F. De Santis

Characterization of the Polycaprolactone Melt Crystallization: Complementary Optical Microscopy, DSC, and AFM Studies

The first stages of the crystallization of polycaprolactone (PCL) were studied using several techniques. The crystallization exotherms measured by differential scanning calorimetry (DSC) were analyzed and compared with results obtained by polarized optical microscopy (POM), rheology, and atomic force microscope (AFM). The experimental results suggest a strong influence of the observation scale. In particular, the AFM, even if limited on time scale, appears to be the most sensitive technique to detect the first stages of crystallization. On the contrary, at least in the case analysed in this work, rheology appears to be the least sensitive technique. DSC and POM provide closer results. This suggests that the definition of induction time in the polymer crystallization is a vague concept that, in any case, requires the definition of the technique used for its characterization.

Modelling morphology evolution during solidification of IPP in processing conditions

During polymer processing, crystallization takes place during or soon after flow. In most of cases, the flow field dramatically influences both the crystallization kinetics and the crystal morphology. On their turn, crystallinity and morphology affect product properties. Consequently, in the last decade, researchers tried to identify the main parameters determining crystallinity and morphology evolution during solidification In processing conditions. In this work, we present an approach to model flow-induced crystallization with the aim of predicting the morphology after processing. The approach is based on: interpretation of the FIC as the effect of molecular stretch on the thermodynamic crystallization temperature; modeling the molecular stretch evolution by means of a model simple and easy to be implemented in polymer processing simulation codes; identification of the effect of flow on nucleation density and spherulites growth rate by means of simple experiments; determination of the condition under wh...

Optical in situ characterization of isotactic polypropylene crystallization using an LED array in avalanche-photoreceiver mode

An experiment that is useful in investigating crystallinity evolution during fast cooling, comparable with cooling rates attained in industrial processes, is extremely attractive. In this paper, a setup able to quench thin polymer films while recording the sample thermal history and light intensity of a laser beam transmitted by the sample is described. A particular feature of the optical-measurement setup is the use of the light-emitting diode (LED) array as a receiver, enabling the monitoring of changes in the polarization properties as changes in light scattering of the polymer during crystallization. Furthermore, it could be demonstrated that the LED array can be used as a linear optical detector with photocurrent gain values exceeding ten when polarized slightly below reverse-bias breakdown.

Spherulitic nucleation and growth rates in a sheared polypropylene melt

In common polymer processing operations such as injection molding, film blowing, and fiber spinning, the molten polymer is subjected to intense shear and/or elongational flow fields and crystallizes during or after the application of flow. The semicrystalline morphology that develops in the final product is typically very different from what is observed during quiescent crystallization of the same polymer, and the properties change accordingly. The possibility of controlling the final morphology and the resulting mechanical and functional properties of semicrystalline polymers based on the study of polymer melt crystallization stimulated by flow is highly intriguing. This work starts from the experimental evidence that there exists qualitatively three regimes of crystallization under shear: (a) very low shear rates, in which there is no effect on kinetics; (b) higher shear rates, in which orientational effects enhance just the nucleation and growth rates, and spherulitic crystallization is observed; and (...

Modeling morphology evolution during injection molding of thermoplastic polymers

The effect of temperature, pressure and flow on relaxation time (or spectrum), crystallization time, nucleation density and rate, spherulite growth rate, the interrelation among these quantities and the distributions of deformation rate and cooling time during the process all together determine the morphology distribution in the final object. A simple model linking all these quantities was developed to describe morphology evolution during polymer processing. The effect of flow on nucleation density and growth rate of an isotactic polypropylene (iPP) is described on the basis of a molecular stretch parameter and the stretch evolution is described by a simple nonlinear Maxwell model, whose relaxation time, in its turn, is determined by the molecular stretch and, obviously, temperature pressure and crystallinity [1]. The model is applied to the description of morphology evolution during the injection molding process of a very accurately characterized iPP as far as rheology, quiescent crystallization and effe...

Fibrillar morphology formation in a sheared polypropylene melt

In common polymer processing operations such as injection molding, film blowing, and fiber spinning, the molten polymer is subjected to shear and/or elongational flow fields that are often so intense to induce the formation of highly oriented crystalline structures, namely a fibrillar morphology. This peculiar morphology highly affects the resulting mechanical and functional properties of semicrystalline polymers and thus the study of the conditions under which it forms are of high scientific and industrial interest. In this work, crystallization during step shear experiments at 140°C were carried out in a plate-plate geometry by means of a Linkam shearing cell. The evolution of crystalline structures was observed during the tests at a fixed radial position. After the shear step the samples were allowed to fully crystallize at the test temperature and then were cooled down to room temperature. The samples were then analyzed by optical microscopy and the radial position at which a transition between spheru...

In-situ characterization of polymer crystallization using a low-cost light emitting diode array as optical receiver with photogain

An experiment useful to investigate crystallinity evolution during fast cooling, comparable with cooling rates attained in industrial processes, is extremely attractive. In this work, a setup able to quench thin polymer films while recording the sample thermal history and light intensity of a laser beam transmitted by the sample is described. A particular feature of the optical measurement setup is the use of a LED array as receiver enabling to monitor as well changes in the polarization properties as changes in light scattering of the polymer during crystallization. Furthermore it could be demonstrated that the LED array can be used as a linear optical detector with photocurrent gain values exceeding 10 when polarized slightly below reverse bias breakdown.

Genomic signature: the mathematical functions associated with it

Extensive data analyses support the proposal that each living organism possess a genomic signature consisting of oligonucleotide relative abundance values calculated from genomic sequences. The Chaos Game Representation shows that the core features characterizing the whole genome are preserved in short subsequences of it, validating the idea of a genomic signature. This paper present an alternative approach to the genomic signature detection. Although ensuring the same information retrieved from classical methods, it presents the advantage to be conceptually very simple and computationally less expensive.Extensive data analyses support the proposal that each living organism possess a genomic signature consisting of oligonucleotide relative abundance values calculated from genomic sequences. The Chaos Game Representation shows that the core features characterizing the whole genome are preserved in short subsequences of it, validating the idea of a genomic signature. This paper present an alternative approach to the genomic signature detection. Although ensuring the same information retrieved from classical methods, it presents the advantage to be conceptually very simple and computationally less expensive.

On some computational problems related to data base coding

A very frequent problem arising in the retrieval of information from data bases is to search for elements matching a given one subject to well defined constraints. Efficiency considerations about the searching algorithms obviously suggest to arrange elements in such a way that the processing time is minimum. Nevertheless, investigations about ordering relations to be established on the key coding set for file access appear much more interesting and results prone. In this paper we show that some interesting properties hold for ordering relations on the key codings; moreover, such properties constitute the starting point to design efficient algorithms for the above mentioned search problems. * Final manuscript not received in time for inclusion in the proceedings.

Factor Analysis and Clustering

Two problems related to the factor analysis model are discussed in the sphere of pattern recognition applications: the determination of the communality values based on the minimization of the trace of a reduced correlation matrix and the relationship between factor analysis and Fisher discriminant analysis.