International Polymer Processing Volume 13 Issue 2

International Polymer Processing

Volume 13 Issue 2

Contents
Journal Overview

June 5, 2013 Page range: 109-109

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Editorial

In Memory of Morand Lambla (1939–1997)

June 5, 2013 Page range: 110-110

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Regular Contributed Articles

Free Radical Grafting of Glycidyl Methacrylate onto PP in a Co-rotating Twin Screw Extruder

G.-H. Hu, H. Cartier June 5, 2013 Page range: 111-117

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Abstract

A typical free radical grafting system is composed of a polymer substrate, a vinyl bearing monomer and a free radical initiator (usually a peroxide). When the reaction is to be carried out in a co-rotating twin screw extruder, there are two main ways to feed the chemicals to the extruder: either they are fed together to the main hopper (one-pot feeding) or only the polymer is fed to the main hopper and the grafting monomer and the peroxide are injected downstream either just before or after the first kneading zone (sequential feeding). In this study, we investigate the influence of feeding mode on the free radical grafting. We use the free radical grafting of glycidyl methacrylate (GMA) onto polypropylene (PP) as a model system. It is found that GMA's grafting yields are very close between the one-pot feeding and the sequential feeding just before the first kneading zone. However, those obtained with the sequential feeding just after the first kneading zone are much lower. This dramatic difference is closely related to the mixing environments GMA and the peroxide are subjected to. When GMA and the peroxide are injected before the kneading zone where the screw channel is fully filled, GMA and the peroxide are forced to mix with PP. When they are fed to the extruder just after the kneading zone, however, they simply drip on the highly viscous PP. As such, before the grafting takes place between PP and GMA, the peroxide may have started to decompose and GMA may have started to polymerize. It is recommended that low molecular weight ingredients be fed to the extruder through a fully filled zone.

Melt Grafting of Glycidyl Methacrylate onto Polyethylene

S. Hojabr, W. E. Baker, K. E. Russell, P. J. McLellan, M. A. Huneault June 5, 2013 Page range: 118-128

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Abstract

The melt grafting of Glycidyl Methacrylate (GMA) onto Polyethylene in the presence of free radical initiators was conducted in a co-rotating twin screw extruder. Reaction kinetic parameters for the overall grafting and homopolymerization reactions were estimated in a batch melt mixer. Residence time distribution (RTD) in the extruder was determined and mean residence time and Peclet number (Pe) were estimated for different sets of reaction conditions. A twin screw simulation program was used to predict the flow characteristics along the length of the extruder. A modular reactor model consisting of plug flow and “axial dispersion” reactor cells was constructed and with the kinetic and transport information and the actual melt temperatures, the overall GMA conversion was predicted. In most cases the predicted conversion agreed well with experimentally determined values.

Generation of Partially Crosslinked Expanded PP-films and -sheets

H. G. Fritz, U. Bölz, R. Lü June 5, 2013 Page range: 129-135

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Abstract

A modified concept for the generation of partially crosslinked expanded PP-films and -sheets, useable in automotive industry, is presented. The paper describes in detail an optimized formulation window for the organosilane crosslinking of the selected PP-copolymers, an adequate plant design for the realization of this innovative processing concept as well as approved process parameters. As derived from experimental studies, gel content and the amount of blowing agent seem to be the most essential parameters with regard to foam structure, foam density and cell size homogeneity.

Continuous Polymerization and Copolymerization of Lauryl Lactam in a Modular Corotating Twin Screw Extruder

S. K. Ha, J. L. White June 5, 2013 Page range: 136-141

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Abstract

A study is presented of the polymerization of lauryl lactam and the copolymerization of lauryl lactam and caprolactam in a modular co-rotating twin screw extruder. Lauryl lactam had not been previously polymerized in a twin screw extruder. It was found possible to do this to high molecular weights. Generally, lower screw speeds result in longer residence times and higher conversions and molecular weights. The copolymers produced have broad melting transitions and their melting temperatures and heats of fusion exhibit minima as a function of comonomer composition.

Peroxide Induced Crosslinking and Degradation of PA

Q. Yu, S. Zhu June 5, 2013 Page range: 142-148

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Abstract

Peroxide induced crosslinking and degradation of nylon-12 were experimentally investigated using an on-line electron spin resonance (ESR) spectrometer. It was found that different types of polymer radicals were involved in various peroxide modification processes. Five-line ESR spectra were observed in the DCP/nylon-12 and TBPB/nylon-12 systems, while the L130/nylon-12 system gave a three-line spectrum initially, followed by a transition to a single line. Based on the radical information, as well as gelation and viscosity measurements, various reaction mechanisms were proposed depending on the type of peroxide. TBPB is in favor of the degradation of nylon-12, while DCP and L130 promote crosslinking of the polymer. The gel formation was followed to facilitate the study of crosslinking kinetics. The initial gelation rate increased linearly with the peroxide concentration and/or temperature. The formation of crosslinked network impeded the crystallization of nylon-12 and reduced the degree of crystallinity. The high crosslinking extent resulted in low melting temperature and heat.

Squalane as Model for Free Radical Reactivity of PP

S. Drillières, R. Mestanza, D. Graebling June 5, 2013 Page range: 149-153

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Abstract

The degradation, grafting and crosslinking of polypropylene have been studied with a free modelling system: the squalane. This study used conditions similar to reactive extrusion in terms of temperature and concentration of actives species. The products of reactions were characterized by mass spectrometry and IR spectroscopy. The reaction between peroxide and squalane confirms the importance of the half-life of the peroxide in limiting the degradation of the squalane chain. In presence of monomer, we observed simultaneously grafting and β-scission of squalane. Comparison between methacrylates and acrylates shows that acrylates are much more effective for grafting than methacrylates. With trifunctional monomers, the main reaction is the crosslinking of squalane (or recombination of macroradicals via the monomer). In this case, triacrylates were also more effective.

Thermal Polymerization of Methyl Methacrylate at High Temperature

F. Fenouillot, J. Terrisse, T. Rimlinger June 5, 2013 Page range: 154-161

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Abstract

Kinetic studies of the bulk polymerization of methyl methacrylate at high temperature have been carried out first without any additives and then in the presence of 1-Butanethiol as a chain transfer agent. A pressurised dilatometric reactor operating at high temperature is used to determine the time-conversion curves at temperatures between 150 and 180°C. A two-stage polymerization is observed. The high polymerization rate obtained initially is attributed to traces of an initiating impurity, while the second, slower polymerization stage could be considered as the actual thermal polymerization. The chain transfer agent or an impurity it may contain also initiates the reaction. Therefore, the rates of both the initial polymerization and of the second stage are increased when the thiol is added. Experimental data on the degree of conversion versus time and on the final average molecular weight are used to determine the chain transfer constants to the monomer and to the mercaptan as well as the initiation rate constants. These constants are used to model the thermal polymerization of MMA at high temperatures where these initiation reactions can no longer be neglected, especially when an industrial polymerization process has to be optimized and controlled.

Using Mold Pressure Rise Data to Obtain Viscosity of Fast Polymerizing Systems

D. S. Kim, M. A. Garcia, C. W. Macosko June 5, 2013 Page range: 162-171

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Abstract

Typical reaction injection molding oligomers gel in less than 5 s, making it very difficult to measure their viscosity rise in a rheometer. The parameters of the viscosity function for two thermoset polyurethane (PU) systems made from modified 4,4'-diphenylmethane diisocyanates and polyether polyols were obtained through nonlinear regression of a mold filling simulation model using pressure rise data. The pressure rises were measured at the inlet point of an end gated rectangular mold. Adiabatic temperature rise experiments were carried out to obtain reaction kinetic equations of the PU systems. A second order Arrhenius type reaction kinetic equation described the adiabatic temperature data well. Viscosity change of a low catalyst PU system during isothermal polymerization was measured using a parallel plate rheometer, and a viscosity function was estimated from these data and the kinetic data. The viscosity function determined through regression of pressure rise data using the mold filling simulation model compared reasonably well to the viscosity function obtained from the rheometer data.

Sensitivity of In-line Rheometry for Extrusion of Mg(OH)2 filled LDPE Compounds

P. D. Coates, R. M. Rose, M. Woodhead, A. L. Kelly June 5, 2013 Page range: 172-182

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Abstract

In-process and off-line rheometry studies are reported for compounds based on Mg(OH) 2 filled low density polyethylene, some of which were first subjected to a range of strain histories in typical compounding operations. In the study reported here, the compounds were processed using an instrumented, computer monitored single screw extruder in the IRC laboratories, fitted with in line rheometers (ILR). In initial experiments a four sensor ILR slit die was used for the in-process shear rheometry, and a Rosand RH7 twin bore capillary rheometer for off-line shear and entry pressure measurements. Off line and in-line results are compared, showing good agreement for shear. Estimates have been obtained for the sensitivity to filler loading of the off line rheometer (shear flow and entry pressure measurements), and the 4 sensor ILR (shear flow measurements), which indicate that the ILR offers similar resolution of filler level to the off line rheometer at the higher loadings, although the ILR appears to have much lower sensitivity at higher shear rates at lower loadings, an effect which appears to be related to processing effects on the rheology of the compound rather than the measurement ability of the ILR. The ILR was also able to discriminate between samples with differing processing histories. Results from a six-sensor ILR die have shown good agreement in shear flow measurements, and have added the ability to measure entry pressures, which are compared with off-line measurements.

Effect of Temperature and Compatibilizer on Interfacial Tension of PE/PA-6 and PP/EVOH

H. Garmabi, N. R. Demarquette, M. R. Kamal June 5, 2013 Page range: 183-191

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Abstract

Interfacial tension measurements for polyethylene/polyamide-6 (PE/PA-6) and polypropylene/ethylene-vinyl alcohol copolymer (PP/EVOH) pairs were performed using the spinning drop method. The effects of the temperature and maleation content of the polyolefin on the interfacial tension were evaluated. The temperature coefficients of interfacial tension were found to be 0.036 and 0.087 dyne/cm/°C for the PE/PA-6 and maleated PP/EVOH systems, respectively. The interfacial tension of PE/PA-6 system showed exponential dependence on the maleation content of PE. The accuracy of the spinning drop method was evaluated against the pendant drop technique. It was found that the spinning drop technique tends to yield lower interfacial tension values than the pendant drop method. The harmonicmean equation was found to provide a fair estimate for the interfacial tension of PE/PA-6 pair.

Predicting Drop Breakup in Complex Flows from Model Flow Experiments

D. I. Bigio, C. R. Marks, R. V. Calabrese June 5, 2013 Page range: 192-198

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Abstract

New experimental results describing the breakup of drops suddenly subjected to shearing forces sufficient to cause drop breakup are presented. The experiments examine fluids which are immiscible and Newtonian under the conditions studied. These results and other breakup mechanism results are then discussed in the context of combining them with kinematic information on more complex flows in order to predict drop size distributions in processing flows. By analyzing the time scales of various breakage mechanisms studied in simple shear flow and comparing them to the appropriate time scales in more complex flows, the relevant importance of a given mechanism in determining the daughter drop size distribution is predicted. This type of time scale analysis is performed for flow in a cavity and flow in an extruder.

Interactions in Binary and Ternary Polyolefin Blends

I. Hénaut, B. Vergnes, J. F. Agassant, J. M. Haudin June 5, 2013 Page range: 199-208

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Abstract

A way for the recovery of plastic waste is the reprocessing. As they cannot be easily separated, the reprocessing of polyolefins appears as a special case of the processing of polymer blends. In order to understand the basic phenomena involved in these systems, binary and ternary blends are prepared from a high density polyethylene, a linear low density polyethylene, and a random ethylene-propylene copolymer. In a first step, the interactions between the different polyolefins are characterized in laboratory experiments (differential scanning calorimetry, optical microscopy, small-angle light scattering, wide-angle X-ray diffraction, mechanical properties). Then, it is shown that the original poor mechanical properties of the blends can be largely improved by optimizing the processing conditions. Finally, an extrapolation of these results to real plastic waste is presented.

Injection Moulding of Rubber Compounds1

S. Karam, M. Vincent, Y. De Zelicourt June 5, 2013 Page range: 209-217

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Abstract

The aim of this study is to show the relevant physical parameters related to rubber injection moulding, and especially compressibility, vulcanisation and wall slippage. Three materials are studied: an SBR compound, without and with a lubricant, and an EPDM compound. The viscosity is determined by capillary rheometry. The modified SBR exhibits wall slippage. Rheological vulcanisation kinetics are determined with a Moving Die Rheometer. Precise moulding experiments are carried out with an injection moulding machine and a mould equipped with pressure and temperature transducers. At low flow rate, the influence of the curing reaction on the pressure appears clearly especially for the fast curing EPDM. The conditions in which surface scorch defects appear are determined. The SBR with lubricant needs a lower pressure to fill the cavity than without lubircant. A model of mould filling is developed. The material is purely viscous, with a state of cure dependence of the viscosity. A Norton friction law is introduced to take into account a possible slippage at the cavity walls. A compressible calculation in the injection chamber allows a realistic evaluation of the flow rate at the entry of the cavity. The comparison with the experimental data confirms the importance of the compressibility, and the influence of the vulcanisation on the viscosity at low flow rate. In moulding conditions for which vulcanisation is not activated during the filling stage, despite uncertainties on the friction law parameters appropriate to the cavity wall roughness, the agreement with experiments is better when wall slippage is taken into account.

Pseudoplasticity and Dilatancy in Shallow Channel Flows

J. T. Lindt June 5, 2013 Page range: 218-223

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Abstract

A novel formulation is presented applicable to flows of inelastic, shear-thinning and shear-thickening, fluids between parallel plates. The solution is documented by comprehensive contour maps allowing flow descriptions to be reconstructed for the Ostwald-deWaele and the Cross-/Carreau fluid model fluids within an exhaustive range of rheological and flow parameters, 0 < n ≤ 2 and 0 ≤ q ≤ 2. The description of pseudoplastic behavior is extended to values approaching zero, numerical stability permitting (0.01 ≤ n < 1). The paper highlights the dilatant behavior, 1 ≤ n ≤ 2, reported previously to arise in certain heterogeneous systems, and shown to affect significantly other types of non-Newtonian flows. It is suggested that in thermally and compositionally developing flows, typical of reactive processing, where dilatancy may arise, the present formulation can facilitate solutions to the coupled rheological and heat/mass transfer problems encountered. The newly generated data on dilatant liquids suggest a dramatic increase in energy dissipation with the increasing degree of dilatancy.

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