Ian J. Britt

Sorption and transport of water vapor in nylon 6,6 film

The sorption and transport of water in nylon 6,6 films as functions of the relative humidity (RH) and temperature were studied. Moisture-sorption isotherms determined gravimetrically at 25, 35, and 45°C were described accurately by the GAB equation. Water-vapor transmission rates were enhanced above ≈ 60–70% RH, primarily due to the transition of the polymer from glassy to rubbery states. The glass transition temperatures (Tgs) of nylon 6,6 were measured at various moisture contents using differential scanning calorimetry. The results showed that the sorbed water acted as an effective plasticizer in depressing the Tg of the polyamide. Fourier transform infrared spectroscopy (FTIR) was utilized to characterize the interaction of water and the nylon. Evidence from FTIR suggested that the interaction of water with nylon 6,6 took place at the amide groups. Based on the frequency shift of the peak maxima, moisture sorption appeared to reduce the average hydrogen-bond strength of the NH groups. However, an increase was seen for the CO groups.

Water absorption in EVOH films and its influence on glass transition temperature

Moisture sorption kinetics of nonoriented ethylene vinyl alcohol copolymer (EVOH) film (EF-E15) were studied at 25, 35, and 45°C. Anomalous diffusion was observed for the polymeric film at high relative humidities (RH) and higher temperatures. Diffusion and solubility coefficients of water were found to be concentration dependent. The moisture sorption isotherms of three types of EVOH films (EF-E15, EF-F15, and EF-XL15) determined at 25, 35, and 45°C, were well described using the GAB equation. Glass transition temperatures (Tg) of the EVOH films, as influenced by RH, were measured using differential scanning calorimetry. Tg values decreased with increasing RH due to the plasticization effect of water, and were found to be dependent on ethylene content and orientation of the EVOH films.

Gellan polymer solution properties: dilute and concentrated regimes

Abstract Flow properties of dilute and concentrated gellan polysaccharide solutions were investigated under low and intermediate shear rates, respectively, to study the behavior of the polymer in water. An apparent stiffness parameter, B′-value, was calculated from the low shear intrinsic viscosity data obtained at various Na+ concentrations. B′-value data suggested that gellan polymer chains are partially flexible. Critical concentration, C ∗ , for gellan solutions was found to be 0.064% w/v, under the measurement conditions used. Flow curves as a function of increasing gellan concentration approached power-law flow. With decreasing temperature, gellan polymer solutions showed a transition to power-law behavior between 28 and 25°C. This transition was attributed to partial gelation of gellan polymer below the transition temperature range.

Aging dynamics in gelatin gel microstructure

Gelatin is a biological polymer that forms thermoreversible gels. Even after formation, the structure of the gel is not static and continues to evolve and change because of the instability of the low energy interactions that connect the gel network. Rheological and dynamic light scattering (DLS) measurements were used to observe the development and evolution of the gel network structure during gelation. Rheological measurements were used to monitor the rate of increase in the number and strength of elastically effective chains as the network forms. Two power law scaling regions were observed; one where the aggregation process dominates and a second, where the rearrangement process dominates. DLS suggested that there were three evolving levels of structure in the gel network: small clusters, large groups of clusters and very large assemblies. For small clusters, the correlation length decreased as the concentration increased. For the large groups, increasing the setting temperature increased the maximum correlation length. Scattered intensity data suggested that large groups lose their integrity as the gel network rearranges.

Sorption and Permeation of Allyl Isothiocyanate Vapor in Nylon 6,6 Film as Affected by Relative Humidity

Sorption and permeation of allyl isothiocyanate vapor (AIT, an antimicrobial flavor compound from Cruciferae plants) in nylon 6,6 film were investigated in this study. AIT sorption by the dry nylon film was low (=0.5%, w/w), but increased to a maximum =3.5% as relative humidity (RH) increased. Above 70% RH, the decrease in AIT solubility was presumably caused by the competitive sorption of water. In contrast, AIT permeability increased exponentially with RH due to the plasticization effect of water upon the polymer. A synergistic Tg depression effect was observed when film samples were exposed to water/AIT vapors simultaneously. FTIR studies indicated that water sorption enhanced hydrogen bonding to the C = 0 sites, but weakened the N-H groups.

Oxygen Ingress in Plastic Retortable Packages during Thermal Processing and Storage

The influence of thermal processing and storage conditions on oxygen ingress in CPET and EVOH-containing PP retortable trays was investigated. Oxygen ingress during retorting was negligible in CPET trays, but increased in PP/EVOH/PP trays at higher retort temperatures, longer process times, and higher oxygen partial pressures. Hydration of EVOH-containing trays did not influence oxygen permeability during thermal processing, but was correlated to oxygen ingress during storage. Oxygen ingress in PP/EVOH/PP trays was minimal during one year of storage at 21. 10C, 60% RH, but increased substantially after 100 d storage at 32.20C, 75% RH. Oxygen ingress in CPET trays was greater than that of EVOH-containing trays during storage under both conditions studied.

Food material science and food process engineering: keys to product quality and safety☆

Abstract Food process engineering and material science provide the foundation on which the food preservation and manufacturing industries are based. To a large extent, availability and quality of the food supply in countries around the world are closely related to the level of development and application of knowledge in food engineering and material science. Moreover, the successful production of specific food items requires a systems approach in which all components of the manufacturing environment are recognized to be interdependent and integrated into the total management of quality reflected in the end product. This paper presents a case study of the production of shelf-stable foods in microwaveable packages to illustrate the systems approach combining food and packaging material science with food process engineering.

Heat Transfer in Liquid-Filled Containers During End-Over-End Rotation

Studies were carried out in a steam/air end-over-end (EOE) rotational batch retort using liquid-filled cans to assess the importance of radial position and processing conditions on the uniformity of product heating. Results of these experiments designed to simulate processing of fluid food materials, indicated a trend toward increased accumulated lethality with increased radius of rotation. However, differences were small in magnitude and not significantly different (p>0.05) for some processes.

Controlled Biaxial Extension of Food Polymer Gels

Aqueous gels of polysaccharides and proteins were formed into cylindrical shapes and compressed between lubricated teflon platens in a mechanical testing machine. The samples maintained a cylindrical form while decreasing in height and increasing in diameter, thereby developing biaxial extensional flow. Viscoelastic properties of the gels were also probed using stress relaxation tests. With experimental values for these properties, stress-time relationships during the biaxial extensional flow were examined using an upper convected Maxwell model.