bluuebunny/crossref_metadata_2025_split huggingface dataset:
Effects of molecular weight distribution and branching on rheological parameters of polyethylene melts. Part I. Unfractionated polymers
Authors: Guillet J. E. , Combs R. L. , Slonaker D. F. , Weemes D. A. , Coover H. W. 
Published: April 2003

AbstractIt is well known that the rheological behavior of polyethylene melts is affected by at least four variables: (1) molecular weight, (2) molecular weight distribution, (3) long‐chain branching and its distribution, and (4) short‐chain branching. Of these, the first three appear to have the largest effects. In the present paper an attempt is made to determine the effect of molecular weight distribution by rheological studies of polymers having similar molecular weight distribution by rheological studies of polymers having similar molecular weights and degrees of branching, but varying considerably in their molecular weight distributions as determined by fractionation. The rheological parameters studied were melt recovery, non‐Newtonian behavior, critical shear rate, and melt strength. It is shown that the melt recovery increases uniformly as the molecular weight distribution broadens. The degree of non‐Newtonian behavior, as measured by the exponent n of the power law, also increases with distribution breadth and is particularly affected by the amount of low molecular weight polymer present. Melt strength increases in a similar manner. Critical shear rate is inversely related to the breadth of the molecular weight distribution and is particularly dependent on the molecular weight of the highest fractions. The log of the critical shear rate is inversely proportional to the melt index recovery.
Dynamic and tensile properties of epoxy resins
Authors: Kaelble D. H. 
Published: April 2003

AbstractThe dynamic mechanical and tensile deformation and ultimate properties are reported for two epoxy resins in the temperature range, from the glass transition Tg to Tg + 100°C. The epoxy resins are stoichiometrically reacted diglycidyl ether of bisphenol A with an aromatic (Tg = 115°C.) and an aliphatic (Tg = 47°C.) diamine curing agent. Dynamic measurements were conducted on a rotating cantilever beam instrument over the frequency range from 0.01–100 cycles/sec. Tensile deformation and fracture characterization were obtained by constant rate of strain measurement at strain rates of 0.000445–0.445 sec. −1. Both dynamic and tensile modulus data as well as ultimate stress and strain response superimpose by time and temperature reduction to form unified “master curves.” The time or frequency shift factor aT for both dynamic and tensile deformation and fracture properties follow the predictions of the familiar Williams‐Landel‐Ferry equation. The rheological and fracture master curves are discussed in terms of both monomer composition and equilibrium response of the crosslinked network. The regions of maximum dynamic dispersion are associated with rubbery state high elasticity tensile response for these epoxies and the magnitude of responses correlated.
Stress–strain properties in the decrimping region of chemically modified crimped keratin fibers, with special reference to the stability of crimp structure
Authors: Balasubramaniam E. 
Published: April 2003

AbstractThe effect of disulfide rupture, reoxidation, and crosslinking with formaldehyde on decrimping parameters of wool keratin is studied in an attempt to establish the comparative role of cystine‐type of bonding in the decrimping region. Large changes in crimp shape accompanied by changes in decrimping forces and energy suggest that the stability of crimp shape is obviously dependent on cystine linkages.
Factors affecting dynamic durability of polycarbonate under bending, torsional, and impacting fatigue and in cavitation erosion and dynamic solvent cracking conditions
Authors: Ohishi F. , Nakamura S. , Koyama D. , Minabe K. , Fujisawa Y. , Tsuruga Y. 
Published: April 2003

AbstractTo understand influences of various factors on dynamic durability of engineering plastics, effects of average molecular weights of samples, molding variables, preparing methods of specimens, and fillers on plane and rotational bending, torsional, and impacting fatigue and cavitation erosion and solvent cracking of polycarbonate were studied. From the experimental results, the following tendencies are observed as a whole in case of polycarbonate: The extent of influence of the factors on dynamic durability varies depending on the type of testing. Increase in molecular weight has a favorable effect on dynamic durabilities. Influence of molding conditions is remarkable: especially, deficient drying of resin pellets before molding decreases dynamic durability noticeably, and specimens prepared by injection molding have much better durabilities than those by machaning from extruded sheet. Polyethylene blending has an unfavorable effect on durability, except for Izod‐type impact strength and solvent cracking. Reinforcement by glass fiber has a favorable effect on fatigue under constant deformation and cavitation erosion.
The tearing test as a means for estimating the ultimate properties of rubber
Authors: Glucklich J. , Landel R. F. 
Published: April 2003

AbstractSBR, unfilled and filled with glass beads, MT, and HAF carbon blacks, was tested for tearing energy, rupture values in simple tension, tear diameter, and strain distribution at four rates and seven temperatures. The energy density to failure at the tear zone Wt was obtained from the tearing energy τ and the natural tear diameter d using a modified Rivlin and Thomas relationship Wt ≈ τ/d. This was then compared with the nominal energy density at rupture in simple tension W. It is shown that always Wt > W (sometimes Wt/W = 10), that Wt is subject to a smaller statistical scatter than W, and that Wt is more amenable to the WLF type of superposition than W. It is concluded that Wt and not W is the strength‐determining property. Where W data permitted superposition, it is followed the WLF equation. It is presumed that so would Wt. τ, although more superposable than W, showed a bigger shift factor than that dictated by WLF, the difference being the result of the temperature dependence of the diameter. The reinforcing effects of the various fillers are also discussed. It is shown that the carbon black fillers increase both Wt and d. Glass beads have only a small effect on d and none on Wt.
Copolymer composition as a function of molecular weight and the effect of conversion on this relationship
Authors: Mirabella Francis M. , Barrall Edward M. , Jordan Edmund F. , Johnson Julian F. 
Published: April 2003

AbstractThe copolymer compositions as a function of molecular weight for three poly(styrene‐co‐vinyl stearate) copolymers of widely varying conversion were determined. A combined gel permeation chromatography–infrared spectroscopy method was used. Theoretical changes in copolymer composition were calculated using reactivity ratios. Comparison of the calculated and observed changes in copolymer composition as a function of molecular weight showed qualitative agreement. However, the observed changes in composition were significantly larger than those calculated.
Solute diffusion through swollen polymer membranes
Authors: Paul D. R. , Garcin M. , Garmon W. E. 
Published: April 2003

AbstractExperiments were designed to study the role of the solvent in the transport of a solute through a solvent‐swollen polymer membrane. A single solute (an organic dye), a single polymer (cross‐linked natural rubber), and 24 different organic solvents were used for this purpose. The solute diffusion coefficient D was calculated from the measured permeability P and distribution coefficient K, and was compared to the diffusion coefficient of the solute in the pure solvent. The main parameters of the solvent were shown to be its viscosity and the degree it swells the polymer. At high swelling, the results are in agreement with a model that pictures the resistance to solute diffusion as hydrodynamic interaction with the solvent while the polymer acts as an obstruction that increases the tortuosity of the diffusion path. At very low swelling, the diffusion coefficient approaches an asymptotic limit which is independent of solvent viscosity. However, even with as low as 10% solvent, some effects of viscosity are still seen. These results are discussed in terms of a quantitative theory for the obstruction effect proposed by Meares and compared to other literature data.
Polysulfone hollow fibers. I. Spinning and properties
Authors: Cabasso Israel , Klein Elias , Smith James K. 
Published: April 2003

AbstractThe development of porous polysulfone hollow fibers and the spinning process used are discussed. An analysis is given of the spinning parameters which determine fiber mechanical properties and permeability. Hollow fibers were prepared which display high modulus and high tensile strength. These fibers can withstand hydraulic pressures of more than 1000 psi. They can thus serve as supports for dense, ultrathin membrance coatings, useful in high‐pressure reverse osmosis and ultrafiltration processes.
Gradient polymers by diffusion polymerization
Authors: Akovali G. , Biliyar K. , Shen M. 
Published: April 2003

AbstractGradient polymers are multicomponent polymers whose structures or compositions are not macroscopically homogeneous, but vary as a function of position in the sample. One method to prepare such polymers is by diffusing a guest monomer into a host polymer and then polymerizing the monomer in position to retain the concentration gradient created by the diffusion. One series of such type of materials was prepared by diffusing acrylonitrile into polystyrene. The gradient profile was determined by analyzing the nitrogen content in succeeding layers of the sample. These gradient polymers exhibit improved resistance to hydrocarbon solvents. The second series of gradient polymers was made by diffusion of methyl acrylate into poly(methyl methacrylate). These materials are shown to possess substantially increased fracture strain. Eyring's stress‐biased activated rate theory of yielding was used to rationalize the observed toughening effect in gradient polymers.
Polymerization of methyl methacrylate in water in presence of the metal oxides TiO2 and Cu2O
Authors: Moustafa A. B. , Ghanem N. A. , Abd‐El‐Hakim A. A. 
Published: April 2003

AbstractRates of sodium bisulfite‐initiated polymerization of methyl methacrylate in water were determined in absence and in presence of the metal oxides TiO2 and Cu2O at 30°, 40°, 50°, and 60°C. Cuprous oxide and titanium dioxide enhanced the rate of polymerization and reduced the molecular weight as compared with the figures obtained in absence of oxide, the effect of the former being more pronounced than the latter. With TiO2, the rate was increased from 2.3 to 3.2 × 10−5, while with Cu2O, it was increased to 8.6 × 10−5 mole/l./sec, both at concentrations of 9 g/l. water. The apparent energy of activation for the polymerization of methyl methacrylate between 40°C and 50°C was found to be 15.6 kcal/mole in absence of the metal oxides, and 7.6 kcal/mole and 2.8 kcal/mole in presence of titanium dioxide and cuprous oxide, respectively. The number‐average molecular weight was found to decrease slightly with the addition of TiO2 but to decrease greatly when Cu2O was added.
Thermally stimulated discharge current studies on low‐temperature relaxations in polycarbonate
Authors: Aoki Y. , Brittain J. O. 
Published: April 2003

AbstractThe β‐relaxation in polycarbonate has been investigated by the thermally stimulated discharge current (TSC) technique. The polarization of the β‐peak in polycarbonate is shown to be uniform. Two broad peaks centered at 130° and 200°K were observed. Furthermore, two single relaxation processes were resolved for the lower temperature peak. The high temperature peak was also resolved into two peaks, however, only one of them was a single relaxation process. The individual peaks satisfied the dipolar theory, and the three peaks are associated with activation energies of 0.24, 0.27, and 0.47 eV, and temperatures of the peak maxima were 121°, 131°, and 193°K, respectively. The mechanism attributed to each peak is discussed and does not appear to contradict the results of conventional dielectric and mechanical relaxation and NMR measurements on the β‐relaxation in polycarbonate.
Studies of polymeric systems for damping of vibrations in the sonic range
Authors: Chen Alex C. F. , Williams H. Leverne 
Published: April 2003

AbstractClosed‐cell foams based on rigid polyurethanes blended with more viscoelastic polymers possess good vibration‐damping properties. The damping characteristics of the various polymers differ, indicating that the chemical nature has an influence on the acoustical performance of the blend. Damping is also temperature dependent. By selection of polymers, foam effective for damping at various service temperatures and over various frequency ranges can be made. The damping characteristics of polymers can be changed by adding fillers. Such methods may be employed to achieve a broader damping peak at the desired service temperature. The damping of vibration of an aluminum strip could be increased by one to two orders of magnitude between 20°C to 60°C when the strip was coated with the experimental materials in comparison with commercial open‐cell, elastic foams of comparable density. A dynamic resilience of only 9% was achieved.
Tailoring closely packed gel–particle systems for use as thickening agents
Authors: Taylor N. W. , Bagley E. B. 
Published: April 2003

AbstractWhen used as a thickening agent in aqueous suspension, hydrolyzed starch–polyacrylonitrile graft copolymer (H‐SPAN) has broadly variable rheological properties, such as viscosity, storage modulus, and stress overshoot characteristics. A series of H‐SPAN preparations with variable swelling ratio Q were made by pretreating portions of stock material. As 1% suspensions in water, they had viscosities η that were non‐Newtonian. At a constant shear rate, η of the suspensions depended on Q and had a sharp maximum in the midrange of Q. In terms of reduced concentration cQ, where c is weight fraction of polymer, the highest η occurred when cQ was approximately 2. With isoionic dilution, each suspension had a constant reduced viscosity function, η/cQ, provided cQ > 2. The value of η/cQ fell rapidly when cQ approached 1. All thickeners of the closely packed gel–particle type so far examined have this relation of the reduced variables. The shear modulus calculated from measurements of primary normal force and corrected for solvent swelling, according to theory for rubber for elasticity, was essentially constant for each suspension measured during isoionic dilution to cQ = 2. The density of crosslinks calculated from the modulus was extremely low for all samples. The variable rheological properties of the preparations resulted primarily from differences in their low effective crosslink densities.
Phase separation phenomena during the formation of asymmetric membranes
Authors: Koenhen D. M. , Mulder M. H. V. , Smolders C. A. 
Published: April 2003

AbstractThe formation of membranes from two systems has been studied. In the system polyurethane–dimethylformamide–water, the mechanism for the formation of the sponge‐like structure proves to be a liquid–liquid phase separation with nucleation and growth of the diluted phase. This mechanism has been confirmed for the system modified polystyrene–polyisoprene–polystyrene/o‐dichlorobenzene/(methanol–water). Crystallization and gelation is discussed. The membranes prepared showed hyperfiltration activity. The mechanism proposed here is believed to be valid for other systems, too.
Initial slow crack growth behavior followed by rapid brittle fracture in a viscoelastic solid
Authors: Kobayashi Akira , Ohtani Nobuo 
Published: April 2003

AbstractInitial dynamic crack propagation behavior in a viscoelastic solid just after crack initiation was investigated by newly devised instrumentation at different temperatures. It was observed that initial slow crack growth precedes rapid brittle fracture. The very initial slow crack growth first appears as ductile fracture and successively as brittle crack propagation, and the latter only exists within very short crack passage. It is also recognized that this slow crack growth in a brittle manner greatly depends on the temperature.
Polyelectrolyte complex prepared from carboxymethylated and aminoacetalized derivatives of poly(vinyl alcohol)
Authors: Hosono Masao , Sugii Shinji , Kitamaru Ryozo , Hong Yeong Man , Tsuji Waichiro 
Published: April 2003

AbstractSome physical and chemical properties of an ionic complex made from the weak polyelectrolytes carboxymethylated poly(vinyl alcohol) (PA) and aminoacetalized poly(vinyl alcohol) (PC) are investigated in comparison with those of another ionic complex made from the strong polyelectrolytes sulfated poly(vinyl alcohol) (PSA) and poly(vinyl alcohol) acetalized with diethoxyethyltrimethylammonium (PTC). It was found that when the complex PC–PA was heated at high temperatures, covalent amide bonding took place, whereas no significant change occurred in the case of the PTC–PSA complex. As a result of these structural changes, the degree of swelling of the PC–PA complex in water was markedly decreased, but that of the PTC–PSA complex was not changed by the treatment. The PC–PA complex was insoluble in water and in 1N HCI and 1N NaOH aqueous solutions even if not heat treated, but the PTC–PSA complex was soluble in such acidic and basic aqueous solutions but not in water if heat treated. The PC–PA and PTC–PSA films exhibited good mechanical properties.
Reclamation of vulcanized rubbers by chemical degradation. V. Degradation of vulcanized synthetic isoprene rubber by the phenylhydrazine–ferrous chloride system
Authors: Yamashita Shinzo , Kawabata Nariyoshi , Sagan Susumu , Hayashi Koji 
Published: April 2003

AbstractThe changes of effective network chain density and soluble fraction were measured for gum vulcanizates of synthetic isoprene rubber (IR) during the degradation by the phenylhydrazine–ferrous chloride system. From the decrease of effective network chain density and the increase of soluble fraction, the network chain was concluded to undergo a severance reaction by the reagents in the following order of ease: polysulfide linkage > monosulfide linkage > carbon–carbon crosslink. Analysis of the relation of soluble fraction with decrease of effective network chain density according to the theory of Horikx indicated that the severance of crosslinks predominated over main‐chain scission in the degradation of sulfur vulcanizate by the reagents. The experiments of the degradation of sulfur vulcanizate in sealed vessels in the absence of oxygen indicated that atmospheric oxygen is necessary for the degradation reaction.
Structure of oriented polystyrene monofilaments and its relationship to brittle‐to‐ductile transition
Authors: Tanabe Yoshikazu , Kanetsuna Hisaaki 
Published: April 2003

AbstractOriented atactic polystyrene monofilaments show brittle‐to‐ductile transition in the vicinity of a degree of birefringence Δn = −2 × 10−3 (at a temperature of 20°C and at the stretching rate of 100%/min) independently of the various spinning conditions. The amorphous orientation of a cylindrically symmetric system was investigated by wide‐angle x‐ray scattering experiments. The orientation of polystyrene monofilaments in real space is denoted by P2(cos α) within the precision of measurement. The coefficient D2(r) of the second term in an expansion of cylindrical distribution function in spherical harmonics has two main peaks, near r = 1.6 Å and r = 4 ∼ 5 Å. The negative peak near r = 1.6 Å indicates orientation of phenyl groups in a plane perpendicular to the fiber axis. The positive peak near r = 5 Å (brittle region) or near r = 4 Å (ductile region) indicates the piling up of phenyl groups for the direction of the fiber axis. It is most probable that the amorphous state of atactic polystyrene consists of an appropriate cohesion of planar zigzag chains of syndiotactic polystyrene. The lower spacing (r = 4 Å) of the positive second peak in ductile region suggests that there are interchain phenyl groups near r = 5 ∼ 6 Å in a plane perpendicular to the fiber axis and that the molecular chains are extended parallel to the direction of the fiber axis. This parallel packing of chain segments along the fiber axis suppresses the formation and growth of cracks of polystyrene monofilaments resulting in ductile fracture.
Internal stresses and activation volumes from the stress relaxation behavior of polyethylene at large deformations
Authors: Kubát J. , Seldén R. , Rigdahl M. 
Published: April 2003

AbstractThe internal stress level in polyethylene has been determined as a function of strain by analyzing the stress relaxation behavior at room temperature. Also the influence of annealing on the magnitude of the internal stresses was studied, both with HD and LD polyethylene. The maximum initial strain was comparatively high: 20% and 40% for HDPE and LDPE, respectively. The internal stresses were found to be introduced during the initial deformation of the sample prior to the relaxation experiment. For both LDPE and HDPE the internal stress varied with the initial deformation in a manner resembling that of a stress–strain curve. In no case was a permanent residual internal stress (due to the molding process, etc.) observed. The activation volume v, evaluated from the stress relaxation kinetics, was found to be related to the effective stress σ* according to vσ* ≈ 10 kT, where k is the Boltzmann constant and T is the absolute temperature. This is in agreement with results reported earlier for both metals and polymers.
The chemistry and development of tannin‐based weather‐ and boil‐proof cold‐setting and fast‐setting adhesives for wood
Authors: Pizzi A. , Roux D. G. 
Published: April 2003

AbstractCondensed tannins, being phenolic in nature, can be chemically modified to undergo reaction with formaldehyde in such a way that the adhesives formed harden at ambient temperature in industrially meaningful times. Resorcinol, m‐hydroxyaniline, and their condensation products with formaldehyde and/or tannin resoles have been used for this purpose. The optimum conditions of application, such as paraformaldehyde amount, pH, and open and close assembly times, were used when comparing the different resins prepared. Results satisfying the requirements of international standard specifications and comparable to those of phenol/resorcinol/formaldehyde cold‐setting resins were obtained.
Fabrication of poly(p‐phenylene) by powder‐forming techniques
Authors: Gale D. M. 
Published: April 2003

AbstractApplication of powder‐metallurgical forming techniques to poly(p‐phenylene), PB, resulted in solid objects with tensile strengths as high as 35 MPa (5000 psi). Powders were characterized by BET surface area, x‐ray crystallinity, scanning electron microscopy (SEM), and impurity levels in an effort to relate intrinsic powder properties with strengths attainable on fabrication. High surface area (>35m2/g) and low Cl impurity levels were generally associated with highest strengths. Forming variables were studied in some detail. Tough objects were obtained in a narrow sintering range of about 580°–615°C. Perchloropoly(p‐phenylene) was also successfully fabricated.