bluuebunny/crossref_metadata_2025 huggingface dataset:
Properties of polypropylene‐polyethylene blends
Authors: Noel Oscar F. , Carley James F.
Published: December 2004

High‐density polyethylene (PE) and isotactic polypropylene (PP) were melt‐blended in the following percentages of PE by weight: O, 10, 33.3, 40, 50, 66.6, 90, and 100. For these blends we obtained data on shear stress vs shear rate; tensile modulus and strength; density; and rates of water‐vapor transmission for films. The shear‐rate/shear‐stress data at 190 and 210°C are well fitted by the Ellis model with a maximum relative error of 5 percent. At 190°C all the mixtures were found to exhibit flow instabilities at high shear rates except the 90 percent and pure PE compositions. These, however, were unstable at 140, 150, and 160°C.

The 10, 33.3, 40, 50, and 66.6 percent PE mixtures ruptured at elongations of less than 15 percent at the maximum tensile stress. The maximum tensile strength and modulus pass through maxima at 10 percent PE. Density is given by the equation ρ = 0.9029 + 0.0544 (wt fraction PE). Water‐vapor permeability was measured using wax‐sealed permeability cups, according to ASTM E96‐66. Valid results were obtained for only a few compositions because of faulty seals that could be detected only during careful dismantling of the specimen dishes. Faulty seals could account for the value, about ten times ours, reported in the literature for linear PE.
Some critical issues in advanced polymer science
Authors: Halpin John C.
Published: December 2004

Theoretical projections, based upon the anisotropic character of the polymer chains and supported by recent fiber technology and composite mechanics developments, indicate that an order of magnitude improvement in bulk polymer properties is both technically possible and achievable. The objective of this discussion is to define and discuss some of the major scientific problems associated with the achievement of the maximum mechanical potential of macromolecular (polymeric) solids. Two material paths to achieve maximum response will be considered in detail.

1. Composite Materials. This deals with the reinforcement of bulk polymers by one or more phases providing enhanced mechanical properties, such as high‐strength high‐modulus graphite, glass, and polymeric fibers. The latter could include high‐modulus fibrous polyethylene in a polyethylene matrix–a molecular composite.

2. Homogeneous Molecular Composites–Ultra Molecular Orientation. Examined here is the way absolute molecular orientation can be developed in both aromatic and olefinic polymers to produce materials with mechanical properties comparable to the defect‐free single crystals of metals. Simultaneously, structure‐property relations are examined in traditional bulk polymers.
High‐performance carbon fibers
Authors: Diefendorf R. J. , Tokarsky E.
Published: December 2004

Graphite has a hexagonal close‐packed crystal structure which is strong and stiff in the two directions of the basal plane and, in the third direction—perpendicular to the basal plane—is weak and compliant. High‐performance carbon fibers must make use of the strong directions while suffering from the poor properties of the third. This paper describes, from fundamentals, the processes used to produce high‐performance carbon fibers. The resulting fiber microstructures and the consequences of these structures on properties are presented.
The potential mechanical response of macromolecular systems—A composite analogy
Authors: Kardos J. L. , Raisoni J.
Published: December 2004

A variety of macromolecular systems including crystalline and oriented thermoplastics, block copolymers, and flexibilized thermosetting resins can realistically be viewed as composite systems. This paper examines the utility of using predictive methods developed for two‐component engineering composites to predict the mechanical properties of macromolecular systems. The concepts presently available for the prediction of stiffness and expansion coefficients of short‐fiber rein‐forced plastics are reviewed with respect to their engineering accuracy in structural systems design. These techniques are then applied to predict the stiffness of a hybrid polymer system lying midway between an engineering composite and a crystalline polymer. The hybrid consists of a polymer matrix (butadiene‐acrylonitrile copolymer) reinforced with in‐situ crystallized, low‐molecular‐weight filler (acetanilide). Finally, the composite approach is applied to the prediction of stiffnesses and expansion coefficients of crystalline polyethylene as a function of volume fraction crystallinity and crystallite morphology.
Conformational considerations of high‐modulus polymers
Authors: Allegra G.
Published: December 2004

Some general considerations are given concerning the conformational factors affecting the inherent elastic modulus of the macromolecular chains in the crystalline state. In particular, the influence of the size of side groups and that of the chain extension are discussed. Some conformational properties concerning two polymers with different stiffness, both containing amide groups, are clarified.
Studies on polymer texture formation in complex external conditions
Authors: Ziabicki Andrzej
Published: December 2004

The program of studies carried out in the Institute of Fundamental Technological Research concerning fundamentals of polymer crystallization and orientation is briefly described. Discussions center on studies of polymer texture formation caused by complex external conditions.
Control of molecular orientation
Authors: Alfrey Turner
Published: December 2004

I. Amorphous polymers. The mechanical performance of a glassy amorphous polymer is strongly dependent upon molecular orientation. The pattern of molecular orientation is governed by the kinematics (and temperature) of mechanical forming operations. Three types of controllable orientation are: (a) uniaxial, (b) biaxial, and (c) “crossed.” The optimum pattern of orientation in a part is one which is appropriate for the mechanical stresses encountered in service. For a fiber subjected to tensile and bending loads, uniaxial orientation is appropriate. A shell structure, subjected to multiaxial stresses, requires either biaxial or crossed orientation for maximum performance. As a rule, the maximum achievable multidirectional strength in such a structure is less than the maximum strength of a uniaxially oriented fiber.

II. Crystalline polymers. Oriented crystalline polymer structures can be created in two distinct ways. An isotropic polycrystalline polymer can be deformed below the melting point, with extensive reorganization of the crystal morphology, or an oriented amorphous melt can undergo crystallization to yield oriented crystalline polymer. Performance of an oriented semicrystalline polymer depends upon orientation of the amorphous portion as well as orientation of the crystallites. As with amorphous polymers, orientation can be uniaxial, biaxial, or crossed. “Orientation” usually denotes c‐axis orientation only, but drawing followed by rolling can result in double orientation—orientation of a‐axis, b‐axis, and c‐axis.
A study of the fatigue behavior of fiber reinforced nylons
Authors: Dibenedetto A. T. , Salee Gideon , Hlavacek Robert
Published: December 2004

A phenomenological model combining a Weibull distribution function with a kinetic equation for flaw growth has been used to describe the static tensile strengths and fatigue lives of short graphite‐fiber reinforced nylon 66 materials. A simple Weibull function of the form \documentclass{article}\pagestyle{empty}\begin{document}$ P\left( {\sigma _b } \right) = \exp - \left( {{{\sigma _b } \mathord{\left/ {\vphantom {{\sigma _b } {\hat \sigma }}} \right. \kern-\nulldelimiterspace} {\hat \sigma }}} \right)^{9.5} $\end{document} described the distribution of static strengths. The scale factor \documentclass{article}\pagestyle{empty}\begin{document}$ {\hat \sigma } $\end{document}
varies with the annealing treatment and, in general, is a function of environmental variables. The cumulative distribution of breaking times in fatigue can be characterized by a translated three parameter Weibull function \documentclass{article}\pagestyle{empty}\begin{document}$ P\left( {t_B } \right) = \exp - \left\{ {\left. {\left( {\frac{{\sigma _{\max } }}{{\hat \sigma }}} \right)^{16} + \frac{{t_B }}{{\hat t}}} \right\}} \right.^{0.59} . $\end{document} The average time to break (which is related to the time scale factor \documentclass{article}\pagestyle{empty}\begin{document}$ {\hat t} $\end{document}), appears to be a function of the flaw growth rate. The distribution equation has been found to predict the number of half cycle failures and is thus a valid model for the proof testing of large populations. An electrical resistivity method was developed to measure flaw growth rates in prenotched cantilever beams. Experimental data fit the following equation: ln (Δa/Δn) = −88.88 + (12.46 ± 5.68) ln (Keff)max. The correlation coefficient was 0.81. From curve fitting of fatigue data it appeared that flaw growth rate varied with the ninth power of flaw length (Δa/Δn) = Ma9. The direct measure of flaw growth rate using electrical resistance gave Δa/Δn = Ma6.23±2.84 with 90 percent confidence. The two measurements overlap within the 90 percent confidence bands, but predictions of fatigue life using the flaw propagation data were not good. Scanning electron microscope studies showed that specimens with a short fatigue life have glassy, fibrillated fracture surfaces while specimens with a long fatigue life exhibit a high degree of ductility in portions of the fracture surface. These differences are traced to differences in the size and shape of flaws.
Some observations on the long‐term behavior of stabilized polyethylene
Authors: Howard J. B. , Gilroy H. M.
Published: December 2004

Much has been written on the theoretical mechanisms by which the oxidation of polyolefins is believed to proceed and on the role of stabilizers in impeding this process. Relatively little information is available on the effects of some of the interesting, practical considerations—stress, stabilizer stability and the consequences of crystalline content and texture to name a few—which exert a controlling influence on the behavior of these materials in real‐life situations. Data are presented on the aging behavior of low‐ and high‐density polyethylenes at temperatues in the range 50‐110°C in the presence of copper and on the utility and limitations of oxygen absorption and differential thermal analysis as tools for accelerated prediction of this behavior.
Mica reinforced polypropylene
Authors: Okuno K. , Woodhams R. T.
Published: December 2004

An experimental study was carried out to investigate the flow behavior and the viscosity of mica flake‐filled polypropylene melts and the mechanical properties of mica‐polypropylene composites. The properties of the molded composites exhibit moduli which are higher than most filled polymers. Tensile strength values are noticeably improved when a silane coupling agent or a carboxyl‐modified polypropylene is employed, although the extent of improvement is not great. A high processing temperature helps to minimize flake damage and to improve flow orientation of the flakes.
Structure and properties of polypentenamer
Authors: Tucker Harold , Minchak R. J. , Macey J. H.
Published: December 2004

Trans‐1,5‐polypentenamer (TPP) has some similarity to natural rubber partly because of properties that relate to crystallinity and to the position of the crystalline melting point. This similarity makes TPP a unique rubber among other synthetic hydrocarbon polymers. Requirements for attaining a good balance of physical properties include adjustment of both micro and macrostructure with processability. Natta, Dall'Asta, Haas and Pampus have described the preparation of polypentenamers based on tungsten or molybdenum catalysts. Since Eleuterio made his disclosure, there have been many important contributions disclosing special conditions for preparing TPP or variations in catalyst preparation including many catalyst activators. Natta and Dall'Asta vulcanized both the TPP and the amorphous cis‐1,5‐polypentenamer (CPP). They showed that TPP (melting point 23°C) gives good tensile properties even in pure gum vulcanizates characteristic of rubbers that crystallize on stretching. CPP gave better low‐temperature characteristics than other hydrocarbon elastomers (SBR rubber, propylene oxide/allyl glycidyl ether copolymer, cis‐1,4‐polybutadiene). For example, the CPP vulcanizates were less brittle down to −90°C measured by 100 per cent moduli and, in a comparison of temperatures at which retraction occurred, CPP showed a superiority. With CPP from 25°C to −70°C, both tensile strengths and moduli increased without appreciable variation of elongation at break. Since the crystalline melting point at rest is near 20°C for TPP, the elastic behavior is governed by this transition rather than the glass transition point (−90°C).

The rate of crystallization for TPP is more rapid compared to natural rubber. Although vulcanization is a factor on elastic behavior, we suggest that further compromise may be necessary to balance the desirable properties related to crystallinity while maintaining elasticity at lower temperatures. The summary of the Haas paper noted that TPP rubber is outstanding except that the abrasion, wet skid and heat build‐up are inferior to existing tread rubber types. Our efforts suggest that TPP is not inferior.

In our examination of TPP's having varied or lowered melting points, vulcanizates (tread recipes) with good low temperature flexibility were developed from TPP with Tm of 5°C. Since tack and green strength are dependent on both the micro and macrostructure, properties lost by decreasing the trans content or the Tm were offset by increasing the molecular weight. With higher molecular‐weight TPP, other properties such as heat build‐up and abrasion were improved or made equivalent to other tire rubbers. Thus, by optimizing molecular weight, oil level and processability with the microstructure, a good balance of properties may be produced for TPP rubber.
Gas transmission through polymers
Authors: Horsfall F. , James D. I.
Published: December 2004

Little data is available on gas transmission through thick polymer samples. There is, therefore, a temptation to assume an inverse relationship between gas transmission rate and thickness and to calculate flow through thick samples using permeability data obtained on thin films. This is incorrect, as the calculation assumes steady flow, and with thick samples this state may not be reached for months or even years. Thus both diffusivity and permeability are needed to calculate the gas flow and the calculations are more complex than simple permeability calculations. Because of the long time scale, the effects of varying the thickness are difficult to demonstrate experimentally. We describe a computer simulation of the manometric method which compares the behavior of two materials with similar permeabilities but different diffusivities. Although thin samples behave identically, they differ increasingly with thickness. The pitfalls in using the gradient and time lag of the pressure curve to calculate permeability and diffusivity are also discussed.
Studies of polyethylene shish‐kebab structures
Authors: George Waller , Tucker Pual
Published: December 2004

An experimental method initiated by Williamson and Busse has been extended to produce veil‐free shish kebab structures in linear polyethylene without need for severe recovery treatments. The technique involves the dilution of polymer in a concentrated solution of low molecular weight paraffin followed by a simple isothermal shear. The resulting shish kebab structures are isolated from the wax matrix and subjected to electron microscopical and electron diffraction study. From the diffraction patterns, it is shown that the shish‐rich ordered structure is similar to the orthorhombic structure of crystalline linear polyethylene, but with certain significant deviations. The resolvable morphology of the shish appears to be characterized by a length‐to‐diameter ratio which is consistent with a prediction based upon Wulff's theorem utilizing certain relevant surface energy values which have been obtained by others for polymeric crystals.
Fatigue crack growth in polymers. I. Effect of frequency and temperature
Authors: Radon J. C. , Culver L. E.
Published: December 2004

The effects of frequency, from 0.1–100 Hz, and temperature, −60°C to +21°C, on fatigue crack propagation in poly (methyl methacrylate) and polycarbonate were investigated. A cyclic crack propagation law proposed by Arad‐Radon‐Culver, namely

where λ is (Kmax2‐Kmin2) and Kmax and Kmin are the respective values of maximum and minimum stress intensity factor, was applied to describe a relationship between crack growth and cyclic life. Cyclic tests performed in tension between zero load and Kmax showed a linear relationship between the crack lengths and the number of cycles for all temperatures and frequencies tested. It was found that, in general, the cyclic crack growth decreased with decreasing temperature and increasing frequency. However, important exceptions to this rule have been noted.
Melt solidification in polymer processing
Authors: Gutfinger C. , Broyer E. , Tadmor Z.
Published: December 2004

This paper treats two cases of polymer melt solidification in rectangular geometry. The cases treated are the one of static solidification and that of solidification during flow in a narrow gap channel. Both cases are solved using the method of Dussinberre, which reduces the two‐phase moving boundary case to a single phase problem, simplifying the mathematics considerably. The numerical solutions are based on a combination of the concept of flow analysis network (FAN), a finite element method developed for solving polymer flow problems, with a Crank‐Nicolson implicit finite difference scheme. The methods may be used in computing the cooling down period and preventing “short” conditions in injection molding dies. Examples of solidification of high density polyethylene illustrate the applicability of the method.
The effects of extrusion on the molecular and rheological properties of general‐purpose polystyrene
Authors: Springer Paul W. , Brodkey Robert S. , Lynn R. Emerson
Published: December 2004

A study of the effect of extrusion on the rheological and molecular properties of general‐purpose polystyrene is presented. Polystyrene was recycled through a 2 1/2‐in. extruder five times at medium and high screw speeds. Rheological properties were measured on‐line and the molecular properties determined by gel permeation chromatography. Results indicated Mw is more susceptible to degradation than is Mn: therefore polydispersity decreases. After five extruder passes, Mw decreased 17 percent at the medium and high screw speeds. Changes in the low shear viscosity correlated with the decrease in Mw on a log‐log plot. An energy‐available‐for‐degradation factor, ED, was calculated from extruder operating conditions. An Arrhenius type correlation related ED with changes in Mw and low shear viscosity. Results indicated a definite effect of screw speed and a critical value of ED above which the degradation rate was increased.
Dehydrochlorination of poly(vinyl chloride)
Authors: Chang Eng Pi , Salovey Ronald
Published: December 2004

PVC has been dehydrochlorinated with alcoholic alkali in soution at 7°C for different lengths of time. At early stages of dehydrochlorination the dominant reaction is intramolecular removal of HCl and this gives rise to two intense Raman bands at ∼ 1126 (ν1) and ∼ 1518 cm−1 (ν2) and following UV irradiation, to a quadruplet ESR spectrum. Increasing polyene sequence length and intermolecular removal of HCl at later stages of reaction alters the quadruplet signal to a singlet, shifts ν1 and ν2 to lower frequencies and increases the molecular weight. The presence of polyene units stiffens the chain and increases the elastic modulus. The Tg is, however, lowered slightly due to the removal of bulky chlorine atoms which relieves steric hindrance and dipole interaction between neighboring chains. The β‐transition is also rendered less distinct.
Crystaline polymers as heat storage materials in passive thermal protection systems
Authors: Kaelble D. H. , Cirlin E. H. , Dynes P. J.
Published: December 2004

Previous studies have evaluated low molecular weight crystalline materials as latent heat sinks for passive thermal protection systems. This study evaluated crystalline polymers as heat storage materials. Differential scanning calorimetry and Instron thermomechanical analysis are applied in dynamic studies of cumulative histories of melting and recrystallization. Commercially available crystalline polymers with melting temperatures Tm ≥ 100°C can provide fully reversible heats of fusion ΔHm ≥ 35 cal/gm under programmed heating‐cooling cycles. A linear polyethylene (Marlex 6050) is modified by radiation crosslinking to retain shape stability above Tm with‐out loss of heat storage capability. The essentially zero vapor pressure and inherent shape stability of crosslinked crystalline polymers may provide unique advantages as uncontained, non‐expendable, heat storage materials.
Materials for biomedical applications
Authors: Le May I. , Lappi V. G. , White W. E.
Published: December 2004

The various materials used in biomedical applications, viz., metals and alloys, polymers, ceramics, and composites, are reviewed, and their respective areas of application discussed. Problems of compatibility with tissue and body fluids are reviewed and the performance of the various materials systems examined. Some examples of failure of implanted devices are shown, and the need for careful control of quality as well as of material specification is emphasized. Finally, the importance of close cooperation between medical, engineering and metallurgical specialists in this area is noted, together with the requirement of a better knowledge of materials on the part of the surgical personnel involved.
Microstructure and ordering in cellulose acetate and reverse osmosis membranes
Authors: Arneri G. , Sauer J. A.
Published: December 2004

The performance of cellulose acetate reverse osmosis membranes for desalination or purification is greatly affected by the microstructure of the membrane. It is, therefore, highly desirable to characterize the microstructure and its dependence on preparation conditions and past history. In this study, various types of cellulose acetate powders, flakes, and solvent cast films have been characterized by differential scanning calorimetry and thermo‐optical analysis. It is shown that ordered microstructures exist in many of these samples and that this ordering can be intensified or diminished by suitable treatments. It is conjectured that a similar microordering occurs in the dense layer of asymmetric cast membranes as a result of solvent evaporation, gelation and annealing and that the extent of orientation and chain packing in the ordered regions greatly affects the performance of reverse osmosis membranes.
Structural damping of composites under sustained vibratory stresses
Authors: Sharma M. G. , Hong C. S.
Published: December 2004

The dynamic properties of a fiber‐reinforced composite under uniaxial sinusoidal stresses have been studied and the dynamic modulus and loss coefficients have been evaluated. Effects of fiber orientation to applied stress, the magnitude of static biaxial stresses, frequencies of fluctuating stresses and the temperature on the dynamic properties have been studied. The paper describes a dynamic biaxial testing machine specially developed for the measurement of dynamic properties of fiber‐reinforced materials for a low frequency range. Results indicate that the single laminate material displays very little damping. However, the multilaminate material reveals an appreciable damping that is dependent on the frequency of fluctuation of applied stress. The loss coefficient for the multilaminate material was found to decrease with frequency and was appreciably affected by fiber orientation, magnitudes of mean biaxial stresses, and temperature. Finally, an examination of data indicated that the time‐temperature equivalence hypothesis can be applied. Using this principle, master loss coefficient curves for an extended frequency range have been obtained.
An analysis of the rheology of polypropylene below its melting point
Authors: Funt John M.
Published: December 2004

Three sets of data for the deformation of crystalline poly‐propylene in uniaxial tensile tests and uniaxial creep, in equal biaxial creep and in planar shear are examined. The methods of analysis used in the original papers, all based on variants of linear elasticity, are critically evaluated, and a constitutive equation based on the theory of a simple fluid with memory is proposed.
The application of structure—Property studies to structural foams
Authors: Hobbs S. Y.
Published: December 2004

A brief review of papers dealing with the formation, physical properties, and characterization of foams is given. Since the number of such articles on structural foams per se is small, an attempt is made to summarize a number of related studies which contain information of general relevance or which may be extended to provide a base for more extensive work in thermoplastic structural foams. Several critical research areas are identified.
Dynamic mechanical evidence for the glass transition of high density polyethylene
Authors: Paauwe Neil A. , Knox Jack R.
Published: December 2004

The effects of shock cooling and swelling with carbon tetrachloride on the dynamic mechanical spectrum of high density polyethylene have been studied with a torsional pendulum. The resulting spectra have a well‐defined loss peak at −65°C which is associated with the glass transition of high density polyethylene. Similar experiments on polypropylene and low density polyethylene demonstrate the similar effects of these treatments on their glass transitions.
Rheovibron determination of the dynamic moduli of polymer melts
Authors: Shah Basit H. , Darby Ron
Published: December 2004

This article describes the use of the Rheovibron Model DDV‐III‐B with a parallel plate modification of the sample holders to obtain oscillatory data in the shear mode for several high density polyethylene melts. A detailed analysis of the Rheovibron to obtain the dynamic shear: moduli of polymer melts using the new sample holders is given, as well as a procedure for determining the instrument compliance and inertia parameters which must be considered in analysis of the data. Using the principle of time‐temperature superposition, the data are extended to an equivalent frequency range of 1500 rad/sec. These data are compared with those obtained using the Weis‐senberg Rheogoniometer Model R‐17 for the same polymers. It is concluded that reliable measurements for dynamic shear moduli for polymer melts using the Rheovibron Model DDV‐III‐B with the modified sample holders can be made for melts with indices of about 5 or less (i.e., zero shear viscosities of 6.0 × 104 poise or greater).
Induced photodegradation of styrene polymers: A survey
Authors: Sheldrick G. E. , Vogl O.
Published: December 2004

Although polymeric materials have a relatively minor role in our solid waste disposal problems, they display a particular prominence as litter because of their environmental permanence, Photodegradation has been suggested as one possible solution, but considerable debate has centered on the need, costs, and limitations of such degradable systems. The chemical mechanisms involved in practical photodegradation are illustrated by a review of the oxidation schemes for normal and sensitized polystyrene. The different mechanisms associated with the use of additives, comonomers, and halogens are considered in some detail. A listing of patent literature relating specifically to photodegradable polystyrene is included in the review.
Impact strength of polymers: 1. The effect of thermal treatment and residual stress
Authors: Broutman Lawrence J. , Krishnakumar Suppayan M.
Published: December 2004

The effect of thermal annealing and quenching on the notched Izod impact strength of several polymers has been studied. Primary emphasis was placed on polycarbonate, but ABS, PVC, polysulfone, and polymethylmethacrylate were also studied. It was determined that residual stresses created by thermal quenching from above the glass transition temperature can have a great effect on impact strength for the polycarbonate, PVC, and polysulfone polymers studied. In fact, it is shown that the thickness transition observed in impact strength for polycarbonates is governed by the residual stresses and not by thickness. In polycarbonates, quenched sheets up to 3/8 in. in thickness have shown impact strengths of 18 ft‐lb/in. whereas sheets 1/8 in. in thickness can be embrittled by annealing, showing an impact strength of 2 ft‐lb/in. However, it has been shown that this embrittlement results from the absence of residual stress. Residual stresses having maximum values up to 3000 psi (in Compression) have been determined at the polycarbonate sheet surface using birefringence measurement techniques. The existence of these compressive stresses is postulated to restrict the extent of craze growth at the notch tip, and the impact specimen can yield rather than fail in a brittle manner if the stress state is sufficient.
Phase structure and continuity in polymer blends and composites
Authors: Sperling L. H.
Published: December 2004

Polymer blends and composites are composed of two different components, and usually, two different phases. Sometimes one phase is continuous and the other clearly discontinuous. Often, however, both phases retain some degree of continuity, as in certain fiber reinforced composites, block copolymers, materials composed of alternating lamellae structures and interpenetrating networks. A semi‐empirical theory is developed to express mathematically not only the known structures, but also two‐phase morphologies not yet synthesized or characterized. Many structures both real and proposed are shown to exhibit dual phase continuity, although for most systems, one phase can be said to be “more continuous” and the other “less continuous”.
A study of chain addition polymerizations with temperature variations: II. Thermal runaway and instability—a computer study
Authors: Biesenberger J. A. , Capinpin R. , Yang J. C.
Published: December 2004

A computer study was made to determine the thermal ignition criteria and ignition boundaries for chain‐addition polymerization in a well‐mixed batch system using a simple kinetic model. The occurrence of thermal runaway was shown to be a function of initiator type, feed conditions, and heat transport parameters. It was found that thermal runaway does not occur early with respect to monomer and initiator conversions and that for strongly dead‐ending systems, the sensitivity characteristic of ignition disappears. The role of various dimensionless parameters in characterizing reaction behavior is also discussed.
Strain‐induced crystallization II. Subsequent fibrillar‐to‐lamellar transformation
Authors: Yeh G. S. Y.
Published: December 2004

Part II discusses numerous examples of a morphological fibrillar‐to‐lamellar transformation that has reportedly been observed in stretched polymers upon additional thermal treatment (or TIC), Stretched polymers containing initially a typical fibrillar morphology for either crystallites in cold‐drawn polymers, crystallites induced by stretching, or simply non‐crystalline fibrils can yield a more or less lamellar morphology after the thermally‐induced transformation. There is no evidence of extended‐chain crystals present in either the original fibrils or the transformed lamellae; however, the extent of the transformation is strongly dictated by the annealing conditions and the stretch ratios, and therefore the local strains on tie molecules between the crystallites. Of particular interest is the observation of lamellar formation in conjunction with decreasing stress (or increasing length) during TIG under strain. This is in conflict with the generally expected stress increase if chain folding is presumed to occur during formation of lamellae, Consequently, it leads to the conclusion that lamellae form from prefolded structures during TIC. In the light of this surprising conclusion, available evidence on the presence of structure or non‐Gaussian chain segments in the amorphous state is also cited. Included are the most recent neutron scattering results from concentrated solutions of polystyrene.
Disruptive processes in the shear crystallization of poly(ethylene oxide)
Authors: Fritzsche A. K. , Price F. P. , Ulrich R. D.
Published: December 2004

The crystallization behavior of samples of poly(ethylene oxide) of varying molecular weights and molecular weight distributions has been studied under varying conditions of shear rate and temperature. These experiments have been carried out in two devices. One is a shearing parallel‐plate instrument that allows direct observation of the crystallizing medium. The other is a shearing concentric‐cylinder dilatometer. In general, shear enhanced the rates of crystallization and nucleation. However, conditions were encountered under which shear retarded crystallization and/or nucleation. Combination of the data from these two devices suggests that, under certain shearing and sample conditions, chain slippage and particle fracture lead to decreased apparent rates of nucleation and/or crystallization.
Flow‐induced crystallization of polypropylene in stretched ribbons
Authors: Andersen P. G. , Carr S. H.
Published: December 2004

Ribbons of molten polypropylene have been extruded into a thermostatted chamber and subjected to elongations ranging as high as 4400‐fold. Some of these ribbons have been shown to possess the unusual ability of recovering nearly all of the strain from large levels of stretch (≤100 percent). This property, as well as the magnitude of the tensile yield drop, has been found to be directly proportional to the uniaxial character of the flow present at the moment of crystallization. The structure in the final solid films has been characterized by wide angle X‐ray diffraction and crystal orientation distribution. Both of these factors have been found to be proportional to the character of flow at the moment of crystallization. Finally, the temperature in the thermostatted chamber has been shown to affect the character of the flow.
Structure studies of chemically etched poly(ethylene terephthalate) film
Authors: Adams G. C.
Published: December 2004

A macrostructure consisting of 1500 Å long network, elements has been studied in unoriented and oriented poly(ethylene terephthalate) film. The long dimension of the structure is oriented transverse to the stretch direction. A length to width ratio of approximately 10:1 is observed. The structure is observed by scanning electron microscopy after room temperature etching with n‐propylamine under special conditions. Also studied are weight loss measurements for up to 80 hrs of etching and molecular weight degradation by gel permeation chromatography. The induction time before weight loss commences depends on sample elongation and thermal history. A coincidence of the following times are observed: (I) commencement of weight loss, (2) development of a well‐defined macrostructure by SEM, and (3) completion of molecular weight degradation. Therefore, visual evidence of a macrostructure occurs when weight loss has commenced which requires degradation to products soluble in the etchant. The GPC curves vs rich time show that etched film oriented to a crystalline state possesses two molecular weight peaks. The peak for polymer in which no degradation occurred is replaced by a peak for polymer of nine to ten repeat units which is highly crystalline and, therefore, resistant to further attack.
Using system identification to determine the thermal properties of plastics
Authors: Peter John W. , Tarvin Ronald L.
Published: December 2004

This article describes a new experimental and analytical method for determining the specific heat and thermal coductivity of plastic materials. This method arrives at these temperature‐dependent properties by analyzing the thermal history of a slab of the plastic material. The procedure is as follows: 1) A partial differential equation model of the heat flow through the slab is established a priori. 2) A varying heat flux is a applied to the slab, and temperature readings throughout the plastic are recorded at fixed time intervals. 3) This temperature data is fed into a digital computer (along with the established mathematical model) and the required specific heat and thermal conductivity values are extracted. The extraction is done by using the maximum likelihood system identification technique.
Relationship between torque and capillary rheometer thermal stability measurements for PVC compounds
Authors: Collins E. A. , Metzger A. P. , Furgason R. R.
Published: December 2004

A method is described to predict the time‐temperature behavior and hence thermal stability of PVC melts in a Brabender Plasticorder torque rheometer from basic rheological data(flow and thermal stability observations) obtained on an Instron capillary rheormeter. The predicted and experimentally determined values of the Brabender thermal stability are shown to be in good agreement.
Rotational molding heat transfer—an update
Authors: Throne James L.
Published: December 2004

In earlier works, a complicated circulation model was chosen to describe heat transfer to powder in a rotating mold. In order to satisfy the model, an experimentally‐determined empty mold temperature response was used. An alternate heat transfer model, in which the powder is assumed to be in static contact with the mold surface at all times, shows significant temperature deviation from the earlier model. The predicted time for complete sinter‐melting is much closer to earlier experimental data than the predicted times from the circulation model. The melting time is seen to follow the form given by the Goodman penetration model. Complete heating and cooling profiles are more easily generated using this static model, and a new interpretation of the air cooling step in the heat transfer cycle results.
The influence of anisotropic phase structure on the properties of crystalline polymers
Authors: Samuels Robert Joel
Published: December 2004

By combining quantitative molecular, microscopic and macroscopic information from an oriented crystalline polymer, it becomes possible to unify, predict, and explain not only processing behavior but such important material properties as failure, shrinkage, modulus, yielding, melting, and storage and loss moduli. Among the advantages gained by this approach are the ability to: (a) identify the particular phase of the two‐phase system which controls a given property‐(b) correlate internal structure quantitatively with a large number of seemingly different types of properties; (c) identify quantitative behavioral rules which are generally valid for Very different crystalline polymers; (d) clarify component roles such that new techniques and processes result; and (e) predict the properties of a crystalline polymer for structural states not previously tested. Using two dissimilar crystalline polymers, isotactic polypropylene and poly(ethylene terephthalate), as examples, the general validity and unifying power of the structural approaches is demonstrated.
The mechanism of the stereoregular polymerization of 2‐vinylimidazole and 2‐vinylbenzimidazole
Authors: Lando J. B. , Litt M. , Shimko T. , Kumar N. G.
Published: December 2004

Conformational energy calculations on poly(2‐vinylimidazole) (PVI) and poly (2‐vinylbenzimidazole) (FBI) indicated that the syndiotactic polymer would exhibit systematic intramolecular hydrogen bonding between side groups along the chain, while the isotactic polymers could not. This fact, together with our previous wor.k using solvent effects to produce highly syndiotactic poly(methacrylic acid) during radical polymerization, indicated that similar techniques could be applied in the radical polymerization, of 2‐vinylimidazole and 2‐vinylbenzimidazole. These mpnomers were polymerized over a wide temperature range using cobalt 60 gamma radiation as the initiator. The conditional probabilities obtained from NMR spectra of these polymers could be fit by second order Markov statistics (FBI) and extended second order Markov statistics (PVI). The difference reflects the effect of the bulkier benzimidazole side group. The nature of the conditional probabilities needed to fit the data for PVI suggest that the stereoregularity depended on the number of consecutive terminal r placements at the end of the growing radical. A marked solvent effect was observed was attributed to the hydrogen bonding strength of the solvent and its ability to disrupt the r directing polymer hydrogen bonding.
Nonlinear viscoelasticity of “hard elastic” polypropylene fibers
Authors: Chen Hyland Y‐L , Ko Frank K. , Lundberg John L.
Published: December 2004

“Hard elastic” polypropylene fibers respond nonlinearly to stress at all strains. Low tenacities at break (less than 1 g/denier), low moduli of elasticity (slopes of stress‐strain curves from 2.8 to 28 g/denier), and large breaking extensions (over 800 percent) are characteristic of “hard elastic” fibers. Behavior in simple extension, cyclic extension, and stress relaxation can be represented by a quasi‐linear viscoelastic model which uses a continuous relaxation spectrum and a quasilinear relation between stress history T(t)and strain history λ(t):

where Te[λ(t)] is the elastic response. When creep data are available, this model should provide a unified representation of experimental observations.
The mechanical and thermal properties of graphite fiber reinforce polyphenylquinoxaline and polyimide composites
Authors: Sung Nak‐Ho , McGarry Frederick J.
Published: December 2004

Comparative studies were made on the fabrication characteristics, mechanical properties and thermal stabilities of three commercially available composite systems based on linear monoether polyphenylquinoxaline, P13N polyimide, and Skybond 703 polyimide, reinforced with Modmor II graphite fibers. Fabrication parameters and prepreg conditions were related to the properties of the laminates. Interlaminar shear strength and flexural properties were evaluated before and after the thermal aging at 600°F for periods up to 500 hrs. Thermal degradation of composites at various stages of thermal' aging was studied using optical and scanning electron microscopes.
Morphology and dynamic mechanical spectra of crystalline copolymers of ethylene and acenaphthylene
Authors: Bailey F. E. , Walter E. R.
Published: December 2004

In a previous paper, results of morphological studies using electron microscopy and X‐ray diffraction were reported concerning random and non‐random olefin copolymers of ethylene. As comonomers, relatively low concentrations of n‐alpha alkenes and 5‐methyl norbornene‐2 were used. It was tentatively concluded that one possibility for morphological changes observed in the n‐alpha alkene copolymers was a change in direction of chain folding. These studies have been continued with copolymers of ethylene and acenaphthylene. The intent was to pursue effects of vicinal substitution; however, the result was to produce ethylene copolymers of quite high comonomer content which were crystalline and showed no evidence of an independent beta mechanical transition. Further, definite evidence was found to indicate a change in the direction of chain folding in the polymer crystals.
Thermal analysis of dielectric insulation, ethylene/propylene rubbers, and cross‐linked polyethylenes decomposed in a nitrogen atmosphere
Authors: Abou‐Shaaban Rafiq R. A. , Haberfeld Joseph L. , Barrall Edward M. , Johnson Julian F. , Simonelli Anthony P.
Published: December 2004

The techniques of thermogravimetric and derivative thermogravimetric analyses have been applied to the determination of temperatures and heats of decompositions of four ethylene/propylene rubbers and seven cross‐linked polyethylenes in nitrogen. These materials are commonly used in the wire and ruble industry as dielectric insulation. The polymers were found to decompose in at least three overlapping stages. Each stage has an activation energy characteristic of the process. Differential thermal analysis was significantly less useful in this study due to the conflict of the endothermal heat of vaporization and the exothermal heat of decomposition.
Parameter testing of epoxy polymer concrete
Authors: Tolbert R. N. , Hackett R. M. , Baluch M. H.
Published: December 2004

The ultimate strength of polymer concrete was investigated utilizing epichlorohydrin/bisphenol A‐type epoxy resin. Parameters were tested in an effort to conclude how variation of a specific parameter would affect the compressive strength of the polymer concrete. The parameter testing included studies to determine the effect of the polymer loading; the catalyst; the exothermic reaction; aggregate type, gradation and moisture content; curing age; and aggregate additives of portland cement and lime‐stone powder.
Mechanical properties of biaxially oriented poly(vinyl chloride)
Authors: Brady Thomas E.
Published: December 2004

This report describes the influence, of (a) degree of biaxial orientation, (b) stretching rate, and (c) stretching temperature on the tensile, dynamic mechanical and dielectric properties of non‐impact modified PVC. A new parameter designated “planar strain” is used to correlate anisotropic property values with both equal and unequal biaxial stretching in a single two‐dimensional plot, thereby providing a direct comparison of the effects of two or more biaxial stretching ratios. It is shown that optimum stretching conditions depend to some extent upon end use and that a 2 × 2 stretch ratio is optimum for impact resistance. The actual property/processing condition relationships exhibit very complicated interactions and are correlated empirically in this study. The dynamic measurements suggest that overall local segmental beta motion is increased after orientation but that the relative chain alignment makes it more difficult to activate this motion.
The quantitative differential thermal analysis determination of polyolefin stabilization
Authors: Wight F. R.
Published: December 2004

Quantitative Differential, Thermal Analysis has been used in the wire and cable industry for determining the degree of oxidative stability of polyolefins for quality control purposes in lieu of a direct antioxidant analysis, However, it has never been shown whether the presence of each additive in a stabilizer package could be detected by this method. The results presented here indicate that the presence of a primary antioxidant and a copper inhibitor in combination can be detected separately by comparing the oxidative induction times in copper and aluminum pans. The addition of a thioester synergist such as distearyl thiodipropionate, DSTDP, is evidenced by an increased induction time in aluminum pans. However, the presence of DSTDP makes it impossible by this method to determine whether an effective level of copper inhibitor is present since the sample shows a reduced stability on copper compared to aluminum. One of two factors can be invoked to explain these results: a) DSTDP interferes with the complexing ability of the copper inhibitor or b) the copper‐inhibitor complex retards the synergistic effect of the DSTDP. In either case, this factor is not important at lower temperatures since oxygen uptake data at 130°C indicate that DSTDP is an effective synergist in the presence of copper.
Open cell poly(vinyl chloride) foams by mechanical frothing of plastisols
Authors: Deanin Rudolph D. , Calcuttawala Aziz H. , Kapasi Vikram C.
Published: December 2004

PVC plastisols were formulated with silicone surfactant, mechanically shipped to form froths, and oven‐fused to form open‐cell foams. These were much softer than conventional chemically‐blown foams which contain mixtures of open and closed cells. Increasing plasticizer content and decreasing foam density also had the expected softening effects on foam properties.