bluuebunny/crossref_metadata_2025_split huggingface dataset:
Melting behavior of solid polymers on a metal surface at processing conditions
Authors: Mount Eldridge M. , Chung Chan I. 
Published: December 2004

AbstractThe melting or plasticating behavior of seven commercial polymers (high density polyethylene, low density polyethylene, polypropylene, polyoxymethylene copolymer, polystyrene, poly(methyl methacrylate), and polycarbonate (PC) was investigated using an experimental apparatus specifically designed to measure the melting rate and the viscous shear stress of a solid polymer on a steel surface under precisely controlled conditions of temperature, velocity, pressure and sample width comparable to actual processing. The melting rate (per unit polymer solid/metal contact area) was found to increase with increasing temperature for all polymers except PC, to decrease with increasing sample width and to increase less than proportionally to velocity. Pressure increased the melting rate somewhat for most of the polymers. The viscous shear stress decreased with increasing temperature for all polymers except PC, decreased with increasing sample width and increased with increasing velocity. Pressure generally increased the viscous shear stress. PC showed an unusual behavior with a maximum in the melting rate near 4200°F(215.5°C) and also a maximum in the viscous shear stress near 445°F (229.4°C). The present melting model could be examined unequivocally for the first time using our experimental results. Comparison of our experimental results with the predictions of the present melting model clearly indicates the inadequacy of the present melting model, Our experimental results will provide a basis for rational development of a reliable melting model.
Dynamic modulus of rubber by impact and rebound measurements
Authors: Bassi A. C. 
Published: December 2004

AbstractWhen rubber is deformed an energy input is involved which is released in part when the rubber returns to its original shape. The part which is not returned as mechanical energy is dissipated as heat. The “rebound resilience” is defined as the ratio of the energy returned to the energy applied for deformation by an indentation due to a single impact. In this experiment, a pendulum mass and a test piece, as long as they are in contact, may be considered an oscillating system having one degree of freedom in which the rubber is a Voigt model. The correlation between rebound resilience and loss angle of the rubber may thus be derived. The measurement of the contact time between pendulum indentor tip and rubber surface, in addition to the rebound resilience, allows calculation of deformation, speed and acceleration of the damped sinusoidal motion. The penetration of the spherical indentor under a constant force depends on Young's modulus. Scott found an empirical relationship among force applied, depth of indentation, radius of the indentor tip and the modulus. This relationship has been recently improved by Stiehler and coworkers, The Stiehler formula has been used here for evaluating the storage modulus of rubber vulcanizates by using the maximum force transmitted by the impacting mass and the indentation depth of the test piece at the same time.
Use of a gas chromatograph for measurement of the rate of monomer desorption from poly (vinyl chloride) resins
Authors: Berens A. R. 
Published: December 2004

AbstractPrevious studies by a gravimetric technique have established that the sorption and desorption of small quantities of vinyl chloride monomer (VCM) by poly (vinyl chloride) (PVC) resin powders obeys Fickian diffusion kinetics. Consequently, the rate of sorption or desorption is very sensitive to the size and structure distribution of the resin particles and is a useful measure of these properties. To facilitate the measurement of desorption rates, an “inverse GC” technique has been developed, with the PVC powder taking the place of the usual gas Chromatograph column. The detector and electronics of the GC are used to follow the VCM content of a carrier gas stream passing through a PVC resin sample initially equilibrated to a uniform VCM content. This method yields results consistent with the gravimetric data and provides a convenient means of characterizing PVC particle structure.
Hardness testing of plastics
Authors: Phillips P. J. , Ramakrishnan N. R. , Oxlade P. L. S. 
Published: December 2004

AbstractThe effect of time of indentation and time of recovery on the Rockwell hardness, of a series of glassy and crystalline polymers has been determined. An analytical technique, based on conventional viscoelastic approaches, has been developed. This technique permits the resolution of the hardness number into its components of permanent deformation, retarded elastic compression, and retarded elastic recovery. Subtraction of components due to retarded elastic response results in hardness numbers dependent only the time‐dependent permanent deformation. Extrapolation of this data to zero time results in an absolute or time‐independent value of Rockwell hardness, designated Ro.
Head to head polymers IX: The rheological behavior of H‐H and H‐T atactic polystyrenes
Authors: Jacovic M. , Vogl O. 
Published: December 2004

AbstractThe rheological behavior of a sample of H‐H polystyrene of Mn of 41,000 and a Mw/Mn of 2 was compared at 160 and 190°C with a sample of H‐T atactic polystyrene of similar molecular weight. The melt viscosity of H‐H polymer (unlike the H‐T polymer) was non‐Newtonian at low stresses and decreased more rapidly with stress. This observation seems to indicate a stiffer polymer chain for the H‐H polystyrene. The flow activation energy (E*) of H‐H polystyrene was found to be dependent on the dynamic shear stress and decreased with increasing dynamic shear stress. The dynamic shear storage modulus of the H‐H polymer has a smaller increase of G′ with ω than that of the H‐T polystyrene.
The impact behavior of ABS over a range of temperatures
Authors: Newmann L. V. , Williams J. G. 
Published: December 2004

AbstractCharpy type tests have been conducted on a typical grade of aerylonitrile‐butadiene‐styrene (ABS) over the temperature range +60 to −80°C. At the higher temperatures, the fractures were fully ductile and have been explained in terms of a constant energy density necessary to produce craze‐whitened material. Below −40°C, the results were analyzed using a linear elastic fracture mechanics approach and values of Gc, the critical strain energy release rate, were obtained. The intermediate temperatures produced partially‐ductile behavior and these data were also analyzed to yield effective values of Gc.
Infrared laser ablation of polymers
Authors: Cozzens Robert F. , Fox Robert B. 
Published: December 2004

AbstractAblation produced by 10.6 μm laser irradiation of eleven polymers is reported. Polymers which formed a carbonaceous residue were found to have much higher ablation energies than cleanly ablating polymers. All non‐char forming polymers studied had observed laser ablation energies in the range 3.4‐3.9 KJ/g except for poly (α‐methylstyrene) which had a value of 2.4 KJ/g. The low value forpoly (α‐methylstyrene) is attributed to an exceptionally efficient depolymerization. The observed ablation energy of poly (methyl methacrylate) was found to decrease with increasing irradiance up to about 15 watts/cm2, reaching a constant value of 3.5 KJ/g at irradiances between 20 and 2600 watts/cm2. The proposed process of laser ablation is one that involves random fragmentation resulting from the accumulation of vibronic energy.
Warm hydrostatic extrusion of polyethylene
Authors: Bigg D. M. , Smith E. G. , Epstein M. M. , Fiorentino R. J. 
Published: December 2004

AbstractHydrostatic extrusion of high density polyethylene at an extrusion ratio of 15:1 was investigated in the temperature range between 100 and 134°C. A thin‐walled tube was extruded having a tensile strength of 370 MPa and a tensile modulus of 10 GPa. The extrusion rate was limited by severe extrudate distortion which occurs at a limiting shear stress under stick‐slip conditions. Even during steady extrusion wall slip was evident. At a constant extrusion speed, the extrusion pressure was found to be very sensitive to the extrusion temperature. An increase from 120 to 125°C reduced the extrusion pressure by half. Various thermal pretreatments of the starting billets were found to have little effect on the extrusion behavior and physical properties of the extrudate.
Effects of some liquids on the creep behavior of high impact polystyrene
Authors: McCammond D. , Hoa V. S. 
Published: December 2004

AbstractThe effects of seventeen different fluids on polystyrene is investigated. The fluids are divided into three groups by their effect on the unstressed polymer, namely dissolving, softening, and non‐softening fluids. The accelerated rates of creep of the polymer when immersed in the dissolving fluids are shown to be due to the reduction in the load‐bearing area resulting from dissolution at the surface, The increase in creep strain rates (relative to that in air) when exposed to the softening fluids result from the combined effects of: (i) the accumulated deformation of numerous crazes; (ii) the reduction in stiffness of the surface layer due to the softening effect of the fluid; and (iii) the swelling of the softened layer. In the case of the non‐softening fluids, the creep rates “accelerated” after a specific delay time which is a function of the applied stress. For these fluids there exists a critical stress below which crazing does not occur. This critical stress is shown to increase with increasing difference between fluid and polymer solubility parameters.
Crazing of fibrous polymers
Authors: Carton A. , Carlsson D. J. , Stepaniak R. F. , Wiles D. M. 
Published: December 2004

AbstractHighly oriented filaments of nylon 6 and polypropylene (PP) are shown to craze when deformed slowly at room temperature. A marked yield point occurs at 20‐40 percent elongation. After this point extensive voiding occurs until at fracture the overall density is reduced by ∽25 percent for PP and ∽15 percent for nylon 6. SAXS analysis indicates that for PP the voids are elongated in the fiber axis while for nylon 6 voiding occurs both parallel and perpendicular to the fiber axis. Optical and electron microscopy show typical craze structures. The use of etching demonstrates that crazing occurs across the whole filament cross section. This yielding behavior is shown to be associated with the use of a low temperature of drawing during fiber production and becomes less important when a higher temperature of drawing or a separate annealing step are used. The crazing mechanism is thought to involve progressive separation of interfibril boundaries with the production of elongated voids.
Elongational flow of polymer melts
Authors: Johnson Eric D. , Middleman Stanley 
Published: December 2004

AbstractA new technique is described whereby the rate of collapse of an air bubble within a molten polymer may be measured without the need for visual observation. The method involves use of a high speed recording dilatometer, From such data it is possible to measure an apparent elongational viscosity of the melt, and such measurements are presented for two polyethylenes (Tennite, a low density PE, and Plaskon, a high density PE), Limitations of the methods are discussed. This is one of a series of papers (1‐3) documenting our development of a new experimental technique, and the corresponding mathematical modeling, whereby one may measure the elongational viscosity of polymeric viscoelastic fluids. Previous experimental work was confined to transparent fluids, since the technique depended on high‐speed motion picture photography of the collapse of an air bubble within the fluid. In this paper we describe an attempt, largely successful, to develop a new experimental system which permits the study of molten polymers, including opaque fluids. Sample results are presented for both a low and a high density polyethylene.
Prediction of rheological properties of well‐characterized branched polyethylenes from the distribution of molecular weight and long chain branches
Authors: Pedersen Sven , Ram Arie 
Published: December 2004

AbstractAn empirical model suggested earlier by B. H. Bersted predicting the rheological properties of linear polyethylene from the molecular weight distribution is modified to account for the rheological properties in steady shear flow of branched polyethylene as well. The shear dependent viscosity, the steady shear compliance, and extrudate swell could be calculated from the distributions of molecular weight and long‐chain branching in good agreement with experimental data for eight commercial low density polyethylenes. Tanner's equation was used to calculated die‐swell from the modified Bersted model. The steady shear compliance was found to be related to \documentclass{article}\pagestyle{empty}\begin{document}$(\overline {gM} )_z .(\overline {gM} )_{z + 1} /(\overline {gM} )_w^2 .$\end{document}.
A cooling time model for plastics processing operations
Authors: Dietz Wolfgang 
Published: December 2004

AbstractThe cooling of a crystallizing polymer is analyzed taking into account the effect of pressure drop on the energy balance. Thermal conductivity and diffusivity of a low density polyethylene are determined at pressures between 0.1 and 150 MPa (1 and 1500 bars). Using a pressure, volume, temperature‐diagram, a complete set of material functions could be obtained. A numerical cooling model based on these material functions was established and tested experimentally. Good agreement between the model and experiment was obtained. The numerical algorithm of the model can be adapted easily to plastics processing operations, e.g., injection molding, blow molding, and extrusion.
Heat transfer to molten polymers flowing through tubes
Authors: Hulatt M. , Wilkinson W. L. 
Published: December 2004

AbstractA theoretical and experimental study of heat transfer to polymer melts flowing through circular tubes is presented. The mathematical model provides for shear heating and expansion cooling effects, and also heat of reaction during flow for various wall boundary conditions. Experimental results, obtained using low density polyethylene, show reproducible temperature and velocity profiles. The measured inlet melt temperature profile and the axial wall temperature profile provide the boundary conditions for the calculations. The experimental data confirm the predictions of the magnitude of the shear heating and expansion cooling effects during tube flow.
Swelling‐controlled, constant rate delivery systems
Authors: Hopfenberg H. B. , Hsu K. C. 
Published: December 2004

AbstractMaterials and conditions required for constant rate absorption of a liquid into a glassy polymer (Case II transport) have been exploited to produce prototype devices for constant rate delivery of a solute, molecularly dispersed within the polymer, to the surrounding liquid environment. Absorption of n‐hexane in polystyrene films, containing between one and two percent of Sudan Red IV dye, resulted in constant rate liberation of the colored solute to the surrounding fluid. The rate of dye release was controlled by the constant rate absorption of n‐hexane in these dye‐containing films. Companion experiments involving microtome sectioning and photomicrographic recording of dye‐loaded films, consequent to immersion in n‐hexane for various time intervals, revealed that the unpenetrated central core retained the dye originally dispersed within the film sample and, conversely, the swollen outer regions were completely denuded of dye consequent to n‐hexane penetration. The constant rate advance of the microscopically observable sharp boundary, between dye‐containing and dye‐denuded polymer, was quantitatively consistent with the independently determined kinetics of dye accumulation in the supernatant n‐hexane. These results indicate that diffusion of invading n‐hexane to the relaxing boundary and back diffusion of dye in the previously swollen outer shell are both rapid compared with the rate‐determining Case II transport of n‐hexane in these dye‐containing films. The delivery of Sudan Red IV to the n‐hexane was not confounded by an initial burst of solute, typically common to so‐called membrane‐reservoir controlled delivery devices. Swelling‐induced delivery from glassy matrices appears useful, therefore, for the design of monolithic devices for constant rate delivery over the entire course of the delivery cycle. The concept is not limited to monolithic devices; membrane‐reservoir devices could be constructed involving a glassy, solute‐containing reservoir which could be activated by penetration of invading liquid consequent to placement in a suitable fluid environment. Development of devices, suitable for swelling‐controlled release of drugs to target organs, will be based upon glassy, hydrophilic polymeric hosts.
Effects of the state of stress on the toughness of polycarbonate
Authors: Petrie S. P. , Dibenedetto A. T. , Miltz J. 
Published: December 2004

AbstractIt is shown that the mechanical properties of polycarbonate are controlled by the state of stress of the test specimen. Whereas the yield stress of the material is relatively insensitive to the state of stress, the tendency of the material to microcavitate is strongly dependent on the residual stresses in the surfaces of a test specimen. The effects of quenching, annealing, post notching, solvent swelling and rate of testing on the modulus of toughness are all related to the state of compression on the free surfaces. The mechanism of deformation is shown by cinematography to consist of the nucleation of a shear band followed by microcavitation along the propagating band. Maximum toughness is obtained by suppressing microcavitation so as to promote shear yielding. When microcavitation occurs, it is the competition between propagating the microcavitation throughout the material and the generation of microcracks in the advancing shear band that controls the ultimate elongation.
Aramid fiber‐reinforced ionomer
Authors: Alesi Anthony L. , Litman Alan M. , Mitchell Douglas F. 
Published: December 2004

AbstractChopped aramid fiber reinforced ionomer formulations were investigated as prototypes of military armor materials effective in providing protection against munition fragments. The dependence of ballistic impact resistance upon fiber openness was demonstrated by radiographs. Concentrations of 30 percent or less by volume of 1/4 and 1/2 in. fibers were injection moldable, However, the greater than optimum dispersion of fibers as a result of extrusion compounding or of the injection molding itself resulted in lower ballistic resistance and in usually lower tensile and flexural strength properties than were achieved by compression molding: Compression molding of suitably opened 1/4, 1/2 and 2 in. fibers produced rigid materials with fiber contents as high as 90 percent by volume. Ballistic impact resistance increased linearly with fiber content.
Fiber‐foam: A rheological phenomenon and a novel product
Authors: Cole E. A. , Cogswell F. N. , Huxtable J. , Turner S. 
Published: December 2004

AbstractWhen certain molten thermoplastics containing glass fibers up to 20 mm in length are extruded through an orifice, the extrudate has a frothy texture and solidifies into an irregular open‐cell structure. The effect is apparently caused by the recovery of the fibers from distortions arising in the region of converging flow near the entry to the orifice. The effect is particularly pronounced in systems with melt viscosities between 50 and 500 Ns/m2. Polypropylene, as an example, containing weight fractions of about 0.25 of glass fibers can be extruded through a zero‐length die 2 mm in diameter to give “ropes” that can be readily formed into flat sheets or three‐dimensional shapes because of adhesion between the still molten polymer in the newly extruded rope. Such sheets can then be bonded to other materials to make a variety of laminates. A range of bonding techniques is available and the rough surface texture of the ropes provides a useful mechanical key for bonding with grossly dissimilar materials. Fiber‐foam is highly resistant to fracture and has a modulus in the range expected by a simple model for the foam.
Aspects of the yield behavior in poly(ethylene terephthalate) fibers
Authors: Sweet G. E. , Bell J. P. 
Published: December 2004

AbstractThe yield behavior during cold drawing of commercially spun poly(ethylene terephthalate) (PET) filament yarn was investigated. Microscopic examination revealed the presence of inherent flaws within the spun filaments; these act as points for localized stress concentration. These inhomogeneities appear to be either internal cracks or crazes developed during the fiber melt spinning process. During elongation, stress magnification at these flaws results in shear band formation, indicating the onset of inhomogeneous yielding. At the yield bend in the load‐elongation curve a circumferential crack propagates within these shear band regions. This yield crack develops into the classical neck geometry which further localizes additional plastic deformation within the sample at the neck.
The influence of structure on the failure of isotactic polypropylene films
Authors: Samuels Robert Joel 
Published: December 2004

AbstractThe failure behavior of uniaxially‐oriented isotactic polypropylene films has been examined over a wide range of rates and temperatures. Above the glass transition temperature the failure behavior is observed to be a direct function of the initial noncrystalline orientation state of the film. Below the glass transition temperature (−80°C, −196°C), both the crystalline and noncrystalline regions contribute to the failure.
Viscoelastic measurements of PVC plastisol during gelation and fusion
Authors: Nakajima N. , Ward D. W. , Collins E. A. 
Published: December 2004

AbstractThis work is concerned with the change of viscoelastic properties of poly(vinyl chloride) (PVC) plastisol during heating. The system changes from a suspension of solid particles in a liquid medium to a swollen gel and further to a fused state as the temperature is raised. The Rheometrics mechanical spectrometer was used in the oscillatory mode at 0.1 Hz. The temperature of the sample was raised in a controlled manner to 195°C. During gelation, the viscosity increased rapidly about three decades. There was a similar increase of the elastic modulus. After reaching a maximum, both viscosity and elastic modulus decreased rapidly with the progress of fusion. The viscoelastic properties depended somewhat on the heating rate. At 170‐195°C, it took a few minutes for the moduli to reach steady values. Continued heating, for several minutes at 195°C, did not change the moduli any further. The temperature range of the decomposition of a blowing agent in the plastisol foam formulation was determined. Over this temperature range, the viscoelastic properties change very rapidly. Quantitative estimates were made for the decrease of moduli during this period.
Thermal response of composite panels
Authors: Kourtides Demetrius A. , Gilwee William J. , Parker John A. 
Published: December 2004

AbstractThe thermochemical and flammability characteristics of laminating resins and composites currently in use and others being considered for use as aircraft interior panels are described. The properties studied included: (a) limiting oxygen index of the composite constituents; (b) fire containment capability of the composite; (c) smoke evolution from the composite; (d) thermogravimetric analysis; (e) composition of the volatile products of thermal degradation; and (f) relative toxicity of the volatile products of pyrolysis. The performance of hightemperature laminating resins such as modified phenolics, polyimides and bismaleimides is compared with the performance of epoxies. The relationship of increased fire safety with the use of polymers with high anaerobic char yield is shown. Processing parameters of the state‐of‐the‐art epoxy resin and the advanced resin composites are detailed.