Dynamic mechanical properties of polyolefin foams studied by DMA techniques

In this work a preliminary study on the viscoelastic behavior of polyolefinic foam sheets with different chemical (polyethylene and polypropylene) and cellular structure by means of Dynamical Mechanical Analysis (DMA), in the low frequency and low compression ranges, is presented. Differential Scanning Calorimetry (DSC) and Scanning Electron Microscopy (SEM) are also used to determine the morphological parameters of the samples. A connection between the morphological parameters (apparent degree of crystallinity, type of cellular structure, homogeneity, cell size and shape, cell-wall thickness) and the viscoelastic behavior, a basic key for the development of mechanical and insulating applications, has been established.     

Characterization of the conformers in poly(3,3-diethyl oxetane) by vibrational spectroscopy

Summary The monoclinic and orthorhombic conformers of Poly(3,3-Diethyl oxetane) can be obtained depending on crystallization temperature. However, if the crystallization of a given modification is unaccomplished, the other modification can be crystallized from the amorphous phase. The molecular vibrations in the region 700–800 cm^–1, which are associated with the breathing mode, are highly dependent on the conformation of the polymer chain. This band is used to study the influence of the temperatures and times of crystallization on the structural modifications of this polymer.     

An estimation of the chain branching effects in butene/ethylene copolymers from microhardness measurements

Summary In this work a simple microhardness test to evaluate the degree of chain braching in butene-ethylene copolymers is proposed. The random introduction into the chain of co-units, reduces the level of crystallinity in the copolymer, a characteristic easily measurable through indentation experiments. A comparative study between density and microhardness values in samples with different concentration of chain braching is presented.     

Polypropylene/clay nanocomposites: Combined effects of clay treatment and compatibilizer polymers on the structure and properties

Combined effects of clay treatment and compatibilizer polymers on the structure and properties of polypropylene/clay nanocomposites were studied. Dynamic mechanical analysis was used to analyze comparatively the dynamic mechanical response of different nanocomposites prepared from polypropylene and montmorillonite‐rich bentonite, and to relate such response with the material microstructure. Two different bentonites were used: a purified Spanish natural bentonite was organophillized by means of 11‐undecyl‐ammonium ion and a commercial bentonite organophillized with dimethyl dehydrogenated tallow ammonium ion. Three different polar copolymers were employed as compatibilizer agents in some of the formulations: maleic anhydride‐grafted polypropylene, maleic anhydride‐grafted poly(styrene‐co‐ethylenebutylene‐co‐styrene), and poly(ethylene terephthalate‐co‐isophthalate) (PET). To ascertain the microstructure characteristics in the nanocomposites, wide angle X‐ray diffraction, transmission electron microscopy, and differential scanning calorimetry techniques were used. The nanocomposites containing both bentonite organophillized with 11‐undecyl‐ammonium ion and PET, and maleated PP as compatibilizer system, were found to have the highest storage modulus and the smallest loss factor values, which was mainly due to the better clay platelets dispersion. The dynamic mechanical response of nanocomposites prepared with bentonite organophillized with dimethyl dehydrogenated tallow ammonium ion and maleated SEBS was strongly affected by the presence of this compatibilizer. The temperature of PP and α, β, and γ relaxations strongly depended on the interactions between the different phases in the nanocomposites. © 2006 Wiley Periodicals, Inc. J Appl Polym Sci 102: 1213–1223, 2006     

Characterisation of the matrix polymer morphology of polyolefins foams by Raman spectroscopy

The spatial resolution provided by micro-Raman spectroscopy is used to probe the morphology of the polymer matrix in a series of closed cell cross-linked polyolefin foams. The experiment set-up allows for the laser beam to be focused with a spatial resolution of 1 μm², permitting the structural characterisation of the polymer in the cell faces, cell edges and vertices; i.e. the main constituents which build up the cellular structure of a closed cell foam. The spectra of the solid sheets utilised to produce the foams are used as reference in the discussion of the results for foams. The results have showed a non-homogeneous spatial distribution of the polymer morphology in the foam, which is different from the morphology of the solid sheets. Orientation and phases content are the main sources for these differences.     

Sample size effect on the effective diffusion coefficients for the gas contained in closed‐cell polyethylene‐based foam subjected to compressive creep tests

In this article, the effect of sample size on the degassing behavior of closed‐cell low density polyethylene (LDPE) foam under long‐term compressive static loading is presented. The creep response was modeled by assuming isothermal compression of the gas. The change in gas pressure with time was obtained and the effective diffusion coefficients were calculated from pressure decrease using an analytical solution of the diffusion equation, and were found to increase when the sample size was reduced. © 2005 Wiley Periodicals, Inc. J Appl Polym Sci, 2006     

Measurement of the thermal diffusivity and specific heat capacity of polyethylene foams using the transient plane source technique

Thermal diffusivity and specific heat at constant pressure of a collection of crosslinked closed cell polyethylene foams have been measured at room temperature using the transient plane source (TPS) method. A theoretical model to predict the thermal diffusivity has been proposed. The predictions of this model are in good agreement with the observed experimental trends. The theoretical model predicts a dependence of the thermal diffusivity on the density and other foam characteristics such as carbon black content and cell size. Copyright © 2004 Society of Chemical Industry     

Effect of Enzymatic Hydrolysis on the Antioxidant Activity of Red and Green Seaweeds and Characterization of the Active Extracts

In the present study, the effect of enzymatic hydrolysis on the antioxidant activity of three red seaweeds (Chondria cornuta, Chondria dasyphylla, and Murrayella periclados) and two green seaweeds (Cladophora sp. and Ulva lactuca) from the Kuwait coast were evaluated. The seaweeds were hydrolyzed with five carbohydrases and three proteases, and the resulting extracts were tested for antioxidant activity. The total phenolic content and yield of the extracts varied greatly depending upon the species and enzyme used for hydrolysis. Of the 40 enzymatic extracts screened for antioxidant activity, the Viscozyme and Alcalase extracts of M. periclados, Neutrase and Ultraflo extracts of Cladophora sp., and Neutrase extracts of C. cornuta had high antioxidant activity compared to other enzymatic extracts in various in vitro assays. Fractionation of the extracts revealed that the radical scavenging and reducing power of the extracts were mainly due to phenolic fractions. In contrast, the iron-chelating ability was mainly due to protein fractions. The level of prevention of lipid oxidation in the liposome model system varied for different fractions of extracts and did not correlate with total phenolic content and other antioxidant properties. The results of the study show that, by hydrolyzing seaweeds with specific enzymes, customized seaweed extracts with specific bioactivity could be obtained.     

Application of an electronic tongue to study the effect of the use of pieces of wood and micro-oxygenation in the aging of red wine

The ageing of red wines matured in oak barrels and wines treated soaking pieces of wood of different sizes (chips or staves) in micro-oxygenated stainless steel tanks has been monitored periodically using an electronic tongue, chemical analysis and a panel of experts. The use of micro-oxygenation in stainless steel tanks, lets get wines with characteristics similar to wines aged in oak barrels. However, differences in the phenolic content and in particular in the anthocyanin levels are observed during the first steps of ageing and in the final product.In the early stages of ageing, Principal Component Analysis (PCA) and Partial Least Squares Discriminant Analysis (PLS-DA) calculated from the electronic tongue outputs have permitted the discrimination between wines aged with traditional and alternative methods due to the faster rate of ageing caused by chips or staves. After 5 months of ageing, the use of alternative ageing methods cannot be longer detected. However, when the ageing continues in a reducing atmosphere (bottled wines), the electronic tongue has demonstrated a good capability to discriminate and classify bottled wines previously aged in oak barrels from those previously treated with oak chips and oak staves. The effect of the size of the pieces and of the type of wood can also be detected by the e-tongue. Using Partial Least Squares (PLS-1) good correlations have been found between the electrochemical signals provided by the array of sensors and the polyphenolic content parameters. Good correlations have also been established with the scores given by the panel of experts, in particular with the astringency.     

FRACTURE BEHAVIOUR OF UNTREATED AND SILANE-TREATED TALC-FILLED POLYPROPYLENE COMPOSITES

Abstract— Fracture behaviour of injection-moulded polypropylene filled with silane-treated talc was studied as a function of filler volume fraction (0–20%) and compared to that of polypropylene filled with untreated talc. High-rate tests (0.57 m/s) on SENB specimens were carried out using an instrumented Charpy impact pendulum, and linear elastic fracture mechanics (LEFM) was applied to calculate the fracture parameters, K _C and G _C. It was found that moderate fractions of talc which were added to the polypropylene matrix increased the fracture toughness of the composite independent of the talc surface treatment. This general improvement seems to be due to the peculiar orientation of the talc platelets in the injection-moulded specimens. The fracture behaviour of the composites was also studied at low strain rate (1 mm/min) by tests on J -integral type specimens with the same SENB geometry. In this case, the composites with silane-treated talc presented poor J -integral values compared to those of the samples with untreated talc. This was attributed to a reduction of the plastic zone at the crack tip, since the improved coupling between the talc platelets and matrix increased the yield strength of the composite. All the results are explained on a basis of morphological and microstructural details.