bluuebunny/crossref_metadata_2025 huggingface dataset:
Rebound test to measure the strength of polymeric materials
Authors: Casiraghi T.
Published: May 2005

In this work it is shown that rebound experiments, carried out at low blow impact and by means of instrumented pendula, can be described in terms of the equation for a freely oscillating linear viscoelastic body with added mass. The experimental and calculated load‐time curves are in very good agreement when the behavior of the material is linear viscoelastic; the assumptions made (transitory time shorter than rebound time, and negligible mechanical friction) are thus proved to be reasonable. The rebound test, which can be carried out on unnotched or notched specimens, allows one to obtain quickly and easily relevant material properties such as Young modulus or compliance, stored and dissipated energies, and the upper linear elastic limit at a testing speed not too far from that of impact testing.
Profile modification of resist patterns in optical lithography
Authors: Vollenbroek F. A. , Spiertz E. J. , Kroon H. J. J.
Published: May 2005

A method is described to modify profiles of resist patterns in novolac and diazo‐oxide containing systems. After patterning of the resist, two successive uniform flood exposures are given, one with deep UV (254 nm) at water‐free conditions and the next with near UV (λ > 300 nm) at normal atmospheric conditions. The profile which results after development is vertical, concave or overhanging depending on flood exposure conditions and development processing. As the method includes a flood near UV exposure at atmospheric conditions the imagewise exposure energy can be reduced to approximately 35 percent of the normal value. Furthermore it gives also the possibility of using the resist as a deep UV resist. Another important implication is that standing wave effects are completely eliminated.
Azide‐phenolic resin UV resist (MRL) for microlithography
Authors: Iwayanagi Takao , Hashimoto Michiaki , Nonogaki Saburo , Koibuchi Shigeru , Makino Daisuke
Published: May 2005

Poly(4‐vinylphenol) sensitized by an aromatic monoazide compound (4‐azidochalcone), called MRL (Micro Resist for Longer wavelengths), has been prepared and evaluated as a negative UV resist. The resist is sensitive to radiation in the 300 to 400 nm region. The sensitivity of MRL is comparable to that of a positive quinonediazide photoresist under exposure to unfiltered light from a high pressure Hg lamp. An aqueous base developer removes the unexposed areas of MRL with no evidence of swelling of the exposed areas, indicating its high resolution capability. The main products in the exposure of MRL films are found to be primary and secondary amines. It is concluded that the formation of secondary amines attached to the polymer chain is responsible for the insolubilization of the exposed MRL in the base developer.
Plasma developable photoresist containing electronic excitation energy quenching system
Authors: Tsuda Minoru , Oikawa Setsuko , Yokota Akira , Yabuta Mitsuo , Kanai Wataru , Kashiwagi Ken‐Ichi , Hijikata Isamu , Nakane Hisashi
Published: May 2005

A dry developable negative working resist composition comprised of poly(methyl isopropenyl ketone) (PMIPK) and 4‐methyl‐2,6‐di(4′‐azido‐benzylidene) cyclohexanone‐1 was examined. The main photochemical product formed in the resist pattern was found to be a secondary amine which crosslinks PMIPK. Post‐annealing forms a hydrogen‐bonded product which shows a powerful electronic excitation energy quenching effect. The quencher is more powerful than the aromatic compound arising from the azide by post‐annealing only. The residual resist thickness of the negative pattern is about 80 percent of the initial thickness of the coating in spite of all the azide compound remaining in the resist coating. The obtained dry developed resist pattern has a high dry etch resistance. Etchings of Si and SiO2 were performed by plasma and reactive ion etching, respectively.
Design of a positive resist for projection lithography in the mid‐UV
Authors: Willson Grant , Miller Robert , McKean Dennis , Clecak Nicholas , Tompkins Terry , Hofer Donald , Michl Josef , Downing John
Published: May 2005

The design, synthesis, formulation, and process optimization of a new mid‐UV resist are described. The synthesis of a spectrally matched sensitizer was guided by semiempirical quantum mechanical calculations that predict the effect of structural changes on optical absorption characteristics. The formulation was guided by computer profile simulation studies and the process development by a response surface analytical procedure. These techniques allowed formulation optimization to be achieved on the basis of an understanding of the complex interactions between the resist dissolution response functions and the modulation transfer function of the exposure tool for which the resist was designed.
Ultrafast deep UV lithography using excimer lasers
Authors: Jain K. , Rice S. , Lin B. J.
Published: May 2005

Various excimer laser wavelengths have been used, both in mid‐ and deep‐UV regions—308 nanometers (nm) from XeCl, 249 nm from KrF and 222 nm from KrCl–to delineate images in a number of resists. The quality of the images obtained with the laser exposures, the absence of speckle, and the insignificant loss of resist reciprocity make excimer laser lithography an attractive technique. The ultrafast exposures possible with this method significantly lessen the sensitivity requirements on deep UV resists, making the choice of the resist more flexible.
Poly(4‐chlorostyrene), a new high contrast negative E‐beam resist
Authors: Liutkus J. , Hatzakis M. , Shaw J. , Paraszczak J.
Published: May 2005

PCS(poly‐4‐chlorostyrene) has previously been evaluated as a negative e‐beam resist, but although the sensitivity was good [2 to 5μC/square centimeter (cm2)], the contrast (γ) was poor (1.1 to 1.5). Recent experiments have shown that contrast is not only a function of molecular weight distribution (MWD), but can also be affected by polymerization conditios. Among these are: branching, head to head linkages, and oxygen in backbone. PCS was prepared via thermal free radical solution polymerization, and then fractionated by differential solvation techniques. Reactions occurring during polymerization and crosslink formation on irradiation will be discussed. For molecular weights of 700 and 300K respectively (same MWD), the sensitivity was 2 and 5μC/cm2, while the contrast (γ) was 3.5 for both. This is the highest reported contrast for a polymeric negative resist. The resist can then be UV hardened after development, and will not flow at 200°C. The RIE etch rate is ∼1/2 that of PMMA in various plasmas.
Kinetics of crack tip craze zone before and during fracture
Authors: Döll W.
Published: May 2005

Irreversible deformations form the main energy consumption routes for absorbing supplied energy and thus determine the resistance of materials to fracture. In many polymeric materials under mode‐I loading conditions three regions of irreversible deformation behavior can be distinguished as a function of the stress intensity factor KI or strain energy release rate GI, respectively:

no crack growth for Ki < KIo

slow crack growth for KIo < KI < KIc

rapid crack propagation for KI < KIc

In the three regions the amount and geometrical extent of irreversible deformations may be different and the influence of time, crack speed, and temperature may generate different results.

In this paper the influences of time and crack speed on the kinetics of the craze zone at the crack tip will be considered in some detail, with respect to results mainly obtained for poly(methyl methacrylate), PMMA, of high molecular weight under quasi‐static loading conditions.
Diffraction studies of craze structure
Authors: Brown H. R. , Sindoni Y. , Kramer E. J. , Mills P. J.
Published: May 2005

Recent work using small angle scattering techniques to study craze structure is reviewed. Three different radiations, electrons, X‐rays, and neutrons were used to study four problems in the area. These were (1) the structure of crazes in thin films, (2) the structure of a single craze/crack in a bulk material, (3) the effect of organic environments, and (4), the effect of mechanical fatigue on craze structures. It is shown that the high intensity of a synchrotron source permits the examination of the process of growth and breakdown of a single craze in polystyrene and also the study in real time of the short‐ and long‐term changes during fatigue of crazes. The H/D neutron contrast effects for neutrons were used to study environmental crazes with the environment still present.
Orientation in amorphous polymers II. Characterization of orientation
Authors: Vrentas J. S. , Vrentas C. M. , Bhombal A. H.
Published: May 2005

A method based on network theory is developed for characterizing molecular orientation in amorphous polymers. The proposed procedure gives not only the orientation distribution function for the chain segments in the polymer network (and hence the average orientation) but also a quantitative measure of how this orientation is distributed among the various types of entanglement junctions. The orientation of chain segments can be characterized by two parameters, one which gives the average orientation and another which reflects how much orientation is concentrated in long time entanglement junctions. The new method of characterizing orientation is used to interpret tensile strength data for both brittle and ductile failures.
Non‐isothermal flow of a molten polymer in a coat‐hanger die
Authors: Vergnes B. , Saillard P. , Agassant J. F.
Published: May 2005

The non‐isothermal flow of a power‐law fluid in a coal‐hanger flat die is studied. Equilibrium and thermal equations are solved by using an iterative finite difference method. The pressure distribution, the flow lines, the residence time distribution, the temperature distribution, and the flow uniformity at the end of the die are obtained, with a stress on the effect of thermal regulation and of temperature dependence of the viscosity.
Mechanical properties and molecular aggregation of soluble aromatic polyimide
Authors: Kochi Masakatsu , Mita Itaru , Yokota Rikio
Published: May 2005

Dynamic and static mechanical properties of a soluble aromatic polyimide (PI 2080) were investigated. It, unlike poly(pyromellitimide) (PI), was essentially amorphous in X‐ray diffraction and did not exhibit any heterogeneous two‐phase structure having ordered phases after annealing at temperatures around its glass transition temperature. The mechanical properties including thermal‐distortion temperature and elastic recovery were not much affected by the annealing. The difference in molecular aggregation and mechanical properties between PI 2080 and PI may be due to their different chemical structures. The flexible carbonyl group and the statistical distribution of copolymeric repeating units in the main chain of PI 2080 seem to prevent the formation of molecular order.
Surface‐modified kevlar fiber‐reinforced ionomer: Dynamic mechanical properties and their interpretation
Authors: Takayanagi Motowo , Katayose Teruo
Published: May 2005

A quasi‐three‐dimensional model was applied to the composite of ionomer and isotropically oriented discontinuous poly(p‐phenylene terephthalamide) (PPTA) fibers having the surface modified by carboxymethyl groups in order to predict the Young's modulus from the properties of the constituent materials over a wide temperature range. The model in which the modified PPTA fibers are dispersed in ionomer matrix in a three‐dimensional network is composed of series and parallel models. A good agreement between calculated and experimental values was eventually obtained. For comparision, the complex modulus of the composite was also evaluated by application of the Halpin‐Tsai equation modified by Nielsen. The calculated values agreed with the observed values below 240 K, whereas the calculated values above 260 K were significantly lower than the observed moduli.
Effects of thermal history on structural recovery of glasses during isobaric heating
Authors: Hutchinson J. M. , Kovacs A. J.
Published: May 2005

The response of glass‐forming systems to isobaric three‐step thermal cycles involving cooling, isothermal annealing, and subsequent reheating has been investigated comprehensively using numerous combinations of the experimental and material parameters. The latter include the retardation spectrum or response function and the parameter x which determines the relative contributions of temperature and structure to the retardation times. The results show that, on heating, multiparameter systems can display three kinds of peak in the expansion coefficient α or the heat capacity Cp originating from the interactions of the elementary retardation processes with the thermal history of the glass. The conditions under which these peaks occur, their shifts with x, and the experimental variables have been investigated in detail. In particular, it has been shown that for a thoroughly stabilized glass reheated rapidly, the temperature at which the main peak occurs is strongly dependent on the experimental variables and on x, and that this dependence can lead to an estimate of the value of x. For poorly stabilized glasses reheated slowly, on the other hand, the main peak apparently vanishes and allows an upper peak to appear, which is small and insensitive to x and the experimental variables. Intermediate situations in which the main and the upper peaks occur separately give rise to a range of effects which may become quite complicated as the two peaks approach each other. The occurrence of such multiple peaks, which has usually been overlooked or misinterpreted in the past, is discussed and explained in detail and is compared with some experimental observations reported in the literature.
Effects of stress and vapor exposure before and during aging on enthalpy relaxation of poly(vinyl chloride)
Authors: Berens A. R. , Hodge I. M.
Published: May 2005

Enthalpy relaxations in glassy poly(vinyl chloride) following varied pre‐aging treatments and under varied aging conditions have been compared through observations of sub‐Tg endothermal DSC (differential scanning calorimetry) aging peaks. The extent of enthalpy relaxation for a fixed time and temperature of aging is progressively enhanced by the imposition and release of increasing mechanical stress before aging. The same effect is produced by sorption and desorption of increasing amounts of CO2 or CH3Cl vapor before aging. In contrast, the continued application of mechanical stress, or the presence of vapor, during the aging period suppresses enthalpy relaxation. The extent of suppression increases with increasing vapor pressure and solubility or increasing stress. These effects are interpreted as consequences of an increase in the enthalpy of the polymer under mechanical or sorptive stress and an enthalpy relaxation following the release of this stress. In addition to these effects on the DSC endotherm, a pronounced exotherm between the aging peak and Tg is observed for samples which have undergone shear yielding or orientation either before or during aging. This exotherm may be the result of release of stored strain energy during the DSC scan.
Anisotropic aspects of the environmental stress cracking of acrylonitrile‐butadiene‐styrene and styrene acrylonitrile copolymers in methanol
Authors: Faulkner Douglas L.
Published: May 2005

Critical strains causing environmental stress cracking of injection‐molded poly(acrylonitrile‐butadiene‐styrene) (ABS) and poly(styrene‐acrylonitrile) (SAN) plaques were determined upon exposure to methanol. Measurements were obtained for samples strained either parallel or perpendicular to the melt flow direction and for samples located at various distances from the mold gate. Critical strains were significantly higher in the direction parallel to the melt flow compared to the transverse direction. The degree of anisotropy increased with increasing rubber content. For ABS containing 46 percent rubber, the critical strain at one point was determined to be 2.99 percent in the direction of melt flow, but only 0.47 percent in the orthogonal direction. For this material, critical strains determined parallel to the melt flow decreased with distance from the gate; whereas, critical strains for SAN and ABS containing 30 percent rubber remained essentially constant. Orientation of the plaques was assessed using shrinkage determinations and a thermal conductivity technique. Though a straightforward correlation of orientation with critical strain is observed for ABS, a similar relationship is not observed for SAN. These results suggest that although stress cracking occurs in the glassy matrix of ABS, it is the dispersed rubbery phase which controls the magnitude of strain required to initiate cracking.
Fatigue life prediction of filled polypropylene based on creep rupture
Authors: Trantina Gerald G.
Published: May 2005

To predict the fatigue performance of talc‐filled polypropylene in engineering applications, a simple relationship using constant stress data to predict the cycles‐to‐failure (Nf) was developed:

where k and n are constants from creep rupture tests, v is the cyclic frequency (≤1 Hz to avoid self‐heating), f(n) is a function that accounts for the wave form, and a is the peak cyclic stress with a zero minimum stress. For stress concentrations produced by central holes, σ is taken as the average net section stress and the effect of the stress concentration is ignored. Extensive tests were used to verify this expression for cyclic frequencies of 1.0 and 0.1 Hz, sinusoidal and triangular waveforms, stress concentrations produced by small and large holes, and 20 and 40 percent talc filler content.
Optimization of the polycondensation step of polyethylene terephthalate formation with continuous removal of condensation products
Authors: Kumar Anil , Sharma Satya N. , Gupta Santosh K.
Published: May 2005

The polycondensation step of poly(ethylene terephthalate) (PET) formation is assumed to include various side reactions in addition to the usual polymerization reaction. Polymerization in the batch reactor at constant pressure has been modeled to flash volatile components at the end of small discrete time intervals with polymerization occurring during the interval. The Hamiltonian has been written for the time interval and optimum temperature history computed for batch reactors for various reactor pressures. For low pressures, computed optimum temperature history is found to be of similar nature as that used in industry.
Thermodynamics of polymer solutions, especially poly(dimethyl siloxane) solutions
Authors: Panayiotou Constantinos G.
Published: May 2005

An improved non‐random free‐volume theory of polymer solutions is presented. It is based on Flory's Equation‐of‐State theory which is modified to account for differences in the size of core volumes of segments in pure liquids and in solution. In addition, it is corrected for non‐randomness through Guggenheim's Quasi‐Chemical approach. The theory is tested against experimental results on heats of mixing, volumes of mixing, and χ interaction parameters of poly (dimethyl siloxane), polyisobutylene and natural rubber solutions with gratifying results. Relations with existing similar theories are discussed.
Thermal energy storage in columns packed with crosslinked polyethylene tubes
Authors: Boneh Hanoch , Marmur Abraham , Narkis Moshe
Published: May 2005

An energy storage system based on solid‐solid phase transition of crosslinked polyethylene was constructed and tested. The energy storage unit consisted of a column packed with crosslinked polyethylene tubes. The solid‐solid phase transition enables heat transfer by direct contact between the form‐stable polymer and the hot (cold) fluid. A theoretical model for the simulation of this system was developed. The heating‐cooling characteristics of the energy storage system were simulated by the model, using measured thermodynamic properties of the crosslinked polyethylene. The potential of various crosslinked polyethylene materials for energy storage applications will depend on sufficient high‐temperature stability.
Manufacture of urea‐formaldehyde concentrates using a gas‐liquid technology
Authors: Frontini P. M. , Borrajo J. , Williams R. J. J.
Published: May 2005

The performance of a laboratory packed‐column for the manufacture of urea‐formaldehyde (UF) concentrates is analyzed. Gaseous formaldehyde was generated by the thermal decomposition of paraformaldehyde in a carrier nitrogen stream. The UF solution was continuously recirculated through a glass column filled with Raschig rings. No pH control was necessary when the operation was started using a solution with a F/U molar ratio higher than 3.5 to 4. Otherwise, insoluble resins appeared during the operation. The formaldehyde absorption rate was controlled by the gas phase resistance. The vapor composition in equilibrium with a typical UF concentrate is provided as a function of temperature.
Shear dependence of thermal conductivity in polyethylene melts
Authors: Wallace D. J. , Moreland C. , Picot J. J. C.
Published: May 2005

Thermal conductivity measurements with a modified Couette flow cell were obtained as a function of shear rate for two linear polyethylene melts of weight‐average molecular weights 27,300 and 56,700, respectively. The lower‐molecular‐weight polyethylene revealed a maximum decrease in thermal conductivity of 55 percent at 150 s−1. After shearing at 400 s−1, approximately 90 minutes was required to recover the value corresponding to the zero shear condition. This was considered consistent with molecular orientation into the flow direction during shear with a subsequent relaxation upon the removal of stress. The higher‐molecular‐weight polyethylene gave a similar decrease in thermal conductivity at 50 s−1. Unlike the lower‐molecular‐weight melt, an increase was observed at higher shear rates. Enhancement of energy transport via cluster flow mechanism was presented as a possible interpretation of these results. A theory of molecular orientation of liquid poly(dimethylsiloxane) (PDMS) under shear flow was previously developed from thermal conductivity and birefringence data of this material. An attempt to clarify the difference in behavior between the two melts examined in this work, and between the polyethylene melts and the PDMS previously studied is presented.
Bubble formation mechanism during heat treatment of polymer films cast from solutions
Authors: Tong Ho‐Ming , Ouano Augustus C.
Published: May 2005

A semiquantitative bubble formation mechanism is presented for the baking of polymer films, utilizing poly(methyl methacrylate) (PMMA)‐ethyl acetate (EA) solutions as the model system. It is shown that bubble growth phenomena can he accounted for in terms of the competition between vapor pressure buildup and the rate of vapor dissolution. According to the proposed mechanism, the local pressure buildup of solvent in the polymer film is controlled by the solvent partial pressure above a solution having a planar interface at the corresponding temperature and solvent concentration. This pressure can he estimated by Raoult's law. The vapor dissolution rate, on the other hand, is dominated by the liquid‐phase diffusion of the solvent. A method of obtaining the diffusion coefficient as a function of temperature and solvent concentration from isothermal thermogravimetric analysis (TGA) is also given.
Mechanical relaxation of flame retardant polycarbonate using the cole‐cole method
Authors: Taylor C. R. , Aloisio C. J. , Matsuoka S.
Published: May 2005

The frequency dependence of the complex‐shear modulus of a nonbrominated flame‐retardant polycarbonate has been successfully represented from 1 hertz (hz) to 1 gigahertz (ghz) at 190°C using a mechanical analog of the Cole‐Cole dielectric analysis. Two sets of retardation times were required centered about 74 msec and 16 μsec. The β value for the short time response was 0.83 and for the longer time response was 0.58. The values of J determined from the common point at which the terminal‐zone arc and the transition‐zone arc touch the Jc″ = 0 axis yields an entanglement molecular weight, Me, of 1470 g/mole.
Recent studies of polymer reactions caused by stress
Authors: Porter Roger S. , Casale Antonio
Published: May 2005

A singular class of polymer reactions can be caused by mechanical stress. Sufficient storage of mechanical energy to break chemical bonds in the main chain is generally possible only on deformation of polymers of high molecular weight. The corresponding appropriate conditions of high stress may occur in both polymer processing and use. This review summarizes reports of such polymer stress reactions published principally after 1980. The survey is organized by polymer type and by analysis technique.
Fatigue crack growth in polyethylene
Authors: Bucknall Clive B. , Dumpleton Paul
Published: May 2005

Fatigue crack propagation (FCP) rates are studied in 6 mm thick specimens of high density polyethylene (HDPE) containing razor notches, Centrally‐notched plates and single‐edg notched bars are subjected to sinusoidal tension‐compressio or tension‐zero cycling at 0.5 or 2.0 Hz under load control a room temperature; crack growth is monitored using a travelling microscope. After many thousands of cycles with no observable damage at the tip of the razor notch, a craze like zone begins to form. This zone grows slowly until it reaches the length characteristic of a mature crack at the same ΔK. Crack growth proper then begins. The number of cycles to initiate crack growth falls linearly with increasing ΔK at the razor notch Subsequent crack growth is determined both by the current value of ΔK and by loading history. When ΔK is increasing, FCP rates follow a standard Paris law curve. However, reduced, FCP rates are observed following an overload.
Multifunctional step growth polymerizations in cascades of isothermal, continuous flow, stirred tank reactors
Authors: Gupta Santosh K. , Bafna Sudhir S. , Kumar Anil
Published: May 2005

The step growth polymerization of RAf type multifunctional monomers (with A reacting with A) in cascades of isothermal, homogeneous, continuous flow stirred tank reactors (HCSTR's) is simulated. It is found that our equations reduce to those of Cozewith, et al. If either f or the molecular weights are large. However, under certain conditions, the low molecular weight correction is significant and the more exact equations of the present work must be used. Several possible start‐up strategies are discussed, of which one is amenable to analytical solution. This is the one in which all HCSTR's are filled initially with the steady state feed from the previous reactor and the outputs from any reactor, during its start‐up period, are discarded to an ‘off spec’ tank. It is found that for this case, in order to ensure nongelling operation, the mean residence time of any HCSTR must lie below a certain critical value, depending on the value of f and the feed conditions.
Response of polycarbonate, poly(methylmethacrylate), and epoxy resins to dynamic contact loading I. Experimental results
Authors: Hillig William B.
Published: May 2005

Measurements of the resistance force to a wide range of contact loadings have been performed on poly(methylmethacrylate), polycarbonate, and epoxy specimens. Rigid spherical indenters of 4.5, 9, and 18 mm diameter, as well as cones of various apex angles, were driven into thick specimens at constant velocity over the range 0.005 to 150000 mm/min. The objective of this study was to develop a data base useful for the understanding and analysis of the phenomena involved when polymeric solids are impacted by small hard bodies. Spheres and cones were used because these symmetrical shapes offer the best chance for analysis in terms of viscoelastic extensions of the classical Hertz elastic contact problem. Measurements covered penetration depths from first detection of contact, where the strains are smallest and the material response should most likely be interpretable in terms of linear viscoelastic analysis, to much greater depths where the strains far exceed the yield values. The observations are tabulated, as are the values of parameters that allow the data to be modeled to within experimental error. These parameters fit into a specially developed empirical law designed to facilitate subsequent treatment of the data using Laplace transform methods. An analysis is offered to try to sort out time‐dependent force relaxation from depth‐dependent force increase during the progress of the penetration. The results of the response at small penetration depths are in broad accord with published relaxation moduli. However, the dependence of force upon indenter geometry does not follow simple expectation.
Minimizing curl induced upon drying layered solvent coated films
Authors: Penwell R. C. , Chow T. S.
Published: May 2005

The problem of minimizing edge curl in a solvent dated layered polymeric composite web is discussed. Basic material relations are presented, with experimental data, which can be used to optimize coating and drying conditions to produce a flat surface. Viscoelastic equations, derived to understand the effects of material and geometrical parameters on curl, are discussed and applied to minimize curl in a dried condition. The results clearly indicate that coating, material, and geometrical parameters can be understood and used to minimize curl.
Diffusion of water in glassy epoxide prepolymers
Authors: Garcia‐Fierro J. L. , Aleman J. V.
Published: May 2005

Sorption isotherms show that epoxide prepolymers sorb water in increasing amounts as the temperature decreases and the water vapor concentration increases. Below Tg the behavior is typical of a Fickian transport combined with a relaxation process. Diffusion coefficients as function of sorption rates provide temperature shift factors from which the activation energy for diffusion is 35.3 KJ/mol. Combined effect of temperature and water concentration is described by a second order polynomial.
High modulus of isotactic polypropylene attained by coextrusion with atactic polystyrene
Authors: Verbraak C. L. J. A. , Van Dam J. , Van Der Vegt A. K.
Published: May 2005

Orientation‐induced crystallization of crystallizable polymer melts can occur, under certain conditions, during flow through converging channels. Attempts have been made to achieve this phenomenon in a two‐phase system, i.e., during simultaneous extrusion of a continuous concentric core of polypropylene within a polystyrene matrix through a conical duct. On one occasion, using Carlona P SY6100 (MFI = 11.0) with Hostyren N2000‐V‐01 (MFI = 25.0), a highly oriented polypropylene thread with a modulus of 14.6 GPa and a melting point of 178°C was extruded at a die temperature of approximately 170°C and a pressure lower than 40 MPa. It is, in principle, possible to form highly oriented, fiber‐like structures as reinforcing elements in a polymer matrix.
Life expectation of polycarbonate
Authors: Ram A. , Zilber O. , Kenig S.
Published: May 2005

Polycarbonate (PC), one of the leading engineering plastics, suffers from deterioration under harsh environmental conditions. It is sensitive to the effects of light (UV) radiation, to thermal degradation, and to the attack of hot water, due to hydrolysis. By exposure of various commercial PC grades—at various molecular weights and stabilization—to either natural or accelerated conditions, a maximum lifetime of three years was predicted for the best‐behaving grades. The criterion for failure was mainly based on loss of ductility in tensile tests, as well as loss of optical clarity and chain scission. Hot water has a significant effect on the performance of PC samples, and this is considered to be its greatest weakness. Degradation after exposure at various temperatures (without UV or humidity) leads to estimation of a temperature‐endurance index, that may serve as a practical limiting criterion for polymer life expectancy.
Residual stresses and toughness of polycarbonate exposed to environmental conditions
Authors: Ram A. , Zilber O. , Kenig S.
Published: May 2005

The role of the size and type of residual stresses and their distribution in the interior of polycarbonate mold‐injected test bars was studied, in view of the interrelationship between toughness and thermal or environmental history. The large thermal gradient during solidification of the polymer in the mold builds up compressive stresses near the wall and tensile stresses in the core. Annealing followed by slow cooling may reverse the type of stresses near the surface, while quenching augments the compressive stress. The latter stress near the wall is responsible for the extraordinarily high impact strength of polycarbonate. Exposure to the atmosphere and immersion in hot water may affect the distribution of residual stresses and thus contribute to the embrittlement of the originally tough polymer. The importance of molecular weight and polymer stabilization is elucidated.
Rotary injection reaction injection molding (RI‐RIM). Part I: Basic design features
Authors: Briscoe B. J. , Khan M. B. , Richardson S. M.
Published: May 2005

This paper describes the basic design features of a new reaction injection molding (RIM) processing device, Rotary Injection RIM (RI‐RIM). The new design includes a novel mixing concept which furnishes high intermaterial contact area upon shear imposed rotary injection of the RIM components for effective in situ polymerization. This system operates in low pressure and laminar flow conditions, as opposed to the high pressure and turbulent flow, found in conventional RIM systems. The mixing process is described and quantified in terms of the various forces which govern the injection process. A progressive diminution in the average size of the dispersions generated is found with increasing rate of shear, continuous‐phase viscosity, and injection rate. These results are compared with those expected from traditional shear mixing (bulk convective shearing) under comparable conditions and the current system found to be more efficacious. Reaction molding experiments with RI‐RIM using a model polyurethane system are described and the influence of operating conditions on the mechanical properties of the finished moldings are elucidated. A detectable change in the morphology of the system is observed following increase in the total shear strain imparted to the initial mix of the multiphase reactants. It is suggested that the observed change is affected by a segregation between the components of the segmented polymer.
Study on the continuous loop tubular reactor for emulsion polymerization of styrene
Authors: Lee Der‐Yuan , Kuo Jen‐Feng , Wang Jenn‐Hwa , Chen Chuh‐Yung
Published: May 2005

A continuous loop tubular reactor (CLTR) with a Bodenstein number of 100 and a recycle ratio of 0.992 (obtained under the conditions of a mean residence time of 25.0 to 59.95 min and a stirring rate of 418 rpm) was used for studying the emulsion polymerization of styrene (St). The recipe used in the study is 76.8 g St/l‐water, 3.73 g sodium lauryl sulfate (SLS)/l‐water, and 2.30 g potassium persulfate (KPS)/l‐water. The effects of the mean residence time on the performance of emulsion polymerization were studied. The overshoots in the monomer conversion and the particle number concentration were found to be higher as the mean residence time increased. The overshoots diminished at about 3 times the mean residence time. The steady state particle number concentration was independent of the mean residence time, while the steady state monomer conversion increased with increasing mean residence time.
Effect of early solvent evaporation on the mechanism of the spin‐coating of polymeric solutions
Authors: Skrobis Kenneth J. , Denton Denice D. , Skrobis Amy V.
Published: May 2005

The effect of solvent evaporation on spun‐on polymer thickness is investigated. Film thickness is shown to be proportional to spin speed raised to the negative of a constant, b. This constant is specifically considered. Of particular interest is the short initial period during spin coating signified by a rapid increase in solution viscosity, but where solvent diffusion in solution is not yet significant. Many previous theories have suggested the existence of a single value for b dependent only upon environment and spin coating system. Here, a single polymer dissolved in five pure solvents is examined. The polymer is Thermid IP‐600 (National Starch and Chemical Co.), an isoimide precursor. The solvents considered are n‐methyl‐2‐pyrrolidinone, dimethyl sulfoxide, dimethyl formamide, ethylene glycol dimethyl ether, and 2‐methoxyethyl ether. Spin Speed ranges from 0.6 to 7.0 kRPM and spin time is held at 15 s. It is shown that b varies from 0.97 for n‐methyl‐2‐pyrrolidinone to 0.57 for 2‐tncthoxycthyl ether. An empirical relation describing the behavior of b for this particular polymer and spin conditions used is b = [(MW)s(Pvap)s]/[(MW)n(Pvap)n]−0.1, where (MW)s and (MW)n are the molecular weights of the solvent and of n‐butyl acetate, respectively and where (PVaP)s and (Pvap)n are the vapor pressure of the pure solvent and the vapor pressure of n‐butyl acetate, respectively.
Molecular structure and morphology of crosslinked polyethylene in an aged hot‐water pipe
Authors: Gedde U. W. , Ifwarson M.
Published: May 2005

Internally pressurized crosslinked polyethylene (XLPE) pipes fail according to one of the three following mechanisms: (a) stage I fracture occurs at the highest stresses and is ductile when large defects are absent; (b) stage II fracture is brittle and occurs at intermediate stress levels; (c) stage III fracture occurs at the lowest stress levels and is brittle. It has been assumed that the material in a pipe which fails according to the last mechanism is chemically degraded. This paper presents data obtained by thermal analysis, X‐ray diffraction, infrared spectroscopy, and gel permeation chromatography on samples taken at different radial positions from a pipe of XLPE (crosslinked by peroxide) which failed according to the stage III mechanism after 17,136 h when subjected to 2.62 MPa hoop stress at 110°C (internal water/external air). These data are compared with data from samples of an unexposed reference pipe. Highly degraded brown spots, referred to as “oxidation spots”, are visible in the aged pipe. The puncture fracture occurred in one of these oxidation spots. The increase in melting point and crystallinity, the decrease in fold surface free energy, the almost invariant crystal unit cell, the decrease in gel content, the decrease in molecular weight of the soluble fraction and the formation of carbonyl arid hydroxyl groups at the inner wall in the aged pipe compared with the properties of the unexposed pipe are consistent with an oxidative degradation of the amorphous chain segments including scission of entangled chains and interlamellar tie chains. The latter is the main reason for the major reduction in strength of the aged pipe leading to stage III failure. The thickness of the inner wall layer of highly oxidized material was about 5 mm in the oxidation spots and only 0.5 mm elsewhere in the aged 10 mm thick pipe.
The plane‐strain essential work of fracture as a measure of the fracture toughness of ductile polymers
Authors: Saleemi A. S. , Nairn J. A.
Published: May 2005

We have extended the essential work of fracture technique to allow for the determination of the plane‐strain essential work of fracture. The new technique is to measure the specific work of fracture as a function of ligament length in deeply double edge notched samples. This type of data is then experimentally corrected to remove the plastic work of fracture and leave only the essential work of fracture as a function of ligament length. By extrapolating the essential work of fracture to zero‐ligament length, we claim to be measuring the plane‐strain essential work of fracture. This new technique was applied to two rubber toughened nylons and to a series of polyethylenes. The plane‐strain essential work of fracture was found to be independent of thickness. Where comparison can be made to J‐integral testing, the plane‐strain essential work of fracture was similar to the critical J‐integral, JIc.
Dielectric behavior of epoxy resin during cure: A vector voltage study
Authors: Lee Sung‐Nung , Liao Yunn‐Hsin , Huang Pieng‐Tsung , Lee Jun‐Lung
Published: May 2005

Vector voltage (Vc), measured across a plate electrode filled with resin, is a function of the resin matrix structure. The variation of Vc during the cure process at various frequencies was studied. A peak with minimum Vc value was observed. It was found that the initial stage of heating is mainly a temperature equilibrating step, where the viscosity decreased to a minimum owing to the rapid alignment of the dipole (and ion) species. Vc then ascended as the major cure reaction took place, as the mobilities of the electrical species were lowered in the rather tight matrix structure of the partially cured resin. The quantity of bound charge is an indicator of dipolar and ionic movements within the resin matrix, and was employed to describe the trajectory of the Vc curve. Bound charge conductance was also found to be the dominating factor in the Vc variation when tests were carried out in a low frequency AC field; whereas free charge conductance became more important for tests at high frequency. It was also observed that the cure phenomenon was not detectable from the Vc variation when monitored with an AC frequency of 38 kHz or higher.
Nonisothermal annual die swelling analysis
Authors: Seo Yongsok
Published: May 2005

The effects of thermal properties of Newtonian liquids on annular die swelling were studied numerically using a finite element method. Fluid viscosity was assumed to be a decreasing exponential in temperature, with a proportionality constant, β, which was assumed to be a material property. Three swelling ratios were found as functions of constant β, Peclet number (Pe), Nusselt number (Nu), and a viscous heat dissipation. The fluid behavior was remarkably different when the viscous heat dissipation was involved or excluded. Explanations are presented for these differences.
Dynamic mechanical response of adhesively bonded beams: Effect of environmental exposure and interfacial zone properties
Authors: Li C. , Dickie R. A. , Morman K. N.
Published: May 2005

The dynamic mechanical response of adhesively bonded metal beams has been examined over a broad temperature range using a dynamic mechanical thermal analyzer (DMTA). The measured dynamic mechanical response of the bonded beam contains rich information about the viscoelastic properties of the adhesive resin such as glass transition temperatures. The measured storage moduli and loss factors of the bonded beams are very sensitive to changes in the properties of adhesive induced by exposing the beam specimens to environmental attack. Dynamic mechanical responses associated with dry adhesive resin, water plasticized resin, and aggregated water were observed for an electro‐galvanized steel/epoxy beam exposed to water. The effect of the presence of an interfacial accommodation zone (IAZ) between adhesive resin and metal substrate was also examined; measured properties were very sensitive to the presence of a low modulus IAZ. It was successfully demonstrated in this study that the DMTA testing of bonded beams is a potentially useful tool for studying dynamic performance and durability of automotive adhesive joints.
Evaluation of poly(1,4‐cyclohexylene dimethylene terephthalate) blends for improved processability
Authors: Auerbach Andrew B. , Sell Joseph W.
Published: May 2005

Poly(l,4‐cyclohexylene dimethylene terephthalate) (PCT) exhibits superior heat deflection temperature when compared to conventional polyesters such as poly(butylene terephthalate) or poly(ethylene terephthalate). It is subject to degradation, however, at the processing temperatures normally employed to extrude or mold this material. Several approaches were taken to broaden the processing window of this material including: blending PCT with other crystalline and amorphous polymers to allow for lower processing temperatures, addition of conventional stabilizers, addition of crosslinking agents to maintain viscosity during processing and the addition of lubricants to improve processing. Key parameters included physical properties, rate of degradation, extruder torque measurements vs. time, and Differential Scanning Calorimetry (DSC) analysis (melting point and glass transition). All systems tested produced significant reduction of the intrinsic viscosity (molecular weight) for PCT during processing. The most successful approach was the blending of various polymers with PCT to lower extruder processing temperatures. Reductions in processing temperature may have resulted from improved heat transfer due to the presence of a lower melting polymer, reduction in melting point of the blend, or changes in the frictional characteristics of the PCT in the extruder. Transesterification may have played a role in compatibilizing some polyester mixtures. As expected, certain polymers had major'effects on the flow behavior of the blend. Tradeoffs were obtained in physical and thermal properties. A combined approach of polymer blending and the use of lubricants, stabilizers or crosslinking agent may hold the most promise for future development work. Thermal resistance under vapor phase soldering conditions was best for LCP/PCT blends and worst for PBT/PCT blends. Additional evaluations of the blend materials will include solvent resistance, processability, thermal resistance, dimensional stability, heat aging resistance, flammability, and specific end use tests.
Polymeric stannous dicarboxylates: Synthesis, properties, and structure
Authors: Ibidapo T. Adesanya
Published: May 2005

A series of polymeric stannous dicarboxylates (i.e., suberate, sebacate, do‐decanedioate, terephthalate, propoxyterephthalate, and isophthalate) has been synthesized from aqueous solution using various conditions of temperature (20, 50, and 98°C) and pH (6.4, 8.0, and 11.6). These were obtained as highly viscous adhesive‐like emulsion phases when synthesized at 50 and 98°C. Polymeric stannous suberate when synthesized at pH 11.6 and temperature of 50°C crystallized to spherulites. When molten they behaved like hot‐melt adhesives. They could be spun into fibers. On the other hand, melt‐synthesized stannous dicarboxylates exhibit simple non‐polymeric salt structures.
Conduction melting of polymer pellets
Authors: Chung C. I. , Wang N.
Published: May 2005

A study of melting a polymer pellet immersed in a hot silicone oil bath was conducted. The temperature rise at the center of the pellet was recorded. This experiment simulates the conduction melting mechanism of polymer solid pieces mixed in the hot melt inside an extruder screw channel. The pellets immersed in the silicone oil melted quite slowly, taking around one minute to melt a spherical pellet of about 4.5 mm diameter. The heating time could be greatly decreased by stirring the silicone oil to increase the heat transfer from the silicone oil to the pellet. Analysis of the conduction melting mechanism showed that the size reduction of the solid would be most effective in decreasing the heating time.
Mechanics of neck formation in the cold drawing of elastic films
Authors: Coleman Bernard D. , Newman Daniel C.
Published: May 2005

A discussion is given of the unidirectional, but nonuniform stretch of long, wide strips of film. It is observed that each of the material functions, τ, β, γ, in a recently proposed unidimensional theory of neck formation and cold drawing for bars of small but not zero thickness is determined, in the case of a strip of film, by the strain‐dependent shear modulus μ of the three‐dimensional material of which the bar is composed. The dependence of the shear modulus μ on shear strain and of τ, β,and γ on axial stretch is evaluated for a model of an elastic material susceptible to cold drawing, and the calculated values of τ, β,and γ, are used to draw film profiles for various stages of neck formation.