Method for routine density measurement of sublimating solid carbon dioxide (dry ice) for cold-chain quality control

With recent development of vaccines and biologics, interest in dry ice for cold chain shipping has increased. However, understanding of how dry ice properties relate to performance is not well understood. This study introduces a simple method for measuring a key property of dry ice that has been shown to correlate to performance. The method involves a variant of the water displacement method for determining volume, where dense solid particles are used in place of water for volume determination. Three particle types (sieved sand, glass beads, and stainless-steel shot) were tested for suitability with the particle displacement method. Items of known mass and volume were used to validate the method. Direct volume measurements of dry ice cut samples using digital calipers were conducted in parallel for relative comparison. Results showed that the proposed particle displacement method using sieved sand produced density readings with an accuracy of 97-99%, whereas digital calipers underestimated density values. The sand and glass particles were less successful due to high thermal conductivity (stainless-steel shot), which led to errors due to condensation, and particles that were too fine and not sufficiently dense to prevent fluidization doe to sublimation gas flow. Sieved sand provided a good combination of particle size, density, thermal conductivity, and heat capacity for routine measurement of density of dry ice regardless of shape

Morphological, Thermal and Oxygen Barrier Properties Plasticized Film Polylactic Acid

Introducing plasticizer poly(ethylene glycol) (PEG400) was applied into poly(lactic acid) (PLA) to produce film matrix packaging by direct casting. Non mechanical properties were carried out plasticized PLA including morphology, crystallinity structure and degree, thermal properties and oxygen barrier properties. Plasticized PLA revealed improving surface structure of PLA film matrix form fractures and homogenous film were achieved at 5% PEG 400. Chromatogram PLA and plasticized PLA were categorized crystal structure an α-form crystal. Intercalated and exfoliated structure did not occur significantly due to dispersion PEG 400 in the matrix but indicated dispersion structure. Thermal properties did not improve plasticized PLA significantly for both glass temperature and melting temperature. PEG 400 accelerated crystal formation that increased the crystallinity degree from 17.71% to 34.64%. Plasticized PLA enhanced permeability value about 20% while largest fraction PEG400 reduced ability to prevent from oxygen through pass the film. The oxygen barrier properties was significantly affected degree of crystalline in the film with a correlation number 0.85

Prostaglandins in breast cancer: relationship to disease stage and hormone status.

Tissue prostaglandin (PG) content and production by human breast cancers were measured in 24 human mammary carcinoma specimens. The 5 compounds studied were PGE1, PGE2, PGF2 alpha, 6-keto-PGF1 alpha, and TXB2. The tissue content of all 5 compounds was higher in neoplastic tissue in comparison with the paired noncancerous breast tissue. However, microsomal PG synthetase activity in vitro in noncancerous and neoplastic breast tissue was comparable. Increased thromboxane formation was associated with three clinical variables--tumour size, axillary lymph node metastases and distant metastasis. A lesion negative for either oestrogen or progesterone receptor content tended to produce more TXB2 but lower PGE2 and 6-keto-PGF1 alpha. Results obtained in this pilot study may provide clues as to what direction future larger studies could take in the search for reliable prognostic indicators for breast cancer

Experimental and numerical investigation of flexural concrete wall design details

Reinforced concrete structural walls are common in mid- to high-rise structures in high seismic regions, and are expected to have good strength and ductility characteristics if designed in accordance with ACI 318-14. However, experimental and analytical investigations of reinforced concrete structural walls and isolated boundary element prisms indicate that the existing design provisions may be insufficient to provide ductile, flexure-dominated response under cyclic loading. Walls designed with an ACI compliant boundary element length are susceptible to shear-compression failures below the maximum ACI allowable shear stress of 10Acv√fc’. Also of concern is the frequent use of thinner walls in modern design; as the wall’s cross-sectional aspect ratio increases, such brittle shear-compression failures occur at even smaller shear stress values. In regards to detailing, special boundary elements with intermediate cross-ties exhibit a minimal improvement in confinement compared to ordinary boundary elements. This response can be linked to inadequacies in multiple code design parameters, including: vertical spacing and area of confinement steel, horizontal spacing and type of restraint to longitudinal bars, and development length provided for transverse reinforcement. Recent in-field wall failures have prompted concerns related to the minimum code required vertical and horizontal web shear reinforcement, as well as the relative amount of vertical-to-horizontal web steel. This paper examines ACI 318-14 special boundary element and web reinforcement provisions and provides design recommendations intended to improve wall performance as compared with current ACI requirements

Predictive Modeling of Oxygen Transmission Through Micro-Perforations for Packaging Applications

Methods for creating precise perforations in respiring produce packaging are being increasingly adopted. Knowledge of oxygen transfer through perforated packaging and oxygen distribution in packages is necessary for successful packaging design of fresh produce. An approach to modeling perforated packaging performance was developed using a cylindrical chamber with precision perforations using Fick’s second law. The model was simulated using two techniques including Finite Element Method (FEM) using commercially available software and Finite Volume Method (FVM) through programming. Perforations were approximated as a source term in the second method. Both simulation techniques showed trends similar to experimental data

Review of Challenges and Advances in Modification of Food Package Headspace Gases

Modified Atmosphere Packaging (MAP) has been widely used as an effective way to preserve foods. Fresh produce, meat and meat products, seafood, and dairy products can benefit from modified gaseous atmospheres, which are usually achieved by reducing oxygen and increasing carbon dioxide concentrations, within limits, defined by product tolerances. MAP of fresh produce is particularly challenging because products are living and respiring. Respiration rates depend on several factors including temperature, oxygen, and carbon dioxide concentrations. Balancing package permeation with respiration is challenging, often due to limited selection of practical packaging materials. Failing to remain within tolerance limits of products leads to rapid quality loss. Gas barrier properties of packages determined rate of gas exchange with the external environment and is a critical factor for achieving tolerable levels. Availability of packaging materials that meet requirement of specific produce is essential. Relative permeability of common films to carbon dioxide is about 3 to 6 times of that to oxygen, often leading to package collapse for package atmospheres that benefit from carbon dioxide. Films often fail to provide desired oxygen transmission rates, high carbon dioxide to oxygen selectivity and desired mechanical properties simultaneously. Despite advances, minimal availability and high cost of selective barrier films limit applications of MAP for fresh produce packaging. Therefore, active packaging components and films are being developed and designed to overcome these limitations. Inserts or films that contain active mixtures as gas emitters and/or scavengers are now commercially available. “Clean label” trends are motivating alternative approaches using active packaging components

Effect of Plasticizer on Oxygen Permeability of Cast Polylactic Acid (PLA) Films Determined Using Dynamic Accumulation Method

Polylactic acid (PLA) is becoming an increasingly important biopolymer for packaging applications. PLA brittleness limits its applicability. This study evaluated PLA properties with increasing amounts of added polyethylene glycol (PEG) plasticizer. Oxygen transmission rate (OTR) of cast films was determined using the newly available Dynamic Accumulation (DA) method. Arrhenius temperature sensitivity of OTR and polymer Permeability was also determined. Permeability of neat PLA is 4.848 ml mm (STP)/m2 s kPa; hence, 4.84 ml mm (STP)/m2 s kPa, 4.07 ml mm (STP)/m2 s kPa and 5.42 ml mm (STP)/m2 s kPa by adding PEG 1 %, 5% and 10% respectively. The main conclusion from this work is increasing PEG will enhance the PLA permeability number but excess PEG in PLA film will decrease the permeability number