Extrudate Swell Research Articles

Investigation of the rheological properties and die swell of polylactic acid/nanoclay composites in a capillary rheometer

The purpose of this research was to investigate the rheological behavior and extrudate swell of polylactic acid (PLA) filled with a nanoclay. The effects of the amount of nanoclay and surface treatment were studied by a capillary rheometer. The dispersion of the nanoclay was inspected by using the scanning electron microscopy. Generally, PLA/nanoclay composites exhibited a pseudoplastic rheological behavior as the shear stress and die swell increased with increasing shear rate. However, the shear viscosity decreased. The die swell also increased with increasing shear stress. The elongation viscosity decreased with increasing elongation rate. The incorporation of nanoclay decreased the shear stress and shear viscosity to a lesser degree than the elongation viscosity.

Effect of co-monomer ratio in ABS and wood content on processing and properties in wood/ABS composites

Acrylonitrile-Butadiene-Styrene copolymers (ABS) reinforced with wood flour were investigated for rheological, mechanical and thermal properties. Three grades of commercial ABS resin (high flow (HF-ABS), medium impact (MI-ABS) and super high impact (SI-ABS) grades) were characterized using H-NMR and elemental analysis for the determination of co-monomer content. Wood flour from Para rubber trees treated with N-2 (aminoethyl)-3-(aminopropyl) trimethoxy silane was blended with ABS in the melt blending process using a twin-screw extruder. Wood flour contents used in this work were 0.0 %, 9.1 %, and 33.3 % wt. The composites with higher acrylonitrile contents showed higher melt viscosity especially at the low shear rate. Carreau’s model was used for curve-fitting. The extrudate swell ratio of the composites tended to increase at the shear rate of 10–500 s−1 and then decreased dramatically once the shear rate were further applied. Neat ABS and wood/ABS composites with higher butadiene content illustrated a higher swelling ratio. The neat MI-ABS and composites showed the highest ultimate tensile strength and modulus due to the butadiene content effect. As the wood flour loading was increased, the tensile modulus of all ABS composites increased with the sacrifice of the tensile strength of composites. The elongation at break and impact strength were noticeably the highest for wood/SI-ABS composites among all because of the effect of rubbery butadiene content. Thermal stability of plastic in 9.1 % wood in HF-ABS composites was improved compared with the neat HF-ABS due to the low acrylonitrile content.

Computer-aided design and optimization of profile extrusion dies for thermoplastics and rubber: a review

A review is provided of issues and techniques in design and optimization of profile extrusion dies for thermoplastics and rubber, with particular emphasis on unplasticized polyvinyl chloride and rubber compounds. Traditional profile die design methods are contrasted with computer-based ones, with respect to efficiency and economic benefits. The main types of die construction are outlined. Physical phenomena relevant to the design and performance of dies are summarized, including: rheology and kinematics of the flow, wall slip, extrusion instabilities, residence time and degradation, extrudate swell, draw-down, and thermal effects. Approaches and strategies for die design are explained, including: flow balancing – with guidance from analytic flow results, the Avoid-Cross-Flow strategy, use of flow separators, and designing for extrudate swell. Published computer simulations of die flow used to assist with design are reviewed. Introducing automatic die design, the structure and elements of a computerized design optimization environment are set out. Key components and options within this are described, including: objective functions, constraints, design variables, optimization algorithms, design parameterization and flow domain meshing, and optimization strategies. Published implementations of computerized profile die design optimization are described. Automatic design optimization is compared with the work of a designer assisted by flow simulations in the industrial environment, showing how substantial reductions in demands on the designer's time are possible. The nature and potential of robust design is outlined, with techniques for its implementation. Conclusions are drawn as to the present state of the art in computer-assisted profile die design and optimization, and potential advances.

Finite‐Element Simulation of Polymer Flow and Extrudate Swell Through Hollow Profile Extrusion Die with the Multimode Differential Viscoelastic Model

AbstractExtrudate swell is a common phenomenon in polymer processing that can significantly influence the quality of final products. In this study, the viscoelastic flow patterns and the swell phenomenon of low‐density polyethylene (LDPE) flowing through a hollow profile extrusion die are investigated by means of the finite element simulation. The mathematical model of three‐dimensional viscoelastic flow and extrudate swell of the polymer melt obeying a multimode differential Phan‐Thien and Tanner (mPTT) constitutive model is established. The rheological parameters of LDPE are obtained by fitting the material functions detected on a strain‐controlled rheometer. A penalty method is introduced to solve the viscoelastic flow and extrudate swell problem with a decoupled algorithm. The computational stability is improved by using the discrete elastic–viscous split stress (DEVSS) algorithm incorporating the inconsistent streamline‐upwind scheme. A streamface–streamline method is introduced to adjust the outlet free surface of the swelling extrudate. The design strategy of the hollow profile extrusion die is discussed. The essential flow characteristics and the mechanism of the swell phenomenon of polymer melt flowing through the hollow profile extrusion die are further investigated based on the proposed mathematical model and numerical scheme. © 2011 Wiley Periodicals, Inc. Adv Polym Techn 32: E1–E19, 2013; View this article online at wileyonlinelibrary.com. DOI 10.1002/adv.20265

Melt processing, mechanical, and fatigue crack propagation properties of reactively compatibilized blends of polyamide 6 and acrylonitrile–butadiene–styrene copolymer

AbstractWithin a IUPAC study, melt processing, mechanical, and fatigue crack growth properties of blends of polyamide 6 (PA 6) and poly(acrylonitrile–butadiene–styrene) (ABS) were investigated. We focused on the influence of reactive compatibilization on blend properties using a styrene–acrylonitrile–maleic anhydride random terpolymer (SANMA). Two series of PA 6/ABS blends with 30 wt % PA 6 and 70 wt % PA 6, respectively, were prepared with varying amounts of SANMA. Our experiments revealed that the morphology of the matrix (PA 6 or ABS) strongly affects the blend properties. The viscosity of PA 6/ABS blends monotonically increases with SANMA concentration because of the formation of high‐molecular weight graft copolymers. The extrudate swell of the blends was much larger than that of neat PA 6 and ABS and decreased with increasing SANMA concentrations at a constant extrusion pressure. This observation can be explained by the effect of the capillary number. The fracture resistance of these blends, including specific work to break and impact strength, is lower than that of PA 6 or ABS alone, but increases with SANMA concentration. This effect is most strongly pronounced for blends with 70 wt % PA 6. Fatigue crack growth experiments showed that the addition of 1–2 wt % SANMA enhances the resistance against crack propagation for ABS‐based blends. The correlation between blend composition, morphology and processing/end‐use properties of reactively compatibilized PA 6/ABS blends is discussed. © 2011 Wiley Periodicals, Inc. J Appl Polym Sci, 2012

Simulation of extrudate swell using an extended finite element method

An extended finite element method (XFEM) is presented for the simulation of extrudate swell. A temporary arbitrary Lagrangian-Eulerian (ALE) scheme is incorporated to cope with the movement of the free surface. The main advantage of the proposed method is that the movement of the free surface can be simulated on a fixed Eulerian mesh without any need of re-meshing. The swell ratio of an upper-convected Maxwell fluid is compared with those of the moving boundary-fitted mesh problems of the conventional ALE technique, and those of Crochet & Keunings (1980). The proposed XFEM combined with the temporary ALE scheme can provide similar accuracy to the boundary-fitted mesh problems for low Deborah numbers. For high Deborah numbers, the method seems to be more stable for the extrusion problem.

Experiment and Numerical Simulation of Extrudate Swell in the Polymer Extrusion Process

The extrudate swell of the polymer extrusion process was studied with the experiment and simulation method. The extrudate swell process was recorded by the high-speed photography apparatus. The swell rate at the different time was calculated. It is found that the extrudate swell rate increase at the first five seconds. The maximum swell rate is about 4.37%. The three-dimensional numerical simulation model of the experiment die path was founded. The extrusion process including the extrudate swell was simulated used the Finite Element Method. Such simulated results as the velocity vector, the shear rate profile and the end of the swell zone were analyzed. The extrudate swell end got by the simulation is similar with the experiment result.

The Finite Element Simulation and Analysis of Polymer Tube Coextrusion Process

The three-dimensional numerical simulation model of two polymer melts flowing through the traffic circle section path was founded. The coextrusion process of composite pipe was simulated used the finite element method. The stream line method was used to simulate the extrudate swell. Such simulated results as the location and shape of coextrusion interface, the shear stress profile were analyzed. It is found that the maximum shear rate occur near the convergence section of the outer polymer. The interface excursion is less than 1mm in the die path. As the melt flow out of the die, the interface excursion increase distinctly, the value is up to 6mm. The extrudate swell rate is 21% along the radial direction.

Numerical Simulation of Three Dimensional Extrudate Swell Using Finite Element Method

The precise prediction of extrudate swell is significant to the control of melt flow and the quality of final products. A mathematical model of power law flow for polymer extrusion is investigated. The penalty function formulation is introduced to the finite element model and the free surface is updated with streamline equation in a decoupled method. A proper penalty constant is determined by comparison of numerical results with different penalty constants. The velocity field is obtained and the distribution of velocity on different cross sections is compared. The effects of volumetric flow rate and die shape on extrudate swell ratio are discussed. The simulation results are very important for the process and die design of the polymer extrusion.

Numerical and experimental studies on extrudate swell of branched polyethylene through axisymmetric and planar dies

Abstract Extrudate swell is simulated using an Arbitrary Lagrangian Eulerian (ALE) technique based finite element formulation and the same has been validated by comparing the results with reported numerical and experimental studies. In the present work we compare our ALE simulations with our own experimental data on the extrudate swell of commercial grade low density polyethylene (LDPE) resin. The resins were characterized for their rheological behavior in both shear and uniaxial extension. The polymers were extruded from a capillary under isothermal conditions and the extrudates were observed on-line using a video camera. ALE simulations were performed using molecular constitutive model like eXtended Pom–Pom (XPP) for branched (LDPE). The simulated extrudate swell was a good match with the experimental data. It was found that the swell values of LPDE through planar die are higher than the axisymmetric die.

On the determination of elastic properties of composites of polycarbonate and multi-wall carbon nanotubes in the melt

In this work, the elastic properties of melts of polycarbonate (PC)/multi-wall carbon nanotubes (MWCNT) composites were studied by means of rotational and capillary rheometry. Linear viscoelastic shear oscillations combined with simultaneous electrical measurements, creep recovery experiments in shear and extrudate swell measurements were performed. The application of the fractional Zener model for the phenomenological description of the viscoelastic properties of PC/MWCNT composites in the linear regime is discussed. The modulus of the spring of the fractional Zener model is a measure of elasticity and increases with carbon nanotubes concentration. The results of creep recovery experiments reveal that the microstructure strongly influenced the viscosity and the reversible deformation of the nanocomposites. Below the rheological percolation threshold, agglomeration of carbon nanotubes generally led to an increase of the reversible deformation up to a maximum value. Above the rheological percolation threshold, a larger concentration of carbon nanotubes caused a decrease of the recoverable deformation. As revealed by capillary rheometry, the extrudate swell of the PC/MWCNT composites at shear rates above 100 s − 1 was lower than the extrudate swell of neat polycarbonate which indicates the decrease of reversible deformation caused by the addition of MWCNT in capillary flows (large stress regime). The experimental data are discussed in the context of the current understanding of the rheological properties and the microstructure of polymer composites with carbon nanotubes.

Evaluation on extrudate swell and melt fracture of polypropylene/kaolin composites at high shear stress

Kaolin-filled PP composites were compounded using a heated two-roll mill prior to extrusion process in order to improve the rheological properties of the samples. The extrudate swell and flow instability (melt fracture) behavior of kaolin-filled PP composite melts were investigated using a constant rate type of capillary rheometer at high extrusion rates and test temperatures varied from 165°C to 220°C. The extrudate swell studies demonstrate that the die swell ratio decreases with an increase in the processing temperature and filler loading at fixed shear stress. Nonetheless, the study on the effect of shear stress and shear rate showed that the die swell ratio (B) of the melts decreases linearly with increasing apparent shear stresses and shear rates for both systems, unfilled and filled PP only up to one point above the critical shear rate (1.8 × 10 s-1). The B values remained almost constant when the shear rate is greater than 1.8 × 10 s -1 at a constant temperature. Kaolin-filled PP composites exhibit a characteristic of flow instability and extrudate distortions upon exiting from extrusion dies at low filler loading and at low processing temperature of 165°C. This type of defect is characterized by highly rough, fractured, and distorted extrudate surface. It was also found that decreasing the shear stress improved the surface appearance of all samples. Finally, the melt fracture tended to be suppressed when a capillary die with a high L/D ratio, which is 10 was used.

Numerical Simulation of Viscoelastic Extrudate Swell Through Elliptical Ring Die

The numerical simulation of extrudate swell is significant in extrusion processing. Precise prediction of extrudate swell is propitious to the control of melt flow and the quality of final products. A mathematical model of three-dimensional (3D) viscoelastic flow through elliptical ring die for polymer extrusion was investigated. The penalty function formulation of viscoelastic incompressible fluid was introduced to the finite element model to analyze 3D extrusion problem. The discrete elastic viscous split stress (DEVSS) and streamline-upwind Petrov-Galerkin (SUPG) technology were used to obtain stable simulation results. Free surface was updated by updating the streamlines which needs less memory space. According to numerical simulation results, the effect of zero-shear viscosity and elongation parameter on extrudate swell was slight, but with the increase of volumetric flow rate and relax time the extrudate swell ratio increased markedly. Finally, the numerical simulation of extrudate swell flow for low-density polyethylene (LDPE) melts was investigated and the results agreed well with others' work. These conclusions provided quantitative basis for the forecasting extrudate swell ratio and the controlling of extrusion productivity shape.

Quantitative Study of Extrudate Swell for Polymer Blends

The extrudate swelling of blends was analyzed quantitatively. The extrudate swell ratio could be predicted from its apparent constitutive parameters and processing conditions (length-to-diameter ratio in capillary, shear rate and temperature). More importantly, it was first suggested that there is one exponential multiplication correlation between blend swell ratio and those of components. This relation was found when considering one component acted as the filler of the other in blend as in composites, in which composite swell ratio was usually reduced from that of the matrix by one concentration shift factor. In contrast, the blend swell ratio exhibited positive derivation against of linear addition of the component swell ratios against the negative derivation in viscosity. The swell ratio data were chosen to verify the theory from publications for incompatible blends. The good agreement of predicted swell ratio with the experimental data confirmed the feasibility of the model in analyzing the swelling behavior of blends. Keywords: Extrudate swell, Incompatible blend, Capillary, Positive derivation, swell ratio, rheological properties, polymer blends, synergistic effects, filler shape, dispersion, concentration, normal-stress difference, LDPE/LLDPE, PP/LDPE Blend, pure composite matrix, shear stress, trade-off rule, Rheological evaluation, polymer blends techology

Quantitative Study of Extrudate Swell for Polymer Blends

The extrudate swelling of blends was analyzed quantitatively. The extrudate swell ratio could be predicted from its apparent constitutive parameters and processing conditions (length-to-diameter ratio in capillary, shear rate and temperature). More importantly, it was first suggested that there is one exponential multiplication correlation between blend swell ratio and those of components. This relation was found when considering one component acted as the filler of the other in blend as in composites, in which composite swell ratio was usually reduced from that of the matrix by one concentration shift factor. In contrast, the blend swell ratio exhibited positive derivation against of linear addition of the component swell ratios against the negative derivation in viscosity. The swell ratio data were chosen to verify the theory from publications for incompatible blends. The good agreement of predicted swell ratio with the experimental data confirmed the feasibility of the model in analyzing the swelling behavior of blends.

Numerical prediction of three-dimensional time-dependent viscoelastic extrudate swell using differential and algebraic models

This study investigates the numerical simulation of three-dimensional time-dependent viscoelastic free surface flows using the Upper-Convected Maxwell (UCM) constitutive equation and an algebraic explicit model. This investigation was carried out to develop a simplified approach that can be applied to the extrudate swell problem. The relevant physics of this flow phenomenon is discussed in the paper and an algebraic model to predict the extrudate swell problem is presented. It is based on an explicit algebraic representation of the non-Newtonian extra-stress through a kinematic tensor formed with the scaled dyadic product of the velocity field. The elasticity of the fluid is governed by a single transport equation for a scalar quantity which has dimension of strain rate. Mass and momentum conservations, and the constitutive equation (UCM and algebraic model) were solved by a three-dimensional time-dependent finite difference method. The free surface of the fluid was modeled using a marker-and-cell approach. The algebraic model was validated by comparing the numerical predictions with analytic solutions for pipe flow. In comparison with the classical UCM model, one advantage of this approach is that computational workload is substantially reduced: the UCM model employs six differential equations while the algebraic model uses only one. The results showed stable flows with very large extrudate growths beyond those usually obtained with standard differential viscoelastic models.

Effects of kaolin and maleic anhydride contents on melt elasticity and flexural behaviour of polypropylene/kaolin and unplasticised poly(vinyl chloride)/kaolin composites

AbstractPolypropylene/kaolin and unplasticised poly(vinyl chloride)/kaolin composites were prepared by directly melt mixing polypropylene (PP) and unplasticised poly(vinyl chloride) (UPVC) with maleic anhydride (MAH) and low cost kaolin via in situ extrusion process. The influences of kaolin particles and MAH in PP and UPVC matrix were discussed through investigating the flexural and morphological properties of filled PP and UPVC composites. The extrudates obtained from the extrusion process were carefully collected in order to investigate the elastic properties (extrudate swell and melt fracture). Results revealed that the above mentioned properties are strongly dependent on the presences of kaolin and MAH in both composite systems. Observation on scanning electron microscopy (SEM) analysis showed that the kaolin books (stacks of kaolin particles) were successfully delaminated thus lead to a well dispersed of kaolin particles in PP and UPVC matrix.

Linear and nonlinear melt rheology and extrudate swell of acrylonitrile‐butadiene‐styrene and organoclay‐filled acrylonitrile‐butadiene‐styrene nanocomposite

AbstractMelt viscoelastic behavior and the die swell of Acrylonitrile‐Butadiene‐Styrene (ABS) and ABS/clay nanocomposites varying in organoclay loading were studied. A pronounced low‐frequency nonterminal behavior exhibited in linear viscoelastic experiments along with an apparent yield stress in transient startup flow tests suggested the existence of a network type, because of interconnection of rubber particles in ABS matrix. From the results of linear and nonlinear viscoelastic measurements, it was found that the incorporation of organoclay can lead to the formation of an additional network formed between organoclay tactoids that caused reduced temperature dependency of linear viscoelastic properties of the nanocomposite samples compared with ABS matrix. The swelling behavior of samples was interpreted using the results of stress relaxation experiments after cessation of steady shear flow. The great reduction in the die swell of nanocomposite samples could be explained in terms of great surface area and anisometric nature of organoclay tactoids and/or platelets, which promote energy consumption and less energy to be stored in chains. POLYM. ENG. SCI., 2010. © 2010 Society of Plastics Engineers

Extrudate swell of linear and branched polyethylenes: ALE simulations and comparison with experiments

Extrudate swell is a common phenomenon observed in the polymer extrusion industry. Accurate prediction of the dimensions of an extrudate is important for appropriate design of dies for profile extrusion applications. Prediction of extrudate swell has been challenging due to (i) difficulties associated with accurate representation of the constitutive behavior of polymer melts, and (ii) difficulties associated with the simulation of free surfaces, which requires special techniques in the traditionally used Eulerian framework. In a previous work we had argued that an Arbitrary Lagrangian Eulerian (ALE) based finite element formulation may have advantages in simulating free surface deformations such as in extrudate swell. In the present work we reinforce this argument by comparing our ALE simulations with experimental data on the extrudate swell of commercial grades of linear polyethylene (LLDPE) and branched polyethylene (LDPE). Rheological behavior of the polymers was characterized in shear and uniaxial extensional deformations, and the data was modeled using either the Phan–Thien Tanner (PTT) model or the eXtended Pom–Pom (XPP) model. Additionally, flow birefringence and pressure drop measurements were done using a 10:1 contraction–expansion (CE) slit geometry in a MultiPass Rheometer. Simulated pressure drop and contours of the principal stress difference were compared with experimental data and were found to match well. This provided an independent test for the accuracy of the ALE code and the constitutive equations for simulating a processing-like flow. The polymers were extruded from long ( L/ D = 30) and short ( L/ D = 10) capillaries dies at 190 °C. ALE simulations were performed for the same extrusion conditions and the simulated extrudate swell showed good agreement with the experimental data.

Rheological characterizations and extrudate swell predictions of an LDPE melt by two KBKZ-type constitutive equations

The shear viscoelastic properties of an LDPE (1I2A-1) melt at 160°C were described by using two KBKZ integral type constitutive equations, i.e. Wagner model and the three- parameter rational type model. The present characterizations were compared with the previous calculations by using PSM model. The results show that there are differences between the descriptions on the stress relaxation property in step strain and the first normal stress difference for the three models, and however, all the three models show the almost same predictions on the shear-thinning viscosity of the ldpe melt. Both Wagner model and PSM model are good choice in describing the rheological properties of the melt due to theirs simplicity. The Tanner theory combined with the Wagner model or the three-parameter rational type model was used to predict the swell ratio of the LDPE melt through a long capillary die, which was also compared with the experimental results and the previous calculations on swell. The predictions by Tanner theory combined with the three different constitutive models on the swell ratio of the LDPE melt are similar, which are apparently lower than the experiments and numerical simulations over the whole experimental shear rate range. The results further indicate that Tanner theory cannot predict the swell ratio of the LDPE melt precisely.