International Polymer Processing Journal of the Polymer Processing Society

Published by Carl Hanser Verlag
Print ISSN: 0930-777X
Since the past few decades, environmental issues have become a serious concern in society. It is a requisite for the industry to minimize waste, in order to protect the environment from being polluted. The term waste here comprises processing waste and post-consumer waste. The amount of processing waste should not be underestimated since it might consist of approximately 10 % of the total production. The recycling of EPDM rubber is an interesting topic, especially if considered in connection with the continuous market growth of EPDM. This paper is a summary of efforts that have been taken so far on this subject. Studies done on EPDM recycling include reusing EPDM as filler in new rubber products and chemical, thermal, and mechanical devulcanization of EPDM in order to achieve a material that resembles the virgin one and could be revulcanized. Such studies on EPDM recycling are discussed extensively and in the conceptual frame of more general rubber recycling processes.
Advances in micromoulding technology are leading to complex,net-shape products having sub-milligramme masses with micro-scale surface features in a range of polymer and nano-composite materials.For such small components subjected to the extreme stress,strain-rate and temperature gradients encountered in the micromoulding process,detailed process monitoring is desirable to highlight variations in moulding conditions and assist in creating a viable manufacturing process with acceptable quality products.This paper covers the implementation of a suite of sensors on a commercial micromoulding machine and detailed computer monitoring during processing of a polyacetal component over a range of processing conditions.The results determined that cavity pressure curve integral data provides the most sensitive factor for characterisation of a moulding process of a 0.34 mm~3(0.49 mg)product.The repeatability of the process is directly compared with that of a 15.6mm~3(22.2 mg)product and shown to beinferior.DSC measurements of the whole products indicated little variation in average crystallinity of the products manufactured over a mould temperature range of 30 to 130deg C.
Several studies have shown that deformation and breakup of dispersed droplets is easier in extensional than in shear flow field and this is particularly true for systems with high viscosity ratios. The simplest way to generate a significant extensional flow field in compounding equipment is to use converging flow conditions. In this work, the mixing efficiency of converging flow has been investigated as a function of the entry profile and the flow rate by using a capillary rheometer equipped with dies of different geometries. The material used for this study was a bimodalpolyethylene presenting inhomogeneities due to the high viscosity ratio between the low and high molecular weight fractions. The results indicated that the mixing performance depended strongly on the die geometry and flow rate. A critical flow rate was observed for each particular entry profile at which the highest efficiency was observed. This critical flow rate was found to correspond to the onset of melt flow instabilities.
The flow of a silicone oil of high viscosity along a block of staggered kneading discs of a co-rotating twin screw extruder was investigated with the use of an acrylic transparent barrel. A digital video camera recorded the flow path of a red dye, dispersed in the silicone oil, along the screws and in the intermeshing zone. Different geometrical configurations were studied, namely various staggering angles (+30degrees, 90degrees and -30degrees) and thicknesses (7.5, 15.0 and 22.5 mm) of kneading blocks. The effects of these geometrical parameters on the pressure generation and filling ratio were investigated. It was observed that, even for negative staggering, the filling ratio of the kneading block was lower than one. Based upon these experiments, analytical expressions describing the filling ratio as function of geometry (staggering angle, thickness and number of discs) and operating conditions (feed rate and screw speed) were derived.
The characteristics of sharkskin surface instability for linear low density polyethylene are studied as a function of film blowing processing conditions. By means of scanning electron microscopy and surface profilometry, is it found that for the standard industrial die geometry studied, sharkskin only occurs on the inside of the film bubble. Previous work suggests that this instability may be due to critical extensional stress levels at the exit of the die. Isothermal integral viscoelastic simulations of the annular extrusion process are reported, and confirm that the extensional stress at the die exit is large enough to cause local melt rupture. However, the extensional stress level at the outer die wall predicts melt rupture of the outside bubble surface also, which contradicts the experimental findings. A significant temperature gradient is expected to exist across the die gap at the exit of the die, due to the external heating of the die and the low conductivity of the polymer melt. It is shown that a gradient of 20°C is required to cause sharkskin to only appear on the inner bubble surface.
This paper describes an original on-line video device developed in order to study bubble instabilities occurring in the film blowing process, taking into account their three-dimensional behavior For a linear low-density polyethylene, two forms of instabilities and combination have been observed: draw resonance and helical instability. These instabilities could be quantitatively described and differences in behavior could be assessed using real objective measurements and criteria. The influence of key processing conditions was investigated and the results showed that the instabilities are enhanced by increasing the draw ratio, blow up ratio and frost line height. These first results are in agreement with the majority of the results reported in the literature, but allow for a more accurate analysis of the phenomena.
Film blowing, as other elongational polymer forming processes, may present marked drawing instabilities leading to unacceptable products. But in film blowing, these instabilities are much more complex than for example in fibre spinning: there is no stabilizing effect of the polymer cooling, and the symmetry of the process may be broken, leading in some processing conditions to so called helical instabilities. Stability of the process has been investigated using a strategy inspired from shell or homogeneisation theory: as the classical approach uses a frame locally affixed to the membrane, the equations of the problem are now written in the cartesian laboratory frame. Making the equations dimensionless introduces naturally a small parameter defined as an aspect ratio (ratio of the film thickness to the bubble radius). Kinematic and stress variables are expanded as a function of this small parameter and introduced in the equations. It leads classically to a sequence of equations at successive orders. This strategy is used to obtain a time dependent membrane model. The stationary solution is equivalent to the one obtained using the classical approach. This model allows to develop a stability analysis, first in the axisymmetric case and then in the non axisymmetric one. Even a crude Newtonian temperature dependent rheology allows to capture qualitatively the observed instability phenomena.
Elongation at break is one of the major end-use properties of polyamide 12 extruded tubes. It is strongly affected by the tube microstructure and the molecular orientation resulting from extrusion conditions. Molecular orientation was characterized by X-ray diffraction and birefringence evaluation in light microscopy. Measurements were carried out on (r z) sections obtained by polishing and microtoming. On the other hand, polymer drawing was measured on line by tracer techniques. Calibration stage was determined as the key step of the process that generates orientation in tubes: as the tube is drawn through a cylindrical calibrator under vacuum and cooled from its outside surface, calibration leads to a highly oriented zone in the twenty external microns. Calibration conditions and elongation at break have been connected through orientation level in this region. Molecular orientation was found to strongly depend on the draw ratio in the calibration tank. Finally, birefringence of the tube external layers and elongation at break were successfully correlated. Elongation at break can be enhanced by reducing orientation resulting from calibration conditions.
In PA12 tube extrusion, calibration or sizing is the key step of the process that affects subsequent mechanical properties. The extruded tube is pulled through a cylindrical calibrator under vacuum. A water flow rate is applied at the inner side of the calibrator, creating a lubricant water layer at the polymer outer surface. The scope of this article is to show how this lubrication influences the elongation at break of tubes through drawing kinematics of the polymer. Lubricant water layer thickness measurements and on-line video recording have been employed to monitor the lubrication dependence of the velocity profiles from the extruder die to the end of calibrator. Velocities were measured through three independent innovative methods and thirty-two calibration conditions have been carried out to validate our work. Three main calibration parameters were found to determine the water layer thickness: the level of vacuum applied in the calibration tank, the water flow rate at the calibrator entrance, and the line speed. The influence of each parameter on lubrication level was found out. Simultaneously, the draw ratio in the calibration tank was deduced from velocity profiles. This parameter was found to affect tensile properties and to depend strongly on the level of lubrication during calibration. We showed quantitatively that using the water layer thickness leads to a diminution of the draw ratio in the calibration tank and an increase of the elongation at break. This implies that we are now able to optimize tensile properties by fitting the main calibration parameters to improve lubrication and restrict draw ratio in the calibration tank.
The purpose of this work is to model the bulk polymerization of epsilon -caprolactone in a corotating twin screw, extruder: Starting from kinetic data and rheological laws previously defined, we nse a twin screw flow modelling software to calculate the progress of the polymerization along the extruder Experiments are performed to assess the influence of processing conditions (feed rate, screw speed, barrel temperature, initiator concentration) and to validate the model. They put in evidence the control of the polymerization process by the temperature and the residence time in the extruder. It is shown that a good correlation between theoretical and experimental results can only be obtained if accurate kinetic and rheological data are used in the model.
Two important instabilities associated with carrier layer formation on the inclined plane of slide-fed coating processes are explored, with a two liquid layer prototype configuration employed to mimic the slide-bead process as used by industry. The work relates to both slide-bead and curtain coating methods. Experiments first reveal how broad diffuse bands, that destroy the quality of the final coating, are formed as the carrier layer flow rate is reduced. The bands are found to be exacerbated by either decreasing the viscosity or flow rate of the carrier layer or by increasing the viscosity of the upper layer. As the flow rate of the carrier layer is reduced further, the upper layer begins to invade the carrier layer delivery slot. Flow visualisations reveal that a parallel sided delivery slot is superior to a chamfered one in terms of robustness against invasion of the interface and that reducing the slot width increases robustness further. Experiments and complementary numerical simulations confirm the existence of a recirculating eddy near the top of the downstream wall as the carrier layer flow rate is reduced and this insight is used to propose an instability mechanism for the onset of the bands. Further experiments expose the mechanism for the formation of cross bars. These can develop downstream of the carrier layer delivery slot and arise because the merging of the layers there becomes increasingly influenced by the flow, demonstrating that the sensitivity of cross bars to pump induced disturbances grows rapidly as the critical carrier layer flow rate for instability is approached and then collapses as the flow rate is reduced to a value where the layer is no longer effective in lubricating the flow of adjacent layers.
The flow of molten polymers in corotating twin screw extruders has been largely studied, but little attention has been paid until now to the melting process. In the present work, we develop an experimental study of melting in twin screw extruders, including pressure and temperature measurements, dead-stop experiments and sampling, observation of cross sections and quantification of solid fraction. The influences of process parameters (screw speed and feed rate), screw profile, pellets size and extruder size are also investigated. An original model of the melting process is proposed, deduced from these observations. This model allows one to calculate the evolution of mean shear, rate, pressure gradient, dissipated energy, pellet radius and both solid and liquid temperatures along the screws, for a sequence of right- and left-handed screw elements and blocks of kneading discs. The results of the model are in good agreement with the experiments.
In view of optimizing the industrial compression molding process of thermoplastic composites, the rheological and microstructural behavior of a polypropylene/glass fiber composite is investigated in model squeeze-flow geometries. The overall stress/strain behavior of the material at various compression rates is recorded and the induced orientation of the fibers is investigated by means of a special electron microscopic characterization method. By contrast to pure polypropylene, it is shown that in the high speed range, the macroscopic flow process is controlled by both the viscous extension and the relative sliding of parallel fibrous layers, the latter becoming unstable when the flow undergoes a rapid transition from divergent to convergent. Under high pressure, voids are dissolved in the polymer melt. In the case of non-isothermal compression, the rheology of the composite is not significantly affected by the cooling of the surface layers. The multilayer plug-flow model based on the sliding mechanism of viscous layers is found to reproduce correctly the experimental stress/strain behavior.
The clay-containing polymeric nanocomposites (CPNC) can be visualized as binary mixtures of strongly interacting, inorganic, plate-like molecules dispersed in a polymeric matrix. To be successful, one must ascertain the thermodynamics, which controls CPNC structure on the molecular level. In this work dispersion of organoclay (Cloisite 15A, C15A) in polyamide 6 (PA 6) or in polypropylene (PP) is discussed. The PA-based CPNC's contained two components: polymer and organoclay, whereas those based on PP in addition contained a mixture of two maleated polypropylene's (PP-MA), as a compatibilizer. The melt compounding was carried out either in a single-screw extruder (SSE), or a twin-screw extruder (TSE). Both compounding lines were used with or without the extensional flow mixer (EFM). Furthermore, two versions of EFM were evaluated - one commercial, designed for polymer homogenization and blending, and the other designed for dispersing nano-particles. It was found that addition of EFM significantly improved clay dispersion. Better dispersion was found compounding the CPNC's in a SSE + EFM than in TSE with or without EFM. The best results were obtained using SSE with the new EFM having a relatively small gap between the convergent-divergent plates. C15A was fully exfoliated in PA 6 matrix. The results in PP/PP-MA matrix were less spectacular, but again the highest degree of dispersion was obtained using SSE + new EFM with a small gap. Tensile, flexural and impact properties were measured and evaluated.
The present paper discusses the uniqueflow behavior in a new type of extruder. The extruder design is based on a hollow conical assembly of static (stators) and rotating (rotor) parts. Extrusion is achieved from each side of the rotor to provide a two-layer annular product. Flow is helicoidal in the vicinity of the rotor tip and die entry where the polymer layers merge. However, it becomes fully parallel to the main extrusion direction after a certain distance downstream from the rotor tip. Numerical simulations based on the resolution of Navier-Stokes equations using a Generalized-Newtonian viscosity showed that the length of the helicoidal flow depends on die design, viscosity and flow rate ratios between adjacent polymer layers. Analysis of flow variables along the interface showed that the helicoidal flow distance can be increased using a die design inducing lower interfacial shear rate and velocity. When the viscosity ratio and the flow rate of the most viscous polymer are increased, the helicoidal flow can be maintained over a longer distance in the die. Finally, experiments have shown that the advantage of the helicoidal flow is for short fiber orientation in pipes. The fibers are oriented along the streamlines in the hoop direction in the mid-gap of the die; however, they are parallel to extrusion direction in the vicinity of the stators.
Variation of torque and temperature during melting process of 50 g LDPE. Temperature: 200 8C and rotation speed: 28 min –1  
Moving standard deviation (MSD) of (A) amplitude of L 1 , (B) peak amplitude of L 2f and (C) time delay between L 1 and L 2f . echoes. Window size of MSD is 3 sample points  
Variation of melting period and peak torque with rotation speed
Mixing chamber with rotating blades, thermocouple and ultrasonic delay line probe  
Real-time, non-intrusive and non-destructive ultrasonic technology has been used to monitor the melting process in an internal mixer. Visual observation, mechanical torque measurement, and ultrasonic signatures. such as amplitude and time delay of transmission and reflection echoes were used for the diagnosis of the melting process of low density polyethylene (LDPE). phenomena during the melting process, including phase change from solid to melt, partially melted pellets, air bubbles inside the melt, were successfully monitored by ultrasound. The ultrasonic signatures were able to determine when the polymer has melted completely. The method of moving standard deviation (MSD) was applied to establish the melting completion timing accurately. Higher temperature of mixing chamber and faster rotation speed of blades reduced melting completion period, indicated by MSD of ultrasonic signatures. The presented ultrasonic technique can be utilized to optimize the melting process.
Mean error of velocity components with respect to the reference solution
This work is aimed at the numerical modeling of the flow inside single and twin-screw extruders. Numerical solutions are obtained using a recently developed immersed boundary finite element method capable of solving the flow in the presence of complex non-stationary solid boundaries. The method is first validated against the solution obtained on a body-conforming grid for a single screw extruder and then applied to a twinscrew mixer. The time dependent single screw problem can also be solved in a rotating reference frame for which a steady state solution can be obtained. This allows the evaluation of time integration errors of the moving immersed interface algorithm. For instance the flow is considered isothermal and the material behaves as a Generalized Newtonian fluid. Because the viscosity depends on the shear rate, solutions will be shown for various rotation velocities of the screw and compared with solutions obtained on body-conforming grids. The method is shown to give very accurate results and can be used for a more in-depth investigation of the material behavior in extruders.
The ability to predict segregation of the solid phase in processes such as powder injection molding and injection molding of semi-solid materials is of special interest since such phenomenon affects the final properties and characteristics of the molded parts. In powder injection molding, for example, defects appear very often in the debinding and sintering stages but are caused by filling problems and determined by a non-uniform distribution of the solid particles within the molded part. In this paper we propose a 3D numerical solution algorithm for the simulation of particle migration in dense suspensions. The particle migration is modeled using the diffusion flux model and integrated into the NRC's 3D injection molding software. The solution algorithm is validated by solving flow problems for which experimental and numerical data are available: circular Couette flow, piston driven flow and sudden contraction-expansion flow. Since it is observed that the piston movement in the sleeve can induce particle migration even before the material enters the cavity, an ALE (Arbitrary Lagrangian-Eulerian) formulation is also developed to include the piston movement in molding simulations. The ALE formulation is first compared with an Eulerian solution for the case of the piston driven flow problem. Then, the approach is applied to injection molding problems and the segregation inside the molded parts is studied.
Particle size distribution strongly affects physical and mechanical properties of filled polymers. A new model has been developed to predict agglomerate size distribution in a twin-screw extruder (TSE). The model considers the break-up and erosion processes and it uses agglomerate size population balance in its mathematical formulation. The model parameters were evaluated in simple field flow. This paper shows the validation of the model along the extruder using different screw configurations of a short twin screw extruder Flow parameters along of the TSE necessaries to apply the new dispersion model have been calculated with (C)Ludovic sofiware. Calcium carbonate filled polypropylene system was used as model compound. The agglomerate size distribution was evaluated from micrographs of polished samples at different locations along the extruder obtained by reflected light microscopy in conjunction with-semiautomatic image analysis.
There are several reports indicating that deformation and breakup of dispersed drops is easier in extensional flow field than that in shear. This is particularly true for the systems containing the dispersed phase significantly more viscous than the matrix, e.g., blends in which the viscosity ratio λ ≡ ηdisp/ ηmatrix ≥ 3.8. These reports led to development of an extensional flow mixer, EFM, a device in which multicomponent, multiphase system [e.g., polymer alloys, blends, master-batches, filled systems] can be hydrodynamically mixed by flowing through a series of convergent/divergent regions of increasing intensity. To be effective, EFM must be attached to a machine capable of melting and pressurizing the compound, preferably a single-screw extruder, SSE. In this paper, efficiency of two compounding systems is compared, the first is made of a SSE and an EFM, while the second is a twin-screw extruder, TSE. To evaluate the efficiency three types of blends, all characterized by high viscosity ratio, λ ≥ 3.8, were used: (i) high density polyethylene dispersed in polystyrene, HDPE/PS, (ii) polypropylene impact-modified by addition of an ethylene-propylene elastomer, EPR/PP, and (iii) ultrahigh molecular weight polyethylene added to high density polyethylene, UHMWPE/ HDPE. System (i) was used to study the effect of compounding on blend's morphology - the dispersion from the SSE + EFM compounding unit was significantly finer than that from TSE. System (ii) was selected to examine usefulness of EFM for impact modification. The results demonstrated that SSE + EFM provided milder compounding conditions that less shear-degraded PP than TSE. The impact strength of specimens prepared in SSE + EFM was superior to that of blends compounded in TSE. The system (iii) was studied to examine the relative merit of SSE + EFM over TSE to produce a finer dispersion of the UHMWPE domains that in turn would result in better dissolution of this ultrahigh molecular weight fraction. Again in this case the SSE + EFM compounder outperformed TSE - the dissolution of UHMWPE was significantly better without parallel degradation of the resin.
Hot embossing is a compression molding technique used for high replication accuracy of small features. One of the most sensitive phases of the process is the de-embossing stage during which the patterned part has to be demolded. In this paper, the demolding stage is considered as a frictional contact problem between a rigid mold insert and a viscoelastic polymer sheet as it deforms and cools inside a mold under an applied force. The contact is modeled with a modified Coulomb's law of dry friction while a generalized Maxwell model is used to describe the polymer behavior during embossing, cooling and de-embossing stages. The heat tran. fer between the mold insert and the patterned polymer sheet is solved through a domain decomposition method. A finite element approximation based on a penalized technique is proposed and analyzed. The purpose of this modeling approach is to predict dimensional stability and residual shape of microcomponents in the hot embossing process. Such a prediction will allow one to assign appropriate processing conditions that minimize geometrical imperfections and increase replication accuracy.
Metal injection molding (MIM) is similar to plastic molding in many respects, but MIM compounds (metal powders with polymer binders) are more susceptible to thermally induced flow instability because of their higher thermal diffusivity. The flow patterns for a 17-4PH MIM compound were observed and simulated for mold filling through a diaphragm gate over a range of filling times and melt-mold interface temperatures. Simulation predicted the observed free annular jet and internal voids in the molded part and also predicted that initial contact with the outside wall of the gate would eliminate the jet, thereby reducing voids and surface defects. Parts made using a mold with a thicker gate verified these predictions. For combinations of operating conditions and mold geometry that gave large thermally induced viscosity gradients, both observation and simulation showed unstable, asymmetric flow. In these cases, flow slowed and stopped in one region of the gate and accelerated in other regions. When the flow was inherently unstable, simulations predicted an exponential growth in maximum temperature differences at symmetric locations in the mold gate. Based on 34 experimental observations and 102 simulations, a boundary was established between regions of stable and unstable flow in terms of the dimensionless Graetz number Gz (ratio of heat conduction time to fill time) and B, a dimension-less ratio indicating the sensitivity of viscosity to temperature differences in the mold. To establish a common basis for comparison of simulation and experiment, the melt-mold interface temperature was estimated using a heat transfer coefficient, which was a fixed value for experiment and a parameter for simulation.
he problem of setting the best operating conditions of a co-rotating twin-screw extruder is solved using an optimization approach based on Genetic Algorithms. Two possibilities are considered: i) the maximization of an objective function; ii) the simultaneous optimization of the individual criteria and the use of Pareto plots. The flow conditions inside the machine are simulated using the Ludovic© software. Various practical case studies are discussed, among them a reactive extrusion application. Generally, the methodology is sensitive to the influence of the main process criteria and provides solutions that are apparently sound.
This paper describes work carried out in order to match experimental processing flows to numerical simulation. The work has brought together a consortium that has developed reliable experimental methods by which processing flows can be achieved in the laboratory and then ranked against numerical simulation. A full rheological characterisation of a selected range of polymers was made and the results compared from different laboratories. The data was fitted to a number of rheological models. Multi-mode parameter fitting was universal for the linear viscoelastic response. Particular attention was paid to the non linear response of the material. Prototype industrial flow experiments were carried out for a number of geometries in different laboratories and the flow birefringence technique was used to map out the experimentally observed stress fields for different polymers in a range of complex flows that contained both extensional and shear flow components. Numerical simulation was carried out using a number of algorithms and a range of constitutive equations. In order to make a quantitative comparison between experiment and simulation, an Advanced Rheological Tool (ART) module was developed that was able in some cases to quantify the level of fit between the numerically predicted and the experimentally observed stress patterns. In addition the ART module was able to optimise certain non-linear parameters in order to improve the quality of fit between experiment and simulation.
This paper presents an application of the Continuous Sensitivity Equation Method (CSEM) for the optimization of the injection molding process and its three-dimensional (3D) simulation by the finite element method. Finding the proper combination of process parameters such as injection speed, and melt and mold temperatures is critical to achieving a part that minimizes warpage and has the desired mechanical properties. Very often a successful design in injection molding comes at the end of a long trial and error process. Design Sensitivity Analysis (DSA) can help manufacturers improve their designs and can produce substantial savings in terms of both time and money. This work explores the ability of sensitivity analysis to predict the effects of design parameters on the performance of an injection molding process. The paper presents results of a 3D finite element solution of the filling stage of the injection molding process. Sensitivities of the solution with respect to different process parameters are computed using the continuous sensitivity equation method. Solutions are shown for the non-isothermal filling of a rectangular plate with a polymer melt behaving as a non-Newtonian fluid. The paper presents the equations for the sensitivity of the velocity, pressure and temperature and their solution by a finite element method. Sensitivities of the solution with respect to the injection speed, the melt and mold temperatures and to the heat transfer coefficient at the cavity/mold interface are shown.
Atactic polystyrene (PS) was used to study the effect of flow field (shear and/or elongational) on the intercalation of polymer/clay nanocomposites (PNC). Three grades of (PS), with different molecular weights, were compounded with an ammonium-modified montmorillonite (Cloisite 10A) in a twin-screw extruder (TSE). The compounds were subsequently fed to a single screw extruder, fitted with one of three specially designed torpedo-attachments. The attachments were designed to provide combinations of different levels of shear and elongational deformations. The resins, TSE compounds, and final PNC's were characterized for the degree of intercalation, degradation, rheological behavior, and mechanical properties. The data showed that the thermal decomposition of the quaternary ammonium intercalant caused severe damage to both PNC components: a collapse of the organoclay interlayer spacing, and the thermo-oxidative degradation of PS. In spite of these detrimental effects, the attachment employing combined elongational and shear flow resulted in generally larger gallery spacing and more improvement of the mechanical properties than the other two attachments.
This paper mainly treats the thermal effects during the thermoforming process while most of the previous analyses consider an isothermal deformation. A non isothermal three dimensional finite element model of the thermoforming process is proposed. It couples the thermal equations in the thickness and mechanical equations on the mean surface of the sheet. The mechanical resolution is done by a finite element method using a membrane approximation. The deformation is driven by a pressure difference through the sheet. The thermal resolution uses a one dimension finite element method in the thickness with convection or conduction at the surface and dissipation of mechanical energy. The polymer cooling is very efficient during the contact with the tools. The coupling is done by the thermal dependent rheology. The respective contributions of friction and thermal effects in the thickness of the part during the process are discussed. The model also considers a possible multilayered material, with specific rheological parameters inside each layer. The rheology of a polystyrene was measured under elongation as a function of temperature, strain and strain-rate and described by a visco-plastic law. The predictions of the model were compared with measurements on an instrumented thermoforming machine and with the local thickness of axisymmetrical parts and with 3-D parts thermoformed with the same polystyrene.
A summary of recent technological developments related to large diameter screw extruders is presented. Special attention is given to cascade screw extruders.
Formulaire Crown Copyright non disponible Boucherville IMI-118613 Yes
In the use of corn raw materials to produce glycol (corn-EG) and 1,2-propanediol (PDO), the output of PDO is more than that of corn-EG and the latter also contains some PDO. In order to produce high-performance polyester fibers by low-cost corn-EG instead of petroleum-EG, the paper initially seeks for the highest percentage of PDO that can be added in the conventional copolymerization of corn-EG/PDO/nano-SiO2 and terephthalic acid (PTA). The experiment shows that as the content of PDO in copolyester exceeds 12 %, the POY breaking strength quickly decreases. The DTY of copolyester fiber with 12 % PDO and 0.1% nano-SiO2 can be dyed in the condition of atmospheric pressure and boiling water.
In the use of corn raw materials to produce glycol (corn-EG) and 1,2-propanediol (PDO), the output of PDO is more than that of corn-EG and the latter also contains some PDO. In order to produce high-performance polyester fibers by low-cost corn-EG instead of petroleum-EG, the paper initially seeks for the highest percentage of PDO that can be added in the conventional copolymerization of corn-EG/PDO/nano-SiO2 and terephthalic acid (PTA). The experiment shows that as the content of PDO in copolyester exceeds 12 %, the POY breaking strength quickly decreases. The DTY of copolyester fiber with 12% PDO and 0.1% nano-SiO2 can be dyed in the condition of atmospheric pressure and boiling water.
This paper presents the results of an experimental study of the unstable capillary flow of HDPE/PA 11 blends with special emphasis on the pressure oscillation region. The main result is the finding that addition of only 1 % by weight of the PA 11 component to HDPE completely suppresses the oscillation phenomenon normally found with the latter polymer when the measurement is carried out in a rheometer with a plane capillary entrance. In comparative experiments with a capillary rheometer with a conical (120°) entrance, the pressure oscillation effect disappeared at a PA 11 content of 5%. In compounds containing 1, 3 and 7 % PA 11, distinct pressure oscillations were recorded in the latter case. The stress and elongation at break of the extrudates change in a monotonic fashion with the composition. SEM photographs and DSC measurements show that the two components are basically immiscible.
A basic study of the development of crystallinity and polymer chain orientation in melt spinning and drawing nylon-11 and nylon-12 fibers is presented. The fibers were examined using wide angle x-ray diffraction, differential scanning calorimetry and optical retardation (birefringence) measurements. Melt spun nylon-11 fibers possesses an α-triclinic structure, while melt spun nylon-12 forms a γ-structure. Orientation factors were computed from wide angle x-ray diffraction measurements. These were correlated together with birefringence as a function of spinline stress. The influence of annealing and solid state drawing on fiber structure was investigated.
XRD patterns of epoxy/C-15A
This paper presents the effect of process parameters of twin screw extruder and addition of Cloisite-15A on mechanical, thermal and moisture barrier properties of epoxy/Cloisite-15A nanocomposites. Four lobed kneading blocks were used the in shearing zone of the extruder, based on their effectiveness in dispersing nanofillers in epoxy. Screw speeds from 100 min−1 to 400 min−1, number of passes up to 15, temperature from 5°C to 80°C and Cloisite-15A contents from 1 wt.% to 2.5 wt.% were considered for designing the L12 Orthogonal Array. Improvements in tensile strength, compression strength, flexural strength, impact strength, hardness and moisture diffusivity in the nanocomposites were 11.89%, 20.06%, 27.73%, 37.26%, 25.48% and 56.22% respectively, when compared to neat epoxy. The improvements were achieved for screw speed of 400 min–1, 5 passes through the extruder, processing temperature of 5°C and 2 wt.% of Cloisite-15A. Dispersion of Cloisite-15A in epoxy was studied by XRD, SEM and TEM. Thermal stability and moisture barrier properties were superior in the nanocomposites.
The potassium hexaniobate was synthesized by reacting, in stoichiometric proportions, Nb 2O 5 and K 2CO 3 at 1100 °Cand modified with octadecylamine from an acid-base reaction. Through X-ray diffraction, an interlayer space of 4.27 nm was observed in comparison with 0.79 nm of unmodified oxide; this was also shown by SEM microscopy. The hybrid nanofiller previously obtained was incorporated into LLDPE by melt intercalation (0 up to 10 wt.%) using a twin screw extruder and LLDPE-g-MAH as compatibilizer. From TGA results, all nanocomposites (LLDPE/LLDPE-g-MAH/lamellar oxide) have increased the onset degradation temperature, while the oxide lost during processing for LLDPE/LLDPE-g-MAH/lamellar oxide nanocomposites was higher for the highest content in comparison with LLDPE matrix. According to the Eyring equation, the activation volume of the samples could be calculated using the relationship between the yield strength and strain rate from tensile stress-strain curves. The activation volume decreased with increase of nanofiller concentration, suggesting a good adhesion between the layered oxide and the polymeric matrix for high concentration. This can be attributed to the restricted segmental motion near the nanofiller/polymeric interface, while a poor interaction between them was observed for low concentration. However, the Young's modulus showed a 50% improvement for low nanofiller concentration, especially in the case of 1 wt.% of nanofiller, which was also confirmed by modulus and toughness balance. Considering all the results, it has been revealed that the proton exchanged layered niobate can improve the thermal and mechanical properties of LLDPE/LLDPE-g-MAH/lamellar oxide nanocomposites.
Nanocomposites of low density polyethylene (LDPE)/C-18 modified multi wall carbon nanotubes (C-18-CNT) were prepared by melt blending. The effect of C-18-CNT loading and compatibilizer (maleic anhydride modified polyethylene, MAPE) on the morphology, mechanical, thermal and rheological properties of LDPE was studied. FE-SEM images of nano-composites show reduced agglomeration of the in LDPE/C-18-CNT in comparison with uncompatibilized C-18-CNT. For uncompatibilized nanocomposites, yield strength and Young's modulus increased with loading of C-18-CNT. Ultimate strength, show improvement up to 2 wt% loading. However, percent elongation and toughness were reduced for C-18-CNT at all loadings. Apart from elongation and toughness, addition of compatibilizer improved all mechanical properties as compared to pure LDPE and nanocomposites without compatibilizer. Percent crystallinity shows a correlation with Young's modulus. Both, Young's modulus and total crystallinity increased with C-18-CNT loading and further increase with the incorporation of compatibilizer was observed. Results of phase angle suggest no presence of network. Also, addition of C-18-CNT did not increase strain hardening, maintained extensional viscosity and time of break up to 1.5 s(-1) Hencky rate. The C-18 modifier is viewed to act similar to a long chain branching on linear polymers. The C-18 modification of CNT resulted in reduced viscous and elastic properties of the composites. In turn, this is expected to lead to enhancement in the processing of these composites. Overall, compatibilized C-18-CNT resulted in improved mechanical properties and better processing behavior.
An attempt is made to give a survey of polymer processing during the past 50 years, with a backward glance to earlier periods and to roots of development in related branches of industrial production. Selected topics are treated in some detail, with comments and comparisons, showing typical trends and forecasting possible progress in the near future: Extrusion, injection molding, blow molding, calendering and sundries. A separate chapter deals with the role of theory and experiment in polymer processing. Generally, it may be stated that in the main fields development is changing from a practical art to applied science. – For rounding-off the article is closed with some anecdotes and stories about pioneers in the front line of plastics progress.
Melt spinning is a polymer processing technique that makes great demands on the extensibility of the polymer melt in the distance between die exit and solidification point [1]. The polymer material is exposed to a rapidly growing deformation rate over a large range of deformation within a short time of about 100 milliseconds. Simultaneously an extreme cooling occurs with cooling rates of about 1000 K/s. For this reason only a few polymer materials are usable for this kind of polymer processing with sufficient take-up speeds. Most polymers show a fiber break in the molten state either by brittle cohesive rupture or ductile failure when approaching critical conditions of deformation. The rheological behaviour of a polymer melt at the critical conditions of deformation in the fiber forming process can not be predicted by means of usual rheological material functions. This paper reports the attempt to find out material functions, which describe the critical deformation states of the melt spinning process. The established material functions are compared with the results of spinning experiments to estimate their practicality.
Recent progress in polymerization easily allows the control of precise structure of a base polymer and accelerates lower-cost production using larger-scale-plants. In addition to this, today's more important issue in our industry is the development of the key-technology corresponding to a sustainable society. Under these circumstances, the polymer industry in Japan has been focussing on down-stream products from upper-stream using advanced processing technology. To meet today's trends, the polymer industry should establish more sophisticated technology in both higher functionality and hybridization to survive in the 21st century. In particular, various hybridized polymerprocessing systems such as the combination of reactive extrusion and injection molding should be applied to create cost-effectiveness and less environmental burdens as well as higher performance.
Top-cited authors
Bruno Vergnes
  • MINES ParisTech
Jordan Leigh White
  • Leeds City College
Gerrit W M Peters
  • Eindhoven University of Technology
Savvas G Hatzikiriakos
  • University of British Columbia - Vancouver
Han E H Meijer
  • Eindhoven University of Technology