Climate-related reporting by publicly listed companies in The Netherlands: an attention-action mapping

Against the backdrop of increasing calls for mandatory and voluntary climate-related disclosures by companies, this article provides insight into how the (integrated) annual reports of companies listed on the AEX index in the Netherlands, communicated companies’ engagement with climate issues from 2016 to 2018. Drawing on research in the cognitive psychology domain, the article examines companies’ reported attention to climate change as well as their climate-related actions. It shows that although there are noticeable climate attention and action differences among AEX companies, over time the companies as a whole have started doing more in relation to climate – for example, in terms of attention, there is increase in the inclusion of climate considerations in strategy making and, in terms of action, there is increase in the inclusion of climate in material risks. The article discusses the research findings, which have implications for effective governance by corporate boards

Modeling of synthesis and flow properties of propylene-diene copolymers

Copolymerization with nonconjugated dienes offers an attractive route for introducing long-chain branching in polypropylene. From a simplified set of rate equations for such copolymerization with a metallocene catalyst, we derive the probabilities of branch formation at different stages of the reaction in a semibatch reactor. Using these probabilities, we generate an ensemble of molecules via a Monte Carlo sampling. The knowledge of the branching topology and segment lengths allows us to compute the flow properties of the resins from computational rheology. We compare our model predictions with existing experimental data, namely the molar mass distribution and small amplitude oscillatory shear response, for a set of resins with varying diene content. The rheology data suggest that the entanglement time Ï.,e depends sensitively and in a well-defined fashion on the diene content

Onset of the sharkskin phenomenon in polymer extrusion

A specific form of melt flow instabilities associated with surface defects for polymer extrudates, and commonly referred to as the "sharkskin effect", is modeled. When this effect occurs, a more or less regular pattern of ridges on the surface is observed resembling the skin of a shark if bent. It is shown that the relaxation oscillation model of Molenaar and Koopmans [J. Rheol. 38, 99 (1994)] developed to describe "spurt" defects — in this perturbation not only the surface but the extrudate as a whole shows distortions — can be expanded to include a description for the dynamics of surface defect appearance. By introducing a nonlinear viscoelastic constitutive equation (Kaye-Bernstein-Kearsly-Zapas model) into the relaxation oscillation model a boundary layer can develop which shows oscillating behavior. Explicit criteria for the onset of this behavior are derived. The relations between these criteria and experimental parameters are pointed out. This allows for an experimental verification of the supposition that this kind of solution is the origin of the sharkskin effect. The current macroscopic approach may form the basis for the reconciliation of the debate on the origin of melt flow instabilities as either a "slip at the wall" or a nonmonotone "constitutive equation" phenomenon

Quantitative modelling of HDPE spurt experiments using wall slip and generalised Newtonian flow

A quantitative model to describe capillary rheometer experiments is presented. The model can generate ‘two-branched' discontinuous flow curves and the associated pressure oscillations. Polymer compressibility in the barrel, incompressible axisymmetric generalised Newtonian flow in the die, and a switch curve that defines a stick-slip boundary condition are key elements in the model. Well defined experimental results of high density polyethylene are used to validate the model. The calculations compare well with the experiments. The only fit parameters are those related to the slip law. The present model can be made fully predictive by relating the slip law to fundamental polymer-wall interaction properties. The model offers a mathematical framework to validate potential slip laws

Constitutive model parameters estimation from rheotens steady state and resonance characteristics

This paper presents a method to determine the parameters in a polymer constitutive model using data obtained from a Rheotens experiment. The novelty of the suggested approach is the simultaneous fitting of model parameters to different types of data given by Rheotens, i. e., force-velocity curve, onset of draw resonance and frequency of oscillations. To determine the onset and frequency of oscillations, a stability analysis is exploited and the spectrum of a quasi-hyperbolic differential operator is calculated. The proposed approach is efficient and accurate. To demonstrate its applicability and consistency, a modified Giesekus constitutive model is chosen and model parameters are fitted to the Rheotens data for three different types of polymer (LLDPE, PP, PS)

Comparing the wall-slip and the constitutive approach for modelling spurt instabilities in polymer melt flows

At high flow rates during polymer melt extrusion, pressure oscillations can be observed. The phenomenon is usually referred to as spurt, due to the irregular—in bursts—emergence of the melt out of the die. Spurt, or equivalently, the associated pressure oscillations have been modelled successfully through the mechanism of relaxation-oscillations by Molenaar and Koopmans. The presence of a non-monotone flow curve is at the heart of this modelling. In this paper the curve is deduced from conservation laws combined with a die wall boundary condition and specific constitutive equations. Subsequently, three ‘model curves' are compared. Model A, a Newtonian fluid with a ‘switch function' defining an alternating stick-slip boundary condition. Model B is a non-monotone constitutive equation i.e. a Johnson-Segalman-Oldroyd (JSO) fluid with a no-slip condition. Model C consists of two Newtonian fluids in concentric die regions and a no-slip condition. It is shown that Models A and C are able to describe spurt that is in qualitative agreement with experiments reported in literature. Model B, however, does not lead to spurt, in spite of the non-monotone nature of the steady stress–strain rate curve! These results tend to show that there are many options to describe experimental flow curves with equations based on geometrical, operational and polymer property parameters. Accordingly, from a mathematical point of view, and in view of the equivalence in results between model A and C, it can be concluded that the existing controversy between slip or no-slip (i.e. constitutive) supporters is not a fundamental one

Numerical prediction of nonlinear rheology of branched polymer melts

In a recent short communication [Read, D. J. et al., Science 333, 1871 (2011)], we showed that a computational scheme can describe the nonlinear flow properties for a series of industrial low-density polyethylene (LDPE) resins starting from the molecular architecture. The molecular architecture itself is determined by fitting parameters of a reaction kinetics model to average structural information obtained from gel-permeation chromatography and light scattering. Flow responses of these molecules in transient uniaxial extension and shear are calculated by mapping the stretch and orientation dynamics of the segments within the molecules to effective pom-pom modes. In this paper, we provide the details of the computational scheme and present additional results on a LDPE and a high-density polyethylene resin to illustrate the dependence of segmental maximum stretch variables on the flow rate

Compatibilization of polypropylene–polyethylene blends

Many plastic waste recycle streams are blends of various types of polypropylene (PP) and polyethylene (PE). When reprocessing these blends into products it is difficult to obtain good mechanical and optical properties due to the immiscibility of the components. Blend morphology is one of the governing factors for these properties. Therefore morphology control is a key challenge when turning plastic waste into valuable materials. In this work, the effect of a novel polymeric compatibilizer on the morphology of PP–PE blends was investigated via rheological and scanning electron microscopy experiments. Homopolymer PP was combined with PE of varying comonomer level. In addition to the effect of including compatibilizer, the effect of blend ratio and viscosity ratio is discussed. It was found that very fine dispersions could be obtained when including the compatibilizing polymer for all studied systems. The blend rheology was compared with predictions from empirical and physics-inspired mixing rules. The difference between measured and predicted rheology is expected to provide insight into the structure of the various blend systems. POLYM. ENG. SCI., 58:460–465, 2018

Compatibilization of polypropylene – polyethylene blends

Many plastic waste recycle streams are blends of various types of polypropylene (PP) and polyethylene (PE). When reprocessing these blends into products it is difficult to obtain good mechanical and optical properties due to the immiscibility of the components. Blend morphology is one of the governing factors for these properties. There-fore morphology control is a key challenge when turning plastic waste into valuable materials. In this work, the effect of a novel polymeric compatibilizer on the morphology of PP – PE blends was investigated via rheological and scanning electron microscopy experiments. Homopolymer javascript:void(0);PP was combined with PE of varying comonomer level. In addition to the effect of including compatibilizer, the effect of blend ratio and viscosity ratio is discussed. It was found that very fine dispersions could be obtained when including the compatibilizing polymer for all studied systems. The blend rhe-ology was compared with predictions from empirical and physics-inspired mixing rules. The difference between meas-ured and predicted rheology is expected to provide insight into the structure of the various blend systems