bluuebunny/crossref_metadata_2025_split huggingface dataset:
Production of super‐tenacity polypropylene filaments
Authors: Sheehan W. C. , Cole T. B. 
Published: April 2003

AbstractThe effects of the conditions fiber formation on structural parameters and tensile properties of melt‐spun, highly isotactic polypropylene filaments were investigated to determine the feasibility of producing supertenacity polypropylene filaments. Meltspun polypropylene monofilaments were prepared from five highly isotactic polymers (94% or more by extraction), under different conditions of extrusion, quenching, drawing, and annealing. The molecular weight, molecular weight distribution, crystalline structure, crystallinity, crystallite orientation, and total molecular orientation (as expressed by total draw ratio) of the experimental filaments were determined, and the relationships between these structural parameters and the tensile properties of the filaments are discussed in the paper. Several of the experimental polypropylene filaments produced had tenacities greater than 12 g./den. and one of them had a tenacity of 13 g./den. Polypropylene filaments having tenacities greater than 13 g./den. appear feasible. To produce the super‐tenacity polypropylene filaments, a polymer with a weight‐average molecular weight of about 470,000 was melt spun into undrawn filaments having the paracrystalline structure, and the filaments were drawn to a maximum and annealed. The tenacity of the polypropylene filaments increased with increasing fiber molecular weight. A narrow molecular weight distribution was beneficial, but was not necessary for obtaining high tenacities. High draw after spinning was important in producing high tenacity. The maximum amount that a fiber could be drawn depended upon its molecular weight, the amount of stretch introduced during spinning, and the drawing time and temperature (filament temperature). Filaments having the paracrystalline structure, which was obtained with proper extrusion and quenching conditions, could be drawn more easily than filaments having the crystalline structure, and hence, under equivalent conditions, the former could be drawn more. The more the filaments were stretched during spinning, the lower were their tenacities. The relationship between crystallite orientation and the tensile properties of drawn and annealed filaments stretched during spinning was different from the relationship for drawn and annealed filaments that were not stretched during spinning. The highly drawn filaments contained voids, but they could be removed by proper annealing conditions, which also increased the tenacity of the filaments.
Block polymers of styrene and acrylonitrile
Authors: Perry Eli 
Published: April 2003

AbstractOne‐to‐one block polymers of styrene and acrylonitrile were prepared by a two step process: (1) styrene was polymerized in the presence of a dialkylphosphine and (2) the polystyrene was used to initiate the polymerization of acrylonitrile. The blocks contained 14–76% acrylonitrile and were 60–100% pure as judged by extraction with toluene at 110°C. Phase and electron microscopy showed that the block polymers consisted of a continuous polystyrene phase when the acrylonitrile content was less than 70% by weight and of a continuous acrylonitrile phase when the acrylonitrile content was above 70% by weight. The polyacrylonitrile dispersed phase was regular and almost spherical. Its measured size equaled the calculated size, assuming that the spheres had a diameter of twice the length of the fully extended polyacrylonitrile chains. Polyblends of homopolymers were similar to the block polymers in structure, except that the dispersed phase was very irregular in size and shape. The physical properties of blocks and polyblends were similar and were inferior to those of polystyrene homopolymers and styrene–acrylonitrile random copolymer except for modulus and for maintenance of modulus over a temperature range. The random copolymer had the highest strength properties, which fact was attributed to the absence of a two phase system and the presence of psuedo‐crosslinks. The relatively poor properties of the blocks and polyblends were ascribed to the inability of bulk polyacrylonitrile to absorb energy and to the buildup of stress concentrations at the phase boundaries.
Carbon black–polymer interaction: A measure of reinforcement
Authors: Brennan J. J. , Jermyn T. E. , Boonstra B. B. 
Published: April 2003

AbstractThe interaction of carbon blacks with high polymers during the mixing process was studied by using fillers having a wide range of surface characteristics. Glass beads, Graphon, high‐structure blacks, and heat‐treated blacks were mixed with elastomers in the Brabender Plasticorder. With the use as a rubber matrix of a high polymer that did not materially change during the mixing process in molecular weight or viscosity, excellent correlation was found between final torque required for mixing and black structure and between peak torque and bound rubber. Increasing interaction was shown to lead to increased mixing torque, increased Mooney viscosity, increased modulus, and higher state of cure, as measured by swelling. If the high polymer matrix breaks down during the mixing process these influences of interaction are mostly obscured by diminishing molecular weight.
Structural turbulence in polymer solutions
Authors: Ram A. , Tamir A. 
Published: April 2003

AbstractThe appearance of structural turbulence in polyisobutylene solutions at low Reynolds numbers has been detected and analyzed. This type of turbulence is characterized by a critical shear stress rather than a critical Reynolds number. The critical shear stress decreases with increasing molecular weights of dilution. The role of deformability of the polymer chains under shear flow is found to be significant.
Elastic modulus of Mylar sheet
Authors: Becker Herbert 
Published: April 2003

AbstractHigh precision stress–strain curves were determined from representative Type A Mylar sheets in several commercially available thicknesses. A representative value for Young's modulus was found to be 0.76 × 106 psi. Measured values were from 0.60 to nearly 0.78 × 106 psi with the maximum value occurring at 0.005‐in. thickness.
The photooxidation of polymers. II. Photolysis of polystyrene
Authors: Grassie N. , Weir N. A. 
Published: April 2003

AbstractIn the vacuum photolysis of polystyrene films at 28°C. under 2537 A. radiation the only gaseous product is hydrogen. At the same time the polymer becomes insoluble and discolors. The intensity exponent of the reaction is unity, the quantum yield of hydrogen is 4.3 × 10−2, the overall energy of activation is 2.9 kcal./mole, and the rate of photolysis is independent of molecular weight. No hydrogen is produced when 3650 A. radiation is used. These observations can be interpreted in terms of a simple reaction scheme in which the primary effect of the 2537 A. radiation is to liberate hydrogen atoms. The subsequent reaction of these and the polystyryl radicals simultaneously formed in a number of competing steps results in the appearance of hydrogen, the occurrence of crosslinking, and the production of carbon–carbon unsaturation in the main chain which ultimately leads to conjugation and color. These theories are supported by infrared and ultraviolet spectral measurements and by the observation that the rate of photolysis is accelerated by nitrogen.
Oxidative degradation of polybenzyl
Authors: Conley Robert T. 
Published: April 2003

AbstractThe primary steps involved in the degradation of polybenzyl at temperatures between 140 and 220°C. in the presence of air or pure oxygen has been found to be an attack at the methylene linkages to give benzhydrol and benzophenone linkages. Kinetic evaluation of the rate of benzophenone‐type carbonyl ingrowth indicated an apparent initial activation energy for the oxidation process of 14.5 ± 3.5 kcal. Vapor‐phase chromatographic analysis of the volatile products of the reaction indicate that the formation of benzoic acid and benzophenone are the major products of oxidation, along with smaller amounts of benzene, toluene, water, and carbon dioxide. It must be concluded that the initial oxidation of polybenzyl closely parallels the oxidation of phenolic resins and other closely related activated methylene polymers. Secondary degradation reactions which produce chain scission are generally equitable to further oxidation at both the benzhydrol and benzophenone linkages. The appearance and spectral substantiation of the formation of benzoic anhydride linkages from thermal dehydration of benzoic acid most adequately accounts for the formation of the secondary reaction products giving new but minor infrared bands in the early and intermediate stages of the degradation.
Role of ozone in dynamic cut growth of rubber
Authors: Lake G. J. , Lindley P. B. 
Published: April 2003

AbstractThe effect of ozone on the growth of cuts in rubber strips subjected to repeated tensile deformations has been investigated. At tearing energies below a critical value ozone accounts for all the cut growth, and in this region the rate of growth also occurs due to mechanico‐oxidative rupture, the rate of this type of growth increasing rapidly with increasing tearing energy so that the effects of ozone are normally slight. For vulcanizates of natural rubber and SBR unprotected by antiozonant, the characteristics of dynamic ozone cut growth can be deduced from static measurements. If a natural rubber test piece is not allowed to relax to zero strain on each cycle, the effects of ozone are important over a wider range of tearing energy.
DTA study of heterogeneous nucleation of crystallization in polypropylene
Authors: Beck H. N. , Ledbetter H. D. 
Published: April 2003

AbstractThe effect of cooling, nucleation, and spherulitic growth rates on the properties of polypropylene is discussed briefly. A differential thermal analysis technique is described for evaluating the relative extent of heterogeneous nucleation that occurs in a particular polypropylene composition. The method is based upon a nucleating agent's ability to reduce the relatively large amount of supercooling that occurs upon crystallization of polypropylene. Compounds are shown to vary widely in their effectiveness as heterogeneous nucleating agents in polypropylene. The relationships between the degree of supercooling of a particular polypropylene composition and its relative clarity, tensile properties, density, and morphology are shown.
Studies on the drawing of polyamide fibers. IV. Effect of drawing on the degree of longitudinal swelling
Authors: Takagi Yasuo , Hattori Hiroshi 
Published: April 2003

AbstractThe longitudinal dimensional change of dried nylon 6 monofilaments of various draw ratios swollen in the atmosphere of 24°C. and 100% R.H. was studied. The degree of longitudinal swelling in equilibrium changes with the conditions of drawing and the draw ratio of the sample; for the samples drawn immediately after spinning, it increases, passes through a maximum near a draw ratio of 2, and gradually decreases as the draw ratio increases; for the samples drawn many days after spinning the maximum point is at a draw ratio near 2.8, while for the samples drawn after heat‐treatment the degree of longitudinal swelling does not change appreciably with the draw ratio of the sample. The rate of longitudinal swelling remains nearly constant or increases slightly in the range of draw ratios of 1–3. It then decreases with the draw ratio at draw ratios higher than 3.
Recrystallization of amorphous cellulose
Authors: Wadehra I. L. , Manley R. St. John 
Published: April 2003

AbstractRecrystallization of amorphous cellulose prepared by saponification of cellulose triacetate in an non‐aqueous medium was found to occur only at very high relative humidities, i.e., near 100%. At lower relative humidities the amount of recrystallization occurring was slight though significant. Correspondingly, the accessibility decreased from 90% (for amorphous cellulose) to a minimum of 79%, the same as that for cellulose II. The mechanism of recrystallization is discussed in terms of the surface tension, plasticizing action, and the hydrogen bonding ability of the solvent used for bringing about the recrystallization.
Characterization of block and random ethylene–propylene copolymers by differential thermal analysis
Authors: Barrall Edward M. , Porter Roger S. , Johnson Julian F. 
Published: April 2003

AbstractA group of C14‐tagged ethylene and propylene polymers consisting of physical mixtures of homopolymers, block copolymers made up of two homopolymer sequences, and block copolymers made up of several homopolymer segments has been studied by differential thermal analysis (DTA). The effect of randomness in copolymers has also been studied in this set of systems, which contains 0–51 wt.‐% ethylene. Block copolymers and physical mixtures have been found to have thermograms with endothermal minima at approximately 138 and 163°C. The ratio of heights of the two minima has been found to be a function of the ethylene and propylene content for mixtures of homopolymers and for block copolymers without randomness. DTA thus provides an analysis for monomer ratios in physical mixtures and in block copolymers of ethylene and propylene. The cooling thermograms of block copolymers have been demonstrated to have two exotherms in all cases where the block ethylene content exceeded 10%; the propylene limit was not fixed. Mixed homopolymers do not exhibit two freezing exotherms. The total heat of fusion of the polymer has been found to be a usable measure of chain randomness and block nature. The conditions for observation of single and multiple transitions have been extended.
Glyceryl methacrylate hydrogels
Authors: Refojo Miguel F. 
Published: April 2003

AbstractHydrophilic three‐dimensional polymer networks (hydrogels) were prepared from glyceryl methacrylate (2,3‐dihydroxypropyl methacrylate). The solubility of poly(glyceryl methacrylate) in water permits the preparation of transparent hydrogels containing variable amounts of water at the equilibrium stage. This is accomplished by varying the degree of swelling at the time of network formation, and by varying the density of crosslinks. The temperature dependence of swelling of the hydrogels in water and in 0.9% sodium chloride solution, was determined. There exists a linear relationship between the refractive index and the per cent of water in the hydrogel. These hydrogels are potentially useful in ophthalmology.
Studies on the drawing of polyamide fibers. VI. Effect of drawing on the dye diffusion parallel to the fiber axis
Authors: Takagi Y. 
Published: April 2003

AbstractThe diffusion rate of an acidic dye (vylene Fast Blue 2P) into polycaproamide fibers along the direction parallel to the fiber axis (longitudinal diffusion rate) was obtained by measuring the dye penetration distance from a cross section of the sample fiber embedded in an acrylic resin. The following results were obtained. The longitudinal diffusion constant decreases monotonically with increasing draw ratio. The difference between the lateral dye diffusion constant and the longitudinal dye diffusion constant passes through a maximum near a draw ratio of 2. The activation energy for the longitudinal dye diffusion increases monotonically with draw ratio.
Effect of impurities on the polymerization of vinylcarbazole by azobisisobutyronitrile
Authors: Ellinger L. P. 
Published: April 2003

AbstractPolymerization of vinylcarbazole by free‐radical initiators, especially azobisisobutyronitrile, yields polymer of higher molecular weight and better appearance than can be made by thermal polymerization. The polymerization is retarded and the molecular weight of the polymer lowered by amounts of anthracene comparable to or somewhat larger than the initiator concentration, but these effects soon show saturation at higher anthracene concentrations. Phenanthrene has a slight inhibiting effect which increases with concentration, the polymerization being almost completely inhibited at very high phenanthrene concentrations. The results are discussed in terms of the formation of an intermediate complex between the aromatic hydrocarbon and the growing polymer chain.
Correlation and prediction of polyamide glass transitions
Authors: Beaman Ralph G. 
Published: April 2003

AbstractA simple scheme for the prediction of glass transition temperatures based on diamine and diacid component part contributions is applied to data for 19 interrelated polyamides. The new results, in conjunction with many prior determinations, lead to the assignment of 65 ± 20°C. for the glass transition of 6‐6 polyamide, contrary to published suggestions that the value might well be −65°C.
Dynamic mechanical behavior of poly(2‐hydroxyethyl methacrylate)–glass beads composites
Authors: Kolařík J. , Janáček J. , Nicolais L. 
Published: April 2003

AbstractThe dynamic relaxation behavior of a model two‐phase system, poly(2‐hydroxyethyl methacrylate)–glass beads, was studied by means of a freely oscillating torsional pendulum. The effect of the filler content on the storage and loss moduli of the composites could be described in terms of the modified Kerner equation in complex form. At temperatures below the glass transition temperature of the matrix, the agreement between experimental and theoretical data was satisfactory after correction for thermally induced stress due to different thermal expansion coefficients of matrix and filler. In the presence of filler, the capacity of the matrix to store and dissipate energy increases, but the character of molecular motions underlying the dispersions observed is preserved because the temperature of the dispersions remains unchanged. The effect of water on the dynamic relaxation behavior of composites is primarily reflected in changes in the shape of the temperature dependence of the dissipating capacity of the matrix. The data allow the conclusion to be drawn that the chain mobility at the interphase boundary does not decrease and that no additional frictional mechanisms appear.
Transitions and relaxations of linear polyesters related to poly(ethylene terephthalate). II. Glassy and gamma
Authors: Yip Harry K. , Williams H. Leverne 
Published: April 2003

AbstractThe β‐relaxation at Tg of the terephthalate and isophthalate series is due to molecular motions of the backbone chains in the amorphous region, but differs for the isophthalate series in that the p‐phenylene group does not exhibit the free rotation possible for the m‐phenylene group. Consequently, the relaxation times of the terephthalate series are longer than for the isophthalate series. The γ‐relaxation (Tγ) for the higher homologues of the terephthalate series cannot be explained in terms of the poly(ethylene terephthalate) analogy. For poly(ethylene terephthalate) and poly(tetramethylene terephthalate), an induced cooperative type of motion of all the moieties is possible, whereby overlapping processes caused by “rocking vibrations” are observed as one γ‐peak. The resolution of the γ‐loss peaks for the above‐mentioned polyesters into components is not possible at the experimental frequency of 110 Hz. For poly(hexamethylene terephthalate) and poly(decamethylene terephthalate), the “rocking vibrations” between the moieties of the skeletal chain are reduced so that even at a test frequency of 110 Hz, the γ‐loss peaks could be resolved into two or three components. In the case of poly(decamethylene terephthalate), three components are resolved; the lowest temperature peak γ1 is attributed to hindered motions of the methylene portions, the γ2 peak is attributed to motions of the carbonyl group in the gauche conformation, and the γ3 peak is attributed to the carbonyl group in the trans conformation of the skeletal chain in the amorphous region. The general observations obtained by other techniques were confirmed by the forced vibration analyses. As the length of the methylene chain increased, Tg decreased. As crystallinity increased, the β‐relaxation moved to higher temperatures and the damping peak was smaller and broader. The damping peak moved to lower temperatures and increased in size as the length of the methylene chain increased. The damping peak was larger for the isophthalate homologue than for the corresponding terephthalate polyester.
Polymer composites containing plasma‐treated mica. II. Dielectric properties
Authors: Wertheimer M. R. , Paquin L. , Schreiber H. P. 
Published: April 2003

AbstractThe complex relative premittivity K*(ω) of polymer–mica composites has been studied in the frequency range extending from about 10−2 to 107 Hz. Microwave plasma treatment in ethylene of the mica flakes leads to significant alterations of K*(ω) for the matrix polymers used—polyethylene, polystyrene, and a mixture of these two polymers. The origins of the dispersion characteristics were investigated using a series of polyethylene samples containing up to 50 wt‐% of untreated mica. Comparing experimental results with theoretical analyses of the Maxwell‐Wagner‐Debye‐like interfacial polarization effect, it is possible to identify two major contributions to K*(ω): a Debye‐like dispersion centered near 102 Hz and a charge‐diffusion mechanism which contributes primarily at low frequencies (≲10 Hz).
Water‐soluble polymers as retention aids in a model papermaking system. I. Polyacrylamides
Authors: Howard G. J. , Hudson F. Lyth , West Jeremy 
Published: April 2003

AbstractA series of polyacrylamides covering a wide molecular weight range were synthesized and employed as retention aids in a model papermaking system of cellulose fibers and titanium dioxide. The ability of the polymer to increase the proportion of added titanium dioxide that is retained in the formed paper sheet is strongly dependent on molecular weight, but not on pH. Adsorption isotherms on both pigment and fibers are strongly molecular weight dependent. Polyacrylamides have no more than a weak flocculating effect on fiber suspensions and stabilize dispersions of titanium dioxide. However, with mixed dispersions of fibers and pigment, in the same ratio (10:1) as in paper formation, strong coflocculation is evidenced by the higher molecular weight polyacrylamides. In this model system pigment retention is a consequence of a heteroflocculation by adsorbed polymer bridging between the particles of titanium dioxide and cellulose fibers, possibly augmented by improved filtration in the forming sheet. Electrostatic effects appear to be unimportant in the system under study.
Polysulfone hollow fibers. II. Morphology
Authors: Cabasso Israel , Klein Elias , Smith James K. 
Published: April 2003

AbstractThe morphology of porous polysulfone hollow fibers which were spun by the dry–wet spinning process is discussed. It was demonstrated that a relatively moderate quenching medium should be employed in the bore of the nascent fiber in order to produce an isotropic fiber free of macrovoids and intrusion cells. A rather delicate quantitative balance between the internal precipitant and the spinning solution has to be maintained, especially when low‐viscosity polymeric solutions are employed. Scanning electron micrographs of fiber cross sections display highly porous, spongestructured walls which in some instances exhibit a rather dense interface skin. However, control of the extrusion/coagulation procedure allows the formation of skinned, porous skinned, and nonskinned fibers.