Young’s modulus and the ultimate strength. Also, the microstructure of the films was studied via polarized optical microscopy (POM) and scanning electron microscopy (SEM). The water uptake capacity was also analyzed. The results indicate that the presence of cellulose nanocrystals modulates the architecture of the prepared hydrogels. Cholesteric microdomains were embedded in PHEMA matrix and their uniaxial alignment was achieved upon exposure to small static magnetic field, already after several hours. Moreover, structural gradient in the distribution of the liquid crystalline microdomains, in dependence on their size, was obtained within the material. This originated from the direct proportionality between the size and the density of liquid crystals. Finally, it was shown that cellulose nanocrystals act as reinforcing structures of the hydrogels, when the degree of their self-assembly is sufficient, and therefore the resulting hydrogel exhibits both higher resistance to elastic deformation and also higher ultimate strength. Finally, we showed that mechanical performance of these nanocomposites can be enhanced by systematic orientation of the liquid crystalline domains.
  • Kinnunen, Moonika (Helsingin yliopisto, 2022)
    In this project, poly(2-methyl-2-oxazoline)-block-poly(2-n-butyl-2-oxazine)-block-poly(2-methyl-2- oxazoline) (PMeOx-b-PnBuOzi-b-PMeOx) and poly(2-methyl-2-oxazoline)-block-poly(2-n-propyl-2- oxazine) (PMeOx-b-PnPrOzi) with block lengths of 35-20-35 and 100-100, respectively, were synthesized. When dispersed in water these thermoresponsive polymers aggregate into micellar aggregates or form hydrogels. Polymers were characterized with 1H-NMR, GPC, and DLS. Age-related macular edema and diabetic macular edema are the most common reasons for blindness in industrialized countries. The triamcinolone acetonide, a corticosteroid used to treat both of these macular edemas, was loaded into the polymeric micelles or hydrogel of synthesized polymers using the thin film method. The loading efficiency for a triblock copolymer ((PMeOx35-b-PnBuOzi20- b-PMeOx35) polymeric micelles was 4 % at the polymer/drug ratio of 10/4 and for a hydrogel (PMeOx100-b-PnPrOzi100) it was 48 % with the same polymer/drug ratio. The properties of the PMeOx100-b-PnPrOzi100 hydrogel formulations with the drug were studied with rheological measurements, DSC, DLS, and GPC of formulations. The formulation showed storage modulus of 3 kPa and the gelation temperature at 16 °C. From the DSC two glass transition temperatures were obtained, Tg1 at around 12 °C and Tg2 at around 74 °C. The particle size distribution of the formulation obtained with DLS showed that there were assumingly micelles or vesicles with a hydrodynamic radius between 20 and 80 nm. The drug release from the hydrogel formulation was studied with the dialysis membrane method and all the drug was released within 24 hours. Both copolymers formed quite unstable formulations with the drug. The results from this study gives information how polyoxazoline- and polyoxazine-based materials can be used to encapsulate and release corticosteroids, such as triamcinolone acetonide. To increase the drug loading capacity and to stabilize formulations, some surfactants for the drug could be tested in the future.
  • Lintala, Aino-Maija (Helsingin yliopisto, 2020)
    Polysiloxanes are silicon-based polymers consisting of R2SiO repeating units. They are commonly used in many commercial applications, for example, as adhesives, additives, or waterproof coatings. This thesis concentrates on polysiloxanes used as optically clear adhesives, which are needed in display applications to, for instance, bond cover lenses to touch panel sensors. This kind of a material needs to have a high refractive index to match glass or plastic, and it has to be transparent and thermally stable. In addition, it must resist degradation and yellowing from UV exposure and humidity. Anionic ring-opening polymerization was used to synthesize optically transparent polysiloxanes with varying side-groups. These polymers exhibited high refractive index values, which were adjusted by changing the amount of phenyl group -containing monomers or with chain terminating agents. End-functionalization reactions were performed for the synthesized polymers to introduce methacrylate groups to the chain ends, which could later be used in crosslinking trials involving a photoinitiator. The results present an effective synthetic route for the ring-opening polymerization for transparent, high refractive index poly(dimethylsiloxane-co-diphenylsiloxane) and poly(methylphenylsiloxane) that could be used as adhesives after selective chain end functionalization and crosslinking reactions. The properties of the synthesized polysiloxanes were characterized with several different methods, such as size exclusion chromatography, rheology, and NMR spectroscopy. End functionalization reactions were performed for some of the synthesized polymers. These were then further characterized to verify the suitability of the reaction.
  • Meriläinen, Kati (Helsingin yliopisto, 2020)
    In this thesis, synthesis and solution properties of the polyampholyte poly(acrylic acid)-b-poly[(vinylbenzyl)trimethylammonium chloride], PAA-PVBTMA-Cl, were investigated in aqueous solutions. First, the diblock copolymer was synthesized via RAFT polymerization where poly(acrylic acid), PAA was used as a chain transfer agent (CTA). In addition, the homopolymer poly[(vinylbenzyl)trimethylammonium chloride], PVBTMA-Cl, was synthesized via RAFT polymerization to compare the solution properties with the block copolymer. Molar masses of the polymers were determined using several methods such as NMR, UV-Vis spectroscopy and SEC. The experimental molar masses were close to theoretical values and block ratio in diblock copolymer from NMR was 30% of AA and 70% of VBTMA-Cl. Furthermore, the solution properties of the polyampholyte were studied under external stimuli such as pH and temperature. UCST type of behaviour was observed for aqueous PAA-PVBTMA-Cl solutions when the hydrophobic trifluoromethanesulfonate (OTf) anion was introduced. In addition, self-assembly of the diblock copolymer was confirmed by zeta potential measurements in different pH conditions. The expected reverse of the micelle structure with changing pH was not observed. However, aqueous PAA-PVBTMA-Cl showed UCST behaviour and micellization induced by the hydrophobic counterion.
  • Bandini, Elena (Helsingin yliopisto, 2019)
    The aim of this work is to synthetize a series of thermoresponsive microgels that have never been reported before, based on strong polycations, and study their properties such as the change in volume in response to a temperature stimulus. Polymer microgels are interesting materials for practical applications as drug delivery systems, in separation techniques and catalysis. The interest on these materials arises from their physical properties of colloids combined with gel properties. The microgels presented in this work can undergo phase transitions not only in water but also in DMF/water mixtures. A crosslinked polymer that displays cloud point behaviour when heated forms a temperature-sensitive gel network. Cloud point is the temperature above which an aqueous solution of a water-soluble polymer becomes turbid in the case of polymer with LCST (Lower Critical Solution Temperature) behaviour. Upon heating such a gel, the gel shrinkage is observed by expelling water over a temperature range. The transition is largely driven by the entropy gain associated with the release of water from the network, and the concomitant collapse of the polymer chains. In addition, the size of the microgels is tuneable by adding NaCl at different concentration. The synthesis is carried out as a normal radical polymerization always in the same conditions except for the solvent mixture. The homopolymer, synthetized for comparison, is polymerized with RAFT (Reversible Addition-Fragmentation chain-Transfer) method. Nuclear Magnetic Resonance (NMR) confirmed the structure of the microgels validating the synthetic method. The hydrodynamic radius of the microgels after the addition of salty solutions at different concentration is determined by Dynamic Light Scattering (DLS). The thermo-responsive properties are investigated in terms of polarity using fluorescence and turbidity measurements and in terms of changes in volume calculated from the hydrodynamic radius with DLS at different temperature. The microgels show a thermo-responsive behaviour in the temperature range between 10 °C and 90 °C. In fact, the raise in temperature causes an increase in volume and hydrophobicity. Finally, it is reported a trend that follows the NaCl concentration of salt solutions added to the microgels. These microgels can be used for a wide range of applications, amongst them, they are useful support for metal nanoparticles for catalytic purposes. Here, AuNPs are formed directly on the microgel and the formation is ascertained by DLS and TGA (Thermogravimetric Analysis). Then, they are tested to effectively work during a catalysis experiment.
  • Eronen, Heli (Helsingin yliopisto, 2020)
    In this thesis, thermoresponsive poly(N-acryloyl glycinamide-co-methacrylic acid) (P(NAGA-co-MAA)) microgels were synthesized via surfactant stabilized free radical precipitation polymerization. Also, PNAGA microgel was synthesized as reference. The upper critical solution temperature (UCST) behavior of the microgels was tuned by changing the molar ratio of the monomers in the copolymer. The phase transition behavior of the formed microgel particles were characterized with NMR spectroscopy, microcalorimetry, turbidimetry and light scattering. It was observed that both PNAGA and P(NAGA-co-MAA) microgels display UCST type temperature response. However, in neutral pH, the phase transition of the copolymer gels was prevented due to the deprotonated acid groups of MAA. Hence, all the measurements were made in pH 3, below the pKa of MAA. The phase transition became sharper when the amount of MAA repeating units was increased in the copolymer. Also, the phase transition temperature of the copolymer gels increased when the amount of MAA was increased. In addition to phase transition behavior studies, the reactivity ratios of the monomers were studied during polymerization to analyze the structure of the forming copolymer gels. It was concluded that, as the both monomers had similar reactivity rates, statistical random copolymer gels are formed.