Understanding the mechanical and biodegradation behaviour of poly(hydroxybutyrate)/rubber blends in relation to their morphology

In this work poly(hydroxybutyrate/poly(vinyl butyral)‐ co‐(vinyl alcohol)‐co(vinyl acetate) (or ethylene propylene diene monomer rubber) blends were prepared by conventional processing techniques (extrusion and injection moulding). A droplet type morphology was obtained for P(3HB)/PVB blends whereas P(3HB)/EPDM blends presented some extent of co‐continuous morphology. In addition, rubbery domains were much smaller in the case of PVB. These differences in morphology are discussed taking into account solubility parameters and rheological behaviours of each component. For both blends, the increase of elastomer ratio led to a decrease of Young's modulus but an increase in elongation at break and impact strength. The latter increased more in the case of P(3HB)/EPDM blends although the rubbery domains were larger. These results are explained in the light of the glass transition of the rubber and the presence of plasticizer in the case of PVB. The addition of elastomer also resulted in an increase of P(3HB) biodegradation rate, especially in the case of EPDM. It is assumed that, in this case, the size and morphology of the rubbery domains induce a geometrical modification of the ‘erosion front’ which leads to an increase of the interface between P(3HB) phase and the degradation medium and consequently to an apparently faster biodegradation kinetics of PHB/rubber blends. Copyright © 2011 Society of Chemical Industry     

Density measurement of fine aerosol fractions from wood combustion sources using ELPI distributions and image processing techniques

Aerosols from combustion sources are of high concern since they present a risk for health and environment. Particle size distribution of aerosols and in particular number size distribution are easily and quickly obtained using an Electrical Low Pressure Impactor (ELPI). However, this technique is depending of aerosol density; ρ, which may lead to biased particle size distributions. Aerosol density from combustion sources is usually not well known and depends on several parameters. Aerosol density cannot be measured with usual methods since there is generally not enough matter collected on each stage of the ELPI. Our approach uses electronic microscopy to evaluate ρ at each impaction stage in order to increase the accuracy of the number size distributions resulting from the ELPI measurements.Particles were collected on glass substrates deposited on each impaction stages. Images were obtained using a scanning electron microscope and image processing tools were applied.This method was first tested with silica particles resulting from a combustion process which have a constant density found to be comprised between 2.2 and 2.4 g cm⁻³ for stages 2 (57 and 95 nm) and 3 (95 and 158 nm), respectively. Once validated, this method was used to determine the density of wood combustion aerosols. The results match well for fly ashes from wood combustion with densities varying from 1.1 to 3.0 g cm⁻³ for particles of mean equivalent diameter ranging from 69 to 157 nm, respectively.     

Influence of the rubbery phase on the crystallinity and thermomechanical properties of poly(3‐hydroxybutyrate)/elastomer blends

Poly(3‐hydroxybutyrate) (PHB) is a very promising biopolymer. In order to improve its processability and decrease its brittleness, PHB/elastomer blends can be prepared. In the work reported, the effect of the addition of a rubbery phase, i.e. ethylene–propylene–diene terpolymer (EPDM) or poly(vinyl butyral) (PVB), on the properties of PHB was studied. The effects of rubber type and of changing the PHB/elastomer blend processing method on the crystallinity and physical properties of the blends were also investigated. For blends based on PHB, the main role of EPDM is its nucleating effect evidenced by a decrease of crystallization temperature and an increase of crystallinity with increasing EPDM content regardless of the processing route. While EPDM has a weak effect on PHB glass transition temperature, PVB induces a marked decrease of this temperature thank to its plasticizer that swells the PHB amorphous phase. A promising solution to improve the mechanical properties of PHB seems to be the melt‐processing of PHB with both plasticizer and EPDM. In fact, the plasticizer is more efficient than the elastomer in decreasing the PHB glass transition temperature and, because of the nucleating effect of EPDM, the decrease of the PHB modulus due to the plasticizer can be counterbalanced. Copyright © 2010 Society of Chemical Industry     

Investigation of the first stages of the localized corrosion of pure copper combining EIS, FE-SEM and FE-AES

During the first 48 h that pure copper is submerged in a chloride containing solution, an oxide layer is formed that acts as a barrier layer between the aggressive solution and the substrate, offering some protection to the material. This barrier layer itself is subsequently attacked and localized corrosion is observed. The study of the corrosion behavior was based on open circuit potential (OCP) measurements. The evolution of this value was concurrent with the evolution of the state of the oxide layer. Furthermore the surface state was evaluated by taking impedance spectra every 2 h. This method proved to be insufficient to elucidate the surface evolution and additional techniques were employed. The thickness and the composition of the oxide layers as well as the different composition of the corrosion products in and around the zones of localized attack were determined by means of an FE-AES equipped with an ion gun. The scanning electron microscope (SEM) allowed us to visually discriminate between the three stages the surface passes through during the first 48 h. Mathematically the equivalent circuit used in literature fits the impedance data very well. The observations in this work are however in contradiction with the different physical meanings attributed to the circuit elements found in literature. Further research is necessary to reveal the real mechanism of copper corrosion in this sort of systems.     

Atomic force microscopy (AFM) characterisation of the porous silica nanostructure of two centric diatoms

The porous silica nanostructure of two marine, centric diatoms, Coscinodiscus sp. and Thalassiosira eccentrica was investigated by atomic force microscopy (AFM). Important morphological features of the silica frustules of diatoms are described, including: the organisation of porous silica layers, their topography, pore size, shape and density. The outer layer of Coscinodiscus sp., commonly called the cribellum, consists of a characteristic hexagonal array of pores with pore sizes of around 45 nm. This thin membrane covers a second structural layer where two different silica surfaces are identified. The outer part, known as the cribrum consists of hexagonally packed pores of about 200 nm diameter. The inner part, known as the foramen layer, consists of larger and radially distributed holes with a diameter of around 1,150 nm. The second diatom species investigated, T. eccentrica produces a frustule with one silica structural layer featuring two different porous surfaces. The outer surface has large (800 nm diameter) holes (foramen) while the inner surface contains a porous wall with pores comparable in size to the Coscinodiscus sp. cribellum. The inner and outer surfaces of the frustule wall of both diatoms are hence in reverse order. However, the size of the small pores is similar for both species. High-resolution AFM also revealed the granular nanostructure of the diatom biosilica with grain sizes from 20 to 70 nm diameters.     

Electronic properties of carbon nanotubes calculated from density functional theory and the empirical <Emphasis Type="Italic">π</Emphasis>-bond model

The validity of the DFT models implemented by FIREBALL for CNT electronic device modeling is assessed. The effective masses, band gaps, and transmission coefficients of semi-conducting, zigzag, (n,0) carbon nanotubes (CNTs) resulting from the ab-initio tight-binding density functional theory (DFT) code FIREBALL and the empirical, nearest-neighbor π-bond model are compared for all semiconducting n values 5≤n≤35. The DFT values for the effective masses differ from the π-bond values by ±9% over the range of n values, 17≤n≤29, most important for electronic device applications. Over the range 13≤n≤35, the DFT bandgaps are less than the empirical bandgaps by 20–180 meV depending on the functional and the n value. The π-bond model gives results that differ significantly from the DFT results when the CNT diameter goes below 1 nm due to the large curvature of the CNT. The π-bond model quickly becomes inaccurate away from the bandedges for a (10,0) CNT, and it is completely inaccurate for n≤8.     

The professionalisation paths of hackers in IT security: The sociology of a divided identity

This article analyses the professionalisation paths pursued by hackers. More specifically, it focuses on the group of those who became socialised as enthusiastic fans of security between 1995 and 2002. The analysis of paths shows that there are four professional routes: integration as an employee, opting to be independent, the path of fraud and parallel remuneration under a masked identity. These paths progressively reflect the procedures for building a divided identity. Either the hacker transforms himself into a security professional through a change of mentality. Or he develops a split identity, by fragmenting his professional identity. Finally, the article highlights two key parameters explaining the orientation towards one or other of these two forms of divided identity: the internalisation of a code of professional practice, a professional ethic and moderation of strategies to build a media reputation.     

The role of gradation on the improvement of effective properties of highly heterogeneous multilayered thermoviscoplastic materials under simple shearing

In this paper we study the role of the gradation on the effective properties of heterogeneous multilayered thermoviscoplastic materials with discontinuous properties under simple shearing. Starting from the bimetallic multilayered material, we produce a new multicomponent material with discontinuous gradation having improved effective properties. We also present the effective properties of the continuously graded material functionally graded material (FGM). The main results are illustrated with some numerical examples.