Showing papers in "Polymer Engineering and Science in 1997"
TL;DR: In this article, a new and convenient approach for the nonisothermal crystallization was proposed by combining the Avrami equation with the Ozawa equation, and the kinetic parameters in this approach, the crystallization behavior of PEEKK was analyzed.
Abstract: Analysis of the nonisothermal melt and cold crystallization kinetics of poly(aryl ether ether ketone ketone) (PEEKK) was performed by using differential scanning calorimetry (DSC). The Avrami equation modified by Jeziorny could describe only the primary stage of nonisothermal crystallization of PEEKK. And, the Ozawa analysis, when applied to this polymer system, failed to describe its nonisothermal crystallization behavior. A new and convenient approach for the nonisothermal crystallization was proposed by combining the Avrami equation with the Ozawa equation. By evaluating the kinetic parameters in this approach, the crystallization behavior of PEEKK was analyzed. According to the Kissinger method, the activation energies were determined to be 189 and 328 kJ/mol for nonisothermal melt and cold crystallization, respectively.
789 citations
TL;DR: In this article, the preparation of lignocellulosic composites by reactive extrusion processing in which good interfacial adhesion is generated by a combination of fiber modification and matrix modification methods is discussed.
Abstract: Biofibers, natural lignocellulosics, have an outstanding potential as a reinforcement in thermoplastics. This study deals with the preparation of lignocellulosic composites by reactive extrusion processing in which good interfacial adhesion is generated by a combination of fiber modification and matrix modification methods. PP matrix was modified by reacting with maleic anhydride and subsequently bonded to the surface of the modified lignocellulosic component, in-situ. The fiber surface was modified by reacting it with a silane in a simple and quick aqueous reaction system, similar to that employed for glass fibers. The modified fibers are then extruded with the modified polymer matrix to form the compatibilized composite. The various reactions between the lignocellulosic fiber/filler and modified polymer chains, is expected to improve the interfacial adhesion significantly as opposed to simple mixing of the two components, since new covalent bonds between the fiber surface and matrix are created in the former case. These composite blends were then injection molded for mechanical characterization. Typical mechanical tests on strength, toughness and Izod impact energy were performed and the results are reported. These findings are discussed in view of the improved adhesion resulting from reactions and enhanced polar interactions at phase boundaries.
460 citations
TL;DR: In this paper, a mixture of a latex and an aqueous suspension of cellulose whiskers has been used to construct a rigid network of hydrogen bonds, and the formation of this network is assumed to be governed by a percolation mechanism.
Abstract: Nanocomposites obtained by casting a mixture of a latex and an aqueous suspension of cellulose whiskers have been studied. Their mechanical properties (e.g. shear modulus) are found to increase by more than three orders of magnitude in the rubbery state of the polymer matrix, when the whisker content is 6 wt%. This large and unusual effect is discussed on the basis of different types of mechanical models, including semi-phenomenological and numerical finite element calculations. It is concluded that cellulose whiskers form a rigid network linked by hydrogen bonds. The formation of this network is assumed to be governed by a percolation mechanism.
343 citations
TL;DR: In this paper, the cell nucleation and initial growth behaviors in the foam processing of polypropylene (PP) in both the linear and branched forms were investigated and the cell morphologies for the two PPs were found to be significantly different.
Abstract: An investigation has been performed of the cell nucleation and initial growth behaviors in the foam processing of polypropylene (PP) in both the linear and branched forms. These materials were foamed in extrusion with the two blowing agents, CO 2 and isopentane. The cell density generally increased with an increased content of the blowing agent, for both CO 2 and isopentane. The effect of processing pressure on the cell density was distinct when CO 2 was used, whereas no pressure effect was observed in the foam processing with isopentane. The cell morphologies for the two PPs were found to be significantly different. A slightly lower nuclei density was observed in the branched PP foams than in the linear PP foams. However, the phenomenon of cell coalescence was observed much less in the branched PP foams. Most cells in the branched PP foams were closed, whereas in the linear PP foams they were connected to each other. The experimental results indicated that the branched structure played an important role in determining the cell morphologies through its effects on the melt strength and/or melt elasticity.
298 citations
TL;DR: In this article, the effects of the materials and the processing conditions on the cell morphology of foamed PVC /wood-fiber composites were studied with a view to establishing their process-structure relationships.
Abstract: In this research, the effects of the materials and the processing conditions on the cell morphology of foamed PVC /wood-fiber composites were studied with a view to establishing their process-structure relationships. Each step of microcellular PVC / wood-fiber composites processing is addressed, including the surface treatment of the wood-fiber, mixing of polymer and wood-fiber, manufacture of the composites, the saturation of the composites with gas, microcellular foaming of the composites, and characterization of the cell morphology. The cellular morphologies of the foamed PVC/wood-fiber composites are a strong function of the content of plasticizer and the surface treatment of wood-fiber as well as the gas saturation and foaming conditions.
202 citations
TL;DR: In this paper, the authors presented data from tests of the stress relaxation response of a polycarbonate under torsional deformations and found that the double logarithmic aging time shift rate, μ, varies significantly with both temperature and strain.
Abstract: Data are presented from tests of the stress relaxation response of a polycarbonate under torsional deformations. Tests were performed on samples over a range of strains from 0.0025 to 0.08, temperatures from 30 to 135°C and aging times from 1800 to 64,800 s. Individual data sets at each strain, temperature and aging time could be described using a stretched exponential form relaxation function, and time-aging time superposition was found to be applicable to the data under all test conditions. The double logarithmic aging time shift rate, μ, was found to vary significantly with both temperature and strain. Over the range of temperatures studied the data could be superimposed using conventional time-temperature superposition. However, the master curve was found not to be described by a stretched exponential function. For strains up to 0.07, the data at each temperature could also be superimposed to form a master curve following the principle of time-strain superposition. Interestingly, the master curves found from time-strain and time-temperature superposition did not have the same form. In both the time-aging time and time-temperature superposition analyses it was found that the application of vertical shifts was required for superposition of data.
182 citations
TL;DR: In this paper, two uniaxial constitutive models are constructed based on the experimental data presented in Part I, based on which a nonlinear viscoelastic (NVE) model is formulated using the mechanical analogy consisting of one independent spring and six Kelvin elements in series.
Abstract: Based on the experimental data presented in Part I, two uniaxial constitutive models are constructed. The first, a nonlinear viscoelastic (NVE) model, is formulated using the mechanical analogy consisting of one independent spring and six Kelvin elements in series. Creep data are used to determine the model parameters. The second model, a viscoplastic (VP) formulation, is developed using the viscoplastic theory proposed by Bodner to characterize the uniaxial viscoplastic behavior of metals. Inelastic strain rate is introduced into the state variable in addition to inelastic work to depict the strong rate dependent behavior of HDPE. Experimental data from constant strain rate tests are employed to construct the material functions of the model. Limitations in the application of each model are discussed in conjunction with possibilities for future work.
173 citations
TL;DR: In this paper, the authors illustrate how the coextrusion of film with three or more polymeric layers is economically used to achieve a desirable mix of end-use characteristics.
Abstract: Numerous examples in the literature illustrate how the coextrusion of film with three or more polymeric layers is economically used to achieve a desirable mix of end-use characteristics. More recently, layer-multiplying devices permit two polymers of widely dissimilar solid-state properties to be combined into unique microlayer and nanolayer structures with hundreds or thousands of alternating layers. If the layers are thin enough, the key properties of the constituents can combine synergistically. The microlayer structure is also an effective research tool. Because the microlayer and nanolayer structures contain large specific interfacial areas, they are ideal for fundamental studies of phenomena such as interdiffusion and adhesion. Three examples of microlayered materials with up to 1024 layers illustrate the versatility of this coextrusion process: talc-filled PP. PC/SAN, and HDPE/ LLDPE.
160 citations
TL;DR: In this article, the nonlinear behavior of high density polyethylene (HDPE) is investigated for samples cut from thick-walled HDPE pipe, and extensive experimental work has been performed to characterize the non-linear time-dependent response of the material tested under uniaxial compression.
Abstract: The nonlinear behavior of high density polyethylene (HDPE) is investigated for samples cut from thick-walled HDPE pipe. Extensive experimental work has been performed to characterize the non-linear time-dependent response of the material tested under uniaxial compression. Tests were conducted under conditions of constant strain rate, creep, stress relaxation, constant loading rate, abrupt change of strain rate, creep-recovery, cyclic strain rate, and various combinations of these loading conditions. Creep and stress relaxation response after strain reversal and the effect of the transient response on the following stress-strain behavior is examined. Permanent strains for the test specimens and their dependence on loading histories are investigated. Specimens cut at various orientations from the pipe are used to quantify the small amounts of local anisotropy in the pipe specimen. The experimental work has been used to develop both nonlinear viscoelastic (NVE) and viscoplastic (VP) constitutive models in a companion paper. Both the test results and the corresponding model predictions are reported in this paper. It is found that the VP model reproduces the nonlinear viscoelastic-viscoplastic behavior of HDPE very well provided that the current strain is not below the maximum strain imposed (there is no strain reversal). The NVE model predicts the material behavior reasonably well for some loading conditions, but inadequately for others.
155 citations
TL;DR: In this article, a bicomponent β-nucleator consisting of equal amounts of pimelic acid and calcium stearate was used to produce β-crystalline phase polypropylene (PP) composites.
Abstract: β-crystalline phase polypropylene (PP) composites containing 5, 10, 20, 30, and 40% (by weight) of CaCO 3 filler were prepared by injection molding. The β-form PP was produced by adding a bicomponent β-nucleator consisting of equal amounts of pimelic acid and calcium stearate. The morphology, static tensile, and impact properties of these composites were investigated in this study. Scanning electron microscopy (SEM) observations revealed that the β-spherulites of the polymer matrix of the composites exhibit curved lamellae and sheaf-like structures. The fillers were observed to disperse within the inter-lamellar spacings of the β-PP composite containing 10% calcium carbonate addition. However, the filler particles tend to link together to form larger aggregates when the filler content reaches 20%. Static tensile measurements showed that the elastic modulus of the composites increases with increasing filler content but the yield strength decreases with increasing filler addition. The falling weight Charpy impact test indicated that the β-PP polymer exhibits the highest critical strain energy release rate (G c ) value. However, there was a drastic drop in G c of the β-PP composites with increasing filler content. The results are discussed and explained in terms of materials morphology.
110 citations
TL;DR: In this paper, the authors presented an analytic method based on error minimization for this data reduction task, and introduced the concept of a total reference curve as an alternative to choosing a single momentary curve for the reference.
Abstract: The ability to include the effects of physical aging is critical to the design of engineering structures involving advanced polymers and polymer composites. Physical aging, a phenomenon caused by material evolution towards thermodynamic equilibrium, is typically described by reducing short-term momentary compliance curves, via time-aging time superposition, into a predictive reference curve and shift factor function. This paper presents an analytic method based on error minimization for this data reduction task, and introduces the concept of a total reference curve as an alternative to choosing a single momentary curve for the reference. Four different predictive approaches are considered to determine the efficacy of the total reference concept, and whether vertical shifting is beneficial. For most of the materials studied, the total reference using horizontal shifting alone is the recommended method; in the few remaining cases, the total reference procedure with both horizontal and vertical shifting resulted in the best outcome.
TL;DR: In this article, a fluid dynamics analysis package was implemented to simulate the 3D isothermal flow patterns in the kneading disc region of a Werner & Pfleiderer ZSK-53 co-rotating twin-screw extruder.
Abstract: Co-rotating twin-screw extruders are widely used for compounding and blending in polymer processing. In a modular machine, the dominant elements determining dispersive mixing efficiency are the kneading discs. A fluid dynamics analysis package - FIDAP, using the finite element method was implemented to simulate the 3-D isothermal flow patterns in the kneading disc region of a Werner & Pfleiderer ZSK-53 co-rotating twin-screw extruder. The kneading discs simulated are three-lobe discs. The flow field characteristics relevant for dispersive mixing are shear stresses generated and elongational flow components. We compare these flow characteristics for the three-lobe kneading discs of the ZSK-53 with the two-lobe discs of a ZSK-30 machine. We also discuss the influence of processing parameters on the flow field mixing efficiency.
TL;DR: In this article, the production of solid section products from highly oriented fibers by a novel compaction procedure is described for melt-spun and gel-splun polyethylene fibers, poly(ethylene terephthalate) and polypropylene fibers and Vectran liquid crystalline copolyester fibers.
Abstract: The production of solid section products from highly oriented fibers by a novel compaction procedure is described for melt-spun and gel-spun polyethylene fibers, poly(ethylene terephthalate) and polypropylene fibers and Vectran liquid crystalline copolyester fibers. Differential scanning calorimetry and electron microscopy have been used to study the structure of the compacted polymers. For the most successful compaction, selective surface melting of a small fraction of each fiber enables the formation of a fiber composite of high integrity, where the matrix phase is formed by epitaxial crystallization of the melted fraction on the initial fibers, retaining a high proportion of their initial strength and stiffness. A wide range of potential applications is envisaged for the composites produced by hot compaction. In many cases these composites will be produced by thermoforming. In addition to the obvious advantages of high stiffness and strength, in several instances the unrestricted exploitation of unique properties of the fibers such as transparency to microwave radiation or low thermal expansion coefficients offer additional incentives for the use of these hot compacted materials rather than conventional fiber/resin composites.
TL;DR: In this paper, the relationship between processing parameters and morphology was studied using optical microscopy and transmission electron microscopy (TEM), and the magnitude of the PTC effect was found to be inversely proportional to the dimension of the carbon black channels in the composites.
Abstract: Conductive polymer composites were prepared by sintering a mixture of ultrahigh molecular weight polyethylene (UHMWPE) powder and carbon black. Two processing parameters-time and temperature-were shown to have a notable effect on the resistivity of the composites. The relationships between the processing parameters and morphology were studied using optical microscopy and transmission electron microscopy (TEM). The results of the optical microscopy studies indicate that the carbon black is distributed in the interfacial regions between the UHMWPE particles. The dimension of the carbon black channels increases with the carbon black concentration. TEM micrographs show that a high degree of intermixing between the carbon black and the polymer occurs at higher temperatures and longer processing times, resulting in higher resistivities. A positive temperature coefficient (PTC) effect was observed for these materials. A mechanism for the PTC effect in this system is proposed. The magnitude of the PTC effect is found to be inversely proportional to the dimension of the carbon black channels in the composites. The dimension is directly related to the carbon black concentration. The PTC effect is a result of the polymer volume expansion caused by melting of the crystallites. A large PTC effect is observed for the composites with a low carbon black concentration and vice versa. No negative temperature effect (NTC) is observed at temperatures substantially above the melting point of the polymer.
TL;DR: Weld line strength has been measured in five engineering thermoplastics and the effect of processing parameters was studied using experimental design as mentioned in this paper, where four parameters-holding pressure, injection velocity, melt temperature, and mold temperature-were varied in two levels.
Abstract: Weld line strength has been measured in five engineering thermoplastics. The effect of processing parameters was studied using experimental design. Four parameters-holding pressure, injection velocity, melt temperature, and mold temperature-were varied in two levels. For each parameter setting the weld line strength was measured and compared with the bulk strength via a weld line factor (WL-factor), defined as: strength of specimens with weld line/strength of specimens without weld line. Results from flexural tests on both filled and unfilled materials showed that the weld line factors for cold weld lines varied between 0.25 and 0.98 depending on material and parameter setting. Highest WL-factors were obtained for unfilled materials and using high melt temperature, high holding pressure, and low mold temperature. Results from instrumented falling weight impact tests on weld lines sometimes showed a WL-factor higher than 1.0. There was generally a poor correlation between results from impact tests and results from flexural tests.
TL;DR: In this article, the authors show the application of several experimental methods to the measurement of the interfacial tension, σ, between two immiscible polymers, where the shape of the interface between the liquids is directly observed using optical microscopy techniques.
Abstract: This work shows the application of several experimental methods to the measurement of the interfacial tension, σ, between two immiscible polymers. A quantitative knowledge of the interfacial tension is important in view of the crucial role that this parameter plays in polymer blend processing. Common to all methods presented here are two main points. The first is that σ is obtained from experiments where the shape of the interface between the liquids is directly observed by means of optical microscopy techniques. The second point is that the interface geometry is controlled by a balance between the interfacial force and the viscous stresses generated by some flow applied to the system. Measurements have been carried out on a model polymer blend, whose constituents are a poly-isobutylene and a polydimethylsiloxane, both transparent and liquid at room temperature. When compared with each other, the values of interfacial tension obtained from the different methods show a good quantitative agreement. Excellent agreement is also found with results for the same system previously published in the literature.
TL;DR: In this paper, surface treated recycled rubber particles with a nominal particle size of approximately 75 μm and a commonly used reactive liquid elastomer, CTBN, have been incorporated in a DGEBA epoxy resin.
Abstract: The objective of this research is to investigate the feasibility of using surface treated recycled rubber particles for toughening of epoxy polymers. These particles are obtained through grinding of scrap tires followed by oxidizing the surface of the particles in a reactive gas atmosphere. Surface treated recycled rubber particles with a nominal particle size of approximately 75 μm and a commonly used reactive liquid elastomer, CTBN, have been incorporated in a DGEBA epoxy resin. It has been shown that the recycled rubber particles are not as effective as CTBN in toughening of the epoxy matrix. However, blending of the two modifiers results in a synergistic toughening. Microscopy reveals that, when used alone, recycled rubber particles simply act as large stress concentrators and modestly contribute to toughening via crack deflection and microcracking. In the presence of micron size CTBN particles, which cavitate and induce massive shear yielding in the matrix, however, the recycled particles “stretch” the plastic deformation to distances far from the crack tip. This mechanism causes plastic zone branching and provides an unexpectedly high fracture toughness value. This study, therefore, provides a practical approach for manufacturing engineering polymer blends utilizing the surface modified recycled rubber particles.
TL;DR: In this article, the morphology and oxygen barrier properties of low density polyethylene (LDPE) and ethylene-vinyl alcohol copolymer (EVOH) blends have been studied.
Abstract: Morphology and oxygen barrier properties of LDPE/EVOH blends have been studied. Laminar dispersion of ethylene-vinyl alcohol copolymer (EVOH) with high oxygen barrier properties was obtained in the matrix of low density polyethylene (LDPE) when extruded through an annular blown film die. Various laminar morphologies were observed and the main factors determining the morphology of the blends were viscosity ratio of the components, processing conditions, and compatibilizer level. Oxygen permeation tests have shown that thinner and longer EVOH layers in larger numbers were more effective in reducing the oxygen permeability. The oxygen permeability of the compatibilized blend having 6 phr of LLD-g-MAH was reduced by a factor of 740. The correlation between morphology and oxygen permeability was explained as a function of the EVOH layer size (L x R) and the number of EVOH layers (N), which were closely related to the predeformed domain size (L ο x R ο ). The high Weber number (resulted from large L ο x R ο and low interfacial tension) and low viscosity ratio yielded large L x R. However, small L ο x R ο produced high N. Experimental results of oxygen permeability were well correlated with (L x R) x N.
TL;DR: Stress relaxation experiments were performed on two grades of polycarbonate at room temperature as discussed by the authors, and the volume change measurements in tension show initial dilatation of the samples followed by a volume relaxation that at the largest strains in one grade of poly carbonate leads to densities greater than those of the other.
Abstract: Stress relaxation experiments were performed on two grades of polycarbonate at room temperature The tests were performed in uniaxial extension and compression at deformations from the small strain, linear viscoelastic regime to the highly nonlinear viscoelastic regime just below yield Simultaneous to the control of axial strain, both stress and lateral strain were measured, the latter providing the volume change for the samples The volume change measurements in tension show initial dilatation of the samples followed by a volume relaxation that at the largest strains in one grade of polycarbonate leads to densities greater than those of the undeformed sample In the case of the compression measurements, the volume decreases upon deformation, but, rather than relaxing back towards the undeformed volume, the samples continuously densify The differences in the tensile dilatation for the two grades of polycarbonate suggest that the volume behavior may be related to the propensity to yield vs fracture
TL;DR: In this paper, a linear relationship was obtained between the specific total work of fracture, w f, and the ligament length, L. Extrapolation of this linear relationship to zero ligament lengths gave the specific essential work, w e, which for PBT/PC blend was 35 ± 5 kJ/m 2, almost insensitive to geometry and the dimensions of test specimens as well as testing rate.
Abstract: Fracture behavior of PBT/PC blend was studied at room temperature using two specimen geometries (SENT and DENT) and a wide range of specimen sizes and crosshead speeds. It was found that the fracture of all SENT and DENT specimens is completely ductile and stable. A linear relationship was obtained between the specific total work of fracture, w f , and the ligament length, L. Extrapolation of this linear relationship to zero ligament length gave the specific essential work of fracture, w e , which for PBT/PC blend was 35 ± 5 kJ/m 2 and was almost insensitive to geometry and the dimensions of test specimens as well as testing rate.
TL;DR: In this article, a scheme is described that enables the simultaneous control of cavity pressure at multiple locations in both multi-gated parts and/or multi-cavity molds.
Abstract: Cavity pressure has been recognized as a critical process parameter for the injection molding of high quality plastic parts. Recent developments in injection molding process technology have enabled closed loop control of cavity pressure at one point in the mold. In this paper, a scheme is described that enables the simultaneous control of cavity pressure at multiple locations in both multi-gated parts and/or multi-cavity molds. This has been achieved by the addition of dynamic valves in the melt delivery system, each of which can be independently controlled to meter the flow and pressure of the polymeric melt to its portion of the mold. The development and capabilities of the control system are presented, demonstrating the feasibility of simultaneous multi-cavity pressure control in both the filling and packing stages of the injection molding process. A description of the ability of multi-cavity pressure control to improve process capability and molded part quality is presented in a companion paper.
TL;DR: In this article, the authors determined multiple viscoelastic properties for poly(methyl methacrylate) in the context of examining experimental limitations on deriving other properties from these measurements, specifically time dependent bulk modulus behavior.
Abstract: Multiple viscoelastic properties were determined for poly(methyl methacrylate) in the context of examining experimental limitations on deriving other properties from these measurements, specifically time dependent bulk modulus behavior. By means of master curves for uniaxial extension on plate and cylinder specimens, as well as shear (torsion) and Poisson behavior from measurements in the temperature range from -40°C to 125°C, it is established that excessive precision is needed for reliable interconversion of some properties to others. While normal inverse relations (modulus-compliance) are readily obtained from one set of measurements, bulk (relaxation or creep) properties cannot be derived reliably from other functions and must be determined directly.
TL;DR: In this article, the authors presented oxidation induction time (OIT) data for samples taken from a range of polyethylene hot-water pipes before and after hydrostatic pressure testing with internal stagnant water and external air.
Abstract: This paper presents oxidation induction time (OIT) data for samples taken from a range of polyethylene hot-water pipes before and after hydrostatic pressure testing with internal stagnant water and external air Linear relationships between OIT and antioxidant concentration were established for the antioxidants/polymers used A model assuming Fickian diffusion of the antioxidant to the surrounding media and chemical consumption of the antioxidant (Regime B model) was applied to the OIT-profile data The Regime B model was successfully applied to OIT-profile data except for in the case of a pipe with a substantial scatter in the OIT data, indicative of compositional heterogeneity The choice of initial conditions for the modeling was critical The use of initial conditions based on insufficiently exposed pipes led to an overestimate of the diffusivities caused by the combined action of Regimes A (internal precipitation) and B loss mechanisms The time period associated with Regime A constituted up to 25% of the lifetime for the pipes studied Antioxidants with sterically accessible polar groups showed a higher melting point and greater interaction with dissolved water and carbon black Obtained radial dependences of the antioxidant diffusivities (D) indicate that the water concentration in the polymer influenced D primarily through cluster formation involving water and antioxidant molecules and by competition between water and antioxidant molecules about adsorption sites on carbon black particles and to a much lesser extent by plasticization Antioxidant concentration profiles calculated for the failure time interval in pressure testing appeared in the same concentration range, and fracture initiation occurs in the regions in the pipe wall first reaching depletion of the antioxidant system
TL;DR: In this paper, the authors present a review of the literature on in situ polymerization of pyrrole within another polymer matrix, which may be accomplished using either electrochemical or chemical oxidative polymerization.
Abstract: Electrically conductive polymer blends can be prepared by in situ polymerization of pyrrole within another polymer matrix. This may be accomplished using either electrochemical or chemical oxidative polymerization. This paper reviews the literature on this subject.
TL;DR: In this article, isotactic polypropylene (PP) samples were subjected to stress-relaxation experiments after simple tensile tests at four strain rates and at different levels of temperature.
Abstract: Samples of isotactic polypropylene(PP) were subjected to stress-relaxation experiments after simple tensile tests at four strain rates and at different levels of temperature. The relaxation moduli were determined in the range of temperature between 20 and 80°C with a relaxation period of 1200s duration. The activation energy value of the shift factor was determined using the time-temperature superposition principle. The calculated stress-strain curves and stress-relaxation curves were obtained from constitutive equations based on an overstress theory in which the temperature dependence of viscosity and the activation energy were considered. The temperature dependence of viscosity was amenable to an Arrhenius type equation. The quasi-equilibrium stress depends on both the current strain and the temperature. The calculated results were obtained by the proposed constitutive equation and compared with the data. The proposed constitutive equations based on the overstress model explain well the viscoelastic-plastic behavior of PP samples.
TL;DR: In this article, two composite gaskets were made from a mixture of high density polyethylene (HDPE) and polyaniline (PANI) powders in different proportions.
Abstract: The use of intrinsically conductive polymers in welding of plastics and composites offers the possibility of developing new welding methods. Intrinsically conductive polyaniline (PANI) composite gaskets were used to microwave weld high density polyethylene (HDPE) bars. Two composite gaskets were made from a mixture of HDPE and PANI powders in different proportions. Adiabatic heating experiments were used to estimate the internal heat generation and electric field strength in the gasket. During welding, the effects of heating time, heating pressure and welding pressure were evaluated. It was found that increasing the heating time and the welding pressure increased the joint strength. The maximum tensile joint strength was achieved using a 60 wt% PANI gasket with a heating time of 60 sec and a welding pressure of 0.9 MPa; this resulted in a tensile weld strength of 24.79 ± 0.34 MPa, which equals the tensile strength of the bulk HDPE.
TL;DR: In this paper, the flow front of molten polymers inside the mold has been probed by a multiple-channel probing system with a time resolution of 2 ms. This information can be used to control the plunger movements.
Abstract: On-line ultrasonic monitoring of injection molding of a simple polymer box is studied using pulse-echo techniques. The flow front of molten polymers inside the mold has been probed by a multiple-channel probing system with a time resolution of 2 ms. This information can be used to control the plunger movements. The gap development, because of the shrinkage of the part in the mold, is also monitored. This information, which is important for the understanding of the part's cooling process, has been found to be superior than that measured by a conventional pressure probe. The relation between the gap formation time and the packing pressure has been investigated at various part locations characterized by different thicknesses. The velocity and the amplitude variations of ultrasonic waves, in a reflection as well as in a transmission configuration, have also been measured in the part's material during its solidification. The behavior of these ultrasonic parameters contributes to the interpretation of the solidification process.
TL;DR: In this article, it was determined that by incorporating the phosphine oxide moiety into the polymer backbone, certain properties of the resulting poly(arylene ether) were substantially improved, such as an increase in T g, thermal stability in air, modulus, and char yield compared with control poly(ARYlene ether sulfone)s.
Abstract: Hydrolytically stable phosphorus-containing monomers, such as 4,4'-bis(fluorophenyl)methylphosphine oxide (BFPMPO), 4,4'-bis(hydroxyphenyl)methylphosphine oxide (BOHPMPO), and 4,4-bis(hydroxyphenyl)phenylphosphine oxide (BOHPPO), were synthesized and used in nucleophilic aromatic substitution polycondensation to prepare poly(arylene ether phosphine oxide) engineering thermoplastics. The synthesis and characterization of these novel polymers are described. It was determined that by incorporating the phosphine oxide moiety into the polymer backbone, certain properties of the resulting poly(arylene ether) were substantially improved, such as an increase in T g , thermal stability in air, modulus, and char yield compared with control poly(arylene ether sulfone)s. The high char yields obtained for these polymers in air along with observed intumescence indicates that these materials have improved fire resistance. Preliminary cone calorimetry measurements support this conclusion.
TL;DR: In this paper, a pattern-based closed-loop control strategy for the injection molding process is presented, which uses artificial neural networks (ANNs) embedded within a cascade design to analyze sensor patterns, identify process character and control part quality.
Abstract: The basis for a novel pattern-based closed-loop control strategy for the injection molding process is presented. The strategy uses artificial neural networks (ANNs) embedded within a cascade design to analyze sensor patterns, identify process character and control part quality. The platform for this work, the injection molding process, is an industrially significant, cyclic manufacturing operation. Final part quality of this process is a nonlinear function of many machine and polymer variables. Part quality control of this process is currently attained via single input-single output machine controls supervised by human operators. Presented here is a method that employs ANN technology to improve upon this approach and provide the basis for closed-loop part quality control. In the cascade design, machine controller set-points of an inner loop are updated based on ANN analysis of mold cavity pressure patterns. The controller action maintains the desired pressure pattern set-point of the outer loop associated with desired part quality. Control strategy details are provided along with set-point tracking demonstrations that support feasibility of this pattern-based approach.
TL;DR: In this article, a linear trans-quinacridone dye (as β-phase nucleator) was used to nucleate Isotactic polypropylene (iPP) for structural and mechanical studies.
Abstract: Isotactic polypropylene (iPP) was nucleated specifically for structural and mechanical studies, especially of impact resistance. Nucleation was accomplished by two red pigments: a linear trans-quinacridone dye (as β-phase nucleator) and a dimethyl quinacridone resulting in the formation of a pure α-phase structure. This procedure allowed the comparison of both the crystal structure and the morphology of the polymer. For the β-nucleated iPP, by means of the WAXS measurements in the transmission mode, a maximum of the k-value (fraction of β-phase) was found for a concentration of 5 x 10 -5 wt% of the trans-quinacridone. By means of polarized light microscopy (PLM), the mold temperature and pigment concentration dependent spherulites distribution on the cross section of the samples was observed. DSC permitted confirmation of the WAXS measurements, giving a characteristic double melting peak for the β polypropylene. By isothermal WAXS measurements the temperature of 135°C as the upper limit of the β phase was detected. For both nucleating agents (linear trans-quinacridone and dimethyl quinacridone) the dependence of the mechanical properties (modulus of elasticity and brittleness by impact resistance) on the pigment concentration was observed. For the β-phase iPP the highest ductility by impact testing corresponds to the highest values of the k parameter. The explanation is based on the SEM observations, which permitted the detection of spherulites with cross-hatched lamellae (for the α-spherulites) and with simple radial growth lamellae for the β-spherulites.