G. A. Mannella

Measurement of cloud point temperature in polymer solutions

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.

PLLA Scaffold via TIPS for Bone Tissue Engineering

Tissue engineering offers a promising new approach to repair bone fractures, fractures that do not heal, and fractures due to bone tumors. In this work, two different approaches were tested in order to obtain Poly-LLactic Acid (PLLA) porous scaffolds via Thermally Induced Phase Separation (TIPS) for bone tissue engineering application. First, the possibility to produce a composite material, by incorporating Hydroxyapatite (HA) particles in a Poly-L-lactic acid (PLLA) matrix was investigated. Two PLLA/HA weight ratios (70/30 and 50/50) were tested. The results showed that the presence of HA does not influence the phase separation process, i.e. the composite scaffolds microstructure is similar to pure PLLA scaffolds. WAXD analysis confirmed the full incorporation of HA particles into the polymer matrix. Moreover, compression tests showed a fourfold increase of Young module with respect to pure PLLA scaffold. Since the production of scaffolds for bone tissue regeneration is a challenging target, scaffolds must mimic the bone morphology, thus requiring a gradient of pore dimension and morphology along one dimension. To attain this goal, the second part of the work describes the design, set up and test of an experimental apparatus able to set different thermal histories on the two sides of a sample. Scaffolds were produced by following various thermal protocols on both sample surfaces. The results showed that through this technique it is possible to produce scaffolds with a pore size that increases along sample thickness. As a matter of fact, the obtained average pore dimension on one side of the sample was about 70 μm, whereas it was around 240 μm on the opposite surface. By moving along the sample thickness, the pore dimension increased steadily. All things considered, a reliable route for the production of composite PLLA/HA scaffolds with a controlled pore size distribution was assessed, thus offering a valid support to bone tissue engineering.

Optical characterization of phase transitions in pure polymers and blends

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 imposed to the sample consisted in a rapid heating from ambient temperature to a certain temperature below the melting point, a stabilization period, and then a heating at constant rate. After a second stabilization period, the sample was cooled. The data obtained were compared with DSC measurements performed with the same ...

Design, build-up and optimization of a fast quenching device for polymeric thin film

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 the following features: - reduced size (30*30*20 cm); - higher heating rates, by using two electrical resistances supported on ceramic plates; - higher cooling rates, carried out through water sprays at very high pressures (120 bar); - thermal insulation of the sample from the sample holder via the application of two wave...

Modeling and experimental approaches for the characterization of phase equilibria in polymer solutions

The morphology of porous structures prepared via phase separation processes is strongly affected by the thermodynamic properties of the considered system: therefore, a deep characterization of phase equilibria in polymer solutions represents a valid support in the design of membrane production protocols. As the experimental derivation of phase diagram is time and cost consuming, a simple route is proposed, combining both experimental and modeling approaches. The compressible lattice fluid model extended to specific interactions was used to fit experimental cloud point curves for the system PLLA-dioxane-water, which is used for the preparation of porous membranes for various applications. The as derived parameters allow the direct derivation of the complete phase diagram of the system. On the other hand, an apparatus for light transmittance measurements was built and set up for carrying out an experimental detection of cloud point curves. By merging the experimental and modeling approaches, a complete phas...

No‐flow temperature and solidification in injection molding simulation

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 crystallization temperature.The NFT is still a parameter not well defined and a standard method to measure it is still lacking. Nevertheless, a simple correlation for NFT estimation, derived from Cross‐WLF equation, is proposed for both amorphous and semicrystalline polymers. The presented correlation takes into account the changes ...

Water Fluxes in Polymeric Membranes for Desalination via Membrane Distillation

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.