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Evaluation of a bio-coating as a solution to improve barrier, friction and optical properties of plastic films
Full text linkThe present research dealt with evaluating barrier, friction and optical properties of three different plastic films after deposition of a gelatin-based bio-coating. The composite films showed improved barrier properties against oxygen and UV radiation. The oxygen transmission rate decreased in the order of 73% for oriented polypropylene (OPP), 56% for low-density polyethylene (LDPE) and 40% for polyethylene terephthalate (PET). The increased UV barrier characteristics ranged from 20% for OPP to 12% for both LDPE and PET. Static and kinetic coefficients of friction significantly decreased both in the film-to-film and in the film-to-metal tests, leading to a desirable value for many applications. However, bio-coated films showed lower optical performances in terms of transparency and haze. Transparency decreased mainly for LDPE (36%), whereas the haze index increased especially for OPP (85%). Non-significant differences were observed as far as the water vapour permeability was concerned, except for a slight reduction for PET (from 15.78 to 13.53 cm3/m2/day at 23°C and 90% of relative humidity), suggesting that non-meaningful effects arose from the addition of a hydrophobic component in the original formulation. Finally, the solubility of the coating in water was around 25% for all the three plastic substrates. The obtained data suggest that the lipid protein coating tested in this study, in spite of its great potential for enhancing some characteristics of plastic packaging films, still exhibits negative aspects which necessitate further improvement
DEVELOPMENT OF HIGH PERFORMANCE BIOPOLYMER COATINGS FOR FOOD PACKAGING APPLICATIONS
Full text linkThis PhD project aims to the optimization of the food packaging materials currently available on the market. The purpose is to develop high performance coatings able to improve the original characteristics of the plastic substrate beneath, as a consequence of the coating deposition. In particular, to fulfil the increasing request for replacing synthetic polymers already used in the nowadays packaging applications as well as to reduce the overall amount of plastics, biomacromolecules, possibly combined with inorganic compounds, will be used to generate a new class of “bio-nanocomposite-hybrid-coatings”. This will lead to a “greener” packaging structure with the same overall performances of the conventional ones.
Some films properties will be considered, in particular the oxygen barrier performances at high relative humidity values, the surface properties and the optical properties.
The overall project has been divided in three parts. In the first part, selected bio-macromolecules have been used as individual coatings onto polyethylene terephthalate (PET) and polylactid acid (PLA) films and the changes induced by the coating application were investigated by different techniques. Rising from the contact angle investigation, a new potential antifog coating has been disclosed, while the barrier analysis allowed highlighting the great potential of pullulan as oxygen barrier coating even at high relative humidity values. A comparison with some commercial synthetic coatings has also been performed.
Ensuing from the obtained results, the second part of the project focused on the coating barrier performance, with special focus on the nanotechnology approach adopted. Specifically, both a bottom-up and a top-down approach were used. With regards to the former, a metal alkoxides was properly treated and combined with a biopolymer (pullulan) to design a final bio-nanostructure to be applied on PET, and the barrier performance was analyzed; concerning the latter, an inorganic clay was exfoliated through an ultrasonication process and mixed with pullulan; the Design of Experiment technique was then used to optimize the formulation in terms of permeability coefficient (P’O2) at the following condition: 23°C and 70% of relative humidity. The best coating formulation allowed decreasing P’O2 of ~84% with respect to the bare substrate (PET), and of ~77% with respect to the film composed by PET coated with pure pullulan (i.e without clays). In addition, microscopy analyses revealed some features of these bionanocomposites and supported the indication about a good exfoliation process.
The third and last part of the PhD project, that is still an ongoing project, concerns the simultaneous combination of the aforementioned approaches (i.e. bottom-up and top-down). In principle, this would allow exploiting benefits arising from each individual approach, as well as exploiting any potential synergism
Proprietà diffusionali, ottiche e meccaniche di tre Differenti films plastici laccati con un coating edibile a base lipo-proteica
No full textBiobased coatings as a solution to improve the overall performances of plastic films
No full textThe present research dealt with evaluating barrier, friction and optical properties of three different plastic films after deposition of a gelatin-based bio-coating. The composite films showed improved barrier properties against oxygen and UV radiation. Static and kinetic coefficients of friction were significantly decreased both in the film-to-film and in the film-to-metal tests, leading to a desirable value for many applications. However, bio-coated films showed lower optical performances in terms of transparency and haze. Not significant differences were observed as far as the water vapour permeability is concerned. The obtained data suggest that the lipid-protein coating tested in this study, in spite of its great potential for enhancing some characteristics of plastic packaging films, still exhibits negative aspects which necessitate further improvemen
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
Lacche da macromolecole naturali, ad effetto barriera ai gas, modulabili in situ, e relativi metodi di preparazione
No full textLa presente invenzione si riferisce a lacche essenzialmente da macromolecole di origine naturale, aventi effetto barriera ai gas, modulabile in situ, destinate in particolare per il rivestimento di substrati plastici, in specie films e contenitori, per applicazioni che riguardano vari settori, in particolare quello dell’imballaggio alimentare e quello medicale. Più in particolare, il trovato concerne matrici naturali (gelatina, chitosano, chitina, pectina, glutine, caseina, zeina, proteine del siero del latte, carragenani, gomma di guar, gomma xantano, alginati, amido, cellulosa nelle sue varie forme) che possono essere associate a componenti inorganiche (alcossidi metallici) e polimeri di sintesi (polivinil alcool, polivinil acetato), per dare origine, attraverso un processo ben definito e controllato, a strutture ibride sotto forma di coatings trasparenti, caratterizzate dall’elevata capacità barriera nei confronti dei gas (ossigeno in particolare) ed unica adesione del coating medesimo al substrato plastico
Effects of different sealing conditions on the seal strength of polypropylene films coated with a bio-based thin layer
Full text linkThis paper presents the results of an investigation through the design of experiment technique regarding the influence of temperature, dwell time and bar pressure on the heat seal strength of oriented polypropylene films coated with a gelatin-based thin layer. This chemometric approach allowed achieving a thorough understanding of the effect of each independent factor on the two different responses (maximum force and strain energy) considered in this work as a measure of the strength necessary to break the bond across the sealed interface. Surprisingly, the factor affecting both responses the most was the bar pressure rather than the sealing temperature. Moreover, whereas the bar pressure negatively affected the seal strength of coated polypropylene films, the sealing temperature had a positive effect. Dwell time did not have any significant influence as a main factor, while influencing negatively the seal strength as an interaction term (i.e. time × pressure), together with the further interaction temperature × pressure. The mathematical models obtained for the two responses provided different results in terms of fitting capability (R2) and prediction ability (Q2). In particular, for the maximum force response, R2 and Q2 were equal to 0.571 and 0.405, respectively, whereas the model supporting the strain energy response gave R2 = 0.932 and Q2 = 0.937, highlighting that for quantifying the seal strength, the energy necessary to break a seal is a better measure than the maximum force. The highest seal strength values obtained during this work were of 0.6615 N and 19.6 N·mm for maximum force and strain energy, respectively
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
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