bluuebunny/crossref_metadata_2025 huggingface dataset:
Synthesis and characterization of a new class of thermosetting resins: Allyl and propargyl substituted cyclopentadiene derivatives
Authors: Mathias Lon J. , Muthiah Jeno
Published: December 2004

A series of all‐hydrocarbon resins were synthesized by reacting cyclopentadiene allyl chloride, propargyl chloride, or a mixture of allyl chloride and propargyl ide, under phase transfer conditions. Phase transfer reactions with and without added solvents, and with either quaternary ammonium or crown ether catalysts, yielded similar products consisting of a mixture of 1,1‐disubstituted cyclopentadiene (minor amount) and 2‐3 isomers each of tri‐, tetra‐, penta‐, and hexa‐substituted derivatives. No further reaction of each these components possible. The overall substitution pattern varied little with changes in reaction conditions although limiting the allyl chloride content led to still reactive, partially substituted products. Incorporation of all‐propargyl and high propargyl‐to‐allyl mixed functionalities on cyclopentadiene yielded products whose stability was very hindering their thorough characterization. Preliminary evaluation was there‐carried out for mixed resins with lower propargyl functionality. The allyl substituted resin (allylated cyclopentadiene, ACP) underwent thermal cure lout initiator at around 200°C while allyl/propargyl substituted resin (7:1 ratio, APCP) showed a faster, lower temperature cure at around 120°C. Cationic cure of ACP was also initiated by a novel sulfonium salt at around 100°C. Neat resin when cured at 200°C gave material with a flexural storage modulus 2 of about 300 MPa. Further cure at 250°C raised the modulus to 1.2 GPa. resin gave composites with excellent properties when used with glass and on fibers. Flexural modulus values (by DMA) of ∼ 66 GPa were obtained for ACP/carbon fiber composites compared with 42 GPa for epoxy/carbon composites made in our laboratories using commercially available materials. The modulus values at 300°C dropped to 10% of the room temperature value for the epoxy composites, while the ACP/carbon composite maintained 60% of its room temperature value at 300°C. When brought back to ambient temperature, the modulus of latter sample had increased to 80 GPa and that of the epoxy composite dropped to 23 GPa. Glass fiber ACP composites performed similar to an epoxy composite up to 200°C but maintained properties up to 300°C while those of the epoxy were drastically reduced. TGA analysis of both cured ACP resin and its composites showed decomposition beginning at 375°C. Three‐point‐bending tests indicated very high modulus with brittle failure for ACP composites. Scanning electron micrographs showed moderate bonding of the new resin to both carbon glass fiber surfaces. This new class of thermosetting resins offers excellent potential for application in low‐cost glass and carbon composites with good thermal and physical properties.
Determining fiber strength vs. gage length
Authors: Curtin W. A.
Published: December 2004

This paper concerns the gage length dependence of fiber strength as established by measuring the fiber fracture stress vs. fragment length in the succession of fragments, which occur in tension testing of a single‐fiber composite (s.f.c.). For fibers with a strength distribution described by a Weibull modulus m, a plot of In (fragment fragment fracture stress) vs. ln (actual fragment length) leads to the deduction of an apparent Weibull modulus mapp ⋍ 0.63 m, whereas the apparently less drigorous procedure of plotting In (fragment fracture stress) vs. ln (average fragment length) allows for accurate assessment of the true Weibull modulus. The mapp < m behavior arising from the use of actual fragment lengths occurs because fragments in the s.f.c. are not random sections of the fiber, but rather sections which have effectively been proof‐tested at a stress corresponding to the strength of last fiber breaking stress occurring in the entire sample length. Hence, the individual fragments appear stronger than random fiber sections, leading to an apparently smaller Weibull modulus. Such complications do not arise if only the average fragment length, or equivalently the location‐independent total number of breaks, is considered. Computer simualtions of the fragmentation process verify analytic estimates of the ratio of mapp/m, and demonstrate the accuracy of using the average fragment length to assess fiber Weibull modulus.
Viscoelasticity of porous composite materials: Experimentals and theory
Authors: Alberola N. D. , Lesueur D. , Granier V. , Joanicot M.
Published: December 2004

The viscoelasticity of latex/PS beads composites, having the same volume content of latex and PS beads, but various porosity ratios and specific surfaces of particles has been investigated in the glass temperature range of the latex matrix. In order to give evidence for the main factors governing the viscoelastic properties, data were compared to numerical simulations based on the Christensen and Lo model and Skorokhod's approach. Such modelings were performed by considering either the latex matrix of the PS beads as the continuous phase. It was concluded that the glassy modulus is mainly governed by the volume fraction of porosity, while the rubbery modulus is controlled by both the interactions between phases and the void volume content. The location of the mechanical relaxation seems to be governed by the mechanical coupling between phases, which implies some local phase inversion. The magnitude of the mechanical relaxation depends not only on the chemical coupling induced by the interactions between phases, but also on the mechanical coupling.
Swelling and dissolution rates of glass fiber sizings in matrix resin via micro‐dielectrometry
Authors: Larson B. K. , Drzal L. T. , Van Antwerp J.
Published: December 2004

Complex fiber‐matrix interactions occur in the processing of glass fiber reinforced polymeric composites, because of the proprietary, complex composition of commercial sizings applied to the glass fiber surface. Research involving a vinyl ester resin system and three model commercial glass fiber sizings, having varying levels of solubility in the resin, has shown that micro‐dielectrometry can provide important information about interactions and may be useful as a tool in optimizing sizing‐matrix resin interactions. Two distinct types of interactions may be monitored by micro‐dielectrometry: The initial resin swelling of the sizing, as well as the dissolution of the sizing into the resin. An estimate of the times associated with swelling and dissolution of the sizing into the matrix resin can be made from micro‐dielectric measurements to optimize composite processing.
Effect of stress on nucleation and crystallization in polymers
Authors: Lindenmeyer P. H.
Published: December 2004

Polymer crystallization is recognized as a non‐equilibrium process and the postulate of local equilibrium is combined with the formalism of small systems thermodynamics to provide a general method of relating structure, kinetics and thermodynamics. In this method a single polymer molecule is assumed to be in equilibrium with its environment and the appropriate partition function is factored into the bulk free energy and the remaining factors which are important only in small systems.
Extended‐chain and folded‐chain crystallite formation during the crystallization of stretched crosslinked rubbers
Authors: Wu W.
Published: December 2004

The strain‐induced crystallization phenomenon of a crosslinked polymer network was studied using statistical, thermodynamics. The basic approach was essentially that used by Flory (1), but in this work Flory's assumption of only a single crystalline phase (the extended‐chain crystalline structure with chain parallel to stretch direction) was abandoned. The dimension of the crystalline vector‐which is assumed to be parallel to the stretch direction and the percent crystallinity is taken as two independent variables instead of being treated as one single variable. A single variable treatment is inherent in the assumption of a single extended‐chain crystallite. By use of the present approach, either the folded‐chain crystallite or the extended‐chain one is found to be thermodynamically stable depending on temperature, stretch ratio and molecular weight. The retractive force of a crystallized polymer network has been calculated. It is shown theoretically that the formation of an extended‐chain crystallite will cause the retractive force to decrease, and that the formation of a folded‐chain crystallite will cause the retractive force to increase in a reversible crystallization process.
Stress‐induced crystallization of branched polyethylene terephthalate films
Authors: Hennessey W. J. , Spatorico A. L.
Published: December 2004

Polyethylene terephthalate (PET) prepolymer containing 0.0 to 0.3 mole percent pentaerythritol was polymerized to an inherent viscosity of 0.63‐0.70 dl/gm by the fluidized bed technique. Rheological studies and gel permeation chromatography (GPC) examination showed the samples to be branched in character. Amorphous films were stretched at 82 and 93°C at elongation rates of 54, 161 and 267 percent‐s−1 using the T. M. Long machine. The extent of stress‐induced crystallization was established by a density determination. The branched samples behaved very similarly to the linear PET material in crystallization and birefringence studies. Neither the percent crystallinity nor the birefringence appears to be a strong function of strain rate over the range 54‐267 percent‐s−1. A cursory examination of the crystallization kinetics of the oriented samples suggests that extent of branching in our samples does not markedly reduce the crystallization rate at annealing temperatures of 180 and 220°C.
Sorption and transport of CO2 above and below the glass transition of poly(ethylene terephthalate)
Authors: Koros W. J. , Paul D. R.
Published: December 2004

At temperatures at least 30°C above the glass transition (Tg) the sorption and transport of carbon dioxide in poly(ethylene terephthalate) (PET) can be described conveniently using Henry's law and Fick's law with a constant diffusion coefficient. Below Tg Fick's law with a concentration‐ dependent diffusion coefficient, coupled with a sorption isotherm which is concave toward the pressure axis adequately describes the observed sorption and transport data. Physical interpretations of the quantitative deviations from Henry's law and the form of the concentration dependence of the diffusion coefficient is provided by a model which hypothesizes dual modes of sorption and separate non zero mobilities of two populations of sorbed species in local equilibrium. The implications of the observed temperature variations of the phenomenological model parameters are discussed. Dilatometric parameters for PET, polycarbonate, and poly(acrylonitrile) (PAN) are shown to correlate well with a simple. relationship developed to explain the existence of the “extra” mode of sorption responsible for deviations from Henry's law for CO in glassy polymers. In the temperature range from Tg to + 20°C, deviations from Fickian behavior are also apparent. These effects are consistent with a transition in the nature of the polymer from an elastic solid below Tg to a viscous liquid above Tg In the narrow temperature range slightly above T the time scale for chain rearrangements apparently approaches that for the diffusion process. The polymer's viscoelastic response to the probing molecule, therefore, causes deviations from the classical time lag predictions. These deviations disappear 30°C above Tg.
Flow‐induced crystallization of polymer melts in convergent flow regimes and imposed temperature gradient to form ultra‐oriented fiber structures
Authors: Crater Davis H. , Cuculo John A. , Boudreaux Edwin
Published: December 2004

Flow crystallization experiments which utilized the Instron rheometer in conjunction with convergent dies were conducted for the purpose of producing high‐modulus poly(ethylene terephthalate) filaments directly from the melt. A temperature gradient was imposed on the lower extremity of the dies in an attempt to control the site of the fluid‐solid phase transformation, and “freeze in” any orientation derived from the elongational flow regime. Comparative studies were made using dies with included angles of 20, 30, and 40°, and extrusion temperatures ranging from 255 to 270°C. Die angle influenced the pressure at which maximum die swell and the onset of extrudate distortion occurred; however, barrel temperature showed little effect on this pressure. The minimum temperature produced by the temperature gradient was the over‐riding factor involved with cessation of flow. In each experiment, the fluid‐solid phase transformation produced by the temperature was always accompanied by extrudate distortion. Thus, only minimal comparative studies of the extrudates could be performed. In view of the above, it appears that utilizing a temperature gradient, by itself, to “freeze in” preferred orientation within the confines of the die presents difficulties. A modification which combines a temperature gradient with external tension and a rapid after‐quench outside the die, now holds appeal for continuing studies.
Temperature‐induced pressure gradient in the clearance between screw flight and barrel of a single screw extruder
Authors: Winter Horst Henning
Published: December 2004

The effect of temperature‐induced pressure gradients occurring in drag flow in a narrow gap between parallel walls, when a viscosity gradient in flow direction is present is described and analyzed. The effect dominates the technologically important clearance flow problem, where the viscosity gradient originates from temperature changes. The polymer layer in the clearance between screw flight and barrel of a single screw extruder supposedly has to separate the metallic surfaces from each other. In certain operating conditions this bearing function breaks down and dry friction between metallic surfaces occurs. This failure, which has not yet been explained, is reasoned to be caused by the temperature‐induced pressure flow in the clearance.
Fracture mechanics of adhesive joints
Authors: Sih G. C.
Published: December 2004

The load carrying capacity of adhesive joints is analyzed by applying the principle of fracture mechanics in which failure is assumed to initiate from sites of initial imperfections such as bubbles, cracks or unbonded portions of the interface. The cohesive and adhesive modes of failure are investigated for a butt joint under angle loading. Based on the prediction of the strain energy density criterion, the lowest failure stress for the adhesive joint occurred when the load is applied at an angle with respect to the crack plane. This is in contrast to the homogeneous material solution where the lowest failure stress corresponds to normal loading. Numerical examples are provided for a joint made of DER 332‐TEPA epoxy with aluminum as the adherends. Discussed in detail are the dependencies of the strength of the joint with reference to the material properties of the constituents, geometries of the components, and direction of loading.
Photoresist development by plasma
Authors: Hughes H. G. , Goodner W. R. , Wood T. E. , Smith J. N. , Keller J. V.
Published: December 2004

Over the past several years the semiconductor industry has placed major efforts into replacing wet processes with dry processes in fabricating electronic devices. Plasma photoresist stripping, plasma cleaning, and other dry etching techniques have replaced wet methods in many product lines. One area that has received little mention but which is vital toward achieving a totally dry manufacturing process is the dry development of photoresist. One production applicable plasma developable photoresist (PDF) process, using a proprietary resist formulation, is reported. Plasma process characterization, such as end point detection, development latitude, and mechanism are discussed. Included also are development temperature, batch film uniformity, and resolution currently obtainable with the PDF process.
Retention of a foaming agent in poly(vinyl chloride) (PVC) and chlorinated PVC
Authors: Khanna Y. P. , Turi E. A. , Sibilia J. P.
Published: December 2004

Poly(vinyl chloride) and chlorinated poly(vinyl chloride) films were saturated at 100°C with fluorotrichloromethane (Genetron‐11, a foaming agent) and then allowed to desorb at RT and 65°C. The desorption data for a three month period was fitted into a mathematical relationship which could be used for long term predictions of the G‐11 retention in the films. Using thermoanalytical techniques, plots of glass transition temperature vs G‐11 concentration were made for the polymers under study. These plots were used to demonstrate the effect of stabilizer, polymer type and temperature on the desorption of the G‐11.
The effect of strain rate on the toughening mechanisms of rubber‐modified plastics
Authors: Maxwell M. A. , Yee A. F.
Published: December 2004

The impact modification mechanisms of polycarbonate (PC) blended with polyethylene (PE) and blends of polyxylenol ether (PXE)/high impact polystyrene (HIPS), were studied using a volume dilation technique. With two extensometers, measurements of volume change during tensile deformation were made on the plastics. Strain rates of 2 × 10−5 s−1 to 4 s−1 were achieved with a MTS servo‐hydraulic testing machine. Analysis of both systems were supported with scanning and transmission electron microscopy. Results on the PC/PE system indicate that the impact modification mechanism is one of voiding and shear banding. The mechanism appeared to be rate sensitive: the amount of voiding increased with rate. The toughening mechanism in the PXE/HIPS blends is identified as a combination of crazing and shear banding. The amount of shear banding that occurs is proportional to the amount of PXE in the blends. The point of craze initiation was found to be delayed by increasing strain rate. The stress for craze initiation appears to be greater than for shear banding.
The development of C‐10 phthalocyanine for composite matrix applications
Authors: Ting R. Y. , Nash H. C.
Published: December 2004

Thermomechanical analysis was carried out for various phthalocyanine resins. The polymer based on the C‐10 diamide resin was then chosen for evaluation as a potential composite matrix material. Prepregs with Thornel 300 graphite reinforcements were successfully prepared using a hot‐melt technique. The processability of this material was studied by employing instrumental techniques including differential scanning calorimetry, thermal gravimetric analysis and dynamic dielectric analysis. A cure cycle was developed for the fabrication of angle‐ply laminate using the conventional vacuum‐bag technique in a hydraulic press. Laminate mechanical properties both in tension and in flexure were determined. The results for the C‐10/T‐300 samples were shown to be similar to those of an epoxy/graphite and a polyimide/graphite composite system.
The physical aging of isotactic polypropylene
Authors: Agarwal M. K. , Schultz J. M.
Published: December 2004

The microstructural changes in isotactic polypropylene (PP), subsequent to quench from the melt to around Tg were studied using dynamic mechanical loss, volume dilatometry, small and wide angle X‐ray scattering, infrared and NMR spectroscopy. The β‐transition loss tangent and the specific volume decreased linearly with logarithm of aging time. Dynamic mechanical loss and NMR spectroscopy results established that amorphous chain mobility reduced during aging. X‐ray and IR techniques showed that the crystallinity, the crystalline density, and the average chain conformation do not change during aging. Tensile tests indicated that diffusion of air or moisture into the polymer is not a competitive mechanism for the aging phenomenon. A simple free‐volume model is quantitatively consistent with these observations. The fraction of the material which cannot age increased as the quench temperature decreased. Further, at lower temperatures a portion of the nonageable fraction is shown to reside in the amorphous fraction.
Residual stresses in polymers. II. Their effect on mechanical behavior
Authors: Siegmann A. , Buchman A. , Kenig S.
Published: December 2004

The distribution of density and tensile properties in quenched modified poly(phenylene oxide) specimens was investigated. Quenching was carried out from temperature level above Tg to below Tg temperatures. Simultaneous to buildup of residual stresses, profiles of density and tensile properties were observed. The profiles were obtained using the layer removal technique, which was found not to affect the measured properties. Quenching of the material results in a steep density gradient in the surface layers. Correspondingly, the tensile modulus increases significantly from the surface to the inner layers and so are also the ultimate tensile properties. This behavior could be accounted for neither by the conventional packing volume approach nor by superposition of internal and external stresses. However, observations of the fracture surfaces are very supportive and indicate that the fracture initiation sites are influenced by the residual stresses. Hence, the mechanical behavior is strongly affected by both density and residual stresses profile. Density is the controlling factor in determining the elastic properties whereas residual stresses determine the ultimate strength and fracture mechanism.
A dynamic mechanical study of the curing reaction of an unsaturated polyester
Authors: Yap C. Y. , Williams H. Leverne
Published: December 2004

The curing process of an unsaturated polyester was followed by employing the dynamic spring analysis (DSA) technique attached to the Rheovibron viscoelastometer. The storage and loss moduli and the gel times of the resin with various concentrations of initiator (methyl ethyl ketone peroxide) were determined at several temperatures. The activation energy for the curing process studied was about 40 kJ/mol. Temperature effects on films partially cured below the ultimate glassy transition temperature (Tg) were studied similarly using the tensile mode on the Rheovibron from room temperature to 120°C. Two modulus peaks were observed upon heating and these were independent of precure conditions. The lower temperature peak was the result of continued curing and the higher temperature peak was attributed to the glassy relaxation of the cured product. The DSA technique were found to be useful for characterization of the curing process and the results showed good qualitative agreement with those obtained by tensile measurements using cast films when the shapes of the curves were compared.
Unsaturated polyesters from 2,2‐dimethyl‐1,3‐propanediol
Authors: Tong S. N. , Horng H. K.
Published: December 2004

A series unsaturated polyesters were made from 2,2‐di‐methyl‐l,3‐propanediol, propylene glycol, fumaric acid, and isophthalic acid by a two‐step fusion process. The effect of catalyst, conversion, composition, unsaturation, and styrene content were studied, and the relationship between composition and properties was established.
Time‐dependent morphologies and viscoelastic properties of block copolymers
Authors: Kelterborn Jeffrey C. , Soong David S.
Published: December 2004

Dynamic mechanical properties of block copolymers over a wide temperature range have been previously correlated with the phase‐separated microstructure of these systems. In the present work, the morphology of the block copolymer is altered by large tensile deformation at various temperatures. Upon removal of the applied stress, the morphological features of such stretched‐and‐released systems become functions of time, as the nonequilibrium microstructure reverts to a thermodynamically stable state. This reformation process is monitored by dynamic mechanical measurements, with a modified torsion pendulum capable of applying both tensile and torsional deformation. Experimental results are analyzed using a modified Nielsen model to obtain information on the time‐dependent structural state of the samples. These results are then compared with stress‐strain curves to provide further insight into the structure breakdown‐reformation mechanisms. Two competing mechanisms, domain fracture and block pull‐out, are proposed to explain these experimental observations.
Dynamic mechanical spectroscopy of sheet compound as a function of deformation
Authors: Ard K. , Kolman H. J. , Beatty C. L.
Published: December 2004

It has been determined that preload and cyclic amplitude have significant effect on the results of dynamic mechanical measurements of tan δ. To illustrate these effects on composites, a particular type of sheet‐molding compound (SMC‐R50) was used in this study. In addition to the effects of preload and cycle amplitude, the effects of frequency, post‐cure, and creep prior to dynamic mechanical testing were also investigated.
Studies of epoxy resin systems: Part B: Effect of crosslinking on the physical properties of an epoxy resin
Authors: Chang T. D. , Carr S. H. , Brittain J. O.
Published: December 2004

An epoxy system consisting of diglycidyl ether of butanediol, DGEB, cured with 4‐4′ diaminodiphenyl sulfone, DDS, has been used for a study of the effect of crosslinking density on the properties of the epoxy resin. Because of the low curing rate at room temperature and the low glass‐transition temperature, this system was amenable to a wide range of controlled cross‐linking density. The crosslinking density was monitored by FTIR (Fourier transform infrared spectroscopy), which followed the change in concentration of the epoxy groups during the curing reaction. The bulk density was found to increase linearly with the crosslinking density. The modulus, the upper yield point, the lower yield point, and the degree of retraction of a deformed sample all increased with the degree of crosslinking. The thermally stimulated depolarization (TSD) β‐peak was found to vary with crosslinking density, but the γ‐peak was not changed. The TSD a peak was found to decrease in strength, but increased in temperature as the crosslinking density increased. This observation suggests that TSD measurements arc a good monitor of crosslinking density of epoxy resins, particularly near the final stage of the crosslinking reaction.
Electron transport processes in conductor‐filled polymers
Authors: Sherman R. D. , Middleman L. M. , Jacobs S. M.
Published: December 2004

This article contends that three distinct physical processes control electron transport in conductor‐filled polymer systems. Percolation is required to explain the macroscopic conduction in the disordered medium. Quantum mechanical tunneling (possibly quantum fluctuation augmented) is needed to describe conduction between adjacent conductive particles at the microscopic level. And, thermal expansion is invoked to deduce constituent volume densities and microscopic tunnel lengths. Each of these mechanisms is given a mathematical form. The ansatz is used to predict resistivity vs. temperature and resistivity vs. conductor‐filling fraction functions. Successes and deficiencies of the theory are discussed with respect to experimental data and theoretical considerations.
Prediction of strain recovery during solid‐phase forming of thermoplastics
Authors: Okine R. K. , Suh N. P.
Published: December 2004

An approach to predict the strain recovery behavior of polycarbonate (PC) and high impact polystyrene (HIPS) under isothermal and non‐isothermal conditions in a solid‐phase forming environment is presented in this paper. The constants A and n of a power law relationship of the form ϵ(t) or δ(t) = Atn, fitted to isothermal creep and stress relaxation data, were determined over a wide range of temperatures for both materials. An expression for isothermal recovery was derived and compared to experimental data. Master curves and the resultant shift factors, obtained by superposing the stress relaxation and creep data (both in tension and compression) were used with the time‐temperature super position principle to numerically evaluate uniaxial strain recovery under a specific temperature history. The average temperature history obtained by numerically solving for the temperature distribution in a disc, at an initially high temperature and in contact with a cold metal surface, was used for the non‐isothermal case. The theoretical results were compared with recovery data obtained from non‐isothermal backward extrusion tests with a temperature history similar to the one described above. Reasonably good agreement was obtained.
Notch sensitivity and fractography of polyolefins
Authors: Goolsby R. D. , Chatterjee A. M.
Published: December 2004

The notch sensitivity of high‐density polyethylene (HDPE), polypropylene (PP), and polybutylene (PB) was evaluated using uniaxial tensile deformation and fractographic analysis. Each polyolefin was tested at relatively low and high molecular weights (MW). Only the lower MW HDPE was found to be clearly notch‐sensitive. The lower MW PP exhibited some tendency toward notch sensitivity. The lower and higher MW PB, the higher MW HDPE, and the higher MW PP displayed notch strengthening. Whereas PB showed similar notched tensile performance regardless of molecular weight, both HDPE and PP showed higher susceptibility to notch sensitivity at lower molecular weights (and concomitant higher crystallinity). Tendencies toward notch sensitivity or notch stengthening were evidenced in the failure modes of these materials.
Analytical melting model for extrusion: Stress of fully compacted solid polymers
Authors: Chung K. H. , Chung C. I.
Published: December 2004

Our laboratory recently published several analytical equations that can be used to predict the melting rate of fully compacted solid polymers sliding on a heated metal surface, modeling the melting mechanism inside an extruder. These equations were obtained by seeking asymptotic solutions to the differential equations describing the melting mechanism, temperature, and shear‐dependent viscosity of polymer melts. Following the same asymptotic approach, we successfully developed accompanying analytical equations for predicting the stress required to slide fully compacted solid polymers on a heated metal surface. The accuracy of these analytical stress equations was found to be reasonable, although not fully satisfactory, by comparing their predictions to the experimentally measured values. The accuracy of the stress calculation is directly related to the accuracy of the viscosity values at high shear rates. The consideration of the temperature and shear dependencies of melt viscosity is most important for accurate prediction of the stress, just as it is for the melting rate. The stress not only depends on the melt rheological properties of the polymer but also on the thermodynamic properties.
Parameter design model for corrugated tubing
Authors: Krein H. L.
Published: December 2004

It is of interest to produce plastic corrugated tubing as strong as possible with a minimum amount of material. Simultaneously, the tubing has to resist stretching, and maintain flexibility for transport purposes. To find the optimum profile geometry, two mathematical models were employed. One model was used to calculate the strength of the tubing per unit length and a second model was used to predict the elongation of corrugated tubing for a given load. Data was then generated for different profile configurations, and plotted for an optimum design procedure. The results showed that, while the wall thickness can be varied during production, the most critical parameter is the corrugation depth. The corrugation depth is fixed by the moldblock design, and the data presented can be used to obtain an optimum geometry.
Vulcanization shrinkage of rubber articles with rigid armoring parts
Authors: Tukachinski L. I.
Published: December 2004

This paper discusses the shrinkage characteristics of armored (reinforced) rubber articles for two types of boundary conditions: (a) cases where the armoring material is neither flexible nor thermoexpansive, and (b) cases where the armoring material has a finite thermal expansion between room and vulcanization temperature. A quantiative analysis of shrinkage strains and stresses is developed for the two boundary conditions.
An observation on the han‐villamizar critical pressure concept in thermoplastic foams
Authors: Throne J. L.
Published: December 2004

This note draws together the Han‐Villamizar experimental observations on the critical pressure at which gas bubbles became visible in flowing thermoplastic melts and a simple method of predicting the equilibrium pressure based on gas solubility. It is shown that the observed pressure is 40 to 75 percent of the calculated pressure.
Characteristics of polynorbornene and ethylene‐propylene terpolymer blends
Authors: Wang C. S.
Published: December 2004

In this study characteristics of polynorbornene (PNR) and ethylene‐propylene terpolymer (EPDM) blends were examined in terms of compatibility, cocuring, and ozone resistance. For most of the blend compositions, two glass transition temperatures (Tg) at about −30 and −50°C were observed from differential scanning calorimetry data for both uncured and cured samples. The transitions correspond to the Tg's of the component polymers, suggesting that the blends are microheterogeneous. The two‐phase blends are difficult to cocure as evidenced by the fact that tensile strengths of the blends, when plotted as a function of blend composition, deviate from the linear or additive behavior. Improved cocuring of the blends, however, can be achieved by matching the cure rates of the components. The ozone resistance of the blends containing 25 percent or more EPDM was substantially improved as compared with that of PNR. Therefore, the newly developed PNR can be used for applications requiring ozone resistance by properly blending it with EPDM.
The dual‐mode solution and transport of water in poly(acrylonitrile)
Authors: Mauze G. R. , Stern S. A.
Published: December 2004

Solubility (sorption) and transport measurements with water in solvent‐free poly (acrylonitrile)(PAN) (23) have been interpreted in terms of an extension of the “dual‐sorption” model for transport of small molecules in glassy polymers. Satisfactory agreement has been obtained between theory and experimental data. An earlier analysis of similar data for water in PAN containing 0.26 percent (by weight) of a residual solvent (1) has been compared with the present results in order to investigate the effects of residual solvent on the dual‐sorption and transport parameters for the water‐PAN system.
Elongation rheology of polyolefins and its relation to processability
Authors: Sebastian Donald H. , Dearborn John R.
Published: December 2004

The rheology of a variety of polyolefin resins, and resin blends, has been examined under conditions of constant strain rate elongation. These include high, low, and linear low density polyethylene, as well as polypropylene, commercially modified polypropylene, and elastomer blends with polypropylene. Two distinctly different classes of behavior are apparent in the viscosity growth patterns during uniaxial extension. Some resins display unbounded stress growth even at low strain rates. Others quickly attain a time independent value of extensional viscosity even at increased strain rates. The former behavior is identified with favorable blow molding behavior, while the latter was characteristic of resins unsuitable for such processing. The class of elongation behavior depends not only on resin type, but may be influenced by molecular weight distribution or blend morphology.
The influence of knit‐lines on the tensile properties of injection molded parts
Authors: Criens R. M. , Moslé H. G.
Published: December 2004

When injection molding complex parts, often knit‐lines are formed during the mold filling stage. These knit‐lines are well‐known as particularly critical regions in the mold when mechanically loaded. Using three test materials, polystyrene (PS), polycarbonate (PC) and polyoxymethylene (POM), the relationship between a design and a processing parameter and the effects of the knit‐lines on the tensile properties of injection molded plates with holes is quantified by the variation of a socalled knit‐line‐factor ak1. Finally, for PS a comparison of the influence of knit‐line‐formation by a splitted melt stream and by multi‐gating on the mechanical level is given.
Compounding extruders for improved polyblends
Authors: Eise Kurt , Curry John , Nangeroni James F.
Published: December 2004

An expanding application for compounding extruders is the production of materials with new and outstanding properties by blending two or more polymer components. Mixing is essential to control domain size and insure nongradient properties whether the components are miscible, multiphase with discreet domains, or multiphase with stratified structure. This paper will comment on important mechanisms for dispersion in single‐screw and twin‐screw compounding extruders. A theoretical model for mixing via kneading blocks in twin‐screw corotating extruders is experimentally verified. The pigment distribution was found experimentally to agree generally with theory. The commercially interesting polyblend systems and compounder geometries are more complicated than the theoretical model. Practical compounder design considerations for miscible, rubber‐toughened and two‐phase stratified systems are presented.
A novel technique for measuring the impact properties of a tough polyethylene
Authors: Truss R. W. , Duckett R. A. , Ward I. M.
Published: December 2004

A novel technique is described which enables reliable fracture toughness measurements to be made in impact test on relatively small specimens of a tough polyethylene. Composite specimens have been made in which a tough polyethylene is sandwiched between two layers of a more brittle polyethylene. The overall fracture toughness is interpreted on the basis of simple additivity of the strain energy release rate associated with each of the component layers. Brittle plane strain failures were obtained for specimens in which the relative thickness of the layers was varied over a substantial range and the fracture toughness of each layer determined by suitable extrapolation. The fracture toughness of the brittle layer obtained in this way agreed well with direct measurements on that material.
Blending of polystyrene with styrene‐siloxane block and graft copolymers
Authors: Bajaj P. , Gupta D. C. , Varshney S. K.
Published: December 2004

A preliminary study on the efficiency of styrene‐siloxane block and graft copolymer as toughening additives for polystyrene has been made. Block and graft copolymers of required molecular weight were synthesized for making compatible blends with polystyrene. Compatibility of these systems was evaluated through differential scanning calorimetry, thermo‐mechanical analysis, rheovibron studies, and scanning electron microscopy. A good miscibility of block and graft copolymers was confirmed by these methods. Higher work of rupture in these blended polystyrene samples further demonstrates the feasibility of styrene‐siloxane block and graft copolymers as good toughening material for a brittle polystyrene matrix. The mechanical properties have been related to the morphology and the amount of siloxane content in the blended polystyrene.
Improved bending fatigue life of Kevlar 29 braid by the use of an impregnating medium
Authors: D'Almeida J. R. Moraes , Hearn D. , Bunsell A. R.
Published: December 2004

Kevlar 29 fiber has been widely considered for the manufacture of very‐long high‐performance cables. Due to low transverse strength fiber‐on‐fiber rubbing leads to rapid deterioration. The usefulness of impregnating Kevlar 29 braids with resin to overcome this drawback has been evaluated by performing reverse bending fatigue tests. Braids of identical construction, one of them being impregnated with a polyurethane resin by a patented process, were fatigued to failure on a purpose‐built rig under varying applied loads. Fatigue tests were also carried out to 30 percent and 50 percent of total braid life and residual strength values measured. It was found that high applied loads (∼50 percent of ultimate) lead to premature braid failure dominated by a creep mechanism. Both braids showed similar behavior, although the impregnated braid was superior. At low applied loads, however, where the failure mechanisms was dominated by wear or internal abrasion, it was seen that resin impregnation could increase braid life by a factor of four. Resin impregnation coupled with bending fatigue significantly stiffens braids, as was demonstrated by tensile testing up to braid failure.
On the nature of polymer interfacesd and interphases
Authors: Sanchez Isaac C.
Published: December 2004

An abbreviated review of the current state of knowledge of polymer interfacial phenomena is given. Classical thermodynamics treats the interfacial zone (the interphase) as a “black box” and yields rigorous relationships among interfacial quantities. A recent reformulation of interphase thermodynamics, which eliminates the use of a Gibbs dividing surface, is shown to be an invaluable tool for investigating interfacial properties. Microscopic theories, such as the gradient theory, yield more details about what is in the black box, but the information is only approximate. The gradient theory has been used to: (1) relate the surface tension of a polymer liquid to its isothermal compressibility, (2) develop a quantitative theory of polymer liquid surface tension, and (3) determine the interfacial tension between two immiscible polymer liquids. The gradient theory will be shown to be in harmony with the microscopic theory of Helfand and co‐workers although the latter treats polymer interfaces from a completely different point of view.
Use of the lower critical solution temperature for the characterization of polymer mixtures and the study of their compatibility: Application to polyethylenes, polypropylene, and their copolymers
Authors: Varennes Suzanne , Charlet Gérard , Delmas Geneviève
Published: December 2004

The Lower Critical Solution Temperature (LCST) of polyethylene (PE), polypropylene (PP), and ethylene‐propylene block and random copolymers have been measured in heptanes. A thermogram related to the variation of the turbidity of the solution is obtained between 100 and 210°C. The temperature of the onset of the turbidity peak is defined as the LCST of the system. The width and the area of the turbidity peaks are tentatively associated with the polymer polydispersity and the amount of polymer involved in the phase separation. The thermograms of solutions containing both homopolymers show two distinct turbidity peaks situated at a 70°C interval. Correlations of molecular orientations in the concentrated phase, possible in PE systems but not in PP solutions, are at the origin of the lower LCST values for PE solutions. The LCST of copolymers are situated between those of the homopolymers but the dependence of the LCST on the copolymer ethylene content is different for block and random copolymers. Examples of thermograms are also given for mixtures of copolymers with PE and PP. By analysis of their thermograms, some commercial block EP copolymers were also found to contain PK and PP. This method seems well suited for characterizing polymer mixtures.
Hot water aging of polycarbonate
Authors: Narkis M. , Nicolais L. , Apicella A. , Bell J. P.
Published: December 2004

Internal cracking and microvoids are shown to form during room temperature storage of polycarbonate samples that have previously been exposed to boiling water. These microcracks or microvoids are actually disc‐shaped pockets filled with water. This formation occurs due to the creation of water super‐saturation conditions by cooling water‐saturated specimens from 100°C to room temperature. As a result, water phase‐separation, clustering, and microvoiding result and lead to deterioration of the mechanical properties. Visual healing of the microcracks is also sometimes observed at room temperature, especially under a dry atmosphere. Water from the water‐filled pockets diffuses through the polycarbonate matrix to the external dry environment; the very thin emptied pockets then close and visually heal. This paper provides experimental data for the microvoiding process and clarifies the special mechanism of cracking/healing in polycarbonate samples.
Photodegradation of some poly(vinyl chloride) (PVC) blends: PVC/ethylene‐vinyl acetate (EVA) copolymers and PVC/butadiene‐acrylonitrile (NBR) copolymers
Authors: Skowronski T. , Rabek J. F. , Rånby B.
Published: December 2004

Poly(vinyl chloride) (PVC) and its blends with polybutadiene‐acrylonitrile (NBR) (containing 21.7 weight‐percent acrylonitrile (AN), a heterogeneous two‐phase system; and containing 41.6 weight‐percent of AN, a homogeneous one‐phase system) and with polyethylene‐vinyl acetate (EVA) (containing 45 weight‐percent of vinyl acetate (VA), a heterogenous two‐phase system; and containing 65 weight‐percent VA, a homogeneous one‐phase system) were UV‐irradiated (at 3500 Å UV‐light (solar spectrum)). After UV irradiation the kinetics measurements were made of the formation of hydroperoxy (OOH) and carbonyl (CO) groups and the changes of mechanical properties: tensile strength, elongation to break, and impact energy. As a result of the photooxidative degradation of PVC blends, decreases of mechanical properties were observed. The effects are more severe in PVC/NBR blends, which contain unsaturated bonds (polybutadiene segments) than in the case of PVC/EVA. The phase structure plays an evident role on the UV degradation only of PVC/NBR blends. The photostability of PVC blends can be slightly improved by introducing Tinuvin P or Ni‐chelates photostabilizers.
Effect of prestrain on the subsequent thermal crystallization of a copolyester of lactic and glycolic acid
Authors: Mohajer Yousef , Wilkes Garth L. , Orler Bruce
Published: December 2004

An investigation was carried out in order to study the effect of prestrain on the subsequent crystallization of a specific copolyester based on lactic and glycolic acid. This polymer, which can be easily quenched into an amorphous glass, has a Tg of 43°C and when in crystalline form has a melting point of 210°C. Using amorphous films, samples were prestrained to various levels at temperatures not far above Tg. In some cases films were immediately quenched at the prestrain level so as to retain the elongation while others were allowed to immediately retract whereby they showed a relatively small degree of permanent Set. Utilizing birefringence, quenched samples whose initial elongation was maintained showed linear behavior with prestrain while those that retracted showed essentially zero birefringence until a prestrain of about 150 percent after which a small degree of positive birefringence resulted. Wide angle x‐ray diffraction (WAXS) showed no signs of crystallinity in all cases. These same films were then quickly taken to 150°C and rapidly crystallized. Again, one series of the prestrained samples were in the elongated state during crystallization whereas the second series was unrestrained during crystallization. Using microscopy and small angle light scattering (SALS), the morphological textures of these crystallized films were investigated. In all cases, spherulitic textures were observed of equivalent size up to a value of about 200 percent elongation the spherulite size systematically decreased with the prestrain an increase in clearly showing that prestrain had a pronounced effect upon the nucleation density. Increasing draw rate displayed a similar effect on nucleation density. Since spherulite size was noted to be the same in either series, it indicated that nucleation was induced as a result of the prestrain and remained irrelevant of whether the sample was allowed to relax or not. The morphology above the transitional state was similar to row structure common to polymers crystallized in the oriented state. WAXS and birefringence was applied to the crystallized materials and it was found that up until the transitional zone, no crystal orientation was observed in either series indicating that although nucleation density was strongly affected up until that point, no orientation was retained within the sample upon crystallization. A simplified model is used to explain the observed results.