Published by De Gruyter

Volume 33 Issue 3

Issue of International Polymer Processing

Contents
Journal Overview

June 18, 2018

Page range: 297-297

Editorial

June 18, 2018

Editorial

Page range: 298-299

Special Issue Contributions

June 18, 2018

Preparation of Poly(l-lactic acid) Scaffolds by Thermally Induced Phase Separation: Role of Thermal History

V. La Carrubba, V. Brucato

Page range: 300-313

Abstract

Poly-L-Lactic Acid (PLLA) scaffolds for tissue engineering were prepared via thermally induced phase separation of a ternary system PLLA/dioxane/tetrahydrofurane. An extension to solution of a previously developed method for solidification from the melt was adopted, the technique being based on a Continuous Cooling Transformation (CCT) approach, consisting in recording the thermal history of rapidly cooled samples and analysing the resulting morphology. Different foams were produced by changing the thermal history, the dioxane to THF ratio (50/50, 70/30, 90/10 v/v) and the polymer concentration (2, 2.5, 4 ° wt) in the starting ternary solution. Pore size, porosity, melting and crystallization behavior were studied, together with a morphological and kinetic analysis of the foams produced. A large variety of morphologies was achieved, the largest pore size (20 μm) was achieved at the highest polymer concentration (4 ° wt) and the lowest dioxane concentration (50/50 dioxane/THF v/v), whereas the largest porosity (90 °) was attained at the highest dioxane concentration (90/10). The average pore size is related to cooling rate, with a 1/3 power law exponent at low polymer concentrations and low dioxane content for thermal histories driven by low undercoolings. At high undercoolings, the growth of the demixed domains significantly departs from the diffusive-like regime.

June 18, 2018

Modification of Syndiotactic Polypropylene with Nano-Calcium Carbonate and Halloysite

L. Pietrzak, E. Piorkowska, A. Galeski, J. Bojda, P. Sowinski

Page range: 314-321

Abstract

Composites of syndiotactic polypropylene (sPP) with 5 to 17 vol.° of halloysite and 2.5 to 7.5 vol.° of stearic acid modified nano-calcium carbonate, having an average grain size of 80 nm, were prepared and examined. The effect of fillers on thermal properties of sPP was different; halloysite increased markedly peak crystallization temperature. The composites with the highest filler contents, 7.5 vol.° of calcium carbonate and 17 vol.° of halloysite, exhibited a solid-like behavior at 170 °C, with the storage modulus exceeding the loss modulus in the entire frequency range, that is 512 to 0.1 rad s −1 . The composites with halloysite exhibited decreased Izod impact strength compared to neat sPP. On the contrary, 2.7 fold improvement of the impact strength was found for the composites with nano-calcium carbonate. Moreover, nano-calcium carbonate did not worsen the drawability of the materials during uniaxial drawing. It was found that debonding at calcium carbonate/sPP interface occurred both during the impact test and tensile drawing facilitating the plastic deformation of the polymer.

June 18, 2018

Enhancement of Heat Seal Properties of Polypropylene Films by Elastomer Incorporation

R. Boutrouka, S. H. Tabatabaei, A. Ajji

Page range: 322-326

Abstract

Seal strength at high and low temperatures as well as the width of the heat sealing temperature range are important properties in packaging industry. In addition, for sterilisable and retort applications, having those properties at elevated temperatures is crucial. Polypropylenes (PP) are usually used for these applications, however, the sealing temperatures are too high and the temperature range for the seal process is narrow, thus blending with a PP elastomer copolymer can be an alternative. In this study, hot-tack and heat seal properties were determined for a homo-polypropylene, a random co-polypropylene and an elastomer co-polypropylene based films and their blends. It is found that the seal initiation temperature (for hot tack and heat seal) is governed by the melting temperature and crystallinity and the increase of the elastomer content in the blends leads to a decrease of the seal initiation temperature. It is also shown that the sealing force depends on the ease of chains diffusion across the sealing interface. Finally, it was found that the strength of the heat sealing increases by recrystallization in the sealing interface after cooling.

Open Access June 18, 2018

Flow-Induced Crystallization of Polyamide-6

R. Massaro, P. Roozemond, M. D’Haese, P. Van Puyvelde

Page range: 327-335

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Abstract

Flow-induced crystallization has been widely studied for a variety of polymers with the main focus on polyolefins. In this work, research has been conducted on the flow-induced crystallization of another important class of polymers, namely polyamides. Different polyamides-6 with varying molecular weight have been studied. At relatively modest values of shear rate, rheology has been used to study the kinetics of flow-induced crystallization. Typical scaling relations based on the longest relaxation time and the Rouse time – usually obtained for polyolefins – are tested for the polyamides under investigation in order to identify the different regimes of flow-induced crystallization. At high shear rates, a correct rheological signal was impossible to collect. However, the rheometer was used in this case to prepare the sample to be studied ex-situ by Wide Angle X-ray Scattering experiments to determine the onset shear rate for the formation of highly oriented shish-kebab structures.

Open Access June 18, 2018

PLA Crystallization Kinetics and Morphology Development

Z. Refaa, M. Boutaous, D. A. Siginer

Page range: 336-344

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Abstract

This paper investigates the crystallization kinetics and morphology development of PLA. The transitory stages in the evolving flow-induced crystallization of PLA are identified and classified in terms of the overall crystallization kinetics and the crystalline morphologies. Under quiescent conditions, temperature governs the crystallization process and the slow crystallization kinetics of PLA is highlighted under these conditions, whereas under shearing conditions, the crystallization is highly enhanced due to the promotion of the nucleation mechanism. The enhancement of the crystallization implies also morphological modifications. Depending on the shear rate and the shearing time the microstructure changes dramatically: spherulitic microstructure, fine grained microstructure and oriented microstructure. For a specific shear rate, depending on the magnitude of the shearing time the microstructure assumes the following states: for low shearing time only an increase of the number of nuclei is observed (leading to fine grained microstructure), followed by a saturation of point-like nuclei, and for a relatively long shearing time (i. e. beyond a critical shearing time) the development of oriented structures looking like “shish-kebabs” is observed. The critical shearing time for the formation of oriented structures in PLA is determined as a function of the shear rate.

Open Access June 18, 2018

Morphology in Multilayer Blown Films of Polypropylene and Ethylene-Octene Copolymer Blends

J. Silva, M. Elias, N. Lima, S. Canevarolo

Page range: 345-354

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Abstract

In this work the microstructure of multilayer blown films consisting of a core layer placed between two external ones is studied. The core layer is a blend with 70 ° (w/w) of a homopolypropylene PP and 30 ° of a metallocene-catalyzed ethylene-octene copolymer mEOC (LLDPE or VLDPE), whereas the external symmetrical layers are composed of LLDPE or they have the same composition as the core layer. The PP and PE crystalline phases formed during the film blowing were investigated by thermal analysis, mechanical properties, TEM morphology and X-ray diffraction pole figures. These films successfully combine the high mechanical strength of PP with the quasi-isotropic behavior of blown PE. Multilayer film containing PP/mEOC blends, particularly blends of PP70/LLDPE30, show better balanced tensile properties when compared at crossed directions. The presence of VLDPE in the blends shifts downwards the melting and crystallization temperatures and crystallinity of PP. X-Ray pole figures suggest the occurrence of epitaxial crystallization of the PE phase upon the PP crystals in these PP/mEOC blend films.

Open Access June 18, 2018

A Criterion for the Formation of Fibrillar Layers in Injection Molded Parts

R. Pantani, V. Speranza, G. Titomanlio

Page range: 355-362

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Abstract

It is quite well known that the morphology of an injection molded part made by a semicrystalline polymer presents several layers. In particular spherulitic structures are found in the core region, a layer characterized by highly oriented fibrillar morphology (the shear layer) usually follows and a skin layer is often observed at the sample surface. The thickness of the fibrillar layer deeply influences the mechanical properties of the part. In this work, a criterion to predict the thickness of the fibrillar layer is proposed and verified. The criterion is essentially based on the amount of viscous work done when the molecular stretch is higher than a critical value: the molecular stretch should be above a critical value while a critical amount of viscous work is accumulated. In order to tune the parameters, and to validate the criterion, a well characterized polypropylene was chosen as test material, and four different injection molding conditions were analyzed. The criterion is verified by comparing some experimental results with the prediction of the UNISA code (an injection molding software developed at the University of Salerno), good comparison between software predictions and experimental data confirms the suitability of the criterion.

June 18, 2018

Abnormal Behaviors in the Capillary Rheometry of Plastisol Formulations

Y. Demay, Y. Abdesselam, R. Castellani, J. F. Agassant

Page range: 363-370

Abstract

The rheology of plastisol formulations for flooring applications using knife-over-roll coating process is studied using both Couette and capillary rheometers. The behavior is similar in many aspects to the rheology of suspensions: Shear thinning behavior at low shear rate, then a Newtonian plateau at intermediate shear rates followed by a dilatancy peak. However several abnormal phenomena may be observed in capillary experiments. At very high shear rates, a second shear thinning behavior is observed which depends on the flow geometry. Due to the non-monotonous behavior of the plastisol viscosity, this is analysed using a dedicated numerical method. An apparent slip velocity has been determined. Otherwise capillary experiments point out the existence of important entrance pressure loss. These measures are interpreted using a modified Cogswell method as an important elongationnal viscosity, around hundred times the shear viscosity.

June 18, 2018

The Effect of Cellulose Nanocrystals (CNC) on Isothermal Crystallization Kinetics of LLDPE and HDPE

V. Tan, W. Abdallah, M. R. Kamal

Page range: 371-380

Abstract

Highly porous agglomerates of spray freeze dried cellulose nanocrystals (SFD-CNC) were prepared, starting with sonicated aqueous suspensions of spray-dried cellulose nanocrystals powder (SD-CNC). Subsequently, SFD-CNC together with the SD-CNC (used as a reference) were incorporated into LLDPE and HDPE via melt compounding in a batch mixer to produce nanocomposites containing 0.5 wt.° and 2 wt.° CNC. Differential scanning calorimetry (DSC) was used to study the thermal properties and the isothermal crystallization kinetics of the polyethylenes and the nanocomposites. Polarized light microscopy (PLM) was used to evaluate the growth kinetics and spherulitic structure of polyethylene in both the filled and unfilled polymers. Avrami crystallization kinetics models were employed to analyze the DSC results. It was observed that CNC acts as a heterogeneous nucleating agent in LLDPE nanocomposites, thus yielding nucleation controlled crystallization. On the other hand, in the HDPE systems (polymer and nanocomposites) heterogeneous nucleation was followed by 3-D growth. It was observed that CNC slightly hindered the formation of chain folding for the HDPE, similar to previous studies on the polypropylene and its nanocomposites. Spray freeze drying produced twice as many nucleation sites compared to spray dried samples and it enhanced the overall crystallization rate and the crystallinity.

June 18, 2018

A Rheological Investigation of the Crystallization Kinetics of Syndiotactic Polypropylene of Varying Degree of Tacticity

R. Pasquino, F. Auriemma, C. De Rosa, N. Grizzuti

Page range: 381-386

Abstract

The crystallization behavior of five Syndiotactic Polypropylene (sPP) samples of varying degree of tacticity has been studied by means of rheological techniques and compared to the results of more standard DSC measurements. Small Amplitude Oscillatory Shear (SAOS) measurements have been performed on a controlled stress rotational rheometer equipped with a nitrogen-fed, forced convection oven, which allows for good temperature stability and relatively high heating/cooling rates. Both non-isothermal and isothermal crystallization tests have been carried out. The former proved useful to determine the melting and crystallization temperature of the polymers. The latter were exploited to determine the temperature dependence of the polymer crystallization rate. The results showed the strong influence of the degree of tacticity on the crystallization behaviour of sPP. In particular, it was confirmed that a decrease in the stereo-regularity of the polymer chain considerably shifts the crystallization process to lower temperatures. For the case of the lowest tacticity sample, rheology was crucial in determining the temperature where the maximum (but very small) crystallization rate is attained, a result that could not be achieved by standard calorimetry measurements.

Open Access June 18, 2018

Effect of Mutual Interaction between High and Low Stereo-Regularity Components on Structure Formation in Melt Spinning Process of Isotactic Polypropylene Blend Fibers

K. Kawai, W. Takarada, T. Kikutani

Page range: 387-396

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Abstract

Fiber formation behavior of the blend fibers consisting of two types of isotactic polypropylene (iPP), i. e. high stereo-regularity/high molecular weight iPP (HPP) and low stereo-regularity/low molecular weight iPP (LPP), was investigated. In the melt spinning of blend fibers of various HPP:LPP compositions, the spinnability was improved significantly not only by blending LPP into HPP but also by blending HPP into LPP. On-line diameter measurement of the spin-line revealed that the increase of LPP composition caused the shift of solidification point to downstream, indicating that the crystallization temperature was lowered. Wide-angle X-ray diffraction (WAXD) analysis of the as-spun fibers clarified that only the α-form crystal was formed, and the crystalline orientation increased with the increases of take-up velocity and HPP weight fraction. The crystallinities obtained from the WAXD patterns of the as-spun fibers of various HPP/LPP compositions prepared at the take-up velocity of 1 and 5 km/min were lower than the values estimated based on the rule of additivity, where the difference was more prominent for the 1 km/min fibers. Analyses of crystallinity through differential scanning calorimetry measurements also suggested the suppression of the crystallization of HPP in the HPP/LPP blend fibers. The thermal analyses basically clarified that in the melt spinning process of the blends of HPP and LPP, both components crystallized independently even though the two polymers are considered to be miscible in the molten state, however, detailed analyses of melting behavior of the as-spun fibers suggested the possibility of the formation of crystals with a certain level of mixing of the HPP and LPP molecules, i. e. the mixing of a certain amount of LPP molecules into the HPP crystals and also the mixing of a certain amount of HPP molecules into the LPP crystals.

Open Access June 18, 2018

Analysis of the No-Flow Criterion Based on Accurate Crystallization Data for the Simulation of Injection Molding of Semi-Crystalline Thermoplastics

V. Hondros, M. Vincent, L. Freire, S. A. E. Boyer, J.-M. Haudin, V. Royer, G. François, L. Ville

Page range: 397-410

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Abstract

It is well known in practice that the shape and dimensions of injected parts are highly dependent on the packing-holding stage. A major problem in semi-crystalline polymers is the prediction of the solidified layer, whose thickness has an important effect on shrinkage and warpage. We propose a pragmatic approach based on the concept of no-flow temperature. This temperature should be related to crystallization temperature, but the choice is not easy because it depends on cooling rate and pressure which are functions of time and position. The objective of the work is to evaluate the sensitivity of an injection molding computation to the no-flow temperature and to evaluate the relevance of its choice. The crystallization temperature of an isotactic polypropylene is determined as a function of cooling rate and pressure in laboratory experiments. The pressure dependence is measured using the original Cristapress cell. As a case study, we simulate the filling and post-filling of a plate mold using Rem3D, a 3D code for injection molding. Three no-flow temperatures and two sets of parameters for temperature dependence of viscosity are tested. Their respective influences on the pressure evolution are shown, and the crystallization temperature calculated a posteriori using the experimental material data is compared to the “arbitrary” no-flow temperature.

June 18, 2018

Interfacial Tension Properties in Biopolymer Blends: From Deformed Drop Retraction Method (DDRM) to Shear and Elongation Rheology-Application to Blown Film Extrusion

K. Lamnawar, A. Maazouz, G. Cabrera, R. Al-Itry

Page range: 411-424

Abstract

Shear and elongation rheology have been used in order to quantify the interfacial tension properties of PLA_PBAT blends. A multi-functional epoxide (Joncryl) has been chosen as a compatibilizer. From small amplitude oscillatory shear (SAOS), the results show that the addition of the Joncryl into the blends increased largely the shear rheological properties (elasticity, shear-thinning behavior) and contributed to very long relaxation process. This relaxation process is characterized by the presence of a G′ shoulder at lower angular frequencies. Scanning and transmission electron microscopy (SEM and TEM) observations show a finer morphology thus confirming the improvement of interfacial properties of the compatibilized blends. The interfacial tension has been firstly quantified using the deformed drop retraction method (DDRM). These experiments elucidated some of the effects of phase elasticity on both deformation mechanism and break-up conditions. A decrease of the interfacial tension has been demonstrated for the compatibilized blends. Secondly, the same trend was also highlighted using the emulsion Palierne model (simplified and generalized versions). Finally, the interfacial tension value was extracted from the measurements of extensional properties. A good accuracy with the two latter methods was obtained. This decrease of the interfacial tension nicely demonstrated the role of Joncryl as an efficient compatibilizer for a better handling of blow PLA-PBAT film extrusion process.

June 18, 2018

Stress Optical Behavior and Structure Development in Melt Spun PEEK/PEI Blends

R. Ozisik, M. Cakmak

Page range: 425-434

Abstract

Stress optical behavior as influenced by blend composition has been investigated by on–line stress monitoring during melt spinning of a series of melt miscible PEEK/PEI blends. At low stresses/draw downratios, the fibers are found to be amorphous. In this range, the linear stress optical rule is obeyed and stress optical constant was found to be composition dependent. Beyond a critical drawdown, the PEEK chains first form very highly oriented ordered domains that exhibit significant translational disorder along the fiber axis. In the processing range observed, this structure persists even at high spinline deformation/stresses. While the stress optical behavior remains linear for those compositions where no stress crystallization was detected, negative deviation from initial linearity was observed when these ordered PEEK regions began to be observed indicating that birefringence saturation is approached while stresses are increased.

PPS News

June 18, 2018

PPS News

Page range: 435-435

Seikei Kakou Abstracts

June 18, 2018

Seikei-Kakou Abstracts

Page range: 436-437

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

Volume 33 Issue 3

Issue of International Polymer Processing

Contents

Editorial

Preparation of Poly(l-lactic acid) Scaffolds by Thermally Induced Phase Separation: Role of Thermal History

Abstract

Modification of Syndiotactic Polypropylene with Nano-Calcium Carbonate and Halloysite

Abstract

Enhancement of Heat Seal Properties of Polypropylene Films by Elastomer Incorporation

Abstract

Flow-Induced Crystallization of Polyamide-6

Abstract

PLA Crystallization Kinetics and Morphology Development

Abstract

Morphology in Multilayer Blown Films of Polypropylene and Ethylene-Octene Copolymer Blends

Abstract

A Criterion for the Formation of Fibrillar Layers in Injection Molded Parts

Abstract

Abnormal Behaviors in the Capillary Rheometry of Plastisol Formulations

Abstract

The Effect of Cellulose Nanocrystals (CNC) on Isothermal Crystallization Kinetics of LLDPE and HDPE

Abstract

A Rheological Investigation of the Crystallization Kinetics of Syndiotactic Polypropylene of Varying Degree of Tacticity

Abstract

Effect of Mutual Interaction between High and Low Stereo-Regularity Components on Structure Formation in Melt Spinning Process of Isotactic Polypropylene Blend Fibers

Abstract

Analysis of the No-Flow Criterion Based on Accurate Crystallization Data for the Simulation of Injection Molding of Semi-Crystalline Thermoplastics

Abstract

Interfacial Tension Properties in Biopolymer Blends: From Deformed Drop Retraction Method (DDRM) to Shear and Elongation Rheology-Application to Blown Film Extrusion

Abstract

Stress Optical Behavior and Structure Development in Melt Spun PEEK/PEI Blends

Abstract

PPS News

Seikei-Kakou Abstracts