bluuebunny/crossref_metadata_2025_split huggingface dataset:
On‐Line determination of density and crystallinity during melt spinning
Authors: Bansal Vishal , Shambaugh Robert L. 
Published: April 2004

AbstractThe density and crystallinity of polypropylene fiber were measured on the moving threadline during the melt spinning process. Heretofore, threadline densities have never been measured on‐line. These density measurements were accomplished by taking parallel, on‐line measurements of fiber diameter, fiber velocity, polymer mass flow rate fiber temperature, and fiber birefringence. Under certain spinning conditions, a distinct rise in density occurs along the threadline. This rise in density corresponds well with the rise in crystallinity as measured by birefringence.
A study of rib geometry for gas‐assisted injection molding
Authors: Yang S. Y. , Huang F. Z. , Liau W. N. 
Published: April 2004

AbstractLarge, thin, plate‐shaped parts usually are strengthened with structural ribs. Ribs also serve as gas channels with gas‐assisted technology. The layout and geometry of these gas‐channel ribs are critical to the gas‐assisted injection molding (GAIM) process. In this study, the effects of rib geometry, including aspect ratio and fillet geometry, on the GAIM process are investigated. Experimental results indicate that increasing the rib width widens the allowable operation range and thus improves the moldability. Adding fillets to the rib corner significantly enhances the moldability. Adding fillets also reduces the loss of rigidity due to void formation in the rib. A curved fillet improves moldability and rigidity more than one that is straight.
Ceramic‐reinforced polymers and polymer‐modified ceramics
Authors: Mark J. E. 
Published: April 2004

AbstractThe composites discussed in this review are prepared using techniques similar to those used in the new sol‐gel approach to ceramics. Organometallis such as silicates, titanates, and aluminates are hydrolyzed in the presence of polymer chains (for example polysiloxanes and polyimides) that typically contain hydroxyl or amino groups. The functional groups are used to bond the polymer chains onto the silica, titania, or alumina being formed in the hydrolysis, thus forming organic‐inorganic composites. When the polymer chains are present in excess, they constitute the continuous phase, with the ceramic‐type material appearing as reinforcing particles. When present in smaller amounts, the polymer is dispersed in the continuous ceramic phase, to give a polymer‐modified ceramic. Under some conditions, bicontinuous systems are obtained. The composites thus prepared are characterized by electron microscopy, X ray, and neutron scattering intensities, density determinations, and stress‐strain and impact‐strength measurements.
Properties of side chain liquid crystal polyesters containing chiral groups in the main chain
Authors: Mehl G. H. , Valvo F. , Lacey D. , Goodby J. W. , Das‐Gupta D. K. 
Published: April 2004

AbstractThe synthesis and investigation are reported for the phase behavior of a set of three liquid‐crystalline side chain polyesters (SCLCPs), consisting of aromatic diacids and diols bearing cyano biphenyl moieties in the side chain. The materials contain a chiral center in the main chain and show a cholesteric phase indicative of a helical order with a preferred twist. In addition, they exhibit Tg's below room temperature and smectic bilayer phases. Depending on the substitution pattern of the aromatic core, Sc* or SA* phases are observed. These polymers were synthesized in a four‐step synthesis, starting from available materials. The dielectric relaxation behavior and the pyroelectric responses of the three SCLCPs tend to conform to their respective structure.
Dielectric and pyroelectric characterization of anionic and native collagen
Authors: Guzzi Plepis Ana Maria De , Goissis Gilberto , Das‐Gupta Dilip K. 
Published: April 2004

AbstractReconstituted collagen membranes (thickness 20–40 microns), used in periodontal guided tissue regeneration, were prepared by solubilization of bovine serosa and bovine tendon using an alkaline treatment and by solubilization of bovine serosa in acetic acid. Dielectric properties of these materials were determined in the frequency range of 10−5−106 Hz (poling temperature = 313 K, poling time = 3 h, E = 107 V/m), using a General Radio Bridge system (high frequencies) and a discharge current technique (low frequencies). The true pyroelectric coefficient p(T) was determined for these materials by a direct method over an appropriate temperature range. Their magnitude appear to be in the range of 10−4 to 10−5 C/m2 K−1, which is considerably higher than that of the ferroelectric poly(vinylidene fluoride) (PVDF) and its copolymer vinylidene fluoride‐trifluorethylene (VDF‐TrFE).
Nonlinear stress‐strain behavior of glassy polymers
Authors: Chow T. S. 
Published: April 2004

AbstractWe have attempted to provide a unified account of the structural relaxation and mechanical properties of glassy polymers by reviewing recent results of a predictive model. One would like to understand how the effects of structural relaxation influence the performance of amorphous solids. The physics of glassy polymers is still evolving and the functional relationships between relaxation and deformation have not been firmly established. However, significant progress has already been made that can be utilized in solving problems in the large deformation of polymers. Equations have been derived that can be applied to provide quantitative prediction of the nonlinear stress‐strain relationships as a function of physical aging, strain rate, temperature, external stress field, and the filler concentration in composites.
Acoustic emission signal detection by ceramic/polymer composite piezoelectrets embedded in glass‐epoxy laminates
Authors: Wenger M. P. , Blanas P. , Shuford R. J. , Das‐Gupta D. K. 
Published: April 2004

AbstractPiezoelectric composites, consisting of a ferroelectric ceramic powder of calcium‐modified lead titanate dispersed in two different polymer matrices, viz. from vinylidene fluoride trifluoroethylene and an epoxy, have been fabricated. The composites show a mixed connectivity structure, and the results of electromechanical characterization are given. Thin films of these materials have been incorporated into surface mounted acoustic emission sensors and their frequency response and ability to detect plate waves, generated by a simulated acoustic emission source, has been examined. In situ transducers embedded into glass‐reinforced laminate plates have also been examined and have been shown suitable for acoustic emission sensors.
Physical aging time scales and rates for poly(vinyl acetate) stimulated mechanically in the Tg‐region
Authors: Delin M. , Rychwalski R. W. , Kubát J. , Klason C. , Hutchinson J. M. 
Published: April 2004

AbstractThe physical aging behavior of poly(vinyl acetate), PVAc, in the Tg‐region has been investigated using dynamic mechanical analysis (DMA). Tests in shear and flexure modes were performed for samples quenched from a stabilization temperature of 40°C to aging temperatures 35.0°C and 32.5°C (down‐jumps), and from equilibrium at a stabilization temperature of 32.5°C to aging temperature 36.2°C (up‐jump). Volume recovery was investigated for the same thermal histories using mercury‐in‐glass dilatometry. The time scales for the evolution of the storage and loss moduli during physical aging have been compared with the volumetric time scales. Aging rates, µ, have been calculated in the frequency and time domains. The evolution of dynamic mechanical properties during aging is found to be different from the volumetric behavior. In the case of the temperature down‐jump, the evolution of the volume ceases earlier than that for the storage and loss moduli. In the up‐jump experiment, the opposite is found. Aging rates for the storage and loss moduli are analyzed. A suggestion is offered that the evolution of dynamic mechanical properties during physical aging is retarded by the cyclic mechanical stimulus, and that this effect (rejuvenation) is more noticeable the higher is the damping; consequently rejuvenation in the Tg‐region can be caused by small strains in dynamic mechanical analysis.
Physical aging in polymers: Comparison of two ways of determining narayanaswamy's parameter
Authors: Godard Marie‐Elodie , Saiter Jean‐Marc , Burel Fabrice , Bunel Claude , Cortes Pilar , Montserrat Salvador , Hutchinson John M. 
Published: April 2004

AbstractIn this work, we have investigated by differential scanning calorimetry the enthalpy relaxation of two poly[methyl(α‐n‐alkyl)acrylates] in which it is possible to change the length of the two alkyl chains. In particular, we have evaluated the Narayanaswamy parameter, which controls relative contribution of temperature and of structure to the relaxation times, by two methods: Grenet's method (GM) and the peak‐shift method (PSM). The data obtained show that both methods lead to equivalent results. Nevertheless, PSM requires fewer experiments than GM, and PSM appears to be more practical. The results obtained on the two acrylates show that the parameter x increases with the lateral chain length, that is to say, that the temperature effects increase as the length of the alkyl chain is increased.
On the correlation between the viscosity of partially hydrolyzed polyacrylamide solution and the diffusion coefficient in the semidilute concentration regime
Authors: Kanatharana Jarujit , Sukpisan Jeerutha , Sirivat Anuvat , Wang S. Q. 
Published: April 2004

AbstractThe solution viscosity of neutral polyacrylamide (PAM), the partially hydrolyzed polyacrylamide (70% HPAM), and polyacrylic acid (PAA) were measured concurrently with the apparent diffusion coefficient in the dilute and semidilute concentration regimes. We identified the scaling relation η − ηs = A/D in the semidilute regime, where η is the solution viscosity, ηs is the solvent viscosity, D is the coefficient of the slow diffusion mode obtained from dynamic light scattering, and A is a prefactor found to have a unique value of ∼1.0 × 10−8 cP cm2/s. The scaling relation as well as the prefactor are independent of the the ionic strength, the solvent quality, the molecular weight, the charge density, the polyelectrolyte, and salt concentrations. For the neutral PAM, the product [η – ηs]D is proportional to the polyelectrolyte concentration Cp, consistent with Rouse theory and previous experimental findings.
Amine modified polyethylenes, prepared in near critical propane, as adhesion promoting agents in multilayered HDPE/PET films
Authors: De Gooijer J. M. , Scheltus M. , Koning C. E. 
Published: April 2004

AbstractHigh density polyethylene [HDPE] grafted with 0.13, 0.04 and 1.04 wt% maleic anhydride (abbr.: PEMA) was modified with an excess of a variety of diamines in near critical propane. The resulting amic acid groups were quatitatively imidized to the corresponding imide (PEMI) in the melt. Increasing the percentage maleic anhydride grafted on the HDPE resulted, upon reaction with the diamines, in an increased gel content, due to crosslinking. Three‐layered films were prepared using HDPE film and polyethylene dterephathalate (PET) film as the outer layers and the PEMAs and PEMIs as the inner layer. Adhesion strengths were measured using a T‐peel test. Increasing the bonding temperature resulted in an improved adhesion. The most optimal system for adhesion proved to be HDPE grafted with 0.40 wt% MA and modified with a pendent secondary amine group. For this system the lowest number of reactive amine groups was lost owing to crosslinking reactions, so the highest concentration of amines is available for interactions with the PET film. The absence of extensive HDPE crosslinking in addition implies a better flow of the adhesive layer during lamination. From contact angle measurements, it was observed for all samples that after delamination of the three‐layered system, PET was present on the PE‐surface and PE was present on the PET‐surface.
Transport processes and feasible operating domain in a twin‐screw polymer extruder
Authors: Zhu Weimin , Jaluria Yogesh 
Published: April 2004

AbstractThe flow of a polymer and the associated heat transfer in a fully intermeshing, co‐rotating twin screw extruder are investigated numerically. The control volume technique is used for numerical modeling and simulation, considering both Newtonian and non‐Newtonian fluids. The velocity distributions in the screw channel are compared with experimental resultlsf and good agreement is obtained. Owing to limitations arising from the physical aspects of the problem, the numerical results show that not all operating conditions are feasible. A feasible domain, in terms of screw speed and mass flow rate, in which the extruder operation is satisfactroy, is obtained for pure starch. To improve the applicable range of this model, an axial formulation is adopted for the translation region that characterizes the domain away from the intermeshing zone of the extruder. This model yields results consistent with the earlier down‐channel model while the feasibility region is extended towards lower mass flow rates. For the upper limit, a physicdal restriction arises in terms of the maximum flow rate for a pressure rise in the extruder. Thus, the model can be used for simulating a wide range of operating conditions while retaining the appropriate physical behavior of the process.
Feasible compositions for random copolymerizations
Authors: Smith Raymond L. , Malone Michael F. 
Published: April 2004

AbstractUsing the attainable region approach, feasible compositions and conversions for random copolymers are determined, along with altermatives for the related reactor configurations. This analysis attempts to find all of the possible compositions that can be produced by any system of reactros and mixing. The average copolymer compositions are bounded by the feed composition and the instantaneous copolymer composition produced at the initial conditions. Since the instantaneous copolymer composition can be found through the Mayo‐Lewis equation, that case and the feed composition mark the limiting feasible compositions. The results can also be used to determine the range of feed compositions for which a specific copolymer product composition is possible. If the addition of monomer at any point in the reactor system is possible, e.g., by side‐feeding, the analysis indicates that any desired copolymer composition can be obtained.
Crystallization kinetics of poly(butylene terephthalate) (PBT): Influence of additives and free carboxylic acid chain ends
Authors: Pillin Isabelle , Pimbert Sylvie , Feller Jean‐François , Levesque Guy 
Published: April 2004

AbstractDegradation of poly(butylene terephthalate) (PBT) induced by blending time at 260°C leads to an increase of both carboxylic end groups and melt viscosity index and a decrease of the molecular weights. Crystallization kinetics of pure PBT and PBT blended with and epoxide, which was used to reduce the free carboxylic acid concentration, were compared. Lower carboxylic acid concentrations were obtained, but the molecular weights still decreased. The crystallization kinetics of PBT blended with pigments and/or mineral fillers were also studied. Dyes, some of which are known for their nucleation activity, were used for differentiating extruded PBT tubes in optical fiber loose cables. Post‐shrinkage appeared to depend on the type of pigment used. Pigments Concentration, particle size and chimical nature have been correlated to the PBT crystallization kinetics. An increase of the nonisothermal crystallization temperature was observed, more or less important according to the pigment used. Talc and mica were also tested in PBT blends, with and without pigments. Their mucleation activity parameters were measured and compared with those for the pigments. An average value of the crystallization temperature, nearly constant and independent of the Pigment, was obtain controlled shrinkage on industrial products with strict dimension requirements.
The morphology of hyperbranched polymer compatibilized polypropylene/polyamide 6 blends
Authors: Jannerfeldt G. , Boogh L. , Månson J.‐A. E. 
Published: April 2004

AbstractThe influence of hyperbranched polymer grafted polypropylene (PP‐HBP) on the morphology of polypropylene (PP)/polyamide 6 (PA6) blends has been investigated. The final morphology was strongly influenced by the PP‐HBP compatibilizer concentration. At low concentrations, PP‐HBP acts as an emulsifying agent, reducing the size of the dispersed phase and preventing coalescence. This is due to the high reactivity and diffusitivity of PP‐HBP rapidly forming a high density of copolymers at the interface. Compared to the use of maleic anhydride grafted PP (PP‐MAH) at identical concentrations, PP‐HBP yielded a smaller dispersed phase particle size. Therefore, PP‐HBP allows the use of less compatibilizer to obtain identical morphologies. At higher compatibilizer concentrations, it has been shown that the PP‐HBP efficiently stabilizes the interface and inhibits both coalescence and breakup of the PA6 droplets. The high concentration of reactive sites and the ability of PP‐HBP to react with both chain‐ends of PA6 suggest that interfacial stabilization occurs because of the formation of a partly crosslinked interface. The interfacial stabilization effects generated by PP‐HBP should allow one to control the morphology of polymer blends in order to create specific functional morphologies.
An analysis of photopolymerization kinetics and stress development in multifunctional acrylate coatings
Authors: Stolov Andrei A. , Xie Tao , Penelle Jacques , Hsu Shaw L. , Stidham Howard D. 
Published: April 2004

AbstractPolymerization kinetics and stress buildup of multifunctional acrylic coatings have been studied simultaneously using a cantilever deflection method and real time one‐bounce infrared reflectance spectroscopy. Cantilever deflection due to stress buildup in the film is correlated with crosslink density in the polymerizing mass. Stress buildup was observed not to occur instantaneously after radiation was introduced but rather after a certain time interval. The time delay between onset of polymerization and initiation of stress indication is attributed to the introduction of crosslinks, leading to a gel state. The measured stress‐conversion relationship can be predicted using an approach incorporating monomer reaction probability. Stress buildup can vary considerably as a function of processing conditions such as film thickness, temperature at solidification point, and the type, concentration and absorptivity of photoinitiator, which govern the degree of crosslinking. Under certain processing conditions, an uneven distribution of the monomer conversion in the film may severely alter the stress‐film thickness relationship. In some cases the cantilever material anisotropy can be detected based on the cantilever deflection measured.
Compatibilizers for thermotropic liquid crystalline polymer/polyolefin blends prepared by reactive mixing: The effect of processing conditions
Authors: Son Younggon , Weiss R. A. 
Published: April 2004

AbstractThe effect of processing conditions on the melt formation of a graft‐copolymer compatibilizer for blends of a thermotropic liquid crystalline polymer (TLCP) and polyolefins was investigated. The compatibilizer was formed by a melt acidolysis reaction of a 50/50 (w/w) blend of TLCP and the sodium salt of a poly(ethylene‐coacrylic acid) ionomer. The effects of various processing conditions in a batch mixer and a single‐screw extruder on the extent of reaction were assessed. The extent of graft‐copolymer formation and the efficacy of the product as a compatibilizer for TLCP/polyethylene blends were affected by the processing temperature and the screw (or rotor) speed.
Kinetics of structural evolution during crystallization of preoriented PET as followed by dual wavelength photometric birefringence technique
Authors: Venkatesvaran H. , Cakmak M. 
Published: April 2004

AbstractA two‐color laser photometric measurement system was used to follow birefringence changes in annealing of prestretched PET films. This technique was shown to be capable of detecting large retardation (and thus birefringence) changes beyond one wavelength of the light. The use of green and red lasers in the photometric system allows the detection of the reversals in birefringence during the course of annealing. Unless critical orienialion/erystallinity levels are developed by stretching the films, heat setting the films at temperatures close to glass transition temper ature results in complete elimination of preferential orientation. At Intermediate stretch ratios, crystalline regions form and Ihe acl as anchor points establishing a network for the orienied amorphous chains. These Dims exhibit partial relaxation followed by rapid increase in birefringence due to the accelerating effect of orientation on crystallization. At high stretch ratios, where substantially oriented and strain crystallized structures are obtained, the initial relaxation stage disappears and birefringence continue to increase throughout the heat setting process even at temperatures very close to glass transition temperature. In these films, however, the total change of birefringence decreases as more of the chains are oriented and crystallized in the stretching stage, leaving a smaller fraction of polymer chains to rearrange during Ihe annealing stage. The kinetics of the structural change exhibit a complex behavior and the largest rates of structural changes were observed in films exhibiting intermidiate birefringence levels.
Light transmission and haze of polyethylene blown thin films
Authors: Wang Lei , Kamal M. R. , Rey A. D. 
Published: April 2004

AbstractThe surface and bulk morphologies of polyethylene blown films are obtained using non‐contact Atomic Force Microscopy (AFM). Based on these experimental observations, a model using the Mie Scattering theory is proposed to describe the forward transmission and scattering of a plane wave through the film. The light transmission properties are computed from the proposed model and the results are validated by experimental measurements.
The mechanical properties of insert‐molded bimaterial composites
Authors: Extrand C. W. , Bhatt S. 
Published: April 2004

AbstractBimaterial composite samples were constructed by injecting various polymers into a mold containing a fraction of a pre‐molded specimen. The resulting series composites were tested in tension. Breaking stresses were independent of fractional length. Conversely, both elongation to break and apparent stiffness varied with Although samples broke at or near the interface, adhesion was reasonably good, as indicated by transfer of material across interfaces.
Open‐celled microcellular thermoplastic foam
Authors: Rodeheaver B. A. , Colton J. S. 
Published: April 2004

AbstractA theoritical model of the production of open‐cell microcellular foam is presented. This model allows the prediction of the conditions necessary to produce these materials. Experiments verify the model quite well. The results of the batch processing experiments indicate the processing parameters that promote the development of open‐celled microcellular polystryene foam. A saturation pressure of 17.2 MPa (2500 psig) provides the nucleation density necessary to form an impinged structure with microcellular bubble density. A foaming temperature of 200°C promotes the formation of both internal and surface porosity. A scaled time between 1 and 2.7 seconds develops a foam structure that intrudes a large volume. Samples foamed at 200°C for 1 and 2 seconds possess pores less than 1 μm in diameter. These samples represent scaled times of 1 and 2 seconds. Therefore, to produce open‐celled microcellular polystyrene foam with batch processing, samples should be saturated at approximately 17.2 MPa (2500 psig) and foamed for a scaled time between 1 and 2 seconds.