International Polymer Processing Volume 27 Issue 5

International Polymer Processing

Volume 27 Issue 5

Contents
Journal Overview

April 6, 2013 Page range: 503-503

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Editorial

Pierre G. Lafleur April 6, 2013 Page range: 504-504

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Invited Papers

Effects of a Multifunctional Polymeric Chain Extender on the Properties of Polylactide and Polylactide/Clay Nanocomposites

Q.-K. Meng, M.-C. Heuzey, P. J. Carreau April 6, 2013 Page range: 505-516

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Abstract

A multifunctional polymeric chain extender (Joncryl) was used in the melt processing of a neat polylactide and polylactide/clay nanocomposites. The effects of Joncryl on morphology, rheology, thermal and mechanical properties, barrier properties and biodegradability were investigated. Three Joncryl loadings (0.1, 0.3 and 0.5 wt%) were used in this study, and the 0.5 wt% loading induced a long-chain branched structure in the PLA matrix, as indicated by the melt rheology results. It is believed that the property variations are all related to the long-chain branched structure as well as on the molecular weight recovery. The use of Joncryl did not change the intercalated and partially exfoliated clay structures in the PLA/clay nanocomposites, as observed by X-ray diffraction (XRD) and transmission electron microscopy (TEM). The tensile modulus and maximum strength slightly increased with Joncryl loading. The oxygen barrier properties were also improved by adding Joncryl. However, the addition of Joncryl prevented the formation of large spherulitic crystals and decreased the creep resistance at low stress level. Joncryl could not only control the thermal degradation of PLA during processing, but also affected its biodegradation in compost: higher Joncryl loading led to slower biodegradation and less molecular weight reduction with time.

Influence of Twin-Screw Processing Conditions on Structure and Properties of Polypropylene – Organoclay Nanocomposites

T. Domenech, E. Peuvrel-Disdier, B. Vergnes April 6, 2013 Page range: 517-526

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Abstract

This study looks at the influence of extrusion parameters such as screw speed, feed rate and barrel temperature on the nanocomposite structure (size of agglomerates, level of intercalation and exfoliation) and its consequences on final mechanical properties. Nanocomposites of polypropylene, maleated polypropylene and organomodified montmorillonite, with respective mass fractions of 85/10/5, were prepared in a co-rotating twin-screw extruder using a masterbatch dilution method. The nanocomposites structure was quantified by scanning and transmission electron microscopy, X-ray diffraction and dynamic rheometry. Relationships between the microstructure at different levels (size and number of agglomerates, interlayer distance, melt yield stress to quantify the exfoliation level) and the processing conditions were established, revealing that specific mechanical energy received during extrusion was the key parameter controlling this microstructure. Mechanical properties in uniaxial tension (apparent Young's modulus) were measured and related to the microstructural parameters resulting from extrusion conditions.

Monitoring the Production of Polymer Nanocomposites by Melt Compounding with On-line Rheometry

S. T. Mould, J. M. Barbas, A. V. Machado, J. M. Nóbrega, J. A. Covas April 6, 2013 Page range: 527-534

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Abstract

Polymer nanocomposites are often prepared by melt compounding due to the suitability of the latter to industrial scale production. Even though monitoring the production process for quality control and/or optimization purposes is generally done off-line, the possibility of using on-line oscillatory rheometry has many inherent advantages. This work illustrates the use of a prototype rheometer to monitor the production of polymer nanocomposites by making measurements at specific locations along the extruder axis. The device is presented and its operation is explained. Examples of its use to characterize polypropylene and polyamide matrix nanocomposites with organoclays and carbon nanotubes are discussed, thus demonstrating the usefulness of the device.

Annular Extrudate Swell of a Fluoropolymer Melt

E. Mitsoulis, S. G. Hatzikiriakos April 6, 2013 Page range: 535-546

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Abstract

Annular extrudate swell is studied for a fluoropolymer (FEP) melt using a tubular die. The rheological data of the melt have been fitted using (i) a viscous model (Cross) and (ii) a viscoelastic one (the Kaye – Bernstein, Kearsley, Zapas/Papanastasiou, Scriven, Macosko or K-BKZ/PSM model). Numerical simulations have been undertaken to study the extrudate swell of the FEP melt in an annular die. Compressibility, thermal and pressure effects on viscosity, and slip at the wall were taken into account. In all cases, slip at the wall is the dominant contribution reducing the swelling when compared with corresponding no-slip simulations. The viscous (Cross) simulations show that the swell decreases with increasing apparent shear rate, which is opposite to what happens in the extrusion of viscoelastic melts. On the other hand, the viscoelastic (K-BKZ) simulations correctly obtain increasing swelling with increasing shear (flow) rates. It was found that due to the mild viscoelasticity of FEP and its severe slip at the wall the swelling of this melt is relatively small, reaching values of about 20% for a wide range of apparent shear rates, exceeding 5000 s −1 . This is corroborated by experimental observations.

Injection Molding of Fibre Reinforced Thermoplastics: Integration of Fibre Orientation and Mechanical Properties Computations

H. Miled, L. Silva, T. Coupez, J. F. Agassant April 6, 2013 Page range: 547-556

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Abstract

Injection molding is widely used to process short fibre reinforced thermoplastics. The quality and especially the mechanical properties of the resulting part are linked to the mold conception (for example the gate(s) and the venting port(s) locations) and to the processing parameters which will govern fibre orientation distribution. Fibre orientation modelling is based on the well known Folgar and Tucker equation. The models differ one from another by the interaction parameter, the closure approximation and by the coupling with the rheology of the reinforced melt. Quantitative comparison with experiments is very tedious and generally limited to simple part geometries (plaque or disk). As a consequence, in complex geometries, fibre orientation distribution is experimentally checked using several techniques and the resulting anisotropic thermo-mechanical properties are computed using various homogenization theories. In this paper, we propose a first integrated approach of the injection molding of fibre reinforced thermoplastics starting from rheology of the material, orientation equation, interaction parameter and closure approximation. The resulting local fibre orientation distribution is then used in two ways in order to predict the mechanical properties of the part: first, using classical analytical homogenization theories, but based on the computed orientation tensor and not on an experimental one, and then, using numerical homogenization which consists in generating a Representative Elementary Volume (REV), determining its unidirectional mechanical properties and finally, in computing directly the anisotropic properties of the part.

Processing of Polymer Nanocomposites Reinforced with Cellulose Nanocrystals: A Challenge

A. Dufresne April 6, 2013 Page range: 557-564

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Abstract

Aqueous suspensions of cellulose nanocrystals can be prepared by acid hydrolysis of the biomass. Due to their nanoscale dimensions and intrinsic physicochemical properties, these nanoparticles are promising renewable biomaterials. The high mechanical properties and reinforcing capability of these nanoparticles make them attractive for the processing of high performance nanocomposites. The main problem is related to the homogeneous dispersion of these nanoparticles within the polymeric matrix. Because cellulose nanocrystals are obtained as aqueous suspensions, water is the preferred processing medium. However, new strategies are envisaged to broaden the polymeric matrices that can be reinforced with these nanoparticles and avoid the liquid medium processing way. This paper reviews the different processing techniques of cellulose nanocrystals reinforced polymer nanocomposites focusing on the challenging melt processing technique.

Structure, Mechanical and Barrier Properties of Uniaxially Stretched Multilayer Nylon/Clay Nanocomposite Films

F. Sadeghi, A. Ajji April 6, 2013 Page range: 565-573

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Abstract

Multilayer films consisting of a core layer of nylon 6 (PA6) sandwiched between two linear low density polyethylene (LLDPE) layers by using a tie layer were produced using a semi industrial cast film extrusion line. The core layer of the films was produced from neat PA6 and PA6/clay nanocomposite resins. The films were consequently uniaxially stretched in machine direction. The effect of stretching on crystalline structure, orientation as well as mechanical and barrier properties of the samples were investigated. Orientation of the films for both layers: polyethylene and nylon was assessed using FTIR (Fourier Transform Infrared Spectroscopy) and it was found that clay inclusion hindered orientation of the core nylon layer. Interaction of nylon molecules with clay influences the crystalline structure for nylon/clay nanocomposite film during the stretching as it hindered crystal transformation of γ to α phase. The effect of clay interaction on phase structure was also observed in DSC (Dynamic Scanning Calorimetry) results. Stretching improved barrier to oxygen for the samples. Oxygen transmission rate was reduced about 62.5% for the films having a nylon core and 50% for those with nylon/clay core when stretched to a draw ratio of 1.5 and remained nearly constant for higher draw ratios up to 3. Haze of the films was reduced with stretching; however the effect was more effective for the sample with neat nylon in the core layer when compared to the nylon/clay core one. Finally, it was observed that puncture resistance of the samples was improved significantly with stretching.

Characterization of Thermoplastic Laser-welded Joints

M. H. Al-Wohoush, M. R. Kamal April 6, 2013 Page range: 574-583

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Abstract

Laser-welded joints were prepared using moldings of polycarbonate, polyamide-6, and polyamide-6 reinforced with 30% glass fibers. Preparation of thin polished samples of the joints facilitated examination of the laser-affected zone (LAZ). The samples were examined using optical and polarized light microscopy, as well as scanning electron microscopy. The study evaluated the influence of laser power on the geometry and dimensions of LAZ, in both the absorbent and non-absorbent parts of the joints. The results indicated a correlation between LAZ dimensions and the tensile strength of the laser-welded joints. There is evidence of melt and fiber migration in the LAZ.

Regular Contributed Articles

Residual Wall Thickness Study of Variable Cross-section Tube in Water-assisted Injection Molding

J. G. Yang, X. H. Zhou, Q. Niu April 6, 2013 Page range: 584-590

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Abstract

Residual wall thickness is an important measure of the quality of water-assisted injection molding (WAIM) parts. Based on the traditional injection molding model, Reynolds stress was introduced into the WAIM model for the turbulent characteristics of high pressure water. In addition, residual wall thickness was computed by a computational fluid dynamics (CFD) method, and the results matched well with experimental data. The results show that the hollowed core ratio changes from small to large in the first half of water penetration, while in the latter half it is just the opposite. Difference of the residual wall thickness is larger at the large-diameter position of a part than other position. Residual wall thickness is mainly affected by water injection pressure, delay time, melt temperature, mold temperature and amount of short shot, in which the amount of short shot is the most obvious.

Design and Validation of a Cable Extrusion Tip with Spiral Channels

D. Haller, J.-M. Gonnet, C. Lankes April 6, 2013 Page range: 591-601

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Abstract

Traditional cable extrusion dies employ a side-fed flow distribution system. In this case, the flow is split into two streams, resulting in the formation of a weld line. The weld line runs as a radial line through the cross section of the cable coating and has the least favorable orientation when the cable coating is exposed to circumferential stresses. Therefore, a new cable extrusion tip based on the principle of spiral mandrel dies was developed to change the orientation of the weld line from radial, that takes place when side-fed mandrel dies are used, to circumferential, when melt distribution resulting from the layering of the leakage flow in spiral mandrel dies occurs. The circumferential orientation of the weld line reduces the exposure of the weld line to circumferential stresses and thus improves the mechanical properties of the cable coating. This paper first outlines the design strategy for the new cable extrusion tip and further presents experimental results. The design strategy is based on two-dimensional flow networks. The network model is applied to calculate the flow channel geometry for a wanted distribution of the flow. Further, it should generate a better understanding of the correlation between the flow, pressure drop, and the flow channel geometry to facilitate the design of the tip. Three dimensional FEM simulations were used in this work to validate the flow network model in terms of pressure drop and velocity profile at the exit of the tip. The results of the calculations with the network model show good accordance with three dimensional FEM-simulations. For the experimental part a tensile test was conducted to compare the tensile strength in circumferential direction of a cable extruded with the new tip with a cable extruded with a conventional cable extrusion tip. The measurements showed an increase of the tensile strength in circumferential direction of 10% to 15% for the cable extruded with the new tip compared to the tensile strength at the location of the weld line in the cable extruded with the conventional tip.

Water Penetration Behavior in Water-assisted Injection Molding (WAIM): A Study of Product Quality for Different Process and Material Parameters

S. Sannen, M. De Munck, P. Van Puyvelde, J. De Keyzer April 6, 2013 Page range: 602-616

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Abstract

This study investigates the relation between water penetration behavior and product quality in water-assisted injection molding (WAIM) for different process and material parameters. The principle mechanisms responsible for both building up the residual wall thickness (RWT) and formation of part defects as well as the influence of these process and material parameters on the RWT and occurrence of part defects could be revealed. This is done by relating the measurements of water pressure and water volume flow rate, visualizing in-mold variations during water injection, to both the part weight and a visual inspection of part cross-sections, for different process settings and materials. It was found that the RWT as well as the formation of part defects depend on the polymer resistance, since the variation of the latter leads to a change in both the water bubble width and velocity. On the one hand, the resistance is determined by the process parameters having an influence on the amount of melt ahead of the water bubble, depending on injector opening time, water volume flow rate and water injection delay time. On the other hand, the resistance also depends on the friction between the polymer chains, which is determined by the zero-shear viscosity and the shear thinning behavior of the polymer. In addition, the occurrence of part defects is directly related to the polymer crystallization behavior. The resulting product quality therefore depends on a combination of the process parameters and the applied material.

Effect of Prepolymerization Time on Morphology and Properties of Epoxy-modified Bismaleimide Foams

X. Liu, H. Lu, L. Xing April 6, 2013 Page range: 617-625

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Abstract

Epoxy-modified bismaleimide (BMI) foams were prepared through prepolymerization and foaming. Density-adjustable BMI foams with closed-cell structures were produced. The influence of prepolymerization time on bubble growth and morphology, as well as the compressive and heat resistant properties of the foams, were thoroughly investigated. BMI prepolymerization was an effective method for controlling the bubble growth rate, the bubble size and its distribution, and the foam density. As the prepolymerization time increased, the matrix viscosity, the number of cells per unit volume and the foam density increased, whereas, the bubble growth rate and cell size decreased, and the cell size distribution became narrower. The compressive strength and modulus increased with increasing prepolymerization time. The dimensional stability temperatures of the BMI foams were all above 200°C, as determined by their base materials, and were unaffected by prepolymerization time.

Rapid Communications

Mechanical Properties and Fracture Morphology of Blends of PC with PMMA

S.-K. Lee, S.-S. Cho, L.-S. Kang, C. G. Lee, H. S. Hong April 6, 2013 Page range: 626-630

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Abstract

The poly methyl methacrylate (PMMA) and polycarbonate (PC) residues were collected from waste LCD panels for use as raw materials to prepare PC/PMMA polymer blends (1/99, 3/97, 5/95, 10/90), which were extruded in a twin screw extruder. The extrudates were subsequently pelletized and then dried in an oven before injection molding into tensile bars of ASTM D638-91, type I. The tensile bars were placed in an Instron-type tensile tester and the load-elongation curves of tested 5/95 specimens demonstrated distinctively varied yielding before final brittle fracture but 10/90 showed some sign of ductile behavior, peak in the load-elongation curve attributable to formation of a neck. The tensile strength increased from 569.6 to 633.3 kgf/cm 2 with PC concentration in the range of 1 to 5 wt% while it decreased at 10 wt% PC. On the contrary, transverse rupture strength increased with added amount of PC. Addition of PC could have toughened recycled PMMA matrix under impact test conditions. Finally, the fractured surfaces were examined by scanning electron microscopy and numerous fine particles dispersed in the matrix of 10/90 are regarded as PC phase, in reasonable agreement with literature results. On the other hand, fracture surface of 5/95 showed nearly homogeneous matrix phase of PC/PMMA.

PPS-News

PPS News

April 6, 2013 Page range: 631-631

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Seikei Kakou Abstracts

Seikei-Kakou Abstracts

April 6, 2013 Page range: 632-633

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About this journal

International Polymer Processing offers original research contributions, invited review papers and recent technological developments in processing thermoplastics, thermosets, elastomers and fibers as well as polymer reaction engineering. For more than 25 years International Polymer Processing, the journal of the Polymer Processing Society, provides strictly peer-reviewed, high-quality articles and rapid communications from the leading experts around the world.
All articles are subject to thorough, independent peer review.
Editor: Polymer Processing Society