bluuebunny/crossref_metadata_2025 huggingface dataset:
Suspension polymerization of unsaturated polyester oligomers
Authors: Natov M. , Vassileva St. , Abood L.
Published: April 2004

A study has been made of an unsaturated polyester resin prepared from maleic anhydride, phthalic anhydride and 1,2‐propene glycol. The resin is transformed by alkalization with ammonia into a water‐soluble emulsion, which was polymerized with initiators and accelerators. It was found that water acts as an inert diluent in the emulsion. By measuring the temperature of the reaction mass during polymerization, the actual conversion has been estimated. The latter is lower than literature values. A correction of the method of A. Rojas et al. for the determination of the actual conversion is proposed, and the polymerization heat is thus determined. A value of 478 J/g is obtained, which is higher than reported. The apparent order of the polymerization reaction has also been determined; it changes from 5 to 18 with reaction progress.
Evaluation of data on the kinetics of isothermal polymer crystallization
Authors: Lambrigger Markus
Published: April 2004

The kinetic crystallization model of Avrami is generally accepted as a starting point for the analysis of isothermal polymer crystallization. However, in most cases, the experimental situation is complicated by an incubation time prior to isothermal crystallization, so that the Avrami equation must be modified. Moreover, the experimental data are often limited in number and restricted to an intermediate crystallinity range. Furthermore, data of isothermal crystallization experiments performed at different temperatures, cannot be evaluated together by using an evaluation procedure being based on the Avrami equation. An iterative procedure and a crystallization‐temperature independent Avrami master curve, which overcome these problems if the Avrami index n is bigger than one, are displayed in this work.
Mechanical behavior of injection molded β‐crystalline phase polypropylene
Authors: Tjong S. C. , Shen J. S. , Li R. K. Y.
Published: April 2004

High purity and a large amount of β‐modification can be produced in polypropylene (PP) by adding a bicomponent β‐nucleator consisting of equal amounts of pimelic acid and calcium stearate. Wide angle X‐ray diffraction (WAXD), scanning electron microscopy (SEM), static tensile tests, Izod impact tests, and instrumented drop weight impact testing were used to characterize the structure, morphology, and mechanical behavior of the β‐phase PP. The WAXD patterns show that the relative content of the β‐phase (K value) in the skin layer of the injection molded specimen is 0.54, whereas the K value in the core section is 0.92. SEM observations reveal that the β‐spherulite exhibits a sheaf‐like structure and there are no clear boundaries between the spherulites. Static tensile tests indicate that the elongation at break of pure PP is enhanced by the addition of a β‐nucleator. The impact and drop weight tests also indicate that the impact resistance of PP is improved by adding the β‐nucleating agent. The improvement in impact toughness is associated with the formation of microcrazes within the PP.
The fracture toughness of thin polymeric films
Authors: Klemann Bruce M. , DeVilbiss Tad
Published: April 2004

A fracture test using the single edge notch (SEN) geometry was developed for thin polymeric films. The SEN specimens were videotaped while they were stressed to fracture within an Instron tensile testing machine operating at a constant crosshead speed. Critical stress intensity factors for fracture instability and for the initiation of crack growth, along with the corresponding fracture energies, were obtained using a residual stress analysis. The method is applicable to brittle films and films of moderate ductility. Critical stress intensity factors ranging from 0.12 to 4.03 MPa√m were determined for thin films under plane stress conditions. Results of the test are presented for poly(di‐n‐hexylsilane), Kapton polyimide, polystyrene, and Trycite biaxially oriented polystyrene film. Validation of the test and interpretation of the results are also discussed.
Studies of polymerization of acrylic monomers using luminescence probes and differential scanning calorimetry
Authors: Serrano Berna , Levenfeld Belén , Bravo Julio , Baselga Juan
Published: April 2004

A fiber optic system has been designed to couple calorimeter and fluorimeter equipment for in situ monitoring of polymerization reactions by both techniques simultaneously. Two acrylic monomers (cyclohexyl methacrylate, CHM, and 2‐ethylhexyl acrylate, EHA) were studied at different temperatures. Pyrene (Py) was employed at a low concentration (≤10−4 mol/L) as a fluorescence probe. The emission spectrum of pyrene shows a broad band peaking at 390 nm, whose intensity grows with polymerization progress. A correlation with conversion degree could be established by collecting fluorescence intensity through the optical fiber at different polymerization times. For the more flexible polymer formed, poly(ethylhexyl acrylate) (PEHA), Py emission sharply increases only when high conversions are reached and continues increasing for a long time after the limiting conversion is attained. For CHM polymerizations, S‐shaped curves are found. Isochronal plots of intensity vs. scaled conversion allow elaboration of master curves for the peak emission. Data at 50°C for CHM cannot be fitted to the master curve, and this is explained in terms of vitrification.
How does “phase transformation toughening” work in semicrystalline polymers?
Authors: Karger‐Kocsis József
Published: April 2004

The possibility of phase transformation toughening is demonstrated by the example of the β‐modification of isotactic polypropylene (β‐iPP), which undergoes βα‐transformation (i.e., from hexagonal to monoclinic) during mechanical loading. The resulting α‐iPP exhibits a higher crystalline density than the initial β‐modification. That, along with the exothermic character of the βα‐recrystallization, is responsible for the improvement in toughness that occurs. The occurrence of this βα‐transformation is evidenced by differential scanning calorimetry (DSC). Toughness of the α‐ and β‐iPP is studied and compared with the “essential work of fracture” concept by using static‐loaded deeply double‐edge‐notched tensile (DDEN‐T) specimens. The main effect of the βα‐transformation is a large increase in the specific plastic work consumed in the necked zone. Light microscopic (LM) and infrared thermographic (IT) pictures reveal that the plastic zone becomes larger and its shape more circular when βα‐transformation takes place. It is suggested that the principle of mechanical stress‐induced phase transformation from a less toward a more dense crystalline state may be a universal tool for toughness upgrading in semicrystalline polymers.
Flexibility of epoxy coatings part 1: Determination of molecular weight of network chains
Authors: Kojima Shunji
Published: April 2004

The chemistry of network formation for an epoxy/phenolic coating determines structure of baked film. The theory of partitioning of components between sol and gel proposed by Flory was applied to determine the crosslink density and the molecular weight of the network chains, Mc. This procedure appears useful to eliminate the problems in the determination procedure of Mc by equilibrium swelling.
Flexibility of epoxy coatings. Part 2: The relationship with the degree of cure
Authors: Kojima Shunji , Watanabe Yoshiki
Published: April 2004

The flexibility of epoxy coating films, crosslinked by a phenolic resin, has been evaluated. The network structures of these films were estimated by the method proposed in the companion paper. The coating films with a higher molecular weight of network chain, Mc, showed more flexibility. This was achieved by the use of an epoxy resin with higher molecular weight or an epoxy resin with a lower content of lower molecular weight components and by control of cure.
Melt viscosity of calcium‐carbonate‐filled low density polyethylene: Influence of matrix‐filler and particle‐particle interactions
Authors: Bomal Y. , Godard P.
Published: April 2004

The melt viscosity of filled polymers depends on the filler particle packing. It is shown that the maximum particle packing for a low density polyethylene, filled with calcium carbonate, depends strongly on the filler surface treatment. This packing can be evaluated from melt viscosity measurements using the Quemada model. From contact angle measurements and using the Lee unified adhesion theory, it has been demonstrated that the maximum packing depends on particle‐particle and matrix‐filler interactions. The competition between both types of interaction leads to different organizations of particles in the composite.
Analysis of polymer membrane formation through spinodal decomposition. Part 4: Computer simulation of early‐stage coarsening
Authors: Caneba Gerard T. , Saxena Rahul
Published: April 2004

In a previous work, an early‐stage coarsening mechanism was proposed, whereby continued growth of structure (via spinodal decomposition) in a polymer‐solvent system will occur because some of the polymer‐rich domains are being depleted. Such a mechanism was explained based on the situation wherein portions of the solvent‐rich domains have already reached their binodal composition while the polymer‐rich domains are still on their way to their corresponding binodal composition. In this work. we have simulated the nonlinear version of the Cahn‐Hilliard theory to verify this phenomenon. Moreover, we have observed that the depleted polymer‐rich domains seem to be uniformly distributed in space. Finally, as a validation of the proposed mechanism, we did not observe this uniform depletion of the domains when portions of the solvent‐rich and polymer‐rich domains reach their respective binodal compositions almost simultaneously.
Quantitative characterization of surface deformation in polymer composites using digital image analysis
Authors: Kody Robert S. , Martin David C.
Published: April 2004

The stress whitening of polymers and polymer composites during surface deformation (scratching) can represent a severe technological problem in certain applications. For example, scratch resistance is particularly important for poly(propylene) automobile interior components. Unfortunately, the addition of reinforcing agents such as talc or mica for improved dimensional stability and rigidity often results in an increased sensitivity to scratching. The ability to design new materials with reduced visible surface deformation requires more sophisticated information about the deformation mechanisms of polymers and polymer composites near surfaces and their relationship to the scattering of incident light. We have developed a technique to quantify the light scattered from polymer composite surfaces due to surface deformation. We first deform the material in a controlled manner using a scratch testing apparatus. We then analyze the region near the scratch with reflected polarized light in an optical microscope coupled to a digital image analysis system. By measuring the light scattering from the sample as a function of incident light polarization and sample orientation, it is possible to obtain information about the nature and extent of deformation at the sample surface. In this report, we describe our technique and demonstrate how it can be used to quantify the surface deformation of poly(propylene)‐talc composites. By examining a series of materials as a function of talc content, we have been able to obtain information that can be related to specific micromechanisms of deformation near the scratch, such as the orientation of the polymer and the voiding near the talc particles. The technique should assist in the improved development of similar materials for applications in which surface appearance is a primary concern.
Study of mixing efficiency in roll‐mills
Authors: Yao Chih‐Hsiang , Manas‐Zloczower Ica
Published: April 2004

A fluid dynamics analysis package (FIDAP) based on the finite element method was used to simulate the 2‐D, isothermal flow of a power law model fluid in the bank and nip area of a two roll‐mill geometry, including the determination of the free surface. Dispersive mixing efficiency was analyzed in terms of the shear stresses generated and the elongational flow characteristics. The latter were quantified using a frame invariant flow strength parameter. We found that the converging region rather than the nip region provides better mixing flow characteristics. We also found that the presence of vortices in the bank region is not beneficial for dispersive mixing.
Free radical polymerizations associated with the trommsdorff effect under semibatch reactor conditions. II: Experimental responses to step changes in temperature
Authors: Srinivas T. , Sivakumar S. , Gupta Santosh K. , Saraf D. N.
Published: April 2004

Several free radical addition polymerizations exhibit the diffusion limited gel or Trommsdorff effect. The models available until recently could not be applied to industrially important semibatch operations and to nonisothermal polymerizations. The recent model of Ray et al. (24) can indeed be applied to such situations. In this study, an experimental setup to study polymerizations under such conditions has been assembled. Methyl methacrylate (MMA) is polymerized in a 1‐liter stainless steel, computer‐controlled reactor. A series of experiments on bulk polymerization of MMA under different temperature histories (near‐isothermal, step decrease, and step increase) at a fixed initiator (AIBN) concentration of 25.8 mol/m3 have been conducted. Two important process output variables, namely, monomer conversion and average molecular weight, have been measured off‐line at different sampling times during the course of polymerization. The conversion and molecular weight data are found to be in reasonable accord with model (24) predictions obtained using the experimental (nonisothermal) temperature histories, and best fit correlations for three parameters evaluated using earlier data from the literature on isothermal batch reactors (with no further curve fitting). The new model (24) can, thus, be used with some degree of confidence to design and control larger scale reactors.
Fluoropolymers and their effect on processing linear low‐density polyethylene
Authors: Xing K. C. , Schreiber H. P.
Published: April 2004

A comparison is made of flow curves for the extrusion of a LLDPE melt through clean metal capillaries and when overcoated by fluoropolymer (FE) process aids. Characteristics differences between the flow traces include a shear‐rate dependent reduction in flow resistance due to the presence of FE at the die surface. The FE preferentially wets high energy die surfaces, but interacts very weakly with LLDPE melts, thus acting as a lubricant at the polymer/stationary phase interface, and promoting the slip of LLDPE melts. Arguments are presented showing that the percent slippage time must attain an equilibrium value at high extrusion rates. Flow curves for extrusion through FE‐coated dies are divided into distinct regions and the slopes of these have been rationalized by equations that combined the concepts of molecular dynamics and of adhesive failure at the die wall/polymer interface as the origins of slip‐stick flow.
Qualitative analysis of twin‐screw extruder performance in stabilization pelletizing of HDPE resins
Authors: Harlin Ali
Published: April 2004

Two twin‐screw extruders of different size and centerline distance CL were compared. To understand better the performance of the extruders, the operation points were optimized for an HDPE (high‐density polyethylene) film product, and the performance of screw configuration was qualitatively analyzed with some numerical methods at the operation points. The machinery with narrower CL was found to have lower average shear rate, higher conveying capacity, and more channeling in the conveying flow. That means also a need for severe processing in the kneading zone. The extruder with narrow CL had a narrow operation window, and that made it more difficult to combine homogenization and degradation of the product.
A survey of advanced control of polymerization reactors
Authors: Embiruçu Marcelo , Lima Enrique L. , Pinto José Carlos
Published: April 2004

A survey of the most recent papers regarding the advanced control of polymerization reactors is carried out. Special attention is focused on optimal control theory, nonlinear control, adaptive control, and predictive control. A review is also performed in related areas, such as optimization and state estimation in polymerization systems. It is shown that there is a huge gap between industry and research practices. Actual implementation of advanced control theory in the polymerization area requires the improvement of measurement and state estimation techniques.
Structure and properties of biaxially stretched poly(ethylene terephthalate) sheets
Authors: Maruhashi Yoshitsugu , Asada Tadahiro
Published: April 2004

Huge numbers of PET (poly[ethylene terephthalate]) bottles are produced in the world. Especially in Japan, the number of hot‐fillable PET bottles used is extremely large and is still increasing. This type of bottle is generally manufactured by the heat‐set method using hot molds after stretch‐blow molding. Herein, we examined how the PET sheet stretching condition affects the PET heat‐shrinkage behavior at 85°C, which is the hot‐filling temperature. Sheets stretched at a higher temperature and higher speed had higher thermal stability for a wider range of draw ratios. This is because those sheets have a higher crystallinity and relaxed amorphous regions. The higher stretch speed gives the sheet a higher crystallinity with self heat generation during rapid deformation. A higher stretch temperature makes the molecular segments relaxed.
A study on the ternary blends of polyphenylenesulfide, polysulfone, and liquid crystalline polyesteramide
Authors: Kim Byoung Chul , Hong Soon Man , Hwang Seung Sang , Kim Kwang Ung
Published: April 2004

Ternary blends of poly(p‐phenylenesulfide) (PPS), thermotropic liquid crystalline polyesteramide (LCP), and polysulfone (PSF) were investigated in terms of processing characteristics, blend morphology, and physical properties. In the incompatible PPS/LCP blends, LCP imparted a nucleating effect to the crystallization of PPS. Up to 10wt% LCP content, the tensile properties of PPS/LCP blends were enhanced with increasing LCP content, but they deteriorated if the LCP content exceeded 20wt%. Addition of a third component, PSF, to the 90/10 PPS/LCP blend promoted development of rodlike or threadlike fibrillar structure and orientation of the deformed LCP domains, which led to improvement of tensile strength up to 20%.
Nondestructive diagnosis of thermal aging for opaque epoxy resin by optical reflective analysis
Authors: Takezawa Yoshitaka , Akasaka Shin‐Ichi , Koyama Tohru , Miya Hisaichi , Shimodera Makoto
Published: April 2004

A novel nondestructive diagnosis using optical reflective analysis is proposed to evaluate thermally aged opaque insulating resins. Values of reflective absorbance (AR) in the visible to near infrared (IR) range were measured under a variety of aging conditions using the bisphenol‐A type epoxy resin tapes containing iron oxide pigment. The AR values increased markedly over 180°C before and after heating. This increase was due to the electronic transition absorption caused by thermal oxidation of the resin. By rescaling the aging time as a reduced time, a master curve to evaluate thermal aging of the resin was obtained. Furthermore, a similar curve was obtained using the difference (ΔAR) of the AR values between two wavelengths in the near IR range. This indicated that the surface reflectivity dependence on raggedness and dust and stain could be reduced. Consequently, when the thermal stress was the main cause of aging, the aging and residual life of the resin could be evaluated using this method.
A new design procedure for profile extrusion dies
Authors: Hurez P. , Tanguy P. A. , Blouin D.
Published: April 2004

A new design procedure for complex profile extrusion dies is presented. This method applies to multiple channel dies, i.e. dies provided with melt flow independent channels in the land. The approach is based on the resolution of the flow inverse problem, which consists of finding the channel topology (channel land lengths, approach angles in the transition region), which gives a balanced flow at the die orifice from the knowledge of the die contour. The methodology uses a blend of the network approach and the cross‐section method. The procedure is used to design an industrial die that has been tested in a manufacturing environment, showing the performance of the proposed approach.
Non‐newtonian flow modeling in the mixing section of a single‐screw extruder with flow analysis network method
Authors: Wang Yeh , Tsay Cheng Chong
Published: April 2004

The flow of non‐Newtonian fluids obeying the power‐law relation through the mixing sections of a single‐screw extruder is analyzed with a modified flow analysis network (FAN) method. Three types of mixing elements, the Maddock, the dulmage, and the blister ring elements, are studied. The Maddock and the blister ring elements are dispersive type elements. They generate high pressure drop, and yield a negative pressure gradient which indicates poor pumping capability. The flow fields are rather regular in these elements. On the other hand, the dulmage element is a distributive type element. It generates a low pressure drop, and yields a positive pressure gradient at low extrusion rate which indicates better pumping capability than the dispersive type elements. Extensive flow splitting and reorientation is observed in this element. The power‐law exponent has significant effect on pumping characteristics. However, the overall flow patterns of Newtonian fluids and power‐law fluids in these mixing elements are quite similar.
Generation of large residual stresses in injection moldings
Authors: Kwok C. S. , Tong Li , White J. R.
Published: April 2004

Large residual stresses have been generated in injection molded bars by ejecting them prematurely and completing the cooling process by quenching into ice water or liquid nitrogen. The stress distribution formed under these conditions was found to be much closer to parabolic than is the case when the moldings cool conventionally. Limited testing on moldings made in this way indicated significant property enhancement and improved resistance to ultraviolet degradation.
Solidification of thermoviscoelastic melts. Part 4: Effects of boundary conditions on shrinkage and residual stresses
Authors: Bushko Wit C. , Stokes Vijay K.
Published: April 2004

The solidification of a molten layer of amorphous thermoplastic between cooled parallel plates is used to model the mechanics of part shrinkage and the buildup of residual stresses in the injection‐molding process. Flow effects are neglected, and a thermorheologically simple thermoviscoelastic material model is assumed. The model allows material to be added to fill the space created by the pressure applied during solidification, so that this model can be used to assess packing‐pressure effects in injection molding. The interactions between the mold surfaces and the solidifying material are accounted for by modeling different types of constraints through different model boundary conditions. For several sets of boundary conditions, parametric results are presented on the effects of the packing pressure—the pressure applied during solidification to counteract the effects of volumetric shrinkage of the thermoplastic—on the in‐plane and through‐thickness shrinkages, and on residual stresses in plaque‐like geometries. Plaques that can shrink in the in‐plane direction while in the mold are shown to shrink more and to have higher residual stresses than plaques that are fully constrained while in the mold. Although the results are presented in terms of normalized variables based on the properties of bisphenol‐A polycarbonate, they can be interpreted for other amorphous thermoplastics such as modified polyphenylene oxide, polyetherimide, and acrylonitrile‐butadiene‐styrene.
Photothermal imaging of dehydrochlorination in poly(vinyl chloride) films
Authors: Prystay M. C. , Power J. F.
Published: April 2004

Impulse (time domain) laser photopyroelectric effect spectrometry uses the time dependence of heat diffusion in an irradiated sample to infer optical and thermal property depth distributions in the sample. This method was used in conjunction with a recently reported method of inverse problem theory to recover the depth dependence of optical absorption in photodegraded thin films of poly(vinyl chloride) (PVC) on a depth scale of a few tens of microns. The thin films were photodegraded under broadband ultraviolet light prior to photothermal analysis to induce subsurface profiles of visible absorption arising from the depth dependence of light initiated dehydrochlorination reactions in the films. Optical depth profile reconstructions could be made in samples that had undergone mild degradation only and where the absence of significant thermal effusivity changes accompanying degradation could be confirmed. Reconstructed optical transmission profiles were compared with optical transmission micrographs and were shown to resolve features that arise from the depth dependence of photo‐induced dehydrochlorination reactions in the films. The extent of these latter reactions is controlled by the depth dependence of the oxygen concentration in the films.
Bulk crystallization of poly(aryl ether ether ketone) (PEEK)
Authors: Medellín‐Rodríguez F. J. , Phillips P. J.
Published: April 2004

Concurrent measurements of transmitted polarized light intensity and recording of the phenomenon of crystallization through polarized optical microscopy have resolved some of the controversies on the bulk crystallization behavior of poly(aryl ether ether ketone) (PEEK). The process of bulk crystallization was studied through the separation of the nucleation and growth steps. Avrami plots have shown three characteristic ranges. It was observed that a first slope at low crystallization times is associated with massive heterogeneous nucleation and/or local‐order‐promoted primary nucleation of spherulitic crystals. A second gradual decrement in intensity follows, showing a logarithmic tendency. It represents a mixture of at least three parallel mechanisms. These are associated with the end of the process of crystallization of the primary spherulites and in large proportion the nucleation and growth, at lower rates, of sporadically nucleated spherulites. In addition, there is some contribution from secondary crystallization to the transmitted light emerging. The whole group of nucleated spherulites continue growing up to the point of impingement, which loosely marks the beginning of the third region. This last region with lower slope than the first one and an exponential tendency reflects secondary crystallization at long times. The general characteristics of the processes of nucleation and growth are discussed.
A review of positron annihilation lifetime spectroscopy as applied to the physical aging of polymers
Authors: Bigg D. M.
Published: April 2004

This paper provides a review of the technology associated with Positron Annihilation Lifetime Spectroscopy (PALS) as applied to polymers. It is not a comprehensive review of the many technical papers published on PALS. Instead it attempts to consolidate the strong theoretical principles upon which the PALS is based, and to correlate those principles with the equally strong theoretical principles associated with the physical aging of polymers. Both sets of principles are centered around the concept of free volume, and there is a strong, useful relationship between the molecular scale measurement technique of PALS and the response of a polymer to physical aging. In essence, the free volume measured by PALS is the same free volume that is affected by physical aging. This relationship was demonstrated with data, obtained from a variety of sources, on bisphenol A polycarbonate, a polymer in which free volume‐mechanical property behavior is readily demonstrated.
Structural properties and impact fracture behavior of injection molded blends of liquid crystalline copolyester and modified poly(phenylene oxide)
Authors: Tjong S. C. , Shen J. S. , Liu S. L.
Published: April 2004

Blends of a thermotropic liquid crystalline polymer (LCP) with modified poly (phenylene oxide) (PPO) were injection molded. The morphology, tensile properties and dynamic mechanical behavior of the blends have been studied as a function of LCP content. Furthermore, the impact performance of these blends has been investigated by the instrumented Izod and Charpy falling weight tests. The critical strain energy release rate (GIC) of the blends were determined and the GIC values were found to be dependent on the LCP content. The results are discussed and explained in terms of materials morphology.
Thermal conductivity and thermal expansivity of in situ composites of a liquid crystalline polymer and polycarbonate
Authors: Choy C. L. , Lau K. W. E. , Wong Y. W. , Ma H. M. , Yee A. F.
Published: April 2004

The thermal conductivity and thermal expansivity of extruded blends of a liquid crystalline polymer (LCP) and polycarbonate (PC) with volume fraction (Vf) of LCP between 0.09 and 0.8 have been measured as functions of draw ratios λ ranging from 1.3 to 15. At Vf < 0.3, the LCP domains are dispersed in a PC matrix and the aspect ratio of the domains increases with increasing λ. At Vf > 0.55, phase inversion has occurred and the LCP becomes the continuous phase. The axial thermal conductivity K∥ increases while the axial expansivity α∥ decreases sharply with increasing λ, as a result of the higher aspect ratio of the LCP fibrils and the improved molecular orientation within the fibrils. Since the transverse thermal conductivity and expansivity are little affected by drawing, the blends exhibit strong anisotropy in the thermal conduction and expansion behavior at high λ. At Vf < 0.3, the behavior of K∥ is reasonably modeled by the Halpin‐Tsai equation for short fiber composites. At high draw ratio (λ = 15), all the blends behave like unidirectional continuous fiber composites, so K∥ and α∥ follow the rule of mixtures and the Schapery equation, respectively.
Comparative study of the cure kinetics of an unsaturated polyester resin using different procedures
Authors: Salla Josep M. , Ramis Xavier
Published: April 2004

The cure kinetics of an unsaturated polyester resin were studied by differential scanning calorimetry (DSC), and different dynamic and isothermal procedures were compared. It was established that the isothermal kinetic analysis through the isoconversional adjustment lnt = A + E/RT is the method that offers the most accurate results for unsaturated polyester resin cure kinetics. From this comparative study it was noted that the activation energy not only varies according to the degree of conversion but also according to the method used to evaluate the kinetic parameters. Furthermore, it was shown that the activation energy cannot be separated from the other adjustment parameters, so the different kinetic procedures used are not generally comparable. Different methods of evaluating the degrees of conversion α and the reaction rates dα/dt according to the experimental reaction heat were also studied. It was found that the method used has a strong influence on the values of α and dα/dt, but only a slight one on the kinetic parameters.
A new method to evaluate solvent stress cracking
Authors: Cornélis Hélène , Kander Ronald G.
Published: April 2004

The effect of crystallinity on the crazing process in isotactic polypropylene (i‐PP) was investigated by using a new static crazing experiment. Strips of i‐PP films are stressed in glass cones, which are placed into a series of solvents. Characterization of the films was performed by hot‐stage optical microscopy, scanning electron microscopy, wide‐angle X‐ray scattering, differential scanning calorimetry, and contact angle goniometry. The affinities of the solvents for the polymer were investigated by dynamic solvent uptake measurements. Crazing experiments revealed that both the sample preparation and the solvent choice play an important role in the crazing process. A “good” solvent is shown to be a “bad” crazing agent, whereas an intermediate solvent behaves as a “good” crazing agent. Two opposite processes are shown to take place: appearance of void and solvent‐induced crystallization.
Measuring the surface energies of spherical cellulose beads by inverse gas chromatography
Authors: Garnier Gil , Glasser Wolfgang G.
Published: April 2004

The effect of the chemical composition of regenerated cellulose solids on surface energy was studied by inverse gas chromatography (IGC). This was to probe a possible relationship between the ability of the cellulose surface to interact with other phases through van der Waals forces and its bonding potential. A model consisting of amorphous cellulose spheres (“beads”) was used to eliminate all effects of morphology and geometry. The surface of the beads was modified by chemical reaction of the hydroxyl groups of cellulose. A thin layer of cellulose derivative, such as cellulose trifluoroethoxyacetate (CW‐TFEA), cellulose laurate (CW‐LA), or directly fluorinated cellulose (CW‐F), was produced on the bead surface. The surface properties of the cellulose beads were fully characterized by X‐ray photoelectron spectroscopy (XPS), scanning electron microscopy (SEM), and nitrogen adsorption. IGC was performed using the adsorption of two kinds of probes: alkanes to measure the dispersive component of the surface energy (γ), and acid/base probes to quantify the specific adsorption enthalpy (ΔHSp). The dispersive component of the surface energy of cellulose was found to depend mostly on the presence and concentration of free hydroxyl groups on the surface. At low degrees of substitution (DS < 1), how these OH groups were replaced by modification, whether by fatty acid type substituents or by fluorine‐containing groups, was essentially irrelevant for surface energies. The dispersive component of the surface energy (γ) declined with DS almost irrespective of substituent type. The surface of cellulose was found to be highly acidic, and this was attributed mainly to the presence of hydroxyl groups.
Three‐dimensional flow modeling of a self‐wiping corotating twin‐screw extruder. Part II: The kneading section
Authors: Van Der Wal D. J. , Goffart D. , Klomp E. M. , Hoogstraten H. W. , Janssen L. P. B. M.
Published: April 2004

Three‐dimensional flow simulations of kneading elements in an intermeshing corotating twin‐screw extruder are performed by solving the Navier Stokes equations with a finite element package, Sepran. Instead of using the whole geometry of the 8‐shaped barrel a simplified geometry is used, representing a large part of the geometry during the rotating action of the kneading paddle. The goal of these calculations is to study the dependence of several factors that influence mixing, such as shear rate, elongation rate, pressure, and the flow profile in the extruder on various extruder parameters, such as fluid viscosity, rotation speed, and throughput.

The shear and elongation rate and the pressure drop are calculated for varying viscosities. The various stagger angles possible for disc configurations in the corotating twin‐screw extruder are modeled. The axial backflow volume is calculated for varying values of rotation speed and throughput.
Rheotens‐mastercurves and drawability of polymer melts
Authors: Wagner M. H. , Schulze V. , Göttfert A.
Published: April 2004

In a Rheotens experiment, the tensile force needed for elongation of an extruded filament is measured as a function of the draw ratio. For thermo‐rheologically simple polymer melts, the existence of Rheotens‐mastercurves is proven. Rheotens‐mastercurves are invariant with respect to changes in melt temperature. Also, for polymer melts with different average molar masses, but similar molar mass distribution and branching structure, Rheotens‐mastercurves are invariant to changes in the average molar mass. It is shown, by testing several polyethylenes with different molar mass distribution and different long‐chain branching, that Rheotens‐mastercurves allow a direct and quantitative assessment of the drawability of polymer melts under actual processing conditions, i.e. under the action of a constant tensile force and including the effects of the rheological prehistory in the extrusion die.
The effect of injection molding conditions on the mechanical properties of an in situ Composite. I: Polypropylene and a liquid crystalline copolyester based on hydroxynaphthoic acid
Authors: O'Donnell Hugh J. , Baird D. G.
Published: April 2004

In this study, the effect of injection molding conditions on the mechanical properties of polypropylene/liquid crystalline copolyester in situ composites was investigated. Molding conditions such as fill time, mold temperature, and mold thickness were varied to determine the most significant variables that influence mechanical properties. The mechanical property variations were correlated to the shear or extensional stress, which deforms a dispersed phase, and to the Graetz number, which indicates the influence of heat transfer. It was found that higher flexural moduli were obtained in thinner molds and that the maximum mechanical properties for a given mold thickness were obtained near a Graetz number of ten. This indicated that heat transfer was a controlling factor in the formation of in situ composites.
Predicting the effect of viscosity ratios on the mixing of polymer blends using the boundary element method
Authors: Stradins Linards , Osswald Tim A.
Published: April 2004

Mixing or blending two or more fluids of different viscosities is an important and complex issue in the polymer industry. Simulating these types of processes leads to a better understanding of the flow phenomena that take place during mixing. The boundary element method is ideal to simulate mixing flows, because of the large deformations and moving boundary nature of internal batch mixers and extruders. This paper presents a boundary element simulation of the flow of multi‐viscous polymer blends inside extruders and internal mixers. In addition, the governing equations, boundary integrals, and their numerical implementation for creeping flows are presented. The simulation is used to predict the mixing quality of polymer blends in realistic mixing processes. A model describing the relationship of drop strain to matrix strain as a function of viscosity ratio is also presented. The flow simulation results are in good agreement with analytical and experimental results.
Optical on‐line measurement of the thickness distribution of blow molding parisons
Authors: Swan P. L. , Kamal M. R. , Garcia‐Rejon A. , Cielo P.
Published: April 2004

An optical sensor has been developed which can measure the thickness profile of the parison on line just prior to its enclosure in the mold. The device determines thickness by striking the parison at an angle with a laser beam and measuring the separation between the beams that are reflected from the outer and inner surfaces of the parison wall. A prototype was built and tested. The prototype uses three lasers at different angles and can make up to 250 point measurements during a one second scan. A personal computer uses specially developed software to reconstruct the profile of the parison wall from the raw data with an accuracy of ±5%.
The effect of colorants on the properties of rotomolded polyethylene parts
Authors: Nagy Tibor , White James L.
Published: April 2004

An experimental study is reported on the effect of colorants on the warpage, shrinkage, and mechanical properties of rotomolded polyethylene (PE) parts. Five pigments were investigated (titanium dioxide white, cadmium oxide yellow, iron oxide red, carbon black, and phthalocyanine blue). Their concentration was in the range of 0.11 to 0.36 wt%. The pigments were added to the linear low‐density polyethylene (LLDPE) by various techniques, dry blended in low intensity or high intensity mixer or compounded with a single‐screw extruder. Some blends also contained 0.077 wt% zinc stearate as surfactant. It was found that zinc stearate surfactant in the dry blend increases warpage by about a factor of 2 and shrinkage by ˜ 30%, but color quality and powder handling properties are improved. The dry‐blended pigments concentrate along the fusion lines of the PE particles in rotomolded parts, which results in >50% decrease of impact strength with some pigment‐surfactant combinations. Mold pressurization minimizes warpage and shrinkage, but causes no significant improvement in impact resistance. Impact resistance can be improved by using compounded pigments or making two‐layer parts with a pigmented outer and unpigmented inner layer.
Measurement and modeling of solvent removal for spin coating
Authors: Gu J. , Bullwinkel M. D. , Campbell G. A.
Published: April 2004

Solvent concentration is an important factor for spin‐coated film planarization. Two techniques, one an on‐line optical method and the other an off‐line gel permeation chromatography method, have been used to investigate the coating concentration change during spinning. The experimental observations are compared with the spin‐coating model predictions. The modeled concentration and thickness are in close agreement with experiment. Under certain conditions, the spin‐coating model can be significantly simplified. These conditions are discussed.
Process optimization of ultrasonic welding
Authors: Van Wijk H. , Luiten G. A. , Van Engen P. G. , Nonhof C. J.
Published: April 2004

An experimental design is presented for optimizing the ultrasonic welding process in series and mass production, which requires a quantitative test method for measuring product quality. In addition to measurements of an average value, the standard deviation is also important. Small standard deviations lead to reduced scrap in production. For the optimization study, a simple welding process was chosen. Welding machines usually have adequate accuracy for a repeatable machine setting with respect to weld quality. In the cases investigated, they were not sufficiently accurate to allow for a simple quality control using the microprocessor in the machine control as a measuring device. Apart from the insufficient accuracy of the welding machines for quality control, there proved to be no correlation between weld quality and weld‐time measurement under energy control.
A rheo‐optical analysis of converging wedge flow for estimation of stress‐optical coefficient
Authors: Subramanian R. , Picot J. J. C.
Published: April 2004

Results are presented from a rheo‐optical study of a poly(dimethyl siloxane) (PDMS) fluid in a converging wedge flow cell at room temperature for estimation of the linear stress‐optical coefficient. The linearity of the stress and polarizability or refractive index tensors were checked by flow birefringence measurements in pure extensional flow along the centerline of the converging flow cell that extended well into the non‐Newtonian region. The stresses were evaluated using (a) shear and extension rates from laser Doppler anemometry (LDA) velocity measurements and (b) information obtained from orientation angle as a test of constitutive equations. All measurements were optical (i.e., non‐intrusive), and a linear stress‐optical coefficient of 1.475 × 10−10 Pa−1 was obtained using a two‐term Goddard‐Miller model for room temperature flow of a PDMS fluid in combined shear and extension in a converging wedge flow cell.
Comparison of fast fracture properties of thermoplastics
Authors: Dear John P.
Published: April 2004

The fast fracture behavior of polyethylene, polycarbonate and poly(methyl methacrylate) are compared for two different thicknesses of material. The aim was to make fracture measurements under precisely defined steady load conditions after the material has reached a stress relaxed state. It was essential that the experimental technique provided good isolation between crack initiation and crack propagation. This was achieved in small rectangular shaped specimens by adding a tongue to one side extending the intended crack path. A fast crack was initiated in the tongue to propagate into the main section after it had been loaded and allowed to stress relax. When necessary the tongue was embrittled by cooling so a crack can be initiated with minimum force. This new method obtains the threshold load to just maintain crack propagation and also the increase of crack velocity with load above this threshold up to the limiting condition.
Moisture effects on isobutylene‐isoprene copolymer‐based composite barrier. I: Moisture diffusion and detection
Authors: Lee B. L. , Yang T. W. , Wilusz E.
Published: April 2004

Experiments have assessed how moisture and heat influence the functional and structural integrity of butyl rubber matrix composites used as protective barriers. This paper, which is first of a series, reports the findings on the subjects of moisture diffusion and its effect on ultrasonic wave propagation of composite barriers. On exposure to high humidity at elevated temperatures, carbon black‐reinforced butyl rubber composite barriers were found to absorb substantial moisture, with the hygroscopic reinforcement phase making a more significant contribution than the matrix. The moisture diffusion coefficients for both composite and unreinforced vulcanizate were close to each other at each exposure temperature, and had the same temperature dependence. The calculated activation energies of moisture diffusion indicate that the moisture absorption rate of the carbon black phase is governed by the moisture diffusion rate of the matrix. Ultrasonic wave speed appeared to be a viable means of monitoring the moisture absorption of composite barriers. On exposure to moist heat, relative ultrasonic wave speeds for both composite and unreinforced vulcanizate decreased continuously.
Real‐time analysis of ethylene vinyl acetate random copolymers using near infrared spectroscopy during extrusion
Authors: Khettry Atul , Hansen Marion G.
Published: April 2004

Poly(ethylene vinyl acetate) (EVA) is a very common polymer used in hot melt adhesives. The rheological and thermal‐mechanical properties of these adhesives are strongly related to the content of vinyl acetate (VA) incorporated into this random copolymer during polymerization. Results of in‐line monitoring of VA content in flowing molten EVA polymers, using fiberoptic near infrared spectroscopy, shall be discussed in detail. In‐line monitoring is not only desired for its numerous advantages (such as high quality products, lower waste, lower developmental cycle time, and lower costs) but also because it eliminates the sample handling concerns associated with molten polymers.
Elastic moduli of a liquid crystalline polymer and its in‐situ composites
Authors: Choy C. L. , Lau K. W. E. , Wong Y. W. , Yee A. F.
Published: April 2004

The elastic moduli of a liquid crystalline polyesteramide (LCP) and polycarbonate/LCP in‐situ composites with 10 to 80 wt% of LCP have been measured as functions of draw ratio λ from 1 to 15 by an ultrasonic method. For the LCP, the sharp rise of the axial Young's modulus E3 and the slight decreases of the transverse Young's modulus E1 and the axial (C44) and transverse (C66) shear modulus with increasing λ result from the alignment of chains along the draw direction. E1, C44, and C66 follow the lower bounds calculated using the series coupling scheme of the aggregate model. Although E3 lies close to the lower bound at low λ, it follows the upper bound calculated according to the parallel coupling scheme at λ > 3. The elastic moduli of the composites have similar draw ratio dependences as those of the LCP. The strong increase in E3 with increasing λ arises from the higher aspect ratio of the LCP domains in the composites and the improved molecular orientation within the domains. The reinforcement effect on the other moduli is much weaker, with E1 and C44 of the composites only 5 to 30% higher than those of polycarbonate at λ = 15. Since C66 of the LCP decreases to a value below that of polycarbonate at λ > 2, there is a positive reinforcement effect at low λ but a negative effect at high λ.