bluuebunny/crossref_metadata_2025 huggingface dataset:
Poly(styrene‐g‐ethylene oxide) copolymers as interfacial agents in immiscible polymer blends
Authors: Kvist L. , Bertilsson H. , Meuller P.
Published: April 2004

A poly(styrene‐g‐ethylene oxide) copolymer with an average of 100 styrene units between the graft points is studied with respect to its interfacial activity in binary incompatible mixtures of polymers having different degrees of miscibility toward the graft copolymer components. The interfacial properties were studied by scanning electron microscopy, dynamic mechanical spectroscopy, and differential scanning calorimetry. The data obtained are compared with previously published data from a graft copolymer with the same composition but with shorter PEO branches and only 20 styrene units between them. In spite of their structure, the two graft copolymers could reduce the size of the dispersed phase in the case of athermal mixing. With a negative heat of mixing between only one graft component and the blend, the short branch graft had no effect, while the longer branch graft caused a reduction of the size of the dispersed phase. With a negative heat of mixing for the graft branches as well as for the backbone a strong compatibilizing effect was found for both types of graft copolymers. The results show that even very short parts of the backbone of a graft copolymer can contribute to compatibilization in a polymer blend, especially when the backbone has a negative heat of mixing with one of the blend components.
Multi‐layer modeling of diffusion of water in acrylamide‐grafted aliphatic polyesters
Authors: Hedenqvist M. S. , Ohrlander M. , Palmgren R. , Albertsson A.‐C.
Published: April 2004

A new mass transfer model for layered structures, based on an implicit multi‐step integration algorithm including concentration dependent diffusivities, has been developed and applied to systems of water diffusing in electron beam pre‐irradiated, acrylamide‐grafted aliphatic polyesters (poly(ϵ‐caprolactone) and poly(1, 5‐dioxepan‐2‐one)). The much higher water solubility and water diffusivity in the amorphous crosslinked poly(1, 5‐dioxepan‐2‐one) than in the semicrystalline poly(ϵ‐caprolactone) is explained as being due to the fact that crystals are more effective crosslinks than the chemical crosslinks. Water solubility in the grafted layer is a function of the concentration of polyacrylamide, but it is believed to be limited by compressive swelling‐induced stresses. The zero concentration water diffusivity in the graft layer passes through a maximum, whereas the graft‐layer density passes through a minimum with increasing acrylamide concentration. It is suggested that this is because the accessible free volume for the penetrating water molecule is increased in the initial stages of grafting because the matrix polymer chains are separated by growing acrylamide graft chains. At later stages, the accessible free volume decreases because additional polyacrylamide chains are growing adjacent to the already existing ones and thus fill up empty spaces.
Nanocomposites based on montmorillonite and unsaturated polyester
Authors: Kornmann X. , Berglund L. A. , Sterte J. , Giannelis E. P.
Published: April 2004

The concept of nanoscale reinforcement provides opportunity for synthesis of new polymer materials with unique properties. Montmorilonite (MMT) was derived from bentonite, purified, activated by sodium ions and mixed with reacting unsaturated polyester (UP). X‐ray and transmission electron microscopy data were in support of the formation of a partially delaminated nanocomposite material. At an MMT content of only 1.5 vol%, the fracture energy,GQ, of the nanocomposite was doubled, 138 J/m2as compared with 70 J/m2for the pure UP.
The crystalline phase transformation of poly(vinylidene fluoride)/poly(vinyl fluoride) blend films
Authors: Kim Bong Shik , Lee Jae Yeon , Porter Roger S.
Published: April 2004

Poly(vinylidene fluoride) (PVDF), poly(vinyl fluoride) (PVF), and their blends were prepared by solution casting, followed by quenching in ice water after melting to obtain an α‐crystalline phase. The films were drawn by solid state extrusion at two different drawing temperatures, 50°C and 110°C. The crystalline phases were analyzed by DSC and FTIR. In the undrawn films, the content of β‐crystalline phase in the blend of PVDF/PVF 88.5/11.5 was higher than in the PVDF homopolymer, but it was lower than in the PVDF film with a draw ratio higher than 4. The α‐crystalline phase in PVDF/PVF blends was mostly transformed into the β‐crystalline phase beyond a draw ratio of 4, regardless of the draw temperature and PVF content. The α‐crystalline phase of PVDF systematically transformed into the β‐crystalline phase with increasing draw ratio. The crystallinity of PVDF/PVF blend films drawn at 110°C was higher than those drawn at 50°C. In the drawn blend films, characteristic IR bands of the α form were shifted to those of the β form and completely changed into those of β form at draw ratio of 4, regardless of the draw temperature and PVF content.
Residence time distributions and basic studies of flow and melting in a modular buss kneader
Authors: Lyu Min‐Young , White James L.
Published: April 2004

Experimental studies of residence time distribution, fill factor, temperature, and melting profiles of thermoplastic resins are presented. Residence time distributions were determined as a function of throughput and screw speed. The melting of polypropylene and low density polyethylene in the entrance region was investigated. Fill factor and temperature profiles are reported.
New models for rotational molding of plastics
Authors: Gogos G. , Olson L. G. , Liu X. , Pasham V. R.
Published: April 2004

We present a detailed theoretical model of the rotational molding process, and identify the key dimensionaless groups affecting the process cycle time. This theoretical model is employed to create differential and lumped parameter numerical models, as well as a simple closed form estimate for the time required for complete powder deposition. Both numerical models give results that are in very good agreement with experimental data available in the literature. The closed form solution gives good predictions over a wide range of processing parameters. In addition, the effects of variations in the dimensionaless groups on processing time are evaluated.
Experimental study and numerical simulation of the injection stretch/blow molding process
Authors: Schmidt F. M. , Agassant J. F. , Bellet M.
Published: April 2004

The injection stretch/blow molding process of PET bottles is a complex process, in which the performance of the bottles depends on various processing parameters. Experimental work has been conducted on a properly instrumented stretch/blow molding machine in order to characterize these processing parameters. The objective being a better understanding of the pressure evolution, preform free inflation has been processed and compared with a simple thermodynamic model. In addition, a numerical model for the thermomechanical simulation of the stretch/blow molding process has been developed. At each time step, mechanical and temperature balance equations are solved separately on the current deformed configuration. Then, the geometry is updated. The dynamic equilibrium and the Oldroyd B constitutive equations are solved separately using an iterative procedure based on a fixed‐point method. The heat transfer equation is discretized using the Galerkin method and approximated by a Crank‐Nicholson's scheme over the time increment. Successful free blowing simulations as well as stretch/blow molding simulations have been performed and compared with experiments.
Environmental stress cracking resistance of blends of high‐density polyethylene with other polyethylenes
Authors: Schellenberg J. , Fienhold G.
Published: April 2004

A special modified tensile creep test was used to investigate the stress cracking behavior of various high‐density polyethylenes (HDPE). Blends of HDPE with other HDPEs, with linear low‐density polyethylene (LLDPE), and specifically with various slightly long‐chain branched linear low‐density polyethylenes (HBPE) were tested for their failure times. Whereas HDPE blends, including higher‐molecular‐weight HDPE components, yield only a minor improvement in stress cracking resistance, a considerable improvement was produced when an LLDPE weight fraction of 0.3 or more was used. Adding HBPE also improves the environmental stress cracking resistance. Environmental stress cracking resistance improves with increasing HBPE content, and, for a constant HBPE concentration, it increases with increasing octene content of the HBPE. Adding HBPE with a low octene content, however, results in reduced failure times of the blend compared with HDPE blends that exhibit relatively good environmental stress cracking behavior. The results are explained in terms of the tie‐molecule density.
Ethylene vinyl alcohol copolymer/high density polyethylene blends compatibilized through functionalization
Authors: Park Seong Ho , Lee Gun Joo , Im Seung Soon , Suh Kyung Do
Published: April 2004

In order to evaluate the compatibilizing effects of isocyanate (NCO) functional groups on ethylene vinyl alcohol copolymer/high density polyethylene (EVOH/HDPE) blends, HDPE grafted with 2‐hydroxyethyl methacrylate‐isophorone diisocyanate (HDEP‐g‐HI) was prepared and blended with EVOH. The grafting was confirmed by infrared spectra, and the grafting ratio was 4.9% from elementary analysis. From the morphologies of EVOH/HDPE‐g‐HI blends, it was found that an improved adhesion between the two components and finer dispersions were produced as a result of chemical reactions occurring during the melt blending. The depression of melting temperature of EVOH in the 10/90 EVOH/HDPE‐g‐HI blend indirectly indicated increased miscibility. The tensile strength of the EVOH/HDPE‐g‐HI blend was much higher than that of the EVOH/HDPE blend having no adhesion at each composition, and a dramatic increase in the impact strength was produced at the 90/10 EVOH/HDPE‐g‐HI blend composing of the fine HDPE‐g‐HI dispersions.
Evaluation of rheological properties of non‐newtonian fluids in internal mixers: An alternative method based on the power law model
Authors: Mallette J. Guillen , Soberanis R. Rios
Published: April 2004

A new method was developed to evaluate rheological properties of polymer melts such as shear stress, shear rate, apparent viscosity and other rheological parameters in internal mixers. It is based on the classical power law model where the power law index n is directly evaluated from a set of data containing speed S, torque M, and the consistency index m is indirectly determined by an empirical relation. The method is based on a model with only one geometrical parameter (α), which involves a chamber radius R2 and an equivalent radius Re. It is assumed that the measuring head consists of two adjacent sets of coaxial cylinders. This method has advantages over previously reported models that use two parameters and do not propose a straightforward method to evaluate m. The pseudoplastic nature of the polymer melt decreases as the rate of loss of structural points, i.e., molecular entanglements and network junctions, increases, which produces greater mobility of the melt. A relationship between α and C(n) is found, which is simpler than other models previously reported. These results further demonstrate the feasibility of evaluating rheological properties of polymer melts in internal mixers.
Structural rearrangements during yielding of glassy polymers
Authors: Kontou E. , Spathis G.
Published: April 2004

The tensile yield and post yield behavior of polycarbonate (PC) are examined by means of a new experimental device, based on a noncontact measurement of the deformation. This method has the advantage of a detailed measurement of the deformation along the gauge length, which leads to the construction of the true stress‐strain curves of the material tested. Especially in the case of nonuniform deformation, where neck initiation and neck propagation occurs, the correct description of the intrinsic response of the material requires true stress‐strain plots. A viscoplastic model based on the fundamental assumptions of Eyring is used to describe the yield and post‐yield behavior of PC. The strain softening is attributed to a relaxation mechanism that was introduced in previous treatments, and this effect is supported by DSC tests. The theoretical results are compared with the results obtained by an elasto‐plastic model, developed elsewhere, and it is shown that the material follows a viscoplastic path in this deformation procedure.
Comparison of isotactic and syndiotactic polypropylene as matrix materials of hybrid composites
Authors: Stricker F. , Mülhaupt R.
Published: April 2004

The structure/property relationships and morphology of glass bead–reinforced syndiotactic and isotactic polypropylene composites containing 0 to 20 vol% thermoplastic elastomer (TPE) were studied. Polystyrene‐block‐poly(ethylene‐co‐butylene)‐block‐polystyrene (SEBS) and the corresponding block copolymer grafted with maleic anhydride (SEBS‐g‐MA) were used as the TPEs. The Young's modulus of hybrid composites based on s‐PP showed no dependence on the type of TPE used, whereas i‐PP hybrid composites containing SEBS had a higher Young's modulus than composites containing SEBS‐g‐MA. A comparison of the data with theoretical predictions of Young's modulus and tensile yield stress gave strong evidence of two different morphologies for the hybrid composites. The increasing tensile yield stress of s‐PP hybrid composites and i‐PP hybrid composites containing SEBS‐g‐MA was attributed to an interlayer formation and in‐situ encapsulation of glass beads, which resulted in core‐shell particles with improved interfacial interactions. In contrast, SEBS in hybrid composites based on i‐PP formed a separate dispersed phase. Crystallization and scanning electron microscopy studies also provided evidence of a core‐shell morphology for hybrid composites based on s‐PP. Results of lap‐shear and peel tests confirmed strong interfacial interaction between glass and SEBS‐g‐MA and between SEBS and s‐PP as well as i‐PP. Only above a critical volume fraction did the TPE provide significant improvement of the notched Izod impact strength of hybrid composites based on s‐PP or i‐PP.
Effects of polyethylenes on the morphology, barrier, and impact properties of polyethylene/modified polyamide blends
Authors: Yeh Jen‐Taut , Jyan Chau‐Fa
Published: April 2004

An investigation of the influence of the melt shear viscosities of polyethylenes (PE) on the morphology, barrier, and impact properties of polyethylene/modified polyamide PE/MPA bottles is reported. The melt shear viscosities of polyethylenes exhibited a significant influence on the deformation and morphology of MPAs during the blow molding of polyethylene/modified polyamide (PE/MPA) blends. Some obscure MPA laminars were observed in PE/MPA bottles as the value of melt shear viscosity ratio of MPA to PE (VR) deviated significantly from the “optimum” range. In contrast, clear and elongated laminar structures of MPAs were found as the value of VR reached the “optimum” range. Similarly, the total impact energies (Ets) and permeation barrier properties of PE/MPA samples improved with the value of VR until it reached the “optimum” range, after which value Ets and permeation barrier properties of PE/MPA samples reduced significantly with further increasing VR. Possible mechanisms accounting for these interesting behaviors are presented in this study.
Liquid‐crystallization induced reactions. Microstructure and morphology of copolyesters synthesized by transesterification of PET with some LCP monomers
Authors: Tonti Maria Silvia , Masseti Marco , Poli Giovanna , Paci Massimo , Magagnini Pierluigi , Forte Claudia , Veracini Carlo Alberto
Published: April 2004

The transesterification of poly(ethylene terephthalate) (PET) with a mixture of sebacic acid (S), 4,4′‐diacetoxybiphenyl (B) and 4‐acetoxybenzoic acid (H), carried out under conditions expectedly favoring the formation of a p(ET‐SBH) random copolyester, produces biphasic materials with an isotropic matrix and a highly fibrous, liquid‐crystalline dispersed phase. Spectroscopic, calorimetric, microscopic and diffractometric characterization of the fractions separated by solvent extraction has shown that the two phases consist of practically random copolyesters having different average composition. Interestingly, the degree of aromaticity of the matrix is even lower than that of PET, whereas that of the minor phase is appreciably higher than that calculated for the SBH copolyester that would be produced from the monomer mixture in the absence of PET. This unexpected result is interpreted on the basis of an enthalpy‐driven progressive diffusion of aromatic‐rich material toward the mesophase which segregates at an early stage of the polycondensation within the isotropic mixture of low molar mass oligomers initially produced by the PET acidolysis. Thus, an increasing differentiation, rather than an equilibration, of the composition of the two phases takes place. It is noteworthy that, despite the strong compositional difference, the two phases of these products show fairly good compatibility and interfacial adhesion.
Experimental study and computer simulation of the effect of spider shape on the weld‐lines in extruded plastic pipe
Authors: Huang Y. , Prentice P.
Published: April 2004

Weld‐lines, also referred to as spider‐lines or knit‐lines, are regions in the wall of an extruded plastic pipe, running the whole length of the pipe, at which there is a change in dimension and a possible reduction in mechanical properties. Weld‐lines result from the flow of the polymer melt around the supports (spiders) that hold the metal core to the outer die assembly in an in‐line annular die. This work examines the fatigue life and the tensile strength of weld‐lines created by a conventionally shaped “torpedo” spider and four modified spider shapes. It is demonstrated that the shape of the spiders has a dramatic effect on the fatigue life of weld‐lines while having a minimal effect on the tensile strength in static loading. The experimental results show that the fatigue life of the weld‐line produced by one of the four new shaped spiders is significantly higher than that of a conventionally shaped spider. Numerical simulations of the flow field around this new and conventional spiders were carried out using the package FIDAP® based on the finite element method (FEM). The simulation results provide a good explanation for the experimental observations and show that the newly designed shape of spider can give rise to a higher relative fatigue life of the weld‐line when compared with that of the bulk material than does the conventional spider.
The effect of temperature on the observed flow‐induced structure in semidilute solutions of gently solubilized starches
Authors: Carriere C. J. , Loffredo A. R.
Published: April 2004

The effect of temperature on the unexpected shear‐thickening behavior exhibited by semidilute solutions of waxy maize starch during a repeated shear‐loop experiment was evaluated. Shear‐thickening behavior, characterized using power law models, was observed for waxy maize starch, but not for normal maize starch at the same concentration. The shear‐thickening region was observed for waxy maize starch at temperatures ranging from 25°C to 80°C and shear rates from 2–100 s−1 during the initial part of the shear‐loop experiment. For waxy maize starch, the power law exponent, n, was found to be 0.539 ± 0.017 in the shear‐thinning region. For normal maize starch, the value of n was found to be equal to 0.751 ± 0.015 and only shear‐thinning behavior was observed. The values of n for both waxy maize and normal maize starch were found to be temperature independent within the precision of the experimental measurements. The differences in n indicate the differences in the conformational dynamics of waxy maize and normal maize starches in solution.
The interfacial tension between a thermotropic liquid crystalline copolyester and polyethersulfone: A comparison of methods
Authors: Machiels A. G. C. , Busser R. J. , Van Dam J. , De Boer A. Posthuma
Published: April 2004

Three dynamic methods to determine the interfacial tension between the thermotropic liquid crystalline polymer (TLCP) Vectra A900 and polyethersulfone were evaluated: (1) thread breakup, (2) fiber retraction and (3) dynamic shear rheometry. The thread breakup and retraction methods, were suitable for measuring the interfacial tension, provided that the shear thinning flow behavior of the TLCP was taken into account. The viscosity of the TLCP during breakup or retraction was estimated from steady‐shear measurements at the observed overall rate of deformation during growth of capillary instabilities or during retraction. The calculation of the interfacial tension from breakup rates of TLCP threads was improved by accounting for transient flow behavior during distortion growth using a single‐element Maxwell model. Determination of the interfacial tension by oscillatory shear measurements on TLCP/PES dispersions using the emulsion model of Palierne, was not applicable for this system. Only for dispersions containing low TLCP volume fractions (e.g. 9 vol%) was there reasonable agreement between the emulsion model and measurements. At higher volume fractions agreement was poor, possibly because of different dynamic flow behavior of the TLCP in the pure form and in blends. The interfacial tension values obtained from thread breakup and fiber retraction ranged from 4 to 6 mN/m, which demonstrate that in‐situ determination of the interfacial tension is possible for blends containing TLCPs, despite their complex flow behavior.
Chain orientation in sheared molten poly(ethylene oxide) fractions by measurement of infrared dichroism
Authors: Skytt M.‐L. , Jansson J.‐F. , Gedde U. W.
Published: April 2004

Rheo‐infrared spectroscopy was used to study the development of orientation of molten narrow molar mass fractions of poly(ethylene oxide) [molar masses between 18,000 and 120,000 g/mol] during non‐Newtonian shear flow at shear rates between 2 and 270 s−1 and temperatures between 75 and 100°C. The steady state degree of orientation [expressed as the Hermans orientation function (fss)] reached a saturation level with increasing shear rate; fss increased with increasing molar mass (M) according to fss = C1 − C2/M (C1 and C2 are coefficients; the latter depended on shear rate and temperature). The coefficient C1 (fss) for a polymer with infinite molar mass took a universal value close to 0.05 for the temperatures and shear rates used. Under large shear stresses, the relationship between stress and orientation deviated markedly from linearity. The time to establish a steady state level of orientation was proportional to M1/2. The recovery of the isotropic state after the cessation of shear could initially be described by a simple exponential relaxation law: f ∝ e, where τρ is the relaxation time. The latter showed a weak molar mass dependence according to τr ∝ M0.6 and an Arrhenius temperature dependence with an activation energy of ∼60 kJ/mol. The relaxation of the shear stress after the cessation of shear was more rapid than the recovery of the isotropic state.
In‐process control of epoxy composite by microdielectrometric analysis. Part II: On‐line real‐time dielectric measurements during a compression molding process
Authors: Stephan F. , Duteurtre X. , Fit A.
Published: April 2004

The curing of a fiberglass epoxy composite based on diglycidyl ether of bisphenol A (DGEBA) with dicyanodiamide (DDA) as the hardener and imidazole as the catalyst agent was analyzed using microdielectrometry. The curing behavior of thick epoxy composite parts was examined in a production environment for compression molding process. The particular focus of this paper is to present the method used to collect on‐line real‐time conversion measurements during an epoxy/fiberglass composite cure. For this purpose, temperature and ionic conductivity profiles during industrial moldings of a thick epoxy part were recorded. Corresponding conversion profiles were deducted from a previous empirically established correlation and discussed in terms of cure gradients as a function of the through‐the‐thickness location and of the cure cycle time.
Phase behavior of blends of poly(ethylene terephthalate) with liquid‐crystalline polymers
Authors: Magagnini Pierluigi , Tonti Maria S. , Masseti Marco , Paci Massimo , Minkova Lilia I. , Miteva Tsenka T.
Published: April 2004

Poly(ethylene terephthalate) (PET) was melt blended with several liquid‐crystalline polymers (LCPs), both with and without Ti(OBu)4 catalyst. The LCPs, referred to as VA, LC5, LC3, and SBH, respectively, were Vectra‐A950, Rodrun LC‐5000, Rodrun LC‐3000, and a laboratory copolyester of sebacic acid (S), 4,4′‐diacetoxybiphenyl (B), and 4‐acetoxybenzoic acid (H). Their degree of aromaticity decreases in that order. The phase behavior and the morphology of the blends were studied by differential scanning calorimetry and scanning electron microscopy. All the LCPs retard the dynamic crystallization of PET. The lower the LCPs degree of aromaticity, the more pronounced was the effect. It was not possible to obtain any evidence of ester exchange reactions by the reactive blending of PET with VA. On the contrary, appreciable changes of phase behavior and morphology were observed under comparable conditions for the other blends. With LC5 and LC3, the transesterification process predominantly involved the ET‐rich phase of those polymers. Extensive transesterification occurred between PET and SBH, as proven by the gradual formation of a quasi homogeneous material, with lowered temperatures and enthalpies of fusion and crystallization. For blends with more than 25% SBH, homogenization is followed by the segregation of a new, highly aromatic phase.
Isothermal and non‐isothermal crystallization kinetics of polyethylene terephthalate: Mathematical modeling and experimental measurement
Authors: Verhoyen O. , Dupret F. , Legras R.
Published: April 2004

Results obtained by differential scanning calorimetry have been used to develop a macro‐kinetic model for the crystallization behavior of semicrystalline polymeric materials. Our model, which takes into account the effects of induction time, final degree of crystallinity and secondary crystallization, describes both isothermal and non‐isothermal crystallization kinetics, including cold‐ and melt‐crystallization. Experimental data obtained with Polyethylene terephthalate in a wide range of thermal conditions compare well with predictions.
Fluid mechanics analysis of a two‐dimensional pultrusion die inlet
Authors: Sharma D. , McCarty T. A. , Roux J. A. , Vaughan J. G.
Published: April 2004

Fluid mechanics plays an important role in many manufacturing processes including the pultrusion of composite materials. The analysis of fluid mechanics problems generally involves determination of quantities such as pressure and velocity. During the pultrusion process, the short, tapered inlet region of the pultrusion die experiences a significant amount of fluid resin pressure rise. The quality of a pultruded product can be affected by the amount of pressure rise in the pultrusion die inlet. Void formation can be suppressed and good fiber “wet out” achieved by a sufficiently high pressure rise in the pultrusion die inlet region. In this study the change in fluid resin pressure rise as a function of die entrance geometry is investigated by developing a finite element model based on the assumptions of Darcy's law for flow in porous media. The momentum equations are combined with the continuity equation to save computational time and memory. A Galerkin weighted residual based finite element method is developed to solve the resulting equation. This model is capable of predicting the pressure rise in the tapered inlet region of the pultrusion die as well as the straight portion of the die. By varying the size of the preform plates the thickness of the fiber/resin matrix approaching the die inlet can be varied. The finite element model predicts the impact of changing the preform plate size on the fluid resin pressure rise in the pultrusion die. The effect of varying the wedge angle for a linearly tapered die inlet region is also studied using this model. The results in this work can be useful for designing a pultrusion die system.
The effect of a new type of pin mixing section on the performance of a single‐screw extruder
Authors: Yao W. G. , Takahashi K. , Koyama K. , Yamashita Y.
Published: April 2004

The effect of a holed‐pin mixing section on the performance of a single screw extruder was investigated and compared with a free flight and a normal pin mixing section, using a practical single‐screw extruder. The effect of axial distance between two pins in a holed‐pin mixing section on performance was also studied. Mixing ability was quantified using the statistical approach of carbon black concentration distribution in the extruded film mixed with a carbon black masterbatch. The results indicate that a free flight gives the lowest melt temperature rise, pressure drop, and driver power, but the worst mixing; a holed‐pin mixing section has better mixing ability, lower melt temperature rise, and lower driver power than a normal pin mixing section does; the value of the pressure drop of the two types of pin mixing sections is approximately identical. A longer axial distance between the two pins in a holed‐pin mixing section gives better mixing and lower melt temperature rise than a shorter one; however, when the distance is longer than a critical value, the improvement of mixing is not so outstanding; for different axial distances between two pins, no great change in pressure drop was found and the extrusion throughput has almost no great relation to the axial distance.
New process for producing an extrusion laminated film without any chemical primer—non anchor coating extrusion laminating process
Authors: Hayashida H. , Ishibashi F. , Takahata H. , Nishio T. , Gotoh Y. , Sato Y.
Published: April 2004

A new process, the Non Anchor Coating Extrusion Laminating Process for producing an extrusion laminated film without any chemical primer, was investigated. Good adhesive properties were obtained by combining an ozone treatment of a molten polyethylene (LDPE) web and an activation treatment of the polyamide (ONy) substrate film. The adhesion mechanism induced by the new process was studied by FT‐IR, ESCA and extraction of unreacted polyamide from the laminated samples. The peel strength between the ONy and LDPE laminated films produced with this process was greater than that for laminated film made with a conventional lamination process using anchor coating agents. A model of the adhesive mechanism is proposed. Hydrogen and covalent bonds through oxygenated functional groups are responsible for the enhanced adhesion.
Transport properties of methanol in blends of a liquid crystalline copolyester and polyethersulfone
Authors: Wiberg G. , Hedenqvist M. S. , Boyd R. H. , Gedde U. W.
Published: April 2004

Data for the diffusivity and solubility of methanol in blends of polyethersulfone (PES) and a liquid crystalline copolyester (polyhydroxy‐benzoic acid (73 mol%)‐co‐hydroxy‐naphthoic acid (27 mol%)) (LCP) are reported. Samples taken from injection molded and compression molded specimens over a wide composition range were studied by gravimetry (sorption and desorption), dielectric spectroscopy, differential scanning calorimetry and scanning electron microscopy. The sorption of methanol in PES led to the formation of an ordered phase. The sorption curves were S‐shaped and they could be described by a diffusion model assuming a concentration‐dependent diffusivity and time‐dependent boundary conditions. The solubility of methanol in the blends was strictly proportional to the PES content. The zero‐concentration‐diffusivity decreased strongly with increasing LCP content and it was dependent on the morphology. Injection molding yielded samples with a fibrillar LCP phase with a greater continuity of the PES component and a high diffusivity (in relative terms). Compression molding led to samples with a more continuous LCP component even at low LCP contents and a low diffusivity.
The role of specific interactions and transreactions on the compatibility of polyester ionomers with poly(ethylene terephthalate) and nylon 6,6
Authors: Boykin Timothy L. , Moore Robert B.
Published: April 2004

The compatibility of polyester ionomers with polar polymers (i.e., poly(ethylene terephthalate) and nylon 6,6) is under investigation for their potential use as minor component compatibilizers. Binary blends have been prepared by both solution and melt‐mixed methods to determine the effect of melt‐processing on blend compatibility. The effect of the sulfonate group and counterion type on compatibility was evaluated by blending sulfonated and nonsulfonated forms of the amorphous polyester ionomer with both nylon 6,6 and poly(ethylene terephthalate). The melting point and phase behavior of the blends were determined by differential scanning calorimetry (DSC) and environmental scanning electron microscopy (ESEM), respectively. A comparison of the melting behavior between the melt and solution blends suggests compatibility due to specific interactions for the ionomer/nylon 6,6 blends, and transesterification for the ionomer/poly(ethylene terephthalate) blends. The phase morphology of the melt blends is consistent with the results obtained by DSC analysis.
Low‐rate dynamic contact angles on polystyrene and the determination of solid surface tensions
Authors: Kwok D. Y. , Lam C. N. C. , Li A. , Zhu K. , Wu R. , Neumann A. W.
Published: April 2004

Low‐rate dynamic contact angles of 13 liquids on a polystyrene polymer are measured by an automated axisymmetric drop shape analysis – profile (ADSA‐P). It is found that 7 liquids yielded non‐constant contact angles, and/or dissolved the polymer on contact. From the experimental contact angles of the other 6 liquids, it is found that the liquid‐vapor surface tension times cosine of the contact angle changes smoothly with the liquid‐vapor surface tension, i.e. γlvcosθ depends only on γlv for a given solid surface (or solid surface tension). This contact angle pattern is in harmony with those from other inert and non‐inert (polar and non‐polar) surfaces (7–13, 24–26). The solid‐vapor surface tension calculated from the equation‐of‐state approach for solid‐liquid interfacial tensions (33) is found to be 29.8 mJ/m2, with a 95% confidence limit of ±0.5 mJ/m2 from the experimental contact angles of 6 liquids.
Transient elongational viscosity of LLDPE/LDPE blends and its relevance to bubble stability in the film blowing process
Authors: Micic P. , Bhattacharya S. N. , Field G.
Published: April 2004

Transient elongational viscosity of linear low density polyethylene (LLDPE) and its blends with 10% and 20% of low density polyethylene (LDPE) was measured at two temperatures by a constant strain rate elongational rheometer. In addition, the performance of the blends in the film blowing process was assessed in terms of bubble stability at two processing temperatures. An operating window for stable bubble production was determined. The elongational viscosity measurements on blends revealed stronger strain hardening characteristics at a higher temperature of testing. These results correlate favorably with findings from a bubble stability investigation where it was found that the size of the operating window for stable bubble production increased with increasing extrusion temperature. This work seems to indicate that increasing processing temperature during the film blowing of LLDPE‐rich blends could lead to a processability improvement of these blends as far as bubble stability is concerned.
Mechanism of void growth in the partial frame process
Authors: Ahn Kyung Hyun , Kim Dong‐Hak
Published: April 2004

The Partial Frame Process (PFP) is a kind of gas‐assisted injection molding, in which the void core is generated by imposing low pressure air into the molded part just after the resin is completely filled, after which the void grows as it compensates the volume shrinkage of resin. It resembles a secondary gas penetration step of gas‐assisted injection molding, but has more advantages, such as its simplicity, design flexibility, ease of control, and cheap utilities. In this study, modeling of the void growth in PFP was carried out. By comparing the results with the experimental data, basic assumptions have been justified and the mechanism of the void growth could be explained in terms of the process parameters such as mold temperature, melt temperature, and the channel size. An experimental approach was also taken. As there are many factors affecting the process, the method of design of experiments was adopted, and the effects of the process parameters on the void growth length and the mechanism of the void growth were investigated. The results are expected to help in mold design and the determination of the operating conditions, as well as our understanding of this new process.
A three‐dimensional analysis of the effect of die body deflection in the design of extrusion dies
Authors: Gifford W. A.
Published: April 2004

Flat extrusion dies operating under high pressure often experience a significant amount of distortion. Satisfactory designs of such dies require an accurate prediction of the deflection of the die body as well as the flow in the internal channels of the die. Here a three‐dimensional deflection analysis is coupled to a three‐dimensional flow analysis. Such analyses are now being used by design engineers on personal computers for routine design of deflecting dies.
The use of birefringence for predicting the stiffness of injection molded polycarbonate discs
Authors: Neves N. M. , Pouzada A. S. , Voerman J. H. D. , Powell P. C.
Published: April 2004

Polycarbonate discs were injection molded with different sets of molding conditions. The parameters studied were the flow rate, melt‐ and mold‐temperature. The discs were subjected to three point support flexural tests. Those tests are specially intended for injection molded discs because of their inherent non‐flatness. The through‐thickness molecular orientation was assessed by birefringence measurements along and across the flow direction using the wedge method. This method is ideal to measure the birefringence of materials that are difficult to cut with a microtome. The through‐thickness stiffness of the discs was calculated from the measured birefringence distributions. A composite model of the disc was used in the Algor finite element method (FEM) package to simulate the flexural tests.
Squeezing flow of viscoplastic fluids subject to wall slip
Authors: Lawal Adeniyi , Kalyon Dilhan M.
Published: April 2004

Polymer processing operations such as compression molding, sheet forming and injection molding can be modeled by squeezing flows between two approaching parallel surfaces in relative motion. Squeezing flows also find applications in the modeling of lubrication systems, and in the determination of rheological properties. Here, analytical solutions are developed for the constant‐speed squeezing flow of viscoplastic fluids. It is assumed that the fluid is purely viscous, and hence viscoelastic effects unimportant. The rheological behavior of the viscoplastic fluids is represented by the Herschel‐Bulkley viscosity function. The deformation behavior of commonly encountered viscoplastic fluids is generally complicated by the presence of wall slip at solid walls, which is a function of the wall shear stress. The slip coefficient that relates the slip velocity to the shear stress is affected by the material of construction and also the roughness of the solid surfaces, leading to the possibility of different slip coefficients at various solid surfaces. The model developed in this study accommodates the use of different slip coefficients at different solid surfaces. The accuracy of the solutions is established, and the effects of various parameters such as slip coefficient and apparent yield stress are examined. The solutions provide useful design expressions that can be utilized for squeezing flows of viscoplastic fluids, with or without wall slip at the solid boundaries.
Continuous extrusion of self‐reinforced high density polyethylene
Authors: Huang Han‐Xiong
Published: April 2004

Continuous extrusion was studied of self‐reinforced high density polyethylene (HDPE) sheets from flow‐induced crystallization at die pressures varying from 30 to 60 MPa. Their morphology, thermal behavior, tensile strength, and light transmittance were tested. Flow fields of a polymer melt through a converging wedge channel were also investigated by direct visual observations in conjuction with a theoretical analysis. The extensional strain rate increased abruptly as the melt approached the exit of the converging channel, this resulting in a higher crystallization rate. So, achieving the crystallization of molecular chains just in front of the exit of the converging channel may favor to extrude the bulk polymeric materials having high properties under lower pressures (e.g., 40 MPa or lower), this having been realized in the present work. The tensile strength of the self‐reinforced HDPE sheet prepared at a 40 MPa pressure was enhanced by a factor of 8.
Low density microcellular foam processing in extrusion using CO2
Authors: Park Chul B. , Behravesh Amir H. , Venter Ronald D.
Published: April 2004

A continuous extrusion process for the manufacture of low‐density microcellular polymers is presented. Microcellular polymers are foamed plastics characterized by a cell density greater than 109 cells/cm3 and a fully grown cell size on the order of 10 μm. Previous research on continuous processing of microcellular polymers has focused on control of microcell nucleation in extrusion. This paper presents an effective means for control of cell growth to achieve a desired expansion ratio with CO2 as a blowing agent in microcellular foam processing. Also, a strategy to prevent deterioration of the cell‐population density via cell coalescence during expansion is presented. Promotion of a desired volume expansion ratio and prevention of cell coalescence in microcellular foam processing were experimentally verified. By tailoring the extrusion processing parameters, microcellular HIPS foams with a cell density of 1010 cells/cm3 and a controlled expansion ratio in the range of 1.5 to 23 were obtained.
Hot compaction and consolidation of polycarbonate powder
Authors: Vick Linda W. , Kander Ronald G.
Published: April 2004

In order to take advantage of the potential benefits provided by solid‐state processing of thermoplastic polymers (1–3), conventional compaction and sintering techniques must be modified to prevent large‐scale recovery (or dimensional changes) that occur upon heating polymeric compacts above their respective glass transition temperature (Tg). Two solid‐state processing techniques that have the potential for reducing recover, hot compaction and consolidation (sintering polymeric compacts under applied pressure), were investigated in this study. The results presented in this paper show that while hot compaction (below Tg) does not prevent large‐scale recovery, consolidation using pressures as low as 50 kPa (7.3 psi) did significantly reduce recovery in polycarbonate compacts.
Crystallization morphology of a thermotropic liquid crystalline polymide
Authors: Liu S. L. , Chung T. S. , Goh S. H. , Torii Y. , Yamaguchi A. , Ohta M.
Published: April 2004

Crystallization morphology of an aromatic thermotropic liquid crystalline polyimide was studied by means of polarized light microscopy. The polyimide was synthesized from 1, 2, 4, 5‐benzenetetracarboxylic dianhydride (PMDA) and 1, 3‐bis[4'(4′ aminophenoxy) cumyl] benzene (BACB), which exhibited three exothermic peaks at onset temperatures of 292, 279, and 250°C in the DSC cooling curve. The results of polarized light microscopy revealed that the polyimide quenched from 350°C in air exhibited fine structure, frozen liquid crystalline texture. The liquid crystalline texture disappeared when the sample was heated to 298°C. However, the polymer melt still exhibited, to some degrees, birefringence until the temperature reached 340°C, where the polyimide was in the truly isotropic state. Isothermal crystallization experiments were carried out at both the isotropic temperature range and the non‐isotropic temperature range. Two types of negative spherulites with lamellar structure and positive needle‐like crystals formed from the isotropic melt have been observed. Interestingly, with a further decrease of the crystallization temperature to the liquid crystalline state temperature, the whole field was covered by the liquid crystalline texture. However, if the sample was kept at 286°C for a long time, and then reheated to 305°C to melt the liquid crystalline phase, negative spherulites with loose structures formed from the liquid crystalline state could be observed. Surprisingly, if the sample was kept at 305°C for a period of time, further crystallization could be observed using the spherulites formed at 286°C as nuclei. Composite spherulites were developed if the low‐high temperature crystallization process was repeated.
Solid state and mechanical properties of injection molded poly(ether ether ketone)/polyarylate blends
Authors: Arzak A. , Eguiazábal J. I. , Nazábal J.
Published: April 2004

Blends of poly(ether ether ketone) (PEEK) and bisphenol‐A polyarylate (PAr) were directly prepared during the plasticization step of an injection molding machine and their solid‐state and mechanical behaviors were studied. Despite the fact that PEEK‐rich blends were apparently miscible by differential scanning calorimetry (DSC), from the dynamic‐mechanical analysis (DMTA) results all the blends were composed of (a) a crystalline PEEK phase, (b) a practically pure amorphous PEEK phase, and (c) a PAr‐rich phase richer in PEEK as the PEEK content in the blends increased. Annealed blends showed a poor mechanical performance in the PAr‐rich region, but the PEEK‐rich blends showed additive modulus of elasticity and tensile strength, and ductility and impact strength values similar to those of the highest of the two pure components. All the as‐molded low‐crystalline blends presented a synergistic behavior in the modulus of elasticity, as well as, surprisingly, in ductility and impact strength in the intermediate and slightly majority PEEK compositions. The different mechanical response of the components in fine dispersed phases and in macroscopic tensile specimens may account for the observed results.
Cell morphology and property relationships of microcellular foamed pvc/wood‐fiber composites
Authors: Matuana Laurent M. , Park Chul B. , Balatinecz John J.
Published: April 2004

Wood‐fiber composites make use of cellulose fibers as a reinforcing filler in the polymer matrix and are known to have a lower material cost and a higher stiffness than neat polymers. However, the lower material cost and enhanced stiffness of wood‐fiber composites are achieved at the expense of other properties such as the ductility and impact strength. Since microcellular plastics exhibit a higher impact strength, higher toughness, and increased fatigue life compared to unfoamed plastics, microcellular foaming of wood‐fiber composites will improve the mechanical properties of the composites and therefore increase the usefulness of the materials. In this paper, microcellular foamed PVC/wood‐fiber composites with unique cell morphology and material composition are characterized. Microcellular structures are produced in PVC/wood‐fiber composites by first saturating the composite samples with CO2under high pressure followed by rapidly decreasing the solubility of gas in the samples. The void fraction of the microcellular foamed PVC/wood‐fiber composites is controlled by tailoring the composition of materials and the foaming process parameters. The results indicate that tensile and impact properties of microcellular foamed PVC/wood‐fiber composites are most sensitive to changes in the cell morphology and the surface modification of fibers.