bluuebunny/crossref_metadata_2025 huggingface dataset:
Biodegradable polymer blends of poly(L‐lactic acid) and gelatinized starch
Authors: Park Jun Wuk , Im Seung Soon , Kim Soo Hyun , Kim Young Ha
Published: April 2004

Gelatinized starches were prepared with various content of glycerol and were investigated in terms of the effect of the glycerol addition on characteristics of starch and its blends. Poly (L‐lactic acid) (PLA) with various ratios of linear/star shaped PLA and starch gelatinized with various ratios of water/glycerol were melt‐blended by using twin screw mixer. The blends were characterized by DSC thermal analysis, tensile test and morphological analysis. Gelatinization of starch was found to lead to destruction or diminution of hydrogen bonding in granules and a decrease of crystallinity of starch. DSC data showed that starch played a role as a nucleating agent and glycerol as plasticizer contributed to an improvement in crystallinity in PLA blends. When the content of starch increased, the size of spherulites in PLA blends was smaller and less regular. In the case of PLA/pure starch blends, the voids appeared, which were formed by the separation of starch particles from the matrix. But for PLA/gelainized starch blends, these voids were not observed. In the case of blends with linear PLA and starch gelatinized with water/glycerol ratio of 100/40, the greatest superiority of mechanical properties was shown and the toughness was improved compared with PLA/pure starch blends.
Effect of strain rate on the fracture toughness of some ductile polymers using the essential work of fracture (EWF) approach
Authors: Ching Emma C. Y. , Poon Wendy K. Y. , Li Robert K. Y. , Mai Yiu‐Wing
Published: April 2004

The plane strain fracture toughness of two ductile polymers, ultra high molecular weight polyethylene (UHMWPE) and acrylonitrile‐butadiene‐styrene (ABS), was measured by using the essential work of fracture approach. Truly plane strain fracture toughness (wIe) was measured for ABS at quasi‐static and impact rates of loading. For UHMWPE, the measured values were only “near” plane strain values (wIe*). It was confirmed both wIe* and wIe were independent of specimen type but dependent on strain rate. For UHMWPE, there was a negative strain rate effect, i.e., wIe* decreased with increasing loading rate. At low quasi‐static loading rate (v = 10 mm/min), wIe* was constant at 55 kJ/m2. It then decreased to 15 KJ/m2 when the loading rate was increased to 100 mm/min, and remained at that value even up to impact rate of loading (v = 3.7 m/s). For ABS, a mild positive strain rate effect was observed. wIe increased from 13 kJ/m2 at v = 10 mm/min to 17 kJ/m2 at v = 3.7 m/s.
A study of the effect of PP‐g‐MA and SEBS‐g‐MA on the mechanical and morphological properties of polypropylene/nylon 6 blends
Authors: Tucker J. David , Lee Sunggyu , Einsporn Richard L.
Published: April 2004

The mechanical and morphological properties of polypropylene/nylon 6 blends compatibilized with PP grafted with maleic anhydride (PP‐g‐MA) and styrene/ethene‐co‐butene/styrene grafted with maleic anhydride (SEBS‐g‐MA) are studied using a special version of a factorial design known as extreme vertices. Properties examined include yield stress, modulus, elongation, toughness, impact strength and morphology. Comparisons are made between various treatment combinations (i.e. a variety of blends) and polypropylene homopolymer using various statistical methods including analysis of variance (ANOVA). Scheffe's Test and Duncan's Multiple Range Test. Significant differences were found for yield stress, modulus, elongation, toughness and impact strength for specific treatment combinations versus PP as well as on average. Ternary diagrams are used to plot response surfaces of the measured data illustrating the main effects and interactions involved, while allowing correlations to be made with blend morphology. Indications from test results and analysis of response surfaces show a strong relationship between nylon/compatibilizer ratio and mechanical properties.
Rubber toughened and optically transparent blends of cyclic olefin copolymers
Authors: Khanarian G.
Published: April 2004

A study is presented of increasing the toughness of Cyclic Olefin Copolymer (COC) while maintaining its optical transparency. The COC consists of a random copolymer of ethylene and norbornene, and the impact modifiers consist of thermoplastic elastomers. It is shown that several requirements must be satisfied, namely: for toughening there is an optimum finite particle size, but in order to minimize light scattering the particles have to be as small as possible. In addition, the refractive index of the elastomer must be closely matched to COC over the visible wavelength range and use temperature. Also for toughening, there are additional requirements of the adhesion of the elastomer to COC and high molecular weight. It is found that styrene butadiene styrene (SBS) is the most effective elastomer in toughening COC while maintaining optical transparency. It is also found that the addition of an index matched styrene‐ethylene‐butylene‐styrene (SEBS) copolymer as a compatibilizer to the SBS elastomer is beneficial in increasing the toughness and lowering the optical haze. Finally, light scattering calculations are presented based on the Rayleigh Debye model to calculate the optical haze and transmission of these blends. These calculations take into account the refractive index of COC and the elastomer, the particle size distribution and volume fraction of the elastomer. It is shown that there is reasonable agreement between calculation and experimental results. It is possible to increase the toughness of COC to greater than 50 J/m (Notched Izod) while keeping the optical haze to below 5% with an elastomer loading of 5% (w/w). We also identify opaque blends of COC with a toughness of greater than 500 J/m with an elastomer loading of 20% (w/w).
Pressure‐volume‐temperature behavior of polylactide, poly(butylene succinate), and poly(butylene succinate‐co‐adipate)
Authors: Sato Yoshiyuki , Inohara Kenzo , Takishima Shigeki , Masuoka Hirokatsu , Imaizumi Mitsuhiro , Yamamoto Hirokazu , Takasugi Masanobu
Published: April 2004

Pressure‐Volume‐Temperature (PVT) behavior of three biodegradable polymers, Polylactide, poly(butylene succinate), and poly(butylene succinate‐co‐adipate), was measured at temperatures from 313 to 493 K and pressures up to 200 MPa. The PVF data in molten state were compared with predicted values of a group contribution modified cell model equation of state (GCMCM EOS). It was found that the GCMCM EOS coupled with one specific volume datum at atmospheric pressure could predict the PVT of the polymer melts to within 0.46% in an average relative deviation of specific volume.
Control of injection velocity using a fuzzy logic rule‐based controller for thermoplastics injection molding
Authors: Tsoi Hoi‐Pang , Gao Furong
Published: April 2004

Injection velocity to a large degree determines the melt injection rate during the injection phase, and it has critical impact on the molded part quality, such as shrinkage, warpage, and impact strength. An injection molding machine operates with different injection velocity profiles, barrel temperatures, molds, and materials. These strongly different molding conditions cause the injection velocity dynamics to very significantly and to make the control performance of the injection velocity poor with a typical PID controller. A real‐time, closed‐loop feedback and feedforward control system based on fuzzy logic has been designed, developed, and implemented to control the injection velocity. The fuzzy logic rules of the controller are optimized by analyzing phase plane characteristics. The controller output membership functions are optimized based on a 2k factorial design technique. The experimental results reveal that the fuzzy logic‐based controller works well with different molds, materials, barrel temperatures, and injection velocity profiles, indicating that the fuzzy logic controller has superior performance over the conventional PID controller in response speed, set‐point tracking ability, noise rejection, and robustness.
The effect of the addition of a low profile additive on the curing shrinkage of an unsaturated polyester resin
Authors: Liu C. J. , Kiasat M. S. , Nijhof A. H. J. , Blokland H. , Marissen R.
Published: April 2004

Composites made of glass fibers and unsaturated polyester resins are widely applied for various products. The failure processes of such composites are insufficiently understood. Fracture of the resin often initiates bulk composite fracture. Residual stresses occur during the curing of the resin due to the resin volumetric shrinkage. These unfavorable stresses may enhance resin fracture. Moreover, resin shrinkage may decrease the surface quality of the product. The addition of Low Profile Additives (LPA) to the resin may decrease or even remove these problems. The shrinkage behavior of unsaturated polyester resin with varying amounts of LPA is investigated in this work. The emphasis is on the development of curing shrinkage occurring after the gel point of the resin and on accompanying shirnkage stresses. These stresses can be reduced and even reversed by the addition of LPA.
On a pure finite‐element‐based methodology for resin transfer molds filling simulations
Authors: Mohan R. V. , Ngo N. D. , Tamma K. K.
Published: April 2004

A physically accurate and computationally effective pure finite‐element‐based methodology for Resin Transfer Molding (RTM) process simulations is presented. The formulations are developed starting with the time‐dependent mass conservation equation for the resin flow. Darcy's flow approximations are invoked for the velocity field, thereby forming a transient governing equation involving the pressure field and the resin saturation fill factor which tracks the location of the resin front surface. Finite element approximations are then introduced for both the fill factor and the pressure field, and the resulting transient discrete equations are solved in an iterative manner for both the pressures and the fill factors for tracking the progression of the resin front in an Eulerian mold cavity. The formulation involves only a pure finite‐element Eulerian mesh discretization of the mold cavity and does not require specification of control volume regions and has no time increment restrictions that exist as in the traditional explicit finite‐element‐control volume based formulations. The present formulations accurately account for and capture the physical transient nature of the mold‐filling process while maintaining improved numerical and computational attributes. Mold‐filling simulations involving various geometrically complex mold configurations are presented, demonstrating the applicability of the developments for practical manufacturing process simulations.
An unsteady multifluid flow model: Application to sandwich injection molding process
Authors: Schlatter G. , Agassant J. F. , Vincent M. , Davidoff A.
Published: April 2004

The sandwich molding process consists of injecting sequentially a skin and core polymers. The thermomechanical model describing the flow of the two polymers into the mold cavity is based on the lubrication approximations. A transport equation characterizes the displacement of the interface between the two fluids. An experimental study has been performed in order to test the influence of processing parameters (viscosities, flow rates, etc.) on the interface location. Numerical simulations are in agreement with measurements.
Measurements and modeling of PS/supercritical CO2 solution viscosities
Authors: Lee Minhee , Park Chul B. , Tzoganakis Costas
Published: April 2004

This paper presents a technology to determine the melt viscosity of a PS/super‐critical CO2 solution using a linear capillary tube die mounted on a foaming extruder. CO2 was injected into the extrusion barrel and the content of CO2 was varied in the range of O to 4 wt% using a positive displacement pump. Single‐phase PS/CO2 solutions were formed using a microcellular extrusion system and phase separation was prevented by maintaining a high pressure in the capillary tube die. By measuring the pressure drop through the die, the viscosity of PS/CO2 solutions was determined. The experimental results indicate that the PS/CO2 solution viscosity is a senstive function of shear rate, temperature, pressure, and CO2 content. A theoretical model based on the generalized Cross‐Carreau model was proposed to describe the shear‐thinning behavior of PS/CO2 solutions at various shear rates. The zero‐shear viscosity was modeled using a generalized Arrhenius equation to accommo‐date the effects of temperature, pressure, and CO2 content. Finally, the solubility of CO2 has been estimated by monitoring the pressure drop and the absolute pressure in the capillary die.
Process‐induced residual stresses in compression molded UHMWPE
Authors: Miller Keith , Ramani Karthik
Published: April 2004

Non‐isothermal cooling during processing causes the development of residual stresses, which are analyzed for compression molded UHMWPE, and affects the dimensional stability. The development of thermal residual stresses was predicted using an incremental stress analysis that included temperature‐dependent material properties. Strain gauges were used to measure the residual stresses as layers were removed from a molded disk using a Process Simulated Laminate (PSL) approach. The PSL technique has not previously been applied to a compression molded neat polymer. For initial surface cooling rates of ∼ 11°C/min, the model predicted a compressive stress at the bottom surface of 14 MPa and a tensile stress near the center of 2.5 MPa and matched the experimental distribution well. Because the compressive residual stress was 70% of the yield strength (∼20 MPa), a lower cooling rate was also tested (2.6°C/min). The maximum tensile and compressive stresses for this cooling rate were, 0.91 MPa and 2.5 MPa, respectively. The model demonstrated its use for predicting thermal residual stresses in compression molded parts, instead of trial‐and‐error experimentation. UHMWPE is shown to develop residual stresses continually from ∼ 120°C to 23°C.
Molecular composites for molecular reinforcement: A promising concept between success and failure
Authors: Schartel B. , Wendorff J. H.
Published: April 2004

The basic principles of molecular reinforcement and especially the specific approaches to obtain homogeneous composites with molecularly dispersed rigid rods are focused on and discussed. Brief overviews and successful examples of the available data covering the main characteristics are summarized.
Water blown free rise polyurethane foams
Authors: Niyogi Debdarsan , Kumar R. , Gandhi K. S.
Published: April 2004

A model is developed in this work for predicting the bubble size distribution in polyurethane foams generated by using water as a chemical blowing agent. The model combines equations of energy balance, kinetics of the reactions of isocyanate with water and polyol, and nucleation and growth of CO2 bubbles. It is found that as the water content of the reaction mixture is increased, the mean bubble size decreases and the bubble size distribution become narrower. Exactly the opposite occurs in polyurethanes foamed with a physical blowing agent, e.g., DuPont Freons. This suggests that a combination of physical and chemical blowing agents can be employed to control bubble size distribution.
Experimental study of post‐shear crystallization of polypropylene melts
Authors: Lee O. , Kamal M. R.
Published: April 2004

In order to study the effects of Processing shear stresses on crystallization behavior, a fiber pullout technique was applied in conjunction with polarized light microscopy and a hot stage. The shear apparatus consisted of a single glass fiber sandwiched between two layers of polypropylene films mounted on the hot stage. At the crystallization temperature, shearing was introduced by pulling the fiber at a constant velocity for a fixed period of time. Static crystallization of the polymer then ensued. Computerized data acquisition and image analysis were employed to observe the evolution of crystallinity, morphology, and growth rates of crystallites in various shear and temperature fields. Two distinct morphological zones were produced upon fiber pullout: bulk spherulites and a shear‐induced layer localized within the vicinity of the fiber surface. The two zones displayed similar kinetic behavior despite the difference in appearance. A comparison of growth behavior in the two zones revealed rates independent of the shear rate but strongly dependent on the crystallization temperature. The main influence of the shear appeared to be in producing higher nucleation rates in the shear zone near the fiber.
Effects of solvent‐particle interaction kinetics on microstructure formation during three‐dimensional printing
Authors: Wu Benjamin M. , Cima Michael J.
Published: April 2004

Lactone‐based absorbable polyesters, such as polylactide‐co‐glycolides, are commonly used for the construction of biomedical devices. Many such devices can be constructed by a novel manufacturing technology known as three dimensional printingTM (3DPTM), which fabricates complex structures by ink‐jet liquid binder onto loose powder in a laminated fashion. The predominant 3DP binding mechanism for lactone based absorbable polyester powder is dissolution‐reprecipitation. The objective of this study is to compare the relative time scales for particle dissolution and solvent evaporation during 3DP processing. An experimental setup was devised to determine the time scale for particle dissolution. This time scale was found to be particle size independent for small particles, but size dependent for larger particles. The time scale for chloroform evaporation from typical 3DP powder beds was determined to be on the same order as the particle dissolution time scale. Dissolution‐evaporation (DE) plots were constructed to illustrate the relationship between evaporation time scale, dissolution time scale, particle size, printing conditions, and external mass transfer conditions. The DE plot provides a good estimate of the necessary printing conditions under which the evaporation time is sufficient for particle dissolution for a given particle dimension. Microstructural analysis of the printed structures demonstrated the importance of the relative time scales of particle dissolution and solvent evaporation. Practical implications of these findings in 3DP are described.
Effect of filler on cure behavior of an epoxy system: Cure modeling
Authors: Lu Mangeng , Shim Mija , Kim Sangwook
Published: April 2004

The effects of filler on the reaction of an epoxy system cured with aromatic diamine have been studied within the temperature range 70 ˜ 130°C using a differential scanning calorimeter. Various kinetic models including homogeneous reaction, diffusion‐controlled reaction, surface reaction and nucleation and growth models have been tested. Kinetic analysis using integral and derivative procedures on the isothermal data indicates that the cure reaction process can be described well with the autocatalytical and surface reaction models. However, it has been found that the catalysis of fillers can be retarded effectively by the curing temperature.
A new approach to analyzing residence time and mixing in a co‐rotating twin screw extruder
Authors: Gasner Glenn E. , Bigio David , Marks Charles , Magnus Fredrick , Kiehl Christopher
Published: April 2004

A series of experiments was conducted to determine what correlations exist between an experimental parameter, percent drag flow, and other parameters such as head, tail and mean residence time. Experimentation was carried out on two polymer systems, a model system of near‐Newtonian fluid and a viscoelastic system of polyisoprene with several additives. To aid in the residence time analysis, data from three literature sources were cited and replotted. A family of residence time curves for a partially filled system can be combined into one curve by plotting the number of screw revolutions carrying the tracer to the extruder exit versus the percent drag flow. This method of plotting the data for each screw configuration estimates the mean residence time for any throughput and screw speed once a few data points are taken. In all four sets of experiments, the number of screw revolutions carrying the tracer to the exit decreases with increasing percent drag flow. The filled volume of the extruder was calculated from residence time data to show that percent drag flow is linearly related to extruder filled volume. When percent drag flow increased in the viscoelastic system the following results were recorded: fraction of polymer residence time spent in conveying elements increased, fraction of residence time spent in mixing elements decreased, polymer Mooney viscosity increased, number and weight average molecular weights increased and polydispersivity increased.
Preparation of macromolecular tracers and their use for studying the residence time distribution of polymeric systems
Authors: Hu Guo‐Hua , Kadri Ilham
Published: April 2004

In this study, an easy route was developed to incorporate antracene moieties in polymer chains. It consisted of copolymerizing the monomer of a polymer of interest with 3‐isopropenyl‐α, α'‐dimethylbenzyl isocyanate (TMI) and then reacting the isocyanate‐bearing polymer with 9‐(methylamino‐methyl)anthracene. Such an antracene‐bearing polymer was then used as a tracer (macrotracer) to determine the RTD function of polymers in a twin screw extruder and compared with an antracene as a microtracer. As long as the tracers were well mixed with a polymer of interest and the resulting mixture had the same geometrical form as the polymer before they were charged to the flow stream, the differences between the microtracer and the macrotracer were not reflected in the measured RTD distribution. A variation in the feed rate (Q) or screw speed (N) changes both the RTD and the intensity of axial mixing. On the other hand, for a given but small Q/N, commonly called specific throughput, variations in Q and N change the RTD but not the intensity of axial mixing. When it is small, Q/N can be used as an operating parameter to separate the effect of the residence time from that of mixing for a small Q/N.
Optimized runner systems for multicavity injection molds. Part I: Runner sizing
Authors: Lee Ching‐Chih , Stevenson James F.
Published: April 2004

A strategy has been developed for optimizing the design of runners in injection molds with multiple identical cavities. This approach is based on mathematically rigorous derivations using the power‐law viscosity model under conditions where the pressure drop in runners is not significantly influenced by temperature variation. The design rule to minimize runner volume for specified injection pressure and rate is simple: The diameter of any runner downstream from a junction is determined by dividing the diameter of the upstream runner by the cube root of the number of downstream branches at the junction. This rule has been extended to noncircular runners using the hydraulic radius approximation and the requirement of equal velocities in the circular and noncircular runners. Minimum volume cross‐sectional shapes have been determined for U‐shaped and trapezoidal shaped runners. For circular runners a method for estimating the pressure drop for nonisothermal flow quantifies the deviation from the pressure drop for isothermal flow at the melt temperature. As runner size decreases, the trend is for viscous heating to dominate over cooling and for the estimated nonisothermal pressure drop to be lower than the isothermal pressure drop.
Brittle to ductile: Fracture toughness mapping on controlled epoxy networks
Authors: Crawford Emmett D. , Lesser Alan J.
Published: April 2004

A series of epoxy networks with controlled molecular weight between crosslinks (Mc) was constructed with a difunctional epoxy resin and a mixture of aliphatic amines. The glass transition and yield strengths decreased as Mc increased, while the elastic properties were independent of Mc. In determining the effect of Mc on fracture toughness, the fracture behavior changed from a brittle fracture to a ductile fracture as Mc increased. The tests and analyses used to evaluate the fracture energy changed from a linear elastic fracture mechanics approach for brittle failures to an elastic‐plastic fracture mechanics approach for ductile failures. The ductile responses also showed an increasing fracture resistance with crack extension. Two popular models were used to describe the fracture energy as a function of yield strength. The analysis showed that a change in fracture energy by a thermally induced change in yield strength was equivalent to a change in fracture energy by a chemically induced change in yield strength. In addition, comparisons between the two models allowed insightful relationships to be drawn.
Rotational isomeric relaxation in poly(ethylene glycols) studied by acoustic spectroscopy
Authors: Striboulevich Anatoly , Sperkach Volodymyr , Sperkach Yaroslav
Published: April 2004

Acoustic spectra have been investigated for a series of poly(ethylene glycols) (PEGs) with molecular masses of 200, 400, and 600. Velocity of sound propagation c and sound attenuation αf−2 were measured in the frequency interval from 5 to 2500 MHz and temperature interval from 278 to 343 K. The acoustic spectra of PEGs in the frequency range studied comprise two simple dispersion regions. Characteristic parameters for these regions were calculated. Possible molecular mechanisms of the processes responsible for the regions are considered. It turns out that the low‐frequency dispersion region is caused by conformational restructuring processes in PEG molecules. The main contribution to the sound attenuation was shown to be caused by rotational isomeric relaxation process of the type trans‐trans↔trans‐gause. Thermodynamical and kinetic parameters of the low‐frequency relaxation region are reported.
Controlled release PVC membranes: Influence of phthalate plasticizers on their tensile properties and performance
Authors: Donempudi Shailaja , Yaseen Mohammed
Published: April 2004

The design of controlled release polymer dispensers (CRPD) for effective release of the active ingredients at desired rates requires a careful study and generation of data on several properties of the polymer membranes. Presence of optimum tensile properties is one of the prerequisites for the CRPD in deciding their suitability for application in the fields. Polyvinylchloride (PVC) membranes containing di n‐alkyl phthalate (alkyl= methyl, ethyl, butyl&octyl) with concentrations ranging from 10–30% with an increment of 2.5% were prepared. The tensile strength and percent elongation of these membranes as a function of concentration of the phthalate plasticizers, their size and aging period were performed. An increase in the tensile strength with increasing phthalate content was noticed up to 17.5% phthalate. Then followed a decrease with further increase of phthalate content. In contrast, the percent elongation was observed to increase constantly with increased concentration of the plasticizer. The ambiguous increase in the tensile strength up to 17.5% plasticized films is attributed to the antiplasticization effect of the plasticizer. The properties showed a linear behavior with respect to the size of the alkyl chain length and also the period of aging. The membranes with 17.5% and 20% were found to have optimum tensile properties and good property retention with aging for their application in controlled release of agrochemicals.
Temperature variation of the photoinduced birefringence of an azo dye doped polymer
Authors: Blanche P.‐A. , Lemaire Ph. C. , Maertens C. , Dubois P. , Jérǒme R.
Published: April 2004

The influence of the temperature on the photoinduced birefringence on an azo dye doped polymer film has been studied. Sample is composed of a polymer matrix PVK (Poly(N‐vinylcarbazole)), doped with 10 weight percent (wt%) of the birefringent molecule DMNPAA (2,5‐dimethyl‐4‐(p‐nitrophenylazo)anisole) and 30 wt% of ECZ (N‐ethylcarbazole) which acts as a plasticizer. Theoretical results can explain the behavior of the amplitude of the photoinduced birefringence versus temperature. Experimental and theoretical results are compared. Holographic recording experiments based on photoinduced birefringence have been carried out. Based on the effect of temperature, we have been able to significantly increase the diffraction efficiency of our sample.
Neutron transmission and quasi‐elastic neutron scattering in polymer hydrogels
Authors: Klepko V.
Published: April 2004

Investigations of hydrogels with high water contents have recently acquired special significance. Hydrogels are crosslinked three‐dimensional networks of water‐soluble macromolecules saturated by water or water solutions of different substances. The interest in examination the fundamental physical properties for such systems is related to their numerious applications. Using neutron transmission and quasi‐elastic neutron scattering (QENS), the mass transfer and self‐diffusion processes of water and water solutions in gelatin and poly(acrylamide) hydrogels were studied. It was shown that the macroscopic liquid flow through network of quasi‐porous polymer gels at relatively low pressure gradients as well as self‐diffusion of water and water solutions in the above systems are adequately described by “effective medium” approach. QENS data were also interpreted using an approach that accounts for the hierarchy of time scales of molecular motions: slow collective motions of liquid molecules contained in Lagrange's clusters and rapid single‐particle motions. The friction and self‐diffusion coefficient data were used to estimate the effective pore sizes of gels at different polymer concentrations as well as the mean Lagrange's cluster sizes.
An optimization approach to practical problems in plasticating single screw extrusion
Authors: Covas J. A. , Cunha A. G. , Oliveira P.
Published: April 2004

Setting the extruder operating conditions, or establishing the adequate geometry of the screw, for a given group of specifications, is dealt with as an optimization problem where the solution is searched in a nonconvex space. In practice, this is a conflicting multi‐attribute optimization problem, where various optima may coexist. The methodology developed involves the maximization of an objective function, quantifying the adequacy of the extruder‐die combination response to particular inputs, whose values are computed using an extrusion modeling package developed for this work. Genetic Algorithms (GAs) are used to generate better sets of inputs. In a second stage, multi‐objective optimization through Pareto curves, coupled to GAs, is implemented since, beyond optimization, it also provides a better understanding of the characteristics of the extrusion system under study.
Rod‐Climbing characterization of kaolinite suspended polyisobutylene solutions
Authors: Choi Hyoung J. , Lee Hong J. , Lim Sung T. , Jhon Myung S.
Published: April 2004

The rod‐climbing constants of kaolinite‐suspended polyisobutylene (PIB) solutions are investigated from rod‐climbing experiments. For a low deformation rate, this particle suspended polymer solution can be regarded as a second‐order fluid, and the rod‐climbing constant for such fluids is correlated with the rheological properties of the particle‐suspended polymer solutions. The rod‐climbing constants for kaolinite suspended PIB solutions were found to decrease with temperature and increase with PIB concentration, molecular weight of PIB, solvent viscosity, and particle concentration. The rheological properties were measured using rotational rheometer, and the shear viscosity and the first normal stress difference of the kaolinite suspended PIB solution show the Boger‐fluid characteristics.
Preparation and characterization of anionic collagen: P(VDF/TrFE) composites
Authors: Goissis Gilberto , Piccirilli Luciana , De Guzzi Plepis Ana Maria , Das‐Gupta Dilip K.
Published: April 2004

Anionic collagen:P(VDF/TrFE) (75/25) membrane composites were prepared by mixing anionic collagen and P(VDF/TrFE) in aqueous concentrated acetic acid:dimethylsulfoxide solutions and characterized by infrared, electron scanning microscopy, thermal analysis and dielectric properties. The results show that under the appropriate conditions anionic collagen:P(VDF/TrFE) composites, with ratios in the range from 4:1 to 1:4 may be conveniently prepared in the form of membranes, without the loss of tropocollagen secondary structure. As suggested by infrared spectroscopy and thermal analysis, mixing is accompanied by macromolecular interaction conditions anionic collagen and P(VDF/TrFE). Although preliminary, the determined pyroelectric coefficient for the 1:1 composite of 1.89 × 10−4Cm−2K−1, is higher than those determined under the same conditions for native, anionic collagen and P(VDF/TrFE) and of respectively 0.37 × 10−4Cm−2K−1, 1.16 × 10−4Cm−2 K−1 and 17 × 10−6 Cm−2K−1, but comparable to that for PZT (4.2 × 10−4Cm−2K−1) at the same temperature. This increase in pyroelectric coefficient for the 1:1 composite, in respect to anionic collagen membranes, may be a result of a anionic collagen: P(VDF/TrFE) interaction. A model based on hydrogen bonding formation between acidic and alcoholic hydroxyl groups of anionic collagen and the flurine atoms of P(VDF/TrFE) is proposed.
The ferroelectric properties of piezoelectric ceramic/polymer composites for acoustic emission sensors
Authors: Wenger M. P. , Almeida P. L. , Das‐Gupta D. K. , Blanas P. , Shuford R. J.
Published: April 2004

Two different mixed connectivity composites, consisting of a ferroelectric ceramic powder of calcium modified lead titanate (PTCa) dispersed in a polymer matrix, have been fabricated and their ferroelectric properties have been investigated. Hysteresis measurements have been conducted on composites of PTCa with a polar polymer of polyvinylidene trifluoroethylene (P(VDF‐TrFE)) and PTCa with a thermosetting epoxy resin to determine the coercive fields and remanent polarization of the two different composites. The composites show noticeable differences in their behavior during poling along with the values of their piezoelectric coefficients, with the composite of PTCa/P(VDF‐TrFE) showing enhanced piezoelectric activity over that of PTCa/epoxy. This paper reports on the polarization properties and the microstructural nature of the composites.
Electrorheological characterization of semiconducting polyaniline suspension
Authors: Choi Hyoung J. , Lee Jin H. , Cho Min S. , Jhon Myung S.
Published: April 2004

Electrorheological (ER) properties of polyaniline suspensions in silicone oil with various experimental conditions were investigated. These suspensions exhibit dramatic changes in their rheological properties which are caused by the formation of particle chain structures induced by an applied electric field. Polyaniline was synthesized by the chemical oxidation of aniline with ammonium peroxysulfate. This study examined the effects of electric field, volume fraction, polymerization temperature and operation temperature on the ER properties of polyaniline suspensions in silicone oil. Rheological measurements were carried out by using a rotational rheometer with a high voltage generator in both controlled shear stress and shear rate modes. Experimental results showed that the ER properties were enhanced by increasing the volume fraction and electric field and were independent of the operating tempertures. The best ER properties were also obtained by using polyaniline particles synthesized at ‐10°C, and these had a conductivity of ˜ 10−10 S/cm.
Effects of dispersing agents on dispersity and mechanical properties of carbon black/PET
Authors: Kim Dae‐Jin , Seo Kwan‐Ho , Hong Ki‐Heon , Kim Sang‐Youl
Published: April 2004

Three kinds of dispersing agents, all copolyesters, were synthesized from the polycondensation reaction of dimethyl terephthalate (DMT), dimethyl isophthalate (DMI), sebacic acid (SA), and 1,4‐butandiol (BD). Copolyester from DMT, SA, and BD was designated as PBTS; from DMT, SA, DMI, and BD as PBTIS; and from DMT, DMI, and BD as PBTI. Carbon black masterbatches were prepared by mixing carbon black into the dispersing agents in a Brabender Plasticorder PLE331. Using single screw extruder, masterbatches were compounded with poly(ethylene terephthalate) in 3 wt% concentration and mechanical properties of the compounds were investigated. Gel permeation chromatography data implied that thermal degradation of polymeric dispersing agents was not very significant. Capillary rheometer tests showed that PBTI has the highest viscosity and shear sensitivity of the three dispersing agents. Volume resistivities of each masterbatch were increased as the rotor rpm of the Brabender and mixing time increased. Transmission electron micrographs showed that dispersion of carbon black was enhanced by increasing the melt viscosity of the dispersing agent. The performance and mechanical characteristics of carbon‐black‐filled PET compounds depends directly on the dispersion quality of the carbon black in the masterbatch. Mechanical properties of compounds were improved by increasing dispersion of carbon black and increasing numbers of rigid aromatic groups in the copolyester dispersing agent.
Characterization and evaluation of piezoelectric composite bimorphs forin‐situacoustic emission sensors
Authors: Wenger M. P. , Blanas P. , Shuford R. J. , Das‐Gupta D. K.
Published: April 2004

Mixed connectivity composites consisting of a ferroelectric ceramic powder of calcium modified lead titanate dispersed in a polymer matrix have been fabricated into piezoelectric bimorph sensors. The piezoelectric, dielectric and electromechanical coupling coefficients of these sensors have been measured and a full characterization of the electromechanical properties are reported. The suitability of these bimorph transducers asin‐situacoustic emission sensors, embedded into glass‐epoxy laminate plate like structures, has been investigated. A comparison of the performance of these sensors to those of previously investigated monomorph sensors fabricated from the same material has been made.
A novel approach to the tailoring of polymers for advanced composites and optical applications, involving the synthesis of liquid crystalline epoxy resins
Authors: Giamberini Marta , Amendola Eugenio , Carfagna Cosimo
Published: April 2004

The authors describe the features of liquid crystalline epoxy resins having both high and low crosslinking densities. These materials seem to be very promising as matrices in advanced composites and in optical and electro‐optical applications because of their peculiar properties. The importance of factors like molecular rigidity, nature of the curing agent, and curing temperature for the development of such properties are analyzed. The authors showed that amines produce thermosets having high Tgs and high fracture toughness. In particular, the enhancement of this last parameter is very promising if a new generation of matrices is to be sought for manufacturing composites. In the case of acids as curing agents, thermosets having lower Tgs and more ordered mesophases can be obtained. In this case, LC elastomers can be prepared that can find applications in the optical industry as waveguides or electro‐optical devices.
Synthesis and characterization of zirconium ionomer dispersions
Authors: Ricardo Nágila M. P. S. , Ricardo Nadja M. P. S. , Holmes Robert , Price Colin
Published: April 2004

Water‐based ionomer dispersions were formed by post‐polymerization addition of zirconium species to polymer latices prepared from butyl methacrylate (BMA), butyl acrylate (BA) and acrylic acid (AA) by semicontinuous emulsion polymerization. The mole fraction of AA in the latex particles was kept at 10 mole% in all cases whereas the ratio of BA to BMA was varied. A method was established which allowed zirconium in the form of ammonium zirconium carbonate (AZC) to be successfully introduced into the latices without affecting their colloidal stability. Dynamic light scattering was used to determine average particle size in diluted latices. The structure and properties of cast ionomer films were investigated by differential scanning calorimetry (DSC), dynamic mechanical thermal analysis (DMTA), tensile strength and swelling measurements. Fourier transform infrared spectroscopy (FTIR) was used to investigate the nature of the carboxylate bonding.
Thermal stability of poly(methyl methacrylate‐co‐butyl acrylate) and poly(styrene‐co‐butyl acrylate) polymers
Authors: Leskovac Mirela , Kovačević Vera , Flě Dragutin , Hace Drago
Published: April 2004

Thermal stability of poly(methyl methacrylate‐co‐butyl acrylate) and poly(styrene‐co‐butyl acrylate) modified with a small amount of acrylic acid and/or N‐methylolacrylamide as a crosslinking agent was studied in this work. Programmed thermogravimetric analysis has been used to study the effect of copolymer composition on thermal stability, over a temperature range from 50 to 450°C, under a constant flow of nitrogen. Kinetic parameters of thermal degradation, activation energy, pre‐exponential factor, and reaction order were obtained by using MacCallum‐Tanner's approach. Kinetic data indicate that the thermal degradation of the investigated copolymer systems is the first order reaction, and that the increase of activation energy may be an indication of thermal stability changes in copolymer systems.
Cycle time predictions for the rotational molding process with and without mold/part separation
Authors: Gogos G. , Liu X. , Olson L. G.
Published: April 2004

We present a detailed theoretical heat transfer model for the entire rotational molding process (including heating and cooling stages) and identify the key dimensionless groups affecting the process cycle time. This theoretical model is employed to generate numerical results that are in very good agreement with the experimental data available in the literature. The effects of variations in the dimensionless groups on the cycle time are evaluated. In addition, part shrinkage has been incorporated in the models, and its effect on the process cycle time has been studied extensively.
A factorial design applied to polypropylene functionalization with maleic anhydride
Authors: Nachtigall S. M. B. , Neto R. Baumhardt , Mauler R. S.
Published: April 2004

Maleic anhydride functionalized PP was prepared in a melt‐mixer according to a factorial design. Two levels of maleic anhydride concentration (MA), dicumyl peroxide concentration (DCP), reaction time, and temperature were employed. The isolated and interaction effects of these variables on the degree of functionalization and molecular weights were analyzed. The products were characterized by Fourier transform infrared spectroscopy (FTIR), gel permeation chromatography (GPC), titration, and torque measures. The reaction time showed no appreciable effect within the studied range (10 to 20 minutes); however, the other three factors showed significant main effects. MA and temperature presented an important interaction effect on the degree of functionalization and molecular weights. The highest degrees of functionalization were found to be related to the smallest molecular weights.
Thermal and mechanical properties of the precursor polymers: Comparison of their properties with poly(amic acid)
Authors: Chang Jin‐Hae , Farris Richard J.
Published: April 2004

The DSC thermograms of P‐PHA show a large endothermic peak at 450–550°C. As the annealing temperature increases from 250°C to 400°C, the endothermic peaks become smaller and then disappear for samples annealed above 450°C. As observed for P‐PHA, the endothermic enthalpy of PHA and PAA became smaller with an increasing annealing temperature. The cyclization onset temperature (T1) of the three precursors increases linearly with an increasing annealing temperature at a constant annealing time (30 min). Otherwise, the initial decomposition onset temperature (T2) was shown to be constant. T2 of P‐PHA, PHA, and PAA were observed in the temperature ranges of 601–603°C, 576–577°C, and 532–534°C, respectively. These TGA results confirm that all of the samples are thermally stable. Increasing the annealing temperature of the three precursor polymers significantly increases the tensile properties of the films. The tensile properties of all annealed precursors were much higher than those of the unannealed films. In contrast, the initial modulus of PAA is improved only slightly when compared with the other two polymers regardless of the heat treatment. The biaxial stresses in the PHA and PAA films were investigated by holographic interferometry. The stresses in the films were 6.85–7.61 MPa for PHA and 27.01–27.70 MPa for PAA.
Transient shear and extensional properties of biodegradable polycaprolactone
Authors: Kapoor Bikram , Bhattacharya M.
Published: April 2004

Transient shear and extensional properties of two grades of partially crystalline biodegradable aliphatic polyesters, poly ε caprolactone (PCL), were investigated at three different temperatures. Uniaxial extensional viscosity at a constant strain rate was obtained using the Meissner apparatus. The magnitudes of the stress‐over‐shoot during stress growth experiments were smaller than those typically observed for other polymers. Higher melt temperature and higher strain led to faster relaxation, while the lower molecular weight PCL 767 relaxed faster than the higher molecular weight PCL 787. The relaxation moduli are independent of strain for strain values below 0.1. Transient extensional measurements were conducted at strain rates of 0.01 to 1.0 s−1. At small stresses the extensional viscosity has the threefold value of shear viscosity as predicted by Trouton. There appeared to be no steady state regime for either grade of PCL studied and as a result ηe(ε) could not be determined. The departure from the linear limit is fastest for the highest extensional rate. Extension thickening behavior is observed at Hencky strains ranging from 1.0 to 2.0. PCL 767 displayed greater extension thickening than PCL 787 at the same temperatures. The Wagner integral constitutive equation was found to give an acceptable fit to the stress growth data in shear and extension, with the fit being better for PCL 767 than for PCL 787.
Characterization of the lubricant layer formed at the interface between the extrudate and the die wall during the extrusion of high density polyethylene and fluoroelastomer blends by XPS, SIMS and SEM
Authors: Lo Horace Ho‐Kei , Chan Chi‐Ming , Zhu Shui‐Han
Published: April 2004

The formation of a lubricant layer at the polymer‐metal die interface, when a blend of high density polyethylene (HDPE) and a fluoropolymer processing aid (Dynamar) was extruded through a slit die, was verified and investigated in depth. Blends containing 0.5 and 5 wt% of Dynamar were prepared by a twin‐counter‐rotating‐scew extruder. The viscosity of the blends was measured with a capillary rheometer. A specially made slit die block containing two pieces of insert was used. The inserts which could be taken out from the slit die block at the end of the measurement were separated from the polymer block by acid etching. The polymer block contains the information about the lubricant layer formed between the extrudate and the die wall. X‐ray photoelectron spectroscopic (XPS), secondary ion mass spectrometric (SIMS), and scanning electron microscopic (SEM) analyses of the polymer blocks confirmed the presence of a Dynamar‐rich lubricant layer at the interface between the extrudate and the die‐wall surface. The thickness of the lubricant layer varied from 5 to 15 μm depending on the shear rate and the concentration of the Dynamar in the blend. For the Dynamar concentrations and shear rates considered in this study, the efficiency of the viscosity reduction appears to be independent of the lubricant layer thickness.