Ruben J. Hernandez

Mechanical, Physical, and Barrier Properties of Poly(Lactide) Films

High molecular mass poly(lactide), (PLA), is an attractive polymer family because in addition to being thermoplastic, biodegradable, compostable, and produced from annually renewable resources, it shows mechanical and barrier behavior comparable to synthetic polymers like polystyrene (PS) and polyethylene terephthalate (PET). Furthermore, technology for large-scale fabrication of PLA has been fully developed. However, there is still a need to better understand the properties of PLA as this polymer is adapted to packaging applications, especially for food packaging. In this work, films from two PLA resins were studied by tensile testing; differential scanning calorimetry (DSC); and permeation of carbon dioxide, oxygen, and water vapor. The data from these two PLA film samples are compared to those of PS and PET.

Characterizing the migration of antioxidants from polypropylene into fatty food simulants

The migration (diffusion and equilibrium) processes of antioxidants (AOs) from polypropylene (PP) films of different thicknesses into n-heptane and 95% ethanol as fatty food simulants were analysed at 20, 37 and 60°C. Heptane fully extracted the AOs from the polymer while a partition equilibrium described the migration to ethanol. The kinetics of migration were also studied via the diffusion coefficients. As expected, diffusion was found to be faster when the polymer was in contact with heptane, due to polymer swelling by the solvent. The kinetics of the process in ethanol was described by different theoretical expressions which are discussed. Equations disregarding partition equilibrium failed to describe the process and the diffusion coefficient values obtained through them were much smaller than the actual ones and dependent on film thickness. The results also showed the significance of food simulant selection in the analysis of food-packaging interactions and migration variability with thickness.

Effect of Water Vapor on the Transport Properties of Oxygen through Polyamide Packaging Materials

The barrier characteristics of polymeric packaging materials are measured by the intensity of the molecular exchange between the packaged product and its external environment. The exchange of penetrant molecules through polymeric materials is determined by the capacity of a polymer matrix to sorb the penetrant molecules, and the ability of the penetrant to diffuse through the polymeric material according to Ficks laws. However, the presence of other small relative molecular mass compounds present in the polymer matrix may change the way in which the permeant is sorbed and diffused. The case is such when water molecules are present in hydrophilic polymers affecting barrier characteristics of those polymers to penetrants such as oxygen or organic compounds. The oxygen barrier properties of hydrophilic polyamides change as a function of the amount of water in the polymer matrix. In addition, polymer morphology plays an important role in controlling the mode in which water molecules affect the transport of the penetrant. The change in oxygen barrier properties is then a function of the polymer water activity and morphology. A dual mode sorption model based on the Flory-Huggins and Langmuir equations is applied to the sorption of water by an amorphous and a semicrystalline polyamide, at three temperatures. The model provides the basis for the interpretation of the effect of water on the permeability, solubility and diffusion of oxygen within the polyamides. Different interaction mechanisms of water and oxygen within the polymers, to include self-association of water molecules and oxygen-water molecular competition, are discussed at different water activity values for both polyamides.

The sorption of water vapor by an amorphous polyamide

Abstract A modified dual-mode sorption model represents the sorption of water vapor by an amorphous polyamide at 23 °C. The Langmuir equation is used to calculate the volume fraction of chemisorbed solute and the Flory-Huggins equation is used instead of Henrys law to calculate the volume fraction of water which is not chemisorbed. This model describes the data over a range of water activities from zero to one and predicts clustering of the sorbant. Fourier Transform Infrared (FTIR) spectroscopy data and dielectric measurements of the gamma relaxation temperature suggest that the water associates with amide groups at low water activities.

Effect of high‐pressure processing on the permeance of selected high‐barrier laminated films

This study investigated the effects of high pressure processing (HPP) on the barrier properties of eight multilayer films. Pouches made from these films were filled with distilled water, sealed and then pressure processed at 600 and 800 MPa for 5, 10 and 20 min at 45°C. Controls were similarly prepared but exposed to atmospheric pressure. After processing, all pouches were dried and their oxygen, carbon dioxide and water vapour permeance determined. Films used in this study were PET/SiOx /LDPE, PET/Al2O3/LDPE, PET/PVDC/nylon/HDPE/PE, PE/nylon/EVOH/PE, PE/nylon/PE, metallized-PET/EVA/LLDPE, PP/nylon/PP and PET/PVDC/EVA. Results showed that metallized PET was most severely affected by HPP, as its permeance values for oxygen, carbon dioxide and water increased as much as 150%. Copyright

The Evaluation of the Aroma Barrier Properties of Polymer Films

HE SHIFT FROM ABSOLUTE BARRIER TYPE PACKAGES, SUCH AS CANS AND bottles, to semi-permeable polymeric packaging systems has created a need to develop a better understanding of the transport of gases, vapors, and other low molecular weight moieties through polymer films. The transport of permeants such as oxygen, carbon dioxide and water vapor through polymer structures has been the subject of numerous investigations, and standard test methods are available for determining transmission rates for these permeants (ASTM E96-66, ASTM D3985-81). In contrast, while the transport of organic penetrants through packaging materials has been the subject of several recent investigations, there is a paucity of data available in this area. This paper will, therefore, focus on the various procedures developed for quantifying the rate of diffusion of organic penetrants through barrier membranes and describe in detail the specific procedures employed in the studies reported. Pye, et al. (1976) described a continuous or isostatic procedure for measuring the diffusivity properties of polymer membranes that employed two gas chromatographs connected to a cell. One chromatograph was equipped with

Evaluation of solubility and diffusion coefficients in polymer film–vapor systems by sorption experiments

Abstract Sorption experiments are commonly used to determine the equilibrium and kinetics of mass-transfer processes of vapors in polymeric materials. Electrogravimetry is recognized as a powerful technique. A discussion of the standard theoretical approach to determine solubility and diffusion coefficients is presented. The reduced mathematical expression commonly used for calculations of D values is discussed. A consistency test to check for common deviations caused by the experimental complexity is discussed and resolved. The sorption of hexanol and ethyl caproate into a metallocene polyethylene and an ionomer was measured by electrogravimetry. Transport was characterized through the solubility and the diffusion coefficients. The formalism presented was used in these experiments and is commented upon.

Packaging: Papers for Sacks and Bags

This work examines wood fiber-based paper materials that are widely used throughout the world in packaging applications. Two of the advantages of using wood fiber based paper are in their strength and cost. They are natural, recyclable, biodegradable, and versatile materials backed by a dynamic and innovative paper industry. As a result of their biodegradability, its impact on environment as compared with plastic bags is very friendly. The recommended specification for normal moisture content of paper on a dry weight basis is 5%±2% and the paper materials must be tested at standard conditions of 23±2°C and 50%±2% RH, according to ASTM D 685 and TAPPI standard T402.

Evaluation of Permeability Through Permeation Experiments: Isostatic and Quasi‐isostatic Methods Compared

Isostatic and quasi-isostatic permeation experiments were used to characterize the permeability of 1-hexanol through polypropylene films. The quasi- isostatic method was considered as an isostatic experiment at the limit a of null purging stream flow rate. Permeability values obtained through the isostatic method showed dependency on the purging stream flow rate. The extrapolated value at zero purging stream flow rate is in agreement with the data obtained via the quasi-isostatic procedure. Diffusion coefficient values were also determined. The isostatically obtained diffusion coefficients behave similarly to P. However, the value at zero flow rate differs significantly from the value obtained through the quasi-isostatic method. From these results the validity of permeation experiments for the evaluation of the diffusion coefficient is questioned.

A determination of solubility coefficient values determined by gravimetric and isostatic permeability techniques

The solubility coefficient (s) values for ethyl acetate in three heat sealant polymer membranes (LDPE, LLDPE and ionomer) were determined over a range of permeant vapour concentrations by a gravimetric procedure and an isostatic permeability technique. The respective solubility coefficient values obtained by the two methods were found to be in good agreement, with no statistically significant difference observed as a function of vapour activity. This agreement suggests that the solubility coefficient values obtained were independent of permeant vapour activity, and the sorption process followed a Henrys law relationship over the vapour concentration range evaluated. Comparison of the solubility coefficient values obtained by the gravimetric and isostatic permeability techniques showed reasonably good agreement over the vapour concentration range considered, with the S values obtained from permeability experiments being approximately 25% higher than those obtained from sorption measurements. Because of the procedural differences between the gravimetric and isostatic permeability techniques, this agreement is considered to be within acceptable limits. For the gravimetric technique, the solubility coefficient value is determined directly from the steady-state portion of the sorption profile curve, while the solubility coefficient value obtained from the permeability experiment is derived from transient state data. Copyright