bluuebunny/crossref_metadata_2025 huggingface dataset:
Water vapor resistance of plasma‐polymerized coatings on potassium bromide windows
Authors: Wydeven T. , Johnson C. C.
Published: December 2004

Plasma‐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

It 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

A 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

Consolidation 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

Binary 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

Volume 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

The 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

Industrial, 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

The 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

The 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

When 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

Reaction 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

The 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

This 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

Vinyl 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

The 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

The 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.
The characterization of blend microstructure
Authors: Carton Andrew
Published: December 2004

Blend microstructure can lie characterized by a wide range of microscopy, spectroscopy and diffraction techniques. The strengths and limitations of the commonly used characterization techniques arc discussed using as examples a range of commercially or scientifically important blends.
Rubber blends opportunities for future research
Authors: Bauer R. F.
Published: December 2004

In 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

The 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

A 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

Diameter 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

Several 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.
Slit flow of molten polyethylene filled with plastic flakes
Authors: Suto Shinichi , Fujimura Toshikazu
Published: December 2004

The processability of polyethylene in sheet‐extrusion or calendering may be improved by the addition of plastic flakes. The effects of plastic flake parameters and flow conditions on the viscosity and the die swell of the suspension were determined, and the structure in flow (morphology or dispersion state) and applications were discussed. Flakes of biaxially oriented polystyrene, high‐impact polystyrene, polypropylene, polyamide or polypropylene spheres were dry‐blended with polyethylene. The viscosity was determined by means of a slit or a capillary rheometer. The quenched extrudate was annealed and its die swell was measured. Flakes of biaxially oriented polystyrene shrunk into rod‐like form during heating, but other plastics retained the flake‐form. The relative viscosity and the swell ratio of the suspensions depended on the type of plastic and operating conditions. The rheological behavior of suspensions qualitatively suggested that polypropylene flakes deformed or crowded (including stacking), polyamide flakes deformed slightly, and polystyrene flakes were difficult to buckle, but crowded slightly. The thickness of extrudates can be controlled easily by flake addition due to decreased die swell, while the output would be reduced to some extent.
Optimization of fiber drawing processes in terms of the filament state variables
Authors: Butler R. H. , Prevorsek D. C. , Kwon Y. D.
Published: December 2004

A new method of optimizing the fiber drawing process involving the feed roll, the heated elements and the take‐up roll is presented. In this method, the process is described in terms of the filament temperature and filament extension in the drawing zone. This is in contrast to the conventional approach in which the machine control variables such as the heated element temperature, fiber feed velocity and the total draw ratio were used to describe the process. It is shown that the drawing process seldom proceeds by a simple yielding mechanism and that a one‐step drawing process usually involves a yield draw followed by a post‐yield stretching. Using the drawing of nylon 6 fibers as an example, it is shown that the most critical factors related to achieving the highest fiber strength in drawing from a given precursor are the yarn temperature and yarn extension at yielding and during the post‐yield drawing.
Thermoset injection molding dynamics and the distribution of cure in thermoset molded parts
Authors: Sidi Shiraz , Kamal Musa R.
Published: December 2004

A detailed characterization of a commercial‐filled unsaturated polyester molding compound has been carried out to determine the kinetics of cure and the rheological behavior of the material at various temperatures and shear rates. Molding experiments were conducted in a 2 1/3 oz, 68 ton reciprocating screw injection molding machine, in conjunction with a simple rectangular cavity. The cavity and nozzle were equipped with pressure transducers to determine, the variation of pressure with position throughout the injection molding cycle. The injection speed was determined with the help of a position transducer. Finally, the moldings were analyzed to determine the distribution of cure states and tensile properties in the molding at various cure times. Significant differences have been observed. It is expected that studies of this type should be helpful in obtaining a better understanding of the thermoset injection molding process and the development of mathematical models to simulate this process.
The hydrolytic stability of some commercially available polycarbonates
Authors: Pryde C. A. , Kelleher P. G. , Hellman M. Y. , Wentz R. P.
Published: December 2004

A number of commercially available polycarbonates, including formulations made flame retardant by two different modifications, have been exposed to conditions producing moderately rapid hydrolysis. Hydrolysis rates were calculated from molecular weight data determined by gel permeation chromatography and, in some cases, from melt flow rate data. The rates calculated by the two methods are in good agreement. In general, the standard formulations containing minimal additive packages are the most hydrolytically stable. Although one relatively new flame retardant polycarbonate demonstrates generally good resistance to hydrolysis, most of the flame retardant formulations appear to be quite susceptible to hydrolytic degradation. For these materials, hydrolysis under conditions encountered in use could cause significant decreases in impact strength within a few years.
Rheokinetics of polymerization of N‐laurylmethacrylate
Authors: Kale L. T. , O'Driscoll K. F.
Published: December 2004

The free radical polymerization of n‐laurylmethacrylate has been studied using a combination of rheological and kinetic methods. In addition to classical dilatometry, the extent of reaction of a polymerization was followed in a cone and plate rheometer by measuring the change in the diffraction of a laser beam shone through the polymerizing sample parallel to the plate of the rheometer. The change in diffraction was caused by the change in index of refraction of the monomer becoming polymer, which was related to the extent of reaction. Simultaneous measurements of loss and storage moduli and dynamic viscosity at 1 Hz provided the data necessary for correlating changes in the kinetics with changes in the rheology of the polymerizing system.
The effect of bromination and inherent vinyl unsaturation on the drawing behavior of high‐density polyethylene
Authors: Tincer T. , Akay G.
Published: December 2004

Various high‐density polyethylenes were brominated in order to eliminate the inherent vinyl Unsaturation in the polymer. They were then drawn uniaxially at three different temperatures, and the resulting fibrous materials were studied under a scanning electron microscope. It was found that the brominated samples yielded transparent fibrous materials that had more regular fibrillar structure and fewer surface overgrowths, cracks, and voids compared with the unbrominated polymers drawn under identical conditions. Bromination also appeared to improve the mechanical properties of the drawn and the undrawn polymer. High‐density polyethylene that had no inherent vinyl Unsaturation also yielded transparent fibrous material with fibrillar structure similar to that of brominated polymers.
A network flow analysis of extrusion dies and other flow systems
Authors: Booy Max L.
Published: December 2004

A method is presented to calculate the slow viscous flow distribution in systems of passages, for which the major velocity components are substantially parallel to the axes of those passages. That condition is generally satisfied in flat extrusion dies, disc filters, in‐line filters, and other now devices. A finite difference matrix method is initially used to determine the flow distribution for an assumed viscosity distribution. That flow distribution is next used to determine a new distribution of resistances, now based on a specified rheological equation. This process is iterated until there is no significant change in the flow distribution. The passages are subdivided in this method and replaced by a network of resistances. A few unknowns are introduced at one end of the network, which are solved at the other end, using a matrix marching routine. The method is described for newtonian flow through a flat die with equalizing channel, for which the analytic solution is known. Results are shown for that die for flow of power law liquids.
Strength and structure of glassy networks formed from dimethacrylates
Authors: Atsuta M. , Turner D. T.
Published: December 2004

Glassy networks were formed by copolymerization of methyl methacrylate (MMA) with both ethylene glycol dimethacrylate (EGDM) and triethylene glycol dimethacrylate (TGDM). The polymerization reaction was followed by estimation of vinyl group concentration from measurements of specific volume and infrared absorption. The sheets of polymer were cracked but gave fragments that were large enough to provide specimens suitable for a three‐point bending test. Flexural strength decreased with increasing feed of dimethacrylate but, nevertheless, gave fairly strong products throughout the range of comonomer compositions c.f. PMMA, 144 ± 9 MPa; PTGDM, 132 ± 10 MPa; PEGDM, 66 ± 15 MPa. Examination of fracture surfaces indicated a predominantly brittle mode of fracture modulated by localized plastic deformation. In order to account for localized plastic deformation, it was postulated that the networks consist of highly crosslinked microgel particles in a much less crosslinked matrix.
Rheological analysis of highly loaded polymeric composites filled with non‐agglomerating spherical filler particles
Authors: Bigg D. M.
Published: December 2004

A non‐agglomerating 15 μm diameter stainless steel spherical powder was used as a filler in a low‐density polyethylene matrix. The factors investigated included volume loading, the use of surface treatments, and method of applying the surface treatments. The rheological parameters measured to analyze the effect of these factors on the melt behavior of the mixtures were the dynamic viscosity, η*, and the real component of the shear modulus, G′. These parameters showed clear differences in the response of the composites to volume loading, type of surface treatments, and method of surface treatment application.
Modeling of poly(ethylene terephthalate) reactors: 4. A continuous esterification process
Authors: Ravindranath K. , Mashelkar R. A.
Published: December 2004

A mathematical model has been developed for the direct, continuous esterification process. Influence of process and operational variables, including temperature distribution, residence time distribution, bis(hydroxyethyl)terephthalate recycle, pressure, and ethylene glycol (EG) to terephthalic acid ratio on the reactor performance have been investigated in a range as close to industrial practice as possible. The variables influencing the amount of EG reflux (which governs the energy economy) and side products (which govern the product quality) have been discussed. This investigation provides an analysis of a continuous, direct esterification process, and the results indicate strategies for optimizing productivity and product quality.
Conversion prediction in high conversion free‐radical polymerizations
Authors: Balke S. , Garcia‐Rubio L. , Patel R.
Published: December 2004

The objective of this article is to introduce anew general approach For conversion prediction in high‐conversion free‐radical polymerizations–“The Method of Kinetic Similarity.” Using a single homopolymer reference curve of methyl meth‐acrylate (MMA) and one to two time‐scaling parameters, the conversion vs. time curves for MM A, ethyl methacrylate (EMA), vinyl chloride (VC), acrylonitrile (AN), styrene methyl methacrylate (SMMA), and styrene acrylonitrile (SAN) could be well‐described. For MMA and VC, these parameters are shown to obey expected Arrhenius relationships over 45 to 90°CC and 30 to 70°C, respectively. The method is simple to apply, continuous over the whole conversion range, utilizes existing knowledge at low and limiting conversions, and avoids application of usual low conversion assumptions into the diffusion‐controlled region.
Determination of the glass transition of polymer by the autovibron
Authors: Murayama Takayuki
Published: December 2004

The automated Rheovibron (Autovibron) has been useful for determining the glass transition behavior of polymers. The standard (manual Rheovibron viscoelastometer has been used sufficiently small intervals, and so, some accuracy on transition location must be sacrificed when the temperature intervals are taken 5 to 10°C apart. However, the Autovibron can be observed over very small temperature intervals (<1.5°C)), which essentially provide a continous monitoring of the changes in storage modulus, loss modulus, and tan δ. An improved accuracy and sensitivity of the Autovibron are provided by a combination of multiprogrammer, programmable calculator, and lock‐in analyzer. The Autovibron are provided by a combination of multiprogrammer, programmable calculator, and lock‐in analyzer. The Autovibron shows a good capability for dynamic thermomechanometry. The glass transition bility for dynamic thermomechnometry. The glass transition of polymers can be determined by analyzing the loss tangent peak. The maximum value in loss tangent, peak temperature, and the newly introduced terms, ΔT1 and ΔT2 which indicate the widths of tan δ peak, are useful indicators of the glass transition. The ΔT1 and ΔT2 show the distribution of the glass transition and are related to order and crystallinity in the structure.
Extended‐chain morphology in ultraoriented polyethylene
Authors: Macchi Edgardo M. , De Micheli Raul
Published: December 2004

The morphology of ultraoriented polyethylene fibers was investigated by means of small‐angle x‐ray scattering and high‐resolution line‐broadening analysis of x‐ray and electron‐diffraction profiles. The comparative consideration of the experimentally‐measured crystal thickness and long period along the c direction allowed the calculation of the fraction of extended‐chain crystals for a simple three‐phase model. The calculations were carried out with the unknown length of the extended‐chain crystals as a variable parameter.
Rheology of reinforced thermoplastics and its application to injection‐molding: IV. Transient injection capillary flow and injection‐molding
Authors: Akay G.
Published: December 2004

A two‐stage injection capillary rheometer fitted to an injection‐molding machine was used to study the transient flow behavior of unfilled polypropylene melt and melts filled with short glass fibers, or long glass fibers, or (alternatively) calcium carbonate particles/Apparent shear rate in the capillaries ranged from 103 to just over 106 s−1, while the initial melt temperature ranged from 180° to 270°C in steps of 30°C. Reservoir pressures at the entrance to the capillaries and the plunger position are also recorded. It is found that the presence of short glass fibers results in more stable flow, especially at low melt temperatures. Significant fiber exclusion at the capillary entrance is only present in long glass fiber‐reinforced melts. At low temperatures, calcium carbonate‐filled melts yield large pressure overshoot, and the flow is the “stick‐slip” type. These melts yield extra pressure overshoot when the flow rate is increased suddenly. If the melt elasticity is high (unfilled polymer), there is a recovery in the reservoir pressures during flow decay following sudden reduction in the flow rate. The significance of injection capillary flow in the injection‐molding of filled polymer melts is demonstrated by following the development of the nozzle pressure during injection‐molding. It is shown that, if the injection speed is high, filled polymer melts yield large nozzle pressure overshoots. Estimates of nozzle pressure based on steady‐flow‐viscosity data will, therefore, be misleading. Fiber‐free and particle‐depleted regions in the moldings are examined. A new mechanism of fiber or particle migration based on flow‐induced crystallization is proposed. The observations reported here for polypropylene concerning fiber migration also apply to nylon 6.6., high‐density polyethylene, and polycarbonate.
Prediction of extrusion pressure loss of polymer melts flowing through noncircular dies
Authors: Tiu C.
Published: December 2004

The geometric parameter method proposed earlier by Kozicki and coworkers for prediction of pressure losses of non‐Newtonian fluids flowing in ducts of arbitrary cross‐section is shown to be applicable for polymer melt flow through complex dies. Good agreement is obtained between the predicted and the published theoretical and experimental results for polystyrene and polypropylene melts flowing in rectangular and trapezoidal dies. The method is simple to use and requires only the knowledge of two geometric parameters to characterize the flow geometry.
Degradation of polyurethane containing phosphorus
Authors: Grassie Norman
Published: December 2004

The fire hazard associated with the use of polymeric materials is partly the destruction of property and partly the hazard to life by toxic fumes. Phosphorus compounds are commonly used as fire retardants. They seem to act principally by modifying the mode of thermal decomposition of the polymer. This results in changes in the pattern of volatile inflammable and potentially toxic products and also in the production of a protective layer on the surface of the burning material. Insight into these processes has been sought by comparing the mechanisms of degradation of a simple polyurethane, pure and in presence of the fire‐retardant ammonium polyphosphate, and of a comparable polyurethane with similar phosphorus structures built into the polymer structure.
Siloxane‐poly(Methylmethacrylate) amphoteric blends
Authors: Blahovici T. F. , Brown G. R. , St‐Pierre L. E.
Published: December 2004

Poly([4‐(methacryloyloxy) butyl]pentamethyldisiloxane), PMBPD, has been prepared for the first time. At the weight average molecular weight of 55,900, it is a clear, viscous liquid with a glass transition temperature, Tg, of 236K. Copolymers with methylmethacrylate have also been prepared. The homo‐and copolymers, all of which have methacrylate backbones with pendant siloxane groups, were blended with poly(methyl‐methacrylate), PMMA. Using the existence of a single Tg as a definition of miscibility, it was found that blends of either PMMA or PMBPD with random copolymers are miscible. However, in spite of a clear appearance, the blend of the two horriopolymers were found to have two distinct Tgs.
Some solid‐state properties of blends of polyethylene terephthalate and polyamide‐6,6
Authors: Kamal M. R. , Sahto M. A. , Utracki L. A.
Published: December 2004

Polymer blends incorporating polyamide‐6,6 (PA) and polyethylene terephthalate (PET) and having the following PA wt,% concentrations were prepared: 0, 5, 10, 25, 30, 35, and 100. Samples were obtained by molding in a reciprocating‐screw injection‐molding machine. The samples were annealed to minimize frozen‐in stresses without increasing the crystallinity level in the material. Melting and heat‐of‐fnsion data, obtained with the differential scanning calorimeter, suggest an overall increased crystallinity in the blends, as indicated by a significant excess heat of fusion. Whereas the neat polymers exhibit ductile failure under both tensile and impact testing conditions, the blends show brittle behavior. Finally, the abrasion resistance of the blends is inferior to that observed for PET but higher than the resistance of PA.
Techniques for the viscometry of suspensions
Authors: Cross M. M. , Kaye A.
Published: December 2004

Techniques are presented for the rotational viscometry of suspensions, using modified cone/plate and parallel plate configurations. For displaced cone‐and‐plate geometry an analysis considers the torque developed on the cone as a function of its angular velocity and the displacement at its apex. The two situations of constant angular velocity and of constant displacement present alternative methods for computing viscosity/shear‐rate data from torque/displacement or torque/angular velocity measurements. Neither method involves any assumption regarding the rheological properties of the test fluid and both can be extended to parallel plate geometry. An alternative and simpler approach uses an annular cone/plate configuration, in which conditions of uniform shear rate can be maintained with an operating gap of the order of 1 mm. The validity of the different techniques is tested by comparison with conventional cone‐and‐plate measurements, using a non‐Newtonian solution of polyisobutylene as a test fluid.
The effect of radical desorption on the particle size distribution in vinyl acetate emulsion polymerization
Authors: Lu Ying‐Yuh , Lin Chen‐Chong
Published: December 2004

The effect of free radical desorption is studied by using a mathematical model of particle size distribution in continuous emulsion polymerization. By comparing the theoretical prediction with experimental data, the value of Do for the vinyl acetate (VAc) system is best chosen as 0.19 × 10−7 cm2/h. The effect of radical desorption as well as mean residence time on the absolute particle size distribution, total concentration of polymer particles, conversion, and average number of radicals per polymer particle are analyzed by the model proposed.
Electrically conductive composites prepared from polymer particles coated with metals by electroless deposition
Authors: Narkis M. , Yacubowicz J. , Vaxman A. , Marmur A.
Published: December 2004

Polystyrene particles were coated by electroless deposition of copper, nickel or copper and nickel. The metal‐coated polystyrene particles were molded at high temperature and pressure into plaques, in which the metallic shell continuity was preserved and a continuous conducting metal network was formed. Very high conductivities at low metal concentrations (less than 1 percent v/v) are obtained by this procedure. The resistivity, dielectric constant, and dissipation factor of these metal containing composites are presented as functions of the metal concentration, frequency, and temperature. The metal containing composites exhibit reasonable flexural properties.
Ethylamine and ammonia as catalysts in the in‐situ precipitation of silica in silicone networks
Authors: Ning Y. P. , Mark J. E.
Published: December 2004

Both ethylamine and ammonia in aqueous solutions catalyze the hydrolysis of tetraethylorthosilicate to precipitate silica filler within poly(dimethylsiloxane) elastomers. The rate of filler precipitation can vary in a complex manner, possibly due to loss of colloidal silica and, in the case of the ethylamine solutions, deswelling of the networks. Increase in catalyst concentration increases the precipitation rate, and increase in amount of filler precipitated dramatically increases the modulus and ultimate strength of the networks, thus demonstrating the desired reinforcing effects.
Process control of polymer extrusion. Part II: Feedforward control
Authors: Yang Bing , Lee L. James
Published: December 2004

A feedforward plus feedback control method (FFC) and an adaptive feedforward plus feedback control method (AFFC) were proposed in this study to control the extrudate thickness of polymer extrusion. They were tested by step changes of screw speed and feedstock, and square wave type of screw speed changes. It is found that these feedforward control methods worked very well for various load disturbances but they required a good process model and accurate on‐line measurements of manipulated variables and load variables. The feedback function was necessary to compensate the over‐ or under‐corrections of the feedforward controllers and to handle other disturbances which were not considered in the feedforward model.
Crystallization in poly(c/s‐1,4‐cyclohexane dimethanol sebacate) model networks in the unstrained and strained states
Authors: Riande E. , Guzman J. , Mark J.E.
Published: December 2004

Rates of crystallization, stress‐optical coefficients, and melting points were determined for unelongated and elongated polysebacate model networks. For the unelongated networks, the maximum rate of crystallization was found to occur at approximately 0°C. For the elongated networks, the stress‐optical coefficients documented the extent to which strain‐induced crystallization was facilitated by increase in elongation and decrease in temperature. Measurements of stress relaxation due to crystallization at constant elongation indicated that the dimensionality of crystallization growth decreased from 3.0 to 2.5 as the temperature increased Melting points increased significantly with increase in elongation as predicted by theory. Fiber (non‐equilibrium) shrinkage temperatures, as expected, showed no correlation with the melting points.
Flame retardation of polypropylene: Effect of organoantimony compounds on the melt flow behavior
Authors: Jha N. K. , Misra A. C. , Bajaj P.
Published: December 2004

The melt flow behaviour of polypropylene filled with organoantimony compounds, triphenylstibinedibromide and its derivatives with tribromo‐, trichloro‐, and pentachloro‐phenols, as flame retardants has been studied in the temperature range of 180 to 220°C, and at shear rates of 29.5 to 588.8's−1, using a capillary rheometer. A decrease in the melt viscosity at all shear rates and temperatures was noticed on addition of these flame retardants, The melt viscosity further decreased upon increasing the concentration (from 5 to 20 phr) of the flame retardants. The die swell was measured in order to determine the melt elasticity of the filled systems. The minimum melt viscosity of filled propylene was observed approximately where the maximum die swell (melt elasticity) occurred.
Acoustic waveguide monitoring of the cure and structural integrity of composite materials
Authors: Harrold R. T. , Sanjana Z. N.
Published: December 2004

We have investigated the use of acoustic waveguide techniques to measure the cure and stress state of epoxy resins and composites. It is anticipated that the waveguides, which are incorporated within the structure, will also be valuable for nondestructive (NDE) evaluation of stress, strain, and damage caused to the structure during its life time. While dielectric techniques are commonly used to monitor the cure of composites, they suffer because metal electrodes intrude into the structure and poor signal‐to‐noise ratios may be encountered with graphite composites. Acoustic waveguides can be made compatible with the host structure and after the cure monitoring function is over, remain in the structure for NDE of flaws and voids, as well as to monitor other parameters. This paper presents results on experiments to monitor the cure and stress state of resins and composites with a 1.5 mm diameter polyester‐fiberglass acoustic waveguide in curing resin. A 1000 to 1 change in the peak value of a 71 kHz acoustic signal was found. Other parameters now being investigated are: frequency of transmission and phase change, transit time, waveguide size and shape, and acoustic wave attenuation characteristics.
The use of melt strength of low density polyethylene as a processability measure in film blowing extrusion
Authors: Montes Sergio A. , Ramírez José L.
Published: December 2004

The melt strength method is analyzed in terms of its ability to predict the axial stress levels found in tubular film extrusion of low density polyethylene. For certain values of the capillary L/D, the level of axial stresses and average Newtonian viscosity found in the filament stretching and film blowing are comparable at the same draw ratio. The elongation to break of the finished film was found to be primarily determined by the axial stress during the film blowing, at constant frost line height.