bluuebunny/crossref_metadata_2025 huggingface dataset:
Recyclability of a continuous e‐glass fiber reinforced polycarbonate composite
Authors: Chu J. , Sullivan J. L.
Published: April 2004

Fiber reinforced plastics are multi‐component materials for which physical properties are strongly dependent on fiber and resin structure. Despite the disruptive nature of recycling methods on such structures, these materials nevertheless can be recycled. In this report, the recyclability of a fiber‐reinforced cyclic BPA polycarbonate has been studied. It is found that ground up composite is recyclable and possesses properties as good as or better than a comparable commercial composite. The processing techniques investigated herein are injection, extrusion compression, and compression molding. As expected, processing technique and parameters are important in determining the mechanical properties of the molded regrind. Our results show that injection and extrusion compression molding yield recycled composites with good tensile properties, though the impact strengths are relatively low. This is due to high fiber orientation and fiber bundle dispersion. On the other hand, compression molded samples, which show random fiber orientation and low fiber bundles dispersion have relatively low tensile properties, but excellent impact strength. Results are discussed in terms of microstructural details, which include resin molecular weight and fiber length and orientation.
Stress distribution in and around a spherically ended fiber embedded in a polymer matrix
Authors: Shuster M. , Sherman D. , Siegmann A. , Narkis M. , Jennewein C.‐M. , Eyerer Peter
Published: April 2004

The effect of fiber end geometry, especially one with an enlarged spherical end, on the stress distribution in a polycarbonate/short glass‐fiber reinforced model composite was studied using photoelasticity and finite element analysis (FEA). The role played by the fiber/matrix interfacial strength was also investigated. The photoelastic method was applied to examine the stress distribution in the vicinity of a single fiber embedded in a thermoplastic polycarbonate matrix. Linear elastic, axisymmetric FEA was carried out to investigate the fibers effectiveness as a load bearing constituent, the effect of interfacial debonding, and stress concentration near the fiber ends. Both photoelastic analysis and FEA demonstrated the efficiency of the spherical enlarged fiber end in load transfer ability and in delayed debonding, which may be important in enhancing strength and modulus of thermoplastic matrices.
In situ composites based on blends of a polyetherimide and thermotropic liquid crystalline polymers subjected to shearfree deformations
Authors: De Souza J. P. , Baird D. G.
Published: April 2004

The effects of shearfree elongational flows on the morphology and mechanical properties of blends of a polyetherimide (PEI) with thermotropic liquid crystalline polymers (TLCP) have been investigated. Extruded sheets and injection molded plaques of PEI/Vectra A and PEI/HX1000 blends, with a TLCP concentration of ≤30 wt%, were subjected to uniaxial elongation, planar and biaxial deformations at 240°C, above the glass transition temperature of the PEI, and at 265°C, which is below the melting point of the TLCPs. Experimental results revealed that each particular mode of shearfree deformation had a distinct effect on the morphology and properties of the blends. For instance, TLCP droplets were deformed into elongated fibrils by application of uniaxial elongation, deformed into elongated ribbon‐like structures after planar deformation, and deformed into a disc‐like shape by application of equibiaxial flow. Regarding mechanical properties, it was observed that the tensile modulus and strength of molded plaques of PEI/HX1000 80/20 wt% increased to about twice their initial values (from 5.13 to 10.40 GPa and from 105 to 198 MPa, respectively) after a strain of 0.75 was applied in a direction parallel to the initial direction of the TLCP fibers. In addition, samples exhibiting equal values of flow and transverse direction tensile modulus of ∼5.0 GPa were obtained when molded plaques of PEI/HX1000 80/20 wt% were subjected to planar stretching in a direction transverse to the initial direction of the fibers. Thus, by subjecting injection molded plaques to planar stretching, it was possible to obtain a sample exhibiting balanced flow and transverse direction mechanical properties and, consequently, reduced anisotropy.
Deep drawing of fabric‐reinforced thermoplastics: Wrinkle formation and their reduction
Authors: Breuer U. , Neitzel M. , Ketzer V. , Reinicke R.
Published: April 2004

Producing highly stiff and strong thin‐walled fabric‐reinforced parts for mass application can be economic using a double‐belt press to consolidate thermoplastic sheet and a hydraulic press for non‐isothermal stamp forming in a second step. During stamp forming, undesired wrinkle formation can occur at sites of three dimensional forming. To understand the mechanisms of wrinkle formation, shear tests were performed with different types of reinforcing glass and carbon fabric, both dry and impregnated with a polyamide (PA12) matrix. Evidence has been found that wrinkle formation during fabric shear is strongly dependent on membrane stresses within the fabric. High membrane stresses of ∼20 MPa can prevent wrinkling even at high shear angles of ∼60°. These stresses can be generated during stamp forming by means of blank holders. A new flexible roller tracking device has successfully been installed on a stamp forming pilot plant. It was possible to form chests sized 450 mm. 300 mm. 40 mm (w. l. d) free of wrinkles with a 4‐ply glass plain weave fabric preimpregnated with polyamide matrix (PA12) and a fiber content of 45 vol%.
Reactions of unconverted isocyanate in molded RIM parts and their implications to outgassing
Authors: Mielewski Deborah F. , Anturkar Nitin R. , Bauer David R.
Published: April 2004

A convenient, cheap, and reliable method was developed and evaluated to measure the extent of conversion and subsequent water/diisocyanate reaction kinetics for injection molded (RIM) parts using cryogenic grinding and conventional Fourier Transform Infra‐Red (FTIR) spectroscopy. The reliability of the method was independently confirmed by using in‐mold fiber‐optic FTIR and attenuated total reflectance spectroscopy (Priester, private communication, The Dow Chemical Company 1994). The reaction of isocyanate with water produces carbamic acid, which is believed to immediately decompose to carbon dioxide (CO2) and amine, leading to outgassing during the paint cure. Given previous measurements of effective diffusion coefficients of water and CO2, if the molded RIM parts are stored under typical humid conditions for hours, most of the CO2 should form as a product of isocyanate/water reaction and diffuse out of the part. However, our results indicate that relatively little CO2 evolution occurs during ambient storage for up to 6 h, and significant evolution occurs for long times during subsequent high temperature post cure. Therefore, in contrast to the earlier expectations, the outgassing phenomenon seems to be due to carbamic acids that decompose slowly at ambient conditions and become unstable at higher temperatures. Therefore, to assure minimum outgassing in this RIM system one must (1) operate the post cure oven at higher temperatures than the paint baking oven, or (2) keep parts in ambient storage at least for 24 h to allow slow decomposition of carbamic acids, or (3) transfer them to the post cure oven immediately after removal from the mold, thereby preventing possible water/diisocyanate reactions.
Moisture effects on the behavior of graphite/polyimide composites
Authors: Burcham Loyd J. , Vanlandingham Mark R. , Eduljee Rushad F. , Gillespie John W.
Published: April 2004

The effect of moisture on the material behavior of Magnamite® IM7 Graphite/Avimid® K3B thermoplastic polyimide composite laminates has been investigated. Laminates consisting of a 62 vol% fiber were laid up with several different stacking sequences: [90]10or unidirectional, [02/90]Sor thin cross‐ply, [02/902/02]Sor thick cross‐ply, [45/0/‐45/90]Sor quasi‐isotropic, and [0/90] laminates. In this study, the glass‐transition temperature,Tg, and the intralaminar fracture toughness,GIC, were measured for dry and moisture‐saturated unidirectional samples. When laminates were saturated with moisture, the value ofTgwas found to decrease from its baseline (dry) value, but recovered upon redrying the samples. This observation is consistent with the effects of moisture on theTgof other polymer composites. Permanent toughness losses have not been observed in samples conditioned in room‐temperature 75% and 100% relative humidity environments. However, during long‐term conditioning of cross‐ply and quasi‐isotropic samples in liquid water, transverse cracks initiated in the absence of an applied mechanical load. Moisture uptake curves for conditioning in room‐temperature liquid water, 80°C (176°F) liquid water, and at room temperature and 75% relative humidity were used to calculate Henry's Law constants and diffusion coefficients. Non‐Fickian behavior, consisting of a postsaturation increase in moisture uptake, was observed in crossply and quasi‐isotropic laminates and might be due to the observed transverse cracking.
Optimal design of the cure cycle for consolidation of thick composite laminates
Authors: Chang Ming‐hui , Chen Chieh‐li , Young Wen‐Bin
Published: April 2004

Autoclave cure of the prepreg lay‐up has been an importance method for fabrication of advanced fiber reinforced composites in the aerospace industry. Quality of the autoclave cured composite is largely affected by the cure cycle. In this study, the genetic algorithm is applied to design a cure cycle for the consolidation of thick laminated composites. The objective of the design is to select a cure cycle that results in a shorter cycle time for the process while avoiding the thermal runaway inside the composites. The results show that the genetic algorithm is a feasible and robust search algorithm to determine the cure cycle for the consolidation process.
Review of failure criteria of fibrous composite materials
Authors: Echaabi Jamal , Trochu Françlois , Gauvin Raymond
Published: April 2004

Composite materials exhibit various and complex failure behavior. Different formalisms have been used to predict failure. Improvement of old theories and new ones continue to be published. In this paper, the most recent and widely used models are presented. Failure criteria such as Tsai‐Wu, parametric formulations, maximal stress and strain, Hashin criterion, Hart‐Smith criterion, and the method based on kriging are presented. These failure theories may be classified in two categories, depending whether they integrate failure modes or not. The formalism of each theory is briefly described and their application to model failure of composite laminates is discussed by comparing the advantages and limitations of each method. The diversity of experimental failure envelopes, as reported in the literature on composites, is outlined and it is shown that most criteria permit modeling only particular failure properties of composite laminates.
Permeability model for a woven fabric
Authors: Šimáček Pavel , Advani Suresh G.
Published: April 2004

The resin transfer molding (RTM) method is used to manufacture composite parts. The reinforcing fibers are placed in a mold cavity and the resin is injected to fill up the empty spaces. After the resin cures, the mold is opened and the part ejected. To predict necessary pressures and filling times and the proper locations for the inlet ports for resin injection and vents for air ejection it is necessary to model the resin infiltration process. A key to this modeling is permeability which characterizes the resistance of fibers to the flow of infiltrating resin. A simplified model for in‐plane permeability of fabric reinforcement (preform) is developed here. This model uses lubrication theory for modeling the flow through open pores and Darcy's law for the transverse flow through the reinforcement. Scaling analysis is provided to justify the simplification and to estimate the range of validity for resulting expressions. Extension of the model to cover multi‐layered preforms is derived. Boundary conditions and the data necessary to specify the problem geometry are discussed. A numerical experiment is conducted to estimate the influence of the transverse permeability of the preform on the solution. A calculation is provided for the permeability of a plain weave fabric.
Liquid‐crystal polymer fiber production and reinforcing in ribbons of poly(ether imide)/vectra‐B blends
Authors: Bastida S. , Eguiazábal J. I. , Nazábal J.
Published: April 2004

Blends of poly(ether imide) (PEI) with a liquid‐crystal polymer (Vectra‐B950) were extruded into ribbon. Two PEI‐rich compositions at three different draw ratios were obtained, and the miscibility and morphology of the blends analyzed. The tensile properties of the ribbons were determined, both in the processing and in the perpendicular direction and were compared with those of the pure PEI. Results showed that PEI/Vectra blends are immiscible and that complex structures were obtained as a consequence of extrusion. The blend composition and the draw ratio determined to a great extent the mechanical properties of the blends. The interfacial adhesion between blend components is low, but enough to break the LCP fibers when significant aspect ratios are attained.
Impact fracture behavior of injection molded long glass fiber reinforced polypropylene
Authors: Skourlis T. P. , Mehta S. R. , Chassapis C. , Manoochehri S.
Published: April 2004

In this work the variation in Izod impact strength with spatial location was examined for injection molded long glass fiber polypropylene composite plaques. These plaques were fabricated at different sets of processing conditions, with injection speed and melt temperature being varied. By carefully machining test specimens, fifteen different plaque locations both in the in‐flow and cross‐flow directions were tested. The part morphology was described with the use of characteristic layer thickness ratios, i.e., the shell and the core to part thickness ratios, which were measured experimentally. It was shown that the variation in impact strength with sample location strongly correlates to shell to part thickness ratio. In addition, it was observed that different failure mechanisms exist for different fiber orientations, i.e., for fibers oriented transversely to the crack plane or on the crack plane itself. Scanning electron microscopy (SEM) of the fracture surface was conducted and the results supported our findings on the microstructural level.
Performance of multilayer films using maleated linear low‐density polyethylene blends
Authors: Sánchez‐Valdes S. , Orona‐Villarreal F. , Lopez‐Quintanilla M. , Yañez‐Flores I. , De Valle L. F. Ramos , Guerrero‐Salazar C.
Published: April 2004

Blends of linear low‐density polyethylene (LLDPE) and linear low‐density polyethylene grafted maleic anhydride (LLDPE‐gMA) were prepared by melt mixing and then coextruded as external layers, with a central layer of polyamide (PA) on three‐layer coextruded flat films. Blends with contents of 0% to 55 wt% of maleated LLDPE, on the external layers, were analyzed. The T‐peel strength and oxygen and water vapor transmission rate of the films were measured. The surfaces of the peeled films were characterized using attenuated total reflection infrared spectroscopy (FTIR‐ATR) and scanning electron microscopy (SEM). The observed increase in T‐peel strength of the films with 10% and higher levels of maleated LLDPE in the blend suggests good interfacial adhesion between layers. This sharp increase in peel strength appears to be associated, besides interdiffusion, with specific interactions between polymers, as the bond formation between maleic anhydride and the polyamide end groups by in situ block copolymer formation across the interface. No significant modifications in oxygen barrier properties of the films were observed; however, the use of higher contents of LLDPEgMA, even though it increases the adhesion performance, also increases the water vapor transmission rate by a reduction in the degree of crystallinity.
Properties and kinetics of thermally crystallized oriented poly(ethylene terephthalate) (PET). I: Kinetics of crystallization
Authors: Varma Pankaj , Lofgren E. A. , Jabarin S. A.
Published: April 2004

The crystallization kinetics of previously oriented poly(ethylene terephthalate) (PET) sheets have been studied under unconstrained conditions, as functions of stretch ratio, mode of extension, and crystallization temperature. Isothermal and dynamic crystallization conditions have been utilized for the determination of half‐times of crystallization and activation energies, respectively. Results indicate that rates of crystallization of pre‐oriented PET increase substantially, with increasing stretch ratios. Half‐times of crystallization, at a given isothermal temperature, were found to decrease from a few minutes to fractions of seconds. Similarly, the activation energies of thermal crystallization have been shown to decrease from 75 kcal/mol for unoriented PET, to less than 20 kcal/mol for highly oriented material. These changes are most apparent among samples with low to moderate levels of orientation. Highly oriented samples have proven to be less sensitive, yielding similar extents of thermal crystallization, regardless of specific initial extension ratios. These samples have also shown less sensitivity to temperature of crystallization, exhibiting only slightly higher levels of crystallinity as a result of exposure to increasing temperatures in the range from 100°C to 120°C.
Study on the surface tensions of polymer melts using axisymmetric drop shape analysis
Authors: Kwok D. Y. , Cheung L. K. , Park C. B. , Neumann A. W.
Published: April 2004

It is shown that Axisymmetric Drop Shape Analysis (ADSA) is well‐suited for the study of polymer melt surface tensions. The technique is not restricted to equilibrium surface (interfacial) tensions; it is also suitable for measuring the time dependence (or kinetics) of surface tension of polymer melts. Results for three polymers, polypropylene, polyethylene, and polystyrene, at temperatures above 170°C are reported. Contrary to the well‐known decrease of surface tension in low molecular weight surfactant solutions as a result of equilibration, an increase in the melt surface tension is observed under isothermal conditions.
Hot plate welding of polypropylene. Part I: Crystallization kinetics
Authors: Nieh Jenn‐Yeu , James Lee L.
Published: April 2004

The crystalline structure formation in the heat affected zone during hot plate welding has a great influence on the performance of the welded semi‐crystalline polymers. The quiescent and flow induced crystallization of polypropylene was investigated experimentally. A simplified, phenomenological crystallization model was developed, which can describe the crystal formation from completely melted and partially melted polymer. Predictions obtained from the model were compared with experimental results.
Packing mechanics of fiber reinforcements
Authors: Toll Staffan
Published: April 2004

Theories of fiber packing, of use in manufacturing composite materials, are developed. The maximum packing fraction of force free fibers is estimated based on a statistical analysis of the distribution of fiber‐fiber contact points. The new expressions are more general than previous ones by allowing for a distribution in fiber length and orientation. The forced packing beyond this limit is governed by the bending of fiber segments between contact points. A micromechanical theory is developed for this, again based on the contact point statistics, and equations relating the force response per unit area of a fiber bed to the fiber volume fraction are derived for three basic types of assembly: a general 3D wad, a planar mat of dispersed fibers, and a bundle of almost parallel fibers. Other types of reinforcement structure, such as woven fabrics, and the effect of lubrication are also treated briefly.
Filamentary extrusion of microcellular polymers using a rapid decompressive element
Authors: Park Chul B. , Suh Nam P.
Published: April 2004

An extrusion process for manufacturing microcellular plastics is presented. In the past, microcellular structures have been produced in batch processes by using a thermodynamic instability of a polymer/gas system. In order to utilize such a thermodynamic instability in a continuous extrusion process, a large amount of gas must be dissolved quickly in a molten plastic flowing in the machine, and a rapid drop in the gas solubility must be induced in the flowing polymer/gas solution. Since the solubility of a gas in a polymer is a sensitive function of pressure, a thermodynamic instability for producing a microcellular structure can be induced by rapidly lowering the pressure. This paper presents a means for continuously forming the polymer/gas solution at an industrial processing rate and a means of nucleating microcells in the polymer/gas solution using a nozzle. Finally, a process model for controlling the cell morphology is presented by identifying the key parameters that control microcellular foaming in a continuous process. The experimental results agree with theoretical analyses, confirming the fact that the processing pressure strongly affects the microcellular foaming process through its effects on the amount of gas dissolved in the polymer and the magnitude of the pressure drop in the nucleation device.
Selection of adhesive system for radio‐frequency heating of structural sheet molding compound components
Authors: Malaczynski Gerard W. , Cinpinski Gerald J.
Published: April 2004

A series of laboratory tests and computer simulations of adhesive curing enhanced by radio‐frequency heating indicated that not all adhesive systems can be effectively used for RF‐based curing because of the danger of thermal runaway. Our investigation of the process mechanism also resulted in several other findings that could lead to further improvement of the processing cycle. Both experimental and theoretical results indicated a high sensitivity of the adhesive exothermal reaction kinetics to the thickness of the bond line, which varies with changes of the thickness of the processed sheet molding compound (SMC) components. Thus, regardless of the type of adhesive system employed, tighter dimensional tolerance would ensure better quality of the bond. Finally, we proved that the initial surface temperature of the SMC members substantially affects the process effectiveness and joint quality, and should be strictly monitored.
Effects of additives on molecular weight correlations to dynamic viscosity of polypropylenes
Authors: Tollefson Norris M. , Roy Suresh , Shepard Thomas A. , Long William J.
Published: April 2004

The relationship between weight averaged molecular weight and zero‐shear viscosity (commonly known as the Mark‐Houwink equation) as determined by dynamic oscillatory rheometry was found to depend upon the absence or presence of viscosity‐modifying additives such as a plasticizing oil. An empirical expression was derived to estimate molecular weights from zero‐shear viscosities and compensated for the presence of plasticizing OIL or nucleating agent and their influence on the viscosity measurement. The model was verified by calculation of weight‐averaged molecular weights of irradiated polypropylenes, and comparison to molecular weight determined by gel permeation chromatography. In the process of derivation, it was found that superposition principles and interpretations of viscosity curves based on pure polymer systems were equally valid when applied to viscosity‐modified polymer systems.
Curing, compatibility, and fracture toughness for blends of bismaleimide and a tetrafunctional epoxy resin
Authors: Lin King‐Fu , Chen Jyh‐Chien
Published: April 2004

The curing, compatibility, and fracture toughness of blends of 4,4 ′‐bismaleimidodiphenylmethane (BDM)/tetraglycidyl diamino‐diphenyl methane (TGDDM) were investigated. Diamino‐diphenyl sulfone (DDS) was used as a curing agent. BDM alone could be both homopolymerized (at a lower temperature) and could also undergo Michael addition reactions with the primary amine of DDS. The secondary amine of DDS did not react with BDM. However, the network produced by homopolymerization was not miscible with that produced by the latter reactions. Curing of TGDDM with DDS took place almost at the same temperature as that of the homopolymerization of BDM, but well below the temperature of the Michael addition reaction. When a BDM/TGDDM mixture was cured with DDS in the stoichiometric ratio, the miscibility of the cured system increased with the amount of TGDDM. This was attributed to the fact that the network produced by Michael addition reactions was diminished. When DDS reacted entirely with TGDDM, the BDM/TGDDM/DDS cure yielded only a TGDDM/DDS network and a BDM homopolymerized network, which were not only miscible, but are also interpenetrating. The superior interpenetrated network, as indicated by the highest fracture toughness, was found at BDM/TGDDM = 40/60 weight ratio in the BDM/TGDDM/DDS curing systems.
Post extrusion hot drawing of polycarbonate/liquid crystalline polymer blends
Authors: Beery D. , Kenig S. , Siegmann A. , Narkis M.
Published: April 2004

The post extrusion hot drawing of polycarbonate/liquid crystalline polymer (PC/LCP) blends, over the entire composition range, was studied. The extruded filament morphology and elastic modulus were followed as a function of blends composition, initial phase morphology, and draw ratio (DR). Hot drawing was found to cause further orientation to the already existing partially oriented LCP phase at the die exit, as reflected by the increased blends modulus. The additional orientation depends on the initial filaments structure, the blend composition, and the DR. Moreover, the orientability of the LCP phase is much higher, similar to that of neat LCP, for blends in which the LCP forms the continuous phase. In low LCP content blends, a critical DR was identified, beyond which the LCP fibrils undergo fragmentation and voids at the fibrils/matrix interface are formed, resulting in a decrease in the drawn filament modulus.
Comparative X‐ray scattering, microscopical, and mechanical studies on rectangular plates injection molded from different types of isotactic polypropylene
Authors: Zipper Peter , Jánosi András , Geymayer Wolfgang , Ingolic Elisabeth , Fleischmann Ernst
Published: April 2004

Rectangular plates were injection molded from two grades of commercial polypropylene (PP) differing in the molar mass distribution. The mold was mechanically sealed when a desired pressure pi,max (up to 1560 bar) was reached. Samples were taken from each plate at different distances from the gate and were investigated by applying various methods. In spatially resolved wide‐angle X‐ray studies, the cross section of the sample was scanned with a fine X‐ray beam (collimated by a Kratky small‐angle camera) and the intensity of scattering was registered by a linear detector as a function of position in the cross section. The evaluation of the scattering data delivered profiles of several parameters, describing the distribution of crystallite modification β‐PP and γ‐PP, the degree of orientation, the size of crystallites, and interplanar spacing, depending on the distance from surface. These results and those from measurements of birefringence and elongation at break, and from polarization microscopy and transmission electron microscopy, provided details of the layered structures in the plates, at different flow lengths, and allowed far‐reaching statements about the influence of molecular properties and processing conditions on the development of texture in the plates.
Blends and thermoplastic interpenetrating polymer networks of polypropylene and polystyrene‐block‐poly(ethylene‐stat‐butylene)‐block‐polystyrene triblock copolymer. 1: Morphology and structure‐related properties
Authors: Ohlsson Bertil , Hassander Helen , Törnell Bertil
Published: April 2004

Blends of polypropylene (PP), the triblock copolymer polystyrene‐block‐poly(ethylene‐stat‐butylene)‐block‐polystyrene (SEBS), and processing oil were found to form thermoplastic interpenetrating polymer network (IPN) structures in a composition range from about 10 to 55% by weight polypropylene. The IPN structure was confirmed by electron microscopy and by solvent extraction. At high elongations, the cocontinuous blends showed a stress‐strain behavior similar to rubber and no signs of the typical necking phenomenon normally associated with polypropylene at large deformations. The processing oil used to improve the processing properties of SEBS was found to partly dissolve in the polypropylene phase, causing a marked lowering of the polypropylene glass‐transition temperature. The distribution coefficient for oil between polypropylene and SEBS was estimated to be 0.35. While the degree of crystallinity of polypropylene did not vary with blend composition, the melting temperature decreased from 162.7°C in the pure polypropylene to 149.3°C in the blend with lowest polypropylene content. The large melting point depression suggests that polypropylene, the EB fraction of SEBS, and the oil may form a homogeneous melt phase. This probably explains the formation of an IPN structure on cooling.
Chemorheology of thermosets—an overview
Authors: Halley Peter J. , Mackay Michael E.
Published: April 2004

A review of current chemorheological techniques and measurement systems is presented for unfilled and filled thermoset resins. The specific measurement techniques for the kinetics, chemorheology, and modeling of these systems are presented, with particular emphasis on the chemorheological techniques and measuring systems. These techniques and measurement systems provide a greater understanding of traditionally complex thermoset processes, provide effective quality control measures for these processes, and will reduce design and operating costs in associated industries.
Improvement of mechanical properties of composites through polyamide grafting onto kevlar fibers
Authors: Salehi‐Mobarakeh Hamid , Ait‐Kadi Abdellatif , Brisson Josée
Published: April 2004

Chemical modifications of the surface of Kevlar fiber were investigated as a means of improving fiber‐matrix adhesion. The fiber surface was used as a polymerization support for interfacial polycondensation. Nylon‐6,6 was successfully polymerized in this way. The grafted nylon was characterized by ESCA (electron spectroscopy for chemical analysis), DSC (differential scanning calorimetry), and extraction procedures. An increase of the transcrystalline layer thickness was observed through optical microscopy, indicating better fiber‐matrix adhesion. Both plasma treated fibers having been submitted or not to chemical treatments were used as reinforcements for nylon‐6,6 unidirectional composites. Improvement of the mechanical properties were related to better interfacial interactions due to grafted nylon chains.
On the use of PET‐LCP copolymers as compatibilizers for PET/LCP blends
Authors: Poli Giovanna , Paci Massimo , Magagnini Pierluigi , Scaffaro Roberto , La Mantia Francesco P.
Published: April 2004

Copolyesters of poly(ethylene terephthalate) (PET) with a liquid crystalline polymer (LCP), SBH 1:1:2, have been synthesized by the polycondensation, carried out in the melt at temperatures up to 300°C of sebacic acid (S), 4,4′‐dihydroxybiphenyl (B), and 4‐hydroxybenzoic acid (H) in the presence of PET. The PET‐SBH copolyesters have been characterized by differential scanning calorimetry, scanning electron microscopy, X‐ray diffraction, etc., and the relationships between properties and preparation conditions are discussed. The copolyesters show a biphasic nature, which is more evident for the products synthesized with a thermal profile comprising relatively lower temperatures (220–230°C) in the initial stages of the polycondensation. Another procedure, whereby the addition of PET to the monomer charge was made at a later stage of the reaction, has also been devised to prepare copolyesters with enhanced blockiness. The compatibilizing effect of the PET‐SBH copolymers toward PET/SBH blends has been investigated. PET/SBH blends (75/25, w/w) have been prepared in a Brabender mixer at 270°C and 30 rpm, with and without the addition of appropriate amounts (2.5, 5, and 10%, w/w) of 50‐50 PET‐SBH copolyesters. Different blending techniques have been used according to whether the three components were fed into the mixer at the same time, or one of them was added at a later stage. The effect of the type and the amount of added copolyester has been studied through morphological, thermal, and mechanical characterizations. The results show that the addition of small amounts ∼5 wt% of copolyesters leads to improved dispersion and adhesion of the minor SBH phase. Moreover, while the tensile modulus of the blends is practically unaffected by the addition of the copolymer, a substantial increase of both tensile strength and elongation to break is found for a concentration of added copolyester of ∼5wt%. Slightly better results were apparently obtained by the use of a block copolyester.
Cavity pressure dynamics and self‐tuning control for filling and packing phases of thermoplastics injection molding
Authors: Gao F. , Patterson W. I. , Kamal M. R.
Published: April 2004

Because of its versatility, cost effectiveness, and ability to produce intricate shapes to tight specifications, the injection molding process is widely used in plastics processing. Mold cavity pressure plays an important role in determining the quality of the molded articles. The dynamic behavior and control of cavity pressure were studied for the filling and packing phases. The dynamics of cavity pressure during filling were investigated and found to be both nonlinear and time‐varying in relation to the hydraulic servo‐valve opening, which is the manipulated variable. A self‐tuning control system was designed and tested for a wide range of conditions. The transition from filling to packing was best detected by the change in the derivative of cavity pressure. The dynamics of cavity pressure during packing were studied and modeled similarly as for filling. The self‐tuning technique was successfully extended and implemented in the packing phase.
An investigation of the spatial and optical behavior of biaxially drawn PET film
Authors: Khan M. B. , Keener C.
Published: April 2004

The paper investigates the evolution of the spatial and optical properties of particle‐doped poly(ethylene terephthalate) PET film, as a function of the degree of biaxial extension. Mean surface roughness and peak particle concentration were the main spatial parameters studied. A sharp increase in the average asperity height has been recorded for early forward draw, followed by an abrupt decline that continues almost linearly through the remaining sideways draw. This behavior has been explained in terms of the unequal stress distribution and subsequent yielding in the polymer film surrounding the particles. The peak concentration drops initially due to stretching of the film surface, but remains constant through the transverse draw. The wide angle haze was found to be an exponential function of forward extension, similar to the stress/strain curve for PET. However, the surface haze followed the same trend as surface roughness, suggesting a probable correlation between the two. A consideration of the transversal particle migration suggests that the screw extrusion part of the process may be instrumental in the augmentation of the base surface roughness of the film leaving the slit die.
Conductive polymer blends with low carbon black loading: Polypropylene/polyamide
Authors: Tchoudakov R. , Breuer O. , Narkis M. , Siegmann A.
Published: April 2004

The electrical resistivity and morphology of polypropylene/nylon (PP/Ny) immiscible blends incorporated with carbon black (CB) were studied. CB was found to be preferentially located in the Ny phase or upon the Ny/PP interface. Blends with a co‐continuous phase morphology depicted especially low resistivity values, due to a “double percolation” effect. The blend preparation sequence tends to affect the phase morphology, thus influencing the system's resistivity. Polymer polarity and crystallinity are important factors determining the blend's morphology, which relates directly to the electrical resistivity obtained.
A microcellular processing study of poly(ethylene terephthalate) in the amorphous and semicrystalline states. Part I: Microcell nucleation
Authors: Baldwin Daniel F. , Park Chul B. , Suh Nam P.
Published: April 2004

Microcellular semicrystalline polymers such as poly(ethylene terephthalate) show great promise for engineering applications because of their unique properties, particularly at higher densities. Recent studies reveal some high density microcellular polymers have longer fatigue lives and/or equal strengths to the neat polymer. Relatively few microcellular processing studies of semicrystalline polymers have been presented. In general, semicrystalline polymers are relatively difficult to microcellular process compared to amorphous polymers. In this paper and a companion paper, the microcellular processing of poly(ethylene terephthalate) in the amorphous and semicrystalline states is studied in order to quantify the processing differences. The microcellular processing steps addressed in this paper include gas/polymer solution formation and microvoid nucleation. Particular emphasis is given to microvoid nucleation comparing the processing characteristics of semicrystalline and amorphous materials. Moreover, this study identifies a number of critical process parameters.

In general, the semicrystalline materials exhibit ten to one thousand times higher cell nucleation densities compared with the amorphous materials, resulting from heterogeneous nucleation contributions. The amorphous materials show a strong dependence on cell density, while the semicrystalline materials show a weaker dependence. Moreover, classical nucleation theory is not adequate to quantitatively predict the effects of saturation pressure on cell nucleation for either the amorphous or semicrystalline polyesters. Both the semicrystalline and amorphous materials exhibit constant nucleation cell densities with increasing foaming time. Foaming temperatures near the glass transition are found to influence the cell density of the amorphous polyesters, indicating some degree of thermally activated nucleation. Furthermore, classical nucleation theory is not adequate to predict the cell density dependence on foaming temperature. Similar to the amorphous polyesters above the glass transition temperature, nucleation in the semicrystalline materials is found to be independent of the foaming temperature.
Measures of mixing for extrusion by averaging concepts
Authors: Kim S. J. , Kwon T. H.
Published: April 2004

This paper proposes modified Deformation Characteristics (DC) as a new deformation measure for three‐dimensional flows in extrusion. In contrast to the previous DC, the modified DC is defined by an averaged length stretch rate with the aid of two subsequent averaging concepts: firstly, average of length stretch rate of all the local elements in a shell, and secondly, average of a fluctuation of the averaged length stretch rate with time using a probability function. The modified DC was applied to the case of a two‐dimensional flow approximation based on the analysis of kinematics during one circulation including the “turning effect.” Consequently, we have proposed useful formulae to determine the modified DC for the two‐dimensional flow approximation. This involves extensive numerical calculations of the modified DC, both for the three‐dimensional flow and for the two‐dimensional flow approximation. Typical results are discussed with comparisons between the modified DC, the previous DC, and a strain proposed by Pinto and Tadmor. It is interesting to note that the Weighted‐Average Deformation Characteristics (WADC) obtained from the three‐dimensional analysis was found to be close to that from the two‐dimensional approximate analysis. Therefore, the formulae proposed for the modified DC of the two‐dimensional flow approximation seems to be useful in analyzing the mixing behavior on extrusion with a large aspect ratio, avoiding the complicated evaluation of the averaging process of the length stretch rate for the three‐dimensional flow.
Infrared temperature measurement of polymers
Authors: Maier Christian
Published: April 2004

Infrared (IR) thermosensors that measure the temperature of polymeric melts in processing equipment by guiding the thermal radiation along optical fibers to the optovoltaic transducer are on the market. The fundamental concepts of thermal radiation must be viewed in a volumetric sense. In sequence, a model is presented to estimate the response of such IR thermosensors. It is dictated by the volumetric absorptivity of the polymer and the transmittance of the optical fiber. For typical commercial IR thermosensors, the entire wavelength range between 1.5 and 2.2 μm is relevant. Penetration depths can vary from magnitudes of mm to dm, since the IR probe is sensitive to the maximum temperatures in its acceptance volume. These findings were put to the test in two different experimental settings. In the first, the calculations overestimated the comparable experimental values by 10 to 20°C, but were reasonable given the relatively simple experimental apparatus. In the second setup, the maximum temperature of melt coming off the screws, measured by penetrating a small thermocouple into the stream, matched the IR temperature sensor's readings. The measurement of temperature excursions in different mixing geometries is demonstrated. No kneading section with forward staggered paddles gave significant increases in temperature. In contrast, maximum temperature excursions could be measured when reverse elements were in place.
Melt grafting of glycidyl methacrylate onto polypropylene and reactive compatibilization of rubber toughened polypropylene
Authors: Chen Li‐Feng , Wong Betty , Baker W. E.
Published: April 2004

Free radical melt grafting of glycidyl methacrylate (GMA) onto polypropylene (PP) was studied. The extent of GMA grafting and the molecular weight of the functionalized PP copolymers were controlled by carefully manipulating various reaction factors, such as monomer concentration, initiator concentration, reaction temperature, and molecular weight of the starting PP homopolymer. The use of a second monomer, styrene, in the grafting process helped to increase GMA grafting further and reduce chain scission. The GMA modified PP copolymer was found to be able to reactively compatibilize PP/acrylonitrile‐co‐butadiene‐co‐acrylic acid rubber (NBR) blends. Up to an eight‐fold increase in the impact energy of the PP/NBR blend was obtained. The compatibilizing capacities of the reactive copolymers, in terms of impact energy improvement of the PP/NBR blend, were found not to be exclusively dependent on the total concentration of reactive functionalities in the matrix of the blend. The characteristics of the reactive copolymers, i.e., the extent of functionalization and the molecular weight, were found to have significant influences on the compatibilizing capacity. A large amount of moderately functionalized copolymer offers better compatibilization performance than a small amount of highly functionalized copolymer. A significant drop in impact energy was observed with declining molecular weight of the copolymer.
Morphology development in immiscible polymer blends
Authors: Luciani André , Jarrin Jacques
Published: April 2004

This paper presents the results obtained using a new method for analyzing polymer blend morphologies. The method is based on the selective solubilization of the matrix followed by a separation of the dispersed phase in suspension by filtering. A suspension of the nodular part going through the filter is obtained and can be analyzed with a particle counter. The other part of the dispersed phase retained by the filter is constituted of fibers. The average droplet diameters were compared with those obtained using a Scanning Electron Microscope on fracture surfaces for different compositions and flow conditions. The average diameter obtained with the counter technique increases with the dispersed phase content up to an optimum where simultaneously a decrease in the mean diameter and an increase of the fibrillar part are observed, which means that there is a concentration range where these two types of morphologies are present in the blends. The results indicates that the stability of the fibrillar part seems to determine whether the blend morphology will evolve into nodules by the Rayleigh mechanism or into phase inversion by coalescence of stable fibers.
Computation of the morphological changes of a polymer blend along a twin‐screw extruder
Authors: Delamare L. , Vergnes B.
Published: April 2004

The control of the morphology of an immiscible polymer melt is of vital importance for the mastering of the final properties of the product. As polymer blends are produced using corotating twin‐screw extruders, understanding and modeling the changes experienced by the blend during this process is of great interest. In the present study, starting from Ludovic software, developed for computing flow parameters in the twin‐screw extrusion process, we present a computation of the droplet morphology development, based on the basic mechanisms of break‐up and coalescence. Depending on the value of a local capillary number and on local flow conditions, different changes may occur: affine deformation, drop splitting, break‐up by capillary instability, and coalescence. It is thus possible to follow, all along the screws, the changes in morphology, either for a single particle or for a particle distribution. Examples of these different computations are presented and compared with experimental results. Generally speaking, orders of magnitude of droplet size and tendencies when modifying processing conditions are correctly described, but the model still suffers from the absence of descrption of the melting process.
Asphalt modified by SBS triblock copolymer: Structures and properties
Authors: Adedeji A. , Grünfelder T. , Bates F. S. , Macosko C. W. , Stroup‐Gardiner M. , Newcomb D. E.
Published: April 2004

Microstructural transformation of a poly(styrene‐b‐butadiene‐b‐styrene), SBS, triblock copolymer blended with asphalt was studied as the asphalt composition was varied from 0 wt% to 96 wt%. Transmission electron microscopy (TEM), dynamic mechanical spectrometry (DMS), and differential scanning calorimetry (DSC) were used. The blends were made in batch mixers at 200°C, or by solution casting from a nonselective solvent (trichloroethane) at ∼28°C. Asphalt partially solubilizes the polybutadene (PB) midblock of the SBS producing saturated PB microdomains along with macrodomains of asphalt. When the asphalt concentration was varied from 10 to 90 wt%, the asphalt phase separated into a variable number of large domains, while the SBS‐rich regions formed a continuous matrix. Networks of SBS‐rich regions were observed at low magnification; these are referred to as macro‐networks. At higher magnification, networks that are stabilized by polystyrene (PS) microdomains (denoted micro‐networks) are also formed. The presence of a macro‐network is also confirmed by stress relaxation tests. The macro‐network broke down into microgel‐like structures when the asphalt composition exceeded 90 wt%. Examination of the interior of the SBS‐rich regions showed that the shape of the PS microdomains transformed from short cylinders to lamellae, hexagonally perforated lamellae (HPL), back to lamellae, short cylinders, and finally to spheres. DMS and DSC indicate a systematic increase in the PB glass transition temperature (Tg) and negligible change in the Tg of PS as the asphalt content increases. Triblock copolymers that can form a macro‐network at low concentration will be more desirable for highway pavement modification.