bluuebunny/crossref_metadata_2025 huggingface dataset:
Polymerization behavior of silver‐filled epoxy resins by resistivity measurements
Authors: Miller B.
Published: April 2003

The cure of heavily silver‐loaded epoxy resins with several amines has been investigated by resistivity–time measurements under isothermal conditions. For favorable cases activation energies in the range of 14–17 kcal./mole have been derived from slope analyses of the ρ−t plots. The relationship of the technique to similar measurements on unfilled or lightly loaded resins is discussed. Many aspects of the electrical behavior of silver‐based conductive adhesive systems are clarified by the kinetic data.
Degradation of natural rubber during mill mastication
Authors: Harmon D. J. , Jacobs H. L.
Published: April 2003

Changes in the molecular weight distribution of natural rubber, after mill mastication, have been studied by using a Water's gel permeation chromatography. This study indicates that as the polymer is milled the distribution is narrowed primarily through the breaking down of large molecular weight molecules. The peak of the distribution curve shifts to lower and lower molecular weight with increased milling time but it appears to be approaching a limiting molecular weight after 76 min. of milling time. One unexpected result is the development of a secondary hump in the distribution curve at the high molecular weight end. This hump gets larger and moves to lower molecular weight with increasing milling time until 76 min. of milling, at which time it disappears entirely.
Synthesis and degradation of poly (alkyl α‐cyanoacrylates)
Authors: Leonard Fred , Kulkarni R. K. , Brandes George , Nelson Joshua , Cameron John J.
Published: April 2003

In order to study structure‐tissue reactivity relationships and ultimately develop a less necrotizing adhesive, this laboratory undertook a study of the synthesis and degradation of the homologous series of α‐cyanoacrylate monomers and polymers. A method for synthesizing high purity cyanoacrylates and some of their chemical and physical properties and presented. In vitro kinetics studies under heterotgeneous and homogeneous conditions indicate that cyanoacrylate polymers degrade by hydrolytic scission of the polymer chain. The products resulting from such a scission are formaldehyde (positively identified by derivative formation) and ultimately and alkyl cyanoacetate. As the homologous series is ascended, the rate of degradation under neutral conditions decreases. In homogeneous solutions, under alkaline conditions, the ràte of degradation is considerably higher than under neutral conditions and the rates obtained with the methyl to the butyl derivative are of the same order. Aproposed mechanism of degradation is presented. Medical evaluation has indicated that as the homologous series is ascended, the greater the tissue tolerance to the monomers and polymers. The relevance of the results of the in vitro studies to this medical finding is presented.
Response of epoxy adhesives when stressed to failure in milliseconds
Authors: Wegman Raymond F. , O'Brien Eugene L.
Published: April 2003

This investigation showed, as did an earlier investigation, that the adhesives tested exhibit greater resistance to rapidly applied stresses than they do to slower or gradually applied stresses. Also, the adhesives were shown to lose strength with test temperature whether tested rapidly or slowly. Within a region bounded approximately by a high‐temperature second‐order transition point (the ASTM heat distortion temperature) and a low‐temperature second‐order transition point, the test data fits an Arrhenius‐type exponential equation, S = AeE/RT, where S is the stress in the joint at failure and the other terms have their usual significance. Energies calculated from this expression are lower for dynamic (fast) than for static (slower) rates of testing. Further, it was shown that little change in bond strength occurs until time to failure is below 100 msec. Plots of stress versus 1/T for a series of test times show a decided discontinuity at 1/T = 0.0039 or −16°C.
Stress softening in natural rubber vulcanizates. Part III. Carbon black‐filled vulcanizates
Authors: Harwood J. A. C. , Payne A. R.
Published: April 2003

Stress softening (Mullins effect) occurs in rubber vulcanizates during the first and subsequent deformations. This paper shows the similarity of the degree of stress softening in both unfilled and carbon black‐filled vulcanizates of natural rubber when stressed almost to break. This confirms the earlier investigations which were confined to moderate stresses. A simple interpretation of the tensile stress–strain results for filled rubber is that the strain in the rubber is increased by the presence of the filler, so that the ratio of the average strain in the rubber to the measured overall strain is given by a strain amplification factor. The usefulness of this concept is confirmed by showing the similarity of the stress‐softened curves after normalizing the strains, provided the vulcanizates of both gum and filled vulcanizates were subjected to the same initial stress.
Structure and properties of cellulose graft copolymers. I. Radiation‐induced rayon–styrene graft copolymer
Authors: Huang Robert Y.‐M.
Published: April 2003

Rayon–styrene graft copolymers were prepared by the direct radiation method, with the use of the preswelling technique, by irradiation with γ‐rays from 60Co. The grafting was carried out in bulk styrene and in styrene–solvent mixtures, such as styrene–methanol and styrene–acetone, to study their effect on the graft copolymerization reaction and the structure of the resulting graft copolymer. The effects of carbon tetrachloride, a chain‐transfer agent, was also investigated. Three different types of rayon yarn were used; Fortisan, a modifier‐type high wet‐modulus rayon, and a high‐tenacity tire yarn, in order to study the effect of rayon microstructure on the grafting reaction. The molecular structure of the rayon–styrene graft copolymers was studied by hydrolyzing away the cellulose backbone and measuring the molecular weights of the grafted polystyrene branches. For grafting in bulk styrene, the molecular weights of the grafted polystyrene ranged from 400,000 to 1,000,000, while those of the polystyrene homopolymer formed in the outside solution were of the order of 30,000–50,000. The molecular weights of the grafted polystyrene branches tended to increase with per cent grafting in the graft copolymer. For grafting in styrene–methanol and styrene–acetone mixtures, the molecular weights of the polystyrene branches decreased with increasing solvent content. The addition of carbon tetrachloride to bulk styrene resulted in a sharp decrease in the molecular weights of the grafted branches. The grafting frequency or number of polystyrene branches per cellulose chain was calculated from the per cent grafting and the molecular weights of the polystyrene branches. The morphology of the rayon–styrene graft copolymers and some of their physical properties are discussed.
Fatigue of rubber at low strains
Authors: Lake G. J. , Lindley P. B.
Published: April 2003

The fatigue failure of natural rubber vulcanizates undergoing repeated low tensile deformations has been investigated. It is found that below a critical deformation the life is greatly influenced by the ozone concentration in the test atmosphere. This result was anticipated theoretically from previous studies of cut growth behavior, and the theory enables the combined effects of the two cut growth mechanisms—mechanicooxidative rupture and ozone scission—to be taken into account in predicting fatigue life.
Molecular weight distribution in a polymer film degraded by light
Authors: Shultz Allan R.
Published: April 2003

An explicit expression is derived for the weight distribution function of polymer molecules in a photodegraded film. A most probable weight distribution of linear molecules is assumed initially present; normally incident, monochromatic light obeying a single Beer‐Lambert absorption relation is the photolyzing radiation. The dependence of the weight distribution upon the film's optical thickness and the integrated incident light flux is illustrated by curves computed according to the derived functions. Predicted gel permeation chromatograms are indicated.
Role of capillary end correction in flow analysis of molten polyethylene
Authors: Ram A. , Narkis M.
Published: April 2003

The role of the capillary end correction in flow analysis of molten low‐density polyethylenes has been analyzed. In spite of limitations of accuracy a quantitative approach has been undertaken. The results are much more complicated than predicted by Bagley in his early reports. The elastic component of the end correction is controlled by shear stress and shear modulus. The latter is affected by the size of the subchain between entangles, Me, and by the degree of long‐chain branches. Both are eventually dependent on the length of the chain, i.e., its molecular weight. In addition shear stress and temperature affect the process of disentanglement. Capillary end correction increases with increasing molecular weight and shear stress and with decreasing temperature. The available analysis of branching is still in controversy, and therefore no numerical parameters are yet proposed. A consistent theory of the response of entanglement couplings to shear forces and temperature is evaluated.
Carboxyethylation of cotton by treatment with acrylamide
Authors: Reinhardt Robert M. , Bruno Joseph S.
Published: April 2003

New methods for the treatment of cotton with acrylamide have been studied which permit the preparation of modified fabrics with relatively high degrees of carboxyethyl substitution. Wet treatment with acrylamide and sodium hydroxide can be used to produce cottons bearing both carboxyethyl and carbamoylethyl ether substituents. Adjustment of reaction conditions controls the amount and ratio of these substituents. The effects of varying the concentrations of the reactants, the time and the temperature of reaction, and the solvent media employed have been determined. Some elucidation of the chemical mechanisms is provided. Previous work has shown that dry heat treatments of cotton impregnated with acrylamide and alkali can be used to produce high carbamoylethyl substitutions with little or no carboxyethyl substitution. The present work provides an extension of the cotton‐acrylamide treatment whereby fabrics can be produced with only carboxyethyl or carbamoylethyl groups, or with mixtures of the two.
Cast polyacrylonitrile. I. Casting methods
Authors: Pellon J. J. , Smyth N. M. , Kugel R. L. , Thomas W. M.
Published: April 2003

Clear sheets of polyacrylonitrile are prepared by casting under conditions whereby an adequate supply of monomer is available to the polymerizing mass and process variables are closely controlled. This surprising behavior can be extended to some copolymers of acrylonitrile and to certain other vinyl compounds that polymerize by precipitation of polymer.
Dependence of physical properties on composition in a series of high load‐bearing polyurethane foams. Part II. Effects of variations in reactant ratios
Authors: Mendelsohn Morris A. , Black Richard G. , Runk Robert H. , Minter Herbert F.
Published: April 2003

Data and interpretations are presented on the effects of chemical variations on the physical properties, and in particular, the compression–deflection characteristics of a series of high load‐bearing, open‐celled, shock‐mitigating polyurethane foams. The load‐bearing capability of the foam is considered to be a function of density and intrinsic stiffness of the polymer. Polyol components of the formulations consisted of a poly (oxypropylene triol) of approximately 4000 molecular weight and ethylene glycol. The blowing agents were water and trimerized linseed fatty acids. A solution of polymethylene polyphenylisocyanate and tolylene diisocyanate comprised the isocyanate mixture. Stannous octoate and N‐ethylmorpholine were th̀e dual catalysts. Load‐bearing capability of the foam was raised by increasing the concentrations of the isocyanates, poly (oxypropylene triol), stannous octoate, and by employing higher ratios of polymethylene polyphenylisocyanate to tolylene diisocyanate. Decrease in compressive strength resulted from increasing the quantity of blowing agents and N‐ethylmorpholine. Increasing the quantity of ethylene glycol gave load‐bearing properties which increased to a maximum and then decreased. Chemical variations are analyzed in terms of their effects on the properties of the polymeric networks. These include crosslink density, number and distribution of hydrogen bonds, chain orientation and mobility, and relative selectivity of the various reactions. Effects on the overall bulk properties of the foam are discussed in terms of the chemical composition.
Kinetic parameters in polypropylene degradation from DTA traces
Authors: Reich Leo
Published: April 2003

A novel and relatively simple procedure is described for the estimation of kinetic parameters in pyrolyses from DTA traces. The expressions derived are tested by utilizing data from experimental thermograms. Calculated values of parameters agree well with reported values.
Effect of γ‐radiation on the dynamic mechanical properties of styrene–butadiene rubbers
Authors: Traeger R. K. , Castonguay T. T.
Published: April 2003

Three different styrene–butadiene, gum rubbers were exposed to γ‐radiation doses ranging from 0 to 200 Mrad. The crosslink densities, hardness, and the dynamic mechanical properties were evaluated. All specimens increased in hardness and crosslink density during radiation. This was reflected in an increased storage modulus, broadened loss tangent maximum, and increased relaxation spectrum. The dynamic data are presented in master curves which were developed by using the WLF equation.
Polyvinylcarbazole foams. I. Preparation
Authors: Ellinger L. P.
Published: April 2003

The polymerization of vinylcarbazole in aqueous dispersion by azobisisobutyronitrile can yield–depending on the protective colloid used–polyvinylcarbazole beads or granules. These require impregnation by a polymer solvent and preferably also by azobisisobutyronitrile before they can be molded to panels or simple shapes.
Polyvinylcarbazole foams. II. Properties
Authors: Ellinger L. P.
Published: April 2003

The uniformity, heat and solvent resistance, and thermal conductivity of foamed polyvinylcarbazole have been examined. Compressive and tensile properties, dielectric constant, and loss factor have been determined between ambient temperature and the softening range. Some features of the properties are attributed to the degree of orientation of the polymer molecules, which is thought to be the greater, the lower the density of the foam. The good high temperature stability is attributed to sterically impeded reversibility of the polymerization of vinylcarbazole.
Thermal degradation of polymers. II. Mass spectrometric thermal analysis of phenol‐formaldehyde polycondensates
Authors: Shulman G. P. , Lochte H. W.
Published: April 2003

The degradation of phenol–formaldehyde polycondensates has been investigated by mass spectrometric thermal analysis to 800°C. The thermal oxidative mechanism proposed by Conley and co‐workers has been confirmed. Direct analysis of products at frequent intervals of a temperature‐programmed heating cycle demonstrates the existence of postcuring, general degradation, and char‐forming stages. Activation energies for formation of each product and for degradation of the polymer have been determined. Phenolic homologs, products of thermal scission of methylene–phenyl bonds, show high activation energies; oxidation products have activation energies comparable to or slightly higher than that for oxidation of methylene bridges to carbonyl groups. The tarry high molecular weight products found on pyrolysis at atmospheric pressure are not formed in high vacuum because recombination reactions of phenols and formaldehyde are minimized. Otherwise, no major change in product composition, as compared to the high heating rate pyrolysis–gas chromatographic investigation of Jackson and Conley, was observed.
Observations on the coefficient of friction of polypropylene film
Authors: Schael George W.
Published: April 2003

Data are presented relating the time change of the coefficient of friction of cast polypropylene films to changes in film density and concentration of surface lubricant. It is shown that during aging the density of polypropylene increases, thus causing a decrease in the friction coefficient. It is also shown that although the lubricant added to the polymer will diffuse to the surface of copolymer films, no diffusion occurred in polypropylene films.
Ultraviolet stabilizing monomers and polymers. II. Synthesis and polymerization of acrylate and methacrylate derivatives of 2,4‐dihydroxybenzophenone
Authors: Fertig J. , Goldberg A. I. , Skoultchi M.
Published: April 2003

In the addition of stabilizing agents to plastic materials, problems such as incompatibility, migration, volatility, and/or solvent extraction of the additive frequently arise. With a view toward overcoming such problems in the use of ultraviolet absorbing stabilizers, acrylate and methacrylate derivatives containing the 2‐hydroxy‐4‐alkoxybenzophenone moiety have been synthesized. The ultraviolet absorbing monomers were synthesized by reaction of 2, 4‐dihydroxybenzophenone with glycidyl acrylate and glycidyl methacrylate. They were homopolymerized and blended with poly(vinyl chloride), poly(vinylidene chloride), polystyrene, and poly(methyl methacrylate). They were also copolymerized with the corresponding monomers. The polymer blends and copolymers were investigated for ultraviolet stability versus corresponding controls. Effective ultraviolet stabilization was observed. Differences in the stability of some blends as compared to corresponding copolymers is thought to be due to incompatibility.
Dynamic mechanical properties of titanium dioxide‐filled poly(vinyl acetate) at 0–40°C.
Authors: Galperin I. , Kwei T. K.
Published: April 2003

The dynamic mechanical properties of titanium dioxide‐filled poly(vinyl acetate) have been studied at filler concentrations of 0, 10, 20, 30, and 40 wt.‐% TiO2 by using a torsional pendulum. The damping factor was found to increase with higher temperatures. At 40°C., the damping factors for the different TiO2 concentrations were estimated to be the same. Damping factors above 40°C. were difficult to obtain due to the rubbery nature of the TiO2–poly(vinyl acetate) systems. From 24 to 35°C., 10 wt.‐% TiO2‐poly(vinyl acetate) was closer in damping factor increase to unfilled poly(vinyl acetate) than to the higher TiO2‐content polymers. At all temperatures, damping factors decreased with higher TiO2 concentration. As the temperature decreased to 0°C., damping factors for the filled systems approached a common value. Potential energy of filled systems as indicated by shear modulus values is increased by higher TiO2 concentrations and lower temperature. Kinetic energy for the filled systems, as shown by the out‐of‐phase modulus, is actually increased by larger filler concentration and higher temperature. A model is proposed where introduction of TiO2 filler acts to increase general long‐range polymer chain stiffening and at the same time enables short‐range chain mobility to rise, possibly through greater side‐chain motion.
Studies with thin membranes. I. Characterization of parlodion membranes formed by multiple dip technique and by incorporation of lipoidal substances
Authors: Lakshminarayanaiah N.
Published: April 2003

Parlodion membranes formed by the dipping technique using solutions of Parlodion in isoamyl acetate of concentrations extending to 3% have been characterized. The thickness of the membrane increased with increase in the viscosity of the membrane‐forming solution. Although the membrane resistance increased with increase in its thickness, the specific resistance ρ of the different membranes was not a constant but increased with increase in thickness and showed a tendency to attain a limiting value. The effects of different cations at the same concentration and of the same cation at different concentrations on membrane properties have been studied. Membranes formed by multiple dips into the same solution and into different solutions of Parlodion have also been characterized in respect of their electrical resistance, capacitance, and specific resistance. In general, all Parlodion solutions on a second dip gave membranes of increased thickness and resistance. Subsequent dips always increased membrane thickness and resistance except in the case of 0.25% solution which produced a membrane of approximately the same thickness and resistivity. The dipping and the spreading techniques of membrane formation have been used to introduce stearic acid, phosphatidyl L‐serine, and cholesterol into the Parlodion matrix, and the lipoidal membranes so prepared have been characterized.
Some physicochemical properties of poly (ethyl acrylate) emulsions containing carboxyl groups
Authors: Muroi Soichi
Published: April 2003

Conductometric and potentiometric titration behavior of emulsions of ethyl acrylate copolymers with acrylic acid and methacrylic acid was investigated. On the conductometric titration curves of the emulsions of the copolymers with more than 5 mole‐% of the acids, two equivalence points, based on the copolymerized acids, were observed, but only one equivalence point was observed on potentiometric titration. Almost all of the copolymerized acids could be detected by both titration methods. The change in optical density of the dilute emulsions with their pH was measured. The particles of these emulsions were studied under an electron microscope. These results showed that, when the pH of the emulsions was raised, the surface layers of the particles began to dissolve and their cores started to swell near the pH of their first equivalence points. When the pH was again lowered the dissolved polymers coagulated, tiny particles were formed, and the swollen cores were dehydrated. The surface layers thickened with increasing amount of the copolymerized acid. These behaviors were very similar in the emulsions of the copolymers with acrylic acid and methacrylic acid. The quantity of water‐soluble polymers formed in the course of the emulsion copolymerization was approximately 3–4% or slightly more. This quantity depended only slightly upon the amount and type of the copolymerized acid. The acid contents of the water‐soluble polymers were higher in cases of the copolymers with acrylic acid than in those with methacrylic acid. No relationship with the amount of copolymerized acid was established.
Experimental determination of ultrasonic wave velocities in plastics as functions of temperature. I. Common plastics and selected nose‐cone materials
Authors: Arnold Ned D. , Guenther Arthur H.
Published: April 2003

An experimental study was conducted to determine previously unavailable data showing the relationship between temperature and the velocity of longitudinal ultrasonic waves through several plastics. The ultrasonic frequencies used were between 1 and 10 Mc./sec., and the temperature range covered was between room temperature and 100°C. Velocity–temperature curves were determined for nylon, a high‐ and a low‐density polyethylene, Plexiglas, Teflon, and for several reentry vehicle nose‐cone materials, including chopped nylon phenolic, tape‐wound nylon phenolic, Castable 124, Avcoat I, and Avcoat 19. Less complete data were obtained for Avco phenolic fiber glass, General Electric phenolic fiber glass, and oblique tape‐wound refrasil. These layered materials are difficult to measure, and the velocity of acoustic waves is very dependent on the direction of propagation with respect to the laminations. For most of the materials studied the velocity was found to decrease more or less linearly with increasing temperature. Typically, the velocities at 100°C. were 9–31% less than at room temperature.
Experimental determination of ultrasonic wave velocities in plastics as functions of temperature. II. Effect of lamination angle for layered materials
Authors: Dorr Anton J. , Guenther Arthur H.
Published: April 2003

Ultrasonic longitudinal wave velocities in layered materials were measured as a function of the lamination angle at several temperatures. It was found that the longitudinal wave velocity versus lamination angle curve maintains the same shape (for a given material) for temperatures between 25 and 125°C. Furthermore, it was found that the wave velocity versus lamination angle curve can be predicted to within 2% by a theoretical equation involving only the lamination angle, & thetas; (taken as the angle between the grain of the sample and the direction of sound propagation); c (0°), the measured wave velocity at an angle of 0°; and c (90°) the measured wave velocity at an angle of 90°. Finally, it was found that the longitudinal wave velocity of certain materials varies as much as 25% between lamination angles of 0° and 90°, while other materials show less variation, and some none at all.
Tensile strengths of glassy plastics with drilled holes and measurement of griffith parameters
Authors: Arends C. B.
Published: April 2003

The tensile strengths of plastics with drilled holes can be analyzed by treating the hole as a nucleus in flaw generation. The analysis is accurate for hole diameters less than the inherent flaw size. Above this value the tensile strengths define a single curve when plotted on a reduced variable scale. Using the analysis in its linear range facilitates evaluation of the Griffith parameters. From such an application it was found that plasticizers markedly reduce the values of the Griffith parameters while affecting tensile strengths only slightly. Temperature has a similar effect.
Effect of molecular structure on the thermal aging properties of flexible urethane foams
Authors: Smith C. H. , Degisi S. L.
Published: April 2003

A series of flexible urethane foams was formulated from diisocyanate‐terminated polyether prepolymers, using both a polyether diol and an ethylenediamine tetraglycol as extenders. The long‐term compression set characteristics and the compression deflection properties of these foams were studied. The swelling effect in a solvent, the free isocyanate content, and the role of a carbon black filler on the flexible urethane foam formulation were also evaluated. It was concluded that the total amount of diisocyanate used in the formulation, rather than a variation in the type of isocyanate, has the greatest influence on molecular structure.
Kinetic study of the hydrolysis of cellulose acetate in the pH range of 2–10
Authors: Vos Kenneth D. , Burris Floyd O. , Riley Robert L.
Published: April 2003

A kinetic study of the hydrolysis of 39.8 wt.‐% acetyl cellulose acetate has been made as a function of pH and temperature over the pH range of 2.2–10 and temperature range of 23–95°C. The hydrolysis reaction was carried out on highly porous membranes under quasihomogeneous conditions and the data have been treated as a pseudo‐first‐order reaction in acetyl concentration. The reaction can be represented by the equation \documentclass{article}\pagestyle{empty}\begin{document}$k_1 {\rm = }\;k_{\rm H ^ +} \left[ {{\rm H^+}} \right]{\rm +}k_{\rm OH^-}\left[ {{\rm OH}^ - } \right] + k_{\rm H_2O} $\end{document}, and where \documentclass{article}\pagestyle{empty}\begin{document}$k_{\rm H} ^ + {\rm = 5}{\rm .24}\;{\rm x 10}^{\rm 5} {\rm exp }\left\{ {{\rm ‐ 16}{\rm .4 x 10}^{\rm 3} /RT} \right\},{\rm }k_{{\rm OH}} ^ ‐ {\rm = 1}{\rm .55}\;{\rm x 10}^{\rm 4} {\rm exp }\left\{ {{\rm ‐ 8}{\rm .1 x 10}^{\rm 3} /RT} \right\}$\end{document}, and \documentclass{article}\pagestyle{empty}\begin{document}$k_{\rm H_2O} {= 4.25\;\times 10}^{- 2} {\rm exp }\left\{ {{- 11.5 \times 10^3 /RT}} \right\}$\end{document} (where the quantities in brackets are activities of the ions shown).
Monolayer film behavior of polymers and their mixtures
Authors: Labbauf Abbas
Published: April 2003

The monomolecular film behavior of polyvinyl acetate (PVAc), polyethyl acrylate (PEA) and mixtures of these ranging in concentration ratio of PEA to PVAc from 0.008 to 11.301 has been studied using a Langmuir‐type filmbalance over an aqueous 0.01N HCl substrate. Hysteresis was observed in the compression–expansion cycle for PVAc. A discussion of polymer–polymer interaction in a mixed monomolecular film at an interface is presented. The extent of this interaction for films comprising PVAc and PEA has been determined in terms of deviations of the film area from the ideal behavior. The data on the film areas of PVAc and PEA are discussed in terms of the molecular orientation of these polymers on the surface. A simple equilibrium thermodynamic treatment is applied to the data on mixed monolayer films. The implications resulting from this study are discussed.
Reduction of shrinkage in epoxy resins
Authors: Klaus Irvin S. , Knowles William S.
Published: April 2003

Volume changes during curing of an unfilled epoxy resin using a series of anhydrides were measured. It was shown that a significant reduction in shrinkage could be achieved by proper choice of structure.
Column fractionation of polymers. VII. Computer program for determination of molecular weight distributions from gel permeation chromatography
Authors: Pickett Harry E. , Cantow Manfred J. R. , Johnson Julian F.
Published: April 2003

Gel permeation chromatography produces a type of differential molecular weight distribution directly and rapidly. Conversion of these data to conventional molecular weight distributions and plots of distributions is time‐consuming. A computer program is described to perform these operations readily. Input data from the automated chromatograph, elution volume, and recorder deflection are converted to unit sensitivity and base line corrections applied. The curve is then numerically integrated and a calibration curve used to convert elution volumes into molecular weights. Various calibration curves can readily be introduced into the program. The output, in addition to tabulation of cumulative and differential molecular weight distributions, contains values of M̄n, M̄v, M̄w, M̄z, and M̄z+1. Importantly, a reduced absolute area, i. e., area computed for unit sensitivity on a unit concentration basis, is tabulated. An additional time‐saving eature is the printing out of differential and cumulative molecular weight distribution curves and of a differential histogram.
Effect of temperature on viscosity of amylose
Authors: Khairy M. , Morsi S. , Sterling C.
Published: April 2003

Viscosity parameters were obtained for maize maylose (molecular weight of 107,000) in 1N KOH at 25, 30, 35, and 40°C. Intrinsic viscosity continuously decreased and Huggins' constant k' continuously increased with increasing temperature. The temperature dependence of intrinsic viscosity, d[η]/dT, was −2.12 × 10−2/°C.
Studies on polymer blends: Blending methods for natural rubber and styrene‐butadiene rubber
Authors: Shundo Minoru , Imoto Minoru , Minoura Yuji
Published: April 2003

The relations between the properties and the blend ratios of natural rubber (NR) and styrene‐butadiene rubber (SBR) blends were studied in comparison with four blending methods. The relations between the properties of unvulcanized and vulcanized blends and the blend ratios of blends prepared by means of solution blending, latex blending, roll blending, and Banbury mixer blending were studied. In practice, such rubber blending methods as roll blending are more effective for obtaining uniform blends than Banbury mixer blending the latter. In roll blending, it is more effective to blend NR and SBR by way of a master‐batch in which the ingredients are compounded beforehand than to blend raw rubber. In solution and latex blending, very uniform blends are easily obtained. It was found, however, that the properties of NR/SBR blends prepared carefully showed a direct relation to their blend ratios, regardless of blending method used.
Sur une méthode d'obtention de polymeres en poudre par précipitation
Authors: Chapiro Adolphe , Palma Giancarlo
Published: April 2003

Many polymers can be obtained in powder form by precipitation from dilute solutions under well‐defined conditions. For this purpose the precipitant is first added gradually until a permanent cloudiness is reached. At this point a large excess of precipitant is suddenly poured into the solution. Many examples are given. Very fine powders have also been obtained from gummy or rubberlike polymers by carrying out the precipitation at a temperature below the glass transition point of the polymer.
Semipermeable membranes of cellulose acetate for desalination in the process of reverse osmosis. IV. Transport phenomena involving aqueous solutions of organic compounds
Authors: Kesting R. E. , Eberlin J.
Published: April 2003

Transport of a solute through semipermeable membranes of secondary cellulose acetate is dependent both upon its capacity for hydrogen bonding with boung water and upon steric factors. The rate of transport of water is influenced by Gibbs adsorption of solute.
Reactivity of functional groups in surface coating polymers. Part I. Hydroxyl groups in alkyd resins
Authors: Solomon D. H. , Hopwood J. J.
Published: April 2003

The factors which can influence the availability of functional groups in polymers are considered. In particular, the importance of hydroxyl groups in the formation and Film‐forming reactions of alkyd resins is discussed, and evidence is presented to suggest that the number of hydroxyl groups available for chemical reaction is not necessarily equivalent to the theoretical value. Factors which influence the availability of the hydroxyl groups are considered, and some of the properties of the alkyd are related to the available hydroxyl content.
Adsorption of surfactant on polystyrene‐styrene interfaces
Authors: Griskey Richard G. , Woodward Clifford E.
Published: April 2003

The adsorption of sodium dodecyl sulfate on polystyrene‐styrene interfaces has been studied. Polystyrene interfaces of 20 and 60% were considered. Initial surfactant concentrations used in the study were 0.0004, 0.0008, and 0.004 mole/l. Two temperature levels, 25 and 75°C., were studied. Results showed no effect of initial surfactant concentration for a 20% interface at 25°C. However, the data for the 60% interface at 25°C. showed an effect of initial surfactant concentration. The apparent anomaly in the results regarding effect of initial surfactant concentration was explained in terms of the behavior of polystyrene‐styrene as a mixed absorbent and the work of Harkins and co‐workers, which showed that surfactant adsorption was a function of initial surfactant concentration over certain concentration ranges. Rate of surfactant adsorption appeared to be a function of surfactant adsorption raised to a power. The order of the adsorption appeared to be first‐order for the 20% interface and second‐order for the 60% interface.
Estimation of kinetic parameters during polymer degradation from two DTA traces
Authors: Reich Leo
Published: April 2003

A method is presented for the estimation of kinetic parameters during polymer degradation from two DTA traces. By this method, changes in mechanism with conversion may be detected. The method is applied to polyethylene, polypropylene, polystyrene, and polytetrafluoroethylene (Teflon). The agreement between observed and reported values of kinetic parameters is good. Advantages and disadvantages of the method are discussed.
DTA and TGA studies of flame‐resistant fabrics
Authors: Perkins R. M. , Drake G. L. , Reeves W. A.
Published: April 2003

Preliminary thermal studies were made of cotton fabrics which had been made flame resistant by chemical modification or by blending with a flame‐resistant modified acrylic fiber. DTA and TGA thermograms were made in both nitrogen and oxygen atmospheres. Differences were found in the thermograms of the untreated controls, depending upon amount of purification. Fabrics treated with the flame‐retardant formulations had lower decomposition temperatures and higher percent residue. Decomposition in oxygen was more complete and proceeded at a lower temperature. Infrared spectra of selected samples, which had been partially or completely charred, were examined. These data are related to theories about the degradation of flame‐resistant cotton fabrics.
Use of the dielectrometer for the determination of the complex dielectric constant in the microwave region in organic high polymers at various temperatures
Authors: Calamia Mario , Butta Enzo , Frosini Vittorio
Published: April 2003

A commercial type dielectrometer has been utilized for determining the complex dielectric constant of insulating materials as a function of temperature. For low‐temperature measurements, modifications of the apparatus have been made, by which the lower section of the guide, containing the specimen, is insulated from the upper section by means of a Teflon disk, in order to permit measurements under vacuum without difficulties arising from moisture condensation. Taking into account the modifications made, relations between the experimentally measured quantities and the complex dielectric constant have been elaborated, and error analysis made, and best conditions to perform experimental measurements determined. For high‐ and medium‐loss materials, in the low‐temperature range, an accuracy of the order of 1% in ϵ′ and of 10% in ϵ″ have been calculated. Better results can be obtained for measurements at high temperature. The apparatus performance and the accuracy of measurements have been checked through measurements of the complex dielectric constant of different polar polymers at frequencies of the order of 9 × 109 Hz, at temperatures between −150 and 200°C. The experimental results are in good agreement with literature data derived from experimental measurements with other techniques and with the behavior expected on the basis of the results from radiofrequency measurements through considerations of molecular mobility in relation to molecular structure.
Nonlinear least squares: A method for simultaneous thermal property determination in ablating polymeric materials
Authors: Pfahl Robert C.
Published: April 2003

A method of data interpretation known as nonlinear least squares has recently been applied by several authors to the study of polymeric materials. Nagler has used a modified method proposed by Blizzard and Jirka and has concluded that the method is impractical because it requires excessive computer time. It is shown that the difficulties Nagler encountered are inherent in Blizzard and Jirka's method, but not in the basic method. Three steps are outlined to minimize computer time, and a summary of successful applications is presented.
Turbidimetric thermal gradient technique for the estimation of compositional distribution of ethylene copolymers
Authors: Imhof L. G.
Published: April 2003

A new experimental technique has been developed for determining the compositional distribution of ethylene copolymers and blends of ethylene homopolymers and copolymers. The method is similar to the turbidimetric titration procedure, but with crystalline precipitation of the various structural species effected by lowering of the temperature. Experimentally, a Brice‐Phoenix light‐scattering photometer, equipped with a stirred heated cylindrical cell is used as a turbidimeter for measuring the light transmission through a liquid system. The decreasing light transmission of a 0.01% solution in a fixed ratio of solvent and nonsolvent of α‐chloronaphthalene and dimethyl phthalate, with a temperature drop of 2°C./min., is plotted against temperature on an X‐Y recorder. The more highly branched molecules, that is, those containing higher comonomer content, are the less crystalline, hence are more soluble and precipitate at the lower temperatures. Compositional distribution is estimated from the cooling curves by two procedures: (1) the broader temperature range over which a nonuniform resin precipitates out of solution is compared to that of a more uniform resin, and (2) the higher initial cloud point of a mixture or nonuniform copolymer is compared to the cloud point–comonomer content relationship developed for uniform resins. The effects of molecular weight and molecular weight distribution are shown to be small relative to the effects of structural distribution. The compositional distribution of the ethylenepropylene copolymers studied varies from narrow to broad, depending on the specific coordination catalyst and polymerization method used. Ethylene–vinyl acetate copolymers, on the other hand, are uniform because of the 1:1 reactivity ratios of ethylene and vinyl acetate. Synthetic mixtures of ethylene–vinyl acetate resins of varying vinyl acetate content exhibit the expected nonuniformity. This technique has also been successfully applied to mixtures of high‐ and low‐density polyethylenes, further demonstrating the utility of this new rapid tool for structural characterization. Experimental time is about 2 hr.
Kinetics of the addition stage in the melamine–formaldehyde reaction
Authors: Gordon M. , Halliwell A. , Wilson T.
Published: April 2003

The addition reaction between melamine and formaldehyde has been kinetically separated from the subsequent condensation stage by suitable choice of concentration and temperature conditions. The reaction, which is reversible, has been monitored by estimation of the free formaldehyde content of the system. It has been investigated over the range of mean degree of methylolation 1 < R′ < 3.7 of the melamine nuclei, the temperature range 25–55°C., and the pH range 5.7–10.2. The rate data thus obtained have been treated according to the random reversible addition scheme for which reasonable, first approximation, agreement was obtained. Average kinetic and thermodynamic constants have been calculated and are discussed in terms of the present model. The factors which are likely to cause deviations from randomness are described. The addition of formaldehyde to melamine proceeds by superposition of an OH−‐catalyzed step with a minor solvent‐catalyzed or uncatalyzed one.
Determination of the thermal stability and trace volatiles content of polymers. A hot‐filament thermal analysis technique
Authors: Eggertsen F. T. , Stross F. H.
Published: April 2003

The thermal stability and trace volatiles content of polymers can be determined rapidly and conveniently by using a hot‐filament pyrolyzer for heating the sample. The filament unit, of a type employed for pyrolysis‐GLC analysis, consists of a platinum coil with an attached platinum/platinum–rhodium thermocouple for measuring the sample temperature. As the sample is heated the volatile products are monitored directly with a flame ionization detector, a dual recorder being used to chart both temperature and volatiles yield. At any stage of heating the products are analyzed, if desired, with a suitable GLC column. Thermal stability measurements of several polymers were generally consistent with results by conventional thermogravimetric analysis. Advantages of the method are high sensitivity for detection of low decomposition rates, speed of the temperature adjustment, simplicity of the apparatus, and small sample requirement.
Studies of the chemical modifications of wool and their effects on the wool‐water relationship. Part I. Chemical modification of wool
Authors: Gervasi J. A. , Stannett V.
Published: April 2003

Wool has been modified to render it more hydrophobic by two methods. The first method involved treating the wool with benzoyl, lauroyl, stearoyl, and dodecenyl chlorides and with trifluoroacetic anhydride. Substantial degrees of reaction with the wool were achieved when the correct solvent media and reaction conditions were used. These varied with the particular reagent employed. Pyridine was particularly effective with the acid chlorides, whereas dimethyl sulfoxide was best with trifluoroacetic anhydride. Pyridine is believed to function both as a swelling agent and as an acid acceptor in these treatments. The second method of treatment was the grafting of vinyl and allyl monomers to wool by the use of high energy radiation. Both 60Co γ‐rays at 0.3 Mrad/hr. and Van de Graaff γ‐radiation at 3 Mrad/min. were found to be highly effective. The presence of a swelling agent in the monomer solution was found to be essential even in the case of acrylonitrile in dimethyl formamide. Water and methanol in small amounts were found to be highly efficient swelling agents. Substantial quantities of monomer could be grafted in most cases without difficulty when the correct conditions were used.
Studies of the chemical modifications of wool and their effects on the wool–water relationship. Part II. Wool‐water relationships of modified and unmodified wool
Authors: Williams J. L. , Stannett V. , Armstrong A. A.
Published: April 2003

The wool–water relationships of the modified wools prepared as described in Part I of this series have been studied. The drained water content of fabric and the solution isotherms and diffusion constants of water vapor into untreated and modified wools have been measured. Most of the treated wool fabrics showed considerable decreases in the drained water contents compared with the untreated wool. However, the degree of improvement depended markedly on the conditions of modification, particularly with the styrene grafted materials. In some cases values close to those of a comparable polypropylene fabric were found. The sorption isotherms also showed that the modifications reduced, substantially in some cases, the regains even when calculated on the wool content only. The diffusion constants were difficult to measure because of the heats of sorption causing temperature changes during the sorption; however, at lower regains this effect could be corrected. It was found that both the direct chemical modification and the grafted wools showed a diffusion behavior which was more characteristic of hydrophobic materials in that the diffusion constants tended to decrease with increasing concentration. At low humidities the diffusion constants were larger than in the untreated wool, but at higher humidities lower diffusivities were found with the modified wools.
Aging of SBR. II
Authors: Bevilacqua E. M.
Published: April 2003

Comparison of aging of a sulfur vulcanizate with a control having stable crosslinks, shows that oxygen affects reactions of the crosslink as well as of the hydrocarbon. Crosslink scission is inhibited. Results are in agreement with an earlier Suggestion that new crosslinking is enhanced by oxygen, although less than observed for natural rubber. This may be an effect of carbon black and amine antioxidants present in the vulcanizates.
A simple theory of filler reinforcement in elastomers subjected to shear
Authors: Zorll Ulrich
Published: April 2003

The effects of a filler in an elastomer can be described by means of a theory based on a simple model in which the filler particles are assumed to be of uniform size, of cubic shape, and dispersed in such a manner as to occupy the points of a cubic space lattice. For the case of shear deformation, simple relations can be derived for the increase in the storage modulus G' and the loss modulus, G″ of the bulk material with an increase in filler content. Furthermore, the theory predicts the temperature shift of two points which can be easily determined experimentally: the inflection point of G' and the maximum of G″.
Practical evaluation of the [η]–M relationship
Authors: Van Krevelen D. W. , Hoftyzer P. J.
Published: April 2003

The Mark‐Houwink equation for the relationship between the intrinsic viscosity of a polymer Solution and the molecular weight can be expressed in the more general form: [η] = 32Kθ(M/1000)a, where the constant Kθ has a theoretical meaning and the constant a is approximately equal to 0.7.