1,721,054 research outputs found
The regression of isothermal thermogravimetric data to evaluate degradation E-a values of polymers: A comparison with literature methods and an evaluation of lifetime prediction reliability
No full textThe thermooxidative degradation of four well known polymers, polyethylene (PE), polystyrene (PS), polycarbonate (PC) and poly(methyl methacrylate) (PMMA), was carried out in a thermogravimetric (TG) analyser, at various temperatures (in the 473-533 K range), in isothermal heating conditions. The resulting set of experimental TG data was used to determine the apparent activation energy (Ea) of degradation through two isothermal literature methods, as well as through a very simple method we set up, based on the direct regression of the experimental mass loss data, in order to verify the general applicability of our method to various polymers. The results from different methods were in good agreement. Degradation experiments in dynamic heating conditions, which were also performed, gave Ea values in good agreement with those in isothermal heating conditions for PS, PC and PMMA, while for PE a large discrepancy was observed, which was discussed and interpreted. The results suggested the general applicability of our method to all polymers, independently on their structure and degradation mechanism. A long-term (about 13 months) isothermal degradation experiment was also carried out with the same polymers at relatively low temperature (423 K). Only PE and PS evidenced appreciable mass loss in the investigated period, but the experimental data were not in agreement with those from the short-term degradations at higher temperatures, thus suggesting different degradation kinetics, and a low reliability of the lifetime predictions for polymers in service based on experiments at higher temperatures. (C) 2011 Elsevier Ltd. All rights reserved
The regression of isothermal thermogravimetric data to evaluate degradation Ea values of polymers: A comparison with literature methods and an evaluation of lifetime predictions reliability. Part II
No full textThe kinetics of the isothermal degradation in static air atmosphere of four well known polymers, polyethylene (PE), polystyrene (PS), polycarbonate (PC) and poly(methyl methacrylate) (PMMA) was studied by both a long-term (more than three years) experiment at relatively low temperature (423 K) and a set of short-term experiments at higher temperatures. The activation energy (E-a) values of degradation were determined by both the MacCallum and Wilkinson literature methods, and were compared with those obtained through a new very simple method we set up, based on the direct regression of TG mass loss data. About two years ago we published the results concerning PE and PS because their mass losses during long-term experiments were sufficiently high. The long-term degradation experiments were continued until now and in this second part we report the results concerning PC and PMMA. The degradation E-a values calculated from short-term experimental data through the three different methods were in good agreement with each other for both PC and PMMA, thus confirming the general applicability of our simple method for the determination of E-a. The experimental data at lower temperature of PC were not in agreement with those at higher temperatures, thus confirming the low reliability of the kinetic parameters (and then of lifetime predictions) at low temperature determined by experiments at higher temperatures. Partially disagreeing results were obtained for PMMA, which were discussed and interpreted. (C) 2013 Elsevier Ltd. All rights reserved.The kinetics of the isothermal degradation in static air atmosphere of four well known polymers,
polyethylene (PE), polystyrene (PS), polycarbonate (PC) and poly(methyl methacrylate) (PMMA) was
studied by both a long-term (more than three years) experiment at relatively low temperature (423 K)
and a set of short-term experiments at higher temperatures. The activation energy (Ea) values of
degradation were determined by both the MacCallum and Wilkinson literature methods, and were
compared with those obtained through a new very simple method we set up, based on the direct
regression of TG mass loss data. About two years ago we published the results concerning PE and PS
because their mass losses during long-term experiments were sufficiently high. The long-term degradation
experiments were continued until now and in this second part we report the results concerning
PC and PMMA. The degradation Ea values calculated from short-term experimental data through the
three different methods wer
GAS PERMEABILITY AND THERMAL BEHAVIOUR OF POLYPROPYLENE FILMS USED FOR FRESH-CUT POTATOES PACKAGING: A CASE STUDY
No full textThis work reports some results of an experimental study on the
permeability and thermal behaviour of commercial Polypropylene (PP) film used for fresh-cut potatoes
packaging. The permeability of PP material was tested and studied using O2, CO2 and N2 pure gases and
different mix of them, normally used for modified atmosphere packaging (MAP) in comparison to Air, in order
to understand if it will be possible to extend the shelf life of food product designed for catering field. The
temperature influence (from 5 to 40°C) on permeability data, was analyzed before and after 4, 8, 12, 15 and
20 days of food contact, pointing out the dependence between temperature and gas transmission rate
(GTR), solubility (S), diffusion coefficient (D) and time lag (tL) parameters. The activation energies of the
permeation at the tested different gases were determined.
Moreover, the thermal behaviour of packaging was studied by Differential Scanning Calorimetry (DSC) and
Thermogravimetric analysis (TG) to well understand the structural stability of the polymer used in the
experiments. Moreover, FTIR/ATR spectroscopy analysis was also performed, in order to study the eventual
influence of the food contact on the chemical characteristics of the polymer films
Design and Thermal and Spectroscopic Characterization of novel architecture’s POSS nanoparticles
No full textPolyhedral oligomeric silsesquioxanes (POSSs), with Si vertices interconnected by –O– linkages, form three-dimensional nanometer size cage structures with substituents attached to silicon atoms. These substituents may contain reactive groups, such as hydroxyl or isocyanate. A combination of a rigid inorganic nanocore with organic vertex groups makes POSS molecules useful hybrid building blocks that can be chemically incorporated in the polymer matrix by copolymerization, grafting or reactive blending, or physically mixed by solvent casting or polymer processing by using, for example, the extrusion technique [1]. The use of POSSs for making polymer composites has grown exponentially since the last few years of the 20th century. In comparison with the other most commonly used fillers, POSSs possess the advantage of being molecules. Thus, this allows us to combine their nano-sized cage structures, which have dimensions that are similar to those of most polymer segments and produce a particular and exclusive chemical composition. These characteristics linked with their hybrid (inorganic–organic) nature allow researchers to modify POSS according to particular needs or original ideas, before incorporating them into polymers [2].
Figure 1. Molecular structure of the prepared and investigated POSSs
In this context, our research group at the University of Catania, in collaboration with eminent researchers in the field, tested the stabilization of different polymers, synthetics or naturals, such as polyethersulfone (PES), ethylene propylene diene monomer (EPDM), polyethylene oxide (PEO), and chitosan by the incorporation of polyhedral oligomeric silsesquioxanes (POSS) molecules [3-6]. Represented in their most common form by the symbol T8 and having a diameter usually falling in the range of 1.5–3 nm, POSS molecules comprise a silicon and oxygen cage completed by organic groups that are covalently bonded with silicon atoms. Novel architectures of POSS with various organic groups were synthesized by using corner capping reaction in order to verify their polimeryzability in the presence of monomer. In this work, after a spectroscopic investigation aiming at verify that the obtained molecules have the structure for which they were designed, their thermal behavior in terms of resistance to thermal degradation were evaluated by means of thermogravimetric analysis (TGA). The obtained temperatures at 5% mass loss (T5%) were compared with each other and with those of the POSSs previously designed and studied by us.
Bibliography
[1] Lichtenhan, J.D., Pielichowski, K., Blanco, I. POSS-Based Polymers. Polymers 2019, 11, 1727
[2] Blanco, I. The Rediscovery of POSS: A Molecule Rather than a Filler. Polymers 2018, 10, 904.
[3] Cicala, G., Blanco, I., Latteri, A., Ognibene, G., Agatino Bottino, F., Fragalà, M.E. PES/POSS Soluble Veils as Advanced Modifiers for Multifunctional Fiber Reinforced Composites. Polymers 2017, 9, 281
[4] Zaharescu, T., Blanco, I., Bottino, F.A. Antioxidant activity assisted by modified particle surface in POSS/EPDM hybrids. Appl. Surf. Sci. 2020, 509, 144702
[5] Legnani, L.; Iannazzo, D.; Pistone, A.; Celesti, C.; Giofrè, S.; Romeo, R.; Di Pietro, A.; Visalli, G.; Fresta, M.; Bottino, P.; et al. Functionalized polyhedral oligosilsesquioxane (POSS) based composites for bone tissue engineering: Synthesis, computational and biological studies. RSC Adv. 2020, 10, 11325–11334
[6] Stipanelov Vrandečić, N., Erceg, M., Andričić, B., Blanco, I., Bottino, F.A. Characterization of poly(ethylene oxide) modified with different phenyl hepta isobutyl polyhedral oligomeric silsesquioxanes. J. Therm. Anal. Calorim. 2020, 142, 1863–187
Caratterizzazione e bioattività di materiali ibridi TiO2/PEI sintetizzato attraverso il metodo sol-gel
Full text linkSintetizzare nuovi materiali ibridi organo-inorganici è da sempre l’interesse di molti ricercatori in quanto possiedono particolari proprietà che li rendono utili per diverse applicazioni (sensori ottici e chimici, componenti bioattivi nelle protesi, materiali isolanti nei circuiti microelettronici). L’utilizzo del metodo sol-gel rappresenta una tecnica promettente per la produzione di tali materiali. Attraverso questa metodologia, sono stati sintetizzati materiali ibridi utilizzando TiO2 e polieterimmide (PEI) al 6 e 12% in peso. L’interazione tra la fase organica ed inorganica è stata studiata attraverso la Spettroscopia Infrarossa con Trasformata di Fourier (FTIR), mentre la microstruttura è stata osservata con l’uso del microscopio a scansione elettronica (SEM), il microscopio a forza atomica (AFM) e diffrazione ai raggi X (XRD). Al fine di valutare la bioattività, è stata determinata la capacità di formare idrossiapatite attraverso il saggio di Kokubo[1] ed osservata con il SEM e la spettroscopia a dispersione energetica (EDS)
- …
