bluuebunny/crossref_metadata_2025 huggingface dataset:
An experimental technique for the characterization of molecular orientation through the thickness of plastic products
Authors: Daly H. Ben , Cole K. C. , Sanschagrin B. , Nguyen K. T.
Published: April 2004

An experimental technique has been developed for the characterization of the molecular orientation through the thickness of plastic products. The technique consists of milling the specimen to the depth where the molecular orientation is to be measured, polishing the exposed surface, and characterizing the polished surface by external reflection infrared spectroscopy. The technique was first tested on both unoriented and oriented poly(ethylene terephthalate). It was found that the intermediate steps of the process change the apparent surface orientation, but carrying the process to completion (to a finish of 0.05 μm) removes the altered material and leaves a surface whose orientation corresponds to that of the original sample. The technique was also tested on polyetheretherketone (PEEK), high density polyethylene (HDPE), and liquid crystal polymer (LCP). For polymers with a high transition temperature, like PEEK and LCP, the conclusions are the same as for PET. However, for polymers like HDPE, with a low glass transition temperature, the milling and polishing process used to prepare the samples can alter the orientation to a greater extent. This effect can be reduced by cooling the sample with liquid nitrogen during preparation.
Effect of natural zeolite on the mechanical properties of epoxy matrix
Authors: Lee Jae‐Young , Shim Mi‐Ja , Kim Sang‐Wook
Published: April 2004

The mechanical properties of epoxy systems filled with natural zeolite were studied. To study the effect of the filler content and particle size, natural zeolites of three different particle sizes were added to epoxy resin at various contents. The effect of strain rate on the tensile strength was also tested. With increasing zeolite content, Tg and Young's modulus increased; however, tensile strength and impact strength decreased. As the zeolite particle size decreased, all these properties increased, and tensile strength increased, with increasing strain rate. The fracture surface of the composite showed more complex morphology with increasing zeolite content.
Mechanical properties of PVC/SBR blends compatibilized by acrylonitrile‐butadiene rubber and covulcanization
Authors: Zhu S.‐H. , Chan C.‐M. , Wong S. C. , Mai Y.‐W.
Published: April 2004

The mechanical properties of poly(vinyl chloride) (PVC)/styrene‐butadiene rubber (SBR) blends compatibilized by acrylonitrile‐butadiene rubber (NBR) were studied. A sulfur curing system was employed to crosslink the rubber of the blends. In the case of the blends without any curing agents, an increase in NBR content did not improve the tensile strength and elongation‐at‐break. However, a significant improvement in the mechanical properties was observed when NBR was added as a compatibilizer and the blend was vulcanized. In the PVC/NBR/SBR (50/10/40) blends, the tensile strength and elongation‐at‐break increased with an increase in sulfur concentration. This improvement was attributed to covulcanization between NBR and SBR. The fracture toughness of PVC/NBR/SBR (50/10/40) blends was characterized by the critical strain energy release rate, Gc. In the case of the PVC/NBR‐29/SBR (50/10/40) blends, an increase in sulfur concentration resulted in a dramatic increase in Gc. However, the Gc value of PVC/NBR‐40/SBR (50/10/40) blends decreased with an increase in sulfur concentration owing to the brittle behavior of one of the blend components—the PVC/NBR‐40 (50/10) phase.
Comparison of residual stress predictions and measurements using excimer laser layer removal
Authors: Jansen K. M. B. , Orij J. J. W. , Meijer C. Z. , Dijk D. J. Van
Published: April 2004

Residual stresses in injection molded polymer parts can have a major effect on product performance and are therefore often undesirable. Two different models for residual stress formation in injection molded products exist in the literature. The first model assumes that stresses in molded parts are identical with free quench stresses. Deviations are attributed to molecular orientation effects. The second model assumes that no slip occurs and that stresses are related to the holding pressure. Careful measurements should be able to differentiate between these models. In this study the layer removal stress measurement technique was improved by using an excimer laser for the milling operation. In that way stress relaxation during measurements was avoided and thin layers of uniform thickness could be removed. Both resolution and measurement accuracy were greatly improved. Stress distributions in polycarbonate plates molded under low holding pressures turned out to be of the free quenching type, whereas those molded under higher pressures were of the pressure type. All stress distributions could be predicted by a recent theory that comprises the two models as limiting cases.
Cycle‐to‐cycle and within‐cycle adaptive control of nozzle pressure during packing‐holding for thermoplastic injection molding
Authors: Yang Yi , Gao Furong
Published: April 2004

Proper control of packing is critical to the quality of injection molded parts. To control the packing phase, nozzle pressure was chosen as a better indicator of the degree of packing than cavity pressure. This allows one nozzle pressure transducer to be used for different molds and is more suitable for industrial applications. The dynamics of nozzle pressure during the packing stage were studied and found to be both nonlinear and time varying. Therefore, an adaptive self‐tuning controller was designed and implemented. Several improvements—an anti‐windup estimate, an adaptive feedforward, and cycle‐to‐cycle adaptation—were incorporated to produce excellent packing pressure control results. The controller works well for a wide range of different conditions, such as set point profiles, barrel temperatures, molds, and materials.
The cocrystallization behavior of binary blends of isotactic polypropylene and propylene‐ethylene random copolymers
Authors: Kim Man‐Ho , Alamo Rufina G. , Lin J. S.
Published: April 2004

Rapidly crystallized blends of metallocene isotactic polypropylene and propylene‐ethylene random copolymers with an ethylene content varying from 0.76 to 7 mol% were found to cocrystallize to different degrees depending on the composition of the comonomer and content of copolymer in the blend. The degree of molecular mixing was studied using differential scanning calorimetry and solvent extraction techniques. A high extent of cocrystallization is obtained in the whole composition range of blends with a copolymer having up to ∼ 2 mol% of ethylene. The degree of cocrystallization decreases gradually with increasing ethylene content or with increasing copolymer content in the blend. It is found that for ethylene contents as high as 5–7 mol% the copolymer rich blends show partial separate crystallization of the propylene ethylene copolymer. Thus, these crystals were selectively extracted at temperatures just above the dissolution temperature of the pure copolymer. In these blends, the fractional content of segments from the copolymer molecules incorporated in the cocrystal is low, yet it prevents extraction of these molecules at temperatures above the dissolution temperature of the copolymer. The degree of cocrystallization is explained by differences in crystallization kinetics of the pure components. The percentage of extracted material was found to be directly related to the dissolution temperature of the cocrystal which was also found to be a linear function of the inverse of the crystallite thickness. The high extent of cocrystallization observed for these polypropylene blends contrasts with comparable blends of polyethylenes. The blends of linear PE with a copolymer of 4 mol% branch units and higher, form separate crystals even after rapid crystallization.
Crystallization behavior and rheological properties of polycarbonate and polypropylene blends
Authors: Chun Yong Sung , Jung Hyun Chul , Han Min Soo , Kim Woo Nyon
Published: April 2004

Crystallization behavior and rheological properties of blends of bisphenol‐A polycarbonate (PC) and polypropylene (PP) prepared by screw extrusion have been investigated by differential scanning calorimetry (DSC), polarized‐light microscopy, scanning electron microscopy, and a Rheometrics Mechanical Spectrometer. In the study of thermal analysis of PC‐PP blends by DSC, double crystallization peaks were observed in the PC‐rich compositions. In the study of spherulite of 7/3 PC‐PP blend, large droplets (>25 μm) of PP were crystallized between 115°C and 105°C, and then small droplets (<10 μm) of PP were crystallized at about 90°C. This result is consistent with the double crystallization behavior such that heterogeneous and homogeneous nucleations have been observed at about 105°C and about 85°C, respectively, by DSC measurements. From the results of rheological properties of the PC‐PP blends, the storage modulus of the PC‐PP blends at low frequencies has larger value than that of the simple mixing rule. The elasticity increase from the simple mixing rule is consistent with the emulsion model for a dispersed system.
Orientation of LCP blown film with rotating dies
Authors: Lusignea Richard W.
Published: April 2004

Liquid crystal polymers (LCPs) have been commercially available for over 10 years, but their use has been limited almost entirely to injection molded parts, totaling only about 7.5 million kg per year. Much larger volume uses of LCP in film, tube, pipe and extruded parts have not been exploited because of uncontrolled orientation in LCP. This paper explains how shear and elongation forces, controlled by rotating extrusion dies, orient LCP film, tube and other extruded parts. Applications to electronic, medical and high barrier packaging markets are discussed.
Characterization of the orientation in synthetic polymer sheets using far‐infrared radiation
Authors: Drouin Bernard , Gagnon Richard
Published: April 2004

Molecular orientation and mass distribution have been measured in various synthetic polymers using a characterization technique developed by the authors. This method is based on the transmission of polarized far‐infrared radiation. Fairly thick samples (polyethylene up to one centimeter thick) can be tested easily with this nondestructive approach. Spatial resolution in the millimeter range is possible. This allows the characterization of various industrial products made of nylon, polyethylene, polypropylene or polyesters, such as liquid containers, injection‐molded parts, thick extruded or drawn sheets and rods, etc. Potential scientific and industrial applications are discussed.
A mechanism for extrusion instabilities in polymer melts
Authors: Fyrillas M. , Georgiou G. , Vlassopoulos D. , Hatzikiriakos S.
Published: April 2004

A mechanism for explaining some of the instabilities observed during the extrusion of polymer melts is further explored. This is based on the combination of non‐monotonic slip and elasticity, which permits the existence of periodic solutions in viscometric flows. The time‐dependent, incompressible, one‐dimensional plane Poiseuille flow of an Oldroyd‐B fluid with slip along the wall is studied using a non‐monotonic slip equation relating the shear stress to the velocity at the wall. The stability of the steady‐state solutions to one‐dimensional perturbations at fixed volumetric flow rateis analyzed by means of a linear stability analysis and finite element calculations. Self‐sustained periodic oscillations of the pressure gradient are obtained when an unstable steady‐state is perturbed, in direct analogy with experimental observations.
A study of cell nucleation in the extrusion of polypropylene foams
Authors: Park Chul B. , Cheung Lewis K.
Published: April 2004

An investigation has been performed of the cell nucleation and initial growth behaviors in the foam processing of polypropylene (PP) in both the linear and branched forms. These materials were foamed in extrusion with the two blowing agents, CO2 and isopentane. The cell density generally increased with an increased content of the blowing agent, for both CO2 and isopentane. The effect of processing pressure on the cell density was distinct when CO2 was used, whereas no pressure effect was observed in the foam processing with isopentane. The cell morphologies for the two PPs were found to be significantly different. A slightly lower nuclei density was observed in the branched PP foams than in the linear PP foams. However, the phenomenon of cell coalescence was observed much less in the branched PP foams. Most cells in the branched PP foams were closed, whereas in the linear PP foams they were connected to each other. The experimental results indicated that the branched structure played an important role in determining the cell morphologies through its effects on the melt strength and/or melt elasticity.
A comparison between apparent viscosity and dynamic complex viscosity for polypropylene/maleated polypropylene blends
Authors: Li Shucai , Järvelä Pentti K. , Järvelä Pirkko A.
Published: April 2004

Apparent shear and dynamic complex viscosity measurements at 200°C and 230°C, for a series of blends of a homopolypropylene (PPVC) with maleic anhydride polypropylene (PP‐g‐MA) and blends of an ethylene‐propylene copolymer (PPSC) with PP‐g‐MA, are reported. The data were taken using a capillary rheometer and a dynamic mechanical thermal analyzer. The results are analyzed in terms of the Cox‐Merz rule. Data taken at 230°C for both matrices (viz. PPVC and PPSC) follow the Cox‐Merz rule. However, deviations are noted in the blends, especially in compositions wherein PP‐g‐MA content is above 10 wt%. Cross phase separation and charges in the dispersed phase size (of PP‐g‐MA) in the two types of measurement appear to be the cause of the failure of the Cox‐Merz rule.
Hybrid effects on mechanical properties of polyoxymethylene
Authors: Hashemi S. , Elmes P. , Sandford S.
Published: April 2004

The present study investigated fracture and various mechanical properties of polyoxymethylene (POM) hybrids in tension and in flexure. The hybrids examined consisted of short glass fibers (GF) and spherical glass beads (GB). Comparisons are made between experimentally observed values and predictions based on the rule‐of‐hybrid mixtures for hybrid strength, modulus, impact strength, fracture toughness, and strain energy release rates. Results indicated that tensile strength, flexural modulus, and fracture toughness of POM/GB/GF hybrid composites can be estimated from the following rule‐of‐hybrid mixtureswherePPOM/GBandPPOM/GFare the measured properties of the POM/GB and POM/GF composites, and χPOM/GBand χPOM/GFare the hybrid ratio (by volume) of the glass bead and that of glass fiber, respectively. In view of this, none of the aforementioned properties show any signs of a hybrid effect. Flexural strengths, impact strengths, and strain energy release rate all showed the existence of a negative hybrid effect where negative deviation from the rule‐of‐mixtures behavior was observed. The latter was closer to the estimation based on the inverse rule‐of mixtures.
Synthesis and mechanical properties of poly(styrene‐b‐lsobutylene‐b‐styrene) block copolymer lonomers
Authors: Storey Robson F. , Chisholm Bret J. , Lee Youngkwan
Published: April 2004

Linear and three‐arm star poly(styrene‐b‐isobutylene‐b‐styrene) (PS‐PIB‐PS) block copolymer ionomers possessing various counterions and levels of sulfonation were synthesized by sulfonating the polystyrene blocks of PS‐PIB‐PS block copolymers. Analysis of compression‐molded films of the ionomers showed that the incorporation of sulfonate groups into the polystyrene blocks of these materials resulted in an increase in tensile strength, a decrease in elongation at break, and a persistence of elastic properties to much higher temperatures as compared with unsulfonated precursors. Among all counterions studied, zinc resulted in the strongest ionomers and potassium yielded the most easily processed ionomers. Dynamic mechanical analysis showed that the block copolymer ionomers possessed a phase‐separated morphology; however, anomalous relaxations observed during the first heating cycle, but that were substantially reduced or completely absent in subsequent cycles, implied that strong ionic interactions were causing reduced processability and the formation of nonequilibrium morphologies. The observed relaxations were interpreted to be domain rearrangements brought about by the thermal energy supplied by the dynamic experiment. Annealing of films of relatively low ionic contents yielded viscoelastic behavior that was consistent with an equilibrium morphology characterized by phase‐separated, partially sulfonated polystyrene domains of the same density and size as the polystyrene domains of the unsulfonated precursor. Compression molded films of high ionic content yielded a higher rubbery plateau modulus than the unsulfonated precursor, suggesting a different morphology. Solution‐cast films of zinc ionomers exhibited two values for the rubbery modulus, a higher values at temperature below the Tg of polystyrene and a lower value at temperature above the Tg of polystyrene. Thermogravimetric analysis revealed the major mass‐loss process of the parent, linear block copolymer at 417°C (mid‐point) and of the tetramethyl ammonium ionomer at 431°C.
Fracture and impact strength of poly(vinyl chloride)/methyl methacrylate/butadiene/styrene polymer blends
Authors: Takaki Akira , Yasui Hideo , Narisawa Ikuo
Published: April 2004

The Izod impact strength of poly(vinyl chloride)/methyl methacrylate/butadiene/styrene(PVC/MBS)polymer blends can be changed significantly with different levels of MBS and/or MBS particle size. The following results were obtained by investigating the fracture of PVC/MBS test specimens: (1) The dependence of the Izod impact strength of PVC/MBS blend on MBS particle size confirms a maximum around a MBS particle size of 2000 Å. When MBS particle size is smaller than 2000 Å, the Izod impact strength increases with MBS particle size, and crazing occurs mainly in this region. When MBS particle size is larger than 2000 Å, then the Izod impact strength, in contrast, decreases with increasing MBS particle size, and both crazing and shear yielding occur, mainly in this region. (2) Tensile experiments of PVC/MBS blends carried out under various conditions showed that the amount of energy absorption increases with decreasing MBS inter‐particle distance and with increasing MBS particle size when crazing is the main energy absorbing mode. The MBS inter‐particle distance dominates the energy absorption when shear yielding is the main energy absorbing mode. (3) Therefore, the Izod impact strength of PVC/MBS blends and the maximum around a MBS particle size of 2000 Å can be explained as follows: Below 2000 Å, the energy absorption by crazing dominates the total energy absorption, and the energy absorption by crazing increases with MBS particle size. Above 2000 Å, the energy absorption by shear yielding is dominant, and the energy absorption by shear yielding increases with decreasing inter‐particle distance, that is to say, decreasing MBS particle size.
Ultimate properties of polycarbonate blends: Effects of inclusion plastic deformation and of matrix phase continuity
Authors: Kolar̆ík Jan , Lednický Frantis̆ek , Locati Giancarlo , Fambri Luca
Published: April 2004

Tensile energy to break (TEB) of polycarbonate (PC) blends has been increased by exploiting (i) the plastic deformation of dispersed or co‐continuous brittle polymer(s) and (ii) higher matrix phase continuity in ternary blends with two dispersed minority components. Monotonic dependence of yield strength on blend composition and micrographs of drawn specimens concurrently evidence a strong interfacial adhesion sufficient for transmission of yield and/or break stress. Good adhesion at created interfaces, was achieved through partial miscibility of PC with other components, i.e., poly(styrene‐co‐acrylonitrile) (PSAN) and poly(styrene‐co‐methyl methacrylate) (PSMMA), which was evaluated from the shifts of the glass transition temperatures of conjugate phases. Binary and ternary blends with PC contents higher than 35% show extensive plastic deformation after yielding. TEB and strain‐at‐break of ternary blends with 50% or 40% PC pass through a maximum at compositions with equal fractions of PSAN and PSMMA, which is in qualitative accord with model calculations of the matrix phase continuity. Thus, the blend PC/PSAN/PSMMA = 40/30/30 preserves 70% of TEB of neat PC.
Mechanical behavior of CaCO3 particulate‐filled β‐crystalline phase polypropylene composites
Authors: Tjong S. C. , Li R. K. Y. , Cheung T.
Published: April 2004

β‐crystalline phase polypropylene (PP) composites containing 5, 10, 20, 30, and 40% (by weight) of CaCO3 filler were prepared by injection molding. The β‐form PP was produced by adding a bicomponent β‐nucleator consisting of equal amounts of pimelic acid and calcium stearate. The morphology, static tensile, and impact properties of these composites were investigated in this study. Scanning electron microscopy (SEM) observations revealed that the β‐spherulites of the polymer matrix of the composites exhibit curved lamellae and sheaf‐like structures. The fillers were observed to disperse within the inter‐lamellar spacings of the β‐PP composite containing 10% calcium carbonate addition. However, the filler particles tend to link together to form larger aggregates when the filler content reaches 20%. Static tensile measurements showed that the elastic modulus of the composites increases with increasing filler content but the yield strength decreases with increasing filler addition. The falling weight Charpy impact test indicated that the β‐PP polymer exhibits the highest critical strain energy release rate (Gc) value. However, there was a drastic drop in Gc of the β‐PP composites with increasing filler content. The results are discussed and explained in terms of materials morphology.
A nonlinear regression approach to model the physical aging of poly(ether imide)
Authors: Woo E. M. , Kuo Sen‐Maw
Published: April 2004

Differential scanning calorimetry (DSC) was used to measure the relaxation enthalpy of glassy amorphous poly(ether imide) (PEI) at three high isothermal aging temperatures between 190 and 200°C. A three‐parameter model based on the Williams‐Watts relaxation function was utilized to describe the aging process of PEI, and nonlinear regression approach was used to estimate the model parameters. The prediction according to this model was found to be more accurate in comparison with the two‐parameter model based on the same Williams‐Watts relaxation function. Furthermore, the peculiar aging behavior at the highest aging temperature of 200°C was explained from the molecular view point of transition from sub‐Tg β‐relaxation to α‐relaxation near Tg.
Wall thickness distribution in plug‐assist vacuum formed strawberry containers
Authors: Aroujalian A. , Ngadi M. O. , Emond J‐P.
Published: April 2004

An experimental study on the influence of processing parameters namely film temperature, plug velocity, and temperature on wall thickness distribution in plug‐assist vacuum thermoformed fresh strawberry container using high‐impact polystyrene is presented. Film temperatures of 118, 125, 136, 150, and 165°C, plug velocities of 0.15, 0.20, and 0.27 m/s, and plug temperatures of 25, 60, 100, 123, and 135°C were used in the thermoforming. Increasing the plug velocity resulted in improved wall thickness distribution due to elastic deformation of the plastic sheet during thermoforming. Decreasing the stretching time and the temperature difference between the plastic film and plug was important for good wall thickness distribution. Better wall thickness was obtained at the plug velocity of 0.27 m/s and the plug temperature of 123°C.
Optimization of the coathanger manifold via computer simulation and an orthogonal array method
Authors: Chen C. , Jen P. , Lai F. S.
Published: April 2004

A well‐designed coathanger die may deliver a polymer melt through the die more uniformly. However, it is difficult to optimize the manifold profile because of the complexity of flow distribution with regard to problems of die geometry, temperature, shear, and viscoelastic effects. The empirical methods have been widely used to design the manifold of a flat slit die. But this approach is time consuming and causes die material waste due to the iterative design process. With computer simulation, die designers can repeat modifications to obtain the optimal manifold shape easily. In this research, the Taguchi method was used to investigate the influences of the materials, die geometry, and processing conditions on optimizing the manifold profile. The comparison of the thickness distributions with and without modified manifold showed that the modified manifold improves the thickness uniformity significantly.
Interaction characterization of PA1010/PP blends using PP‐g‐AA as compatibilizer
Authors: Zhang Xiao‐Min , Yin Jing‐Hua
Published: April 2004

The morphology of polyamide 1010/polypropylene blends was found to significantly depend upon the concentration of the compatibilizer[polypropylene‐grafted‐acrylic acid (PP‐g‐AA)]. A significant reduction in phase size was observed because of the interaction that existed between the PP‐g‐AA and polyamide. These interactions have been confirmed by several methods. The tensile mechanical properties and impact behavior of the prepared blends were investigated and correlated with scanning electron microscope (SEM) analysis of the fracture surfaces. It was found that PP‐g‐AA as the compatibilizer has a profound effect upon the properties of the blends. This behavior is attributed to a series of chemical and physico‐chemical interactions taking place between the two components.
Incorporation of density relaxation in the analysis of residual stresses in molded parts
Authors: Ghoneim H. , Hieber C. A.
Published: April 2004

Thermo‐rheologically/piezo‐rheologically simple viscoelastic constitutive equations are adopted for the material behavior of a generic polystyrene, in both the deviatoric and dilatational domains, in order to investigate the effect of density relaxation on the development of the thermal residual stresses in a thin injectionmolded strip. A preliminary study is undertaken to assess the ability of the proposed dilatational viscoelastic constitutive equations to capture some of the density‐relaxation behavior such as the isobaric volume relaxation following a sudden quench from above the glass‐transition temperature and upon constant rates of cooling at different temperatures and pressures. In this preliminary study, different combinations of relaxation functions and shift factors are investigated. An appropriate combination is selected and used for the residual‐stress analysis. The numerical simulation of the development of the stresses in a one‐dimensional cavity qualitatively predicts the correct stress profile across the thickness of the molded part, as well as the dependency of this profile on some of the material properties and molding conditions. In general, the investigation presented in this paper suggests that density relaxation plays an important role in the development of residual stresses in molded parts.
Morphology and mechanical properties of injection molded articles with weld‐lines
Authors: Kim Jin Kon , Song Ju Ho , Chung S. T. , Kwon T. H.
Published: April 2004

The effect of weld‐lines on the morphology and mechanical properties of injection molded articles made of neat poly(butylene terephthalate) (PBT) and glass fiber‐reinforced PBT was investigated. The weld‐line was introduced to a molded article by using a rectangularly shaped insert inside a mold cavity, and tensile specimens were prepared at various positions through the entire molded article. The weld‐line position was further checked by a short‐shot experiment. Although the maximum tensile stress for specimens of neat PBT with a weld‐line is almost the same as that without a weld‐line, the maximum tensile stress and the elongation at break for fiber‐reinforced PBT with a weld‐line were found to be about half of those without the weld‐line. This is attributed to the fact that the fibers near the weld‐lines are oriented parallel to the weld‐line direction (or perpendicular to the tensile force direction) due to stretching flow. Finally, we compared experimental results of flow pattern and fiber orientations with numerical simulations. We found that the predictions of flow fronts and fiber orientations are in good agreement with experimental results.
The effect of block structure of an ethylene terephthalate/hydroxybenzoate copolymer on its ability to form compatible blends
Authors: Stachowski M. J. , Dibenedetto A. T.
Published: April 2004

A thermotropic liquid crystalline polymer (TLCP) containing aliphatic linkages exhibits properties of both a random‐coil and a rigid‐rod. By varying its block structure, one can change its ability to form compatible blends with other polymers. In this work, the ability of the TLCP p(ET/HBA60) with a high degree of block structure, X‐7GTM, to form compatible blends with polycarbonate and aromatic TLCPs is compared to that of a p(ET/HBA60) with a more random molecular structure, RodrunTM LC‐3000. It was found that both materials formed compatible blends through transesterification of the block structure and that a higher degree of blockiness enhanced the rate of transesterification. NMR spectra and differential thermal analysis were used to quantify the degree of transesterification and scanning electron microscopy was utilized to examine the effects of the blending process on the degree of compatibilization and the morphology of the resulting blends.
Stress relaxation of elongated strip of poly(vinylidene fluoride) in ethyl acetate vapor
Authors: Phillips J. C.
Published: April 2004

Poly(vinylidene fluoride) films in ethyl acetate vapor were studied at 30°C for vapor pressures of p = 0, 12, 30, 40, 66, 85 torr and elongations ε = 4.5%, 7%, 9.5%, 19%, 29%, and 44%. A cyclic experiment was also performed at ε = 7% and p = 40 torr for three sorption/desorption cycles. Assuming, as a first approximation, that the stress relaxation of the “dry” and “wet” polymers is proportional to the elastic strain, εel, empirical calculations were performed and compared to experimental results. In general, the presence of a vapor or gas in a polymer matrix enhances the stress relaxation by softening or plasticizing the polymer and transforming a portion of the elastic strain, εel, into the plastic strain, εpl. As the transformation continues, the sorption and stress of the wetted elongated sample change simultaneously with time until an optical “overshoot” and a mechanical or stress “undershoot” is observed. This result seems to be the consequence of the differential change of the stress of the “dry” and “wetted” samples with sorption time, τ = t − to(t = time; to = initial sorption time), which depends on the differential time dependencies of the transformations of the elastic and plastic strains.
A fracture mechanics approach to weld‐line fracture in an amorphous cellulose acetate propionate
Authors: Pecorini Thomas J.
Published: April 2004

The fracture properties of molded articles containing weld‐lines are analyzed by a fracture mechanics approach, treating the weld‐line as a sharp crack. The theoretical length of the weld‐line crack is estimated from diffusion properties and a simple model of cooling in a mold. These estimated weld‐line crack lengths are found to be in excellent agreement with weld‐line crack lengths calculated from measured fracture properties. Above a critical melt temperature, this weld‐line crack length will fall below a critical crack length, whereby the weld‐line will no longer initiate brittle fracture. This critical crack length is a function of the material's inherent yield strength and fracture toughness. The embrittling effect of weld‐lines can also be easily removed by surface treatments such as surface milling or solvent polishing. Weld‐lines are, therefore, determined to be near‐surface flaws, which embrittle notch sensitive materials such as most amorphous polymers.
Residual stress distribution modification caused by weathering in polypropylene and polystyrene
Authors: Tong Li , White J. R.
Published: April 2004

A study has been made of changes in residual stress distributions caused by weathering in polypropylene and polystyrene. Chemi‐crystallization has a major effect in polypropylene and an analysis based on the volumetric changes that occur on crystallization has been developed. Close to the surface, fractional crystallinity changes up to 4% are caused by photodegradation (X‐ray measurements by Rabello and White (18)). It is estimated that this would cause a tensile residual stress of ∼2MNm−2 to form at the surface if there were no preexisting residual stresses; in the case examined here, the effect of this shrinkage stress was to reduce the compressive residual stress to a small value (<1MNm−2). Additional changes caused by stress relaxation prior to completion of chemi‐crystallization resulted in net tensile stresses near to the surface of the photo‐degraded polypropylene. The changes occur almost symmetrically in polypropylene even if the molding is exposed on one surface only. A similar analysis has been made for thermoplastics in which the changes occur only at the exposed surface, comparing the results with measurements made on a glass fiber reinforced grade of polypropylene. In this case the analysis predicts that the stress changes by 2–3MNm−2 near the surface, enough to develop tensile stresses up to 2MNm−2 there if the compressive residual stress at the beginning is fairly small, in fairly good agreement with observed changes. Glass fiber reinforced polypropylene does not relax as readily as unfilled polypropylene and better agreement is to be expected without any allowance for stress relaxation. The analysis for one‐sided chemi‐crystallization allows calculation of the resulting distortion in terms of the curvature: this was estimated at 0.33m−1, compared to the measured value of 0.44 m−1. Volumetric changes also occur in noncrystalline polymers and a similar analysis based on data obtained with polystyrene (17) confirms that these changes can explain the observed development of tensile residual stresses on weathering. In the example studied here surface stress changes of 2–3MNm−2 are predicted and this accounts for a large proportion of the change in residual stress obtained by direct measurement.
Evolution of the three‐dimensional orientation distribution of glass fibers in injected isotactic polypropylene
Authors: Avérous Luc , Quantin Jean Christophe , Crespy Alain , Lafon Dominique
Published: April 2004

The mechanical properties of fiber reinforced thermoplastics depend on the characteristics of the fibers, such as their three‐dimensional orientation distribution, which is the result of the processing conditions and of the initial products before mixing. Different composites were obtained by injection of reinforced isotactic polypropylene containing 30 wt% fibers. Different size distributions of fibers were investigated. Their average lengths range from 60 to 470 μm. Specific new tools were developed by combining microscopy and image analysis to determine the microtextural characteristics of the fibers, such as their size distribution or their orientation in the matrix. Our technique allows the following of the size distribution evolution of the fibers as the composite is processed. The three‐dimensional orientation of the fiber is established using the in‐plane angle and the angle of inclination. The evolution of the three‐dimensional orientation distribution is studied in the sample, by differentiating central and border behavior and also as a function of fiber size. It is concluded that the coupling of scanning electronic microscopy with image analysis is an interesting technique that allows the 3‐D orientation of the fibers to be determined. This technique is validated by showing that the results obtained agree with those that other authors obtained on comparable materials.
Novel structures by microlayer coextrusion—talc‐filled PP, PC/SAN, and HDPE/LLDPE
Authors: Mueller Chad D. , Nazarenko Sergei , Ebeling Thomas , Schuman Thomas L. , Hiltner Anne , Baer Eric
Published: April 2004

Numerous examples in the literature illustrate how the coextrusion of film with three or more polymeric layers is economically used to achieve a desirable mix of end‐use characteristics. More recently, layer‐multiplying devices permit two polymers of widely dissimilar solid‐state properties to be combined into unique microlayer and nanolayer structures with hundreds or thousands of alternating layers. If the layers are thin enough, the key properties of the constituents can combine synergistically. The microlayer structure is also an effective research tool. Because the microlayer and nanolayer structures contain large specific interfacial areas, they are ideal for fundamental studies of phenomena such as interdiffusion and adhesion. Three examples of microlayered materials with up to 1024 layers illustrate the versatility of this coextrusion process: talc‐filled PP, PC/SAN, and HDPE/LLDPE.
Structures and tensile properties of a magnetically and mechanically oriented liquid crystalline copolyester, Xydar
Authors: Kossikhina S. , Kimura T. , Ito E. , Kawahara M.
Published: April 2004

A wholly aromatic thermotropic liquid crystalline copolyester consisting of p‐hydroxybenzoic acid, terephthalic acid, and p,p′‐biphenol, one from the Xydar series, was aligned by means of magnetic fields and mechanical methods. The tensile properties of these samples were different depending on the orientation degree and the means used for the orientation. Magnetically oriented films exhibited lower elastic modulus and ultimate tensile strength than mechanically oriented films of the same orientation degree, but the elastic modulus of magnetically oriented films was comparable to that of the mechanically stretched films of lower orientation degrees. This suggests that magnetic fields could be used as an additional means of controlling the orientation of thermotropic liquid crystalline copolyesters during molding or film fabrication. The difference in tensile properties was discussed in relation to the oriented structures examined by scanning electron microscopy, polarizing microscopy, and wide angle X‐ray measurement.
Nonlinear mechanical response of high density polyethylene. Part I: Experimental investigation and model evaluation
Authors: Zhang Chuntao , Moore Ian D.
Published: April 2004

The nonlinear behavior of high density polyethylene (HDPE) is investigated for samples cut from thick‐walled HDPE pipe. Extensive experimental work has been performed to characterize the non‐linear time‐dependent response of the material tested under uniaxial compression. Tests were conducted under conditions of constant strain rate, creep, stress relaxation, constant loading rate, abrupt change of strain rate, creep‐recovery, cyclic strain rate, and various combinations of these loading conditions. Creep and stress relaxation response after strain reversal and the effect of the transient response on the following stress‐strain behavior is examined. Permanent strains for the test specimens and their dependence on loading histories are investigated. Specimens cut at various orientations from the pipe are used to quantify the small amounts of local anisotropy in the pipe specimen. The experimental work has been used to develop both nonlinear viscoelastic (NVE) and viscoplastic (VP) constitutive models in a companion paper. Both the test results and the corresponding model predictions are reported in this paper. It is found that the VP model reproduces the nonlinear viscoelastic‐viscoplastic behavior of HDPE very well provided that the current strain is not below the maximum strain imposed (there is no strain reversal). The NVE model predicts the material behavior reasonably well for some loading conditions, but inadequately for others.
Effects of diffusional water removal and heat transfer in nylon 6 reactors
Authors: Ahn Young‐Cheol
Published: April 2004

The effects of diffusional water removal and heat transfer on the polymerization of ε‐caprolactam were investigated by solving the systems of differential mass and energy balance equations using a finite difference method. Two types of contacting scheme between inert gas and reaction mass have been chosen for study. One is a hollow sphere system and the other is a wetted‐wall type hollow cylinder system. The reaction system was designed to be in equilibrium with respect to monomer conversion. The interfacial area per unit volume and the diffusional depth have profound effects on the water content and the temperature of the reaction mass, and consequently on the molecular weight of the polymer produced. Larger interfacial area per unit volume and smaller diffusional depth lead to a higher rate of water removal and heat transfer. In case of larger interfacial area per unit volume, the higher interfacial temperature gives rise to higher molecular weight polymer. For the interfacial area per unit volume of 26.67 m2/m3, the number average chain length reaches as high as 277 and the polydispersity as high as 2.06 when the interfacial temperature is 270°C. The heat transfer greatly affects the content of cyclic dimer in the product so that the hollow cylinder type reactor is preferred, because it is easier to control the temperature of the later portion of the reactor.
The working domain in reactive extrusion. Part I: The effect of the polymer melt viscosity
Authors: van der Goot A. J. , Hettema R. , Janssen L. P. B. M.
Published: April 2004

This article describes the radical copolymerization of styrene (St) and n‐butyl‐methacrylate (BMA) in a counter‐rotating twin‐screw extruder. In order to investigate the effect of the polymer melt viscosity on the working domain in reactive extrusion, the copolymer was crosslinked with different amounts of divinylbenzene (DVB). Crosslinking of the polymer resulted in a higher polymer melt viscosity. It was demonstrated that not only the product properties but also the process characteristics were strongly influenced by the addition of divinylbenzene to the reaction mixture. The product properties changed as expected: more crosslink agent led to a higher molecular weight or an increase in gel fraction, and a much higher melt viscosity of the polymer. Besides these effects on the product properties, the addition of DVB resulted in a more stable process, leading to an enlarged working domain.
The working domain in reactive extrusion. Part II: The effect of the polymerization rate
Authors: van der Goot A. J. , Klaassens S. A. , Janssen L. P. B. M.
Published: April 2004

This article describes the influence of the polymerization rate on the working domain of a counter‐rotating twin‐screw extruder used as a polymerization reactor. The rate of polymerization was varied by changing the maleic anhydride (Mah) content in the feed, which consisted of styrene, n‐butylmethacrylate, and maleic anhydride. It appeared that the Mah content influenced the operating window of the extruder. Higher Mah percentages resulted in higher throughputs and a decreased dependence on the extruder parameters. On the basis of these results, a new theory concerning reactive extrusion was developed, which resulted in a diagram that is useful in optimizing the extruder, when it is used as polymerization reactor. In addition to the effect of Mah on the process, its effect on product properties was studied.
Aliphatic/aromatic copolyester thermoset adhesives: Synthesis and characterization
Authors: Shi Frank F. , Economy James
Published: April 2004

In this paper, the synthesis and characterization of a new family of aliphatic / aromatic copolyester resins is described. This new resin is derived from a two component oligomeric system consisting of a mixture of Novolac acetates and several specially designed oligomers with carboxylic acid end groups. In this new material, aliphatic units have been incorporated into the oligomers in order to reduce the processing temperature. When used as an adhesive, the new resin offers good lap shear strength of about 14 MPa (2000 psi) at room temperature and retains useful properties to 80°C–100°C. This new system provides good thermal stability, environmental resistance and char yield of 25–40%.
Experimental study on distributive mixing characteristics of a new type of pin mixing section
Authors: Yao W. G. , Takahashi K. , Koyama K. , Dai G. C.
Published: April 2004

To eliminate two shortcomings of normal pin mixing sections, namely, the lack of efficient mixing mechanisms and the formation of dead spots, a new type of pin (pins channeled from top‐front to bottom‐rear) was previously proposed. As an experimental verification of the effectiveness of this type of pin, a dye decoloration experiment with a visual single screw extruder was carried out. The comparative experiments show that a “//” type pin mixing section (the orientation of holes in the pins is parallel) has the best mixing ability; a 45° angle between the projected line of orientation of holes in the pins and the screw axial line provides maximum mixing; however, a 45° angle between the orientation of the pin array and the screw axial direction results in poor mixing. The effect of density of the pins along the screw circumferential and axial direction on distribution mixing was also investigated experimentally.
Reactive extrusion of in‐situ composite based on PET and LCP blends
Authors: Hong Soon Man , Hwang Seung Sang , Seo Yongsok , Chung In Jae , Kim Kwang Ung
Published: April 2004

The “in‐situ” compatibilization for a PET/LCP blend via transesterification reactions in a twin‐screw extruder having a very short residence time is investigated through thermal, rheological, and mechanical studies. Inclusion of a small amount of liquid crystalline polymer (LCP) enhanced the crystallization rate of the poly(ethylene terephthalate) (PET) matrix. It acted as a nucleating agent. LCP lowered the blend viscosity above Tcn (crystalline‐nematic transition temperature), working as a processing aid. However, the addition of dibutyltindilaurate (DBTDL) as a reaction catalyst was found to increase the viscosity of the blends, diminish the size of the dispersed phase, enhance its adhesion with the matrix, and lead to an increase of mechanical properties of two immiscible phases. Hence DBTDL is helpful in producing a reactive compatibilizer by reactive extrusion at the interface of this polyester blend system. The optimum catalyst amount turned out to be about 500 ppm when the reaction proceeds in 90/10 PET/LCP polyester blend systems. Its effect on the mechanical properties is discussed in detail. The structural change of reactive blend was identified by H1 NMR and wide angle X‐ray diffraction patterns.
Investigation of composite materials selection and joint layout design to enhance EMI shielding of electronic equipment
Authors: Mottahed Behzad D. , Manoochehri Souran
Published: April 2004

Electromagnetic shielding is a critical issue in the design of electronic equipment. This is mostly due to the high receptivity of electronic components to unwanted electromagnetic emission and interference. To reduce this interference, a study is initiated to determine the effect of material and joint types on the shielding effectiveness of an electronic enclosure. Eight different but progressively more complex joints are designed and investigated in this study. Filled polymers and metallized filled polymers are selected and compared with the all metallic structures. An analytical approach utilizing conformal mapping to calculate the shielding effectiveness of joints is attempted. An experimental apparatus is designed and manufactured to aid in finding the best possible joint configurations. Economic factors in selecting optimum joint layout are also studied. A cost index relating the effective length, design factors, and the total length of the part is developed. Results are presented for the best joint configuration and material with the highest shielding effectiveness.