Staff Publications

Staff Publications

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    'Staff publications' is the digital repository of Wageningen University & Research

    'Staff publications' contains references to publications authored by Wageningen University staff from 1976 onward.

    Publications authored by the staff of the Research Institutes are available from 1995 onwards.

    Full text documents are added when available. The database is updated daily and currently holds about 240,000 items, of which 72,000 in open access.

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    Comparing the social costs of biofuels and fossil fuels: A case study of Vietnam
    Thanh, L. le; Ierland, E.C. van; Zhu, X. ; Wesseler, J.H.H. ; Ngo, G. - \ 2013
    Biomass and Bioenergy 54 (2013). - ISSN 0961-9534 - p. 227 - 238.
    diesel-engine - methyl-ester - performance - emissions - biodiesel - blends - combustion
    Biofuel substitution for fossil fuels has been recommended in the literature and promoted in many countries; however, there are concerns about its economic viability. In this paper we focus on the cost-effectiveness of fuels, i.e., we compare the social costs of biofuels and fossil fuels for a functional unit defined as 1 km of vehicle transportation. We base our empirical results on a case study in Vietnam and compare two biofuels and their alternative fossil fuels: ethanol and gasoline, and biodiesel and diesel with a focus on the blends of E5 and E10 for ethanol, and B5 and B10 for biodiesel. At the discount rate of 4%, ethanol substitution for gasoline in form of E5 or E10 saves 33% of the social cost of gasoline if the fuel consumption of E5 and E10 is the same as gasoline. The ethanol substitution will be cost-effective if the fuel consumption of E5 and E10, in terms of L km-1, is not exceeding the consumption of gasoline by more than 1.7% and 3.5% for E5 and E10 respectively. The biodiesel substitution would be cost-effective if the fuel consumption of B5 and B10, in terms of L km-1 compared to diesel, would decrease by more than 1.4% and 2.8% for B5 and B10 respectively at the discount rate of 4%.
    Polymer microspheres with structured surfaces
    Wagdare, N.A. ; Baggerman, J. ; Marcelis, A.T.M. ; Boom, R.M. ; Rijn, C.J.M. van - \ 2011
    Chemical Engineering Journal 175 (2011)11. - ISSN 1385-8947 - p. 561 - 568.
    phase-inversion membranes - double-walled microspheres - controlled drug-release - polyethersulfone membranes - immersion precipitation - ppo membranes - blends - morphology - separation - emulsions
    Microspheres from polymethyl methacrylate (PMMA) and Eudragit FS 30D (a commercial copolymer of poly(methyl acrylate-co-methyl methacrylate-co-methacrylic acid) 7:3:1) were prepared using microsieve emulsification. A mixture of these polymers in dichloromethane (DCM) was dispersed into water, leading to extraction of DCM in water and the formation of microspheres with a PMMA core and a partially demixed Eudragit shell. With a higher ratio of Eudragit to PMMA, more and bigger pores can be seen on the surface of the microspheres. Eudragit can be removed from the shell of the microspheres under alkaline conditions. Depending on the initial Eudragit to PMMA ratio, PMMA microspheres with different surface morphologies are obtained. At low Eudragit concentrations microspheres with a crumpled surface are formed, while at higher Eudragit concentrations microspheres are formed with a core to which dendritic PMMA structures are attached. At even higher Eudragit concentrations the microspheres obtained after dissolving the Eudragit show a nanorough surface.
    Addition of Oils to Polylactide Casting Solutions as a Tool to Tune Film Morphology and Mechanical Properties
    Sawalha, H.I.M. ; Schroën, C.G.P.H. ; Boom, R.M. - \ 2010
    Polymer Engineering and Science 50 (2010)3. - ISSN 0032-3888 - p. 513 - 519.
    premix membrane emulsification - poly(lactic acid) - poly(ethylene glycol) - poly(l-lactic acid) - blends - plasticization - pla - crystallization - miscibility - succinate)
    Poly(L-lactide) (PLLA) films exhibit toughening by the addition of oils to the polymer casting. This was investigated by casting films from solution and evaporation in air; the investigated oils were linear alkanes, cyclic alkanes, and two terpenes (limonene and eugenol). The addition of the oils greatly influenced the morphology and thermal and mechanical properties of the films. Most oils rendered porous films, and a variety of morphologies was obtained. Films prepared with hexane and eugenol showed a solid, nonporous structure similar to neat PLLA films, with similar mechanical properties. The thermal transition temperatures of the films decreased through the addition of oil, depending on the oil used, the decrease could be up to 30°C (glass transition), 45°C (cold crystallization), and 15°C (melting temperature). The films prepared without oil were stiff and brittle. Upon addition of most of the oils, the maximum strength and elastic moduli decreased, but their ductility improved considerably. Limonene, the most extreme case, gave a very ductile film with an elongation at break up to 200%. The main conclusion of this study is that various oils can be used to tune and improve the properties of PLLA films
    Influence of process parameters on formation of fibrous materials from dense calcium caseinate dispersions
    Manski, J.M. ; Zalm, E.E.J. van der; Goot, A.J. van der; Boom, R.M. - \ 2008
    Food Hydrocolloids 22 (2008)4. - ISSN 0268-005X - p. 587 - 600.
    extrusion-cooking - mozzarella cheese - simple shear - moisture - microstructure - deformation - particles - proteins - blends - matrix
    Concentrated calcium caseinate (Ca-caseinate) in the presence of palm fat forms hierarchical fibrous materials after enzymatic crosslinking under well-defined deformation. The presence of fat induces the protein fibers to be arranged in bundles of 200 fibers, separated by layers that are concentrated in fat. We investigated the effect of shear rate; shear time and protein concentration on the formation of fibrous materials in the two-phase protein¿fat system. The ratio between crosslinking rate and shear rate determined whether a fibrous structure was formed or not, indicating a subtle interplay between material properties and process conditions. Prolonged shear time influenced the transition from fibrous materials into damaged structures accompanied by syneresis. The experimental results are concluded in a generalized diagram, which provides an initial explanation of the structural transitions induced by solidification and shear.
    Gentle Immobilization of Nonionic Polymersomes on Solid Substrates
    Li, F. ; Ketelaar, T. ; Cohen Stuart, M.A. ; Sudhölter, E.J.R. ; Leermakers, F.A.M. ; Marcelis, A.T.M. - \ 2008
    Langmuir 24 (2008)1. - ISSN 0743-7463 - p. 76 - 82.
    atomic-force microscopy - block-copolymers - drug-delivery - vesicles - morphology - solubilization - curvature - stability - blends
    Vesicles from Pluronic L121 (PEO5-PPO68-PEO5) triblock copolymers were first stabilized by a permanent interpenetrating polymer network and then gently immobilized onto a glass or mica surface. Fluorescence-labeled micrometer-sized vesicles were visualized with confocal laser scanning microscopy, and smaller sized capsules, around 100 nm, were probed by liquid atomic force microscopy. The immobilized vesicles were weakly attached to a negatively charged surface via negatively charged polyelectrolytes in combination with Mg2+ ions and can be reversibly detached from the surface by slightly elevated temperatures. To illustrate that the immobilized vesicles remain responsive to external stimuli, we show that it is possible to transform their shape from spherical to cylindrical by introducing a second Pluronic, namely, P123 (PEO20-PPO70-PEO20). The detailed transition process has been recorded in real time by confocal laser scanning microscopy. Electron microscopy studies confirmed that a similar morphology change also occurs in the bulk.
    Co- and Terpolyesters based on isosorbide and succinic acid for coating applications : synthesis and characterization
    Noordover, B.A.J. ; Staalduinen, V.G. van; Duchateau, R. ; Koning, C.E. ; Benthem, R.A.T.M. van; Mak, M. ; Heise, A. ; Frissen, A.E. ; Haveren, J. van - \ 2006
    Biomacromolecules 7 (2006)12. - ISSN 1525-7797 - p. 3406 - 3416.
    end-groups - polyesters - esterification - poly(ethylene-terephthalate) - 1,4/3,6-dianhydro-d-glucitol - 1,4-3,6-dianhydrosorbitol - blends - uv
    Co- and terpolyesters based on succinic acid and isosorbide in combination with other renewable monomers such as 2,3-butanediol, 1,3-propanediol, and citric acid were synthesized and characterized. Linear polyesters were obtained via melt polycondensation of nonactivated dicarboxylic acids with OH functional monomers. Polymer end functionality (i.e., hydroxyl or carboxylic acid) was controlled by adjusting the monomer stoichiometry. The glass transition temperatures of the resulting polyesters could be effectively adjusted by varying the polymer composition and molar mass. By adding polyfunctional monomers such as trimethylolpropane or citric acid, polyesters with enhanced functionality were obtained. These biobased polyesters displayed functionalities and Tg values in the appropriate range for (powder) coating applications. The polyesters were cross-linked using conventional curing agents. Coatings from branched polyesters-hydroxyl as well as acid functional-showed significantly improved mechanical and chemical resistance compared to those formulated from linear polymers. These renewable polyesters proved to be suitable materials for coating applications with respect to solvent resistance, impact resistance, and hardness.
    Effect of Permeability on Aqueous Biopolymer Interfaces in Spinning Drop Experiments
    Scholten, E. ; Sagis, L.M.C. ; Linden, E. van der - \ 2006
    Biomacromolecules 7 (2006)7. - ISSN 1525-7797 - p. 2224 - 2229.
    phase-separated gelatin/dextran - shear-flow - tension - mixtures - relaxation - diffusion - emulsions - blends
    In this paper we show that interfaces in aqueous phase-separated biopolymer mixtures are permeable for all components present in the system. In spinning drop experiments, droplets of the low-density phase decreased up to 90% in volume over a time span of days to weeks, when inserted in a matrix of the high-density phase. We propose an expression for this change of volume in time in terms of diffusion coefficients of the components. From the magnitude of these coefficients, we conclude that the transfer of gelatin from inside the droplet to the outer phase was the rate-determining step in this process. Since the interfaces are permeable to all components, the properties of the system change in time. Therefore, the spinning drop technique is not an accurate method for the measurement of the equilibrium interfacial tension of these aqueous phase-separated systems.
    Effect of Interfacial Permeability on Droplet Relaxation in Biopolymer-Based Water-in-Water Emulsions
    Scholten, E. ; Sprakel, J.H.B. ; Sagis, L.M.C. ; Linden, E. van der - \ 2006
    Biomacromolecules 7 (2006)1. - ISSN 1525-7797 - p. 339 - 346.
    phase-separated gelatin/dextran - shear-flow - aqueous mixtures - immiscible polymers - retraction method - na-caseinate - tension - deformation - blends - diffusion
    In this paper, we show that for aqueous phase-separated biopolymer mixtures (water-in-water emulsions) both interfacial tension and permeability of the interface are important for the relaxation process of deformed droplets. We give an expression for the characteristic relaxation time that contains both contributions. With this description, the interfacial tension and the permeability can be deduced from cessation-of-flow experiments. The results show that for samples that are very close to the critical point the interfacial tension, calculated without taking into account the permeability, are overestimated significantly. For samples close to the critical point, the permeability has to be taken into account in the description for the relaxation time to get a reliable estimation of the interfacial tension. Our experiments show that for these systems the effective permeability is inversely proportional to the interfacial tension, eff 1/, and proportional to the square of the interfacial thickness, eff 2. We find that the permeability is related to an effective diffusion coefficient as Deff eff. From this relation, we find that the diffusion coefficient is equal to 0.9·10-9 m2/s, which is close to the self-diffusion coefficient of water; = 2.3·10-9 m2/s. This indicates that only water diffuses through the interface, and the diffusion coefficient is independent of the composition of the system for the concentration regime that is used
    Stationary dynamics approach to analytical approximations for polymer coexistence curves
    Scheinhardt-Engels, S.M. ; Leermakers, F.A.M. ; Fleer, G.J. - \ 2004
    Physical Review. E, Statistical nonlinear, and soft matter physics 69 (2004)1. - ISSN 1539-3755 - p. 1 - 13.
    monte-carlo simulations - gibbs-ensemble simulations - phase-equilibria - molecular simulation - lattice polymers - mixtures - interdiffusion - blends - diffusion - homopolymer
    The stationary dynamics approach to analytical approximations for polymer coexistence curves was studied. It was found that the approach became an approximation when the fluxes, written in terms of diffusion coefficients, were calculated analytically instead of numerically. It was demonstrated that the stationary dynamics approach also yielded approximations for coexisting phases in symmetrical multicomponent systems, though the accuracy decreased as the number of coexisting phases increased. The fast and slow mode flux expressions for a specific nonstationary situation were also analyzed.
    Fractionation in a Phase-separated Polydisperse Polymer Mixture
    Heukelum, A. van; Barkema, G.T. ; Edelman, M.W. ; Linden, E. van der - \ 2003
    Macromolecules 36 (2003)17. - ISSN 0024-9297 - p. 6662 - 6667.
    lattice multichain systems - time dynamic properties - flory-huggins model - spinodal decomposition - monte-carlo - entangled polymers - ising-model - blends - fluctuations - compatibility
    If a solution of polydisperse A- and B-polymers undergoes phase separation, the molar mass distribution of the A-polymers in the A-rich phase becomes different from that in the B-rich phase. This phenomenon is known as fractionation. Here, we compare experimental results on fractionation with Flory-Huggins theory and computer simulations. We study the degree of fractionation f(m) A in B(m)/A in A(m), in which A in A(m) is the density of A-polymers with molar mass m in the A-rich phase and A in B(m) that of A-polymers in the B-rich phase. We find that f(m) obeys the simple scaling f(m) ~ exp(-km), where k is a temperature-dependent constant.
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