bluuebunny/crossref_metadata_2025_split huggingface dataset:
Some critical issues in advanced polymer science
Authors: Halpin John C. 
Published: December 2004

AbstractTheoretical 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

AbstractGraphite 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

AbstractA 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

AbstractSome 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.
Control of molecular orientation
Authors: Alfrey Turner 
Published: December 2004

AbstractI. 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

AbstractA 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

AbstractMuch 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

AbstractAn 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

AbstractTrans‐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

AbstractLittle 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

AbstractAn 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

AbstractThe 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

AbstractThis 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

AbstractA 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

AbstractPVC 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

AbstractPrevious 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

AbstractThe 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

AbstractThe 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

AbstractThe 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

AbstractThree 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

AbstractA 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.