The SPE Library contains thousands of papers, presentations, journal briefs and recorded webinars from the best minds in the Plastics Industry. Spanning almost two decades, this collection of published research and development work in polymer science and plastics technology is a wealth of knowledge and information for anyone involved in plastics.
Formulation of droplet deformation and breakup in an extensional flow for viscoelastic fluid systems were carried out, and parametric study was performed. The interfacial tension, and both droplet viscosity and elasticity reduce the droplet deformation, while the matrix viscosity and droplet size increase the droplet deformation. The matrix elasticity affects the droplet deformation in a more complex manner. The viscoelastic properties of the matrix are more influential on the droplet deformation than that of the drop phase. For viscoelastic systems, the capillary number, viscosity ratio, and the elasticity of both phases all have effects on the broken drop size and the critical deformation, and the relations between all these parameters are very complicated. The formulation then was used to numerically simulate the deformation and breakup of a liquid crystal polymer droplet suspended in polypropylene matrix during a film casting process. Although the result was not quantitatively accurate, the trend in terms of the particle size and aspect ratio was correctly predicted.
Polypropylene (PP) of various molecular weights were mixed with a thermotropic liquid crystal polymer (LCP) and strands were prepared by extrusion and stretching. The strands were subsequently pelletized and then injection molded at temperature below the melting point of LCP. The mechanical properties and the morphology of the strands and injection-molded specimens were investigated as a function of draw ratio, LCP concentration, and PP molecular weight. The results for strands show that an increase in the draw ratio, LCP concentration and matrix molecular weight in general enhance the modulus and tensile strength. However, the tensile properties of injection-molded specimens are found to be reduced compared with those of the original strands, in particular at high LCP concentration. The morphology of LCP changes from spherical or ellipsoidal droplets to elongated fibrils in the strands as the draw ratio increases, but this aligned LCP fibrillar morphology was not transferred to the injection-molded specimens due to the disorientation of fibrils during injection molding. Compatibilization of PP/LCP blends was also studied by using various polymers. Maleic anhydride and acrylic acid modified PPs improved the tensile properties modestly, but maleic anhydride modified EPDM reduced the tensile properties.
The effect of shear modification and blending on the coating performance of a commercial LDPE resin was studied. Shear modification of the virgin resin as well as of its blends with another LDPE was performed in a single and in a twin screw extruder. The rheological properties of the modified materials were measured and no significant differences in their behavior under shear deformation were detected. On the other hand, changes in the entrance pressure drop and extensional viscosity were observed. These changes in extensional behavior were found to affect coating properties. Overall, neck-in improved through shear modification while it was not sensitive to blending with a higher molecular weight resin. On the other hand, blending had an effect on the draw-down speed and it may be used to achieve a balanced coating performance.
Executing a color change is a routine operation for plastic processors. With on-line coloring in extrusion, the polymeric melt continuously flows shaping the product and changing its color from one color (color A) to another color (color B). At the moment of initiating the color change, there is a period of time in which the product will yield acceptable color (in color A). After some amount of time elapses, the transition phase from color A to color B will yield off-color product until the color change for color B is fully established in the system. The amount of time it takes to make this change from color A to color B depends on a variety of factors including the extruder size and type, shaping die, resin that is extruded, coloring system, and the color to be changed, whether from light to dark or vice versa. In this report, an approach for minimizing both the color-change extrusion time and off-color rejected product is presented. An extrusion simulation is applied to determine temperature - residence time -shearing correlation and the correct let down ratio for a PVC compound/pigmentation system. A Brabender mixer was used as an instrument. The information obtained was then applied for studying color change kinetics in a production environment.
Vibration welding is a useful technique for joining thermoplastics. This vibration welding study examined the microstructure of joints made of 33% glass reinforced nylon 66. Joints were made under different vibration welding conditions. The microstructural analysis techniques were: optical microscopy of weld cross-sections under polarized light, scanning electron microscopy of both weld cross-sections and fracture surfaces, and thermal gravimetric analyses near the weld line. These tests provide information on the thickness of the heat-affected zone, glass fiber orientation and level respectively. The microstructural analyses reported in this study assist in the interpretation of experimental tensile weld strengths.
Flame retardant polyethylene compounds fabricated from rotational moulding technique are finding widespread applications for Industrial applications, stadium seats, children`s toys in parks etc. In the present work , the objective was to assess rotational moulding characteristics of flame retardant -LLDPE. The end application identified for the purpose was a hollow box for packaging of explosive materials. The material currently used is wood. With increasing pressure to conserve natural resources, the present work acquires significance and provides impetus in that direction. Compounds were designed to meet V0, V1, and V2 Flammability rating as per UL 94 test protocol. FR-LLDPE compounds were prepared on Berstoff ZE-25 twin-screw extruder. Mechanical properties are determined on the injection moulded ASTM test specimens and cut specimens from rotational moulded boxes. The flammability test on rotational moulded hollow containers has been captured in a compact disk.
N-isopropylacrylamide (NIPA) was copolymerized with different concentrations of N, N'-methylenebisacrylamide (MBA) to obtain networks of different crosslinking densities. Semiinterpenetrating networks of the same crosslinking densities were obtained by copolymerization of NIPA and MBA in the presence of linear polyacrylamide (5 wt.%). The equilibrium swelling degree in water at 25°C varied from 7.61 to 16.8 times the original volume when the molar ratio NIPA/MBA increased from 10:1 to 100:1. The transition temperature determined by DSC was largely unaffected by the crosslinking conditions in this work. Crosslinking density obtained from dynamic shear measurements was much lower than predicted from the molar ratio of the monomer and crosslinker, which was explained by the incomplete reaction. The sol fraction varied from 12% to 30%. Thermomechanical analysis showed contraction followed by the expansion of the gels during transition. The broadening of the temperature range of the gel collapse was observed as the crosslinking density increased. Tensile strength of the 10% swollen semiinterpenetrating NIPA networks was higher (15-23 kPa) than that of the 10% swollen single NIPA networks (9-13 kPa). Elongations at break were significantly higher for semi IPN gels compared to the single ones, especially at lower crosslinking densities.
The apparent extensional properties of three injection molding grade, high density polyethylenes (PE) and their composites containing 20vol% hydroxyapatite (HA) were studied using orifice pressure drop data from a capillary rheometer followed by Cogswell's analysis. The effects of temperature, molecular weight and filler have been investigated. For unfilled PE extensional viscosity was found to decrease as the molecular weight decreased or the temperature increased. The addition of HA appears to increase the extensional viscosity at low strain rates and decreases due to extension thickening at high strain rates. HA addition tended to decrease the Trouton ratios of PE at moderate to high strain rates.
The objective of this work was to compare simulation and experimental results for a flat specimen injection mold. The study was made using standard and film" gates. The results were obtained through a simulation program for the injection process C-MOLD for theoretical data and for the experimental data results were obtained in an injection molding machine. In both cases the injection molding conditions were the same. Differences between the gates and also between experimental and theoretical results mainly in the injection pressure and pattern flow were found."
The tolerances on injection molded thermoplastic parts have grown tighter over the past several decades, and concomitantly the range of applications for thermoplastic injection molded parts have grown dramatically. Now, tolerances of one micron can be achieved, expanding the range of applications for injection molded thermoplastics even more. The tolerances on the injection molded thermoplastic parts are precipitated by the combination of the tolerances from the feedstock, the injection mold, the injection molding machine, the peripherals, the control system and the part measurement devices. So, in simple terms, each of these contributing tolerances must be minimized in order to minimize the tolerances on the injection molded part. In the specific applications herein described, which is a single part fabricated in a multi cavity mold the tolerances on the injection mold are found to be the primary contributing tolerances, the tolerances on the control system are found to be the secondary contributing tolerances, and the tolerances on the injection molding machine and the feedstock are less significant.
Weldlines, which are a common feature in many injection molded parts, are known to be inherently weak. The present experimental study focused on improving weldline strength through the addition of oscillatory vibrational energy during molding processes. Both filled and unfilled polymers were studied, and comparisons between the tensile strength of ASTM specimens made with and without vibration were made. It was found that minimal product strength increases were realized when optimized vibration-assisted molding conditions were applied. Details related to the critical vibration-assistance parameters studied and optimization processes utilized will be presented and discussed.
Polypropylene (PP) nano-composites are prepared by melt intercalation in this study. Nano-clay is mixed with PP by twin screw extrusion. Maleic anhydride modified polypropylene (PP-MA) is added to enhance the dispersion of the clay in PP. Nylon 6 is also added to this PP/PP-MA/clay composite to partially replace the content of PP-MA in order to decrease the material cost. The basal spacing of the clay in the composites is measured by X-ray Diffraction (XRD). The morphology of the composites is observed by SEM. The mechanical properties of the composites are also measured. It was found that the molecular weight and MA content strongly affect the nano-structure and the properties of PP nano-composites. PP-MA with a lower molecular weight (LMW) and a high MA content can lead to good clay dispersion in PP-MA. However, it causes a decrease in the mechanical properties of PP/PP-MA/clay composites. It was also found that the addition of nylon 6 further expands the basal spacing of the clay in PP composites. However, the mechanical strength decreases by adding nylon 6 to the nano-composites.
In this paper, design and fabrication of a CD platform, where different fluidic structures are micromachined into a plastic CD, are presented. Various ways to fabricate mold inserts (traditional CNC-machining of tool steel vs. photolithography/electroplating) and microfluidic platforms (micro-embossing, thin wall injection molding, and reactive molding) based on optically clear thermoplastic and thermoset polymers (e.g. optical quality polycarbonate, PMMA, PDMS) are introduced. The effects of mold inserts, molding methods, and feature size on replication accuracy and 'molded-in' stresses are also discussed.
The presence of low profile additives (LPAs) can reduce the shrinkage of unsaturated polyester (UP)/styrene (St) resins cured at low temperatures, but the final shrinkage is still quite high. In this study, secondary monomers (e.g. divinylbenzene (DVB) and trimethylopropane trimethacrylate (TMPTMA)) and co-promoter 2,4-Pentandione (2,4-P) were added into the UP/St/LPA system to investigate their effect on shrinkage control of resins cured at low temperatures. Dilatometery results showed that the addition of both TMPTMA and 2,4-P resulted in earlier volume expansion during curing and in turn; better shrinkage control. The phase separation, reaction kinetics and viscosity changes in the LPA-rich and UP-rich phase during curing were investigated. Results revealed that the increased reaction rate in the LPA-rich phase led to an earlier formation of microvoids and, consequently, less volume shrinkage of the cured resin.
Unsaturated polyester and vinylester resins are the two major thermoset resins used in low temperature composite manufacturing processes, such as the Seemann Composite Resin Infusion Molding Process (SCRIMP). Understanding the reaction kinetics and network formation can be critical to SCRIMP. A series of well-defined polyester resins are used to study the effect of resin chemistry on the reaction kinetics. The effects of styrene concentration and temperature on the cure kinetics of styrene/vinylester systems are also studied. The glass transition temperature of polyester/vinylester resins cured at different temperatures is measured and used to monitor the final conversion change. A mechanistic kinetic model is proposed to simulate both the reaction kinetics and the final conversions of various resins in low temperature copolymerization. The results may shed light on resin modification and process innovation.
Supercritical carbon dioxide (scCO2) was added during compounding of polystyrene (PS)/poly(ethylene-methyl acrylate) copolymer (SP 2207) and poly(methyl methacrylate) (PMMA)/SP 2207 blends and the resulting phase inversion, morphology, and mechanical properties were studied. SP 2207 is a 80 wt.% ethylene-20% methyl acrylate copolymer used to increase the toughness of polystyrene and PMMA. Carbon dioxide was added at 2.0 wt.% based on polymer melt flow rates. Carbon dioxide injected into the extruder sped up the phase inversion of the two components by reducing the glass transition temperature of PMMA and PS. This allowed for an enhanced dispersion of the rubber phase after phase inversion. An earlier extruder location at which phase inversion occurred along with a reduced viscosity ratio greatly improved the dispersion of the rubber copolymer in the polystyrene and PMMA matrix. An increase in impact strength and a reduction in the flexural modulus of blends prepared with CO2 were measured, indicating that CO2 aided in dispersing the rubber into the brittle matrices of polystyrene and PMMA. Reprocessing did not result in a loss of morphology for PMMA/SP 2207 blends.
For low temperature composite manufacturing processes, a major concern for the fabricators is how to design and control the mold filling and curing time. Curing agents like inhibitors or retarders are needed to prevent premature gel and provide a sufficiently long time to complete mold filling. However, the addition of inhibitors or retarders tends to result in a slow mold curing rate and low resin conversion. In this study, a chelating agent, 2,4-pentanedione (2,4-P), is used to manipulate the resin gelation and curing. 2,4-P can interact with promoters (i.e., metal compounds such as cobalt carboxylates) and affect the catalytic activity of the promoter to decompose the initiators, by either retarding or promoting the resin system depending on the initiator and resin system used. It was found that the function of 2,4-P as a retarder or co-promoter for the co-polymerization of styrenic resins depends greatly on the acidity of the resin system used. Based on this observation, a series of SCRIMP molding experiments using a novel resin design was carried out. This design allows 2,4-P to serve as a retarder during mold filling to achieve a long gel time; it then becomes a co-promoter during curing to increase the curing rate and conversion when the acidity of the resin changes.
A flow visualization cell with an abrupt entry pseudo-axisymmetric geometry has been used in the study of a low density polyethylene melt flow. The flow cell was mounted on a Davis Standard Betol BK38 single screw extruder. Birefringence and imaging velocimetry techniques have been used to observe changes in the stress and velocity fields in the melt at various processing conditions. Flow development of the melt was observed using pigment tracers. Start-up and steady state flow regimes are investigated. A transient instability occurred on start-up flows. The time stabilization of the flow increased with dwell time between extrusion trials. The instability was observed as oscillatory motion of the stress birefringence pattern and fluctuations in measured pressure.
Full field velocity measurements in planar contraction geometries are reported - these having been evaluated using the techniques of particle image and particle streak velocimetry for HPDE and LDPE melt flows. Measurements were made in a specially designed flow cell that enables laser sheet lighting to be used to illuminate planes of the polymer at precise locations across the die, mounted on a Betol BK38 extruder. Stress measurements obtained by flow birefringence complement the velocity field information. Steady state and start up flow regimes were investigated with results presented in a form suitable for direct comparison with ongoing numerical simulations.
Good injection moulding machine control is a necessary requirement for control of the process, however there is an acknowledged lack of process understanding, related in turn to a lack of understanding of the polymer under process conditions which inhibits the development of standardised route to process control. In our laboratory, specific pressure indices in an identified low noise region of the primary injection stage of injection moulding have been found to provide a sensitive indicator of changes in a polymer, including batch to batch changes and process-induced changes, which in turn allows meaningful Statistical Process Control to be undertaken. Growing concern for environmental issues, including international standards agreements such as ISO14001, demonstrate a clear requirement to conserve energy for both environmental and cost issues. Detailed energy measurements on injection moulding machines both in the laboratory and in industry demonstrate the potential of process energy measurements as an aid to the development of a systematic management approach to the environmental concerns of an organization. Laboratory DOE studies allow a further insight into the influence of a variety of machine variable settings on the total energy consumption. We are currently in the process of combining both process variable and process energy measurements, to provide processors with the richest level of process information.
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