bluuebunny/crossref_metadata_2025 huggingface dataset:
Processing effects in production of composite prepreg by hot melt impregnation
Authors: Chmielewski C. , Jayaraman K. , Petty C. A.
Published: May 2005

The hot melt impregnation process for producing composite prepreg has been studied. The role of the exit die is highlighted by operating without impregnation bars. Experimental results show that when a fiber two is pulled through a resin bath and then through a wedge shaped die, the total resin mass fraction and the extent of resin impregnation in the two increase with the processing viscosity. The penetration of resin into a fiber bundle is greater when the resin viscosity is higher. This trend is unchanged over a range of two speeds up to the breaking point. A theoretical model is developed to describe the effect of processing conditions and die geometry on the degree of impregnation. Calculations with this model indicate that for a given die geometry, the degree of impregnation increases from 58% to 90% as the ratio of the clearance between the two and the die wall, to the total die gap is decreased from 0.15 to 0.05. Physical arguments elated to the effective viscosity of the prepreg show that the clearance ratio is independent of the two speed, but decreases as the ratio of the effective shear viscosity of the prepareg to the resin viscosity increases. This provides a connection between the experimental results obtained with varying resin viscosity and the computational results obtained with varying clearance values at the die inlet.
Influence of the impregnating property on mechanical properties of commingled yarn composites
Authors: Hamada Hiroyuki , Maekawa Zen‐Ichiro , Ikegawa Naoto , Matsuo Tatsuki , Yamane Masachika
Published: May 2005

Three types of glass/nylon 6 intermediate material forms‐film stacking, uncommingled yarn, and commingled yarm‐were selected study the correlations between the impregnating property and mechanical properties. The size of the glass fiber block to be filled with matrix and the porosity in glass fiber bundles by spearing out the fiber bundle was different in these materials. Unidirectional glass fiber reinforced thermoplastic composites were fabricated by compression molding. The being test was performed by using the three‐point loading system, and the fracture behavior and the degree of impregnation were observed to examine the influence of processing conditions on the bending properties, relative to the form of the intermediate material. Bending strength increased, in accordance with the impregnating property, least in the film stacking form, second most in uncommingled yarn, and most in commingled yarn. The impregnating property was affected by the size of fiber blocks and the porosity in fiber bundles, because bending strength was improved by spreading out the fiber bundles. Commingled yarn is an excellent intermediate materials, which has both the fineness of matrix/fiber mixing and large porosity in fiber bundles.
Resin transfer molding with powder‐coated preforms
Authors: Shields K. , Colton J.
Published: May 2005

Incomplete fiber wetting in a resin transfer molded composite may result in poor surface finish, high void content, and reduced mechanical properties. This work studied the use of tows that are precoated with a powdered version of the liquid molding resin (towpregs). The goal is to see if such preforms improve the final part properties because of better fiber wetting. Hercules 12K AS‐4 fibers and PR500 (liquid) and PS500 (Powder) resins (3M) were used to make fabrics from towpregs containing 50 wt% total resin (liquid and powder combined). The powder fractions were 0, 13, 21, 50 wt%. Samples were resin transfer molded from preforms made from the towpreg fabrics. Results showed that samples molded with powder‐coated preforms had improved surface finishes and reduced void contents (1.4 vs. 5%), but that the mechanical properties were not improved (transverse moduli of ∼ 7.8 Gpa and axial moduli of ∼ 100 Gpa), probably because of defects inherent in the hand‐woven towpreg fabric that was used.
Controlled interactions in cellulose‐polymer composites. 1: Effect on mechanical properties
Authors: Felix Johan M. , Gatenholm Paul , Schreiber H. P.
Published: May 2005

The surface properties of cellulose fibers have been modified by heat treatment, by silane coupling agents, and by maleated polypropylene grafts. The effectiveness of these methods has been evaluated by electron spectroscopy (ESCA), by contact angle measurements, and by inverse gas chromatography. The latter analyses yielded information on the fibers' acid/base interaction potential. Cellulose was found to be amphoteric, with prevalent acidic properties. Heat and chloro‐silane treatments accentuated acidity, while amino‐silane treatment produced net basicity in the fiber surface. Modification with maleated polypropylene reduced specific interactions and converted the fiber to a predominantly dispersion‐force solid. The modified fibers were used in composites with polypropylene (neutral), polystyrene (base), and chlorinated polyethylene (acid) as matrix. Stress/strain and dynamic mechanical parameters were found to vary with acid/base interactions between polymer and fiber, significant improvements being noted in elastic and storage moduli, in tensile strength and elongation. In polypropylene, properties were unaffected by acid/base considerations. Acid/base forces, not necessarily dominant, merit consideration in the design of surface modification strategies intended to optimize composite mechanical properties.
Particulate interlayer toughening of dicyanate matrix composites
Authors: Zeng Shangying , Hoisington Mark , Seferis James C.
Published: May 2005

Toughening of dicyanate matrix composites with particulate‐modified resin‐rich interlayers was investigated in this study. Specifically, the cure behavior, viscosity, and fracture toughness of the modified dicyanate systems were analyzed. Creation of a layered composite structure showed no improvement in Mode 1 interlaminar fracture toughness (GIc), but greatly increased the Mode II interlaminar fracture toughness (GIIc). Furthermore, the concentration of modifier particles in the interlayer resin was found to directly affect the toughness improvement and fracture path.
Influence from process parameters on void formation in resin transfer molding
Authors: Lundström T. Staffan , Gebart B. Rikard
Published: May 2005

The influence of different process variables on the void content in resin transfer modling (RTM) has been investigated experimentally. The moldings were made in a flat mold filled by a parallel flow from one edge of the laminate to the other. The viods were found concentrated in a narrow region close to the ventilation side of the laminate. The void volume fraction in this region was almost constant and dropped over a short distance to basically no voids in the rest of the laminate. Micrographs from cross sections in different directions revealed that the voids were of two different types, long cylinderical bubbles inside the fiber bundles. An efficient way of reducing the void content was to use vacuum assistance during mold filling. This technique was benefical both for the magnitude of the void content and for the extent of the void region. The void content with the highest level of vacuum assistance (≈︁ 1 kPa absolute pressure), was practically negligible. Strong indications for void generation by mechanical entrapment at the flow front was found. The lowering of the void content with vacuum assistance can be interpreted as aresult of compression of voids when the vacuum is released and a higher mobility of voids created at a lower pressure.
Formation and elimination of voids during the processing of thermoplastic of matrix composites
Authors: Leterrier Y. , G'Sell C.
Published: May 2005

The mechanisms of void formation and elimination during the stamping process of a polypropylene/glass fiber composite have been infestigated as a function of temperature, pressure, and time. Experiments were performed in a temperature and pressure controlled chamber, equipped with a rapid cooling facility. Samples of the composite as well as model polypropylene specimens containing calibrated voids were held at 200°C at different levels of hydrostatic pressure (1,10,100, and 300 bars), for a period of either 1 or 10 min. The speciments were subsequently characterized by denstiy measurements and morphologival observation. It was shown that: i) the expansion of the composite observed during the heating at 200°C under atmospheric pressure is largely induced by the gases previously dissolved in the polymeric matrix, ii) the rapid increase of the pressure during the stamping process leads to the closing of voids and, iii) the final holding under high calculation of void growth and shrinkage is in agreement with the morphological observations.
Interfacial adhesion and failure modes in single filament thermoplastic composites
Authors: Pisanova E. V. , Zhandarov S. F. , Dovgyalo V. A.
Published: May 2005

The single filament composite (SFC) test has been uses to investigate the adhesion of carbon and glass fibers to thermoplastic matrices. A new modification of the test is proposed, consisting of SFC specimens stretched until the neck formation is complete. This makes the measuring of fiber fragment lengths much easier and allows a wider class of matrices to be investigated. The adhesion between fiber and thermoplastic matrix is strongly dependent on the contact forming conditions. With increased time of thermal treatment, interfacial bonding is improved and the failuere mode is changed. In the case of por fiber‐mitrix adhesion, interfacial failure occurs. With an increase in interfacial shear strength, the martix cracks perpendicular to the fiber at the fiber breaks.
Predicting shrinkage and warpage of fiber‐reinforced composite parts
Authors: Tseng Shi‐Chang , Osswald Tim A.
Published: May 2005

One major problem that arises in the design of plastic parts, especially those that are fiber reinforced, is the change of shape and dimension as a result of shrinkage and warpage. These material inhomogeneities are caused by flowinduced fiber orientation, curing, poor thermal mold lay‐out, and other processing conditions. This paper presents a simulation that predicts shirnkage and warpage of 3‐D compression molded fiber reinforced composite parts. The simulation represents the structure with the 3‐noded shell elements used in mold filling simulations. The calculated results indicate that fiber orientation strongly affect the final properties, which vary with different chage locations, have a significant effect on warpage. Unsymmetric curing, caused by uneven mold temperatures, could lead to a thermal moment that could possibly help reduce warpage.
In‐plane permeability measurement and analysis in liquid composite molding
Authors: James Wang T. , Wu C. H. , James Lee L.
Published: May 2005

This work presents methods to measure and analyze in‐plane permeabilities of various fabric reinforcements. The principal flow directions need to be determined first by conducting flow visualization. From the flow front pattern, the ratio of the permeabilities in the two principal directions can be determined. The pressure and the flow rate relationship from both radial and unidirectional flow measurement methods are then used to calculate the values of the permeabilities. By the use of the unidirectional flow measurement method, the edge flow effect can also be estimated.
Trans‐plane fluid permeability measurement and its applications in liquid composite molding
Authors: Wu Cheng‐Hsien , James Wang T. , James Lee L.
Published: May 2005

This work discusses tow independent methods to measure and analyze the trans‐plane fjuid permeability of various fiber reinforcements. In the unidirectional flow method, the measured injection pressure and flow rate, together with a one‐dimensional Darcy's law were used to calculate the trans‐plane permeability of fiber mats was independent of flow rate only at low injection pressure. Flow‐induced fiber mat permeability change occurred when the injection pressure exceeded the clamping pressure. Measured permeability in conjunction with a three‐dimensional mold filling computer program was used to simulate the effect of stacking sequence for a combination of different fiber mats on the mold filling pattern. Finally, a method is proposed to simplify the simulation of a three‐dimensional flow through the fiber perform.
In situ sensor monitoring and intelligent control of the resin transfer molding process
Authors: Kranbuehl D. E. , Kingsley P. , Hart S. , Hasko G. , Dexter B. , Loos A. C.
Published: May 2005

An intelligent closed‐loop expert control system has been developed for automated control of the resin transfer molding process of a graphite fiber preform using an epoxy resin, E905L. The sensor model system has been developed to make intelligent decisions based on the achievement of landmarks in the cure process, such as full preform impregnation, the viscosity, and the degree of cure of the resin rather than time or temperature. In‐situ frequency dependent electromagnetic sensor (FDEMS) and the Loos resin transfer model are used to monitor and control the processing properties of the epoxy resin during RTM impregnation and cure of an advanced fiber architecture stitched preform. Once correlated with viscosity (η) and degree of cure (α), the FDEMS sensor monitors and the RTM processing model predicts the reaction advancement of the resin, viscosity and the impregnation of the fabric. This provides a direct means for monitoring, evaluating, and controlling intelligently the progress of the RTM process in situ in the mold throughout the fabrication process and for verification of the quality of the composites.
An electrostatic powder spray process for manufacturing thermoplastic composites
Authors: Ramani Karthik , Woolard Daniel E. , Duvall Mark S.
Published: May 2005

Manufacture of thermoplastic composites is expensive because of the difficulty of impregnating the resin into the fibers. Powder processing shows great promise as an impregnation technique for cost‐effective manufacturing. This paper discusses an electrostatic powder spray impregnation technique that uses glass fibers. A geodesic fiber spreader is used to spread the fibers locally in the region of maximum powder deposition. A negative corona electrostatic spray gun is employed to charge and direct the powder for coating both sides of the spread fiber tow. The process has been used to impregnate glass fibers with poly(aryl ether ketone ketone) powder. The effect of the powder mass flow, corona voltage, and fiber tow velocity on powder deposition has been investigated. Particle image velocimetry is utilized to determine particle velocities. Compression molded panels have been produced and tested in three point bending.
Strain recovery of polyester and nylon 66 monofilaments under various temperature histories
Authors: Lunn A. C. , Lee B‐L. , Yannas I. V.
Published: May 2005

Strain recovery of polyester and nylon 66 monofilaments, following stress relaxation at constant strain, has been measured under two types of temperature history. In the first (experiments here called type A), the monofilament, extended at an elevated temperature, was held at constant strain at that temperature, and then air‐quenched to room temperature while still under stress. The stress was later removed with the fiber at ambient temperature, and the recovery from strain determined. In the second (experiments of type B), the monofilament was also extended at an elevated temperature, but it was then allowed to recover, under zero load, at the same temperature, prior to quenching. A cylindrical heater is described which surrounded the fiber specimen and which could be removed suddenly to permit rapid air quenching of the specimen. Recovery was characterized by the percent of applied strain which was recovered 100 sec after load removal. The percent recovery, in type A experiments, decreased to low values with increasing stretch temperature. Recovery in type B experiments, however, was markedly different, and showed a minimum value at stretch temperatures in the vicinity of the glass transition. At higher temperatures, recovery was high, but it decreased rapidly as TM was approached due to the onset of viscous flow. There was thus a discontinuity in recovery behavior as the time of quenching increased through the time of unloading (transition between type A and type B conditions). The results were interpreted to show that the achievement of good heat setting (poor recovery) is critically dependent on the temperature of the fiber during both stretching and recovery periods.
Flow analysis network (FAN)—A method for solving flow problems in polymer processing
Authors: Tadmor Z. , Broyer E. , Gutfinger C.
Published: May 2005

A finite element method is proposed for solving two dimensional flow problems in complex geometrical configurations commonly encountered in polymer processing. The method is applicable to flow in relatively narrow gaps of variable thickness and any desired shape. It was developed for analyzing flow in injection molding dies and certain extrusion dies. The fluid can be any non‐Newtonian fluid which is incompressible, inelastic, and time independent. The flow field is divided into an Eulerian mesh of cells. Around each node, located at the center of the cell, a local flow analysis is made. The analysis around all nodes results in a set of linear algebraic equations with the pressures at the nodes as unknowns. The simultaneous solution of these equations results in the required pressure distribution, from which the flow rate distribution is obtained. Solution for the isothermal Newtonian flow problem is obtained by a one‐time solution of the equations, whereas solution of a non‐Newtonian problem requires iterative solution of the equations.
High modulus/high strength polyethylene obtained by high‐pressure injection molding
Authors: Kubáut J. , Månson J.‐A.
Published: May 2005

Increasing the nominal injection pressure up to 500 MP a improves the mechanical properties (modulus and strength) of injection‐molded high‐molecular‐weight high‐density polyethylene substantially. By a proper combination of barrel and mold temperature, the modulus of the molded parts (test bars) may be increased at least eight times compared to parts molded at 100 MPa. This improvement is partly due to the formation of high‐strength crystalline modifications of the polyethylene induced by flow and pressure. The extent to which these structure modifications occur in the samples molded at various conditions has been determined by thermal analysis (DTA). When increasing the thickness of the samples, a sharp reduction of the modulus and strength was observed, even though the concentration of the crystalline high‐strength phase was higher. An explanation of this effect in terms of the relaxation of the tie‐molecules connecting the crystallites is suggested.
Effect of morphology on stress relaxation of polypropylene
Authors: Attalla G. , Guanella I. B. , Cohen R. E.
Published: May 2005

Samples of isotactic polypropylene having different morphologies and crystallinities were prepared and subjected to stress‐relaxation experiments at different levels of strain. The relaxation moduli were determined in the range of temperature between – 20 and 40°C over a period of time from 1 to 1000 seconds. Using the time‐temperature superposition principle, the activation energy values of the shift factors aT were determined and the master curves were obtained for the various structures. Increasing crystallinity and/or crystalline aggregate size increases the relaxation modulus of the material and changes both shape and location of the spectrum of relaxation times so that no simple method can be found to correlate the various master curves.
Submicron patterns in substituted polystyrene resists by focused‐ion‐beam lithography
Authors: Brault R. G. , Kubena R. L. , Jensen J. E.
Published: May 2005

Submicron lines in negative working, substituted polystyrene resists by focused‐ion‐beam lithography were demonstrated. These features were transferred into an underlying molybdenum layer by plasma etching using the resist as an etch mask, with the minimum continuous line having a width of 0.20 μm.
Poly(methyl α‐trifluoromethylacrylate) as a positive electron beam resist
Authors: Willson C. Grant , Ito Hiroshi , Miller Dolores C. , Tessier T. G.
Published: May 2005

A mechanistic hypothesis is presented which explains the radiation chemistry of poly(methyl α‐haloacrylate)s. In order to test the hypothesis poly(methyl α‐trifluoromethylacrylate) PMTFMA was synthesized together with copolymers of methyl methacrylate (MMA), and the α‐trifluoromethyl analog. The mechanistic hypothesis predicts that PMTFMA should have a higher G scission than PMMA and that it should have no crosslinking propensity. This prediction was verified by experiment. Imaging of PMTFMA as a positive e‐beam resist is also presented. The new material is a more sensitive resist than PMMA.
Chemical amplification in the design of dry developing resist materials
Authors: Ito Hiroshi , Willson C. Grant
Published: May 2005

A new resist system is described which undergoes spontaneous relief image formation. The resist is formulated from end capped poly(phthaladehyde), PPA, and a cationic photoinitiator such as a diaryliodonium or triarylsulfonium metal halide. The extreme sensitivity of the resist is the result of designing for chemical amplification. The desired amplification results from the fact that photolysis of the sensitizer generates acid which catalyzes main chain cleavage of the polyaldehyde. The uncapped polymer is thermodynamically unstable with respect to reversion to monomer at room temperature so a single acid catalyzed scission results in complete depolymerization to volatile monomer. A single radiochemical event is thereby amplified in the sense that it produces an enormous number of subsequent chemical transformations. PPA/onium salt resist films are so sensitive that exposure to low doses of e‐beam, X‐ray or ultraviolet radiation results in complete self development without post‐exposure processing of any kind. The exposed area simply vaporizes.
A new negative working resist for UV light lithography
Authors: Nakane Hisashi , Yokota Akira , Yamamoto Shirushi , Kanai Wataru
Published: May 2005

A new negative working photo resist for UV lithography has been produced based on poly(methylisopropenylketone). Its significant characteristic is a minimal swelling upon development, with resulting high resolution capability.
Mathematical modeling of melting of polymers in a single‐screw extruder
Authors: Elbirli B. , Lindt J. T. , Gottgetreu S. R. , Baba S. M.
Published: May 2005

This paper addresses the apparent controversy surrounding the role of the solid bed mechanics in the Maddock melting mechanism. It is demonstrated that the inability of the melting models based on the freely deformable solid bed concept to predict accurately the pressure gradients in the melting zone is not exclusively due to the highly simplified isothermal Newtonian treatment of the melt pool as presumed previously. This study has shown that when using a non isothermal non‐Newtonian flow model for the melt pool, the freely deformable solid bed concept still results in unrealistically low pressure gradients while it may give good predictions of the melting rates. To the contrary, when a rigid solid bed is assumed, the pressure predictions tend to represent the experimental data more closely, whereas the theoretical melting rates seems to become less realistic. In view of the fact that both the freely deformable and the rigid solid bed concepts show such inconsistencies, it has been concluded that the mechanics governing the solids and melt transport in the melting zone require some additional examination, most notably, the influence of the constitutive behavior of the solid bed and of the cross‐channel melt circulation around the solid bed, and possibly of the melting kinetics for semicrystalline polymers.
Wood fibers as reinforcing fillers for polyolefins
Authors: Woodhams R. T. , Thomas G. , Rodgers D. K.
Published: May 2005

Wood pulp fibers possess strength and modulus properties which compare favorably with glass fibers when the differences in fiber densities are considered. Softwood pulp fibers with fiber aspect ratios near 100 are readily dispersed into high‐density polyethylene or isotactic polypropylene with the aid of carboxyic dispersing agents to form mixtures containing 50 weight‐percent wood pulp which can be readily injection molded. The mechanical properties of the molded specimens were similar for all types of pulp including Kraft (bleached and unbleached), mechanical and chemical‐mechanical pulps, waste pulps, and reclaim newspapers. Comparisons of the stiffness/weight efficiencies revealed that pulp composites equal or exceed the stiffness of most traditional materials of construction including steel, aluminum, glass‐fiber composites, and talefilled polyolefins, while retaining a major material cost advantage. The measured strength values of the pulp composites were less than the theoretically predicted values due to the presence of voids created by the formation of volatiles during processing. Mechanical pulps which were available in dry form were preferred because of lower cost and ease of handling. Wood fibers are non‐abrasive so that relatively large concentrations may be incorporated into polyolefins without causing serious machine wear during mixing and fabrication.
Enhancement of melting through corotating disk processors
Authors: Mekkaoui Abdallah M. , Valsamis Lefteris N.
Published: May 2005

Melting mechanisms in the corotating disk processor (DISK‐PACK)

Farrel Company trademark.

are presented and discussed. This polymer processor consists of disk elements attached to a shaft with the entire assembly fitted into a housing. All polymer processes are induced by the drag action of the jointly moving disks, compared to only one moving surface characteristic of single screw extruders. Experiments carried out in a 150 and 7‐1/2″ diameter corotating disk polymer processors indicate that polymers can be melted by either of two mechanisms: The drag melt removal mechanism and the dissipative mix‐melting mechanism. The former mechanism occurs when a molten film is constantly removed from both sides of the solid bed, while the latter takes place throughout a system of molten and solid particulate mixture occupying the space between the disks. A theoretical model is presented for the drag melt removal (DMR) mechanism in such corotating disk polymer processors. The additional capability to induce a dissipative mix‐melting (DMM) mechanism can increase the melting rate obtained from conventional mechanism by 300 percent and lower the exit melt temperature substantially. Melting rates over a broad range of conditions are presented for a variety of polymers.
The plasticization of an epoxy resin by dibutylphthalate and water
Authors: Thomson K. W. , Wong T. , Broutman L. J.
Published: May 2005

The glass‐transition temperature of an epoxy resin cured at two different temperatures and plasticized with water and dibutylphthalate has been studied. Both modulus of elasticity and yield stress were measured as a function of temperature to determine the glass‐transition temperature. Drying a saturated material appeared to restore the glass‐transition temperature to its original value but some broadening of the transition occurred. The behavior of an undercured epoxy when saturated with water could not be predicted by theory. A substantial increase in the transition temperature was observed which may have been caused by the presence of water and an expanded structure.
Theoretical and experimental study of the molten polymer flow in the calender bank
Authors: Agassant J. F. , Espy M.
Published: May 2005

The flow of molten polymers in the calender bank has been computed using a finite‐element method with stream function and vorticity. Two nonsymmetrical‐recirculating regions have been obtained fully in agreement with the experimental observations on poly(vinyl chloride) melt banks. The pressure distribution along the flow axis is very close to the one obtained using the classical‐lubrication approximation.
Dynamic mechanical properties of some polyurethane‐acrylic copolymer interpenetrating polymer networks
Authors: Fox R. B. , Bitner J. L. , Hinkley J. A. , Carter W.
Published: May 2005

Dynamic mechanical properties have been investigated for interpenetrating‐network systems based on polyol‐cured polyurethanes (PU) and 2 to 1 n‐butyl acrylate‐n‐butyl methacrylate (Ac) networks. The systems were formed simultaneously (SIN) from all of the precursors and reactants for both networks in the same vessel, and sequentially (SIPN) by swelling a precured PU with the reactants that will form the Ac network. If the Ac network is formed after gelation of the PU, the IPNs are transparent and appear to have single T (tan δmax) between those of the homonetworks; visible‐phase separation occurs if the Ac is intentionally polymerized prior to PU gelation. Damping curves were lower and broader and the T (tan δmax) and rubber moduli were higher for the SIN than for the SIPN systems. Up to 65 percent Ac, the T (tan δmax) data for both SIN and SIPN fit the Gordon‐Taylor equation if a T (tan δmax) for the Ac homonetwork 7°C higher than observed is used, suggesting a higher crosslink density for the Ac network under these conditions. The differences in properties of the SIN and SIPN are assumed to be dependent on sample homogeneity and upon the presence of a tin catalyst in the SIN preparation. This can result in limited Ac‐network formation and consequent phase separation before PU gelation has occurred, and the catalyst may also increase the extent of interaction, such as grafting or hydrogen‐bond formation between the networks.
Free‐radical polymerization of methyl methacrylate in tubular reactors
Authors: Baillagou Pierre E. , Soong David S.
Published: May 2005

Mathematical modeling and experimental studies of the freeradical polymerization of methylmethacrylate in tubular reactors have been performed to ascertain the operating constraints, reactor behavior, and product quality of this process. This paper focuses on reactions at a temperature below the glass transition of poly(methyl methacrylate). This class of experiments is here referred to as low‐temperature runs, in contrast to above‐Tg polymerization. Reactor temperature and conversion histories of these low‐temperature experiments are successfully described by a rheokinetic model, incorporating both detailed considerations of velocity profile development in the reactor and conversion‐dependent kinetics. The limitations of this process are discussed in light of the complex fluid flow and heat transfer problems encountered in the system.
Rheokinetics for reactive polymer processing
Authors: Biesenberger J. A. , Kumar R. , Garritano R. , Starita J. M.
Published: May 2005

An important aspect of all reactive polymer processing methods, including reactive injection molding (RIM) and reactive extrusion (REX) is the dramatic increase in viscosity of the material being processed. This paper describes an instrument designed to study rheokinetics of polymerizations relevant to reactive processing. The instrument is capable of measuring simultaneously both viscosity (dynamic or “steady”) and reaction rate during isothermal polymerizations in a closed system. Design aspects of the instrument and some preliminary results are presented.
Nucleation of crystallization of polyester by catalyst remnants—a review
Authors: Lawton E. L.
Published: May 2005

The antimony catalyst content of poly(ethylene terephthalate) has an appreciable effect on the tendency of the polymer to crystallize upon cooling from the melt. Nucleation density increases significantly as antimony catalyst concentration increases. The crystallization tendency of the polymer at a given molecular weight correlates strongly with both the antimony content and the diethylene glycol comonomer content. The behavioral patterns of nucleation by catalyst remnants are similar in polyester prepared from terephthalic acid or dimethyl terephthalate. The antimony catalyst is deposited in the polyester matrix in a form suitable to nucleate quiescent crystallization. The differences in tendency to crystallize that correlate with catalyst and diethylene glycol comonomer content are reflected in the crystallinity of injection molded samples.
Effect of flow history on the morphology of thermotropic liquid crystalline copolyesters
Authors: Joseph Eugene G. , Wilkes Garth L. , Baird Donald G.
Published: May 2005

Morphological studies have been carried out on a thermotropic liquid crystalline copolyester based on poly(ethylene terephthalate) (PET) and para hydroxybenzoate (PHB) that has been subjected to different types of flow histories. Wide angle X‐ray scattering investigations and chemical etching (n‐propylamine is the etchant) in conjunction with electron microscopy studies conducted on end gated injection molded plaques of the 60 percent PHB and 80 percent PHB copolyesters indicate that a highly oriented skin region and a less oriented core region is present. Chemical etching studies performed on microtomed layers of end gated and center gated plaques show that the etching is less pronounced in the skin region and is more pronounced in the core. The microtomed layers of the end gated injection molded plaques when analyzed by ESCA indicate the presence of a “PHB rich” skin region and a “PET” rich core region. Biaxial orientation, as denoted by WAXS measurements, is observed when the 60 percent PHB copolyester is squeezed between lubricated parallel plates.
Phase separation effects in processing of glass‐bead‐ and glass‐fiber‐filled thermoplastics by injection molding
Authors: Hegler R. P. , Mennig G.
Published: May 2005

Dumb‐bell specimens and rectangular boxes were used to study phase separation effects occurring in injection molding of glass‐bead and glass‐fiber‐filled thermoplastics. The separation effects were more pronounced with beads than with fibers and they increase with increasing bead diameter. The filler distribution is further influenced by mold geometry, filler concentration, matrix material, and processing conditions. If the use of fillers, which promote inhomogeneity, is unavoidable it is possible to improve the distribution of the rigid phase by a favorable choice of injection speed and melt temperature. With the theories available at present a qualitative interpretation of the origin of the observed separation phenomena is feasible.
A heat storage module with a polymer structural matrix
Authors: Feldman D. , Shapiro M. M. , Fazio P.
Published: May 2005

Test results are presented for a matrix type phase change thermal storage tile module with no surface covering, intended to transfer heat directly to and from room air at small temperature differences. Heat is stored and released by melting and freezing mixtures of fatty acids, which constitute up to half the weight of the tile. The polymeric matrices tested were powders or granules of poly(vinyl chloride) (PVC), poly (vinyl acetate) (PVAc), poly(vinyl alcohol) (PVA), vinyl acetate‐vinyl chloride copolymer (VAc‐VC), and high density polyethylene (HDPE). The tiles keep their shape and dimensions without any weeping of liquid fatty acid, up to 37 or 51°C, depending on their composition. In the case of PVC and PVA, infrared spectra and differential scanning calorimetry indicate interactions between the polymer and the fatty acids, which may increase the surface tension and allow larger matrix pores before weeping begins. Some of the tiles were reinforced with glass fibers, and others with cellulose fibers. The best mechanical properties were obtained with 5 percent of long (85 to110 mm) glass fibers. Paraffin chloride and antimony trioxide served as satisfactory fire retardants.
Flame retardation of polypropylene: Effect of silane treated antimony compounds
Authors: Jha N. K. , Misra A. C. , Tiwary N. K. , Bajaj Pushpa
Published: May 2005

Flame retardation of polypropylene was accomplished by blending with antimony compounds (Sb2O3 and SbPO4) in conjunction with polyvinyl chloride (PVC) or ferric oxide. The compatibility and dispersion of antimony compounds in the polymer matrix was enhanced by using silane coupling agents, viz., vinyltriethoxysilane (A‐151) and γ‐aminopropyltriethoxysilane (A‐1100). Rheological properties of filled polypropylene were studied in the temperature range 180 to 220°C at shear rates of 29.5 to 119.5 sec−1. An increase in the melt viscosity was found in the filled polypropylene as compared to virgin polymer. Silanation of antimony compounds also influenced the melt rheology of flame retardant polypropylene. Incorporation of 6 phr Sb2O3 and 19 phr PVC raised the oxygen index of polypropylene to 22.9 and this sample was found to be self extinguishing in 65 s with a burning rate of 0.06 mm/s as compared to 1.1 mm/s for unfilled polypropylene. Though silanation of antimony compounds slightly reduced the oxygen index of flame retardant polypropylene, yield strain and flexural rigidity of injection molded samples was improved over unsilanated flame retardant polymer.
Moisture diffusion in epoxy resins Part I. Non‐Fickian sorption processes
Authors: Wong T. C. , Broutman L. J.
Published: May 2005

Diffusion of water in a glassy epoxy resin has been studied by the sorption method. Film thickness scaling is used as a diagnostic tool for non‐Fickian sorption processes. A sorptiondesorption cycle effectively increases the preexisting free volume in the resin and renders the subsequent sorption process different from the original. The effect is understood by considering the time scale for diffusion and that for molecular relaxation of the glassy polymer network. A non‐Fickian sorption process is observed for an insufficiently cured resin and is caused by the resin undergoing further postcuring in the sorption process. It is shown that oxidation of the resin during sorption also gives rise to non‐Fickian processes previously described in the literature as diffusion anomalies for epoxies. It is further shown that the difference between sorption and resorption curves is not caused by irreversible damage to the resin but due to reversible changes in network conformations.
Transition mechanism from elastic deformation to plastic flow in poly(methyl methacrylate)
Authors: Nanzai Yukuo
Published: May 2005

Sudden changes of compressive strain‐rate on glassy poly(methyl methacrylate) lead to the conclusion that the post‐yield state under a constant stress is a state of steady flow in the polymer. Non‐linearity between the stress divided by temperature and the logarithm of strain rate for this steady plastic flow can successfully be analyzed using the Eyring equation with structural factors variable depending on stress and temperature. This analysis gives a unique functional relationship between the activation entropy and the activation enthalpy, which agrees fairly well with that for the melt derived from the WLF equation. This agreement provides a direct evidence verifying structural change of the glass into liquid‐like structure and enables us to recognize the conformational arrangement as an essential structural parameter controlling molecular mobility. Another experimental relation between the Eyring factors—the activation volume and the activation enthalpy—permits us to estimate the magnitude of an elementary volume for the molecular movement in the melt as a function of temperature. Moreover, the experimental finding of the steady flow in the glassy polymer motivated us to propose a transition mechanism from elastic deformation to plastic flow in which the internal viscosity or the activation volume is introduced as a single parameter representing the transient state of the structure.
Phenol/cresol‐formaldehyde resin characterization and contribution to product hardness
Authors: Brauman S. K. , Myers‐Acosta B. L. , Lokensgard P. C. , Steiner M. M.
Published: May 2005

Lot‐to‐lot variations in a phenol/cresol‐formaldehyde resin were fully characterized. Resin property‐product hardness relationships were examined to elucidate the cause of variable hardness in product insulators and to establish acceptance criteria for the resin. A high methylol content (ϕCH2OH), determined by quantitative carbon‐13 nuclear magnetic resonance (13C‐NMR), and a narrow molecular weight distribution (MWD), determined by size exclusion chromatography, were found necessary for resin to produce insulator meeting the minimum Shore D durometer specification of 40.
Nucleation in polymer crystallization: A physical or a chemical mechanism?
Authors: Mercier J. P.
Published: May 2005

Primary nucleation is in general heterogeneous in polymer crystallization. In unseeded polymers, the crystallization originates from a very small concentration (<0.1 percent) of unknown submicroscopic heterogeneous nuclei. Only in three cases have the nucleation mechanisms been identified with precision. The first example is self‐nucleation, which relates to the nucleation of a polymer melt by fragments of its own crystals previously present in the melt. Another example of heterogeneous nucleation is represented by epitaxial nucleation of polymers on inorganic and organic substrates recently established by Lotz and Wittmann. More recently, it was discovered that finely divided organic salts added to reactive polymers do not behave as inert heterogeneous substrates but rather dissolve and cut molten macromolecules producing ionic chain ends which precipitate into the melt and form organized aggregates which are the true nucleating species. It is clearly shown that mechanisms of physical and chemical origin are involved in heterogeneous primary nucleation of polymer crystallization.
Internal antiplasticization in diglycidyl ether of bisphenol A diamino diphenyl methane non‐stoichiometric epoxy networks
Authors: Bellenger V. , Dhaoui W. , Verdu J. , Boye J. , Lacabanne C.
Published: May 2005

DGEBA‐DDM (diglycicyl ether of bisphenol‐A‐diamino diphenyl methane) networks of various epoxide/amine molar ratios ranging from 0.7 to 1.4, were studied by density, quasi static (10−4 s−1), and ultrasonic (5 106 s−1) modulus, and thermostimulated creep measurements. Any step aside stoichiometry leads to an antiplasticization, e.g. an increase of the quasi static modulus, whereas Tg decreases. The previous interpretations (based on volumetric property considerations), of this phenomenon are questionable. The only common feature of all the antiplasticized systems is an unexplained decrease of the population of macro‐molecular segments involved in beta motions.
Polypropylene/polyethylene terephthalate blends compatibilized through functionalization
Authors: Xanthos M. , Young M. W. , Biesenberger J. A.
Published: May 2005

In attempts to improve the compatibility of polypropylene with polyethylene terephthalate, an acrylic acid functionalized polypropylene was evaluated as the blend component in polyblends containing 40 percent by weight polyethylene terephthalate and compared with an unmodified polypropylene. The preliminary experiments in a batch laboratory mixer were followed by compounding in a co‐rotating twin‐screw extruder. Additives such as magnesium acetate and p‐toluenesulfonic acid were evaluated as catalysts for potential interchange or esterification reactions that could occur in the melt. The blends were characterized through scanning electron microscopy, infrared spectroscopy, differential scanning calorimetry, and for mechanical properties. The results show that the functionalized polypropylene promotes a fine dispersed phase morphology, improves processability and mechanical properties, and modifies the crystallization behavior of the polyester component. These effects are attributed to enhanced phase interactions resulting in reduced interfacial tension (calculated as a 4‐fold decrease). The presence of the additives does not, in general, improve any further the blend morphology and properties, or its processability.
Molecular design of multicomponent polymer systems. XVIII: Emulsification of high‐impact polystyrene and low density polyethylene blends into high‐impact alloys
Authors: Fayt R. , Teyssié P. H.
Published: May 2005

The interfacial activity of a hydrogenated polybutadiene‐polystyrene tapered diblock copolymer, (HPB‐b‐PS) is investigated in blends of a low density polyethylene (LDPE) with a high impact polystyrene (HIPS) prepared in the melt state on a two‐roll mill. Optical and scanning electron microscopy examinations of smoothed or fracture surfaces and also surfaces obtained after THF‐extraction of PS phases demonstrate that the copolymer promotes the dispersion and interfacial adhesion of the components, whatever the composition and is able to create and stabilize particular dispersions of the rubber particles in these blends. Tensile and Charpy impact properties are also very significantly improved. All these features demonstrate that the ductility and toughness of PS and LDPE/PS blends can be closely controlled by adequate combinations of rubber particles and a HPB‐b‐PS copolymer.
New approaches to the processing of rutile‐filled polyolefins
Authors: Duchesne D. , Schreiber H. P. , Johnson B. V. , Blong T. J.
Published: May 2005

The performance of a fluorocarbon elastomer processing additive in rutile‐filled linear low density polyethylene (LLDPE) compounds was evaluated by capillary rheometry, and blown film extrusion. Different compounding sequences were considered and their effects on the performance of the processing additive in the presence of various rutiles examined. Lower apparent melt viscosities and higher shear rates for the onset of melt fracture were observed when using certain surface treated rutiles. The nature of the surface coating applied to rutiles was found to have a great influence on the Theological properties of the filled compounds and on the dispersibility of the solids. The acid‐base characteristics of rutiles were determined by inverse gas chromatography techniques, and inherent agglomeration indexes for the pigments were measured by an application of powder rheology principles. It was found that those rutiles with high agglomeration indexes or those with highly basic surfaces interfered the most with the processing additive. Mechanisms by which rutile dispersibility and acid‐base character influence the effectiveness of the fluorocarbon elastomer processing additive are discussed.
Prediction of fiber orientation in injection molded parts of short‐fiber‐reinforced thermoplastics
Authors: Matsuoka Takaaki , Takabatake Jun‐Ichi , Inoue Yoshinori , Takahashi Hideroh
Published: May 2005

Fiber orientation induced by injection mold filling of short‐fiber‐reinforced thermoplastics (FRTP) causes anisotropy in material properties and warps molded parts. Predicting fiber orientation is important for part and mold design to produce sound molded parts. A numerical scheme is presented to predict fiber orientation in three‐dimensional thin‐walled molded parts of FRTP. Folgar and Tucker's orientation equation is used to represent planar orientation behavior of rigid cylindrical fibers in concentrated suspensions. The equation is solved about a distribution function of fiber orientation by using a finite difference method with input of velocity data from a mold filling analysis. The mold filling is assumed to be nonisothermal Hele‐Shaw flow of a non‐Newtonian fluid and analyzed by using a finite element method. To define a degree of fiber orientation, an orientation parameter is calculated from the distribution function against a typical orientation angle. Computed orientation parameters were compared with measured thermal expansion coefficients for molded square plates of glass‐fiber‐reinforced polypropylene. A good correlation was found.