bluuebunny/crossref_metadata_2025 huggingface dataset:
Studies on the γ‐irradiation of natural rubber latex. The effects of organic halogen compounds on crosslinking by γ‐irradiation
Authors: Minoura Yuji , Asao Mamoru
Published: April 2003

As the accelerating effect of water in the crosslinking reaction of rubber in natural latex by γ‐irradiation was assumed to stem from the decomposition of water into radicals by γ‐irradiation, more effective reagents were sought among the organic halides which have greater G values for radical formation by γ‐irradiation and, simultaneously, an affinity for rubber greater than that of water. 1,2‐Dichloroethane, chloroform, carbon tetrachloride, and benzene (for comparison) were tested, and these compounds, except for benzene, were found to accelerate the reaction in proportion to their G values for radical formation. Benzene was found to have no effect, in concentrations between 1 and 5 phr. The optimum dosage was decreased to 2.1 × 106, 1.0 × 106, and 7.6 × 105 r by the addition of 1, 3, and 5 phr of carbon tetrachloride, respectively, and was assumed to have decreased to 1.17 × 107, 9.0 × 106, and 7.6 × 106 r with 1, 3, and 5 phr of 1,2‐dichloroethane, and to 8.6 × 106, 6.2 × 106, and 5.2 × 106 r with 1, 3, and 5 phr of chloroform, respectively. The physical properties of the films obtained at the optimum dosages under these accelerating conditions were equal to those of the latex irradiated up to the optimum dosage with no addition of halide. No side reactions occurred during the halide‐accelerated crosslinking that were sufficiently extensive to influence the infrared spectra.
The mechanism of post cure of viton A Fluorocarbon elastomer
Authors: Smith J. F. , Perkins G. T.
Published: April 2003

The necessity for oven post‐curing Viton A vulcanizates is explained in the following way: The formation of crosslinks is accompanied by the elimination of HF from the polymer. In the subsequent reaction of HF with the magnesium oxide present as acid acceptor water is formed which acts to inhibit the full development of cure unless it is removed from the vicinity of the polymer by post‐curing in an open system. Measurement of the rate of elimination of water from the polymer serves as a method of following the development of crosslinking during cure. Approximately two moles of water, derived from four moles of hydrogen fluoride, are associated with the use of one mole of diamine curing agent. This ratio is confirmed by independent estimates of the relationship of crosslinking density to curing agent level based on measurements of swollen compression moduli.
Studies on straining of amorphous polyethylene terephthalate above the glass temperature
Authors: Kawaguchi T.
Published: April 2003

A viscoelastic theory based on a simple model is developed to describe the stress–strain relation of amorphous plastics above the glass temperature. One of the bases of the theory is that the stress is proportional to the number of molecular chains traversing a unit cross section. Experimental results for the stress–strain relation of amorphous polyethylene terephthalate in the range 80–120°C. are presented. These are shown to agree with the theory within the experimental error.
The effects of sodium salts on the additive in viscose regeneration process
Authors: Levine M. , Burroughs R. H.
Published: April 2003

Various chemical additives are commonly used in viscose to reduce the swelling of the resultant fibers and films. It was found that inorganic sodium salts, introduced into the additive‐containing viscose, alter the action of the additive. The following salts, listed in order of the values of gel swelling ratios obtained with them, interfere with the deswelling of the viscose during regeneration: citrate > thiosulfate > tartrate > sulfate > chloride = phosphate = thiocyanate > acetate > nitrate > control. Sodium idodide did not affect the usual deswelling of the films, and sodium sulfide and sodium carbonate caused the films to deswell slightly more than the control sample. It was proposed that the effectiveness of the salts follows a Hofmeister or lyotropic series.
Crosslinking of cotton cellulose with diglycidyl ether
Authors: Jones Eugene W. , Rayburn James A.
Published: April 2003

Certain diepoxides react with cellulose under a variety of conditions to give covalent crosslinks. The ether linkages formed with diepoxides are stable to hydrolysis and offer advantages over crosslinks formed with N‐methylol compounds. Diglycidyl ether (DGE) has many advantages over other diepoxides. It has a high epoxide equivalent, low vapor pressure, and is completely water‐soluble. Both epoxide groups have equal reactivity and their reaction with cellulose can be catalyzed by acids or bases. Fabric properties obtained with DGE with the use of acidic and basic catalysts at various temperatures and concentrations are compared. DGE applied with acidic catalysts by the conventional pad‐dry‐cure process gave both dry and wet crease recovery. The same catalyst in a wet‐cure process promoted polymerization instead of crosslinking and resulted in only slight improvement in crease recovery, but did increase the tear strength. Under conventional conditions of drying and curing, weakly basic catalysts did not promote crosslinking. However, concentrations of sodium hydroxide around 3% gave both dry and wet crease recovery. Strong concentrations of sodium hydroxide at room temperature or in a wet‐cure process promoted crosslinking and gave predominantly wet crease recovery.
The role of crosslinking in enhancing wet crease recovery of cellulosic fabrics
Authors: Tesoro Giulana C.
Published: April 2003

Considerable experimental evidence has been reported in recent years in support of the theory that covalent crosslinkages between cellulose chains are essential to impart dry crease recovery to cellulosic fabrics. It has been proposed also that wet crease recovery can be increased by simple substitution in the total absence of crosslinking. It is the purpose of this paper to report a direct comparison of the effects of monofunctional and bifunctional reagents of identical size and unequivocal functionality on the wet crease recovery and other properties of cotton, rayon and other regenerated cellulose fabrics. The compounds employed are derivatives of vinyl sulfones. The synthesis of these products is briefly described, with some emphasis on the new compounds and intermediates prepared. The procedure selected for reacting the sulfones with cellulosic fabrics is described, and the differences observed in the chemical behavior of the mono‐ and bifunctional compounds are discussed. A comparison of the physical properties, and particularly of the wet crease recovery of fabrics modified to the same extent with mono‐ and bifunctional reagents, suggests that side chains are ineffective in enhancing wet crease recovery of cellulosic fabrics. The increase in wet crease recovery resulting from the reaction of swollen cellulose with polyfunctional reagents must therefore be attributed to the formation of covalent crosslinks.
Methods for determining stress distribution in adherends and adhesives
Authors: Hahn K. F. , Fouser D. F.
Published: April 2003

Loading a lap joint in tension causes the adherends to increase their tensile stress over the nominal because of the bending produced by the offset of the joint. Knowing the configuration of the joint and the tensile stress, the stress distribution in the adherends outside the joint can be determined. The theory, with resulting equations, is based on the assumption that the adherends act like a plate bent to a cylindrical surface. If the bending of the adherends is eliminated by the use of a double overlap joint, the stress distribution in the adhesive can be determined. This analysis is based on existing mathematical findings of the load distribution in riveted joints. The resulting equations have been proven experimentally by the use of the photo stress technique, and can be applied to adhesively bonded, soldered, brazed, welded, and under certain conditions, riveted joints.
Room‐temperature curing adhesives for structures
Authors: Dickstein J. , Blommers E. A. , Karo W.
Published: April 2003

Methods by which synthetic adhesives can be cured at ambient temperatures are covered. The alkyl cyanoacrylates, epoxies, and MPL monomers can be cured, with little shrinkage, to obtain metal adhesive bonds which compare favorably to those obtained by high temperature modes of curing. An investigation by which novolac epoxies were rendered more flexible with accompanying increases in the temperature and salt spray resistance is described.
Characterizing impact behavior of thermoplastics
Authors: Wolstenholme W. E.
Published: April 2003

Conventional impact testing of thermoplastics gives a single numeric criterion of impact behavior in terms of total breaking energy. It is shown that impact behavior is characterized by an elastic phase and, after yielding, a plastic phase may occur. An autographic impact tester was built by modification of a standard pendulum hammer Izod impact unit. Force‐time impulse curves show three characteristic categories in breaking; catastrophic, plastic drawing with tearing, and tearing. Photographs of impulse curves on five commercial thermoplastics clearly depict the three breaking categories. The impulse as measured by the area under the force‐time curve shows a linear correlation with impact strength. The peak force at yielding exhibits over a 2 to 1 variation among the five commercial plastics. The three materials with highest impact strengths absorb approximately 70% of the total impulse after yielding. These results indicate that impact strength is not a good single measure of the mechanical behavior of the impact properties of thermoplastics.
A study of the compression fatigue and the damping phenomena of tire cord
Authors: Kemmnitz Güunter
Published: April 2003

The dynamical properties of tire yarns were investigated, the De Mattia method being used for compression fatigue and the Meskat‐Rosenberg‐Hoffmann instrument for the performance during an alternating tensile strength test. Various influences in the test of compression fatigue after De Mattia were investigated. The intensification of the test by increasing the flex angle leads to a considerable decline in tenacity. With increasing the ply twist, the residual strength shows a maximum which lies at an optimum of cord construction. The maximum of the residual strength follows from the increase of the static twist loss and the decrease of the compression fatigue according to the ply twist. The influence of dipping, temperature, and frequency as well as the properties of different cord types were examined. The correlation between tension and flexibility is shown during the alternating tensile strength test of raw cords assuming that both change sinusoidally. Equations for the calculation of the complex modulus, the Young modulus, and the viscosity modulus as well as of the specific damping and the loss energy are stated. Measurements were carried out with viscose improved and viscose super cords and some of the results compared to those for nylon cords. The damping shows in relation to the twist construction a minimum at a constant ply twist and at a certain cable twist which is represented by the ratio Vz of ply/cable twist. A comparison of the two dynamical test methods, i.e., the compression fatigue and the tensile strength test, shows that a maximum residual strength of a certain twist construction corresponds to a minimum in damping and in twist loss. So far there exists a correlation between the static and the two different dynamic tests. Finally, the results of the two dynamic test methods are compared with the properties of cords in the tire. This comparison shows that not even in one case do the results of the laboratory tests contradict the properties of cords in tires, but in most cases correspond to them. Therefore, it can be assumed that it is possible to investigate the dynamic properties of cord twists in tires by laboratory tests with both test methods, i.e., the compression fatigue after De Mattia and the loss energy with the Meskat‐Rosenberg‐Hoffmann instrument.
Morphology of thermally degraded polyethylene
Authors: Fujiwara Yasuna , Harada Kenyū
Published: April 2003

As a clue to the solution of the spherulite structure of polymers, dendrites of thermally degraded polyethylene crystallized from the melt were studied by optical and electron microscopy. The crystal habit of the dendrites was very special, resembling neither that found in polyethylene, which has much longer chains, nor that of paraffin wax which has considerably shorter chains. Electron microscopic observation revealed the existence of developed terraces about 100 A. in height, which is in accordance with the structure of polymer single crystals. The molecules appear to fold themselves into the lamellae on crystallizing from the melt.
The effect of carbon black on thermal antioxidants for polyethylene
Authors: Crompton T. R.
Published: April 2003

The presence of 2 to 3% of carbon black prevents photooxidation of polyethylene but affords only slight protection against thermal oxidation. Small quantities of amine or phenolic antioxidants are also added therefore to prevent thermal oxidation during processing. The influence of various types of carbon black on the decomposition of one particular amine antioxidant, N,N′‐di‐β‐naphthyl‐p‐phenylenediamine which occurs during milling with polyethylene has been studied in detail. Acidic channel blacks of small particle size have been shown to accelerate the oxidation of the antioxidant. Further degradation, or adsorption onto the carbon black, of this antioxidant also occurs. With the alkaline furnace blacks of large particle size, however, oxidation takes place only to the same extent as that which occurs in clear polyethylene.
The electrical properties of some crosslinked isophthalic polyesters
Authors: Tucker R. W. , Hastings C. C.
Published: April 2003

The a.c. electrical properties (dielectric constant and loss index) of several series of crosslinked isophthalic polyester resins were investigated over the frequency range 50 to 105 cycles/sec. and over the temperature range −60°C. to above the temperature for maximum loss index. In one series of these resins, the ratio of isophthalic acid to maleic anhydride was varied, in another the chain length of the diol was varied, and in another the concentration of styrene was varied. The temperatures at which the maximum values of the electrical properties occurred are shown to be related to the heat distortion temperature, and within the range of compositions studied, could be predicted from chemical structure. The data suggest that a ratio of isophthalic acid to maleic anhydride of less than 1 : 1, short‐chain diols, such as 1,2 propanediol, and more than 50% by weight of styrene will yield the best electrical properties in polyesters of the type studied.
Differential thermal analysis of high polymers. IV. Saturated linear polyesters
Authors: Ke Bacon
Published: April 2003

Glass transition, cold crystallization, premelt crystallization, and melting in polyethylene terephthalate and copolyesters have been studied by differential thermal analysis. The transitions are affected by changing the chemical composition of the polyesters through replacing one monomer partially or completely with a different monomer. Quenching, annealing, and/or drawing, which render different degrees of crystallinity to a polyester, can also be detected directly from the thermograms.
Instrumentation for angular dependence measurements of light scattering
Authors: Dandliker W. B. , Schapiro Harriette
Published: April 2003

A filtration‐type light scattering cell effectively sealed against contamination by a liquid trap and by a long helical impingement filter is described. Very low stray light levels are achieved by means of large cell diameter and a narrow light beam. Modifications in the Brice‐Phoenix light scattering instrument necessary for the proper application of the cell are discussed. The intensities and angular dependence for water observed in this cell are in very good agreement with those obtained after multiple distillation. The excess scattering curve for 3% phosphotungstic acid in 0.3M NaCl and 1M HCl is that of a Rayleigh scatterer in the range observed (25.8 to 135°).
Polymerization studies with allyl starch
Authors: Wilham C. A. , McGuire T. A. , Rudolphi A. S. , Mehltretter C. L.
Published: April 2003

Industrial evaluation of allyl starch as a coating material in the late 1940's established that properties such as brittleness, nonhomogeneity of product, solvent solubility, and poor water resistance limited its potentialities to specialty uses. Infrared absorption analysis of allyl dextrin coatings before and after curing established that 50% of the allyl groups oxidatively polymerized. Since some degradation occurs in this process, attempts were made to limit this degradation and to improve coating properties by polymerizing pendant allyl groups with free‐radical initiators. Homopolymerization studies involving effets of molecular size and dextrin concentration indicated that intra‐molecular polymerization dominated early stages of the reaction. Graft copolymerization of a few unsaturated monomers resulted in products containing 3.6% acrylonitrile, 8.5% acrylic acid, and 15–18% acrylamide. Only with the acrylamide did no concurrent homopolymerization of dextrin allyl groups occur. Neither variations in method for polymerizing the allyl dextrins nor use of copolymers was effective in producing suitably cured coatings.
The miscibility of polymers: Interaction parameter for polybutadiene with polystyrene
Authors: Paxton Thomas R.
Published: April 2003

We have measured the solubility of mixtures of polybutadiene and polystyrene in toluene, benzene, and carbon tetrachloride, using polymers of various molecular weights and mixed in various proportions. The equations developed by Maron for solutions of nonelectrolytes have been modified for three components and for solutions of low molecular weight polymers at high concentrations. The application of these equations has provided estimates of the polymer–polymer interaction parameters χ23. The polymer–solvent interaction parameters χ12 and χ13 apparently are functions of the concentration and are not readily obtained from the present limited data.
Theory of mechanical properties of fibrillar structures
Authors: Hearle J. W. S.
Published: April 2003

A theory of the extension of a roughly oriented fibrillar structure is worked out. Two mechanisms are involved: an extension of the fibrils, and a bending of the fibrils with accompanying deformation of noncrystalline material lying between them. The combined equation for both mechanisms does not fit experimental results for nylon and ordinary rayon, but does fit results for high modulus (polynosic) rayons.
Effect of structure on temperature stability and solubility of polyester‐urethanes
Authors: Engel J. H. , Reegen S. L. , Weiss P.
Published: April 2003

The composition of crosslinked polyester–urethanes has been varied by adjusting the ratio of ester to urethane groups. The crosslinking density of these materials has been varied by changes in the polyester functionality. The polyester–urethanes have been subjected to solvent extraction, wherein it was found that at high crosslinking densities, the solubility of the polymers is unaffected by the ester‐urethane ratio. At low crosslinking densities, solubility increases slightly with increasing urethane concentration. The solubility was also found to increase with decreasing crosslinking density. Data obtained from isothermal heat aging and thermogravimetric analysis, both carried out in air and in inert atmosphere, indicate that thermal stability increases with increasing ester/urethane ratio and is independent of crosslinking density where the ester/urethane ratio is held constant. In addition, data obtained from heat aging and thermogravimetric analysis have indicated that decomposition of the samples occurs as rapidly in inert atmosphere as in air, indicating that the decomposition occurs chiefly by a nonoxidative mechanism.
Interferometric method for determining the distribution of graft concentration in radiation‐induced graft copolymer
Authors: Matsuo H. , Iino K. , Kondo M.
Published: April 2003

Microinterferometry was applied as a quantitative method for determining the transversal distribution of graft concentration instead of the usual determination of an overall graft concentration of the radiation‐induced polypropylene–styrene graft copolymer. Since polystyrene has a higher refractive index than polypropylene, the features of the interference fringe provide direct visualization of the distribution curve of graft concentration. The application of the method leads to clarify the effects of radiation dose rate, film thickness, monomer concentration, temperature, and grafting technique on the graft composition. A retardative effect on grafting appears in the vicinity of the surface, when the grafting is performed in lower radiation field and with thinner film. This is well explained by the variation in the grafting rate constant as a function of monomer concentration in the film. Furthermore, the post‐irradiation effect and accelerative effect of methanol were followed. They act effectively to form the surface, volumetric, and embedded grafts. The method has also proved useful in routine examination for a qualitative estimate of the graft copolymer.
High speed compression properties of textile structures and sheet‐like materials
Authors: Victory E. L.
Published: April 2003

High speed compression properties of textile structures and sheetlike materials that pass through a set of press rolls are found to be the controlling factor in determining the pressure schedule within the nip region, the loading of the rolls, and the minimum separation of the roll surfaces (nip thickness) of the press. Factors affecting the high speed compression properties of felts (napped textile structures) which are used to carry a wet sheet of paper through the press section of a paper machine are examined. The compressive stress‐strain curves of a single felt design are obtained using the Plastechon High Speed Tester to simulate the strain schedule within the nip region of the press section of the paper machine. Compression curves of new, used and worn felts are obtained at deformation rates from 20 in./sec. to 100 in./sec., equivalent to paper machine speeds ranging from 1000 ft./min. to 5000 ft./min. and at various levels of water content (dry, wet and saturated). The results show that the felt offers more resistance to compression as the strain rate and/or its water content is increased. Similarly, worn felts are found to require more force to achieve a given level of compression than new, napped felts. These compression curves are used to verify a general theory for determining the load versus nip strain relationship of the press section. The results of the experiments conducted on an experimental press section tend to confirm the theory and have thus pointed to the extreme importance of the high speed compression characteristics of the material in the nip region in determining the dynamics of a press.
A new class of block polymers
Authors: Tobolsky A. V. , Rembaum A.
Published: April 2003

The reaction of industrially available “prepolymers,” containing one or several isocyanate groups per chain, with tert‐butyl hydroperoxide yielded long‐chain peroxycarbamates. These were found able to initiate the polymerization of a wide variety of vinyl monomers as well as dienes leading to a new class of block polymers of very interesting physical properties. Polyether and polyester “prepolymers” with one, two, or three isocyanate functionalities were linked chemically to polystyrene, polymethyl methacrylate, poly‐n‐butyl acrylate, polyarylonitrile, and polyisoprene. The formation of block polymers was proved by both physical and chemical methods. Their mechanical properties were illustrated by means of torsional modulus–temperature curves. The effect of varying composition and of a crosslinking agent on the elastic modulus was examined. Tentative reaction mechanisms were also presented.
Cleavage of disulfide polymers. III. By disulfides
Authors: Fettes E. M. , Mark H.
Published: April 2003

A study was made of the cleavage of polymeric disulfide by organic disulfides of different structures in the presence and absence of sodium disulfide. While aliphatic disulfides will cleave polymeric disulfides only in the presence of sodium disulfide, hydroxyethyl disulfide and aromatic disulfides will cause partial cleavage in the absence of inorganic disulfide. It is believed that cleavage results not from a disulfide–disulfide interchange, but from cleavage of the organic disulfide by water to form a RS− anion. Other salts known to cleave disulfide groups promote the cleavage of polymer by butyl disulfide, sodium sulfoxylateformaldehyde being particularly active. Benzothiazyl disulfide and tetraalkylthiuram disulfides reacted to cleave in the absence of sodium disulfide but had no effect when sodium disulfide was present. By carrying out the reaction stepwise, it was found that sodium disulfide reversed the softening action of the disulfide reforming the cleaved linkages. When the disulfide polymer contained terminal thiol groups, tetramethylthiuram disulfide would reform the high polymer by converting thiol terminals to disulfide links. In spite of the known ability of these complex disulfides to dissociate homolytically into radicals and initiate vinyl polymerization, no evidence was found that the cleavage of polymeric disulfides involved RS·radicals.
Transport of liquids in structurally modified polyethylene
Authors: Baddour Raymond F. , Michaels Alan S. , Bixler Harris J. , De Filippi Richard P. , Barrie James A.
Published: April 2003

Cast linear polyethylene films subjected to dry and solvent annealing display markedly different sorption and difusion barrier properties than do untreated films. The subsequent sorption of liquid o‐ and p‐xylene and cis‐ and trans‐acetylene dichloride per unit volume of amorphous polymer increases as the annealing temperature and/or treating solvent concentration increases. Integral diffusivities calculated from sorption and steady‐state permeation rates show a monotonic increase with sorption per unit volume of amorphous polymer. The concentration dependence, however, is less marked than observed in similar systems at low permeant activity. Apparently the above treatment reduces the effective crosslinking imposed by the crystallites on the amorphous polymer chains through disentangling and incorporating some of these chains into crystallites. Thus the polymer is capable of a greater degree of swelling when brought into contact with a compatible liquid in a spite of a higher degree of crystallinity. The low concentration dependence of the diffusivities is probably due to heterogeneous distribution of excess permeant in a treated film. If the excess permeant were preferentially sorbed in regions of low polymer concentration then the above observations could be explained. Long‐duration, osmotic stress‐induced swelling and recrystallization have been cited to account for time‐dependent permeation rates in treated and untreated films.
Temperature dependence of tensile properties of polycarbonate films
Authors: Ekvall R. A. , Low J. R.
Published: April 2003

The tensile properties of bisphenol A polycarbonate films were measured as a function of temperature from +25 to −180°C. The tensile properties at a given temperature were determined from the measured true stress‐true strain behavior of the polycarbonate films by means of a photographic strain recording technique. The temperature dependence of the following tensile properties is presented: the yield stress, the fracture stress, the strain to yield, the cold‐drawing strain, the fracture strain, and the strain‐hardening rate.
Sorption of organic vapors by wool keratin
Authors: Watt I. C.
Published: April 2003

The absorption and desorption behavior of organic vapors and wool keratin has been investigated. At low relative vapor pressures sorption is Fickian and the rate of diffusion is determined by the size and configuration of the sorbate molecule. For absorption to saturation vapor pressure a second absorption mechanism is involved, depending on the ease with which the sorbate can disrupt the keratin network structure. This mechanism is superimposed on the Fickian mechanism, and the uptake shows non‐Fickian anomalies. On desorption there is an initial rapid removal of sorbate before the rate of removal becomes extremely slow. The amount of retained sorbate in the region of slow removal is dependent on the temperature, the size, and the configuration of the sorbate molecules and has been qualitatively related to the measured diffusion coefficients at low relative vapor pressures.
Factors affecting the heptane solubility of polypropylene polymers and yarns
Authors: Ross S. E. , Wolf H. W.
Published: April 2003

The heptane solubility of polypropylene yarns prepared under a variety of experimental conditions from several molecular weight ranges of polymers has been examined. The heptane solubilities of the yarns have been found to vary over a wide range, depending upon the conditions of extrusion during fiber formation and the subsequent degree of orientation of the fibers. The solubility of the yarns increases with higher spinning temperatures presumably as a function of the formation of low molecular weight soluble fractions formed as a result of thermal degradation. A reduction in the solubility occurs as the yarns are oriented either during the winding operation or by subsequent drawing. The reduced solubility has been explained on the basis of increased molecular alignment thereby promoting increased crystallinity as well as the possible entrapment of normally soluble atactic polymer. The fact that the polymer solubility can be decreased by bringing the polymer to a higher state of crystallinity has been shown by annealing studies. The solubilities of the original polymers, therefore, exhibit little correlation with the yarns produced from them. The solubilities of the annealed polymers, however, more closely approach the values obtained for the highly oriented yarns.
Effect of morphology on biaxial stress rupture of polyethylene
Authors: Cooney J. L.
Published: April 2003

The relationship between biaxial stress‐rupture behavior and polymer morphology has been investigated for a series of compression‐molded disks of linear polyethylene. Rupture data were obtained over a range of temperatures on polymers of several melt indices that had been solidified at two rates. Two failure mechanisms were observed: one at high stress levels, which was ductile; the other at low stress levels, which was brittle. The stress level at which the mechanism changed from ductile to brittle decreased as the measurement temperature increased, as the melt index of the polymer increased, and as the rate or solidification decreased. It was shown that initial pressurization of the disks causes the formation of microscopic surface fissures along spherulite boundaries as well as within individual spherulites. The extensive growth of these fissures at high stress levels sufficiently raises the stress on the sound portions of the polymer to cause large‐scale macroscopic drawing of the spherulites. At low stress levels the initially formed fissures grow by a localized drawing process at their ends. A macroscopic crack forms by a chance coalescence of a number of individually growing fissures. This process is more rapid in disks of polymer that form large spherulites when cooled slowly from the melt. The spherulite size in disks of polymer of low melt index is much smaller under the same conditions of cooling and is less sensitive to the cooling rate than in disks of polymer of high melt index. Annealing of rapidly cooled disks whose microstructure contains relatively small spherulites reduces the stress at which the failure mechanism changes without appreciably altering the spherulite size. Oxidation of the polymer also reduces the transition stress.
Mechanism of ultraviolet stabilization of polymers by aromatic salicylates
Authors: Newland G. C. , Tamblyn J. W.
Published: April 2003

Many derivatives of phenyl salicylate turn yellow when they are exposed, in solution, to ultraviolet light. This limits their usefulness as ultraviolet stabilizers for plastics. Evidence is presented to support the postulation that the yellowing is due to the formation, by a photochemical ortho rearrangement, of a derivative of 2,2′‐dihydroxybenzo‐phenone. Aromatic salicylates, such as 2,6‐dialkylphenyl salicylate, in which the ortho rearrangement is blocked, are found to be nonyellowing stabilizers, although less effective than the better yellowing varieties, such as p‐octylphenyl salicylate. Loss of stabilizer by volatilization, either in compounding or during subsequent exposure, is shown to be an important factor in limiting the effective performance of the stabilizer.
Mechanism of ozone cracking. II. Nucleation and growth of cracks in a plastic film
Authors: Salomon G. , Van Bloois F.
Published: April 2003

Partly unsaturated natural rubber hydrochloride films undergo stress cracking in ozonized oxygen. The origin of cracks and the correlation between stress distribution and rate of crack growth have now been studied. Cracks are initiated at foreign particles and/or surface fissures of microscopic dimensions. Fracture is promoted only if the shape of the incipient crack fulfils certain geometric conditions. These films become highly birefringent when stretched beyond the elastic limit; specific birefringence increases linearly with strain. It follows from stress optical studies that large plastic deformations take place ahead of the crack, whereas the film is deformed only elastically. Cut growth experiments confirm these conclusions. Fractography reveals that cracking consists mostly of a series of discontinuous events on a microscopic scale. The influence of crack length and polymer modulus on the critical stress, necessary for the onset of ozone cracking, is predictable from the Griffith criterion. The maximum stress at the tip was calculated from the observed dimensions of the crack and found to surpass the yield stress of the polymer. Mechanical brittle fracturing and ozone‐induced stress corrosion have been compared. The remaining empirical element, which determines the rate of cracking, is the rate of hardening on ozonization of the fresh surface.
Acid–base properties of fibers. Part II. A polyelectrolyte theory of the combination of fibers with acids and bases
Authors: Mathieson A. R. , Whewell C. S.
Published: April 2003

A. new theory for the acid–base properties of fibers is presented, resembling those for polyelectrolytes, and based on the normal titration of the charged groups of the fibers and the energy needed to remove the protons from the fiber to the solution, against the electrostatic, osmotic, and affinity differences. The acid titration equation for a poly‐ampholyte fiber is:

where pK0′ is the intrinsic dissociation constant of the titration groups in the fiber, α is the degree of dissociation, χ is the electrostatic potential of the fiber, τ the osmotic pressure, V̄H the partial molar volume of the hydrogen ion, and Δμ the difference of standard chemical potential in the fiber and the solution. In all cases examined, the osmotic term proved to be negligible. The electrostatic potential was calculated as suming it to be uniform over the fiber. For wool, pK0′ is independent of salt concentration but varies linearly with degree of dissociation, indicating that two pK's are operating, pKq = 3.585 for paired groups and pKp = 4.855 for nonpaired groups at 0°C., present in equal proportions. Titrations of wool with sulfuric acid and a wide range of strong monobasic acids also obey the theory, and values of the anion affinities in general agreement with those given by Gilbert and Rideal are found. The acid titration of native ox‐hide collagen gave a constant value of pK0′ = 4.0. For nylon, the value of pK0′ is, to a first approximation, independent of degree of dissociation and salt concentration, in agreement with the theory.
Synergism of free radical initiators with self‐extinguishing additives in vinyl aromatic polymers
Authors: Eichhorn J.
Published: April 2003

Vinyl aromatic polymers such as polystyrene can be made nonflammable by the addition of halogen compounds. The amount of halogen required to make such polymers nonflammable can now be greatly reduced by the addition of small amounts of certain free radical initiators. Normally about 5 phr of acetylene tetrabromide (parts of additive per hundred parts of polymer) must be added to polystyrene to obtain a self‐extinguishing polymer. Only 0.5 phr of acetylene tetrabromide is required if 0.5 phr dicumyl peroxide is added. This synergistic effect has been observed with a series of peroxides, hydroperoxides, azo compounds, quinone imines, benzothiazole sulfenamides, disulfides, and a bibenzyl compound. The synergistic mechanism seems to be based on a series of reactions involving attack of the polymer by the initiator and subsequent reaction between polymer fragments and the halogen compound. The result is a delay in the loss of halogen from the polymer mass and thus a more efficient use of the halogen additive for flame quenching. Known inhibitors of free radical reactions have a detrimental effect on the synergistic mechanism.
Preparation and chelating properties of 8‐hydroxy‐quinoline—formaldehyde polymers
Authors: Degeiso R. C. , Donaruma L. G. , Tomic E. A.
Published: April 2003

Condensation of 8‐hydroxyquinoline with formaldehyde in acid solution yielded a polymer of molecular weight ∽3300. Modification of this polymer with resorcinol resulted in improved physical properties of this material. 8‐Hydroxyquinoline‐formaldehyde polymers can be used as selective chelating ion‐exchange rains which permit separation of various cations. The polymeric metd chelates are thermally less stable than the unchelated polymer.
Fracture surface work measurements on glassy polymers by a cleavage technique. II. Effects of crosslinking and preorientation
Authors: Broutman L. J. , McGarry F. J.
Published: April 2003

It has recently been postulated that viscous flow, or plastic deformation, occurs near the tip of an advancing crack in glassy amorphous polymers such as Plexiglas, and this results in molecular orientation at the fracture surface. The evidence for this has been the appearance of colors on fresh fracture surfaces of Plexiglas and the extremely high measured surface work which is 1000 times greater than the theoretical surface energy. The effect of crosslinking has been studied by measuring the surface work of crosslinked forms of Plexiglas and highly crosslinked thermosetting polymers. The surface work decreases as the degree of crosslinking in Plexiglas increases. Colors are absent on the fracture surface of the highly crosslinked Plexiglas, and the surface is mirror‐smooth. The effect of crosslinking is to inhibit viscous flow or plastic deformation at the tip of the crack. The surface work of polyester and epoxy resins have been measured and found to be a factor of 10 smaller than the linear polymers, but still remain much higher than the theoretical estimates. Preorienting Plexiglas or polystyrene reduces the surface work of a crack propagating parallel to the orientation and increases the surface work of a crack normal to the orientation. The colors on the fracture surfaces of preoriented Plexiglas samples either disappear or change to colors of shorter wavelengths if the crack is propagated parallel to the orientation. This is a good indication that orientation occurs at the tip of a crack and is responsible for the appearance of colors on Plexiglas fracture surfaces. The surface work of 150% hotstretched polystyrene is 7000 erg/cm.2, and the fracture surface is mirror‐smooth. This surface work is greater by only a factor of 10 than the theoretical estimate and suggests that only a small amount of molecular motion has taken place.
Structural effects in metal ion catalysis of isocyanate–hydroxyl reactions
Authors: Robins Janis
Published: April 2003

Metal ion catalysis of isocyanate–hydroxyl reactions is considerably enhanced by the presence of certain “activating” groups α, β, even γ to the carbon carrying the reactive hydroxyl. Few metal ions can significantly catalyze the isocyanate–butanol reaction. In general the metal ion catalysts fall into two groups: catalysts which maintain a fair portion of their activity, even in systems containing hindered isocyanates, and catalysts which are very sensitive to changes in steric factors. It is believed that metal ions fulfill a two fold function: they increase the electrophilic character of the isocyanate group by coordinating either at the oxygen or nitrogen, and they bring the isocyanate and alcohol in closer proximity. The “activating” groups are believed to have two major opposing effects: to increase the overall stability of the ternary complex while allowing the hydroxyl group to retain most of its nucleophilicity and to produce in some cases urethanes which preferentially chelate the metal ion and kill the catalysis. All metal ions exhibit greater catalytic activity in systems containing 1,2‐ than 1,4‐glycols; furthermore the sensitivity to steric hindrance increases from 1,2‐ to 1,4‐glycols, indicating that only chelation can sufficiently increase the stability of the ternary complex to produce the maximum catalytic effect.
Ultraviolet stabilizing monomers and polymers. I. Synthesis and polymerization of phenyl 5‐methacryloxymethylsalicylate
Authors: Fertig J. , Goldberg A. I. , Skoultchi M.
Published: April 2003

With a view to permanently incorporating ultraviolet stabilizing moieties into polymer systems, monomers containing the phenyl salicylate structure have been prepared and polymerized. Phenyl 5‐acryloxymethylsalicylate and phenyl 5‐methacryloxymethyl‐salicylate were prepared by the chloromethylation of phenyl salicylate and subsequent reaction with sodium acrylate or methacrylate. Homopolymers and copolymers of the methacryloxymethyl monomer were prepared and studied. The ultraviolet spectra of the chloromethyl derivative, the monomers, and the homopolymers were essentially similar to that of the starting material, phenyl salicylate. Copolymers of the ultraviolet‐absorbing monomers (2%) with vinyl acetate, vinylidene chloride, and vinyl chloride were prepared. The ultraviolet stability of these copolymers was then compared to that of an unstabilized control series and a series containing phenyl salicylate. While there were some differences in the behavior of the copolymerized absorber it was at least as effective as phenyl salicylate in stabilizing the polymers.
Oxidative degradation of phenol–formaldehyde polycondensation initial degradation reactions
Authors: Conley Robert T.
Published: April 2003

The initial degradation of phenol–formaldehyde polycondensates has been found to follow two distinct pathways. Oxidation of the dihydroxydiphenylmethane unit to substituted dihydroxybenzophenone and dihydroxybenzhydrol species has been observed and substantiated using model compounds to support the characteristic infrared spectral changes. The ingrowth of ketonic species has been evaluated kinetically on phenol–formaldehyde polymers which have been cured fully to remove residual methylol groups. The rate constants have been found to be a factor of 33 times slower than those observed earlier for partially cured resins having relatively large numbers of residual methylol groups present. The activation energy for the initial ketonic carbonyl was found to be 15.6 ± 3.9 kcal. This value compares favorably with other values obtained for phenolic oxidation. The potential oxidation of methylol groups to substituted salicylic acid moieties could not be substantiated spectrally. However, a polymer containing 2‐methylol‐p‐cresol on oxidation gave a small quantity of 5‐methylsalicylic acid, thus substantiating methylol oxidation in competition with the further curing reaction which produces new diphenylmethane linkages. The secondary oxidation resulting in chain scission can be separated on a time scale from oxidations of the methylol type. The present study therefore significantly extends the initial oxidative degradation chemistry of phenol–formaldehyde polycondensates.
Incremental modification of styrene‐butadiene rubber with tert‐nonyl mercaptan
Authors: Uraneck C. A. , Burleigh J. E.
Published: April 2003

A model equation derived for the viscosity‐average degree of polymerization (P̄v) for the incremental addition of modifiers, P̄v = K{(exp{arx1} − 1) + [2/(2 + exp {x1r})]a(exp{arx2} − exp{arx1})}1/a indicates a minimum should occur in a curve of P̄v versus conversion at which the increments are added, x1. Incremental addition of commercial tert‐dodecyl mercaptan in the laboratory to SBR recipes at 5°C. showed effects contrary to those predicted by the model equation, but incremental addition experiments with tert‐nonyl mercaptans resulted in a minimum in viscosity versus x1 curves, changed the molecular weight distribution, and required 34 wt.‐% less mercaptan than did the tert‐dodecyl mercaptan control (all the tert‐dodecyl mercaptan added initially). Incremental addition of tert‐nonylmercaptan in pilot plant 20‐gal. autoclave reactors gave essentially the same results found in the laboratory bottle experiments. The stress‐strain and mixing properties of the incrementally modified polymer and the tert‐dodecyl mercaptanmodified control were essentially the same within experimental error. Conditions required for successful application of the incremental modifier technique are given.
Thermoplasticity of acetylated cotton yarn as influenced by degree of substitution, temperature, and other factors
Authors: Creely J. J. , Harbrink P. , Conrad C. M.
Published: April 2003

The relative degree of thermoplasticity of acetylated cotton yarns has been determined by a technique developed for the purpose. The interfering contribution of hydrogen bonding could be eliminated by a wetting‐out process. The yarns were acetylated to degrees of substitutions ranging from 0.77 to 2.93. Heat setting was applied either in vacuum or at atmospheric pressure in the presence of water vapor at temperatures in the range of 110–225°C. The thermoplasticity observed over a period of 30 days was permanent but readily removable by another application of heat setting. The effect of degree of substitution upon thermoplasticity could be represented by sigmoidal curves beginning at about DS = 1 and increasing rapidly and asymptotically to a maximum at about DS = 2.25. In vacuum or water vapor the maximum thermoplastic response occurred at 175°C., but the response was greater with water vapor. Under vacuum heating a very distinct minimum response occurs at 180°C., due to second‐order transition effect. Upon heating in the presence of water vapor a distinct minimum response occurs at 200°C. with secondary minima at 150 and 120°C. Prior crystallization (by heating to 200–225°C.) greatly reduces thermoplasticity due to reduction of the amorphous component, but does not completely eliminate it.