| 1. |
- Colombini, Didier, et al.
(författare)
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Effects of thermal annealing on the viscoelastic properties and morphology of bimodal hard/soft latex blends
- 2005
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Ingår i: Journal of Polymer Science. Part B, Polymer Physics. - : Wiley. - 0887-6266 .- 1099-0488. ; 43:17, s. 2289-2306
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Tidskriftsartikel (refereegranskat)abstract
- The effects of thermal annealing on the viscoelastic properties and morphology of films prepared from bimodal latex blends containing equal weight fractions of soft and hard latex particles with controlled sizes were investigated. The thermal and viscoelastic properties of as-dried and annealed samples were investigated with differential scanning calorimetry and dynamic mechanical analysis (DMA). Throughout the thermal annealing, the latex blend morphologies were also followed with atomic force microscopy and transmission electron microscopy (TEM). A particulate morphology, consisting of hard particles evenly dispersed in a continuous soft phase, was observed in the TEM micrographs of the as-dried latex blends and resulted in an enhancement of the mechanical film properties at temperatures between the a relaxations of the soft and hard phases in the DMA thermograms. As soon as the thermal annealing involved temperatures higher than the glass-transition temperature of the hard phase, the hard particles progressively lost their initial spherical shape and formed a more or less continuous phase in the latex blends. This induced coalescence of the hard particles was confirmed by the association of the experimental viscoelastic data with theoretical predictions, based on self-consistent mechanical models, which were performed by the consideration of either a particulate or cocontinuous morphology for the bimodal latex blends. (c) 2005 Wiley Periodicals, Inc.
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| 2. |
- Colombini, Didier, et al.
(författare)
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Influence of the particle size and particle size ratio on the morphology and viscoelastic properties of bimodal hard/soft latex blends
- 2004
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Ingår i: Macromolecules. - : American Chemical Society (ACS). - 0024-9297 .- 1520-5835. ; 37:18, s. 6865-6873
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Tidskriftsartikel (refereegranskat)abstract
- The morphology and viscoelastic properties of films prepared from bimodal latex blends containing equal weight fractions of soft and hard latex particles were investigated as a function of the particle sizes and the particle size ratio (soft particle diameter/hard particle diameter). Minimum film formation temperature (MFT) measurements were associated with transmission electron microscopy (TEM) to emphasize the particle size ratio dependence of the film formation properties. A significant increase of the MFT values with the soft/hard particle size ratio was observed. As long as the particle size ratio was low, TEM micrographs showed that the film forming soft particles, undergoing complete coalescence, clearly act as the continuous phase where the non film forming hard particles are found evenly dispersed while keeping their initial spherical shape. At higher values of the particle size ratio, TEM micrographs pointed out that the soft particles are prevented from coming into contact with each other by the surrounding hard particles, therefore dramatically increasing the MFT of the sample and resulting in a non film forming latex blend. The existence of a critical volume fraction of hard particles that is directly related to the soft/hard particle size ratio was then established on the basis of geometrical arguments involving the percolation theory. The higher the particle size ratio, the lower the critical volume fraction of hard particles that leads to a macroscopic phase inversion resulting in a non film forming bimodal latex blend. Subsequently, the mechanical film properties were investigated by solid-state dynamic mechanical analysis. The size of the dispersed hard phase was found to affect the final viscoelastic film properties. The smaller the size of the hard particles, the better the mechanical enhancement of the mechanical film properties. Last, the experimental viscoelastic thermograms were compared with some theoretical predictions based on self-consistent mechanical modeling. The final film properties of the bimodal hard/soft latex blends were then directly connected to the film formation properties.
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| 3. |
- Colombini, Didier, et al.
(författare)
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The effect of the polymerization route on the amount of interphase in structured latex particles and their corresponding films
- 2005
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Ingår i: Polymer. - : Elsevier BV. - 0032-3861. ; 46:4, s. 1295-1308
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Tidskriftsartikel (refereegranskat)abstract
- Three series of hard/soft styrene-acrylic latex based systems with equivalent compositions were prepared either by blending of homopolymer latexes or by preparing structured latex particles having core shell (CS) or inverted core shell (ICS) morphologies. Transmission electron microscopy (TEM) was used to investigate the particle morphologies, which were correlated to the calculated fractional radical penetration for the propagating species during the reactions. The thermo-mechanical properties as well as the morphology of the resulting latex films were analyzed by differential scanning calorimetry (DSC), dynamic mechanical analysis (DMA) and TEM. The viscoelastic properties of the interphase between the first and second-stage polymers formed in the structured hard/soft latex films, as well as its qualitative amount and also the film morphologies were found to depend on the interplay between thermodynamic and kinetic parameters during the synthesis of the samples. (C) 2004 Elsevier Ltd. All rights reserved.
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| 4. |
- Hassander, Helen
(författare)
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Morphology of Polymers - Development of Electron Microscopy Methods
- 2004
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Doktorsavhandling (övrigt vetenskapligt/konstnärligt)abstract
- Most polymeric materials used today are not simple homopolymers, but consist of more than one polymer, which lead to morphologies of different length scale and shape. It is important to receive knowledge of the morphologies because the properties of the materials change depending on the structure. This thesis describes methods developed to study polymer morphologies by electron microscopy and also how to make a correct interpretation of the result. TEM (Transmission Electron Microscope) and SEM (Scanning Electron Microscope) are described for studying morphologies in PVC (polyvinyl chloride) resin, polymer blends, compatibilizer in polymer blends, latex particles, latex films and bitumen/polymer blends. Following polymer blends were studied: Carbon black filled NBR/EPDM (nitril butadiene rubber/ethylene-propylene-diene terpolymer), PP/PA (polypropylene/polyamid) Modified with SEBS-MA (polystyrene-block-poly(ethylene-stat-butylene)-block-polystyrene) modified by grafting with maleic anhydride, PS/PA (polystyrene/polyamide) compatibilized by a PS/PEO (polystyrene/poly(ethylene oxide)) grafted compatibilizer. Waterborne two-phase latexs are used as binding material in paints, adhesives, paper and other coatings. Methods to examine the morphology of the particles and the films in TEM were developed and PS/PMMA (polystyrene/poly(methacrylate)) and PS/PI (polystyrene/polyisoprene) was studied. Bitumen roofing material is improved by mixing the bitumen with polymers. The morphology of bitumen/SBS (polystyrene-block-butadien) was studied by fluorescence microscope, SEM and TEM and the results were compared.
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| 5. |
- Jannasch, Patric, et al.
(författare)
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On the macro- and microphase separation of compatibilizers in immiscible polymer blends
- 1996
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Ingår i: Journal of Polymer Science. Part B, Polymer Physics. - 0887-6266. ; 34:7, s. 1289-1299
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Tidskriftsartikel (refereegranskat)abstract
- Macro- and microphase separation of compatibilizing graft copolymers in melt-mixed polystyrene/polyamide-6 blends was studied by transmission electron microscopy and thermal analysis. Three different graft copolymers with main chains of polystyrene and side chains of poly(ethylene oxide) were used as additives at various concentrations. The polyamide-6 domain sizes decreased with increasing amounts of compatibilizing graft copolymers in the blends up to a saturation concentration, after which no further reduction was noted. Macrophase separation of the graft copolymers into discrete macrodomains 20-200 nm in size occurred at concentrations equal to or slightly lower than the saturation concentration. The macrodomains of the graft copolymers were microphase separated, and the sizes and shapes of the microdomains were found to largely depend on the graft copolymer structure and composition. As a consequence of microphase separation, poly(ethylene oxide) crystallinity was noted in blends with sufficiently high macrophase contents. Observations of a graft copolymer interphase between the polystyrene matrix and the polyamide-6 domains confirmed that the graft copolymer was present at the blend interfaces in some of the compatibilized blends.
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| 6. |
- Jönsson, Jan-Erik, et al.
(författare)
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Semi-continuous emulsion polymerization of styrene in the presence of poly(methyl methacrylate) seed particles. Polymerization conditions giving core-shell particles
- 2007
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Ingår i: European Polymer Journal. - : Elsevier BV. - 0014-3057. ; 43:4, s. 1322-1332
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Tidskriftsartikel (refereegranskat)abstract
- This work reports the morphology of two-phase latex particles prepared by semi-continuous seed emulsion polymerization of styrene in the presence of polar poly(methyl methacrylate), PMMA, seed particles, using different conditions of non-polar styrene feed rate, rate of initiation, seed particle concentration and temperature of polymerization. The expected latex particle morphology at thermodynamic equilibrium is an inverted core-shell structure where the non-polar polystyrene would form the core. However, depending on the set of process conditions used the morphology of the resulting two-phase particles varied from that of a pure core-shell structure, over intermediate structures in which a shell of PS surrounded a PMMA core containing an increasing number of PS phase domains, to a structure in which the entire PS phase was present as discrete PS phase domain, more or less evenly distributed in a matrix of PMMA. By the use of a caloirimetric reactor system the monomer concentration in the particles during the different polymerization experiments could be calculated by comparing the integral of the polymerization rate curve with the integral of the monomer feed rate. A comparison between particle morphology and the calculated concentration of plasticizing monomer in the polymerizing particles strongly suggested that the diffusivity of the entering oligo radicals determined by the difference between polymerization temperature and the glass transition temperature of the monomer-swollen core polymer is a key factor determining the morphology of two-phase particles prepared by semi-continuous seed emulsion polymerization. Two-phase particles with a true core-shell structure were obtained in experiments where the estimated glass transition temperature of the PMMA phase was only a few degrees below the polymerization temperature. The results show that such particles can be obtained under conditions of high as well as low styrene feed rates, provided that the rate of initiation is properly adjusted.
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| 7. |
- Karlsson, Ola, et al.
(författare)
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The effect of first-stage polymer Tg on the morphology and thermomechanical properties of structured polymer latex particles
- 2003
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Ingår i: Comptes Rendus. Chimie. - : Elsevier BV. - 1631-0748. ; 6:11-12, s. 1233-1244
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Tidskriftsartikel (refereegranskat)abstract
- A series of heterogeneous latexes having stage ratios of 40:60 between the first and second stage polymers were prepared by emulsion polymerization. The first-stage polymers were non-polar S-BuA with Tgs ranging from + 100 °C to + 20 °C and the second stage polymer was polar MMA–BuA–MAA having a Tg of 20 °C. The latex particle morphologies were studied using TEM and the thermomechanical properties of the resulting latex films were studied with DSC and DMA. Calculated diffusion rates for propagating species during the reactions were correlated to the observed morphologies and to the amount of interphase in the latex particles.
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| 8. |
- Licea Jimenez, Liliana, 1977, et al.
(författare)
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MWNT reinforced melamine-formaldehyde containing alpha-cellulose
- 2007
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Ingår i: Composites Science and Technology. - : Elsevier BV. - 0266-3538 .- 1879-1050. ; 67, s. 844-854
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Tidskriftsartikel (refereegranskat)abstract
- Multi-wall carbon nanotubes (MWNT) were used as reinforcement for melamine-formaldehyde (MF). They were oxidised in HNO3/ H2SO4 mixture and analyzed by means of X-ray Photoelectron Spectroscopy (XPS). Two anionic surfactants: sodium dodecyl sulphate (SDS) and sodium dodecylbenzenesulfonate (NaDDBS) were used to assist the dispersion of nanotubes. The MWNT content was varied from 0 to 1.0 wt%, and the influence of nanotubes on viscosity (flow curves) was measured. The viscosity of SDS-assisted aqueous solution of MF containing a small amount (0.1 wt%) of MWNT is low, and thus promising towards manufacturing processes. A film stacking-like manufacturing route was adapted to prepare ternary MWNT/cellulose/MF thin composite layers. Transmission electron microscopy (TEM) and Light microscopy (LM) were used to observe dispersion. The addition of 0.1 wt% MWNT assisted with SDS increased the storage modulus and tensile strength by 50%. Conventional calculations of the Young's modulus were made. Values underestimating the modulus were found. The observed discrepancy was attributed to polymer chain immobilisation as a result of crosslinking.
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| 9. |
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| 10. |
- Munch Elmér, Anette, et al.
(författare)
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Ion Conductive Electrolyte Membranes Based on Co-Continuous Polymer Blends
- 2003
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Ingår i: Journal of Materials Chemistry. - : Royal Society of Chemistry (RSC). - 1364-5501. ; 13:9, s. 2168-2176
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Tidskriftsartikel (refereegranskat)abstract
- Solid electrolyte membranes based on comb-shaped poly(ethylene glycol) (PEG) doped with lithium bis(trifluoromethanesulfonyl)imide (LiTFSI) salt in blends with poly(vinylidene fluoride-co-hexafluoropropylene) (PVDF-HFP) have been studied. Membranes containing between 70 and 100 wt% PEG were prepared by a convenient two-step process where films containing a mixture of mono- and dimethacrylate-terminated PEG macromonomers, PVDF-HFP, LiTFSI, and a photoactivator were cast from acetone solutions, followed by UV-initiated polymerization of the macromonomers. Microscopy of the membranes revealed a phase separated morphology with a microporous PVDF-HFP network embedded in comb-shaped PEG. The membranes were thermally stable at temperatures below the melting point of PVDF-HFP at 140 °C. Dynamic mechanical analysis (DMA) in the tension mode showed that the mechanical properties of the membranes were greatly improved both by the addition of PVDF-HFP and of dimethacrylate-terminated PEG macromonomer. For example, the storage modulus at 25 °C and 1 Hz showed a three-fold increase after increasing the percentage of dimethacrylate-terminated PEG from 0 to 10 wt% in the macromonomer mixture. A broad shoulder on tan as a function of temperature indicated the existence of a PVDF-HFP rich amorphous interphase. At room temperature, the membranes containing more than 80 wt% PEG reached ionic conductivities exceeding 10–5 S cm–1.
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