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Designing bioactive materials, with controlled metal ion release, exerting a significant biological action and associated to low toxicity for humans, is nowadays one of the most important challenges for our community. The most looked-for nanoantimicrobials are capable of releasing metal species with defined kinetic profiles, either by slowing down or inhibiting bacterial growth and pathogenic microorganism diffusion. In this study, laser ablation synthesis in solution (LASiS) has been used to produce bioactive Ag-based nanocolloids, in isopropyl alcohol, which can be used as water-insoluble nano-reservoirs in composite materials like poly(3-hydroxybutyrate-co-3-hydroxyvalerate). Infrared spectroscopy was used to evaluate the chemical state of pristine polymer and final composite material, thus providing useful information about synthesis processes, as well as storage and processing conditions. Transmission electron microscopy was exploited to study the morphology of nano-colloids, along with UV-Vis for bulk chemical characterization, highlighting the presence of spheroidal particles with average diameter around 12 nm. Electro-thermal atomic absorption spectroscopy was used to investigate metal ion release from Ag-modified products, showing a maximum release around 60 ppb, which ensures an efficient antimicrobial activity, being much lower than what recommended by health institutions. Analytical spectroscopy results were matched with bioactivity tests carried out on target microorganisms of food spoilage.

A mathematical model able to describe the release kinetics of antimicrobial agents from crosslinked polyvinylalcohol (PVOH) into water is presented. The model was developed by taking into account the diffusion of water molecules into the polymeric film, the counter-diffusion of the incorporated antimicrobial agent from the film into water, and the polymeric matrix swelling kinetic. To validate the model the water sorption kinetics as well as the release kinetics of three antimicrobial agents (i.e., lysozyme, nisin and sodium benzoate, all approved to be used in contact with food) were determined at ambient temperature (25 degrees C). The three investigated active agents were entrapped in four films of PVOH with a different degree of crosslink. The model was successfully used to fit all the above sets of data, corroborating the validity of the hypothesis made to derive it.

Metallized polymeric films are amongst the most favoured candidates for replacing aluminum foil-based multilayer films. The main advantages in using the former instead of the latter are: weight saving of about 40%; much less aluminum (320 time less in weight); improved recyclability; and the possibility of optimizing package barrier properties. It is generally assumed that metallization decreases the permeability of the polymeric substrate by reducing the total area available for permeation, even though the validity of such a hypothesis has never been proved experimentally. In the present paper an attempt has been made to elucidate the role of metal coating in reducing the permeation flux of polyolefine films. For this purpose, permeability tests were performed using oxygen, nitrogen and carbon dioxide at temperatures of 20–40°C. Permeation tests have been performed on two different metallized films, on their substrates alone and on two laminates. From the analysis of the experimental results, it has been concluded that, contrary to what generally thought, gas molecules can permeate through the metallized films investigated due to both the permeable porous structure of the deposited aluminum layer and the presence of pin-holes uniformly dispersed on the metallized film surface. Copyright © 1999 John Wiley & Sons, Ltd.

Differential scanning calorimetry (DSC) analysis has been performed on modified and commericial amorphous samples of poly(ethylene terephthalate) (PET) crystallized by high pressure carbon dioxide (CO2). Two endothermic peaks are present in the DSC scans of all the carbon dioxide-treated samples. A qualitatively analogous behavior has been detected in the case of amorphous samples heat treated at temperatures slightly exceeding the glass transition temperature of virgin material. Wide angle X-ray scattering analysis has confirmed the structural analogies between samples CO2 crystallized at 50°C and thermally crystallized slightly above Tg. A differential scanning calorimeter capable of working at high pressure of CO2 has been adopted in order to examine the effect of carbon dioxide on the crystallization temperature range.

Sorption and transport of oxygen in dry and water saturated Kapton® polyimide films of different thickness were investigated at 25°C with pure oxygen using: (i) a manometric permeation apparatus (gasmembranegas configuration), (ii) a high pressure gas sorption equipment, and (iii) an electrochemical technique based on the oxygen Clark electrode (liquid-membrane-liquid configuration), respectively. A sharp increase of permeability, solubility, and diffusivety coefficient as thickness increased in the range 13–50 μm was observed for the oxygen transport through both dry and water-saturated Kapton. The variation of the oxygen parameters in the range of thicknesses investigated were small in the case of dry polyimide compared to the case of the water-saturated polymer. An interpretation is presented in which the oxygen transport parameters in both dry and water-saturated conditions are analyzed in terms of ‘dual-sorption—dual-mobility’ model and related to the different polymer morphologies. such as crystallinity level, crystallinity orientation and excess free volume content, characterizing samples of different thickness.

The sorption kinetics and equilibrium isotherms of water, methylene chloride, n-heptane and methylene chloride/n-heptane mixtures in glassy amorphous poly(aryl-ether-ether-ketone) (PEEK) have been investigated. Ideal Fickian diffusion, anomalous non-ideal Fickian diffusion, "Case II" sorption mechanism, and diffusion con trolled swelling were observed depending on temperature, solvent type, and external sol vent activity. Gas-chromatographic analysis performed on PEEK samples contacted with methylene chloride/ n-heptane mixtures indicated that the presence of methylene chloride enhances n-heptane mobility and equilibrium sorbed amount.

Sorptions of methylene chloride and methylene chloride/n-heptane liquid solutions in poly(aryl-ether-ether-ketone) (PEEK) are analysed and interpreted assuming multiple transport mechanisms. The presence of the highly interacting methylene chloride is responsible for anomalous sorption behaviours. PEEK films immersed in methylene chloride poor n-heptane solutions sorb by non-ideal Fickian diffusion, while limiting Case II and diffusion controlled swelling accompany equilibration in progressively richer methylene chloride solutions. The optical microscopy observation of cryogenically fractured samples conditioned in pure liquid methylene chloride at 5, 20 and 36 ° C for different times, revealed the presence of a sharp moving front. Differential scanning calorimetry (DSC) indicates that the glass transition temperature of the penetrated shells was always lower than the treatment temperature. The high levels of solvent swelling and plasticization were probably responsible for the crystallinity detected in DSC thermograms and wide angle X-ray scattering (WAXS) diffractograms of the solvent treated and initially amorphous samples. The differences of WAXS diffractograms of samples crystallized by immersion in methylene chloride at 5 and 36 ° C for various times and by thermal treatment are discussed. Increasing levels of crystallinity were induced in the samples equilibrated in progressively richer methylene chloride solutions.

In this paper a mathematical model aimed to predict the oxygen permeability coefficient of Nylon film as function of the water activity at the upstream and downstream side of the film is presented. The solubilization and diffusion process of oxygen were separately described. The Henry’s law was used to model the oxygen solubilization process, while the oxygen diffusion process was described by means of the First Fick’s Law with a diffusion coefficient depending on local water concentration. To validate the model, oxygen permeability tests were conducted at 25 °C. The fitting and predictive ability of the proposed model was successfully tested by fitting and predicting the oxygen permeability coefficient. The obtained results point out the need for a more accurate analysis of the oxygen and water transport phenomena in the case of water sensitive packaging films such as Nylon.

Water transport properties of a degradable polyamide to be used for food packaging applications have been analyzed. The polymer under investigation, poly((4,9)-dioxa-1,12-dodecamethylenesebacamide) (sample A), can be envisaged as modified nylon 12/10 (sample B) in which two of the C–C linkages of the backbone have been replaced with two ether linkages. The introduction of ether linkages should enhance the degradability of the polymeric material compared with nylon 12/10, but, in turn, is also expected to increase both macromolecular mobility and hydrophilicity, promoting an increase in water diffusivity and water sorbance compared with nylon 12/10. Water vapour sorption tests were performed at three temperatures (30, 40 and 50°C) and at several water activities on both samples A and B. Water diffusivity and solubility as well as mixing enthalpies and activation energies were evaluated as a function of water concentration and their values related to macromolecular chain modification deriving from the introduction of ether linkages. © 1997 John Wiley & Sons, Ltd.