Curing Kinetics of Bioderived Furan-Based Epoxy Resins: Study on the Effect of the Epoxy Monomer/Hardener Ratio.

The potential of furan-based epoxy thermosets as a greener alternative to diglycidyl ether of Bisphenol A (DGEBA)-based resins has been demonstrated in recent literature. Therefore, a deep investigation of the curing behaviour of these systems may allow their use for industrial applications. In this work, the curing mechanism of 2,5-bis[(oxiran-2-ylmethoxy)methyl]furan (BOMF) with methyl nadic anhydride (MNA) in the presence of 2-methylimidazole as a catalyst is analyzed. In particular, three systems characterized by different epoxy/anhydride molar ratios are investigated. The curing kinetics are studied through differential scanning calorimetry, both in isothermal and non-isothermal modes. The total heat of reaction of the epoxy resin as well as its activation energy are estimated by the non-isothermal measurements, while the fitting of isothermal data with Kamal's autocatalytic model provides the kinetic parameters. The results are discussed as a function of the resin composition. The global activation energy for the curing process of BOMF/MNA resins is in the range 72-79 kJ/mol, depending on both the model used and the sample composition; higher values are experienced by the system with balanced stoichiometry. By the fitting of the isothermal analysis, it emerged that the order of reaction is not only dependent on the temperature, but also on the composition, even though the values range between 0.31 and 1.24.

Survey on Adsorption of Low Molecular Weight Compounds in Cu-BTC Metal-Organic Framework: Experimental Results and Thermodynamic Modeling.

This contribution aims at providing a critical overview of experimental results for the sorption of low molecular weight compounds in the Cu-BTC Metal-Organic Framework (MOF) and of their interpretation using available and new, specifically developed, theoretical approaches. First, a literature review of experimental results for the sorption of gases and vapors is presented, with particular focus on the results obtained from vibrational spectroscopy techniques. Then, an overview of theoretical models available in the literature is presented starting from semiempirical theoretical approaches suitable to interpret the adsorption thermodynamics of gases and vapors in Cu-BTC. A more detailed description is provided of a recently proposed Lattice Fluid approach, the Rigid Adsorbent Lattice Fluid (RALF) model. In addition, to deal with the cases where specific self- and cross-interactions (e.g., H-bonding, Lewis acid/Lewis base interactions) play a role, a modification of the RALF model, i.e., the RALFHB model, is introduced here for the first time. An extension of both RALF and RALFHB is also presented to cope with the cases in which the heterogeneity of the rigid adsorbent displaying a different kind of adsorbent cages is of relevance, as it occurs for the adsorption of some low molecular weight substances in Cu-BTC MOF.

Chemical Vapour Deposition Graphene-PMMA Nanolaminates for Flexible Gas Barrier.

Successful ways of fully exploiting the excellent structural and multifunctional performance of graphene and related materials are of great scientific and technological interest. New opportunities are provided by the fabrication of a novel class of nanocomposites with a nanolaminate architecture. In this work, by using the iterative lift-off/float-on process combined with wet depositions, we incorporated cm-size graphene monolayers produced via Chemical Vapour Deposition into a poly (methyl methacrylate) (PMMA) matrix with a controlled, alternate-layered structure. The produced nanolaminate shows a significant improvement in mechanical properties, with enhanced stiffness, strength and toughness, with the addition of only 0.06 vol% of graphene. Furthermore, oxygen and carbon dioxide permeability measurements performed at different relative humidity levels, reveal that the addition of graphene leads to significant reduction of permeability, compared to neat PMMA. Overall, we demonstrate that the produced graphene-PMMA nanolaminate surpasses, in terms of gas barrier properties, the traditional discontinuous graphene-particle composites with a similar filler content. Moreover, we found that the gas permeability through the nanocomposites departs from a monotonic decrease as a function of relative humidity, which is instead evident in the case of the pure PMMA nanolaminate. This work suggests the possible use of Chemical Vapour Deposition graphene-polymer nanolaminates as a flexible gas barrier, thus enlarging the spectrum of applications for this novel material.

Role of Air Bubble Inclusion on Polyurethane Reaction Kinetics.

In this study, we investigated the influence of mixing conditions on the foaming process of water blown polyurethane (PU) foams obtained at different mixing speeds (50, 500, 1000 and 2000 rpm). In particular, the morphological evolution during the foaming process, in terms of the bubble size and bubble density, was studied via optical observations, while the effects on the reaction kinetics were monitored using in situ FTIR spectroscopy. At the slow mixing speed (50 rpm), no air bubbles were included and the early foaming process was characterized by the formation of new bubbles (CO2 nucleation), provided by the blowing reaction. Later on, it was observed that the coalescence affected the overall foaming process, caused by the gelling reaction, which was inhibited by the indigent mixing conditions and could not withstand the bubbles expansion. As a result, a PU foam with a coarse cellular structure and an average bubble size of 173 µm was obtained. In this case, the bubbles degeneration rate, dN/dt, was -3095 bubble·cm-3·s-1. On the contrary, at 500 rpm, air bubbles were included into the PU reaction system (aeration) and no formation of new bubbles was observed during the foaming process. After this, the air bubbles underwent growth caused by diffusion of the CO2 provided by the blowing reaction. As the gelling reaction was not strongly depleted as in the case at 50 rpm, the coalescence less affected the bubble growth (dN/dt = -2654 bubble·cm-3·s-1), leading to a PU foam with an average bubble size of 94 µm. For the foams obtained at 1000 and 2000 rpm, the bubble degeneration was first affected by coalescence and then by Ostwald ripening, and a finer cellular structure was observed (with average bubble sizes of 62 µm and 63 µm for 1000 rpm and 2000 rpm, respectively). During the first foaming stage, the coalescence was less predominant in the bubble growth (with dN/dt values of -1838 bubble·cm-3·s-1 and -1601 bubble·cm-3·s-1, respectively) compared to 50 rpm and 500 rpm. This occurrence was ascribed to the more balanced process between the bubble expansion and the PU polymerization caused by the more suitable mixing conditions. During the late foaming stage, the Ostwald ripening was only responsible for the further bubble degeneration (with dN/dt values of -89 bubble·cm-3·s-1 and -69 bubble·cm-3·s-1, respectively).