Extrusion compounding of polyethylene with blowing agent

Cellular plastics are very attractive for the production of lightweight, structural and/or large dimension parts, e.g., boats, floaters, decks, etc. For their production, polymers and chemical blowing agents are either mixed or compounded prior to processing by injection or rotational moulding. It is essential to ensure good dispersion of the blowing agent in the polymeric matrix, and prevent its activation from occurring during compounding, i.e., an optimal processing window must be used. The aim of this work is to produce medium density polyethylene with Azodicarbonamide (MDPE/ADCA) masterbatches in pellet form for further processing by rotational moulding. For that purpose, a set of experimental procedures was conducted to evaluate the correct processing window without premature expansion during extrusion. Upon melt compounding of the masterbatch in pellets of different sizes, foamed parts were produced and characterized in terms of visual aspect, expansion ability and morphology.This project has received funding from the European Union’s Horizon 2020 research and innovation programme under the Marie Skłodowska Curie grant agreement No. 734205 – H2020-MSCA-RISE-201

Film blowing of PHB-based systems for home compostable food packaging

One of the routes to minimize the environmental impact of plastics waste is the use of bio-sourced and biodegradable alternatives, particularly for packaging applications. Although Polyhydroxyalkanoates (PHA) are attractive candidates for food packaging, they have poor processability, particularly for extrusion film blowing. Thus, one relatively successful alternative has been blending PHA with a biodegradable polymer. This work proposes film blowing of a co-extruded Poly (hydroxybutyrate) (PHB) layer with a poly butylene adipate-co-terephtalate (PBAT) layer to enhance bubble stability, mechanical and barrier properties. Co-extrusion is detailed, together with the different strategies followed to improve adhesion between film layers and the PHB content in the films. Films with thicknesses below 50 micron and elongation at break beyond 500 % were consistently produced.This project has received funding from the European Union’s Horizon 2020 research and innovation programme under grant agreement No. 774088. LH also acknowledges funding from the Portuguese Foundation for Science and Technology Investigator Programme through grant IF/00606/2014

Numerical and experimental study of agglomerate dispersion in polymer extrusion

A model for agglomerate dispersion in screw extruders was developed and superimposed on the flow patterns as simulated using the FIDAP software. A particle tracking algorithm with an adaptive time step was used to follow the agglomerates trajectory. Along this flow path, the breakup probability was estimated using a Monte Carlo method and in conjunction with the local fragmentation number. Particle size distributions and Shannon entropy were computed along the screw channel. The results show good qualitative agreement between model predictions and experimental data

The Radial Distribution of Magnetic Helicity in the Solar Convective Zone: Observations and Dynamo Theory

We continue our attempt to connect observational data on current helicity in solar active regions with solar dynamo models. In addition to our previous results about temporal and latitudinal distributions of current helicity (Kleeorin et al. 2003), we argue that some information concerning the radial profile of the current helicity averaged over time and latitude can be extracted from the available observations. The main feature of this distribution can be presented as follows. Both shallow and deep active regions demonstrate a clear dominance of one sign of current helicity in a given hemisphere during the whole cycle. Broadly speaking, current helicity has opposite polarities in the Northern and Southern hemispheres, although there are some active regions that violate this polarity rule. The relative number of active regions violating the polarity rule is significantly higher for deeper active regions. A separation of active regions into `shallow', `middle' and `deep' is made by comparing their rotation rate and the helioseismic rotation law. We use a version of Parker's dynamo model in two spatial dimensions, that employs a nonlinearity based on magnetic helicity conservation arguments. The predictions of this model about the radial distribution of solar current helicity appear to be in remarkable agreement with the available observational data; in particular the relative volume occupied by the current helicity of "wrong" sign grows significantly with the depth.Comment: 12 pages, 8 Postscript figures, uses mn2e.cl

Global mixing indices for single screw extrusion

The present work presents numerical simulations of dispersive and distributive mixing of a two phase system being processed in a single screw extruder under various conditions. Models were developed to quantify the degree of mixing of liquid-liquid and solids-liquid systems, for a given set of material properties, operating conditions and extruder geometry

Stress–strain analysis of a toric pipe for inner pressure loads

This research aims to enhance the knowledge on stress–strain states of a coiled pipe used for Hydraulic transient experiments. The membrane theory of shells of revolution has been applied for the description of axial and circumferential strains while an inverse method has been used to analyse bending effects. The developed stress–strain model has been successfully validated for dynamic loading. Finally, a simplified version of the stress–strain equations is presented with the go alto facilitate fluid–structure interaction FS Iimple- mentation in the hydraulic transient model. The fluid waves peed formula for coiled pipes has been presented

Magnetic field generation in fully convective rotating spheres

Magnetohydrodynamic simulations of fully convective, rotating spheres with volume heating near the center and cooling at the surface are presented. The dynamo-generated magnetic field saturates at equipartition field strength near the surface. In the interior, the field is dominated by small-scale structures, but outside the sphere by the global scale. Azimuthal averages of the field reveal a large-scale field of smaller amplitude also inside the star. The internal angular velocity shows some tendency to be constant along cylinders and is ``anti-solar'' (fastest at the poles and slowest at the equator).Comment: 12 pages, 11 figures, 2 tables, to appear in the 10 Feb issue of Ap

Transverse instability for non-normal parameters

We consider the behaviour of attractors near invariant subspaces on varying a parameter that does not preserve the dynamics in the invariant subspace but is otherwise generic, in a smooth dynamical system. We refer to such a parameter as ``non-normal''. If there is chaos in the invariant subspace that is not structurally stable, this has the effect of ``blurring out'' blowout bifurcations over a range of parameter values that we show can have positive measure in parameter space. Associated with such blowout bifurcations are bifurcations to attractors displaying a new type of intermittency that is phenomenologically similar to on-off intermittency, but where the intersection of the attractor by the invariant subspace is larger than a minimal attractor. The presence of distinct repelling and attracting invariant sets leads us to refer to this as ``in-out'' intermittency. Such behaviour cannot appear in systems where the transverse dynamics is a skew product over the system on the invariant subspace. We characterise in-out intermittency in terms of its structure in phase space and in terms of invariants of the dynamics obtained from a Markov model of the attractor. This model predicts a scaling of the length of laminar phases that is similar to that for on-off intermittency but which has some differences.Comment: 15 figures, submitted to Nonlinearity, the full paper available at http://www.maths.qmw.ac.uk/~eo

Do students with immigrant and native parents perceive themselves as equally engaged in school during adolescence?

Student engagement in school needs to be considered when comparing immigrant and native students, particularly at a timeof increasing migratory movements throughout the world. Diferences in cognitive, afective, behavioral, and agentic studentengagement dimensions were examined for students with immigrant and native parents, and for early and middle adolescence.A four-dimensional measure of student engagement was completed by 643 students (52.7% women). Results indicated that:students with native parents present higher cognitive and agentic engagement than students with immigrant parents; earlyadolescents are more cognitively engaged than middle adolescents; early adolescents with native parents present highercognitive engagement than early adolescents with immigrant parents and middle adolescents. These results contribute toknowledge advancement, enhancing the understanding of student engagement with immigrant and native parents duringearly and middle adolescence, which might stimulate additional research moving towards a more inclusive school. Basedon the fndings and conclusions from this study, possibilities for future research and political-educational recommendationsare presented.info:eu-repo/semantics/publishedVersio