bluuebunny/crossref_metadata_2025_split huggingface dataset:
Environmental stress cracking in impact polystyrene
Authors: Bubeck R. A. , Arends C. B. , Hall E. L. , Sande J. B. Vander 
Published: December 2004

AbstractEnvironmental stress cracking (ESC) measurements for various impact polystyrenes were performed using a constant load technique with the specimens in contact with a 50/50 solution of cotton seed oil and oleic acid. It was shown that ESC in impact polystyrene is controlled by the transport of the aggressive liquid through a pre‐established dry craze structure where capillary pressure is the driving force. At moderate stress levels just above the critical stress for environmental cracking, there is an apparent incubation time for the dry craze formation. The craze incubation time is strongly influenced by thermal stresses induced by the gel particles. As a consequence, ESC is two‐stage process involving both an incubation time and actual crack growth. Control of the craze structure to maximize fibril content is essential for good ESC resistance. The craze fibril content can be altered by variables such as gel particle size, matrix molecular weight, plasticizer content, and rubber content.
The flow of thermosets through the nozzle of an injection molding machine
Authors: Rojas Alfredo J. , Adabbo Humberto E. , Williams Roberto J. J. 
Published: December 2004

AbstractThe conservation equations of momentum, energy, and mass are numerically solved for the flow of thermosets through the nozzle of an injection molding machine. The following working hypotheses are stated: perfect mixing of reactants, validity of the lubrication approximation, steady state (based on previous results for thermoplastic materials), negligible diffusional mass transfer, adiabatic boundary condition, and wall slip. Numerical results for a particular case‐show that the value of the slip friction coefficient is very important for defining the process feasibility. The apparent viscosity of the material is also relevant to the process. Materials of low viscosity gel at the wall of the nozzle inlet section; high viscosity materials may gel at the outlet section, requiring great pressure gradients and showing high wall temperatures at the exit. These high temperatures may cause degradation or undesirable side reactions.
Water vapor resistance of plasma‐polymerized coatings on potassium bromide windows
Authors: Wydeven T. , Johnson C. C. 
Published: December 2004

AbstractPlasma‐polyme rized (PP) coatings of chlorotrifluoroethylene (CTFE), tetraluoroethylene (TFE), and ethylene were deposited in a capacitively‐coupled 13.56‐MHz radio‐frequency glow discharge on potassium bromide (KBr) infrared windows for moisture protection. The PPTFE coatings deposited slightly downstream of the internal plasma reactor electrodes provided the best moisture protection for the KBr windows. The PPTFE‐coated windows tolerated an upper limit relative humidity of about 80 percent at 297°K without visible damage occurring to either window or coating within 24 h (86.4 ks). It appeared from environmental tests that some of the coatings failed to protect the KBr windows from moisture because of defects in the coatings (pinholes, cracks); others failed because of their high water permeability. Elemental analysis of the bulk and photoelectron spectroscopy (ESCA) of the surface of PPTFE coatings deposited downstream of the electrodes revealed that these samples contained less oxygen (from the atmosphere) than coatings deposited between the electrodes. The lower oxygen content of the coatings deposited downstream may have accounted for the improved moisture resistance of these coatings. The PPTFE coatings were posttreated by heating and by cross‐linking with activated species of inert gases (CASING). Neither post‐treatment technique was effective in improving the moisture resistance of the PPTFE coatings.
Dynamic mechanical properties of polystyrene‐polydimethylsiloxane blends
Authors: Clark Allan J. F. , Shaver Alan , Eisenberg Adi 
Published: December 2004

AbstractIt was found that commercial silicone grease incorporated accidentally into polystyrene bars yields a major dynamic mechanical loss peak at ca. −128°C. This finding was followed up with a study of various polydimethylsiloxanes and silicone rubber, in which up to three peaks were found. In order of increasing temperature (at 1 Hz) these are the glass transition (Tg; ca. −128°C), crystallization (Tc; ca. −110°C) and melting peaks (Tm; ca. −50°C). Hydrocarbon‐based greases were also investigated. The results indicate that the methods employed may be of use for the investigation of the dynamic mechanical properties of small amounts of material of varying particle sizes, such as powders of cross‐linked polymers, that need not be compatible with, or soluble in, the host matrix. The sensitivity of the method is such at a 1 percent by weight contamination of silicone grease in polystyrene gives a loss tangent peak of at least 0.002 above background, and emphasizes the necessary care to be taken during sample preparation to exclude unwanted substances.
Semi‐stiff chain aromatic polyamides: New candidates for thermotropic liquid crystalline polymers
Authors: Adduci J. , Chapoy L. L. , Jonsson G. , Kops J. , Shinde B. M. 
Published: December 2004

AbstractA spectrum of newly synthesized polyamides have been characterized with the intent of elucidating crystalline and possible liquid crystalline behavior. The different polymers contained various rotatable linkages in the main chain as well as substituent methyl groups in some cases. These were deemed as important variables for controlling the propensity to form ordered morphologies in these polymers. Methods of characterization included: X‐ray diffraction analysis, differential scanning calorimetry, and optical birefringence.
Pretransitional effects in the isotropic phase of a lyotropic polymer liquid crystal
Authors: Dupré Donald B. 
Published: December 2004

AbstractConsolidation of chiral orientational ordering in concentrated solutions of poly(benzylglutamates) has been investigated by polarization microscopy, measurements of birefringence and optical rotatory dispersion. A pretransitional region was examined where the temperature and concentration of polymer are held just below critical conditions for phase separation of anisotropic, liquid crystal spherulites. Optical rotations observed in this visually isotropic region are considerably in excess of those found in dilute solution of the polymer and exhibit a strong temperature dependence. This critical enhancement of optical activity is attributable to short‐range chiral ordering of the long axes of macromolecules in the isotropic phase.
Tensile properties of polyethylene blends
Authors: Shishesaz M. R. , Donatelli A. A. 
Published: December 2004

AbstractBinary and ternary blends were prepared from low, medium, and high density polyethylene. The tensile properties of these materials indicated that the blends formed either compatible or semi‐compatible mixtures. One of the ternary blends exhibited a slight synergism in properties which could be partially attributed to an enhancement in crystallinity. Such blends may have practical utility by yielding materials having a combination of strength, stiffness, and toughness.
Probing the nonequilibrium nature of polymer glasses by Fickian diffusion of alkane permeants
Authors: Chen Stephen P. 
Published: December 2004

AbstractVolume relaxation of glassy polymers has been followed by diffusion of simple alkane permeants. The changes in diffusion rates allow direct monitoring of changes in segmental mobilities of the polymers. In general, the diffusion rates decrease linearly with annealing time on double‐logarithmic plots and then level off as equilibrium is reached. The reduction in diffusion rates, however, can be recovered by raising the temperature above the glass transition temperature and then cooling to the same annealing temperature. Such behavior indicates that the predominant molecular process responsible for changes in mechanical properties of glassy polymers that accompany volume relaxation is not “structure formation” but is the loss of segmental mobilities arising from a reduction of the total free volume in the polymers.
Non‐equilibrium processes in poly(vinyl chloride) glasses vitrified at elevated pressures
Authors: Prest W. M. , O'Reilly J. M. , Roberts F. J. , Mosher R. A. 
Published: December 2004

AbstractThe conformational and enthalpic changes that occur in poly(vinyl chloride) (PVC) glasses that have been vitrified from the melt under pressure have been examined by Fourier transform infrared spectroscopy and quantitative differential scanning calorimetry. It is shown that these pressures freeze in the high energy states that are characteristic of the vitrification temperature and increase the apparent glass transition temperature of the polymer. In addition, pressures in excess of the vitrification pressure, cause intermolecular effects that can be relaxed out below Tg. Both of these processes create characteristic endothermic and exothermic changes in the apparent heat capacity of the glass that appear over a period of time and are sensitive functions of the glass formation. processes as well as the subsequent annealing history. The endothermic events are interpreted as the stress perturbed volumetric relaxation process while the exotherms are associated with the release of the frozen in stresses.
Studies on physico‐mechanical properties of some new light weight engineering materials
Authors: Aminabhavi Tejraj M. , Patel Ramesh C. , Biradar Ningond S. 
Published: December 2004

AbstractIndustrial, agricultural, and naturally occurring waste materials in conjunction with liquid epoxy resin, silica and asbestos were employed to make light weight engineering composite materials. To bring down the cost of the expensive resin, additives such as linseed oil and urea formaldehyde were added to replace the bulk of epoxy resin. Various physico‐mechanical properties of these composites were studied. In comparison with ordinary cement concrete, properties such as water absorption and fire resistance improved substantially for the majority of mixes, whereas other physico‐mechanical properties did not improve greatly in many cases. Such composites, which are similar to (and in some cases better than) ordinary cement concrete can be of use in building technology because of substantially lower prices.
Rheology of diallyl phthalate polymers below the gel point
Authors: Sundstrom D. W. , Burkert S. J. 
Published: December 2004

AbstractThe analysis of molding operations for thermosetting polymers requires information on the reaction rates and rheology of the materials. The purpose of this research was to measure kinetic and rheological data on diallyl phthalate resins and to develop models describing the flow behavior. The rheological data were measured with a mechanical spectrometer equipped with eccentric rotating discs. For the region below the gel point of the polymer, the elastic modulus and viscosity were correlated with molecular weight, temperature and shear rate through fairly simple models. By combining kinetic and rheological correlations, the viscosity of a reacting thermoset can be predicted as a function of time, temperature and shear rate.
The viscosity of fiber suspensions at low fiber volume fractions
Authors: Miles J. N. , Murty N. K. , Modlen G. F. 
Published: December 2004

AbstractThe viscosities of suspensions of glass fibers in an aqueous solution of sucrose have been studied by use of a capillary viscometer. In the aligned condition in the capillary, the viscosity depends little on shear rate within the range studied or on fiber length, but increases with increasing volume fraction of the fibers. The entrance effect was found to depend strongly on fiber volume fraction and fiber length: this indicates that the suspensions are relatively resistant to flow during the initial stages while alignment takes place.
Temperature rise in a thermoplastic under completely reversed bending stresses
Authors: Vinet R. , Connolly R. , Gauvin R. 
Published: December 2004

AbstractWhen a thermoplastic specimen is tested in flexural fatigue, the viscoelastic behavior of the material combines with the heat dissipation mechanism to generate an equilibrium temperature distribution. In order to locate the starting point of an eventual fatigue crack in the most stressed section of a particular geometry, it is important to know where the temperature reaches its maximum value. A first mathematical model has been proposed to evaluate the temperature distribution across the thickness of the specimen. Solutions have been obtained analytically and by a finite difference method. A comparison of the solutions enabled us to optimize the mesh size, the relaxation factor and the convergence criterion in the finite difference scheme in order to get results within a chosen accuracy. Preliminary test results are given and compared with the theoretical temperature distribution for two thermoplastics, nylon 66 and acetal homopolymer.
The effect of annealing on the thermal properties of reaction injection molded urethane elastomers
Authors: Dominguez Richard J. G. 
Published: December 2004

AbstractReaction injection molded (RIM) polyurethanes, especially reinforced RIM polyurethanes, are promising candidates to replace metal exterior body panels on automobiles. One of the most important performance properties which these RIM parts must possess is thermal dimensional stability. Thermal dimensional stability is defined as the ability of a part to withstand distortion or change in size during thermal cycles. This property is important for two reasons. First, during paint operations parts are exposed to high paint bake temperatures. Second, parts may be exposed to relatively high temperatures in use. Thermal dimensional stability is mostly controlled by formulation and post‐treatment. Formulation can change the structure of the polymer leading to different thermal properties. Posttreatment such as annealing can change (a) the degree of hard segment phase order, (b) the degree of phase separation and (c) the relative continuity of the phases. Experimental evidence is given to support all these factors.
Molecular weight distribution in novolac‐type polymerization in homogeneous, continuous‐flow stirred tank reactors
Authors: Kumar Anil , Gupta Santosh K. , Phukan Uzzal K. 
Published: December 2004

AbstractThe kinetic model for irreversible novolac type phenol formaldehyde polymerization and equations governing the molecular weight distribution (MWD) of the polymer formed in homogeneous continuous‐flow stirred tank reactors (HCSTR) have been derived. The set of algebraic equations involves three reaction parameters R1, R2, and R3 and have been solved using Brown's algorithm which was found to be more efficient than the Gauss‐Jordon technique of solution. A sensitivity analysis of different reaction parameters has been carried out and the reactivity of the para position was found to be an important factor affecting the MWD. In view of the fact that parameters R1 and R2 have a negligible effect on MWD, the phenomenon of molecular shielding described by Drumm et al. (1) can be neglected. The novolac formation can then be equivalently described by assuming R1 = 1 and R2 = R3 and the kinetic description so obtained is completely based on the experimentally observed different reactivities of ortho and para sites. The results for HCSTR have been compared with those for batch reactors and the former is found to give polymer of lower average molecular weights having higher polydispersity index.
Mechanisms of flow induced crystallization
Authors: McHugh A. J. 
Published: December 2004

AbstractThis paper presents a review of the field of flow induced crystallization from solution. Experimental facts concerning the nature of fibrous nucleation and the “shishkebob” morphology which results are reviewed. The discussion of growth models emphasizes the details of the nucleation control and flow control calculations which have been presented in the literature. A major problem in the development of quantitative models for the growth mechanisms has been the lack of a reproducible growth rate data base and the reasons for this are discussed. The review emphasizes those areas of the field both experimental and theoretical, where further studies are needed before a unified theory of flow induced crystal growth can emerge.
Graft copolymerization of vinyl chloride onto ethylene propylene rubber (EPR) and ethylene propylenediene monomer (EPDM) by bulk process
Authors: Takahashi Akio 
Published: December 2004

AbstractVinyl chloride was graft copolymerized on ethylene propylene rubber (EPR) and ethylene propylene diene‐monomer rubber (EPDM) by a bulk process to give a multi‐component end product consisting of three components and two phases. The reaction system forms a pseudo‐emulsion at an early stage of reaction where the phase morphology of graft poly(vinyl chloride) (PVC) is determined. The formation of pseudo‐emulsion was confirmed visually, by the particle size of PVC prepared in the presence of rubber and by the phase morphology of rub be r‐g‐PVC which is similar to that from an aqueous emulsion system. The degree of graft depends on the unsaturation of the rubber used as backbone. The amount of grafted EPR does not exceed 60 percent of the initial rubber; however, the amount of grafted EPDM is always higher than 60 percent of the initial rubber and increases further as the unsaturation increases. The degree of graft was found to be independent of the type of radical initiator used indicating that the abstraction of hydrogen from the rubber is carried out by the PVC radical to generate the grafting point. The graft PVC shows considerably improved processability which is equivalent to that of commercial vinyl chloride copolymers containing small amounts of propylene. It also shows dramatically improved impact strength which ranges from ten to twenty times that of PVC homopolymers.
The thermodynamics of liquids and their blends: High and low molecular weights
Authors: Simha R. 
Published: December 2004

AbstractThe physical basis and results of a theory of the liquid state are outlined. Quantitatively successful applications to the pressure‐volume‐temperature relations of n‐paraffins and high polymer melts are illustrated. An extension of the theory to mixtures permits corresponding analyses of various combinations of low and high molecular weight components, including composites. Finally, results of the theory can be introduced into discussions of such transport properties as viscous flow and creep, based on free volume concepts.
Temperature dependence of the viscoelastic shift factor in ionomers
Authors: Utracki L. A. 
Published: December 2004

AbstractThe temperature dependence of log a of poly(styrene ‐co‐ sodium methacrylate) was analyzed by means of the relation based on the free volume and the hole theories of liquids. For the near‐Tg region the relation becomes a single parameter equation of T/Tg. The analysis revealed a transition in flow pattein at TT associated with disintegration of the ion multi plets. The Tt‐transition was previously detected in other theological functions, viz, relaxation modulus, mechanical and dielectric tan δ plots.
Rubber blends opportunities for future research
Authors: Bauer R. F. 
Published: December 2004

AbstractIn measurements of dynamic mechanical properties over a temperature range, the appearance of intermediate loss peaks and the concomitant decrease of the loss peaks of the individual polymers in a blend is a useful criterion of blend compatibility. Microscopy and x‐ray data are reviewed which demonstrate that phase heterogeneity prevails in rubber blends, Compatibilization of these blends, as judged by dynamic loss measurements, can be achieved through a vulcanization process, which promotes interaction between the heterogeneous phases, The matching of solubility parameters of the blend polymers is not a necessary condition, because compatibility, as defined above, can also be observed in blends of rubbers with significantly different solubility parameters, provided an appropriate vulcanization system is used to promote phase interaction.
The principles of pipe‐line design for molten poly(ethylene terephthalate)
Authors: Kembłowski Z. , Torzecki J. 
Published: December 2004

AbstractThe flow of molten poly(ethylene terephthalate) in pipes is discussed. The considerations made are based on the results of previous investigations by the authors, concerning the rheological behavior of the melt which exhibits thermal degradation. A procedure is proposed which enables the design of a pipe‐line system for the distribution of molten, spinnable poly(ethylene terephthalate) in a fiber plant to be made.
Shear‐induced anisotropy in thermal conductivity of a polyethylene melt
Authors: Picot J. J. C. , Goobie G. I. , Mawhinney G. S. 
Published: December 2004

AbstractA rotating concentric‐cylinder thermal conductivity cell for polymer liquids is described. Thermal conductivity can be measured at temperatures approaching 200°C and at strain rates up to 400 s−1, The transient heat flux probe (with inner cylinder as heat source and temperature probe) method is used to permit the separation of the viscous heating effect from the probe heating effect.A polyethylene melt was studied and showed that at 50 s−1, a 2 percent increase in thermal conductivity occurs, followed by a gradual decrease until a value 10 percent less than the no‐shear thermal conductivity was found at 400 s−1. This effect is due to molecular orientation.
Swell of extrudate from an annular die
Authors: Garcia‐Rejon A. , Dealy J. M. 
Published: December 2004

AbstractDiameter and thickness swells have been measured as functions of time and wall shear rate for three high density polyethylenes at 170°C and one polypropylene at 190°C. By extruding into an oil having the same temperature and density as the extrudate, it was possible to measure isothermal swell in the absence of drawdown. Seventy to 80 percent of the swell occurs in the first one or two seconds, while several minutes are required to reach an equilibrium state. Relationships between various swell parameters, including parison weight swell and capillary extrudate swell, are examined. Important differences between the behavior of the polyethylenes and that of the polypropylene are noted.
Factors affecting metering accuracy in reaction injection molding
Authors: Olabisi Olagoke , Gau Y. 
Published: December 2004

AbstractSeveral parameters affecting the metering accuracy in reaction injection molding (RIM) are identified and their effects evaluated on a laboratory‐scale machine (mini‐RIM HP‐6. Polyurethane Technology of America). The experimental results show that the delay time must be greater than a critical value in order for the system pressure to attain the steady‐state value; that the matching of the recirculation and pouring pressure is necessary to have consistent amounts of materials at the calibration or mixing head; and that a variable momentum ratio can have an adverse effect on the metering accuracy. Two approaches are used in the determination of the optimum process parameters for the mini‐RIM machine and an attempt is made to explain the effect of momentum ratio variation on the metering accuracy in RIM.