bluuebunny/crossref_metadata_2025_split huggingface dataset:
Influence of molecular weight and molecular weight distribution on mechanical properties of polymers
Authors: Nunes Ronald W. , Martin John R. , Johnson Julian F. 
Published: December 2004

AbstractThis work reviews the literature published over the last ten years on polymer mechanical properties as a function of molecular weight and molecular weight distribution, Thermal properties, stress‐strain properties, impact, fracture, fatigue, creep, stress relaxation and cracking and crazing are examined for a wide variety of homopolymers and a limited number of copolymers. In general, mechanical properties increase as the molecular weight increases. However, above some limiting molecular weight the mechanical property is usually unaffected. Although much work has been done to describe the effects of molecular weight on mechanical properties, little quantitative correlation exists. The available equations to predict such properties as cracking and crazing, Tg, Tm and tensile strength from molecular characteristics are discussed in detail. However, a more quantitative description incorporating a wider range of mechanical properties would be more useful. This would facilitate use of the vast amount of information available and enable it to be applied more readily to new polymer systems.
Property‐morphology relationships of polymethylmethacrylate/polyvinylidenefluoride blends
Authors: Mijović Jovan , Luo Hong‐Lie , Han Chang Dae 
Published: December 2004

AbstractAn investigation was conducted to establish property‐morphology relationships in polymethylmethacrylate/polyvinylidenefluoride (PMMA/PVDF) blends. All blends were compounded in a twin‐screw extruder and then processed by injection molding Mechanical properties of blends of various compositions were studied by dynamic mechanical and impact strength measurements. The presence of crystalline regions in blends was determined by Differential Scanning Calorimetry (DSC). Morphology of fracture surfaces of blends was studied by Spinning Electron Microscopy (SEM). PMMA/PVDF blends were found to form compatible mixtures over a wide range of blend composition. Changes in dynamic mechanical properties upon annealing were found to be a direct function of blond morphology. Electron microscopic evidence showed no signs of phase separation. DSC measurements detected crystalline regions in all blends containing 40 percent or more (by weight) PVDF.
The limiting pressure‐velocity (PV) of plastics under unlubricated sliding
Authors: Yamaguchi Yukisaburo , Kashiwagi Kiyoteru 
Published: December 2004

AbstractThe limiting pressure‐velocity (PV) of plastics materials under normal contacting pressure P and sliding velocity V when the sliding goes on continuously unlubricated has been discussed theoretically in this study. The sliding friction tests between the rotating edge of a hollow cylinder against a stationary metal surface were carried out in room air and when the metals were cooled with circulating water.The results obtained were as follows:

The relation between PVmax and the critical temperature τbmax of the surface above which ordinary frictional conditions are not maintained may be represented by the following formula,

Where C = Hn/μk, and H is the mean total heat conductivity between materials and environment in cal/cm2. °C · s, n the area ratio of heat radiation surface to frictional surface, μ the kinetic frictional coefficient, k the thermal equivalent of frictional work in cal/kg · cm · s, and τa the cooling or environment temperature.
The value of C ranges from 1 to 10 in cal/kg · cm s · °C, and the value of PVmax from 45 to 750 in kg/cm2 · cm/s under prevailing room temperature air cooling in this experiment, however, the value of C has been increased about 2.3 times as much as those values by circulating water of 2°C around the lower side of the test piece.
Anisotropy and dimensions of blow‐molded polyethylene bottles
Authors: Kamal Musa R. , Kalyon Dilhan , Tan Victor 
Published: December 2004

AbstractA commercial blow‐molding grade, high‐density polyethylene resin was employed to produce cylindrical bottles in a commercial reciprocating screw‐extrusion blow‐molding machine. The distributions of thickness, crystallinity, birefringence, and impact strength were obtained at various positions. The thickness is greatest near the parting lines, while minimum thickness occurs at the top and bottom of the bottle. The thickness tends to be uniform in the middle section, in agreement with earlier studies of the parison during processing. Density and crystallinity distributions are closely associated with the distribution of thickness and its effect on the cooling rates prevailing during molding. Frozen stresses and birefringence are largest at the outer surface, where cooling rates are highest. The impact strength is lowest near the parting line. Photomicrographs suggest that this is associated with internal flow and crystallization phenomena.
Estimation of injection pressure during mold filling
Authors: Titomanlio G. 
Published: December 2004

AbstractDimensionless diagrams for estimating the bulk temperature of the flow front and injection pressure in the limit of small viscous generation are obtained. Also, a criterion for neglecting viscous generation is identified. The diagrams, based on the Lord and Williams model, refer to rectangular geometry and amorphous materials. A satisfactory comparison is obtained with literature data taken on polystyrene. A reasonable estimate of polyethylene injection pressure was obtained by roughly accounting for latent heat of crystallization through modified thermal diffusivity.
The compressive deformation of polymeric foams
Authors: Tsai James T. 
Published: December 2004

AbstractAn alternative approach has been developed to evaluate compressive stress on polymeric foams. Compressive stress depends primarily on three factors: foam density, deformation strains, and deformation rates. The density dependency derived from this approach agrees closely with the empirical models reported in the literature. Correlations between the dynamic compression and shear deformation are also derived. Experimental data are presented which show that G′ and G″ increase with increasing strain rates, while the damping factor reaches a maximum at low strain rates. Note that the proposed model for the prediction of cell‐wall rupture would not apply to foams with high open‐cell contents.
Residual stresses in polymers III: The influence of injection‐molding process conditions
Authors: Siegmann A. , Buchman A. , Kenig S. 
Published: December 2004

AbstractFollowing the evaluation of Residual Stresses (R.S.) in quenched specimens (Part I) and the resulting mechanical‐physical properties (Part II), the, present study deals with the effect of injection‐molding process conditions on R.S. and the respective properties of amorphous polymers. Melt temperature, mold temperature, injection rate, and injection pressure were the parameters studied. Experimental results indicated that the melt temperature caused two maxima in R.S. The second one reverses from compressive to tensile. In general, most changes occur in the surface regions, while R.S. decreases with increasing melt temperature, as is the case in zones far away from the gate. Furthermore, tensile modulus increased, in general, with rising melt temperature. In the case where the effect of mold temperature was studied, it was found that R.S. are compressive in the surface layers and tend to decrease upon increase in mold temperature and distance from the entrance region. Significant changes in R.S. were also detected in the interior layers. As the mold temperature approached Tg, low values of R.S. were measured, as was the case in quenched specimens. Injection rate affects surface R.S. to a large extent. With low flow rates, tensile stresses were developed in the exterior, reversing to compressive stresses at higher speeds. The reversal in sign depends on the location relative to the gate. Once compressive stresses were formed, further increase in rate caused a reduction in R.S. In addition, variations in tensile modulus, as high as 30 percent, were measured at high injection rates. As far as injection and holding pressures are concerned, experimental results showed that a maximum in R.S. was obtained, with increasing pressure, at the surface. Close to the gate entrance, a reverse from compressive to tensile R.S. was detected at high injection pressures. As in the other cases, injection pressure influenced mostly the exterior layers. Only in zones close to the entrance and at high pressures were high levels of R.S. measured in the core regions.
Reactivity of ethylene vinyl acetate copolymers: A critical evaluation of the comprehensive patent literature on the acetoxy‐hydroxide transformation of ethylene vinyl acetate copolymers
Authors: Koopmans R. J. , Van Der Linden R. , Vansant E. F. 
Published: December 2004

AbstractThe comprehensive patent list concerned with the acetoxyhydroxide transformation of ethylene vinyl acetate Copolymers is examined. The possible reaction mechanisms and processing techniques for this kind of transformation are described. Finally, a survey of about 55 of the most interesting patents is given, together with some general features of the acetoxyhydroxide exchange.
The mechanical properties of styrene‐butadiene‐styrene (SBS) triblock copolymer blends with polystyrene (PS) and styrene‐butadiene copolymer (SBR)
Authors: Diamant Joram , Soong David , Williams Michael C. 
Published: December 2004

AbstractMeasurements were made of linear viscoelastic properties and nonlinear stress‐strain properties of phase‐separated styrene‐butadiene‐styrene (SBS) copolymers and their blends with several homopolymer polystyrenes (PS) and one random copolymer (SBR). Torsion pendulum testing yielded shear moduliG′,G″, and Rheovibron experiments produced tensile moduliE′,E″, over a 220°K range of temperature, both at low frequencies. For pure copolymers and their PS blends,G′ andE′ correlated quite well with the total PS content, butG″ andE″ were more sensitive to how the additive was distributed. Results suggest that a PS additive whose molecular weight (M) is less than that of the copolymer PS‐block (Ms) causes expansion of both the interphase and the homogeneous PS‐rich phase, while an additive withM>Msmixes less well with these phases (probably forming separate domains of pure PS) and is less effective in enhancing the linear moduli. The blending with SBB produced reduction inG′ but a broad midrange peak inG″, suggesting that SBR was localized almost entirely within an expanded interphase. Tensile stress‐strain data were obtained with an Material Testing System at room temperature. For PS blends, properties did not correlate well with the total PS content, the blends being always weaker than the SBS of the same overall composition. The amount of set also increased with PS content in the blends. Cyclic tests to increasing strain showed progressive structural alterations (as for the host SBS), with blend behavior resembling host properties more closely with each new cycle. When SBR was the additive, amounts as small as 1 percent reduced the curves by 15 percent. The yield stress was eliminated entirely with an addition of 10 percent SBR, but for all cases the set was the same. Results are discussed in terms of interphase force barriers to chain flow.
Relationship between rheological properties and impact strength in high impact polystyrene
Authors: Dalal Mukund D. , Armstrong Robert C. 
Published: December 2004

AbstractTwo batches of a commercially available high‐impact polystyrene having different impact strengths were investigated. The steady‐shear flow properties, dynamic shear properties, and elongational flow properties of the two were measured. Transmission electron microscopy (TEM) was used to study the microstructure. It is suggested that melt rheology can be a sensitive tool in the characterization of final product properties of rubber‐modified polymers: the zero‐shear‐rate viscosity and the dynamic storage modulus G′, at low frequencies, were experimentally shown to correlate directly with the impact strength, despite the fact that TEM revealed no gross differences in the morphology of the two batches.
Fatigue fracture of polycarbonate
Authors: Takemori Michael T. 
Published: December 2004

AbstractThe fatigue fracture process in polycarbonate can be different for cracks grown from notches and from surface crazes. During the discontinuous crack growth process (which occurs during the very slow crack growth regime), full‐width cracks grown from notches have a very different crack tip plastic zone when compared to that observed in localized cracks grown from surface crazes. These localized surface cracks have a pair of sharply defined shear bands at the crack tip (forming the “epsilon” plastic zone) that are absent from notched‐grown cracks, The presence of the shear band pair in this plastic zone produces two major modifications. The discontinuous crack growth is extended to higher stress intensity ranges due to the (crack tip) craze stabilization by the shear band pair. Moreover, a shear fatigue fracture mode, absent in the notched specimens, occurs upon termination of the discontinuous growth process. The implications of this comparison are that estimates of fatigue lifetimes of smooth samples based on fatigue crack growth data (on notched specimens) may be erroneous.
The effect of moisture on the fatigue resistance of an aramid/epoxy composite
Authors: Roylance Margaret E. 
Published: December 2004

AbstractAn investigation has been carried out concerning the effects of moisture on the mechanical properties of a unidirectionally reinforced aramid/epoxy composite; specifically, Kevlar 49‐Fiberite 934. (Fiberite 934 is a 350°F‐cure epoxy composed primarily of tetraglycidyl methylene dianaline and hardened by diaminodiphenyl sulfone.) Absorption of water has been found to plasticize the resin so as to produce a decrease in the glass transition temperature from, 210°C to 150°C, and this plasticization serves to increase substantially the room‐temperature ductility of the resin. Moisture also serves to increase the static tensile strength, of the laminate, presumably by enhancing resin ductility and making the composite more forgiving of local flaws and fiber misalignments. The moisture‐induced enhancement of static strength is observed to carry over to an increase in fatigue lifetime at a given stress, although the fraction of ultimate tensile strength lost per decade of fatigue loading is the same in wet and dry materials. It is concluded that the mechanism of fatigue damage—probably a form of fiber abrasion—is unaffected by moisture, but the fatigue resistance of the wet composite is improved by virtue of its increased static strength.
Tensile yield in poly(4‐methyl pentene‐1)
Authors: Hartmann B. , Cole R. F. 
Published: December 2004

AbstractUniaxial tension tests to the yield point were performed on a crystalline polymer, poly(4‐methyl pentene‐1) (PMP) as a function of temperature from 21° to 200°C at a strain rate of 2 min−1. After testing, the specimens showed considerable stress whitening as a result of microvoid formation. Yield energy was found to be a linear function of temperature extrapolating to zero at the melting point (240°C). Thus, the behavior of this crystalline polymer is similar to that of glassy polymers, but with the melting temperature, rather than the glass transition temperature, as the reference point. The ratio of thermal to mechanical energy input to produce yielding is an order of magnitude smaller for PMP than it is for glassy polymers. The ratio of yield stress to Young's modulus is about 0.02, which is typical for polymers. Yield stress is a linear function of log strain rate, which implies that yielding can be described as a segmental flow rate process in which the applied stress biases the activation energy. The activation volume is on the order of 20 monomer unit volumes and increases as the temperature increases. The activation energy is 19 kcal/mol.
A model of compression mold filling
Authors: Tucker C. L. , Folgar F. 
Published: December 2004

AbstractA model is proposed for the flow, reaction, and heat transfer during compression molding of thin, flat parts. The isothermal Newtonian version of the model is implemented using the finite element method, and is capable of handling arbitrary planar geometries. Automated mesh expansion and boundary condition modification allow the simulation to run without operator interaction. The model accurately predicts mold filling pattern for non‐Newtonian and non‐isothermal flows.
Characterizing photoresists by thermal analysis
Authors: Appelt B. K. 
Published: December 2004

AbstractPhotoresists and solder masks are used extensively for manufacturing printed circuit boards to define and protect the circuits, respectively. These systems exhibit exothermic polymerization and crosslinking reactions upon exposure to UV light or to elevated temperatures. Differential scanning calorimetry (i.e., the heat of reaction) was, therefore, employed to characterize batch‐to‐batch variations and to characterize the photoreaction in these photosensitive materials. This technique allows unambiguous evaluation of the photoreaction independent of other parameters such as developer reactivity, temperature, and other variables that commonly interfere with functional tests.
Aspects of dispersion and flow in thermoplastic‐elastomer blends
Authors: Schreiber H. P. , Olguin A. 
Published: December 2004

AbstractPolypropylene, polystyrene, EP (ethylene/propylene) rubber, and bromobutyl rubber were blended under standardized conditions and the sizes of minor phase domains determined by Quantimet analysis. Dispersion effectiveness was found to depend on the melt viscosities of components under mixing conditions and on their “compatibilty” as inferred here from surface‐tension data. Dispersion was optimized when components wet readily at contact surfaces and when melt viscosities were similar. Shear heating during dispersion appeared to offer an empirical index of component compatibilty. Apparent melt viscosities of the blends further reflected the component compatibility factor.
The effect of storage temperature on the mobile water content and the fracture toughness of a filled‐polymeric system
Authors: Cahill R. W. 
Published: December 2004

AbstractCharpy specimens of a filled‐polymeric system from two partially cured and two completely cured lots obtained from one supplier were stored at selected temperature and relative humidity (RH) conditions to determine the relationship between mobile water content and the fracture toughness of the material. The fracture data showed that specimens from three of the structures exhibited similar ductile‐to‐brittle transition temperatures (DBTT) as a result of exposure to these environments even though samples from one of the three units were subjected to only part of the pure cycle. Samples from the other partially cured structure consistently displayed a more ductile fracture behavior throughout the conditioning range studied. Exposure to 100°F/75 percent RH environments, the highest temperature and RH of this study, appeared to enhance the fracture toughness of the material from all four units, and no evidence of deleterious chemical aging was found. Mobile water contents were measured on Charpy fracture residues, and these results correlate well with DBTTs of the filled polymer, as does RH. Charpy specimens from the partially cured structure with the best fracture performance have essentially the same water concentrations as the others, suggesting that the lower DBTTs associated with this unit may be due to a lesser degree of crosslinking.
Stress corrosion cracking of poly(vinylidene fluoride) in sodium hydroxide
Authors: Hoa S. V. , Ouellette P. 
Published: December 2004

AbstractStress corrosion cracking of poly(vinylidene fluoride) in sodium hydroxide solution is investigated. Poly(vinylidene fluoride) (PVDF) is embrittled in the presence of solutions of sodium hydroxide. Cracks developed in specimens of PVDF subjected to load and solution of NaOH. Reddish‐brown deposits appear before cracks can be seen. Straining the material slightly above its yield point retards the cracking activity. An explanation for this behavior is provided.
Effects of strain rate and temperature upon tensile properties of acetal copolymers
Authors: Wissbrun K. F. 
Published: December 2004

AbstractThe strength and elongation to break of an acetal copolymer were measured at four elongation rates, from 0.2 to 20 in./min, at temperatures from 239 K to 339 K. Both strength and elongation results could be reduced to master curves by means of time‐temperature superposition. The temperature dependence of the shift factors was given by an equation of the WLF form, with parameters close to those found for most amorphous polymers, at a reference temperature equal to the γ‐transition temperature of the polymer. Extrapolation to much higher testing rates and to much slower creep rates was satisfactory. Similar but less extensive tests were run on two other samples with different molecular weights. The yield stress was independent of molecular weight, but elongation increased with increasing molecular weight at all conditions.
The specification of orientation and its development in polymer processing
Authors: White James L. , Spruiell Joseph E. 
Published: December 2004

AbstractA critical review of the specification of orientation and its development in polymer‐processing operations is presented. Orientation may in general be specified by orientation distribution functions, but is most conveniently expressed in terms of orientation factors which are second moments of the distribution. The Hermans orientation factor represents polymer‐chain orientation for systems with fiber symmetry (uniaxial orientation) and the Hermans‐Stein orientation factors express uniaxial orientation for each of the crystallographic axes of crystalline polymers. Biaxial orientation is, however, developed in tubular film extrusion, blowmolding and, indeed, all processing operations other than fiber formation. Orientation factors developed previously by the authors express biaxial orientation in terms of the angles between the machine and transverse directions and the polymer chain axis or crystallographic axes. In flowing polymer melts, the Rheo‐Optical Law, which relates birefringence and stress, represents a relationship between polymer‐chain orientation and stress. In vitrified polymeric glasses (e.g. polystyrene), the orientation factors are related linearly to the stress field at vitrification. This has been shown experimentally for melt spinning and tubular film extrusion. The results of studies of blowmolding and injection molding are consistent with this. The crystalline orientation factors have also been found to be determined by the stress field at solidification in melt spinning and tubular film extrusion.
Super strong polymers in planar directions
Authors: Zachariades Anagnostis E. , Economy James 
Published: December 2004

AbstractA novel approach for producing multiaxially oriented polymers with ultrahigh mechanical properties in more than one direction is discussed. According to the approach, which is adaptable to conventional commercial processes, the polymer is processed in a contained geometry at a temperature near to but below the isotropic crystalline melting point under curvilinear flow conditions generated by the combined effects of a compressive force and a rotational force perpendicular to the compressive force. The process is demonstrated with thermoplastic and thermotropic polymers using simple torsional flow. The general features of the process and the properties of the multiaxially oriented polymers are discussed in view of the different flow conditions.