bluuebunny/crossref_metadata_2025_split huggingface dataset:
Quantitative characterization of surface deformation in polymer composites using digital image analysis
Authors: Kody Robert S. , Martin David C. 
Published: April 2004

AbstractThe 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

AbstractA 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

AbstractSeveral 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

AbstractA 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

AbstractTwo 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

AbstractA 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

AbstractHuge 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

AbstractTernary 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

AbstractA 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

AbstractA 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

AbstractThe 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

AbstractLarge 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

AbstractThe 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

AbstractImpulse (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

AbstractConcurrent 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

AbstractThis 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

AbstractBlends 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

AbstractThe 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

AbstractThe 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

AbstractThe 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.