bluuebunny/crossref_metadata_2025 huggingface dataset:
Rheological Properties of Glass Fiber Filled Nylon 6 Composite System
Authors: Park T. S. , Kim K. U.
Published: December 2013

The dynamic and physical properties of neat and glass fiber filled nylon 6 systems were examined. The dynamic viscosity of neat nylon 6 melt was well fitted to:

(I)

η
′

=
a
/

(

1
+
b
 
ω

)

c

For the glass fiber filled nylon 6 composite systems, however, a modification of Eq. (1) was required to accommodate the viscosity data. Various types of rheological models are examined to describe the effect of glass fiber on the suspension viscosity, and respective constants of models were determined by a curve fitting. A silane coupling agent had a profound influence on the rheological and physical properties. It increased the dynamic viscosity of composite and yield value, but slightly decreased the activation energy of flow, particularly at high frequency range. Further, it increased the loss factor over the frequency range examined. Plot of storage modulus against loss modulus instead of frequency eliminated the effects of temperature and coupling agent. From the tensile fractured surface of coupling agent treated system, a fibrillar structure was observed.
Effect of Screw Stagger on Mixing in a Tangential Counter-Rotating Twin Screw Extruder
Authors: Bigio D. , Erwin L.
Published: December 2013

The Counter-Rotating, Tangential Twin Screw Extruder (CR TSE) is a polymer processing device which has been in industrial use for dozens of years. Over this period of time, many of the design parameters have been studied for their effect on processing issues that are related to a particular application. Recent studies have shown that the CR TSE is a greater-than-linear mixer and that is due primarily to the flow in the nip region. This study seeks to determine the relationship between mixing rates and percent of screw stagger. Using a flow visualization technique of an acid-dyeeradication, experiments were conducted varying the stagger setting every 10%. In this experiment the total mixing length was used as the measure of mixing. Data was taken at the time of the experiment and the process was videotaped for later review and data evaluation. The technique provides both qualitative and quantitative information. A discussion of the nature of the extruder performance as a function of screw stagger is reported and important design considerations presented.
Optimization of Cooling Systems for Injection Molding
Authors: Pandelidis I. O. , Lingard T. J.
Published: December 2013

An optimization methodology has been developed for the design of injection molding cooling systems. The cooling system design problem has been decomposed to determine the independent and dependent variables of the process and system design. The design goals were quantified and optimal solutions obtained by using numerical optimization techniques. A gradient driven solution method was implemented to perform the optimization task. Several complex molding examples were analyzed and significant improvements in cooling system performance were realized. Both quality and productivity concerns are addressed by the methodology. Commercial mold filling and cooling software are integrated with the optimization code to perform the cooling system analysis.
Modelling Twin Rotor Mixers and Extruders
Authors: David B. , Sapir T. , Nir A. , Tadmor Z.
Published: December 2013

A mathematical model for simulating flow in batch and continuous twin rotor mixers and extruders is presented. The model is a lumped parameter model based on the Flow Analysis Network (FAN) method.
State of Dispersion – Mechanical Properties Correlation in Small Particle Filled Polymer Composites
Authors: Suetsugu Y.
Published: December 2013

Correlation between state of dispersion and mechanical properties is obtained and failure mechanisms from falling weight impact tests are discussed. The state of dispersion is characterized for calcium carbonate filled polypropylene model composites by using a scanning electron microscope. A dispersion index is defined in terms of the fraction of agglomerates of the filler remained in the composites. Improvement of dispersion uplifts tensile strength and more prominently falling weight impact strength. It is pointed out that an initial failure in the falling weight impact test rises at the agglomerate existing near the loading point. Falling weight impact strength is found to be dependent upon the distance from loading point to failure initiation point where the agglomerate exists. This explains the dependency of impact strength on the state of dispersion and a large sample deviation often observed in the falling weight impact test.
Innovative Extrusion Systems for Advanced Fiber and Film Extrusion
Authors: Hensen F.
Published: December 2013

Advanced fiber and film extrusion is a term used to describe high speed spinning of low denier filaments and stretching of thin films at high output rates and high efficiencies. Using the advantages of separated process steps, extrusion systems have been developed in which the main process steps, such as feeding, melting, homogenizing, filtering, mixing and metering, take place in special separate equipment aggregates. In comparison to standard extruders with combined process steps, these extrusion systems give better melt quality as measured by the uniformity of melt flow, drawability of the fibers or films and the dispersion of additives. Examples of extrusion systems for PET or PP with appropriate operating conditions and output rates are described. The different applications of these systems and their main details are listed in a survey.
Melt Strength Behavior of PE and its Relation to Bubble Stability in Film Blowing**
Authors: Ghijsels A. , Ente J. J. S. M. , Raadsen J.
Published: December 2013

Melt strength data are presented on the three major classes of commercial polyethylenes (LDPE, LLDPE and HDPE). The LDPE samples studied were polymerised by both tubular and autoclave reactor technology and the LLDPE samples were produced with different α-olefins as comonomer. Melt strength was assessed from uniaxial tensile experiments with a Rheotens apparatus. The melt strengths of both LLDPEs and HDPEs are much lower than those of LDPEs when compared at equal melt index or zero-shear viscosity level. Among the LDPEs the highest melt strength is observed for the LDPEs made by autoclave technology. The type of comonomer present in LLDPEs does not significantly affect its melt strength. The molecular factors controlling the melt strength of pure polyethylenes are discussed. A high melt strength is identified with a good bubble stability in the film blowing process.
Dynamics of Double Bubble Tabular Film Process for Producing Biaxially oriented Nylon 6 Film
Authors: Takashige M. , Kanai T.
Published: December 2013

A double bubble tubular film process for nylon 6 was investigated. This report discussed three topics: Relationship between process conditions and film stretching stresses; deformation rate during double bubble process, birefringence and film thickness uniformity; and scale-up rule for double bubble tubular film process. The optimum stretching stress during the double bubble tubular film process exists. The bubble break occurs over stress of 1300 Kg/cm2 and bubble stability occurs below stress of 600 Kg/cm2. The cross point of stretching stress, which means stress in the machine direction is equal to stress in the transverse direction, is influenced by a deformation rate which is closely related to birefringence and bubble stability. Bubble stability and film thickness uniformity are improved with increasing deformation rate. It is found that the scale-up rule which was set up theoretically is applicable to predict the physical properties and bubble stability for large scale double bubble tubular film process once the same process is carried out by using the same scale machine and a small amount of resin.
A Finite Difference Study of Roll Design in Calendering Processing
Authors: Tseng A. A. , Sun P. F.
Published: December 2013

A numerical model has been developed to simulate the polymeric flow and heat transfer in calendering processing. In the flow calculation, the polymer is treated as a thermal-dependent power-law fluids; in the coupled heat transfer calculation, both the roll and the polymer are modeled in order to assess the performance of various designs of calendering rolls. The numerical predictions agree very well with the on-line measurements. The generalized finite difference scheme was selected to cope with the numerical difficulties involved in the modeling of the process, especially the curved boundary and the free surface conditions. The computational aspects of the finite difference scheme in modeling of polymer behavior are also discussed.
Relationship between Rotor Designs in an Internal Mixer and Physical Properties of Mixed Rubber Compounds
Authors: Kawanishi K. , Yagii K. , Obata Y. , Kimura S.
Published: December 2013

Internal mixers are commonly used for rubber compounding in industry. However, the relations among the designs of equipments, mixing conditions and the properties of the resulting compound are little known. In this paper we tried to reveal some manners of the relations concentrating, particularly, on rotor designs. A specially designed internal mixer (Banbury type) was developed. A number of double winged rotors of various shapes and replaceable mixing chambers were prepared. In developing the equipment, eight parameters were taken into consideration concerning the shape of rotors, that is, lengths, twist angles and overlap ratio of the wings, width and clearance at the rotor tip, angles of flow-in and flow-out at the gap area and total bulkiness of the rotor. Measured properties concerning mixing are: unit work, Mooney viscosity of dumped compound, the amount of bound rubber, weight average molecular weight of the extracted portion of the compound, and peaks in a torque curve, i.e., values of first peak torque and second peak time. In order to estimate the degree of influences of the design parameters mentioned above and mixing conditions, each measured properties were expressed as functions of these parameters by means of multiple regression analysis.
Feed Variance Limitations for Co-rotating Intermeshing Twin Screw Extruders
Authors: Curry J. , Kiani A. , Dreiblatt A.
Published: December 2013

The extent of feeder error to survive a plasticating compounding extruder is addressed in this theoretical and experimental study. Results of unit step and cyclic variation of tracer concentration were used to define the transfer function and damping ratio respectively. The frequency dependent damping ratio of cyclically varying tracer content in the feedstream was predicted for three screw configurations with fair agreement to experiment.
A Stick-Slip Problem Related to Melt Fracture in Polymer Processing Operations
Authors: Adewale K. E. P. , Olabisi O. , Oyediran A. A. , Olunloyo V. O. S.
Published: December 2013

A ‘Stick-Slip’ mixed-boundary model is postulated to support the mechanism of transition from no-slip to slip at the polymer/die interface during capillary extrusion of polymeric materials at and above a critical shear rate at a fixed throughput. The predicted shear stress singularity explains the occurence of gross extrudate distortion known as melt fracture.
Effects of Plasticizers on Extrusion of Dry Blended PVC
Authors: Datta A. , Baird D. G.
Published: December 2013

This research was concerned with the effect of two different plasticizers on the plasticating extrusion behavior of polyvinylchloride (PVC). Diisodecyl pthalate (DIDP) and dihexyl pthalate (DHP) were the the two plasticizers used in this study. First some differences in the extrusion performance of the two differently plasticized PVC compounds were identified. In particular, it was observed that pressure build-up and power requirement were affected by the plasticizer type with the DIDP plasticized materials generating higher pressures and requiring more power than the DHP plasticized materials. Also the DIDP plasticized material fused earlier in the screw channel and in general exhibited slightly higher flow rates. The differences in extrusion characteristics were observed for two different dies attached to the extruder.
Pressure Oscillations during Capillary Extrusion of High Density Polyethylene
Authors: Becker J. , Bengtsson P. , Klason C. , Kubát J. , Sáha P.
Published: December 2013

This paper demonstrates the usefulness of frequency analysis in monitoring melt flow instabilities. The flow behavior of a film-blowing grade of high density polyethylene has been studied using a capillary rheometer at constant piston velocities. The pressure in the reservoir was measured by a transducer fitted to the driving end of the piston. The signal was amplified and processed in a Fast Fourier Transform (FFT) frequency analyzer. The pressure fluctuations (noise) have a very low intensity at low flow rates in the sharkskin region. The noise signal increases dramatically at a critical shear stress of about 1.5 × 105 Pa, where the flow assumes a pulsating character (spurt defect). Above the pressure oscillation region the melt goes through a pseudostable region, followed by a secondary pressure oscillation region, eventually reaching a chaotic stage. The noise spectrum intensity seems to be related to the severity of the surface disturbances of the extrudate in this latter branch of the flow curve.
Biaxially-oriented Polyethylene Films by Compression of Injected Moldings
Authors: Ania F. , Bayer R. K. , Baltà Calleja F. J.
Published: December 2013

Biaxially oriented PE films were prepared by compression of uniaxially oriented elongational-flow injection-molded precursors. The films so prepared, having different extents of biaxial stretching were compared on the basis of two derived functions, biaxial draw ratio (ƛ) and degree of biaxiality (B). The former gives a quantitative measure of the average draw ratio of the film surface. The latter describes the strain distribution along the principal directions of the film plane. It is shown that ƛ and B depend on the final applied pressure and on the type of pressing surfaces used. The dependence of ƛ and B on the initial orientation and on the initial anisometry of the precursors is also discussed in the light of structural arguments.
Influence of Process Data on the Throughput of Large Extruders within the Range of 600 to 6 000 kg/h
Authors: Hensen F. , Imping W. , Stausberg G.
Published: December 2013

A summary of recent technological developments related to large diameter screw extruders is presented. Special attention is given to cascade screw extruders.
Dynamics and Stability of Double Bubble Tubular Film Extrusion
Authors: Kang H. J. , White J. L.
Published: December 2013

A basic study of the kinematics and dynamics of the double bubble tubular film process as applied to polyethylene terephthalate (PET), poly p phenylene sulfide (PPS), polycarbonate (PC) and low density polyethylene (LDPE) is presented. The stability of the four resins was investigated for both a single bubble tubular film and a second bubble of a double bubble process. For the single bubble the LDPE is very stable and the PET, PPS and PC have more limited regions of stability with periodic axisymmetric instabilities near blowup ratios of unity and helical instabilities at higher blowup ratios. It is found that in the first bubble the PC vitrifies to a glass, PET and PPS crystallize to 4 to 9% levels and LDPE to nearly 50%. In the second bubble it is found possible to operate in a stable manner with a heated air ring and stable bubble for PET and PPS but not PC and LDPE. In the second bubble PET and PPS show substantial levels of increase of crystallinity. This is not the case for PC and LDPE. It appears that a strain hardening process such as crystallization is necessary for stability of the second bubble. Stress fields in the second bubble are computed using membrane theory.
Issues Concerning the Rate of Heat Transfer from a Spinline
Authors: Vassilatos G. , Schmelzer E. R. , Denn M. M.
Published: December 2013

Two-dimensional convective heat transfer in a non-isothermal spinline is analyzed. A rigorous derivation of the macroscopic, one-dimensional energy balance describing the cooling of a spinline leads to an equation that differs subtly from the commonly used one-dimensional equation; this difference has practical implications for the correct computation of convective heat transfer coefficients from experimental data obtained from spinlines exhibiting significant radial temperature gradients and, in turn, for the prediction of correct spinline temperature profiles. The errors involved are illustrated with computed results and a method is proposed for the determination of the correct heat transfer coefficients in the presence of radial temperature gradients. Further, it is shown that the radial convective heat flux resulting from the inward radial velocity of an attenuating spinline is important and its omission can lead to significant errors in the computed temperature.
Molecular Orientation in Injection-Molded Polypropylene Copolymers with Ethylene
Authors: Fujiyama M. , Wakino T.
Published: December 2013

The molecular orientation process in injection molding of polypropylene copolymers with ethylene was theoretically analyzed from a view point of growth of melt orientation (recoverable shear strain) at the gate and its relaxation in the mold cavity. Regardless of the characteristics of raw resin (copolymerization type and ethylene content) and molding conditions (cylinder temperature), there exist unitary correlations between calculated degree of molecular orientation and experimentally measured degrees of molecular orientation such as the thickness of skin layer and crystalline c-axis orientation function. According to this analysis, the fact that molecular orientation is decreased by copolymerization with ethylene is due to decrease in melt orientation (recoverable shear strain), decrease in the relaxation time and reduction of crystallization temperature.
Processing Characteristics of Thermoplastic Sheet Composites
Authors: Bigg D. M.
Published: December 2013

While there are several alternatives for producing thermoplastic sheet composites, only two have the characteristics needed for large scale manufacturing; continuous melt impregnation, and deposition of a polymer-impregnated, fiber-dispersed mat from an aqueous slurry. The most important factor affecting the melt impregnation process was found to be the rate of penetration of the molten polymer into the fiber structure. While Darcy's Law, using the Kozeny-Carmen permeation coefficient, provides an initial estimate of penetration rate, it does not adequately consider the slow flow around closely spaced fibers. The slurry deposition process incorporates the polymer directly within the fiber structure, and is not flow rate limited. The most important parameter affecting the consolidation of slurry formed mats was found to be the rate of heat transfer prior to consolidation. In both processes the time of contact between the molten polymer and glass fiber was shown to be important to the development of good adhesion.
Compounding of Thermoplastic Elastomers using Organosilanes
Authors: Anderlik R. , Fritz H.-G.
Published: December 2013

To enhance the material properties of polypropylene/rubber blends the rubber phase is crosslinked. In this study an organosilane crosslinking system is used which creates stable Si-O-Si bonds between the rubber chains and produces a polyfunctional network structure with a high crosslinking density. This organosilane system allows in principle to prepare blends which are statically or dynamically crosslinked. Results concerning the morphology of blends prepared under different compounding parameters are presented. Particular attention was directed to the interrelationship of rheological properties of the blend components and the morphological structure of the created blends. In the closing chapter of this paper the material properties of blends, including EPM or EPDM in a silane-crosslinked mode are compared with those of only physically mixed PP/EPDM-blends.
Microstructure Formation in Extruded and Drawn Polyblends of PC with a Thermotropic LCP
Authors: He J. , Bu W. , Zhang H. , Xie P. , Xu X.
Published: December 2013

Melt blending, extrusion and drawing of polycarbonate (PC) blends containing a thermotropic liquid crystalline polymer (LCP) are reported for a copolyester PCDT synthesised in this laboratory. A single screw extruder is used at four temperatures. The rheology of the PCDT/PC blend, PCDT and PC was measured by means of a capillary rheometer at these temperatures. The morphology of extruded and subsequently drawn strands was studied with the help of a scanning electron microscope and analysed. In PCDT/PC extruded strands, the morphology of the PCDT dispersed phase, changes from spherical through ellipsoidal to elongated with decreasing processing temperature. In contrast to this, in drawn strands with a draw ratio of 10, the morphology of the PCDT changes from ellipsoidal through elongated to fibrillar with increasing processing temperature. It is believed that the relative viscosity of the two phases is the decisive factor determining the microstructure formation of polymer blends containing thermotropic liquid crystalline polymers. Fibril formation is related to the deformation and coalescence of PCDT melt droplets by the drawing at higher temperatures.
Effect of Biaxial Stretching on Mechanical Properties and Surface Roughness of PMMA Films
Authors: Wang Y. D. , Cakmak M.
Published: December 2013

Recently the use of PMMA films as the top layer of dish membrane solar collectors has gathered popularity. The mechanical properties and surface smoothness of PMMA films are the important factors affecting the durability and optical performance of these stretched membrane solar collectors. In this paper, we present the results of our experimental study on the effect of biaxial stretching on mechanical properties and surface roughness of PMMA films. Biaxial stretching was found to improve both the mechanical properties and surface smoothness of PMMA films.
Detailed Investigations of Structural Layering Phenomena in Injection Molded Thermotropic Liquid Crystalline Polymers
Authors: Hsiung C. M. , Cakmak M.
Published: December 2013

The structural gradients developed in the injection molding of thermotropic wholly aromatic copolyester parts were characterized using a specially developed micro-beam wide angle X-ray diffraction camera technique and wide angle X-ray pole figure analysis techniques.

Wide angle X-ray pole figure analyses indicate that the local macro-symmetry throughout the sample seems to he uniaxial. The polymer chains are generally oriented in the flow direction except in the core regions after the diverging section, where molecular chains tended to orient transversely to the flow direction.

The local orientation of chains is determined from the micro-WAXS film patterns using DIA (Digital Image Analysis) technique. This enabled us to map the orientation of the local symmetry axes as well as local chain orientation through the thickness direction. The data indicate that the chain orientation is highest at the skin layer, becomes lower at the sub-skin layer, then increases gradually toward the shear layer and finally decreases to very low levels in the core regions.
Flow and Heat Transfer Simulation of the Mixing of Polymer Blends Using the Boundary Element Method
Authors: Gramann P. J. , Stradins L. , Osswald T. A.
Published: December 2013

In most polymer processes the quality of the final part stems back in great part to the mixing of the polymer blends and the viscous heating that occurs during the process. To date, these processes have been simulated using the finite difference or finite element methods which rely on cumbersome remeshing techniques, restricting the analysis to simple geometries. However, mathematical manipulation of the governing equations results in boundary integrals, allowing the solution of complicated moving boundary problems without domain meshing. The resulting boundary element model and simulation results of flow with heat transfer and the blending of two or more fluids of different viscosity effects during mixing of polymer blends is presented in this paper. The results give insight to the complex phenomena that take place during mixing processes.
Flow Simulation of a Polymer Melt in a Roller Die
Authors: Kegasawa T. , White J. L.
Published: December 2013

The flow characteristics of Newtonian and non-Newtonian fluids in a roller die are simulated. Both pre-form and Tmanifold entry regions are considered. Calculations are made using a modified Flow Analysis Network procedure. We take into consideration the interaction of roller dies with the screw extruders that feed them. We show operating conditions that can cause starvation to develop in screw extruders feeding roller dies.
Control Strategies for Cyclic Polymer Processes
Authors: Ralston P. , Wright A. , Stoll K. , Harper D.
Published: December 2013

This paper presents the simulation of a typical cyclic polymer processing operation with respect to the performance of different control strategies for part quality when subjected to disturbances with realistic load-profiles. Disturbances enter the simulation in a complex, probabilistic manner creating a unique flexibility in load representation which helps the simulation more accurately capture the performance of real processing operations. Realistic simulations can provide necessary information and be less costly than benchmark studies on actual processes. The objective of the research is to examine the effect of different control strategies on the overall control of part-to-part quality, not the control of the continuous processes that occur in part fabrication. The performance of six different control strategies is compared; two strategies are conventional feedback, and four strategies are statistically based. The statistically based algorithms effect closed loop control, but only when a true load exists. Results are analyzed using statistical analysis of variance (ANOVA) via a completely randomized block experimental design, and Duncan's multiple range test is used to rank the control strategies. The results indicate that as more disturbances enter the system, the conventional controllers perform better than the other strategies. When fewer disturbances are present, however, the statistically based controllers perform better. The most notable result is that one statistically based controller, the Western Electric runs rules controller, performs well over the entire range of disturbances.
Design of Tightly Intermeshing Co-Rotating Twin Screw Extruders
Authors: Potente H. , Ansahl J. , Klarholz B.
Published: December 2013

Composite models for the calculation of the filling level profiles, the pressure profiles, the melting profiles, the residence time distributions, the temperature profiles, the shear stress profiles, and the power consumption in modular tightly intermeshing co-rotating twin screw extruders (ZSK) are developed. A complex systematic design procedure was compiled, which is explained in part in this paper. The simulation of the intermeshing co-rotating machine involves both screw and kneading disc elements, including left- and right-handed sections. Kneading blocks were approximated by a screw of “equivalent pitch” with making allowance for the leakage flow across the flights from one channel to the adjacent channel. The mathematical treatment of co-rotating twin screw extruders has been based up according to the theory of single screw extruders. There was seen to be a good correlation between calculated and experimental results.
Devolatilization of Polymer Solutions
Authors: Chen L. , Hu G. H. , Lindt J. T.
Published: December 2013

A simulator to emulate the working of a counter-rotating twin screw extruder was constructed for studying devolatilization (DV) of reactive polymer solutions. The rate of the release of the volatiles was measured by an in-line mass flow meter. The operating pressure and solution temperature were measured by a pressure transducer and a thermocouple. The vapor sample compositions were determined by UV spectrophotometer. The transesterification of ethylene-vinyl acetate copolymer with 3-phenyl 1-propanol in 1-nonane solution was chosen as a model reaction. The volumetric mass transfer coefficient K1A was determined at various temperatures, pressures, shaft speeds and sample sizes. The effect of the reaction on K1A was also examined. It was found that K1A of the solvent (1-nonane) increases significantly with a decrease in operating pressure, and that it also increases appreciably with shaft speed, whereas temperature and the initial sample size have little effect on it. The reaction shows undetectable effect on K1A of the inert solvent.
Cooling and Wall Thickness Uniformity in Plastic Pipe Manufacture
Authors: Pittman J. F. T. , Whitham G. P. , Beech S. , Gwynn D.
Published: December 2013

A mathematical model of cooling and solidification, coupled with gravity induced flow during the cooling of extruded plastic pipe is set up and solved by the finite element method. Detailed and comprehensive experimental data are obtained from a commercial extrusion line producing 315 mm O.D. SDR 11 MDPE pipe using vacuum sizing and external spray cooling, including temperatures measured within the pipe wall using embedded thermocouples, which are carried down the entire cooling line.

The computer simulations are successfully fitted to experimental temperatures by adjusting transfer coefficients for the outer surface. The deduced values are: tank (1) (vacuum) 750 W/m2 K; (2) 200 W/m2 K; (3) 150 W/m2 K. Heat loss to the bore is shown to be negligible. Predicted final pipe wall thicknesses – starting with a concentric extrudate – agree within 4 % with measured values. Wall thickness variation is predicted to be 16.6 %, compared with 13.9 % measured.
High-Speed, Non-Isothermal Fiber Spinning
Authors: Papanastasiou T. S. , Alaie S. M. , Chen Z.
Published: December 2013

Spinning of PET fibers of low elasticity at high speed, and of polypropylene (of moderate elasticity) and polystyrene (of high elasticity) under non-isothermal conditions that contain their glass transition temperature, is analyzed by means of a unique BKZ-type constitutive equation that is augmented by the appropriate form of shift factors to apply in both, the rubbery and the glassy states of amorphous polymers. This approach eliminates the necessity of tracking the glassification point by trial and error, required in attempting to match different constitutive laws across it. Predictions of velocity and temperature distribution along the PET fiber agree with available experimental data, and the predicted glass transition point of polystyrene occurs indeed at about its glass transition temperature. Comparisons of predictions to those with an inelastic constitutive equation show that they apply to PET (of low elasticity) alone.
Finite Element Modelling of Non-isothermal Viscometric Flows in Rubber Mixing
Authors: Nassehi V. , Salemi R.
Published: December 2013

Attempts to find a general viscoelastic fluid model which would be applicable to all different classes of flow problems and could produce experimentally verifiable results, have so far failed. Instead efforts have been concentrated in finding a suitable viscoelastic model for the particular class of flow problem in hand. Bearing this in mind, a simple viscoelastic fluid model which has shown promising results for cases where there is a dominant flow direction (i.e. the flow is viscometric) is considered here. Such conditions may occur inside a rubber mixer where in cylindrical coordinate system (r,θ,z), the elastomer is flowing dominantly in θ direction. This paper deals with the Galerkin finite element modelling of viscometric flows under non-isothermal conditions. The novel aspect of this work is the extension of the application of a viscometric constitutive equation known as (CEF) model to the simulation of predominantly circumferential flow in a two-dimensional representation of an internal mixer using polar coordinates. For a given set of boundary conditions, the mathematical model can simulate the velocity, pressure and temperature fields inside a mixer. Comparison of the numerical results with the available experimental evidence confirm the general validity of the mathematical model used.
Modification of Polypropylene by Maleic Anhydride
Authors: Martínez J. Ma. Ga. , Taranco J. , Laguna O. , Collar E.P.
Published: December 2013

The Box-Wilson experimental design method is employed to study the free radical process between polypropylene and maleic anhydride in the presence of a peroxide like radical initiator. The batch processes in the solution and in the molten state have been considered in an attempt to know how the physical characteristics of the reaction medium are affecting the modification level of the polypropylene. The analytical titration method proposed by Gaylord is used in order to evaluate the maleic anhydride grafting onto the polypropylene. The main goal of this preliminary study is to know and to show the quantitative values reached in the grafted maleic anhydride level inside the experimental range scanned. From the results the influence of the reaction and several observations can be made in order to evaluate and finally optimize the continuous process by reactive extrusion.
Extrusion of Short Fibre Reinforced PP
Authors: Dospis~il D. , Kubát J. , Plešek M. , Sáha P.
Published: December 2013

Data regarding the influence of screw geometry on homogeneity and fibre length reduction during single screw extrusion of short glass fibre reinforced PP are presented. Three screw geometries, two grades of PP with different melt flow indices, and four levels of filling (10 to 40 wt.%) were the main variables studied. The fibre breakage mechanism was evaluated with respect to solid and melt conveying and melting mechanisms in the screw channels. The screw with a long compression zone produced a material of poor homogeneity, a stable melting mechanism and a medium level of fibre length reduction. The very short compression zone screw produced unstable melting which considerably improved the homogenization process of the fibres in the polymer matrix. In this way the extrudates remained smooth up to the 30 wt.% filling level. The homogeneity was comparable to that obtained by a process including two steps of compounding: twin screw and single screw extrusion. However, the fibre degradation in the screw with a very short compression zone was substantially lower than in the process including two compounding steps.
An Experimental Study of a Bicomponent Coextrusion Fiber Spinning
Authors: Lee W.-S. , Park C.-W.
Published: December 2013

The draw resonance instability in a concentric bicomponent coextrusion fiber spinning has been studied experimentally using a linear low density polyethylene (LLDPE) for the core and two low density polyethylenes (LDPE) for the skin-layer. These materials have been chosen to investigate a coextrusion flow in which each components have quite different extensional rheology. When they were spun individually, the LLDPE showed the draw resonance at a certain critical draw ratio whereas the LDPEs did not show the oscillatory instability. When the LLDPE and LDPE were spun together, the presence of the more viscoelastic LDPE layer delayed the onset of draw resonance of the LLDPE to a higher draw ratio. The degree of changes in the critical draw ratio was observed to be dependent on the rheological properties of the LDPEs. Although the experiments were conducted in a non-isothermal condition, various aspects of the experimental observations appeared to be in qualitative agreement with the predictions of isothermal linear theories. The present study is specifically for a coextrusion fiber spinning. Nevertheless, the observed trend of the instability should be also relevant to other coextrusion processes such as extrusion coating or film casting.
Blends of PVC with Miscible Polymers
Authors: Nakajima N. , Kwak S.-Y.
Published: December 2013

Polymer blends consisting of miscible components may form single phase structures; however, it requires solution blending to ensure complete homogeneity. For a large scale mixing, however, mechanical blending is the common practice. The resulting blends are homogeneous on the macroscale, but often contain microscopic domains of the component polymers as well as domains of mixed phases. This work describes mechanical blends of PVC with miscible polymers (nitrile rubber, poly-e-caprolactone, and a copolyester thermoplastic elastomer). The complex morphology of these blends has been studied and identified by means of the frequency- and temperature-dependence of their viscoelastic behavior.
Simulation of Heat Transfer and Melting in Rotational Molding
Authors: Bawiskar S. , White J. L.
Published: December 2013

A new model of the heating and melting process in rotational molding is presented. The improvement of the melt front during the melting process is followed. The model is applied to mold design.
Polyarylamide/Polypropylene Blends
Authors: Haddout A. , Villoutreix J. , Villoutreix G.
Published: December 2013

This work deals with the experimental study of the rheological behaviour, the growth and evolution of the morphology of two components polyarylamide/polypropylene blends during injection molding. In the case of compatibilized blends, the viscosity shows two main results depending on shear rate. For low shear rates, up to 103 s−1, we notice a positive deviation in comparison with the additivity low, whereas a negative deviation is observed for high shear rates including injection molding conditions. The analysis of the morphology of the blend by scanning electronic microscopy shows a dispersed phase with nodules. The injection flow rate acts on the shape of the nodules and also on their repartition as obtained from a rectangular molded plate. The thermomechanical analysis of pure composition samples (100 % PA) and of a compatibilized mixture PA (70 %)/PP (30 %) has been studied.
Flexural Stiffness of Injection Molded Glass Fiber Reinforced Thermoplastics
Authors: Xia M. , Hamada H. , Maekawa Z.
Published: December 2013

Using a simulated laminated-plate model, an analytical method is presented for predicting stiffness of fiber reinforced injection moldings including the effects of fiber orientation and fiber length distributions. The mechanical properties of fiber reinforced composites depend not only on the elastic properties and the volume fraction of the constituent materials, but also on the fiber orientation and fiber length distributions in the molding. In this study, two probability density functions are proposed for modeling the distributions of fiber orientation and fiber length in the injection moldings, respectively. Inserting the fiber orientation and fiber length distributions into the components of the stiffness constant, the elastic moduli of the fiber reinforced injection moldings are predicted on the basis of a generalized laminated-plate theory.
Morphology in Blends of a Thermotropic Liquid Crystalline Polymer and Polypropylene
Authors: Sabol E. A. , Baird D. G.
Published: December 2013

By monitoring the development of morphology a novel dual extrusion process from the point that the thermotropic liquid crystalline polymer (TLCP) stream meets the matrix material to the final drawn strand, a clear mechanism for the development of the TLCP reinforcement is presented. It was found that under appropriate mixing configurations the fibrillar TLCP morphology seen in strands produced from this method originate at the onset of mixing in the phase distribution system and are subsequently refined as the melt passes through the static mixing elements. The axially continuous morphology seen at the entrance of the die is maintained and further developed as the blend passes through the die and is drawn. In contrast, strands produced using the single extruder blending or the dual extrusion method with excessive mixing produce a droplet morphology prior to the die. At a very low concentration of TLCP, the droplets are too small and well dispersed to sufficiently coalesce and deform into fibrils in the elongational flow field of the die and drawing process. These phenomena result in an undesirable morphology for self reinforcement which clearly has been seen in the measured mechanical properties of the strands.
Viscosity and the Formation of Die Drool at the Polymer-Metal Interfaces
Authors: Chan Chi-Ming
Published: December 2013

The effects of the die-wall material on the apparent viscosity of a blend of Hytrel and Viton and on the formation of a particle-like material, which is commonly referred to as die drool, at the polymer-metal interface were studied. The blend, which consisted of approximately 15 % Viton and 85 % Hytrel, was prepared by using a twin-co-rotating-screw extruder. During extrusion of this blend, small particles appeared on the surface of the extrudates; these particles were determined by XPS to be a material which consisted largely of Viton. The apparent viscosity of the blend and the amount of die drool were found to decrease as the surface energy of the material used for the construction of the die decreased. The reduction in the production rate of die drool is attributed to reduction of adhesion at the interface.
Biaxially Oriented Polyethylene Films by Compression of Injection Moldings
Authors: Bayer R. K. , Ania F. , Calleja F. J. Baltá
Published: December 2013

The tensile strength, σ, of biaxially oriented polyethylene (PE) films with various degrees of biaxial stretching has been measured. The dependence of σ in the two principal directions x and y is investigated as a function of two parameters: the biaxial draw ratio (average draw ratio of the film) and the degree of biaxiality (strain distribution along the principal directions). Both parameters are related to the final applied pressure PF. The influence of initial orientation and anisometry of the injection molded precursors on the final σx and σy values along the principal directions is studied. Results are discussed in the light of the deformation mechanism which transforms the original uniaxial fiber structure of the moldings into the biaxial fibrillar structure of the final films. Direct evidence of this transformation is provided by small angle X-ray scattering (SAXS).
A Study of Distributive Mixing in Counterrotating Twin Screw Extruders
Authors: Li T. , Manas-Zloczower I.
Published: December 2013

Counterrotating twin screw extruders are widely used for compounding, devolatilization, blending, and reactive extrusion. A fluid dynamics analysis package-FIDAP, using the finite element method, was implemented to simulate the 3-D, isothermal flow patterns in intermeshing and tangential counterrotating twin screw extruders. The rheology of the fluid was described by a power-law model. We developed a framework to evaluate the distributive mixing efficiency. The dynamics of distributive mixing were studied numerically by means of tracking the evolution of particles originally gathered as clusters. The extent or goodness of mixing was characterized in terms of length stretch, pairwise correlation function and volume fraction of islands. The length stretch reflects the capability of the mixer to spread particles away from their neighbors initially present in the same cluster. The pairwise correlation function characterizes the global distribution of particles in the mixing region. The volume fraction of islands quantifies the regions void of minor component and provides the local analysis of mixing. This framework can then be used to differentiate among various operating conditions or various designs of the same type of equipment.
Comparative Wide-angle X-ray and Microscopical Studies on the Layered Structure in Injection Molded Polypropylene Disks
Authors: Zipper P. , Abuja P. M. , Jánosi A. , Wrentschur E. , Geymayer W. , Ingolic E. , Friesenbichler W.
Published: December 2013

Circular disks (280 mm diameter, 2 mm thickness) were injection molded from isotactic polypropylene under systematic variation of processing parameters (melt temperature, mold temperature, screw velocity, packing pressure, and packing time). Sections were taken from the disks perpendicular to their surface, at 40 mm distance from gate, in different orientations, and were investigated by means of optical microscopy using polarized light and by spatially resolved wide-angle X-ray scattering. The results from X-ray scans of the cross-sections are presented in terms of several parameters characterizing the state of orientation of α-PP crystallites and the relative amount of β-PP crystallites. The profiles of the various X-ray parameters versus the distance from surface deliver a detailed picture of the layered structure of the cross-sections which is supported and supplemented by micrographs taken with polarized light. The comparison of the results obtained for disks molded under different conditions unveils clear correlations between processing parameters and morphological characteristics of the disks.
Tool Heat Transfer Analysis in Resin Transfer Molding
Authors: Wang T. J. , Lin R. J. , Lee L. J.
Published: December 2013

This work presents four different numerical approaches to analyze heat transfer in the mold halves. The formulations, numerical methods and simulated results of each method are presented and compared to the experimental results based on a metal (aluminum) and a non-metal (reinforced epoxy) molds. Several examples are also presented to show the importance of tool heat transfer analysis in reactive processing.
Injection Molding of Microcomposites Based on Polypropylene and Thermotropic Liquid Crystalline Polymers
Authors: Handlos A. A. , Baird D. G.
Published: December 2013

This work is concerned with the injection molding of pellets of polypropylene (PP) containing pregenerated microfibrils of thermotropic liquid crystal polymers (TLCPs), referred to as microcomposites. The TLCPs used are HX6000 and Vectra A950. The microcomposites are produced by drawing strands of PP and TLCPs generated by means of a novel mixing technique and pelletizing the strands. The work was undertaken in an effort to improve on the properties observed for in situ composites in which the TLCP fibrils are generated during mold filling. In situ composites usually exhibit highly anisotropic mechanical properties and the properties do not reflect the full reinforcing potential of the TLCP fibers. Factors considered include the effect of in situ composite strand properties on the properties of the injection molded composite, the melt temperature used in injection molding, TLCP concentration, and the melt temperature of the TLCP. It is found that when processed at appropriate temperatures, the TLCP microfibrils are maintained through injection molding, and the composites show a good balance between machine and transverse direction properties (with ratios of the machine and transverse direction moduli ranging from 1.1 toto 1.35). The use of HX6000 rather than Vectra A allows for higher processing temperatures to be used during injection molding. The moduli of the injection molded composites increase with both increasing TLCP composition and in situ composite strand moduli. At 10 wt.-% TLCP the moduli of the injection molded composites approach the predictions of composite theory while at 20 and 30 wt.-% TLCP negative deviations from the theoretical moduli are seen. This is believed to be the result of a loss of fiber aspect ratio from fiber breakage and agglomeration. It is believed that with future studies on the effect of shear and elongational stresses during processing on the aspect ratio of the fibers a means of overcoming this problem may be found. The modulus of a 20 wt.-% HX6000 composite is similar to that of a 20 wt.-% glass composite (3.21 GPa versus 3.66 GPa), but the tensile strength of the HX6000 composite is about 28 % lower than that of the glass composite. It is expected that as the modulus and strength of the reinforcing TLCP fibrils are improved the properties of the injection molded microcomposites should exceed those of glass reinforced composites.