Effective diffusion coefficient for the gas contained in closed cell polyethylene-based foams subjected to compressive creep tests

In this paper, a new method to obtain the effective diffusion coefficient of the gas contained in closed cell foams under static loading is presented. Compressive creep experiments were performed on six low-density polyethylene (LDPE) and two polyethylene-co-vinyl acetate (EVA) foams of different densities using a home-designed compressive creep apparatus. The modelling of the evolution of pressure inside the cells was performed using an isothermal compression model. The effective diffusion coefficients were obtained from pressure decrease with time using an analytical solution of the diffusion equation. The values obtained agreed with those in literature and were dependent on both foam density and chemical composition.     

The Metabolic Efficacy of a Cannabidiolic Acid (CBDA) Derivative in Treating Diet- and Genetic-Induced Obesity

Obesity is a global medical problem; its common form is known as diet-induced obesity (DIO); however, there are several rare genetic disorders, such as Prader–Willi syndrome (PWS), that are also associated with obesity (genetic-induced obesity, GIO). The currently available therapeutics for treating DIO and GIO are very limited, and they result in only a partial improvement. Cannabidiolic acid (CBDA), a constituent of Cannabis sativa, gradually decarboxylates to cannabidiol (CBD). Whereas the anti-obesity properties of CBD have been reasonably identified, our knowledge of the pharmacology of CBDA is more limited due to its instability. To stabilize CBDA, a new derivative, CBDA-O-methyl ester (HU-580, EPM301), was synthesized. The therapeutic potential of EPM301 in appetite reduction, weight loss, and metabolic improvements in DIO and GIO was tested in vivo. EPM301 (40 mg/kg/d, i.p.) successfully resulted in weight loss, increased ambulation, as well as improved glycemic and lipid profiles in DIO mice. Additionally, EPM301 ameliorated DIO-induced hepatic dysfunction and steatosis. Importantly, EPM301 (20 and 40 mg/kg/d, i.p.) effectively reduced body weight and hyperphagia in a high-fat diet-fed Magel2^null mouse model for PWS. In addition, when given to standard-diet-fed Magel2^null mice as a preventive treatment, EPM301 completely inhibited weight gain and adiposity. Lastly, EPM301 increased the oxidation of different nutrients in each strain. All together, EPM301 ameliorated obesity and its metabolic abnormalities in both DIO and GIO. These results support the idea to further promote this synthetic CBDA derivative toward clinical evaluation in humans.     

Moulded polypropylene foams produced using chemical or physical blowing agents: structure–properties relationship

Polypropylene (PP) foams have become essential items due to their excellent properties. Nevertheless, obtaining net-shaped PP foams with medium relative densities is a complicated issue. In this article, two processes able to produce moulded PP foams in this density range are presented. One of them is based on a modification of the pressure quench foaming method and therefore uses a physical blowing agent (CO₂). The second one is the improved compression moulding technique which uses a chemical blowing agent (azodicarbonamide). PP foams with relative densities in the range between 0.25 and 0.6 and cylindrical shape were prepared using these foaming techniques. A common PP grade (instead a highly branched one) was used to obtain the samples, showing, that by combining the appropriate foaming technique, the adequate moulds, suitable blowing agent and proper foaming parameters, net-shaped PP foams with excellent properties can be produced starting from a conventional PP grade. Samples were characterized by analyzing their cellular structure and their mechanical properties. Results have showed that depending on the chosen foaming route isotropic or anisotropic structures with cell sizes ranging from 40 to 350 μm and open cell content in the range between 0 and 65% can be obtained. Moreover, mechanical properties are highly influenced by the production route and chemical composition of the foams. For instance, the stiffer materials at relative densities higher than 0.4 are the ones produced using the chemical blowing agent while at relative densities lower than 0.4 are the ones produced using the physical blowing agent.     

A novel approach for audio file encryption using hand geometry

Multimedia Tools and Applications - This paper suggests a new proposed algorithm for encryption/ decryption audio files based on discrete wavelet transform (DWT) and biometric features to provide a...     

Anisotropy and Microstructure Heterogeneity of Injection‐Moulded Discs of Poly(propylene) Filled with Platy Magnesium Hydroxide

The anisotropy and microstructure heterogeneity induced by filler presence and processing has been studied on injection‐moulded discs of poly(propylene) homopolymer (PP) filled with a wide range of concentration (0–60 wt.‐%) of uncoated platy magnesium hydroxide. Differential scanning calorimetry (DSC), wide‐angle X‐ray diffraction (WAXD) and scanning electron microscopy (SEM) techniques were used to help state the microscopic structure and justify properties measured by dynamic mechanical thermal analysis (DMTA). On the one hand, the anisotropy has been analysed by measuring samples in the parallel and perpendicular directions to the discs surface. On the other hand, the heterogeneity has been characterised by testing samples cut from different zones of the discs. It has been found that the nucleation activity of magnesium hydroxide on the α‐phase of poly(propylene) increases with the filler concentration up to the maximum level studied (60 wt.‐%). The polymer crystalline β‐phase was only detected in unfilled PP and in samples containing less than 20 wt.‐% of magnesium hydroxide. Remarkable differences in the polymer (α‐phase) and particle orientation degrees have been observed in the composites depending on the filler concentration, the disc zone, and depending on whether the analysis was carried out over the disc skin or core. The anisotropy degree of poly(propylene) crystals in the composites was independent on that of the filler particles up to 10 wt.‐% of Mg(OH)₂ concentration; however, from 20 wt.‐% of filler the orientation of magnesium hydroxide particles clearly influenced the orientation and anisotropy of the polymer. Moreover, the differences of orientation in the specimen skin were mainly responsible for the heterogeneity of the discs. Composites with lower magnesium hydroxide concentration exhibited the higher heterogeneity. These factors were found to be the main causes of the different dynamic mechanical properties obtained for these materials when the experiments were performed in different zones and/or through different directions in the injection‐moulded discs.     

Crystallization behavior of polypropylene filled with surface-modified talc

Talc-filled polypropylene (PP) composites were prepared by extrusion in a wide composition range (0–40 wt %). To improve the affinity relation between talc and the PP matrix, we modified the talc surface with silane coupling agents. Differential scanning calorimetry investigations on test samples, prepared by injection moulding, revealed that the talc content and its surface modification had a pronounced effect on the crystallization behavior of the filled PP composites. The experimental results indicate that a talc concentration of 2 wt % strongly affects the nonisothermal crystallization process of the PP, especially when talc is silane treated Isothermal crystallization experiments on samples with minimum amounts of talc (2 wt %) revealed an improved nucleation activity with silane-treated talc. © 1996 John Wiley & Sons, Inc.     

Aluminium foams as a filler for leading edges: Improvements in the mechanical behaviour under bird strike impact tests

The use of aluminium foams as filler materials in aeronautical leading edges is investigated. Particularly, the improvement of the mechanical behaviour of the filled structure respect to the hollow one is analysed by means of standard bird strike impact tests. For this purpose, a collection of AlSi₁₀ foams were fabricated using the powder metallurgical route (PM), and introduced into leading edges profiles, maintaining or reducing the total weight of the composite structure (leading edge + aluminium foam) in comparison with the original one (hollow structure). Bird strike impact tests were carried out in both types of structures, comparing the global deformation and total load transferred in the tests. The results showed that the composite structure, a 13% lighter than the original one, showed four times better behaviour in terms of global deformation and an improvement of two times in the transmitted load.