Giuseppe Storti

École Polytechnique Fédérale de Lausanne, Lausanne, VD, Switzerland

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Publications (170)199.86 Total impact

  • 14 AIChE Annual Meeting; 11/2014
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    ABSTRACT: By combining elements from colloidal and polymer reaction engineering a new approach towards macroporous, mechanically robust polymer particles is presented, which does not require any porogenic additives. Specifically, aggregation and breakage in turbulent conditions of aggregates originating from fully destabilized primary latex particles is applied to produce compact, micrometer-sized clusters. Post-polymerization of monomer introduced initially to swell the primary particles is imparting mechanical rigidity and permanence to the internal structure. The resulting microclusters exhibit an internal porosity in the order of 70% and relatively broad pore size distribution, with exceptionally large pores, ranging from about 50 nm to 10 μm in diameter. These particulate microclusters, produced via reactive gelation under shear, are fractal objects with fractal dimension around 2.7, as opposed to the more open fractal structure of a monolith produced via stagnant reactive gelation, with fractal dimension of 1.9. Such macroporous particles are thought to be useful in applications requiring pores in the micrometer scale, e.g. in the chromatography of biomolecules or for packing beds perfusive to convective flow.
    Langmuir : the ACS journal of surfaces and colloids. 05/2014;
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    ABSTRACT: Radical desorption from polymer particles is a kinetic event peculiar to the emulsion polymerization process. A careful modeling of this phenomenon is highly valuable in order to achieve accurate predictions of polymerization rate and average properties of molecular weight. In this work, radical desorption is described accounting for an aspect fully neglected in previous modeling literature. Specifically, particle state dependent desorption coefficients are used instead of a single average coefficient, and the corresponding rate expressions are developed and applied to the solution of the well-known Smith–Ewart equations. Parametric model simulations show that the higher level of detail introduced in the description of radical desorption improves the accuracy of the predicted values of the average number of radicals per particle, especially in the cases of high desorption rate and slow reactions in the aqueous phase.
    Industrial & Engineering Chemistry Research. 01/2014; 53(22):9049–9057.
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    ABSTRACT: The molecular weight distributions of poly(lactic acid) produced by ring-opening polymerization of l,l-lactide in bulk melt are measured and compared with the ones predicted using a kinetic model accounting for reversible catalyst activation, reversible propagation, reversible chain transfer to cocatalyst, and intermolecular transesterification. The same values of the model parameters as evaluated in previous works are used without any adjustment; i.e. the model is used in a fully predictive way. In order to calculate the complete molecular weight distribution, the model equations are solved through two different numerical methods, “direct integration” of the population balances at all values of chain length, and “fractionated moments”, where the chains are artificially classified into two different categories, depending upon the experienced reaction steps. The accuracy of the molecular weight distributions calculated in the latter case is evaluated by comparison with those computed by solving the model equations with the “direct integration” method. It is found that the “fractionated moments” method provides enough accuracy and much smaller computational effort, thus representing an optimal tool for most modeling applications. Finally, the model predictions are compared with the experimental molecular weight distributions measured experimentally in bulk melt at 130 °C and various initial concentrations of catalyst and cocatalyst. The generally good agreement verified between model and experiment after correcting for peak broadening represents a convincing confirmation of the model’s reliability.
    Industrial & Engineering Chemistry Research. 01/2014; 53(18):7333–7342.
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    ABSTRACT: A model of free-radical cross-linking copolymerization in solution, based on Flory’s gelation theory and developed by Tobita and Hamielec [Macromolecules 1989, 22, 3098–3105] has been applied to the system acrylamide/N,N′-methylenebisacrylamide. The evaluation of missing rate constants was performed by comparing model predictions with experimental measurements of swelling ratios and literature data. This way, the interplay of cross-linking and intramolecular cyclization reactions, regulating the network formation and its properties, has been deepened. It turns out that the primary intramolecular cyclization is practically independent of the cross-linker amount employed, but it is affected by the total monomer concentration. For the latter dependency, an empirical correlation was proposed, which was tested in parametric simulations, showing its impact on the properties of hydrogels.
    Industrial & Engineering Chemistry Research. 01/2014; 53(22):9035–9048.
  • Ivan Kryven, Stefano Lazzari, Giuseppe Storti
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    ABSTRACT: A complex interplay between aggregation and coalescence occurs in many colloidal polymeric systems and determines the morphology of the final clusters of primary particles. To describe this process, a 2D population balance equation (PBE) based on cluster mass and fractal dimension is solved, employing a discretization method based on Gaussian basis functions. To prove the general reliability of the model and to show its potential, parametric simulations are performed employing both diffusion-limited-cluster aggregation (DLCA) and reaction-limited-cluster-aggregation (RLCA) kernels and different coalescence rates. It turns out that in both DLCA and RLCA regimes, a faster coalescence leads to smaller sized and more compact clusters, whereas a slow coalescence promotes the formation of highly reactive fractals, resulting in larger aggregates.
    Macromolecular Theory and Simulations 01/2014; · 1.61 Impact Factor
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    ABSTRACT: The hydrolysis of lactic acid oligomers involves several different reactions, acid-catalyzed, base-catalyzed as well as non-catalyzed. In the present paper a pH-dependent kinetic model has been developed and its kinetic constants evaluated by fitting to experimental data of degrading lactic acid oligomers at 37 °C in aqueous solution at pH = 1, 2, 3.5, 5.7 and 7.4. The model was able to properly describe the experimental data with an average error of about 5%. The estimated values of the kinetic constants at the selected temperature are: kDα=4.44×10−3L2mol−2h−1L2mol−2h−1, kDβ=9.29×10−4L2mol−2h−1L2mol−2h−1 (acid-catalyzed), kRH=1.56×310kRH=1.56×103L2mol−2h−1L2mol−2h−1, kBB=2.88×610kBB=2.88×106Lmol−1h−1Lmol−1h−1 (base-catalyzed) and kW=2.49×10−5kW=2.49×10−5Lmol−1h−1Lmol−1h−1 (non-catalyzed).
    Polymer Degradation and Stability 01/2014; 110:80–90. · 2.77 Impact Factor
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    ABSTRACT: Cross-linked polymer networks are materials of great technological relevance, such as rubbers, multi-component adhesives and hydrogels. Whereas rubbers and adhesives are the oldest examples of cross-linked polymer networks, the research on hydrogels has been more recently fueled by their growing importance in biology and biomedicine. The presence of cross-linkers confers to these networks unique properties, such as high mechanical and chemical resistance, thermal stability and even stimuli-responsiveness. A great number of network properties can be controlled by tuning the degree of cross-linking. Therefore, modeling free radical polymerization processes in the presence of cross-linkers is a challenging problem that has been addressed for over more than half a century using numerous techniques. However, a model providing a comprehensive description of the phenomenon has not been proposed yet. In this work, we implement a simple free-radical polymerization scheme of a mono-vinyl (di-functional) monomer and a di-vinyl (tetra-functional) cross-linker in a Monte-Carlo (MC) scheme, which describes polymer dynamics using a bond-fluctuation model[1]. MC simulations allow us to follow the entire polymerization kinetics and the formation of percolating network (gel phase) by realistically taking into account diffusion limitations, to extract scaling information at the percolation threshold and to recover the distribution of number of monomer units between two successive fully cross-linked units, from which the extent of swelling can be computed. The predictions of MC simulations are also successfully compared to a kinetic model based on numerical fractionation[2], with kinetic constants used as fitting parameters. MC data and kinetic simulations are compared to some experimental data on the swelling behavior of polyacrylamide hydrogels and of polymethyl methacrylate (PMMA) gels, exhibiting good agreement. We conclude that the proposed MC simulation scheme represents a powerful tool from which precious and experimentally inaccessible information on polymerization processes in the presence of crosslinkers can be extracted. [1] Carmesin, I.; Kremer, K. Macromolecules 1988, 21, 2819–2823 [2] Teymour, F.; Campbell, J. D. Macromolecules 1994, 27, 2460–2469
    13 AIChE Annual Meeting; 11/2013
  • Stefano Lazzari, Giuseppe Storti
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    ABSTRACT: In the present work, a kinetic model of crosslinking free-radical copolymerization based on multidimensional population balances and accounting for multiradicals is developed. The model is applied to the simulation of bulk copolymerization of methyl-methacrylate (MMA)/ethylene-glycol-dimethacrylate (EGDMA). A literature criterion proposed to elucidate the model type best suited for a given system (i.e., with or without MRs) is extended to the industrially relevant case of diffusion limited systems. Moreover, a master plot for the system under investigation is proposed: given the reaction recipe, the error on the gel point prediction employing the monoradical assumption is identified, thus allowing more conscious model selection.
    Macromolecular Theory and Simulations 10/2013; · 1.61 Impact Factor
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    ABSTRACT: In protein chromatography, the size of the protein determines which fraction of pores it can access within a resin and at which rate of diffusion. Moreover, in the presence of grafted polymers like in advanced materials, adsorbed proteins and electrolytes complicate the interaction pore-protein. In this study, we evaluated in a comparative way the behavior of Fractogel(®) EMD SO3 (M) and (S), "tentacle"-type, strong cation exchangers, as well as a reference material without tentacles, all of which are commonly used for protein purification. ISEC experiments were carried out with a set of Dextran tracers of largely different molecular size covering the typical range of protein sizes. Experimental values of porosity (internal and external to the particles) as well as of pore diffusion coefficients have been measured at different NaCl concentrations and under protein loading. These results provide useful insights into the complex interplay among mentioned factors: first, the presence of tentacles induces size exclusion selectivity in the materials; second, the salt induces conformational changes of the tentacles, leading to porosities larger than expected in tentacle materials; third, protein adsorption mainly leads to a reduction of porosity due to pore space occupied by the protein and to a decrease of pore diffusion coefficient.
    Journal of Chromatography A 02/2013; · 4.61 Impact Factor
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    ABSTRACT: Modeling free radical polymerization processes in the presence of cross-linkers is a challenging problem that has been addressed using numerous techniques for over more than half a century. However, a model providing a comprehensive description of the phenomenon has not been proposed yet. In this work, we implement a simple free-radical polymerization scheme of a monovinyl (difunctional) monomer and a divinyl (tetrafunctional) cross-linker in a Monte Carlo (MC) scheme, which describes polymer dynamics using a bond-fluctuation model. MC simulations allow us to follow the entire polymerization kinetics and the formation of a percolating network (gel phase) by realistically taking into account diffusion limitations, to extract scaling information at the percolation threshold and to recover the distribution of number of monomer units between two successive fully cross-linked units, from which the extent of swelling can be computed. The predictions of MC simulations are also successfully compared to a kinetic model based on numerical fractionation, with kinetic constants used as fitting parameters. MC data and kinetic simulations are compared to some experimental data on the swelling behavior of polyacrylamide hydrogels and of poly(methyl methacrylate) (PMMA) gels, exhibiting good agreement. We conclude that the proposed MC simulation scheme represents a powerful tool from which precious and experimentally inaccessible information on polymerization processes in the presence of cross-linkers can be extracted.
    Macromolecules 01/2013; 46:5831. · 5.93 Impact Factor
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    ABSTRACT: We propose a novel, single step method for the production of polyacrylamide hydrogels with a gradient in mechanical properties. In contrast to already existing techniques such as UV photo-polymerization with photomasks (limited penetration depth) or microfluidic gradient mixers (complex microfluidic chip), this technique is not suffering such limitations. Young's modulus of the hydrogels was varied by changing the total monomer concentration of the hydrogel precursor solution. Using programmable syringe pumps, the total monomer concentration in the solution fed to the hydrogel mold was varied from 16 wt% down to 5 wt% over the feeding time to obtain a gradient in compliance ranging from 150 kPa down to 20 kPa over a length of 10 mm down to 2.5 mm. Polymerization was achieved with the dual initiation system composed of ammonium persulfate and N,N,N',N'-tetramethylethylenediamine, which were both fed through separate capillaries to avoid premature polymerization. Functionalized with the model ligand collagen I, the substrates were bioactive and supported the attachment of human foreskin fibroblasts (around 30% of the cells seeded attached after 1 hour). A kinetic morphology study on homogeneous hydrogels of different stiffness's indicated that fibroblasts tend to spread to their final size within 2 hours on stiff substrates, while the spreading time was much longer (ca. 4 - 5 hours) on soft substrates. These trends were confirmed on hydrogels with compliance gradients, showing well spread fibroblasts on the stiff end of the hydrogel after 2 hours, while the cells on the soft end still had small area and rounded morphology. Biotechnol. Bioeng. © 2012 Wiley Periodicals, Inc.
    Biotechnology and Bioengineering 12/2012; · 4.16 Impact Factor
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    ABSTRACT: In this work, the preparation of poly(lactic acid) (PLA)-based degradable nanoparticles (NPs) with tunable hydrophobicity and degradation kinetics via starved emulsion free-radical polymerization is studied. The synthesis of macromonomers, constituted of a tunable number of lactic acid units functionalized with 2-hydroxyethyl methacrylate (HEMA), has been performed via bulk ring opening polymerization (ROP) of L, L-lactide catalyzed with 2-ethylhexanoic acid tin (II) salt. Macromonomers were characterized through SEC, NMR, and FTIR and are subsequently polymerized through monomer-starved semi-batch emulsion polymerization (MSSEP). The effect on the polymerization process of various emulsifiers on the final diameter and particle size distribution has been studied. The resulting PLA-based NPs are characterized by a narrow size distribution and a small particle size, down to 25 nm. Finally, a degradation study of selected NPs has been carried out to verify their degradability in aqueous media. It has been demonstrated the complete degradability of these PLA-based NPs which occurs upon the hydrolysis of the PLA pendant chains leaving poly-HEMA chains, which, being hydrophilic causes the NPs to dissolve in the aqueous suspension. © 2012 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem, 2012
    Journal of Polymer Science Part A Polymer Chemistry 12/2012; 50(24):5191-5200. · 3.54 Impact Factor
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    ABSTRACT: The hydrolysis of water soluble PLA oligomers of different chain lengths and chirality was investigated at acidic pH and temperatures in the range from 40 to 120 °C. The time evolution of the concentrations of all oligomers was measured by HPLC and the corresponding degradation rates were evaluated for each specific chain length. In agreement with the preferential chain end scission mechanism suggested in the literature, the ester groups were classified as α (chain end esters) and β (backbone esters). A kinetic model was developed from the resulting kinetic scheme and it was found to well reproduce the concentration values of all different oligomers during degradation as a function of time. The corresponding rate constants kdα and kdβ were estimated over the whole temperature range, with activation energies of 73 and 58 kJ/mol and pre-exponential factors of 8.21·107 and 1.77·105 l/mol/h, respectively. It is seen that the faster hydrolysis of the ester groups close to the carboxylic and hydroxyl chain end groups (α) with respect to those inside the polymer chain (β) is mainly due to the largely different pre-exponential factors. This steric effect can be explained considering that the water approach is favoured by the hydrophilic nature of the chain end groups compared to the hydrophobic character of the polymer backbone. No dependence of kdα and kdβ on chiral composition was found, suggesting that the differences reported earlier in the literature are due to the effect of crystallinity on diffusion phenomena rather than to different reactivity of the two stereoisomers.
    Polymer Degradation and Stability 11/2012; 97(11):2460–2466. · 2.77 Impact Factor
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    ABSTRACT: Macroporous chromatographic supports are ideal for preparative applications, where good throughput, i.e. speed of separation, is required. In this regard, large throughpores provide high bed permeability, which allows operation at high flow rates. Meanwhile, if these large pores are able to accommodate a fraction of convective flow, so-called perfusive pores, then separation efficiency is independent of the flow rate. To this end, by combining elements from colloidal and polymer reaction engineering, a novel macroporous packing material with advanced mass transfer properties was developed. Specifically, aggregation and breakage under flow of polymeric microclusters allows the control final cluster size and pore size distribution, while post-polymerization imparts high mechanical stability. Owing to surface-bound ATRP initiators a versatility of functionalities can be realized, in order to employ different separation modes, relying on different types of substrate-solute interaction. So far, conventional cation and anion exchange chromatography have been addressed, as well as an alternative temperature-responsive modality, where instead of ionic strength or polarity of the mobile phase, temperature is utilized to control interactions. This is advantageous from the environmental and cost-reduction viewpoint, as well as for preserving bioactivity of the purified compounds. As polymer brushes are grafted from the substrate surface, multiple active sites are available per unit area, offering increased binding capacities. Meanwhile, the flexibility of such chains allows for favorable steric distributions, so that large molecules like proteins, can be better accommodated. As a matter of fact, application examples demonstrate that our functionalized adsorbents may compete with existing commercial chromatographic supports. Figure 1. SEM image of supporting microcluster. White circles indicate large throughpores. Figure 2. Pore functionalization scheme. Figure 3. Illustrative separation of Lysozyme, α-Chymotrypsinogen and Cytochrome-c (elution order) by an anionic-PE functionalized column versus a commercial exchanger. Conditions: 30mM phosphate buffer pH7.0, linear gradient elution from 0.0M to 1.0M NaCl (dashed line) at 1ml/min. Peak resolution was calculated using the indicated formula.
    12 AIChE Annual Meeting; 11/2012
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    ABSTRACT: The controlled synthesis of degradable nanoparticles (NPs) made from a brush copolymer constituted of a 2-hydroxyethyl methacrylate (HEMA) backbone with PEG and PLA pendants both tunable in length and composition has been developed. Using ring-opening polymerization (ROP) of L,L–lactide, vinyl end-functionalized PLA macromonomers were produced and then copolymerized with HEMA–PEG macromonomers. Narrow dispersed PEGylated NPs with size down to 25 nm with different PEGylation degree and PEG chain lengths were obtained. Surfactant-free MSSEP in the absence of any solvent was implemented to produce NPs suitable for biomedical applications. The colloidal stability in isotonic solutions of these NPs was investigated and the corresponding critical coagulation concentration (CCC) of the NPs was determined.
    Macromolecular Chemistry and Physics 10/2012; 213(19). · 2.39 Impact Factor
  • Macromolecular Chemistry and Physics 10/2012; 213(19). · 2.39 Impact Factor
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    ABSTRACT: The effect of polymeric surfactants, copolymers of n-butyl acrylate (BA) and acrylic acid (AA), on shear-induced gelation of a colloidal system in the absence of additional electrolytes is studied. One random (PBA-co-PAA) and two block copolymer (PBA-b-PAA, with different PAA lengths) surfactants have been synthesized by ATRP and used in this work. The colloidal system is composed of strawberry-like particles with a rubbery core, partially covered by a few grafted plastic patches. In the absence of any surfactant, as the colloidal system passes through a microchannel at a Peclet number of 220 and a particle volume fraction of 0.15, shear-induced gelation occurs and the particles coalesce partially, due to the rubbery core, leading to a fractal dimension of the clusters constituting the gel equal to 2.78. On the other hand, in the presence of any of the three polymeric surfactants, shear-induced gelation occurs only in the range of low surfactant surface density. Meanwhile, the fractal dimension of the clusters decreases with adsorption of the two block surfactants, reaching a plateau value of about 2.58, while for the random surfactant it remains constant and equal to 2.78, like in the absence of any surfactant. This indicates that adsorption of the block surfactants can reduce the particle coalescence, while adsorption of the random surfactant cannot. Moreover, for all three surfactants, as their surface density increases progressively, a transition from solid-like gel to a liquid-like state occurs and finally no shear-induced gelation or even aggregation occurs. Since the three surfactants comprise carboxylic groups, considering also the results in the literature (Zaccone et al., J. Phys. Chem. B, 2008, 112, 1976; 6793), we can reach a general conclusion that carboxylic groups on the particle surface not only stabilize the particles through electrostatic repulsion, but also generate very short-range, strongly repulsive (e.g. hydration, steric) forces, which when high enough protect the particles from intense shear-activated aggregation.
    Physical Chemistry Chemical Physics 09/2012; 14(41):14374-82. · 4.20 Impact Factor
  • Macromolecular Reaction Engineering 08/2012; 6(8). · 1.64 Impact Factor
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    ABSTRACT: The kinetics of ring-opening polymerization of D,L-lactide with 2-ethylhexanoic acid zinc (II) salt as catalyst and methanol as co-catalyst at different temperatures is investigated. A previously proposed kinetic model accounting for reactions such as activation, propagation, chain transfer, transesterification and thermal non-radical random chain scission has been applied to simulate the experimental results of conversion and average molecular weights. The relevance of some side reactions, mainly transesterifications and chain scission, has been verified all over the studied temperature range and the corresponding rate constants have been estimated. Copyright © 2011 Society of Chemical Industry
    Polymer International 02/2012; 61(2). · 2.13 Impact Factor

Publication Stats

1k Citations
199.86 Total Impact Points

Institutions

  • 2005–2011
    • École Polytechnique Fédérale de Lausanne
      • Institut des sciences et ingénierie chimiques
      Lausanne, VD, Switzerland
    • Eawag: Das Wasserforschungs-Institut des ETH-Bereichs
      Duebendorf, Zurich, Switzerland
  • 1998–2011
    • Politecnico di Milano
      • Department of Chemistry, Materials and Chemical Engineering "Giulio Natta"
      Milano, Lombardy, Italy
  • 1989–2011
    • Università degli studi di Cagliari
      • Department of Mechanical, Chemical and Material Engineering
      Cagliari, Sardinia, Italy
  • 2010
    • Università degli studi di Palermo
      • Dipartimento di Ingegneria Chimica, Gestionale, Informatica, Meccanica (DICGIM))
      Palermo, Sicily, Italy
  • 2000–2008
    • Technische Universiteit Eindhoven
      • Department of Chemical Engineering and Chemistry
      Eindhoven, North Brabant, Netherlands
  • 1999–2008
    • ETH Zurich
      • • Institute of Process Engineering
      • • Institute for Chemical and Bioengineering
      Zürich, ZH, Switzerland
  • 2006
    • University of Rome Tor Vergata
      Roma, Latium, Italy
  • 2003–2004
    • University of Padova
      Padua, Veneto, Italy
  • 2001
    • LTC
      Peshawar, North-West Frontier Province, Pakistan