bluuebunny/crossref_metadata_2025 huggingface dataset:
Dynamic mechanical properties of supported polymers. II. Application of the torsional braid technique to the study of the curing and stability of resins
Authors: Gillham John K. , Lewis Armand F.
Published: April 2003

Transformations, physical and chemical, which occur in polymeric systems are usually accompanied by changes in rigidity. In the present method, a modified torsional pendulum is employed such that the vertical specimen shaft consists of a fabric braid which is impregnated with the polymeric material under investigation. Therefore, in principle, any changes in the mechanical properties of the composite will be reflected by changes in frequency of free oscillation of the system. This dynamic mechanical technique provides a very sensitive tool for following nondestructively, the liquid to solid transitions accompanying the curing of polymers. In this communication the utility of the torsional braid technique in the study of heat resistant polymers is emphasized. Curing and thermal softening behavior, as well as pyrolytic and oxidative degradations are monitored with precision. A comparative study between three thermosetting resins, i.e., a phenolic, an unsaturated polyester and a phosphonitrilic, is presented.
Dynamic testing of elastomer mountings
Authors: Cardillo R. M.
Published: April 2003

Elastomer mountings are used extensively for impact and shock absorption and for the control of noise and vibration. Dynamic testing has become increasingly important in the formulation, design and evaluation of effective mount materials. A servocontrolled hydraulic tester has been used for the forced vibration testing of various elastomer compounds. The essential dynamic properties of such materials can be obtained directly over a broad range of operating conditions. Frequency, amplitude, and preload can be independently controlled and different test temperatures can be obtained through the use of an insulated control chamber. A production type automotive engine mount was used for most of the tests. Experimental compounds were molded into test mounts and checked for dynamic spring rate and coefficient of damping. The effect of different operating conditions such as frequency, amplitude, preload, and temperature on the dynamic properties of butyl mounts is described. Data are also presented on the role of compounding in altering the properties of mounts. Some data are also presented on the characteristics of natural rubber, SBR, and EPR mounts. The dynamic properties of the mount determine its performance features in a mounting system. The transmission of forces in a simple mounting system can be calculated using dynamic property data and the appropriate transmissibility equation. This has been done for several of the mounts tested and the vibration isolation characteristics of each are discussed. The data illustrate the effect of mount properties on transmissibility.
Memory effects in irradiated polyethylene
Authors: Odian George , Bernstein Bruce S.
Published: April 2003

The memory of irradiated polyethylene has been studied with emphasis on the magnitude of the restoration force exerted by the deformed polymer during the process of restoration to the nonstressed state and on the degree of completeness with which restoration occurs. The particular form of the memory effect studied has involved the deformation of the heated polymer followed by “locking‐in” of the memory via cooling. Subsequent heating restores the deformed specimen to the undeformed state. The memory effect has been studied under both nontransparency (NT) and transparency (T) deformation conditions. The effects of parameters such as the polymer properties (Tm, density, molecular weight), radiation dose, and deformation and restoration conditions on the degree of restoration and restoration force have been investigated. The results of this study may be summarized as follows. Restoration temperatures equal to or above the crystalline melting point (Tm) of the polymer are required in order to obtain complete restoration. The restoration temperature increases with increasing polymer crystalline melting point. The degree of restoration increases with increasing restoration temperature for NT deformed specimens. T deformed specimens do not begin to restore until the temperature approaches the Tm of the polymer. The restoring force increases with decreasing deformation temperature. NT deformation results in larger restoring forces and faster restoration relative to T deformation. The restoring force increases with increasing radiation dose for both T and NT deformations, the effect being greater for NT deformation. Radiation dose, however, above a minimum value does not affect the degree of restoration. The restoring force increases with increasing polymer initial molecular weight for T deformation.
Self‐extinguishing polystyrene foaming‐in‐place beads
Authors: Jahn A. K. , Vanderhoff J. W.
Published: April 2003

The preparation of practical self‐extinguishing polystyrene foaming‐in‐place compositions by suspension polymerization is described. The halogen necessary for self‐extinguishing characteristics is incorporated by chain transfer. The synergistic effect of organic peroxides decreases drastically the amount of halogen necessary. For example, 0.3 pph 1,2‐dibromotetrachloroethane in the presence of 0.2 pph dicumyl peroxide renders the composition self‐extinguishing, while 1.0 pph is necessary without peroxide. The rate of polymerization is unaffected by the presence of this chain transfer agent, while the molecular weight is reduced considerably. The effectiveness of other halogenated chain transfer agents and peroxy compounds has been demonstrated. Silicone mold release agent exerts a deleterious effect on the self‐extinguishing properties.
Behavior of cis‐polybutadiene during mastication
Authors: Kraus Gerard , Rollmann K. W.
Published: April 2003

Cold mastication of natural rubber in presence of oxygen leads to scission by a shear mechanism with subsequent stabilization of the free radicals by oxygen, while at high temperatures oxidative scission becomes the dominant mechanism. Studies of the behavior of cis‐polybutadiene reveal that similar reactions are effective, but occur at much reduced rates. Shear degradation is particularly difficult to achieve in typical cis‐polybutadienes. This is related to the molecular weight distribution of these polymers which usually lack the very high molecular species most subject to shear‐induced degradation, in agreement with the theory of F. Bueche. It is shown that when such a high molecular weight fraction is supplied, shear breakdown may be realized. All cis‐polybutadienes undergo oxidative breakdown at high temperatures, the scission rate becoming appreciable above 140°C. A number of oxidation catalysts have been found which markedly increase the scission rate without leading to a correspondingly large increase in crosslinking. Significant improvements in processing may be realized in this manner.
Determination of polyolefin film properties from refractive index measurements
Authors: Schael George W.
Published: April 2003

A technique is described for determining the density of polyolefin film from refractive index measurements. The procedure involves the measurement of the refractive indexes (nx, ny, and nz) along the three major axes of a film sample and conversion of the arithmetic average refractive index to a density value. The refractive index data are also used to calculate the per cent crystallinity and birefringence in the film.
Properties of semicrystalline polyolefins: Poly‐4‐methyl‐1‐pentene
Authors: Isaacson R. B. , Kirshenbaum I. , Feist W. C.
Published: April 2003

A study has been carried out of the thermodynamic properties, physical and mechanical properties, and crystallization behavior of poly‐4‐methyl‐1‐pentene (poly‐4‐MP). Data were obtained for the heat and entropy of fusion. Poly‐4‐MP is characterized by a comparatively high tensile strength, stiffness, and surface hardness. The impact is low at room temperature. The adverse effect of temperature on tensile strength, creep, and other polymer properties is greater for poly‐4‐MP than for polypropylene. Poly‐4‐MP is highly transparent, probably due to limited spherulite growth. Spherulitic growth was promoted through copolymerization with propylene by a technique of sequential monomer addition. The resultant product had an increased crystalline melting point (244 vs. 238°C. for the poly‐4‐MP homopolymer). The significance of these results and the effect of temperature on the birefringence of poly‐4‐MP are discussed.
Extracellular polysaccharide produced from glucose by Arthrobacter viscosus NRRL B‐1973: Chemical and physical characterization
Authors: Jeanes Allene , Knutson C. A. , Pittsley J. E. , Watson P. R.
Published: April 2003

The polysaccharide produced in good yields by Arthrobacter viscosus NRRL B‐1973 when grown in liquid medium containing glucose has been isolated from the culture fluids, purified and characterized. The constituents of this water‐soluble polysaccharide have been shown to be D‐glucose, D‐galactose, and D‐mannuronic acid (as the potassium salt) in approximately equimolar proportions, and about 25% of O‐acetyl groups. The rarity of known occurrences of D‐mannuronic acid in polysaccharides other than alginates is documented. Properties which have been observed as significant for utilization include, for both native and deacetylated forms of the polysaccharide: high viscosity of dispersions in water and in solutions containing chlorides, stability of viscosity to shear and to pH change in the normal range, and excellent quality of unsupported films; and for the native polysaccharide: stability in storage and the favorable influence of alcohol‐water solvent on rate of dispersion and viscosity attained.
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

It 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

The 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

The 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

To 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

SBR, 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

The 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

Experiments 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

The 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

Gradient 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

Rates 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

The 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

Closed‐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

When 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

The 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

Initial 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

Some 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

The 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

Oriented 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

The 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

Condensed 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

Application 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.
Polyester–polycarbonate blends. I. Poly(butylene terephthalate)
Authors: Wahrmund D. C. , Paul D. R. , Barlow J. W.
Published: April 2003

Melt blends of bisphenol A polycarbonate with poly(butylene terephthalate) were studied by DTA and dynamic mechanical behavior to determine their state of miscibility. Both techniques showed multiple glass transitions indicative of incomplete miscibility in the amorphous phase. However, these transitions in some cases did not correspond to those in the pure components and varied with overall blend composition in some instances. This indicates that there are amorphous phases containing both components, i.e., partial miscibility. This view was supported by the crystallization behavior of the polyester. Two crystallization exotherms were observed for quenched samples, which is interpreted as polyester crystallization from two separate phases, one richer in this component than the other. Other interpretations of these results are discussed.
Rheology of high solid coatings. II. Analysis of combined sagging and leveling
Authors: Wu Souheng
Published: April 2003

The rheology of combined sagging and leveling of high solid coatings is analyzed in terms of non‐Newtonian power‐law model. The results indicate that, in order to have good leveling, good sag control, and good sprayability at the same time, high solid coatings should have pseudoplastic rheology with power constant of about 0.5 and viscosity at sec‐1 of about 50 poises. This theoretical prediction is confirmed experimentally.
Thermal degradation of poly(2,6‐dimethyl‐1,4‐phenylene oxide). I. The mechanism of degradation
Authors: Jachowicz J. , Kryszewski M. , Kowalski P.
Published: April 2003

An analysis of products obtained from thermal degradation of poly(2,6‐dimethyl‐1,4‐phenylene oxide) is presented. The techniques used for identification of monomeric and dimeric degradation products were gas chromatography and mass spectrometry. On the basis of this analysis a mechanism of thermal breakdown is established. It consists of the Fries‐type rearrangement of the polymer chain in the first degradation step and statistical scission of benzyl bonds. The proposed degradation scheme accounts for the retention of ether linkage in the afterdegradation residue.
Drawing and annealing of polypropylene fibers: Structural changes and mechanical properties
Authors: Nadella Hari P. , Spruiell Joseph E. , White James L.
Published: April 2003

A study has been carried out on the influence of cold drawing (25°C), hot drawing (140°C), and annealing (140°C) on the structure and mechanical properties of a series of four different well‐characterized melt spun polypropylene filaments. The influence of the interaction between melt spinning and drawing variables was given special attention. Cold drawing increased the orientation in the samples, disrupts the initial monoclinic crystal structure and the morphology of the filaments, and it results in extensive fibrillation. Annealing restored the monoclinic structure but eliminated only a small part of the fibrillation. Hot drawing produced changes which were qualitatively similar to the combined effects of cold drawing and annealing. The orientation and morphology of the asspun filaments were found to have major effects on drawing behavior and the mechanical properties of the drawn fibers for a given draw ratio. It was found, however, that the mechanical properties (tensile strength, tangent elastic modulus, and elongation to break) of the melt spun, hot drawn and cold drawn, and annealed fibers could all be correlated with birefringence measurements.
Mechanism of action of PVC thermal stabilizers
Authors: Wypych Jerzy
Published: April 2003

Based on experimental data, changes of properties of plasticized PVC containing stearates of Ca, Zn, Cd, and Pb stabilizers during thermal degradation are discussed. The mechanism of action of these stabilizers is described in kinetic form.
Correlating and predicting polymer thermal conductivities
Authors: Luba Michael , Pelt Thomas , Griskey Richard G.
Published: April 2003

General correlations were developed to estimte polymer thermal conductivities for four cases—amorphous polymers above the glass temperature; amorphous polymers below the glass temperature; semicrystalline polymers above the melting temperature, and semicrystalline polymers below the melting temperature. The correlations based on readily available parameters (mer weights, densities at 25°C, specific heats) yielded calculated thermal conductivities that deviated by only 1%–2% from experimental values.
Effects of composition and processing conditions on the properties of a series of shock mitigating phenolic foams
Authors: Mendelsohn M. A. , Meier J. F. , Rudd G. E. , Rosenblatt G. B.
Published: April 2003

The effects of variations in the chemical composition and processing conditions of the series of phenolic foams described in the two previous papers were studied. Compressive stiffness and density increased with increasing concentrations of the acid catalysts, the slower reacting phenolic resin component, water, the lipophilic component of the surfactant system, and age of the phenolic resins. These properties decreased with increasing concentration of the fluorocarbon blowing agent and process temperature. The compressive stiffness and density increased to a maximum and then decreased with increasing concentrations of the hydrophilic surfactant. Permeability or “breathability” of the foam decreased with the hydrophilic surfactant at low concentrations and then became essentially independent of further increases of this component. Increasing concentrations of the lipophilic surfactant gave foam having greater breathability. In all other cases the permeability of the foam decreased as its density increased. Effects of the variations in processing and composition on the dependency of load bearing upon density, on relationships between permeability and density and permeability and compressive stiffness, and upon cell structures are also described.
Biodegradable polymers: Chymotrypsin degradation of a low molecular weight poly(ester‐urea) containing phenylalanine
Authors: Huang Samuel J. , Bansleben Donald A. , Knox James R.
Published: April 2003

A low molecular weight poly(ester urea), poly(L‐phenylalanine/ethylene glycol/1,6‐diisocyanatohexane), and a model diester diurea, dimethyldiphenylalaninehexamethylenediruea, were synthesized and found to be hydrolyzed by α‐chymotrypsin solutions at pH 7.8. After ten‐day exposure to 0.1 mg/ml enzyme solution at room temperature, 79.9% weight loss was observed for the model diester diurea (containing two ester linkages per molecule). A weight loss of 19.4% was observed for the poly(ester urea) of M̄n 1930 (containing an average of eight ester linkages per molecule) after the same period of exposure. A poly(ester urea) of similar molecular weight, but derived from glycine instead of phenylalanine, was found to resist chymotrypsin hydrolysis.
Flame retardant polyesters based on bromine derivatives
Authors: Ram Arie , Calahorra Arie
Published: April 2003

Unsaturated polyesters containing halogens in the backbone of the polymer chain were synthesized. Derivatives used had brominated functional groups such as tetrabromobisphenol A, tetrabromophthalic anhydride, and dibromoneopentyl glycol. These were compared to chlorine‐containing polyesters based on HET acid and tetrachlorophthalic anhydride and an additive exhibiting a synergistic effect of phosphorus and halogen, trichloroethyl phosphate. Optical properties before and after artificial weathering (up to 1650 hr), were determined on cast specimens, and mechanical properties (flexural strength, modulus, and hardness) and flame retardancy were determined on glass fiber laminates. The flammability tests consisted of the “oxygen index” and the “self‐extinguishing time” tests, which were correlated for various halogen concentrations and different compositions. The efficiency of bromine in flame retardancy has been found to be much higher than that of chlorine. The minimal concentration of bromine required for self‐extinguishing is 10–12%, as compared with 20–25% for chlorine. A general performance index for polyesters has been derived which incorporates both flame and weather resistivity factors of the modified polyesters.
Emulsion of polyurethane having thermosetting properties. II. Relation between the mechanical properties of film and the polyurethane structure
Authors: Matsuda Kazuo , Ohmura Hidemasa , Sakai Takeyo
Published: April 2003

A self‐emulsifiable polyurethane emulsion having thermosetting property was prepared by the following procedure: the polyurethane–urea–amine was first prepared by the reaction of diethylene–triamine with a prepolymer containing terminal isocyanate groups in a ketone solvent, and then the primary amino group in the polyurethane–urea–amine was reacted with epichlorohydrin. The mixture was neutralized with an aqueous acid, and finally the ketone solvent was removed by distillation in vacuo. In the polyurethane, polytetramethylene glycol (PTMG) was the base polymer functioning as the soft segment. The present paper reports the effects of the following variables on the mechanical properties of the film prepared from the polyurethane emulsion, i.e., the Mn of PTMG, the molar ratio of diethylene–triamine (DTA) to prepolymer containing terminal isocyanate groups, the structure of the isocyanate end group and the molar ratio of tolylene diisocyanate (TDI) with PTMG. The best elastomer property was realized when Mn of PTMG was 2000, TDI/PTMG molar ratio was 2.0, and prepolymer/DTA molar ratio was 0.85.
Basic principles of thermal degradation and thermal stabilization of poly(vinyl chloride). Synergism of stabilizer action
Authors: Prochaska Krzysztof , Wypych Jerzy
Published: April 2003

Changes in the quantities of active stabilizing components during thermal aging of plasticized poly(vinyl chloride) containing a mixture of calcium and zinc stearates were analyzed. A mathematical model of the stabilization process by using the stabilizer mixture and a computer program for analyzing the process of PVC thermal degradation after the beginning of HCl evolution are given.
Flame resistant cotton fabrics prepared by radiation‐initiated polymerization with vinyl phosphonate oligomer and N‐methylolacrylamide
Authors: Harris James A. , Arthur Jett C. , Goynes Wilton R.
Published: April 2003

Radiation‐initiated polymerization of vinyl phosphonate oligomer (molecular weight 500–1000) and N‐methylolacrylamide from aqueous solutions was investigated with cotton printcloth, flanelette, and sateen fabrics and with cotton (50%)–polyester (50%) flannelette fabrics. Determinations were made of the effects of radiation dosage, mole ratio of vinyl phosphonate in the oligomer to N‐methylolacrylamide in aqueous solution, concentration of reactants, wet pickup of solutions on fabrics, and irradiation of both dry and wet fabrics on efficiency of conversion of oligomer and monomer in solution to polymer add‐on. The effects of vinyl phosphonate oligomer and N‐methylolacrylamide radiation‐initiated polymerization on some of the textile properties of cotton printcloth and on flame resistances of cotton and cotton–polyester fabrics were evaluated. The breaking strength of modified cotton printcloth was about the same as that of unmodified fabric; however, the tearing strength and flex abrasion resistance of modified fabric were reduced. The textile hand of the modified printcloth fabrics that had flame resistance indicated: interaction between cellulose and vinyl phosphonate oligomer–poly(N‐methylolacrylamide) and uniform deposition in the fibrous cross section (transmission electron microscopy); surface areas of heavy deposits of oligomer–polymer (scanning electron microscopy); and phosphorus located throughout the fibrous cross section (energy dispersive x‐ray analysis). Polymerization of vinyl phosphonate oligomer and N‐methylolacrylamide was radiation initiated with cotton–polyester fabric; however, this modified fabric did not have flame‐resistant properties.
Plasma polymerization of ethylene in an atmospheric pressure‐pulsed discharge
Authors: Donohoe Kevin G. , Wydeven Theodore
Published: April 2003

The polymerization of ethylene in an atmospheric pressure‐pulsed discharge has been studied. Partial pressures of ethylene up to 4 kN/m2 were used with helium as a diluent. Deposition rates (on glass slides) were the same throughout the discharge volume over a wide range of operating conditions. These rates were in the 1–2 Å/sec range. The films were clear, soft, and showed good adhesion to the glass substrates. Oligomers large enough to visibly scatter 637.8‐nm light were observed in the gas phase under all conditions in which film deposition occurred. The experimental results suggest that Brownian diffusion of these oligomers was the rate‐limiting step in the film deposition process.
Electrical resistivity and ESCA studies on neutral poly(alkylbenzimidazoles), their salts, and complexes
Authors: Aharoni Shaul M. , Signorelli Anthony J.
Published: April 2003

A series of metal and acid salts having poly(alkylbenzimidazoles) as the parent ligand were synthesized. The room‐temperature electrical resistivity of the parent and the salts was measured. Values for the dc electrical resistivity varied from ∼1 × 1013 ohm.cm for the neutral polymers to ∼1 × 106 ohm·cm for the acid conjugate formed by reaction with HCl. Unexpectedly, changes in resistivity did not correlate with acid strength as measured by us but could be roughly correlated with the molar volume of the corresponding acid or metal salt. The nature of the complexes was elucidated using the ESCA technique. The electron core levels of nitrogen, chlorine, and the various metals were examined. The observed photoelectron spectra indicated the formation of polybenzimidazole/acid and polybenzimidazole/metal salts. In addition, one was able to conclude that the complexes of Co and Ni were high spin, thus ruling out a planar geometry for the Ni(II) complex.
NH3‐modified swelling of silica‐filled silicone rubber
Authors: Vondráček Petr , Schätz Miroslav
Published: April 2003

The NH3‐modified swelling method was used for fume silica‐filled silicone rubber compounds and vulcanizates. The method provides an estimation of the polymer–filler interaction in the system. Bound rubber reduction due to the modified swelling is shown to be dependent on the silica surface silanol content in the compound. The swelling behavior of silica‐filled vulcanizates was also studied in an NH3 atmosphere. The fraction of polymer–filler attachments in the vulcanizates was found not to depend on the particle size of silica and its surface modification, depending only on the total polymer–filler contact area in the system. No relation was found between bound rubber content in a compound and swelling of a filled vulcanizate of the same composition. The strong rubber‐to‐filler adherence found in toluene changed to nonadherence under NH3‐modified swelling conditions. The NH3‐induced cleavage of silica–silicone rubber attachments was found to be nearly completely reversible. In the silica‐filled silicone rubber vulcanizates, the fraction of polymer–filler attachments due to polymer–filler interaction represents a substantial contribution to the total number of network chains.