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Industria alimentare - Ottimizzazione lavorazione di HDPE / polimeri mediante compressione. Studio per la sostenibilità
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Gas chromatographic determination of volatile and semi-volatile organic compounds (VOCs and SVOCs) in polyethylene and effects of processing conditions
No full textProcessing of HDPE by compression moulding: study of the volatile substances content
No full textAccording to the most recent European directive, any organic compound with a boiling temperature lower than 250 °C at atmospheric pressure must be considered as a volatile organic compound (VOC). These substances can migrate from the matrix in which they are contained, such as food packaging. In the case of food contact materials, regulation (EC) 1935/2004 2 provides a harmonized EU legal framework and establishes the general principles of safety and inertness for all materials intended to come in contact with food. Therefore, the design of any product that will have such use must be suitable to minimize the release by the polymeric material of all the substances mentioned in the European directives.
In this study, the compression moulding process (a technology developed by SACMI Imola S.C.) was evaluated from the point of view of volatile organic compounds profile. Compression moulding offers numerous advantages, including a low extrusion temperature and low mechanical stress applied to the polymeric material.
We have implemented different VOCs extraction methods and gaschromatographic analysis for quali-quantitative studies of such compounds. In particular, GC-MS analysis were carried out on HDPE samples subjected to a thermodesorption by analyzing the substances produced. This type of analysis is necessary for the identification of different compounds in the polymer matrix.
In order to quantify the VOCs, a more accurate GC-FID determination with internal standard has been run on microwave assisted extracts.
Afterwards, compression moulding tests were conducted with two types of commercial HDPE. Two process parameters are evaluated in the tests, namely the temperature profile of the extruder zones and the cycle time (productivity).
Finally, the volatile compounds present in the molten polymer at the extruder outlet and in the caps moulded with the most robust analytical techniques (GC-FID) were analyzed.
The results show that the passage in extruder, in the condition used for subsequent compression moulding, implies a decrease in volatile compounds, and the subsequent compression molding increases this effect. Moreover, for both polyolefin matrices processed, any type of processing used does not lead to a degradation of the material, but to a reduction of volatile substances already present in the starting material (linear chains oligomers with even number of carbon atoms).
Continuous Compression Moulding (CCM) is therefore a packaging manufacturing process that does not modify the characteristics of polymeric starting materials. This process could prove to be important, even fundamental whenever the starting material shows to be subject to significative degradation
Going Beyond Counting First Authors in Author Co-citation Analysis
Full text linkThe present study examines one of the fundamental aspects of author co-citation analysis (ACA) - the way co-citation
counts are defined. Co-citation counting provides the data on which all subsequent statistical analyses and mappings
are based, and we compare ACA results based on two different types of co-citation counting - the traditional type that
only counts the first one among a cited work's authors on the one hand and a non-traditional type that takes into
account the first 5 authors of a cited work on the other hand. Results indicate that the picture produced through this non-traditional author co-citation counting contains more coherent author groups and is therefore considerably clearer. However, this picture represents fewer specialties in the research field being studied than that produced through the traditional first-author co-citation counting when the same number of top-ranked authors is selected and analyzed. Reasons for these effects are discussed
Variations on the Author
Full text link“Variations on the Author” discusses two of Eduardo Coutinho’s recent films (Um Dia na Vida, from 2010, and Últimas Conversas, posthumously released in 2015) and their contribution to the general question of documentary authorship. The director’s filmography is characterized by a consistent yet self-effacing form of authorial self-inscription: Coutinho often features as an interviewer that rather than express opinions propels discourses; an interviewer that is good at listening. This mode of self-inscription characterizes him as an author who is not expressive but who is nonetheless markedly present on the screen. In Um Dia na Vida, however, Coutinho is completely absent form the image, while Últimas Conversas, on the contrary, includes a confessional prologue that moves the director from the margins to the center of his films. This article examines the ways in which these works stand out in the filmography of a director who offers new insights into the notion of cinematic authorship
Appropriate Similarity Measures for Author Cocitation Analysis
Full text linkWe provide a number of new insights into the methodological discussion about author cocitation analysis. We first argue that the use of the Pearson correlation for measuring the similarity between authors’ cocitation profiles is not very satisfactory. We then discuss what kind of similarity measures may be used as an alternative to the Pearson correlation. We consider three similarity measures in particular. One is the well-known cosine. The other two similarity measures have not been used before in the bibliometric literature. Finally, we show by means of an example that our findings have a high practical relevance.information science;Pearson correlation;cosine;similarity measure;author cocitation analysis
Dispelling the Myths Behind First-author Citation Counts
Full text linkWe conducted a full-scale evaluative citation analysis study of scholars in the XML research field to explore just how different from each other author rankings resulting from different citation counting methods actually are, and to demonstrate the capability of emerging data and tools on the Web in supporting more realistic citation counting methods. Our results contest some common arguments for the continued
use of first-author citation counts in the evaluation of scholars, such as high correlations between author rankings by first-author citation counts and other citation
counting methods, and high costs of using more realistic citation counting methods that are not well-supported by the ISI databases. It is argued that increasingly available digital full text research papers make it possible for citation analysis studies to go beyond what the ISI databases have directly supported and to employ more
sophisticated methods
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