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.
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Effect of Shear Rate and Mixer Residence times on Morphology Development and Correlation to Young’s Modulus in PS/PP Blends Approaching Co-Continuity
Mixer residence times and shear rates are crucial for development of desired morphologies in polymer blends. Immiscible blends of PS and PP are being studied for development of morphology in a single screw extruder in the co-continuous region. The effect of mixer resident times and shear rates on the morphology development is analyzed. Flexural modulus measurements show strong correlations to selective morphologies obtained at intermediate shear rates and resident times. The influence of morphology on crystallinity of the semi-crystalline phase is considered, and theoretical investigations into the relationships between morphology and mechanics presented.
Dynamic Mechanical Analysis of Polypropylene-Clay Nanocomposites
Polypropylene-clay nanocomposites have become of great interest over the last several years due to their enhanced properties with uncommonly low filler loadings. Dynamic mechanical thermal analysis (DMTA) is a valuable characterization tool because it will give us information about the polymer chain relaxations in the presence of nanoparticles, thermodynamic transitions, and the extent of polymer confinement/clay gallery intercalation. DMTA results are combined with x-ray diffraction, differential scanning calorimetry, and transmission electron microscopy to give a more complete picture of the effect of montmorillonite nanoparticles and a compatibilizer on polypropylene properties.
Effect of Nanoclay on Efficiency of Low Profile Additives (LPAs) on Shrinkage Control of Unsaturated Polyester (UP) Resin
The addition of a small quantity of nanoclay (3 wt%) can greatly enhance the efficiency of low profile additives (LPAs) on volume shrinkage control of low profiled unsaturated polyester (UP)/styrene (St) /LPA systems. In this study, the effect of nanoclay on volume shrinkage of low profiled UP resins containing polystyrene, poly(methyl methacrylate) and poly(vinyl acetate) respectively has been investigated by an integrated approach of static phase characteristics of uncured resin mixture, morphology of the cured samples, reaction kinetics, and shrinkage measurement. The results revealed that nanoclay greatly increased the fraction of LPA-rich phase, leading to a more micro-cracking in the LPA-rich phase or at the interface of the LPA-rich and UP-rich phases, and therefore an prominent improvement of volume shrinkage control. The effect of structure/properties of low profile additives and surface property of nanoclay on shrinkage of UP resin were also investigated.
Rapid Crack Propagation (RCP) Failures in HDPE Pipes: Structure-Property Investigations
The RCP resistance of a wide variety of HDPE pipes was measured using the S4 test, and the relationships between molecular architecture and low-temperature toughness of HDPE pipes are presented. Specifically, we conclude that high molecular weight, high crystallinity and a relatively narrow molecular weight distribution are important. Further, for a given HDPE, our investigations clearly demonstrate that the room-temperature impact energy (razor-notched Charpy Impact test per ASTM F2231) is an inadequate or a poor indicator of the RCP resistance (S4 critical temperature) of the ensuing pipe. However, the ductile-brittle transition temperature, as measured on compression-molded specimens using the razor-notched Charpy impact test, appears to be a reasonably good indicator of the S4 critical temperature of the resultant pipes.
Influence of Branching Distribution on the Physical Properties of High Density Polyethylene
Three sets of two-component blends from various narrow-MWD (molecular weight distribution), linear (no rheologically significant long branches) polyethylenes were prepared with multiple compositions in each set of blends. These blends were deliberately prepared such that the branching (from 1-hexene co-monomer) was present exclusively on either the high or the low molecular weight blend component. In this study, the influence exerted by such selective placement of branching on the physical properties of the resulting blends is discussed. We find that while the instantaneous tensile properties depend exclusively on crystallinity, the ultimate tensile properties depend strongly on branching distribution. Resistance to slow crack growth, impact toughness and the ductile-brittle transition temperature were all noted to depend strongly on branching distribution, with preferential placement of branches along the longer molecules being beneficial. Lastly, the tear resistance and impact toughness of oriented cast films produced using the above blends were also observed to depend on branching distribution.
Analysis of Ductile and Brittle Failures from Creep Rupture Testing of HDPE Pipes
A comprehensive analysis of ductile and brittle failures from creep rupture testing of a wide spectrum of HDPE pipes was conducted. The analysis indicates that the ductile failure of such pipes is primarily driven by the yield stress of the polymer. Examination of ductile failure data at multiple temperatures indicates a systematic improvement in performance with increasing temperature. It is proposed that testing at higher (above-ambient) temperatures leads to progressive relaxation of the residual stresses in the pipe; this causes the pipe to perform better as residual stresses are known to help accelerate the fracture process. Finally, our investigation indicates no correlation, whatsoever, between brittle failures in pressurized pipes and the PENT failure times. Therefore, one has to be extremely cautious in interpreting the true value of the PENT test when developing polymers and pipes for high-performance pressure pipe applications.
Application of Co-Rotating Twin-Screw Extruders Based on Torque, Volume and RPM
Twin-screw extrusion processes, while in general very robust and flexible, can have limitations in throughput and/or product quality that will reduce their economic efficiency. The source of these limitations can be one of the many unit operations performed in the twin-screw extruder, such as feeding, plastification, mixing, degassing and discharge. For example feeding is often volume limited when one of the feed ingredients has a very low bulk density or is prone to fluidize.In order to minimize the potential for process limitations, twin-screw extruders have different design criteria. There are both high torque and high volume machines, and both use screw rpm as an independent variable to provide broader operating flexibility.The utilization of both machine variations is shown for several typical applications. On one hand, there is the latest design for high torque compounding technology resulting in a machines with a specific torque (M/a3, M = torque, a = centerline distance between screws) of 13.6 Nm/cm3. On the other, there is the high free volume design with an outer to inner diameter ratio (Do/Di) up to 1.8. The third variable, screw rpm, has values up to 1800 rpm. Therefore, there is not one solution of all processes, but rather the best one for each task.
Use of Surface-Confined Photografting to Tailor the Wettability of Poly(Lactic Acid) Film
The major objective of this research is to modify the surface characteristics of poly(L-lactic acid) (PLA), by grafting a single or a combination of hydrophilic polymers to produce a continuum of hydrophilicity with an ultimate aim of making a bioactive surface. The PLA film was solvent cast and the film surfaces were activated by UV irradiation. A single monomer or combination of two monomers selected from vinyl acetate (VAc), acrylic acid (AA), and acrylamide (AAm) were then grafted to the PLA film surface using a UV induced photopolymerization process. The film surfaces resulting from each reaction step were analyzed using ATR-FTIR spectroscopy and contact angle goniometry. Results showed that Aam dominated the hydrophilic characteristics of the film when copolymerized with VAc and AA, while PLA films grafted with copolymers of poly(vinyl acetate)-poly(acrylic acid) (PAA-PVA) showed linear variation of water contact angles.
Controlled Growth of Linear Carbon Nanofibers
This approach investigates how the changes on surface area of the tip effect growth of linear nanofibers using a standard electrospinning procedure with modification to the collection surface and implementation of a step-down voltage collection uptake. The apparatus consists of a tip, a syringe pump, a rotating deposition disk, a rotating uptake disk, and two voltage supplies. The system works in the following manner, a high voltage is applied to the tip, a low voltage is applied to the deposition disk, and the uptake disk is grounded. Polymer solution from the tip is elongated by an applied electric field which is collected on the rotating deposition disk and transferred to the uptake disk by the change in voltage. Coupling this apparatus with the developments made in electrospinning temperature-controlled air blowing, which facilitates additional shearing-stretching forces of the nanofibers and allows for controlled solvent evaporation rates, will result in linear carbon nanofibers.
Structural Development in Thin-Wall Injection Molding Process
Thin-wall injection molding of polypropylene (PP) and cycloolefin copolymer (COC) were performed to clarify the structure and mechanical properties of microscale molded products. Effects of mold thickness and process conditions on processability in micro-scale injection molding were evaluated. Furthermore, the structure and mechanical properties of molded products were analyzed using wide angle X-ray diffraction, birefringence, DSC measurements, and tensile testing. In the case of PP, the molecular orientation in the vicinity of the gate was higher than that at any other positions. Birefringence increased with decreasing mold temperature, whereas crystallinity decreased with decreasing mold temperature. The molecular orientation of COC showed a similar tendency as in the case of PP, where birefringence showed the highest value at low mold temperature and in the vicinity of the gate.
Evaluation of Material Properties and Processability Using the Intelligent Micro-scale Polymer Processing System
A new system has been developed for measurement of material properties such as melt shear viscosity and PVT behavior. The new rheometer and high-pressure dilatometer comprises of four pistons, a pressure gauge, and heaters. The melt viscosity and PVT behavior were analyzed using a small amount (<10 g) of resin. The combined rheometer and dilatometer were combined and installed to a micro-scale injection molding machine. The measurements of material properties and micro-scale injection molding (micromolding) process were carried out simultaneously. We call this system as the Intelligent Micro-scale Polymer Processing System. The measurements of material properties of polypropylene and cyclo-olefin copolymer were conducted. The melt shear viscosity and PVT behaviors were found to be similar to those measured using a conventional measurement apparatuses. The processabilities of PP and COC also were analyzed using this system.
Injection Moulding of ?- and ?-Polypropylenes: Morphology Consequences
The specific effects of mould temperature (MT) and holding pressure (HP) on the structure of neat and ?- nucleated isotactic polypropylenes have been studied. Commercially available isotactic polypropylene was modified by 0.03 wt.% of ?-specific nucleator. From both original (?-iPP) and ?-nucleated (?-iPP) materials test specimens were injection-moulded using two sets of processing parameters. In the T-set the MT was varied within a range of 40-120 °C by 10 °C steps, while in the Pset the HP was changed from 5 to 13 MPa in 1 MPa steps. Polarized-light microscopy showed a strong effect of MT but minute influence of HP on the morphology of ?- and ?-iPP specimens. The increase of MT positively influenced the crystallinity and the ?-form content, particularly in the skin of specimens as wide-angle X-ray scattering displayed. On the contrary, the rising HP depressed the crystallinity within the bulk of specimens proportionally.
On-Line Check-Ring Failure Detection and Compensation in Injection Molding
The performance of check-ring affects strongly the product dimensional and weight stability in injection molding. Check-ring valve may fail to close properly during injection thus causes a drop of the product weight. In this paper, an on-line method has been developed to detect check-ring failure based on the available real-time process measurements. A model has been established to predict online the weight loss due to check-ring failure. A compensation mechanism has also developed to maintain product weight consistency despite of the failure. Experiments show that the proposed detection and compensation methods are very effective in controlling weight consistency.
Hot Embossing of Micro-Featured Devices
Polymer microfabrication methods are becoming increasingly important as low-cost alternatives to the silicon or glass-based MEMS technologies. In this study, micro molding via hot embossing was applied to micro-featured used for DNA/RNA test. LIGA like process using UV light aligner was used to prepare silicon based SU-8 photoresist followed by electroforming to make Ni-Co based stamp. The micro features in the stamp with 5 inch diameter size and 0.2 mm thickness includes 30?m in depth by 100?m in width micro-channel size and 50?m pitch size. PMMA film of 1 mm thickness was utilized as molding substrate. Effect of molding conditions on the replication accuracy was investigated. The imprint width, imprint depth and angle of sidewall of micro-channels were analyzed and correlated. It was found that the molding condition including applied force and embossing temperature are found to all affect the molding accuracy significantly. The imprint depth increases with the imprint force until a saturation value. The imprint depth also increases with the embossing temperature until a saturation value. Basically, 20 kN and 180°C for applied force and embossing temperature can obtain acceptable results when considering molding cycle time. However, 25 kN and 220°C, respectively, under 5 minutes embossing time can obtain a nearly perfect replication in our experiment.
Effects of Molding Conditions on the Electromagnetic Interference Performance of Injection Molded ABS Parts with Conductive Fibers
Polymers filled with conducting fibers to prevent electromagnetic interference (EMI) performance have recently received great attention due to the requirements of 3C products. In this paper, effect of fiber content and processing parameters including melt temperature, mold temperature, injection velocity on the electromagnetic interference shielding effectiveness (SE) in the injection molded ABS polymer composites filled with conductive stainless steel fiber (SSF) was investigated. It was found from measured results that fiber content plays a significant role in influencing part EMI SE performance. Higher melt and mold temperature would increase shielding effectiveness due to a more uniform and random fiber orientation. However, higher injection velocity leading to highly-orientated and less uniform distribution of fiber reduces shielding effectiveness. SE value can reach highest values of approximately 40 dB, 60 dB and 72 dB at 1000 MHz frequency for fiber content 7%, 14% and 21%, respectively, if proper molding conditions were chosen. The result indicates that molding conditions are very important on the SE performance instead of fiber content alone.
Study on the Mechanical Properties of Injection Molded Nylon 6 Nanocomposites
In this study, the effects of the molding conditions including melt temperature (T), mold temperature (Tm), holding pressure (Ph), and injection speed (V) on the mechanical properties of injection molded nylon-6/fluoromica nanocomposites (Unitika) were investigated. With the additional of 5% nano-fluoromica particles, the tensile strength (?s) and flexural strength (Eb) increased and impact strength decreased as compared to those with of pure nylon-6 parts. The result also indicates that ?s and Eb of Unitika increased with T, Tm, Ph, and V. However, the impact strength of Unitika increased with T and Ph and decreased with increasing melt temperature and injection speed. The DSC measurement reveals that the crystallinity of Unitika increases with all molding parameters. SEM results also indicate the different fracture characteristics between pure nylon-6 and Unitika parts.
Development of Compression Moldable Thermoplastic Bipolar Plates
A method with the potential to produce economical bipolar plates with high electrical conductivity and mechanical properties is described. Thermoplastic composite materials consisting of graphite particles, thermoplastic fibers and glass or carbon fibers are generated by means of a wet-lay process to yield highly formable sheets. The sheets together with additional graphite particles are then stacked and compression molded to form bipolar plates with gas flow channels and other features. One of the key elements to the economical manufacturing of the plates is the minimization of the heating and cooling times. Various heating schemes are evaluated including induction, radiation, and resistance to determine how fast the composite preforms can be brought to the forming temperature and compression molded to give bipolar plates with well-defined channels. The electrical and mechanical properties of the plates were determined for several different compositions and two different polymer matrices.
3D Finite Element Modeling of the Blow Molding Process
In this work, both the heating stage and the blowing stage of the blow molding process are numerically modeled. The heat transfer between the infrared oven and the preform is modeled using a ray tracing method. The cooling fan effect is taken into account thanks to a forced convection coefficient. Regarding the blowing step, a Mooney-Rivlin hyperelastic model has been implemented in Forge3® software in order to account for the rheological behavior of the polyester. The numerical finite element model is based on velocity pressure formulation and tetrahedral elements. In order to validate the implementation of the hyperelastic behavior, computations are compared to Mooney-Rivlin analytical model results for tube free inflation. Finally, the global blow molding process of a PET bottle is studied.
Stress Cracking Caused by Hot Plate Welding – Theoretical Analyses
In the field of hot plate welding, experimental investigations show that the stress cracks are caused by inherent stresses in the component, which are induced in the part while it is being heated on the tool.First, the process parameters and the phenomena of stress cracking in amorphous thermoplastics are discussed. Than, the development of a theoretical model for the one-dimensional temperature and stress calculation of simple hot plate welded geometries is described.The prescribed method makes it possible to estimate the effects of the process parameters on the phenomena of stress cracking. The results of the physical-mathematical model are compared with the results of experimental investigations.Finally, our understanding of the phenomena of stress cracking, as well as of the process involved, is enhanced with the aid of the physical model that is presented.
Modification of Polymers Using Polyvinyl Butyral Based Additives
Polyvinyl butyral (PVB) is the tough polymer film widely used as the interlayer in safety glass laminates, such as automotive windshields.This material is now available in pellet form (Ecocite®) for easy blending into other polymer resins. It has been shown to act as an impact modifier and/or processing aid when blended, at low levels, into a variety of engineering resins, polyolefins and PVC. At relatively high loadings, it performs as a permanent plasticizer imparting toughness, flexibility, enhanced processibility and oil resistance.The residual hydroxyl groups in PVB provide active surface sites to enhance paintability and adhesion to other materials. PVB’s adhesion has been found to enhance stiffness/compatibility when glass fibers and minerals are incorporated into engineering resins. The hydroxyl functionality has been used as crosslinking sites to form tough oil-resistant thermoplastic elastomers (TPE) via dynamic vulcanization.
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