Effect of processing conditions on the formation of polypropylene/organoclay nanocomposites in a twin screw extruder

Polypropylene (PP)/organoclay (Cloisite^©20A) nanocomposites are prepared via direct melt intercalation in a co‐rotating twin screw extruder. Maleic anhydride (MA)‐grafted PP (PP‐g‐MA) is used as a compatibilizer to improve the dispersion of the clay. The formulation used to prepare the nanocomposites is fixed and is equal to 80/15/5 (PP/PP‐g‐MA/Cloisite^©20A), expressed in mass fraction. The objective of the present study is to investigate the effects of processing conditions as well as screw profile upon the formation of PP nanocomposites. The parameters studied are the feed rate and the screw speed, which are varied independently, from 4.5 to 29.0 kg/h and from 100 to 300 rpm, respectively. The state of dispersion is quantified by wide angle X‐ray diffraction (WAXD), transmission electron microscopy, and rheological measurements. WAXD results show that the nanocomposites obtained in different conditions have an intercalated structure, with an increase in interlayer spacing. However, this interlayer spacing is globally unaffected by processing parameters. On the opposite, the proportion of exfoliation, estimated by rheological measurements, is depending on operating conditions (screw speed and feed rate). It increases when the feed rate decreases and the screw speed increases. Investigations on the state of dispersion along the screw profile are also presented. They show that no evolution of intercalated structure is observed along the screws and that screw geometry is only efficient in particular extrusion conditions to delaminate clay platelets. Numerical simulations of the twin screw extrusion process, using the software Ludovic^©, put in evidence that the total strain is a key factor for characterizing the level of exfoliation in the nanocomposites. POLYM. ENG. SCI. 46:314–323, 2006. © 2006 Society of Plastics Engineers     

Shock-induced aggression and reactivity following raphe lesion in rats. Effects of physostigmine (author''s transl)

The hyperkinetic syndrome, such as it is abundantly described in the literature of American authors, is clearly defined by the association in a young child, essentially at the beginning of schooling, of hyper-activity, psycho-motor instability, affective and learning disorders, emotional lability, immaturity, etc. It would appear that psycho-stimulants (in particular amphetamines) bring about a spectacular improvement in these children, representing a therapeutic test that confirms the diagnosis. In America, insistence is placed on the physiopathogeny of the disorders, and on the minimal cerebral dysfunction. This pathology, which, it would appear, does not seem to have been recognised in France, where the psychomotor instability is only one among many symptoms. We report here a synthetic clinical study of hyperkinetic children observed over a period of several years. They are particular in that they were seen at an early age (between 18 months and 4 years old). The psychopathological study of the early stages (which is usually missing in the literature) makes it possible to objectify a preliminary phase dominated by negative signs, of the "silent series": depressive and regressive tendencies, later hidden by agitation. We underline the importance of the early distorsion of the mother-child link, which appears to be a determining factor in the appearance of the hyperkinetic syndrome. These date (which tend to contradict many studies) lead one to reject the chemotherapy solution, and in particular psychostimulants for the greater majority of cases, and rather to intervene at an early stage, and ideally speaking preventively, to instigate above all a psychotherapy of the child and often of the mother (co-therapy), to restore a good level of communication, and the mother-child link. This in-depth approach should make it possible to avoid a purely symptomatic treatment, with its uncertain effects, and its often undersirable evolution.     

Simulation of polymer flow through a coat-hanger die: A comparison of two numerical approaches

Coat-hanger dies are commonly used for the extrusion of plastic sheets and films. To describe the flow of a molten polymer through a coat-hanger die, a two-dimensional approach is necessary. Moreover, the thermal effects, which play an important role in the flow distribution, have to be taken into account. In this paper, two numerical models for the simulation of coat-hanger dies are described and compared. These models differ mainly in the simplifying assumptions used and in the treatment of the thermal problem. The simulations obtained with the two models were compared with each other and with experimental data. The discrepancies between the two models can be explained by the different theoretical treatments.     

Morphometric study of trout gills: a light-microscopic method suitable for the evaluation of pollutant action

1. Methods are described for the morphometric estimation of parameters of the gill system of trout which are relevant to its function in gas exchange. The methods have been used with 1 mum sections viewed under the light microscope. 2. In particular the diffusion distances between water and blood are measured, which together with determinations of gill area, provide figures for the morphometrically estimated diffusing capacity. 3. The methods have been used to compare the diffusing capacity of gills from control fish and those treated in polluted waters. The concept of relative diffusing capacity (Drel) is introduced which enables comparisons to be made without the need to determine the absolute diffusing capacity. 4. Quantitative estimation of changes in relative volumes and surface areas of components of the secondary lamellae were determined, and employed to explain the possible anatomical causes of changes in Drel. 5. It is suggested that these methods can be of value in the comparison of the gills of fish treated in different waters.     

Transfert de matière entre un electrolyte et une paroi cylindrique immergée dans un lit fluidisé liquide—solide: influence de la masse volumique des particules fluidisées

We have studied the influence of the density of fluidised particles on the electrochemical mass transfer rates between a liquid and a surface immersed axially in a fluidised bed. This study leads to the conclusion that for a given flow-rate an increase of the density of the solids causes a corresponding increase in the mass transfer rate to the immersed surface. An empirical correlation of the results and a quantitative interpretation of the influence of the density of the solids on the transfer are given.     

Effects of calcium carbonate and its purity on crystallization and melting behavior,mechanical properties,and processability of syndiotactic polypropylene

Calcium carbonate‐filled syndiotactic poly(propylene) (CaCO₃‐filled s‐PP) was prepared in a self‐wiping, co‐rotating twin‐screw extruder. The effects of CaCO₃ of varying particle size (1.9, 2.8 and 10.5 μm), content (0–40 wt %), and type of surface modification (uncoated, stearic acid‐coated, and paraffin‐coated) on the crystallization and melting behavior, mechanical properties, and processability of CaCO₃‐filled s‐PP were investigated. Non‐isothermal crystallization studies indicate that CaCO₃ acts as a good nucleating agent for s‐PP. The nucleating efficiency of CaCO₃ for s‐PP was found to depend strongly on its purity, type of surface treatment, and average particle size. Tensile strength was found to decrease, while Young's modulus increased, with increasing CaCO₃ content. Both types of surface treatment on CaCO₃ particles reduced tensile strength and Young's modulus, but improved impact resistance. Scanning electron microscopy (SEM) observations of the fracture surfaces for selected CaCO₃‐filled s‐PP samples revealed an improvement in CaCO₃ dispersion as a result of surface treatment. Finally, steady‐state shear viscosity of CaCO₃‐filled s‐PP was found to increase with increasing CaCO₃ content and decreasing particle size. © 2004 Wiley Periodicals, Inc. J Appl Polym Sci 92: 201–212, 2004     

Measurement of the coefficient of dynamic friction at extrusion processing conditions

The dynamic friction coefficients of several polymers have been investigated using a specific rotating device similar to an extruder. The increase in temperature during the measurements made it necessary to develop a theoretical approach in order to interpret the experimental data correctly. The rotation speed and particle shapes were found to have little influence on the friction coefficient. For HDPE and PVC, the friction coefficient decreased slightly with interfacial temperature, whereas it remained constant for PP. The order of magnitude of the friction coefficients was similar to what has already been published in the literature.