0000000000021512
AUTHOR
G. A. Mannella
showing 17 related works from this author
Evidence of Mechanisms Occurring in Thermally Induced Phase Separation of Polymeric Systems
2014
Thermally induced phase separation is a fabrication technique for porous polymeric structures. By means of easy-to-tune processing parameters, such as system composition and demixing temperature, a vast latitude of average pore dimensions, pore size distributions, and morphologies can be obtained. The relation between demixing temperature and morphology was demonstrated via cloud point curve measurement and foams fabrication with controlled thermal protocols, for the model system poly-l-lactide–dioxane–water. The morphologies obtained at a temperature lower than cloud point showed a closed-pore architecture, suggesting a “nucleation-and-growth” separation mechanism, which produced larger po…
Preparation of polymeric foams with a pore size gradient via Thermally Induced Phase Separation (TIPS)
2015
Abstract Foams with a pore size gradient are promising materials for tissue engineering applications where a complex architecture involving morphological variations in space must be mimicked, e.g. in bone tissue repair. In this paper, a technique to obtain a porous scaffold with a pore size gradient is presented. The preparation procedure is based on Thermally Induced Phase Separation (TIPS), by imposing a different thermal history on the two sides of a polymeric solution. In this way, a gradient in thermal history is produced, which will generate a pore size monotonously varying along scaffold thickness. By controlling some parameters easy to manipulate, such as demixing temperature and/or…
No-Flow Temperature in Injection Molding Simulation
2010
Most injection molding simulation packages use the no-flow temperature (NFT) as a means of determining whether the polymer flows or is solid. The NFT is not well defined, and a standard method for measuring it does not exist. A sensitivity analysis of the filling stage has been carried out with two different packages [VISI Flow (Vero Software Limited, Gloucestershire, UK) and Moldflow (Autodesk, Inc., San Rafael, CA)] to estimate the influence of the NFT on the main processing parameters. The NFT has a large influence on the thickness of the frozen layer, but it does not appreciably affect the filling pressure. Because the NFT affects the frozen layer, an effect on the estimation of shrinka…
Measurement of cloud point temperature in polymer solutions.
2013
A temperature-controlled turbidity measurement apparatus for the characterization of polymer solutions has been instrumented and set up. The main features are the coupled temperature-light transmittance measurement and the accurate temperature control, achieved by means of peltier cells. The apparatus allows to measure cloud point temperatures by adopting different cooling protocols: low rate for quasi-equilibrium measurements and high rate for detect kinetic effects. A ternary polymeric solution was adopted as case study system showing that cooling rate affects the measured cloud point temperature.
Phase separation of polymer blends in solution: A case study
2016
Abstract The phase behavior and phase separation features of the quaternary system poly- l -lactide (PLLA)/poly-rac-lactide (PLA)/dioxane/water were investigated. Experiments were performed with fixed total polymer concentration of 6 wt%, by varying the PLLA/PLA weight ratio. Blend weight compositions examined were 100/0, 80/20, 50/50, 20/80 and 0/100, at fixed dioxane/water weight ratio (87/13). Cloud point measurements reported that the demixing temperatures of blends are close to PLLA in the same mixed solvent, in line with the calculated spinodals. As regards to foam preparation, above the PLA cloud point, morphology is similar to pure PLLA foams; conversely, below PLA cloud point, the …
Some Features of Polymeric Membranes for Water Purification via Membrane Distillation
2011
Polymeric membranes are currently adopted in water purification processes, such as reverse osmosis (RO) and membrane distillation (MD). This latter technique is very promising for separation effectiveness and energy savings. A valuable and effective MD unit must be equipped with polymeric membranes that exhibit specific properties, for example, hydrophobicity, a narrow pore size range, a high water penetration pressure, and a large vapor permeability. In this work, we present and examine the main features of membranes for MD processes, with the aim of experimentally evaluating the related performances. Scanning electron microscopy analysis was carried out for a first estimate of the pore si…
CHARACTERIZATION OF HYDROPHOBIC POLYMERIC MEMBRANES FOR MEMBRANE DISTILLATION PROCESS
2010
Hydrophobic microporous membranes are utilized in membrane distillation (MD) processes, e.g. seawater desalination at moderate temperatures. The vapour permeability of commercial hydrophobic membranes with different pore sizes (0.2-1 micron) was characterized through a simple apparatus designed-on-purpose. A cylindrical vessel had a face closed by the membrane and the other connected to a thin graduate tube. The water level variation in the tube is recorded and related to the vapour flux across the membrane. Measurements were taken in the temperature range 20-80°C. A fan tangential to membrane surface was employed to maintain a constant driving force for vapour transport. Vapour flux did no…
Study on heat transfer coefficients during cooling of PET bottles for food beverages
2015
The heat transfer properties of different cooling systems dealing with Poly-Ethylene-Terephthalate (PET) bottles were investigated. The heat transfer coefficient (Ug) was measured in various fluid dynamic conditions. Cooling media were either air or water. It was shown that heat transfer coefficients are strongly affected by fluid dynamics conditions, and range from 10 W/m2 K to nearly 400 W/m2 K. PET bottle thickness effect on Ug was shown to become relevant under faster fluid dynamics regimes.
Optical characterization of phase transitions in pure polymers and blends
2015
To study the optical properties of polymeric samples, an experimental apparatus was designed on purpose and set up. The sample is a thin film enclosed between two glass slides and a PTFE frame, with a very thin thermocouple placed on sample for direct temperature measurement. This sample holder was placed between two aluminum slabs, equipped with a narrow slit for optical measurements and with electrical resistances for temperature control. Sample was enlightened by a laser diode, whereas transmitted light was detected with a photodiode. Measurements were carried out on polyethylene-terephtalate (PET) and two different polyamides, tested as pure polymers and blends. The thermal history impo…
Water Fluxes in Polymeric Membranes for Desalination via Membrane Distillation
2010
Membrane distillation is an emerging technique for seawater desalination. Hydrophobic polymeric membranes are used to separate the solute‐free water vapour from the hot solution. Vapour fluxes of commercial polymeric membranes were measured in various conditions, i.e. natural and forced convection and vacuum. Vapour fluxes were also predicted with models and compared with experimentals. Higher fluxes were recorded in vacuum conditions.
Evaluation of vapor mass transfer in various membrane distillation configurations: an experimental study
2011
Vapor mass transfer phenomena in four different membrane distillation (MD) configurations were examined through a self-built laboratory scale experimen- tal apparatus: Air Gap MD, Sweeping Gas MD, Vacuum Sweeping Gas MD and Vacuum MD. Vapor fluxes were measured and compared with those predicted by various models, showing that MD performance under usual processing conditions is severely controlled by the permeate side resistance to mass transfer.
On the calculation of free energy of mixing for aqueous polymer solutions with group-contribution models
2010
Abstract Liquid–liquid phase separation processes are currently used as a route to prepare polymeric porous structures for various applications (membranes and scaffolds for tissue engineering). In membrane and foam fabrication technologies, binary and mainly ternary polymer solutions are used. Membrane morphology is strongly affected by phase equilibria of processing solution. In order to achieve a better control of membrane morphology and to explore a wide quantity of solvents, a predictive tool addressing experimentals would be strongly advisable. In this paper, group contribution models were chosen to test the applicability on a PLLA–dioxane–water ternary polymer solution, whose experime…
Peltier cells as temperature control elements: Experimental characterization and modeling
2014
Abstract The use of Peltier cells to realize compact and precise temperature controlled devices is under continuous extension in recent years. In order to support the design of temperature control systems, a simplified modeling of heat transfer dynamics for thermoelectric devices is presented. By following a macroscopic approach, the heat flux removed at the cold side of Peltier cell can be expressed as Q ˙ c = γ ( T c − T c eq ) , where γ is a coefficient dependent on the electric current, Tc and T c eq are the actual and steady state cold side temperature, respectively. On the other hand, a microscopic modeling approach was pursued via finite element analysis software packages. To validat…
Lattice fluid model generalized for specific interactions: An application to ternary polymer solutions
2011
Abstract The phase diagram of the Poly- l -Lactic-Acid (PLLA), dioxane and water system was derived by using the lattice fluid model generalized for specific interactions. A qualitative analysis of Hansen solubility parameters together with empirical observations were adopted to reduce the number of adjustable parameters. The as-selected model parameters were derived by fitting a set of cloud point curves; consequently, the complete phase diagram of the system was computed. The use of specific interactions between species gave out a quantitative agreement with a set of experimental data, whereas changing the polymer polydispersity the agreement is only qualitative. In principle, the present…
Design, build-up and optimization of a fast quenching device for polymeric thin film
2014
In this work an innovative apparatus for the characterization of polymer solidification under very high cooling rates (up to thousand of K/s) is described, according to the continuous cooling transformation approach adopted in metallurgy for studying structure development in metals. The proposed model experiment is addressed to design a method for the characterization of non-isothermal solidification behaviour, encompassing typical cooling conditions of polymer processing. Only temperature history determines the structure formed, as melt solidification takes place in quiescent conditions. With respect to the device previously developed by the authors [1, 3] the present equipment presents th…
No-flow temperature and solidification in injection molding simulation
2011
The no‐flow temperature (NFT) is a parameter representing the rheological solidification temperature of a polymer. A polymer, during injection molding filling stage, can stop its flow because of its high viscosity, although it is not yet fully solidified by means of glass transition or crystallization. The NFT is used in most of injection molding simulation packages: with this simple parameter it is possible to reduce the errors deriving from viscosity extrapolation at relatively low temperatures. The viscosity measurements for polymers are usually carried out at high temperatures, and the viscosity models can fail in prediction at temperatures close to the glass transition or crystallizati…
Coagulation bath composition and desiccation environment as tuning parameters to prepare skinless membranes via diffusion induced phase separation
2015
Diffusion Induced Phase Separation (DIPS) is a currently used technique to produce porous membranes for a large variety of applications. A strong limitation is represented by the occurrence of a dense skin, which is formed during the process, highly reducing the membrane permeability. To overcome this issue, two modifications of the standard DIPS protocol were investigated: the use of coagulation baths composed by a solvent/nonsolvent mixture and the desiccation in a controlled environment, by modulating the partial pressure of nonsolvent vapor. An appropriate choice of coagulation bath composition, together with an appropriate desiccation protocol (i.e., the use of a nonsolvent vapor), wil…