bluuebunny/crossref_metadata_2025 huggingface dataset:
Crystallization studies of semi‐crystalline polymers under oscillatory shear using the rheometrics mechanical spectrometer
Authors: Chang Eng‐Pi , Kushner Brian
Published: December 2004

A method has been developed on the Rheometrics mechanical spectrometer using the eccentric rotating disks mode to study the crystallization kinetics of different semi‐crystalline polymers (polyethylene, polypropylene, poly(butylene terephthalate) and Nylon 11) under oscillatory shear. Dynamic shear moduli (storage G′ and loss G″), loss tangent (tan δ), and dynamic viscosity (η′) were simultaneously, monitored during the crystallization process. The onset and completion of crystallization were characterized by the initial rise and final levelling off of G′, while the peak time, of crystallization (tp) is calculated from the time elapsed between the onset and peak of crystallization which is indicated by the G″ or η′ maximum. In the case of polypropylene, going from a low frequency of ≃0.1 rad/s, to higher frequencies of up to 10 rad/s, there is a monotonic decrease in peak time of crystallization (tp) together with a progressive decrease in spherulitic morphology. The observed acceleration in crystallization is due predominantly to the increase in nucleation rate and orientation of chains in melt crystalline aggregate. The progressive disappearance of the spherulitic morphology is attributed to the disruption of the spherulite superstructure at higher frequencies of shear.
Realistic analysis of flow in wire‐coating dies
Authors: Carley James F. , Endo Tadakazu , Krantz William B.
Published: December 2004

We have constructed a rigorous numerical solution of the equations of flow and energy within a general wire‐coating die that provides a far more accurate and detailed description of the flow than any previously available. The program* can accommodate uni‐ or multi‐sectional dies, in which the sections have conical or cylindrical shapes. Melt rheology was satisfactorily represented over the full range of shear rate at processing temperatures by a model with three regions for each isotherm, requiring six constants evaluated from rheometric data. Thirty‐three cases have been run, all of them in the domain of moderate‐to‐high wire speeds, with the two most important wire‐coating resins, low‐density polyethylene (LDPE) and plasticized polyvinyl chloride (PVC). Although the radialconvection term was omitted from the energy equation to overcome calculational instability, we believe the accuracy of our calculated results is chiefly limited by knowledge of melt properties. Temperature profiles typically exhibit two maxima, the more pronounced one being found close to the die wall. In coating a No. 22 AWG wire with LDPE at 2000 ft/min in one cylindrical die, the maximum rise, occurring at the die exit, was 100 K. Profiles of axial velocity across the stream exhibited maxima in some cases, not in others. Shear rates ranged from zero to about 106 s−1 and viscosity profiles were highly variable. Because the melt passes through the die so quickly, the calculated results for isothermal and adiabatic walls were not very different, even though the melt streams were only about 0.3 mm thick. While the investigation was focused on high‐speed wire coating, in which viscous dissipation is extreme, the program can also be used for analysis and design of dies for making pipe and blown film.
Melt spinning and draw resonance studies on a poly (α‐methyl styrene/silicone) block copolymer
Authors: Blyler L. L. , Gieniewski C.
Published: December 2004

Fiber spinning experiments were carried out with an α‐methyl styrene/silicone block copolymer under various sets of spinning conditions. The behavior observed was very sensitive to the ambient axial temperature profile employed along the spinline and to the initial melt temperature at the die. By optimizing these parameters, very high draw ratios (>400 to 1) could be achieved. Under less optimum conditions, filament rupture and instabilities such as draw resonance, accompanied by periodic diameter and spinline tension fluctuations, were noted. Tensile stress and axial velocity gradient profiles were obtained along the spinline under a variety of spinning conditions. These profiles, together with an independent: rheological characterization of the polymer, provide insights into the mechanisms giving rise to the various types of behavior observed.
Topomorphic states and phase transitions connected with the crystallization of polymers
Authors: Poddubny V. I. , Elyashevich G. K. , Baranov V. G. , Frenkel S.
Published: December 2004

The crystallization of flexible‐chain molecules of different degrees of coiling is considered. The nature of the phase transition during crystallization is discussed. The revision of established notions on phase transitions in polymers leads to the concept of crystalline topomorphism, i.e., the existence of two crystalline types with different modes of packing of macromolecules in the macroscopic crystal though they belong to the same lattice class: folded‐chain crystal (FCC) and extended‐chain crystal (ECC). Phase diagrams in coordinates of degree of coiling vs temperature are plotted. The values of molecular orientation and temperatures at which each of both mechanisms of crystallization takes place are evaluated. The mechanisms of ECC growth under equilibrium conditions and under conditions of molecular orientation are discussed. It is shown that the melting of ECC obtained by the process of orientational crystallization is a second order phase transition, being analogous to a crystal‐nematic phase transition. At the same time the melting of FCC provides all the features of a first order transition.
Plane stress and plane strain fractures in polypropylene
Authors: Fernando P. L. , Williams J. G.
Published: December 2004

The concepts of Linear Elastic Fracture Mechanics (LEFM) are applied to polypropylene, a homopolymer and two copolymers, with a view to characterizing their brittle behavior at slow rates (0.5 cm/min) in terms of a fracture toughness, KIc. The effect of thickness, notch sharpness, and the mode of loading on KIc have been investigated in order to determine the plane strain toughness values, KcI for the materials. The two types of material are compared in terms of their toughness values over a range of temperatures between +30 and −160°C. Evidently, the small amounts of ethylene added to the copolymers show plasticizing effects, suppressing the yield stress and the ductile‐brittle transition temperature. In addition, the copolymers exhibit a ductile‐brittle region between −100 and −45°C where notch strengthening is apparent in the tension mode and a slow crack growth region between −45 and −30°C where slow growth precedes unstable fracture. The homopolymer, however, shows no clear evidence of such intermediate regions, except for slight amounts of slow growth above 0°C, and becomes ductile around 30°C.
Diffusion with discontinuous swelling. IV. Type II diffusion into spherical particles
Authors: Peterlin Anton
Published: December 2004

In the last few years some new features of the so‐called type II diffusion have been established which confirm the first theoretical description of such a material transport into a semi‐infinite glassy medium which at a certain concentration of the sorbate is transformed into a gel. The boundary between the glass and the gel progresses at a constant velocity into the interior of the sample thus yielding a linear term in the weight gain. The gradual establishment of the concentration profile in front of this boundary yields at the beginning a square root term in the weight gain. A detailed analysis of the extensive measurements of Hopfenberg, et al. of the diffusion of n‐hexane into extremely small polystyrene spheres demonstrates that the weight gain always starts with a square root of time term. In sufficiently large spheres this contribution is soon completely overridden by the term linear in time. The spherical geometry substantially modifies the concentration profile and the weight gain. In particular the weight gain divided by the square root of time vs the square root of time shows a maximum as soon as the geometrical factors prevail over the effect of the constant velocity progression of the boundary between the glass and the gel.
Concentration dependence, boundary layer resistance, and the “time‐lag” diffusion coefficient
Authors: Skaarup Klemen , Hansen Charles M.
Published: December 2004

Diffusion coefficient measurements have been shown to be strongly influenced by boundary layer resistance and concentration dependence. When half‐times for desorption or absorption are used to find diffusion coefficients from the equation for a constant coefficient (T½ = Dt/L2 = 0.049), the values so obtained require correction. Diffusion coefficients found by the “time‐lag” method are also influenced strongly by surface resistance and concentration dependence. The usual equation for a constant diffusion coefficient gives a break‐through curve with an extrapolation to the time‐lag, TL = Dt/L2 = 1/6. This factor can rise to ½ for concentration dependence. Where boundary layer resistance is encountered, (a situation which appears to be quite common), TL is significantly increased and the slope at steady state is decreased.
Sorption and diffusion of weak acids in nylon—dual sorption and diffusion model
Authors: Iijima Toshiro , Miyata Eiji , Komiyama Jiro
Published: December 2004

The sorption and diffusion of fluoro‐substituted acetic acids in nylon‐6 were measured. Hydrochloric acid was also used for comparison purposes. The results were successfully interpreted quantitatively by a dual sorption model, namely by contribution of associated and dissociated species of the acids concerned. As was expected in the case of the sorption of the weakest acid among the acids used, acetic acid, the contribution of associated species is large. The analysis of the diffusion behavior of acetic acid has shown that the contribution of associated species plays a dominant role in the diffusion process in nylon.
The glass point of elastin as a function of diluent concentration
Authors: Hoeve C. A. J. , Hoeve M. B. J. A.
Published: December 2004

Elastin shares the properties of rubberlike elasticity and its capability to form a glass with crosslinked polymers in general. The glass transition temperature of dry elastin at 200°C is strongly depressed by water, as well as by ethylene glycol. On a volume fraction basis, both diluents depress the glass point equally. This result is strong evidence against any specific binding of diluent molecules and indicates relatively high mobility of diluent molecules in glassy elastin. This deduction is in agreement with the conclusions reached on the basis of heat capacity and dielectric measurements. Proposed small sections of β turns in the elastin chain are compatible with the concept of naturally occurring elastin chains in the amorphous state. Our results, however, do not confirm the existence of proposed β spirals with periodicities of 100 Å which were suggested to be the basis for the banded filaments observed in electron micrographs.
Effects of sorption modes on the transport and physical properties of nylon 6
Authors: Sfirakis Alexander , Rogers C. E.
Published: December 2004

The presence of low molecular weight molecules in a polymeric matrix often has a marked effect on material properties. Knowledge of specific penetrant distributions and component interactions is important for an elucidation of structure‐property relationships, plasticization phenomena, and any modification of structure induced by the presence of penetrants. The sorption‐mode characteristics of water, methanol, and ethanol in Nylon 6 films have been investigated by the application of the differential sorption method. The sorption and diffusion behavior were interpreted in terms of clustering theory with suitable account being made for penetrant molecular size and hydrogen‐bonding capability. The examination of transport and mechanical properties of these films indicates a pronounced dependence of those properties on the concentration of penetrants. The effect of penetrant cluster formation at characteristic concentrations of sorbed penetrant is to decrease the concentration dependence of both diffusion and mechanical relaxation processes in the case of alcohols. The onset of water clustering apparently only affects the mechanical relaxation process. The samples were further characterized by DSC, X‐ray diffraction and density measurements to detect any significant changes in the structure of Nylon 6 induced by the penetrant conditioning.
A rheometer for measuring the viscoelastic response of polymer melts in arbitrary planar and biaxial extensional flow fields
Authors: Denson C. D. , Hylton D. C.
Published: December 2004

In this paper we describe the operation of a rheometer that is capable of measuring the viscoelastic response of a polymer melt in a biaxial or planar extensional flow field under circumstances wherein the deformation history can be varied in an arbitrary manner. The principal feature of this rheometer is the use of a closed loop feedback system to control the inflation of a flat, molten polymer sheet clamped around its periphery. The feedback system is especially designed so that either stress or strain can be used as the reference point, thus permitting the deformation history to be varied arbitrarily. Illustrative data are presented on the viscoelastic response of a molten acrylonitrile‐butadiene‐styrene copolymer subjected to a planar extensional flow for the following deformation histories: constant stress, constant strain, constant strain rate, oscillatory stress and oscillatory strain.
An anomaly in the necking behavior of polyethylene, Part 2
Authors: Gedde U. W. , Jansson J.‐F.
Published: December 2004

Dumb‐bell shaped specimens of three polyethylenes were subjected to constant uniaxial tensile loads at test temperatures from 298 to 353 K. For the high density polyethylenes, a marked transition appeared in the neck/fracture behavior. At a certain stress level, the instantaneous fracture of the neck formed at high loads was replaced by the formation of a neck that resisted fracture for a considerable time. This transition was more gradual for the medium density polyethylene. Furthermore, at all test temperatures the transition shifts towards higher nominal stresses with increasing molecular weight. Mainly on the basis of measurements of the local strain rate in the neck forming region, a hypothesis is proposed which explains the appearance of the marked transition. The draw ratios and the densities of the fractured neck fibers were also measured and are in accordance with current molecular deformation theories.
Estimation of the shear deformation exerted by a roll‐mill upon a rubber compound
Authors: Ng T. S. , Angerer G.
Published: December 2004

The shear deformation which a rubber compound undergoes when passing through a mill nip was calculated. For this purpose the pressure distribution was measured using a strain gauge mounted in the table of a RAPRA micro‐mill. The method has been applied to black‐loaded master batches of natural rubber and styrene‐butadiene rubber, where the shear deformation was estimated as a function of the mill nip opening. Furthermore, the physical properties of a latex‐mixed powder vulcanizate was measured as a function of the estimated shear deformation.
Manufacture of high stiffness solid rods by the hydrostatic extrusion of linear polyethylene. Part I: Influence of processing conditions
Authors: Hope P. S. , Parsons B.
Published: December 2004

High stiffness solid rods, up to 25 mm diameter, have been produced by the solid phase hydrostatic extrusion of a single linear polyethylene grade. Factors affecting the processing behavior and the product properties, as characterized by the enhanced axial Young's modulus and long term creep behavior, have been examined and sources of product flaws have been identified. At high product diameters extrusion occurred in a predominantly adiabatic thermal régime, for which the magnitude of the temperature rise was estimated by measurement of the long periods of the products. This adiabatic regime allowed high production rates to be obtained at lower extrusion pressures, but caused a reduction in the Young's modulus of the products and limited the maximum degree of deformation which could be obtained in stable extrusions.
Radiation degradation behavior of chlorine‐containing vinyl copolymers. Search for improved electron‐beam resists
Authors: Helbert John N. , Poindexter Edward H. , Pittman Charles U. , Chen Chi‐Yu
Published: December 2004

Vinyl copolymers with high radiation degradation sensitivity have been synthesized by copolymerizing vinylidene chloride (VDC), CH2 = CCl2, with methyl methacrylate (MMA), methacrylonitrile, methyl α‐chloroacrylate, and dimethyl itaconate using emulsion techniques. In addition, copolymers of methyl α‐chloroacrylate with methyl methacrylate and poly(α‐chloroaerylonitrile) were studied. Introduction of vinylidene chloride into methyl methacrylate polymers caused a sharp increase in Gs even at relatively low VDC incorporation. Upon 29 percent VDC incorporation, the Gs value increased from 1.3 (homopolymer of MMA) to 3.4. Gs was found to be a linear function of copolymer content for several systems, but Gx was not. At higher VDC levels, the increase in Gs was countered by increases in Gx. At lower VDC levels, Gx was suppressed below the values predicted by a linear Gx dependence on composition for such systems as VDC/MMA, MCA/MMA, and α‐chloroacrylonitrile/MMA. The VDC/MMA co‐polymer(29 percent VDC) gavea sensitivity of 4.0 × 10−5C/cm2 to electron beam exposure using the 0 percent unexposed resist thickness loss criterion and is 2–3 times more sensitive than PMMA. Poly(α‐chloroacrylonitrile) is a negative resist with a sensitivity of 5 × 10−5 C/cm2 using one‐micron line images for testing.
Rapid response of a growing environmental craze to a stress pulse
Authors: Conners Andrew , Kramer Edward J.
Published: December 2004

Double exposure holographic interferometry has been used to measure the response of a growing craze to a pulsed stress. The craze was grown in situ by application of methanol to a crack in a poly (methyl methacrylate) (PMMA) strip under tension (K1 = 0.4 MN/m3/2). An incremental stress, approximating 15 percent of the overall crazing stress, is applied to the growing craze in a 1 s pulse. Incremental strain and stress profiles are measured along a line parallel to, but displaced 1.0 mm from, the growing craze, from a double exposure hologram triggered just before and during the pulse. The craze deforms rapidly, relieving the incremental stress concentration that can be shown to exist before craze growth. In a second set of experiments one holographic exposure is triggered during the incremental stress pulse, and a second exposure is triggered afterward. The results of such experiments indicate that the craze deformation is primarily plastic, and corresponds to a plastic strain rate of not less than 0.2 s−1. Consideration of the diffusion limitation of the rate of craze thickening leads to the conclusion that this plastic deformation is attributable to fibril creep rather than a surface drawing mechanism.
The effect of variations in light intensity on the photo‐oxidation of polypropylene
Authors: Kollmann T. M. , Wood D. G. M.
Published: December 2004

When polypropylene foil was photo‐oxidized in a laboratory UV aging apparatus, the rate of photo‐oxidation was proportional to various fractional powers of the light intensity depending on the type of lamp(s) used and whether the polymer was stabilized or unstabilized.
Degradation of polycarbonate during recycling in a capillary rheometer
Authors: Abbås Kent B.
Published: December 2004

Polycarbonate was recycled in a capillary rheometer at high constant shear stresses (0.15–0.95 MPa) and at temperatures between 275 and 320°C. Changes in melt viscosity and molecular weight were evaluated. Significant polymer degradation was observed on repetitive extrusion. An activation energy of 113 kJ/mol was determined for the initial stages of the process. The degradation kinetics were in agreement with a non‐random chain scission. It was concluded that bonds were more susceptible to scission the closer they were to the middle of the polymer molecule and that the extent of degradation increased with an increase in molecular weight.
Preparation of aligned discontinuous fiber pre‐pregs by deposition from a suspension
Authors: Salariya A. K. , Pittman J. F. T.
Published: December 2004

In a process for production of aligned short fiber pre‐pregs, fiber suspension passes through a converging channel to emerge as a thin free‐surf ace sheet which is laid down onto a reciprocating horizontal filter surface. Following our previous work on fiber alignment in the channel, detailed studies are reported of the suspension sheet falling under gravity, and of the deposition stage. Close agreement is found between computed and experimental velocity profiles for sheets of fiber‐free liquid. Modification of the velocities resulting from the presence of fibers aligned in the flow direction is taken into account using an increased extensional viscosity. This is evaluated using pre‐existing theory which is tested experimentally and found satisfactory. A simple relationship between velocity and fiber alignment change in the falling sheet is derived and tested experimentally. Alignment is marred by surface disturbances to the sheet. Comments are made on the stability of the free‐surface sheet. An experimental study is made of alignment changes as fibers are deposited on the filter, and the results related qualitatively to operating conditions. In general there is little difference in alignment before and after deposition, except close to the leading edge of the filter where alignment loss occurs. Previous work is reviewed and recommendations made on optimum operating conditions.
Bulk polymerization of styrene in plate and frame batch reactors
Authors: Kovenklioglu Suphan
Published: December 2004

Thermal bulk polymerization of styrene in the plate and frame batch reactor i.s simulated with a mathematical model which accounts for chain transfer to monomer and gel effect. The design parameters are: the frame thickness, the temperature policy, and the level of prepolymerization in the feed. The recommended frame thickness with 27% prepolymerization is 5 in. The resulting polydispersities and number average chain lengths range from 2.2–2.3 and 2000–2100 respectively. The implementation of temperature policy, particularly the timing of the application of the coolant, is critical to obtain satisfactory polymer quality. When pure styrene feed is used the reactor displays thermal ignition unless the frame thickness is less then 2 in. For a 5 in. frame prepolymerization should be at least 25 percent to permit adequate temperature control.
The effects of light and heat on the rubber content and impact strength of acrylonitrile‐butadiene‐styrene
Authors: Bair H. E. , Boyle D. J. , Kelleher P. G.
Published: December 2004

DSC analysis of acrylonitrile‐butadiene‐styrene (ABS) samples either weathered outdoors for up to 10 years or aged at 71°C has shown that these plastics deteriorate most readily through the polybutadiene (BD) component. Oxidation of the BD in ABS leads to an increasing and broadening Tgas well as a decrease in ΔCp at Tg. The latter quantity can be used to quantitatively assay the amount of unoxidized rubber in a photo‐ or thermal‐oxidized sample. The loss of impact strength of these resins with chemical aging can be correlated with the oxidation of the polybutadiene phase. Studies of rubber content as a function of sample thickness have revealed that an embrittled layer containing oxidized BD develops at the surface of an aged, 100 mil. ABS plaque (natural) and grows to a thickness of about 10 mils after 3 years exposure to sunlight. ABS containing carbon black is effectively screened from this photo induced degradation and consequently has much better retention of its initial impact strength values. In addition, carbon black was observed to retard thermal oxidation in some ABS samples. Lastly, it appears possible to do accelerated aging studies at elevated temperatures to evaluate the relative stabilities of various ABS formulations.
Co‐extrusion of polymers with one single screw having a specially devised double channel
Authors: Iwakura Kenji , Fujimura Toshikazu
Published: December 2004

Co‐extrusion by means of only one single screw with a double channel was studied. The effects of the operating conditions, the material properties and the screw geometries on the inter‐channel flow and the output rate were determined. The flow mechanism and the application to the composites with stratified structures were discussed. The inter‐channel flow rate decreased with decrease in the back pressure, the stock temperature, the screw rotational speed and the viscosity difference between polymer melts in both channels. The decrease in the compression ratios of channels, the barrier flight in the compression zone and the sealing at the flight clearance with the polyamide‐packing reduced the inter‐channel flow significantly without a decrease in the output rate. With this method, co‐extrudates with distinctly stratified cross‐sections were prepared. The single screw with double‐channel could be applied effectively to the co‐extrusion of composites with stratified structures such as sheath‐and‐core structures, and it is particularly suitable to distribute the additives heterogeneously or to enclose the waste polymer.
Rheology of molten blends of polyoxymethylene and ethylene‐vinyl acetate copolymer and the microstructure of extrudates as a function of their melt viscosities
Authors: Tsebrenko M. V. , Rezanova N. M. , Vinogradov G. V.
Published: December 2004

Blends of polyoxymethylene (POM) with a copolymer of ethylene and vinyl acetate (CEVAc) have been studied. The effect of viscosity ratio for melts of the components on the processes of fiber formation in extrudates and on the rheological properties of the molten blend has been tested. The viscosity ratio of the fiber‐forming POM and the matrix varied in the range 0.35‐27.7. POM ultrathin fibers of unlimited length can be formed in the CEVAc only at a viscosity ratio close to unity. For ratios much greater than unity, the extrudate is found to contain short fibers and a finely dispersed powder or no fibers at all. If the viscosity of the POM melt is lower than that of the matrix, films are formed in addition to fibers. The second factor that governs fiber formation is the extrusion shear stress. An optimum shear stress exists at which the amount of ultrathin fibers is a maximum.
Shear‐rate‐dependent viscosity of non‐Newtonian suspensions and entangled polymer systems
Authors: Soong David , Shen M.
Published: December 2004

A simple equation is proposed to calculate the shear‐rate‐dependent viscosities of entangled polymers and particle suspensions. The rate‐dependence of the viscosities is attributed to changes in certain structural parameters associated with the fluids, such as entanglement density or degree of particle agglomeration. The state of these structural parameters for fluids subjected to a given shear flow is determined by two competing process, i.e., structural breakdown and reformation, which in steady How arc in a state of dynamic equilibrium. For the polymer systems structural degradation and reformation are tantamount to entanglement loss and creation, whereas for the suspensions they are correlated with the particle breakup and flocculation. The regeneration process is driven by thermal diffusion and is assumed to be independent of shear rate. The degradation process is caused primarily by the imposed shear and is assumed to be proportional to the shear rate to a power m (0<m<1). Based on these assumptions, structural variation for fluids undergoing not only steady‐state but a I so transient flows can be calculated. Model predictions and their implications are discussed. The derived equation can be applied to many non‐Newtonian pseudo‐plastic fluids.
Analysis of plasticizer activity in cellulose esters
Authors: Seymour R. W. , Minter J. R.
Published: December 2004

β′‐relaxation temperatures (Tβ′) provide a sensitive measure of the relative efficiencies of plasticizers in altering such properties of cellulose ester plastics as their impact strength, melt‐How, and modulus. Anomalies may occur, however, if the plasticizer‐compatibility limit in the polymer is surpassed. In addition, different correlations of Tβ′ and polymer properties are observed for liquid and solid plasticizers.
Influence of initiation mode on stability and control of a chain reaction
Authors: Chen H. T. , Chartier P. A. , Setthachayanon S.
Published: December 2004

Initiation of chemical reactions by ultra‐violet light is characterized by essentially complete lack of temperature dependence and by physical separation of the source or initiating agent from the reaction medium. The advantage of these features for reactor stability and control are discussed in a theoretical study of the photo‐sensitized polymerization of styrene in a continuous stirred tank reactor and a comparison is made with the behavior of the thermally initiated reaction.
The influence of residual stresses and orientation on the properties of amorphous polymers
Authors: Thakkar B. S. , Broutman L. J.
Published: December 2004

The effect of cold rolling on impact strength of poly(vinyl chloride) (PVC) acrylonitrile‐butadiene‐styrene (ABS), and an alloy of ABS and polycarbonate (Cycoloy) was studied. The results were presented in terms of Izod impact strength and present oil thickness reduction. The residual stresses molecule orientation and modification of mechanical properties due cold rolling were measured. It was shown that the mechanism of toughness enhancement in PVC, ABS, and Cycoloy different than the one observed in rolled polycarbonates. In the case of a highly localized failure initiation event (a single eraxe), which appears to be present in polycarbonate, the influence of residual stresses, is great, whereas in rubber modified polymers having multiple erasing over a large volume, orientation is more important than residual stress. Hot rolling of poly(methyl methaerylate) holds promise for a continuous process to achieve orientation and toughness enhancement.
High stiffness polymers by die‐drawing
Authors: Gibson A. G. , Ward I. M.
Published: December 2004

The application of die‐drawing to the production of highly oriented polymers is considered, ft is shown that a variety of useful products can be obtained including not only rod and multifilament, but also tube and filled polymer. The investigations under discussion include the processing of several grades of linear polyethylene, polypropylene homopolymer and co‐polymer. In favorable cases, products of very high stiffness were obtained, reaching modulus values of 50 GPa for linear polyethylene and 20 GPa for polypropylene.
Molten poly(methyl methacrylate) under electron irradiation: Studies of depropagation and chain scission
Authors: Ficke H. H. , Merrill E. W. , Vasa N. K.
Published: December 2004

The degradation rates of free radical polymerized and syn‐diotactic poly(methyl methacrylate) (PMMA) under electron radiation were explored at temperatures ranging from 225 to 325°C and at electron dose rates from 10,000 rads/min to 100,000 rads/min. Scission of bonds between main‐chain atoms resulted in pairs of radical chain ends, of which some disportionated, thereby reducing polymer molecular weight without loss of volatile, while others proceeded to depropagate via the usual radical transfer, causing complete volatilization of the chain without significant change of molecular weight of the residual polymer. Electron irradiation at a dose rate of 100,000 rads/min produced a significant enhancement in the reaction, rate, and reduced the overall activation energy from 140 KJ/g‐mole observed for thermally induced depropagation to a value of 75 KJ/g‐mole observed during simultaneous irradiation and/thermal depropagation.
The effect of orientation on radiation‐induced degradation in high density polyethylene
Authors: Akay G. , Tincer T.
Published: December 2004

The oxidative degradation of cold drawn highly oriented high density polyethylene is studied by IR spectroscopy. Both gamma and ultraviolet radiation sources are used. It is found that under gamma radiation the oxidative degradation, as determined from carbonyl formation, is reduced very significantly but that the trans‐vinylene unsaturation in the polymer increases with draw ratio. Similar results are obtained for samples irradiated in vacuum or when the polymer is stabilized with a radical quencher. Annealing (with free‐ends) of the samples restores the rate of carbonyl formation over and above that of the undrawn polymer although restoration after annealing with fixed‐ends is not complete. There, is further increase in trans‐vinylene development after annealing. In stabilized samples, the effect of annealing on carbonyl and trans‐vinylene development appears to depend on draw ratio.

Under ultra‐violet radiation, the oxidative degradation of drawn and unannealed samples is also reduced with increasing draw ratio. The same effect is observed in stabilized samples. Annealing, once again, restores the rate of oxidative degradation to that of the undrawn polymer. The main unsaturation product during ultraviolet irradiation is the vinyl end group and its development is suppressed with drawing. During ultraviolet irradiation of unannealed drawn samples, cracks, generally perpendicular to the draw direction (intrafibrillar cracks) appear on the sample and with further irradiation they penetrate into the sample. In the case of stabilized and unannealed drawn samples, cracks parallel to the draw direction (interfibrillar cracks) appear first and continued irradiation results in the appearance of intrafibrillar cracks. These observations may have significance in modelling the fibrous structures obtained by drawing semicrystalline polymers.
Polyurethane and polyblend sealants
Authors: Feldman D.
Published: December 2004

A study has been carried out on the properties of a fast‐curing two‐part polyurethane sealant, and on its blends with other polymers, such as poly(vinyl acetate), poly(vinyl chloride) and poly(vinyl alcohol). Different substrates, such as Portland cement mortar, wood, and aluminum in three different thermal conditions were used. Tension tests by Universal Testing machine Model 1175 have been made, and stress‐strain curves have been devised and discussed. A two‐component fastcuring polyurethane sealant demonstrates good adhesivity for the supports mentioned. The elasticity of polyurethane sealants may improve even at low temperatures if mixing with other polymers.
Gel permeation chromatography: Automatic data acquisition and reduction in real‐time with a process computer
Authors: Meira G. R. , Johnson A. F.
Published: December 2004

A real‐time computer system is described which minimizes the total analysis time in gel permeation chromatography by automatically acquiring the data, performing the necessary calculations and displaying the molecular weight distribution and molecular weight averages as soon as the polymer peak has eluted. The calculation method described here is valid for linear homopolymers only, and does not include corrections for instrumental peak broadening. The experimental results show good reproducibility and precision. On‐line changes of the constants and other parameters may be implemented by means of an auxiliary program which runs in parallel with the data analysis program. A system such as that described here is suitable for utilization as a measurement technique in process control applications. The programs are written in CORAL 66 for a Ferranti Argus 700 E computer.
The influence of non‐Newtonian flow on effective viscosity and channel efficiency in screw pumps
Authors: Booy M. L.
Published: December 2004

A method is given for selecting the “effective viscosity” for isothermal flow of non‐Newtonian liquids in screw pumps or melt extruders. Effective viscosity is the Newtonian viscosity that would give the same screw‐pump performance with non‐Newtonian liquids at the same flow rate and speed. When effective viscosity is known, it can be inserted in performance equations for simple Newtonian flow. The analysis is restricted to shallow screw‐pump channels with large aspect ratios and to shear stress/shear rate curves with modest curvatures when shown in a double logarithmic plot. The shear stress/shear rate curve is replaced by a power‐law tangent to that curve in the domain of prevailing shear rates, but the analysis could be extended to more complex behavior. Curves are also included for calculating the efficiency of the screw‐pump channel, which can be used to estimate the energy dissipated in screw‐pumps. It is shown that efficiency decreases with decreasing power‐law exponent.
Deep channel operating characteristics of a single screw extruder: Finite element predictions and experimental results for isothermal non‐Newtonian flow
Authors: Choo K. P. , Hami M. L. , Pittman J. F. T.
Published: December 2004

Finite element solutions are presented for developed, isothermal, power‐law flow in an extruder channel, based on a variational formulation in helical co‐ordinates. The success of the method in handling non‐Newtonian flow in a deep, highly‐curved channel is tested by comparison with experimental results. Operating characteristics were determired under virtually isothermal conditions for a screw with depth to diameter ratio 0.25 pumping an aqueous glucose solution containing high molecular weight hydroxyethyl cellulose. Shear stress and first normal stress differences of this solution were determined in a rheogoniometer. It was both highly shear‐thinning and elastic. Computed and experimental screw operating characteristics agree well, except near closed discharge, where effects due to viscous heating and elasticity are tentatively suggested.
Estimation of thermal conductivity of polyethylene resins
Authors: Kraybill Richard R.
Published: December 2004

Methods of predicting and correlating thermal conductivity of polyethylene resins in solid and melt states are discussed herein. Dependence on crystallinity or density is estimated for the solid state by a form of Maxwell's equation for electrical conductivity. An equation is presented for predicting melt thermal conductivity based upon Bridgman's theory of energy transport and pressure‐volume‐temperature (PVT) data. The effect of pressure on melt thermal conductivity is calculated from the theory. The effect of pigmentation for near spherical particles up to approximately 2.5 volume percent is also correlated by a form of Maxwell's equation. Experimental thermal conductivities of unpigmented and pigmented polyethylene resins from 50 to 300°C are in good agreement with theoretical predictions and with literature data.
Filler effect on the recoil kinetics of drawn polystyrene
Authors: Nicolais L. , Apicella A. , Nicodemo L.
Published: December 2004

Recovery experiments above Tg have been performed on glass bead and short glass fiber polystyrene composite sheets obtained from extrusion and subsequent hot drawing. A shift procedure has been applied to recoil data using the Williams‐Landel‐Ferry (WLF) equation with the same values of C1 and C2 used for unfilled polystyrene. The data reported show that an improvement of the dimensional stability of a drawn thermoplastic material can be obtained by adding very low volume percentage of fibers. Moreover, all the recoil data have been reduced to a unique generalized master curve which takes into account the draw ratio, the filler content, and geometry, using a fractional distance from equilibrium as a measure of the recovery. These results indicate that the presence of the filler does not affect the recoil kinetics of the polymeric matrix.
An anomaly in the necking behavior of polyethylene, part 4
Authors: Gedde U. W. , Terselius B. , Jansson J.‐F.
Published: December 2004

It is shown that the annealing of a high molecular weight, high density polyethylene at different temperatures ranging from 393.2 to 405.2 K influences the density of the material, the lamellar structure as studied by differential scanning calorimetry and transmission electron microscopy, and the necking and fracture behavior at constant uniaxial tensile loading in air at 313 K. In previous reports, a marked transition in the necking and fracture behavior of high density, high molecular weight polyethylene under constant uniaxial tensile loading has been reported. The nominal stress and the maximum strain rate of this transition show minima for polyethylenes annealed at temperatures of about 401 K. By combining these data with data for the lamellar structure a hypothesis that explains the necking/fracture behavior is set up. The heat treatment at temperatures from 393.2 to 403.2 K of the original non‐equilibrium lamellar structure causes a molecular fractionation preferentially of low molecular weight and branched material. These segregated parts may then act as fracture initiators and thus lower the resistance towards fracture. Other structural effects such as those proposed by McCready and co‐workers may also be of importance. The fracture curves at nominal stresses below transition of the materials annealed at 396.7 and 401.2 K for 24 h are shifted to shorter times in comparison with that of the non‐annealed material and this can also be explained by molecular fractionation. The time to necking at 14 MPa nominal stress seems to be related to the lamellar thickness of the samples.
Compatibility and physical properties of a new polyester blend
Authors: Slagowski E. L. , Chang E. P. , Tkacik J. J.
Published: December 2004

The compatible nature of a new polyester blend, polybutylene‐terephthalate (PBT) and a copolyester of bisphenol‐A‐neopentyl glycol‐terephthalate (CP‐350), has been inferred from the single Tg by DSC and dynamic mechanical studies. Compatibility is further confirmed from the progressive melting point depression of PBT, and the increasingly coarse and open spherulitic morphology of the blends as the weight percent of CP‐350 increases. At and above 40 weight percent of CP‐350, crystallization of PBT is impeded by the presence of high concentrations of CP‐350 which results in a low degree of PBT crystallinity (0‐8 percent) in such blends. The melt viscosity as a function of blend composition shows a good fit to the Hayashida model.
Sorption and diffusion of alcohols in amorphous polymers
Authors: Sfirakis Alexander , Rogers Charles E.
Published: December 2004

The effects of polymer composition and penetrant molecular size on the solubility and diffusivity of alcohol vapors in a series of well characterized isoprene‐methyl methacrylate copolymers and their corresponding homopolymers has been investigated at room temperature. The rate of sorption behavior changes progressively from Fickian to non‐Fickian, to Case II to “Super Case II” transport with increasing methyl methacrylate (MMA) content in the polymers. The equilibrium solubility of the alcohols increases linearly with increasing penetrant molecular size for polymers which are above their glass transition temperature and decreases for polymers which are below their Tg. The solubility also initially increases as an approximately linear function of MMA content in the copolymers. At about 55 mole percent MMA, the sorbed concentration either levels off or passes through a maximum depending on the size of the penetrant. The apparent “diffusion coefficients” (D) decrease with increasing molecular volume of the penetrants. An exponential dependence was found between these two variables for PMMA. These “diffusion coefficients” also decrease exponentially with increasing MMA content in these polymers. However, at 55 mole percent MMA the copolymer undergoes a rubber to glass transition at the temperature of the experiments. On this basis, it is suggested that the hindered chain segmental motion contributes to the sorption process in addition to strictly thermodynamic considerations. Free volume theory can be used to explain the mechanism of diffusion through the rubbery polymers while the “hole” theory can be applied to explain the transport of the penetrants through the glassy polymers.
Structural changes in the surface layer of plastic as a result of sliding friction in a metal‐thermoplastic system
Authors: Krzemiński Jerzy L. , Wiechowicz‐Kowalska Ewa
Published: December 2004

Studies on structural changes in the surface layer of plastics during internal sliding friction (friction upon seizing) of metalthermoplastic systems have been carried out. These structural changes were carried out by means of polarized light microscopy, density measurements, X‐ray diffraction and IR absorption spectroscopy (ATR). They were carried out for high density polyethylene (HDPE), polypropylene (PP) and nylon 6 (PA6). As a result it was found that the formation of completely different structures was caused by internal sliding friction.
Viscoelastic behavior of suspensions of particles in polymer solutions
Authors: Umeya Kaoru , Otsubo Yasufumi
Published: December 2004

Suspensions, consisting of glass beads about 1 μm in diameter and a 20 wt percent polystyrene solution in diethyl phthalate, were prepared at concentrations up to 13 vol percent. The viscoelastic properties were measured by means of a conventional dynamic method and by the raised cosine pulse method. The relaxation intensity and relaxation times of suspensions increased with increasing particle concentration. However, at concentrations > 13 vol percent, the stress against the raised cosine pulse strain did not approach zero. It was found that concentrated suspensions were complicated by a combination of viscous, elastic, and plastic effects. The experimental results have been qualitatively explained on the base of the network structure of particles.
Environmental stress cracking in impact polystyrene
Authors: Bubeck R. A. , Arends C. B. , Hall E. L. , Sande J. B. Vander
Published: December 2004

Environmental stress cracking (ESC) measurements for various impact polystyrenes were performed using a constant load technique with the specimens in contact with a 50/50 solution of cotton seed oil and oleic acid. It was shown that ESC in impact polystyrene is controlled by the transport of the aggressive liquid through a pre‐established dry craze structure where capillary pressure is the driving force. At moderate stress levels just above the critical stress for environmental cracking, there is an apparent incubation time for the dry craze formation. The craze incubation time is strongly influenced by thermal stresses induced by the gel particles. As a consequence, ESC is two‐stage process involving both an incubation time and actual crack growth. Control of the craze structure to maximize fibril content is essential for good ESC resistance. The craze fibril content can be altered by variables such as gel particle size, matrix molecular weight, plasticizer content, and rubber content.
The flow of thermosets through the nozzle of an injection molding machine
Authors: Rojas Alfredo J. , Adabbo Humberto E. , Williams Roberto J. J.
Published: December 2004

The conservation equations of momentum, energy, and mass are numerically solved for the flow of thermosets through the nozzle of an injection molding machine. The following working hypotheses are stated: perfect mixing of reactants, validity of the lubrication approximation, steady state (based on previous results for thermoplastic materials), negligible diffusional mass transfer, adiabatic boundary condition, and wall slip. Numerical results for a particular case‐show that the value of the slip friction coefficient is very important for defining the process feasibility. The apparent viscosity of the material is also relevant to the process. Materials of low viscosity gel at the wall of the nozzle inlet section; high viscosity materials may gel at the outlet section, requiring great pressure gradients and showing high wall temperatures at the exit. These high temperatures may cause degradation or undesirable side reactions.