Felice De Santis

Melt compounding of poly (Lactic Acid) and talc: assessment of material behavior during processing and resulting crystallization

The influence of talc incorporation by melt compounding on a commercial grade of poly (lactic acid) (PLA), and the choice of the optimal compounding conditions were investigated. Two types of talc, having micrometric and submicrometric distribution, were adopted. Since the compounding itself has a dramatic influence on the properties of PLA, a study was carried out aimed at assessing the effect of processing on this resin and choosing the most suitable processing conditions. It was found that the incorporation of talc increases the viscosity during the compounding and helps the stability of the viscosity during the mixing. Furthermore, the talc, acting as a nucleating agent, enhances crystallization kinetics, so that crystallization half time can be reduced by one order of magnitude with respect to the pure PLA processed in the same way.

The influence of dissolution conditions on the drug ADME phenomena.

In this work, a review of the apparatuses available to mimic what happens to a drug (or to foodstuffs) once ingested is presented. Similarly, a brief review of the models proposed to simulate the fate of a drug administered to a living body is reported. Then, the release kinetics of extended release of diclofenac from a commercial enteric-coated tablet was determined both in a conventional dissolution tester (USP Apparatus 2, Method A) as well as in an apparatus modified to reproduce a given pH evolution, closer to the real one than the one suggested by USP. The two experimental release profiles were reported and discussed; therefore, they were adopted as input functions for a previously proposed pharmacokinetic model. The obtained evolutions with time of plasma concentration were presented and used to assess the effectiveness of the commercial pharmaceutical products. The importance of a correct in vitro simulation for the design of pharmaceutical dosage systems was thus emphasized.

Nucleation density and growth rate of polypropylene measured by calorimetric experiments

A novel experimental protocol was adopted, based on calorimetric measurements, but varying each time the minimum temperature before the isothermal crystallization step. This method allows to measure nucleation density and growth rate for commercial semicrystalline polymers, for which the nucleation phenomenon is essentially heterogeneous. The protocol was applied to a commercial grade isotactic polypropylene, well characterized in the literature. Crystallization kinetics was evaluated using the Avrami model, through nucleation and growth, describing all experimental results. Morphological characterizations were modeled using the classical Lauritzen–Hoffman theory. Detailed comprehensive description of the crystallization kinetics of i-PP is provided, predicting nucleation and growth with the tailored thermal history.

Crystallization during fast cooling experiments, a novel apparatus for real time monitoring

Although many efforts have been spent on polymer crystallization kinetics, reliable results, if typical industrial processing conditions are applied, have been attained only in few cases. The main problem is related to the availability of data obtained under fast cooling conditions. Only those data can indeed discriminate between available models, or lead to the development of new ones. A new apparatus, able to provide real time crystallization data under high cooling rates, has been designed, built and tested. Description of apparatus and methods are discussed together with preliminary data obtained.

Polymer Crystallization Under High Cooling Rate and Pressure: A Step Towards Polymer Processing Conditions

Even if many efforts have been spent on the explanation of the mechanisms involved during the polymer crystallization in typical industrial processing conditions, they are still only partially understood. Up to now, due to the remarkable experimental difficulties, in literature only few systematic works have been focused on the effect of high cooling rates and/or solidification pressure on the mechanical and physical properties of the semi-crystalline polymers. In this work, we present two experimental apparatuses, designed and assembled with the aim of obtaining polymer samples under controlled temperature and pressure histories. High cooling rates and pressure, comparable with those experienced by the polymer during industrial processes, were attained in order to produce polymer samples with different morphologies. Exemplar results obtained with Syndiotactic Polystyrene (sPS) show that high cooling rates as well as external pressure are important factor for inducing changes in crystalline polymeric structures.

Optical Properties of Polypropylene upon Recycling

In the last few years there has been an increasing interest in the possibility of recycling polymeric materials, using physical recycling. However, is it well known that polymers experience a depletion of all the properties upon recycling. These effects have been widely characterized in the literature for what concerns the mechanical or rheological properties. The changes of optical properties after recycling have been much less studied, even if, especially in food packaging, optical characteristics (above all the opacity) are of extreme importance, and thus it is quite significant to assess the effect of recycling on these properties. In this work, the influence of recycling steps on the opacity of films of a commercial grade of isotactic polypropylene (i-PP) was studied. The material was extruded several times to mimic the effect of recycling procedures. After extrusion, films were obtained by cooling samples of material at different cooling rates. The opacity of the obtained films was then measured and related to their crystallinity and morphology. It was found that opacity generally increases on increasing the amount of α phase and for the same amount of α phase on increasing the size of the spherulites.

PLA Melt Stabilization by High-Surface-Area Graphite and Carbon Black

Small amounts of carbon nanofillers, specifically high-surface-area graphite (HSAG) and more effectively carbon black (CB), are able to solve the well-known problem of degradation (molecular weight reduction) during melt processing, for the most relevant biodegradable polymer, namely poly(lactic acid), PLA. This behavior is shown by rheological measurements (melt viscosity during extrusion experiments and time sweep-complex viscosity) combined with gel permeation chromatography (GPC) experiments. PLA’s molecular weight, which is heavily reduced during melt extrusion of the neat polymer, can remain essentially unaltered by simple compounding with only 0.1 wt % of CB. At temperatures close to polymer melting by compounding with graphitic fillers, the observed stabilization of PLA melt could be rationalized by scavenging traces of water, which reduces hydrolysis of polyester bonds. Thermogravimetric analyses (TGA) indicate that the same carbon fillers, on the contrary, slightly destabilize PLA toward decomposition reactions, leading to the loss of volatile byproducts, which occur at temperatures higher than 300 °C, i.e., far from melt processing conditions.

Physical changes of poly(lactic acid) induced by water sorption

One of the main limits to the use of Poly(Lactic Acid), PLA, is its extreme sensitivity to moisture. The objective of this work is to study the physical changes induced by water sorption on a commercial PLA grade. To this goal, samples of PLA having thickness of about 400 µm, obtained by compression molding, were put into contact with water at 58 °C. The samples were partially immersed in water in a closed and mixed vessel, so that the lower part was in contact with liquid water whereas the upper part was in contact with air with a relative humidity of 100%. The opacity of the samples, their crystallinity degree, their density and molecular weight were monitored during time. It was found that the samples became white and opaque after a few hours, crystallinity reached an equilibrium value after about 48 h. Density was found to decrease with time, thus suggesting that the whitening was due to crazing. Surprisingly, it was found that the mentioned phenomena are more evident for the samples immersed in water...

PLA-Based Nanobiocomposites with Modulated Biodegradation Rate

The disposal of polymeric waste is increasingly becoming an issue of international concern. The use of biodegradable polymers is a possible strategy to face most of the problems related to the disposal of the durable (non-biodegradable) polymers. Among biodegradable polymers, polylactic acid (PLA), obtained from renewable sources, is a very attractive one, due to its relatively good processability, biocompatibility, interesting physical properties. Hydrolysis is the major depolymerization mechanism and the rate-controlling step of PLA biodegradation in compost. The propensity to degradation in the presence of water significantly limits specific industrial applications such as automotive, biomedical, electronic and electrical appliances, agriculture. Therefore the control of biodegradation rate is somewhat even more important than the characteristic of biodegradability itself. In this scenario, it is critical to find additives able to modulate the biodegradation rate of biodegradable polymers, in relationship to the expected lifetime. Since the kinetics of hydrolysis strongly depend on the pH of the hydrolyzing medium, in this work some fillers able to control the pH of water when it diffuses inside the polymer were added to PLA. In particular, fumaric acid, a bio- and eco- friendly additive, and magnesium hydroxide, a common antiacid, were used. These fillers were added to the material using a melt-compounding technique, suitable for industrial application. The results obtained are encouraging toward the possibility of effectively controlling the degradation rate.

Effect of processing conditions on the cell morphology distribution in foamed injection molded PLA samples

Foam injection molding uses physical blowing agents under high pressure and temperature to produce structural foams having a cellular core and a compact solid skin. This technology is particularly interesting for biodegradable polymers, which often present a very narrow processing window, with the suitable processing temperatures close to the degradation conditions. The addition of a supercritical gas can lead to the reduction of both the viscosity and the glass transition temperature of the polymer melt, which therefore can be injection molded adopting lower temperatures and pressures. In this work, the effect of different processing parameters on foam morphology of Poly(lactic) Acid, PLA, was studied. In particular, two commercial grades of PLA having different rheological properties were adopted to obtain foamed parts by injection molding process with nitrogen as a physical blowing agent. For both PLA grades, the effect of mold temperature on the crystallinity and the resulting cell morphology was asse...