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Transport of water in an epoxy network with high cross-link density was investigated at several water vapor activities by time-resolved FT-IR spectroscopy and gravimetric measurements. The analysis of the infrared spectra provided information about the molecular interactions occurring in the system. In particular, several interaction complexes were identified and their structures were proposed. An estimate was made of the concentration of the various water species present in the system, based on the knowledge of the respective molar absorptivities. An excellent agreement between the spectroscopic and gravimetric determinations of sorbed water was found throughout. The evolution of the different water species was monitored by resolving the complex profile of the water spectrum in the νOH frequency range. This information, coupled with the results of the gravimetric analysis, was used to evaluate the effect of polymer/penetrant H-bonding interactions on the diffusion process of water molecules. Transport of the different water species was found to follow a Fickian behavior characterized by an effective diffusion coefficient which increases with total water concentration.

The transport of chloroform in films of semicrystalline syndiotactic polystyrene (s-PS) in its nanoporous form (δ-form) has been investigated by gravimetric analysis and time-resolved FTIR spectroscopy. Experimental tests have been performed at 56 °C and at several vapor pressures ranging from 5 to 100 Torr. Sorption and desorption kinetics have been monitored with both techniques, and the dependence of diffusion coefficients with penetrant concentration was investigated, evidencing Fickian features typical of systems characterized by diffusivity increasing with concentration. Analysis of the vibrational spectrum of chloroform sorbed in the crystalline phase showed significant perturbations when compared to the spectrum of the isolated molecule or the molecule absorbed in amorphous s-PS. This perturbation has been attributed to host−guest molecular interactions whose strength was found to be relatively small. Conformational rearrangements of macromolecular chains in the amorphous phase were detected as a consequence of chloroform sorption. These rearrangements, which lead to an increase of the overall crystallinity degree, were quantified using the concept of critical sequence length (CSL). The kinetics of the conformational ordering process was found to parallel the sorption kinetics, and the associated increase of crystallinity was not reversible upon chloroform desorption.

The formation of foams of biodegradable poly(ε-caprolactone) (PCL) from CO2 solutions in molten PCL was investigated. This study included characterization of the CO2 diffusion and equilibrium solubility in molten PCL in contact with supercritical CO2 (scCO2). Experiments were performed at 70, 80, and 90 °C at CO2 pressures up to 25 MPa. The effective mutual diffusivity of CO2 in molten PCL was measured as a function of the CO2 pressure. The data revealed a dramatic increase in apparent effective diffusivity at elevated pressure, likely related to the formation of fluid bubbles, phase-separated from the previously homogeneous, molten PCL solution of CO2. Microcellular PCL foams were produced by starting from an equilibrium CO2−PCL solution at 70 °C over a wide range of initial pressures (from 6.9 to 32 MPa) by quenching down to foaming temperatures (from 24 to 30 °C) followed by rapid depressurization to atmospheric pressure. Foam structures were characterized by scanning electron microscopy, and cell sizes and density were determined quantitatively. The various foam structures were analyzed and interpreted in connection with the independently measured kinetics and equilibrium of CO2 sorption in PCL by considering the effects of starting pressure and foaming temperature on bubble nucleation and growth.

Solution thermodynamics and mutual diffusivity of the system carbon dioxide-molten poly(caprolactone) (PCL) have been investigated experimentally in the temperature range 70-85 °C and at pressures up to 6.5 MPa. Sorption data have been interpreted on the basis of Sanchez-Lacombe lattice theory. Sanchez-Lacombe parameters for pure PCL have been evaluated by fitting experimental pressure-volume-temperature data obtained by using a high-pressure dilatometer, while parameters for carbon dioxide have been taken from the literature. Information on the free volume of the mixture, as gathered from the solution thermodynamics analysis, has been used in the classical free-volume theory proposed by Duda and Vrentas to fit mutual diffusivity data, obtained from sorption kinetics experiments.

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Fatigue crack growth experiments on different carbon black–filled rubber compounds have been carried out to evaluate the influence of pure-shear and strip tensile testing mode by using sine and pulse as waveforms. In a previous set of experimental investigations regarding the influence of both waveform and tested material, it was found that the mode I of crack opening sometimes propagates too quickly to be properly monitored in tests involving strip-tensile specimens. An alternative test methodology based on pure-shear test mode has been investigated, optimizing both the shape of the specimen and the test equipment. Data obtained from the different compound formulations were consistent with the theoretical background and resulted in similar ranking of compound crack growth resistance for the two testing modes; in addition, pure-shear mode showed a higher sensitivity to formula variations.

Fatigue crack growth experiments on carbon black-filled rubber compounds have been carried out to evaluate the influence of testing conditions over different compound formulations. Investigations on the influence of waveform, data acquisition, and compound formulation have been performed on strip-tensile specimens reproducing the model of crack opening. The response of three different compound formulations (based on either natural rubber, butadiene rubber, or styrene-butadiene rubber) to the application of two different waveforms, pulse and sine, has been analyzed, showing significant differences in fatigue behavior and ranking of the various compounds. Compared to the sinusoidal waveform, the use of a pulse waveform provided an improved correlation of the tearing energy with the crack propagation speed. This difference was particularly evident in the case of natural rubber and butadiene rubber, while it resulted negligible in the case of styrene-butadiene rubber. Such a different behavior could be attributed to differences in macromolecular chains orientation. Fine-tuning of video acquisition parameters provided an accurate observation of the crack growth process, as confirmed by the low standard deviation of the estimated tearing energy and crack growth rate