bluuebunny/crossref_metadata_2025_split huggingface dataset:
Impact fracture mechanisms in polymer blends: Rubber‐toughened nylon
Authors: Wu Souheng 
Published: April 2003

AbstractThe impact fracture mechanisms of rubber‐toughened nylon are analyzed by measuring the energy dissipated in several different processes during notched fracture. An energy balance is thus established for the impact fracture. The stress‐whitened zone is shown to be the energy dissipation zone, having an energy dissipation density of 5.30 cal/g. About 25% (i.e., 1.44 cal/g) of the impact energy is dissipated by matrix crazing. About 75% (i.e., 3.86 cal/g) is dissipated as heat by matrix yielding, causing a temperature rise of 9.1 °C in the energy dissipation zone. Surface energy storage on the fracture surfaces is negligible (i.e., 1.45 × 10−5 cal/g). During matrix yielding, about 12% of α‐triclinic nylon crystals is transformed into pseudohexagonal crystals.
Raman scattering from the longitudinal acoustic mode of oligo‐oxyethylene
Authors: Viras K. , Teo H. H. , Marshall A. , Domszy R. C. , King T. A. , Booth C. 
Published: April 2003

AbstractLow‐frequency Raman spectra are reported for monodisperse oligo‐oxyethylenes with hydroxy and alkoxy end groups. Assignments are made to the longitudinal acoustic modes. The results are modeled by a rod with a longitudinal modulus E ≥ 2.2 × 1010 N m−2 and perturbing forces as large as (alkoxy‐ended oligomers) or larger than (hydroxy‐ended oligomers) those suggested for the n‐alkanes.
The swelling interface number as a criterion for prediction of diffusional solute release mechanisms in swellable polymers
Authors: Peppas Nikolaos A. , Franson Nancy M. 
Published: April 2003

AbstractWhen a glassy polymer containing a uniformly dispersed solute is brought in contact with a penetrant, solute diffusion will be associated with the transport mechanism and penetration velocity of the penetrant in the polymer. Analysis and prediction of mechanisms of diffusional solute release may be obtained through a new dimensionless number, the swelling interface number, Sw, which compares the relative mobilities of the penetrant and the solute in the presence of macromolecular relaxations in the polymer. It is shown that a sufficient and necessary criterion for time‐independent diffusional solute release rates from these swellable systems is that the Sw be smaller than 10−2. The swelling interface number Sw may be related to easily determined structural and thermodynamic parameters of the solute/polymer/penetrant system. Preliminary experimental results of dynamic water swelling of poly(2‐hydroxyethyl methacrylate‐co‐methyl methacrylate) and diffusional release of theophylline from initially glassy copolymers show that decreasing values of Sw are related to increased pseudo‐case‐II transport kinetics of the solute.
An investigation of the compatibility and morphology of semicrystalline poly(ε‐caprolactone)–poly(vinyl chloride) blends
Authors: Russell T. P. , Stein R. S. 
Published: April 2003

AbstractBlends of poly(ε‐caprolactone) (PCL) and poly(vinyl chloride) (PVC) were investigated at concentrations of PCL greater than 50 wt % using purified materials. For these concentrations, PCL partially crystallizes with degrees of crystallinity ranging from 50% for pure PCL to < 10% for the 50% mixture. Small‐angle x‐ray scattering was used to characterize the resultant morphologies. Model calculations for the interference functions and for the integrated scattering indicate that PVC is incorporated between the PCL lamellae and that the two polymers form a homogeneous mixture in the amorphous phase. These results were compared to previous results on the same system using the identical technique. Purification of the two homopolymers proved to play a critical role in the overall mixing characteristics of PVC and PCL
Time‐dependent reactivity of species trapped in polymer matrices: Decay of allyl radicals in irradiated polyethylene
Authors: Płonka Andrzej 
Published: April 2003

AbstractUsing a time‐dependent rate constant of the form k(t) = Btα−1 it is possible to describe adequately the time‐dependent reactivity of species trapped in polymer matrices. The constant 0 < α ≤ 1 characterizes the initial distribution of species: the smaller the numerical value of α the wider is the distribution related to the kinetic curve by inverse Laplace transformation. Data of Auerbach and Sanders and of Patel et al. on allyl radical decay in irradiated polyethylene are discussed.
Diffusivity of gases and main‐chain cooperative motions in plasticized poly(vinyl chloride)
Authors: Sefcik M. D. , Schaefer Jacob , May F. L. , Raucher Daniel , Dub S. M. 
Published: April 2003

AbstractPermeability and time‐lag measurements for H2 and CO in poly(vinyl chloride) (PVC) plasticized with tricresyl phosphate show that the apparent diffusion coefficients at first decrease as the plas‐ticizer concentration is increased. The diffusion coefficients then increase as the additive concentration is raised above 15 wt %. These changes in the apparent diffusion coefficients can be related to the behavior of a variety of mechanical properties and are attributed to antiplasticization and plasticization effects of low and high concentrations of tricresyl phosphate, respectively. The antiplasticization‐plasticization effects reflect altered molecular motions of the polymer. Carbon‐13 NMR rotating‐frame relaxation rate measurements show directly that the cooperative main‐chain molecular motions of PVC are reduced when the additive acts as an antiplasticizer and are increased when the polymer is plasticized. Both the apparent diffusion coefficient and the rotating‐frame relaxation rate have a similar dependence on additive concentration. An application of the molecular theory of diffusion of Pace and Datyner accounts qualitatively for the way in which additives alter the average chain interaction energy, cooperative polymer main‐chain motions, and the diffusion coefficients of gaseous penetrants.
Mesomorphic solutions of cellulose triacetate in trifluoroacetic acid halogenated solvent mixtures: Phase separations and factors affecting the cholesteric pitch
Authors: Patel D. L. , Gilbert R. D. 
Published: April 2003

AbstractCellulose triacetate (CTA) forms cholesteric mesophases in trifluoroacetic acetic acid (TFA) and mixtures of TFA and CH2Cl2, 1,2‐dichloroethane (1,2‐DCE), and CHCl3. Cholesteric pitches and solution flow times indicate that the order of solvent powers is TFA‐CH2Cl2> TFA‐1,2‐DCE > TFA > TFA‐CHCl3, which is the order of decreasing acidity of the solvent systems. With TFA‐CH2Cl2as solvent, the one‐fourth power of the pitch varies inversely with the CTA concentration, and increases linearly with temperature. The pitch increases exponentially with time and increases faster the more acidic the solvent. In a magnetic field a cholesteric to nematic transition occurs. A minimum in solution viscosity occurs at 34% w/v of CH2Cl2for solutions in TFA‐CH2Cl2. The miscibility gap as a function of molecular weight depends on the solvent composition and is smaller the higher the acidity of the solvent. Agreement between the experimentally observedAandBpoints and the theoretical points is better for the Khokhlov and Semenov theory for semiflexible chains than for the original Flory theory or the Flory‐Ronca modification.
Molecular orientation of spider silks in the natural and supercontracted states
Authors: Fornes R. E. , Work R. W. , Morosoff N. 
Published: April 2003

AbstractTwo theoretical models are presented to predict average molecular orientation properties of spider silk which has unknown molecular orientation and chemical structure. Birefringence and elongation (or shrinkage) data are required for two distinct lengths of a sample in order to fit the data. The first model is based on the assumptions that each molecule behaves as the average and that the deformations are affine. The second model is based on a random distribution of the molecules as the fiber is first formed and that the molecular deformations are affine when the fiber is elongated to any length. Data were taken from spider silks in the natural state and in a shrunken state (due to water). The second model gives a much better fit of the data. The models are applicable to other systems.
Scattering from copolymer solutions at finite concentration
Authors: Benmouna M. , Benoit H. 
Published: April 2003

AbstractWe consider the variation of the coherent elastic scattering structure factor S(q) with momentum transfer q for a solution of block copolymers at finite concentration. We introduce the effect of concentration using a generalization of Zimm's model to copolymers which enables us to express intermolecular scattering functions in terms of intramolecular form factors only. We show that the shape of the scattering curve is very sensitive to the polymer concentration as well as to the contrast factors, the relative composition of co units, and the second virial coefficients characterizing constituents of the copolymer. In particular, we show that the scattering curve develops a maximum at low q for certain values of these parameters. We also discuss the variation of the apparent radius of gyration with polymer concentration.
Localized volume deficiencies as an effect of spherulite growth. II. The three‐dimensional case
Authors: Gałeski A. , Piórkowska E. 
Published: April 2003

AbstractAs in the two‐dimensional case, the density change due to crystallization leads to a buildup of internal strain in some regions of a polymer melt occluded by growing spherulites. The occluded parts of the sample are called “weak spots.” Computer simulation of spherulite growth in bulk samples shows that the largest weak spots have the size of an average spherulite. The total volumes of weak spots are 0.47, 0.094, and 0.119% of the sample for athermal, thermal, and mixed primary nucleation, respectively. The weak spots in the bulk material exhibit distance correlation. Within weak spots, internal strain is released (Raman spectroscopy), and holes develop. Polypropylene bulk spherulite samples contain holes distinctly visible under a microscope with infrared optics and illumination. The number of visible holes is in agreement with the computer prediction. The increase of impact strength with decreasing spherulite size is explained in terms of changes in the number and size of weak spots.
Effect of amorphous sequences on the longitudinal acoustic modes in partially crystalline polymers. I. Transfer matrix method
Authors: Strobl G. R. 
Published: April 2003

AbstractA novel theoretical scheme is developed which enables the determination of the LAM‐like vibrations of polymer chains made up of crystalline and amorphous parts as they occur in partially crystalline structures. The boundary conditions effective at the junction points are formulated in terms of the compliances of the associated amorphous sequences. These compliances can be derived from their eigenfrequencies and eigenvectors in a disconnected state. The treatment uses a matrix formalism which can be extended to include bending and torsional motions in a general state of vibration of the crystalline stem. A first numerical example demonstrates that the LA mode of a crystalline stem can be strongly perturbed by the coupling to the adjacent amorphous sequences. Interpretation of frequencies and line shapes of observed LA modes should always include these coupling effects; their neglect can lead to considerable errors.
Relationship between the cohesive strength and the tack of elastomers
Authors: Hamed G. R. , Shieh C.‐H. 
Published: April 2003

AbstractThe autohesion (tack) and cohesion of a random styrene‐butadiene elastomer have been examined as a function of test temperature and speed using a T‐peel geometry. Both properties have been reduced to a single master curve by horizontally shifting the data with the same set of shift factors. The cohesive strength increases with increasing reduced test rate RaT and appears to approach a plateau at the highest rates. Tack also increases with RaT but decreases abruptly at a critical rate and peeling the occurs in a stick‐slip fashion. Tack again increases at sufficiently high test rates. In the range of rates where tack is maximized, its value is essentially the same as its cohesive strength. Above or below this range, tack is substantially less than the elastomer's cohesive strength. Mechanisms are proposed to explain why relative tack (i.e., tack divided by cohesive strength) is not a simple measure of the extent of completion of a tack bond and may indeed be equal to one in spite of incomplete tack bond formation.
Diffusion of iodine into PE and PET
Authors: Pender L. F. , Mak H.‐B. , Wintle H. J. 
Published: April 2003

AbstractWe show that the Rutherford backscattering technique is very useful for studying the kinetics of diffusion processes in polymers. We have measured the diffusion of iodine into low‐density polyethylene (LDPE) by optical absorbance and by Rutherford backscattering. The optical results appear to be normal, and show no electric field dependence, but the backscattering results reveal that this is misleading, because there is fast diffusion in the bulk accompanied by large surface concentrations of iodine. We have studied PET by the backscattering technique, and in this case the behavior corresponds to a weakly concentration‐dependent diffusion coefficient with no observable surface effects. Neither set of results gives support to the domain theories of low‐frequency electrical oscillation in these materials.
The relationship between the physical structure and the microscopic deformation and failure processes of poly(p‐phenylene terephthalamide) fibers
Authors: Morgan Roger J. , Pruneda Cesar O. , Steele Wayne J. 
Published: April 2003

AbstractRelations between the physical structure and the deformation and failure processes of poly(p‐phenylene terephthalamide) (PPTA) fibers are reported. The effects of the physical processes involved in fiber fabrication, including the crystallization of PPTA‐H2SO4 dopes under stress, are considered in relation to their effect on the structure of the fiber. The deformation and failure processes together with the structure of the fiber are discussed in the light of fracture‐topography studies of fiber‐epoxy composite strands, single filaments, HCl‐etched and unetched yarns, and transmission optical microscopy studies of stressed and unstressed yarns. In view of these observations, the physical structure of PPTA fibers is discussed in terms of pleated H‐bond sheets, the macromolecular chain‐end concentration and distribution, and the presence of impurities. The structural parameters that affect the failure processes of these fibers and how such parameters can be modified by service environment conditions are also addressed.
Characterization of lattice disorder in the low‐temperature phase of irradiated PTFE by vibrational spectroscopy
Authors: Rabolt John F. 
Published: April 2003

AbstractIn an effort to elucidate the structure of the low‐temperature phase of PTFE, a spectroscopic study of the effect of progressive irradiation on the low‐frequency infrared spectrum was undertaken. Previous infrared and Raman measurements indicated that irradiation of PTFE decreases its crystalline content, resulting in a lowering of the 19°C phase transition temperature due to the introduction of disorder and defect structures into the lattice by chain scission. Far‐infrared studies of virgin and irradiated PTFE at liquid nitrogen temperatures show that the medium to strong bands at 45, 54, 58, and 71 cm−1, attributed to lattice vibrations, decrease in intensity as the crystalline content decreases. These findings support the assignment of these bands to intermolecular vibrations of the crystalline lattice and are an indication of the presence of more than one molecule in the crystallographic unit cell.
Morphology of poly(p‐phenylene terephthalamide) fibers
Authors: Panar M. , Avakian P. , Blume R. C. , Gardner K. H. , Gierke T. D. , Yang H. H. 
Published: April 2003

AbstractFibers of poly(p‐phenylene terephthalamide) (PPTA) have a fibrillar morphology, the individual fibrils having a high proportion of extended chains passing through periodic defect layers. A pleat structure is superimposed. The fibers are fully crystalline (within the limits of determination) with a small fraction of randomly oriented crystalline material. The major distinction between PPTA and conventional fibers lies in the high level of extended chains passing through the defect layers of the former structure. These extended chains result in crystallographic register being maintained between adjacent ordered zones. Quantitatively, a measure of this order is obtained from a comparison of the correlation length, obtained from meridional x‐ray peak widths, and the defect spacing. In conventional fibers the defect spacing, i.e., long period, is longer than the correlation length (i.e., crystal size). In PPTA, the analog of the long period, the defect spacing (about 35 nm) is smaller than the correlation length, which is over 80 nm.
Thermotropic homopolyesters. IV. Study of fiber formation
Authors: Acierno D. , La Mantia F. P. , Polizzotti G. , Ciferri A. , Krigbaum W. R. , Kotek R. 
Published: April 2003

AbstractWe report a melt spinning and viscosity study of two semiflexible homopolyesters containing both rigid and flexible segments in the repeating unit. Single filaments of the polyesters formed from 4,4′‐diacetoxybiphenyl and azelaic acid (PB7) and sebacic acid (PB8), and from 4′‐hydroxyphenyl‐4‐hydroxycinnamate and azelaic acid (C7), were spun at temperatures between 205 and 255°C. The temperature dependence of the Newtonian melt viscosity of PB7 and C7 was investigated, and a range of molecular weights was studied for PB7. The spinning parameters, fiber characteristics, and viscosity‐temperature behavior are related to the type of mesophase formed. The mechanical properties of fibers spun from both the nematic and smectic phases of these semiflexible chain polymers were poor. Increasing the polymer molecular weight or extrusion rate only afforded a modest improvement in fiber properties. Most polymers could not be spun at temperatures corresponding to the existence of the single mesophase. Hence the low viscosity typical of the nematic mesophase is not necessarily an advantage in fiber formation from the melt. It appears from these results that this type of polyester does not possess adequate chain extension to develop ultrahigh‐modulus properties. The director, which describes the local orientation of molecules within the mesophase, may undergo more frequent variations than is the case for rigid chain polyesters. Mechanisms relevant to flexible polymers may contribute to the development of orientation for this class of nematogenic melts.
The effect of restricted rotational diffusion on the dynamics of rodlike molecules in concentrated solution
Authors: Williams Graham 
Published: April 2003

AbstractThe model of Doi for the rotational dynamics of rodlike molecules in solution is compared with that of Warchol and Vaughan and Wang and Pecora. The similarities in the results for dielectric relaxation are discussed and the application of the models to the behaviour of isotropic solutions, anisotropic (lyotropic‐nematic) solutions, and mixtures of small molecules with polymers is briefly discussed.
The effect of polymer side chains on vapor sorption in polyacrylate and polymethacrylate solutions
Authors: Saeki S. , Holste J. C. , Bonner D. C. 
Published: April 2003

AbstractThe segment fraction Ψ1 activity coefficients, a1/Ψ1, of solvents have been determined by the piezoelectric sorption method for 0.1 ≤ Ψ1 ≤ 0.5 in binary solutions of chlorinated methanes [carbon tetrachloride (CCl4), chloroform (CHCl3), and dichloromethane (CH2Cl2)] with aromatic hydrocarbons (benzene and toluene) in poly(methyl methacrylate), poly(methyl acrylate), poly(ethyl methacrylate), and poly(n‐butyl acrylate) at 23.5°C. The present results for toluene in PMMA agree with previously published values obtained by gas‐liquid chromatography. For CCl4 and the aromatic hydrocarbons, the polymer–solvent interaction parameter χ is positive and constant, while for the polar solvents (CHCl3 and CH2Cl2), χ is negative and increases with increasing Ψ1. The effect of the polymer side chains on vapor sorption in nonpolar and polar solvent systems is discussed in terms of the χ parameter.
Orientation of isotactic polypropylene in crystalline and amorphous phases: IR methods
Authors: Kissin Y. V. 
Published: April 2003

AbstractTwo methods based on polarization infrared spectroscopy are described for measurement of polypropylene orientation. One method, for the crystalline phase, allows precise measurement of polypropylene orientation in three orthogonal directions. It is based on the polarization characteristics of two crystallinity bands, those at 841 and 809 cm−1, which exhibit opposite polarization characteristics. The other method, for the amorphous phase, provides a semiquantitative estimate and is suitable for uniaxially oriented films. It is based on polarization characteristics of the 1155‐cm−1 band. Both methods are applied to the measurement of orientation in polypropylene films uniaxially stretched at various speeds and temperatures.
Small‐angle x‐ray scattering measurements of diffuse phase‐boundary thicknesses in segmented polyurethane elastomers
Authors: Koberstein Jeffrey T. , Stein Richard S. 
Published: April 2003

AbstractThe diffuse phase boundary thicknesses of two segmented polyurethane block copolymers have been determined by small‐angle x‐ray scattering analyses of deviations from Porod's law. A self‐consistency test of these measurements is performed by comparing results of experiments carried out under a variety of collimation geometries, and using a number of different analytical procedures. Self‐consistent values of the diffuse phase boundary thickness are obtained for both of the materials examined. The discrepancies between these values and previous literature values are discussed and possible origins of these differences are presented.
Pulsed NMR observation of ultradrawn polypropylene
Authors: Ito M. , Serizawa H. , Tanaka K. , Leung W. P. , Choy C. L. 
Published: April 2003

AbstractProton spin‐spin relaxation times have been measured as a function of temperature for ultradrawn polypropylene with draw ratios λ up to 24. The three relaxation times T2a (the longest), T2i (intermediate), and T2c (the shortest), observed for all the samples, have been ascribed to the relaxations of the amorphous, constrained amorphous, and crystalline components, respectively. T2i and T2a, which reflect the changes in structure and mobility in the noncrystalline regions, decrease with increasing λ; T2i becomes saturated at λ > 9, whereas T2a shows a substantial decrease up to λ = 24. The continued decrease in T2a indicates that the constraint on the amorphous segments keeps increasing up to the highest λ. The associated mass fractions Fa, Fi, and Fc also change with λ. At λ < 9, the increasc in Fi with increasing λ is accompanied by a decrease in Fa, with Fc remaining unchanged. At higher λ, however, Fa is almost constant, and stepwise rises in Fc at about λ = 12 and 24 are accompanied by corresponding drops in Fi. It seems that, in this high draw ratio range, some of the taut molecules are fully extended and are in sufficiently good lateral register to transform into crystalline bridges. This conjecture is supported by the similarity in the λ dependence of Fc and the mass‐fraction crystallinity obtained from the heat of fusion.