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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Thermal Analysis of Blends of Recycled HDPE and Virgin Polyolefins
This paper investigates the melting point and crystallinity behaviour of blends of recycled milk bottle HDPE with injection moulding and film blowing grade high density polyethylene (HDPE), linear low density polyethylene (LLDPE) and low density polyethylene (LDPE) as part of a larger investigation into blends of recycled HDPE and virgin polyolefins. The variation in melting points and crystallinity levels for blends of recycled HDPE with either HDPE or LLDPE were linear with composition, and displayed only one melting point, while recycled HDPE with LDPE displayed separate melting points for each compositional component.
The Effect of Inertia on Fill Pattern in Injection Molding
By numerical simulation of the full three dimensional Navier-Stokes flow equations, it is possible to observe the influence of inertia effects on the filling pattern of an injection molded part. Traditional shell-based Hele-Shaw flow simulations have assumed that the momentum (inertia) contribution to the fluid flow is negligible. However, thick walled parts and complex parts are poorly represented by shell models. Under certain processing conditions for these thick geometries, inertia effects will influence the flow pattern. Simulation studies are presented in this paper which compare flow solutions with and without inertia effects.
New Cost-Efficient Process for the Production of Large-Volume High-Voltage-Insulators Made of Liquid Silicone Rubber (LSR)
The unique combination of chemical and physical properties predestines LSR for applications in the field of electrical insulation. Due to high investment for mold and machine technology an economical production can be reached for medium or large series only. In this thesis a new technology is developed for casting large volume parts at a low level of cavity pressure. Separate heating of the material components to a temperature level just below mold temperature leads to a controlled decrease in cavity pressure. Simultaneously, a considerable reduction in cycle time is reached due to a faster curing process. Since the new technology developed enables the use of simple mold designs without clamping units, a significant reduction in investment is achieved.
Recycling of Crosslinked Multi-Layer Thermoplastic Films - Miscibility Studies
This study was part of a program of work undertaken to develop recycling technology for multi-layer films which are not currently recycled. These multi-layer films comprise barrier layers with surface layers for mechanical strength, and tie layers between. Crosslinking is used to enhance various mechanical properties. The crosslinked layers have a high viscosity which creates processing problems, eg. if the film is recycled, high processing pressures are required. Furthermore, material blend component incompatibilty can result in inferior mechanical properties. Monolayer films of the virgin materials were produced. Multi-layer film with crosslinked EVA/LLDPE and a barrier layer was produced on a blown film line. This multi-layer film was agglomerated" then reprocessed in a twin screw extruder with virgin LDPE and LLDPE and blown into film. The blend miscibility was then determined using a TA Instruments TMDSC. It was found that LDPE blends were initially miscible with the containing scrap whereas LLDPE blends were immiscible. The LDPE miscibility was partly reversible as the blend components phase separated after the second heat treatment during testing in the TMDSC instrument. The initial miscibility was attributed to being induced by high shear during processing."
Thermal and Mechanical Properties of Silane-Grafted Moisture-Crosslinked Polyethylene
The vinyl trimethoxysilane VTMS" was grafted onto various polyethylenes ( HDPE LLDPE and LDPE) using DCP as an initiator in a twin screw extruder. The grafted polyethylenes were able to cross-link utilizing water as the crosslinking agent. The effects of varied crosslinking time on the mechanical properties of the crosslinked polyethylenes were studied. It was found that the HDPE and LLDPE were apt to cross-link during the grafting process and thus decreased the grafting ratio. Multiple melting behavior was observed for cross-linked LDPE and LLDPE. The mechanical and thermal properties of the crosslinked PE are better than uncrosslinked PE." LLDPE and LDPE) using DCP as an initiator in a twin screw extruder. The grafted polyethylenes were able to cross-link utilizing water as the crosslinking agent. The effects of varied crosslinking time on the mechanical properties of the crosslinked polyethylenes were studied. It was found that the HDPE and LLDPE were apt to cross-link during the grafting process and thus decreased the grafting ratio. Multiple melting behavior was observed for cross-linked LDPE and LLDPE. The mechanical and thermal properties of the crosslinked PE are better than uncrosslinked PE."
Application of Liquid Gas-Assisted Injection Molding to the X-Arm of a Chair
Application of gas-assisted injection molding (GAIM) has been expanded within last 15 years because of many advantages such as design flexibility, dimensional stability, reduction of machine tonnages, and so on. But, for thick parts, it is observed the surface defects including hesitation mark and gloss difference. Difficulties in lay-out of the gas channel and processing condition are another disadvantages. Liquid gas-assisted injection molding (LGAIM) is a good alternative of conventional gas-assisted injection molding especially in manufacturing simple and very thick parts. The heat-activated liquid vaporizes and pushes the melt downstream and creates hollow channels within parts[2,3]. We developed the total system that includes control unit (control of volume, pressure, and time of the liquid), liquid-injection nozzle, recipe of liquid system, and part/mold design (CAE analysis). As an applicable part, X-arm of a chair was selected. From experiments, it was observed stable hollow formation without hesitation mark and sink mark. And we was able to reduce the cycle time and weight
Polymer/clay nanocomposites prepared from intercalated montmorillonite and PVC were compounded in KO-kneader with dioctylphtalate (DOP) as a plasticizer. An influence of the type of used organoclay on thermal stability was observed. Problems with the composition thermal stability during compounding can be eliminated by pretreatment of the organoclay with plasticizer which creates a barrier between polymer and quaternary amine. Simultaneously co intercalation of plasticizer facilitates exfoliation and dimension clay platelets in the polymer matrix. A positive influence of nanoclay on dimensional stability and permeability was observed.
Influence of Temperature and Initiator Type on the Functionalization of High Density and Lineal Low Density Polyethylenes
The obtaining of compatibilizers for blends by functionalization has led the study of this modification in the polyethylene. Three initiators were used in the grafting of High-Density Polyethylene (HDPE) with diethylmaleate. Also was investigated the dependence of the functionalization degree on the temperature of Linear-Low Density polyethylene (LLDPE). The compared initiators were 2,2'- Azobisisobutyronitrile (AIBN), benzoyl peroxide (BP) and 2,5-dimethyl-2,5-di-(t-butylperoxy)hexane (DBPH). It was found that under the same experimental conditions the grafting degree in the HDPE decrease follows the order of the initiators: DBPH > BP > AIBN.
Morphology and Mechanical Behavior of Poly(3-Hydroxybutyrate)/Functionalized Ethylene Copolymers Blends
The possibility of poly(3-hydroxybutyrate) (P(3HB)) mechanical properties improvement through reactive blending with ethylene-methacrylic acid copolymers either in the acid form (I-H) or partially neutralized with Zn (I-Zn) and Na (I-Na) was investigated. Blends of P(3HB) and I-H, I-Zn and I-Na were prepared in an internal mixer and in a double screw extruder. The blend with I-H showed the best results for mechanical properties. All the blends showed a significant reduction in the Young modulus, which was smaller for P(3HB)/I-Zn blends. Blends containing 30% of I-Zn presented the higher impact resistance and morphology containing the dispersed phase as cylindrical domains.
Strain Hardening Behavior in Elongational Viscosity for Blends of Linear Polymer and Crosslinked Polymer
Rheological properties for the binary blends of a linear polymer, such as isotactic polypropylene (PP) and polystyrene (PS), and gel fraction of a crosslinked terpolymer composed of ethylene, 1-hexene, and ethylidene norbornene (gEHDM) have been studied. Blending of the gEHDM, which is characterized as the gel just beyond the sol-gel transition point, much enhances the strain hardening behavior in the elongational viscosity of PP, even though the amount of the gEHDM is only 1 wt%. On the other hand, the PS/gEHDM (97/3) blend shows no strain hardening in the elongational viscosity. The entanglement couplings between the gEHDM and the PP will be responsible for the strain hardening behavior.
Influence of the Dispersed Phase Composition on the Mechanical Properties of Toughened PP Ternary Blends
Polymer blends offer nowadays a quick and economic way of improving properties at competitive costs. Such blends have already reached a massive application in the case of thermoplastics. This work presents results obtained for blends of polypropylene (PP), linear low-density polyethylene (LLDPE) and ethylene-propylene rubbers (EPR or EPDM). Different dispersed phase particle sizes are obtained varying the content of LLDPE and the viscosity of elastomers. The morphological features of such blends prepared in a twin screw extruder have been studied by TEM. Notched Charpy impact resistance of injection-molded samples was determined at different temperatures. Fracture surfaces were observed by SEM and elastic modulus were measured and correlated with dispersed phase composition.
Mechanical Mixing in Pin Screw Extruders: Experimental and Numerical Analysis
Pin extruders are frequently used in rubber processing. They are designed to exhibit good mixing capabilities and deliver an important mechanical work to facilitate the processing and mixing of elastomers. The design of such single screw extruders (SSE) is based on empirical know-how and trial-and-error. In this study, we compare three extruder configurations: a simple, continuously flighted single screw, a single screw with interrupted flight and finally a pin barrel screw. The calculation of the flow rate vs. pressure drop confirms that the interrupted flight reduces the pumping efficiency and the addition of the pins does not increase this effect any further. Statistical analysis of the trajectories obtained from the transient velocity field allows us to evaluate directly indices linked to the mixing quality. We obtain a good qualitative agreement between the calculated and measured RTD and confirm that there is an increasing mixing capability in the grooved screw and even more so in the pin barrel extruder.
Studies on the Rotomolding of Liquid Crystalline Polymers
This work investigates the rotational molding (RM) of liquid crystalline polymers (LCP) for making storage tank liners for storing cryogenic and corrosive fluids. We had previously reported work done on sintering of LCPs in order to determine the right candidate for rotomolding (1). This paper reports the studies conducted on the rotational molding of a standard polyethylene and the LCP chosen as a result of sintering studies. The various parameters examined include the rotational molding times, oven temperature, and rotor speed on final mechanical and morphological characteristics of the part formed. Low shear rate viscosity is a very important aspect determining the feasibility of rotomolding of LCPs. This has been examined in case of two LCPs, Vectra A and Vectra B230.
Modification of Clay Intercalate Structure and Properties of TPO Based Nanocomposites
Intercalated montmorillonite (MMT) is the most important organoclay for production of polymer/clay nanocomposites. Understanding the structure-properties relationship is crucial for the successful development of new materials based on organically modified clays. Structure analysis based on X-ray diffraction and computational molecular modeling reveals details of Na-MMT intercalated with octadecylamine. Properties of polypropylene and polyethylene nanocomposite films prepared from clays intercalated with octadecylamine by ion-dipole method and with alkylammonium organocations intercalated by more conventional ion-exchange method are discussed.
Performance and Structure of Highly Oriented Toughened Polypropylene
In this paper, two solid state forming processes, namely roll-drawing and die-drawing were evaluated for inducing high levels of orientation in toughened polypropylene (PP). PP was toughened using a metallocene polymer (mPE) at two levels, 10 and 25 wt%. Orientation, structure and properties of the resulting materials were evaluated. Draw ratios obtained ranged from 1 to 10 using the roll-drawing process and up to 15 using the die-drawing process. Moduli and strengths were affected in proportion to the elastomer content and the die-drawing process showed an improvement in the drawability of the toughened material. Morphological examination revealed the orientation of the dispersed phase domains.
Vibration-Assisted Injection Molding Applied to Recycled General Purpose Polystyrene
Because of their previous thermal and shear history, recycled plastic materials have properties that are significantly inferior to those of their unrecycled counterparts. Thus, the applications of these materials are limited. With the aid of Vibration-Assisted Injection Molding (VAIM) technology, during the present study the properties of products made from recycled polymeric materials were improved. In this paper, the property enhancements realized with recycled polystyrene are presented compared with those obtained through the convention injection molding of virgin material. Also, a potential theoretical basis for the phenomena is discussed.
A Vision for the Rational Design of Polymer Nanocomposites
This paper maps out a systematized approach to the design of nanoscale composite structures in heterogeneous polymer systems to meet application performance requirements, the processing technologies to generate those structures and the resulting material properties. Implementation of such a program would focus materials development on performance objectives while also serving to establish commercially viable process routes and define property benchmarks. It addresses the need to identify and understand nanophase interactions in order to realize desired enhancements in engineering properties. Understanding of these phenomena may best be achieved through a synergistic combination of modeling and experimentation. Examples will be provided to illustrate selected facets of the overall scheme with a focus on commercially significant applications.
The Influence of Processing Parameters on the Properties of Melt-Spun Polypropylene Hollow Fibers
Isotactic polypropylene hollow fibers were produced by melt spinning. Spinning speeds up to 1880 m/min were used, and sample hollowness (percent void in cross section) ranged from 0 to 69%. The fiber samples were characterized using dynamic mechanical analysis, birefringence, tensile testing, and differential scanning calorimetry. The hollow fibers were found to have higher crystallinity, orientation and strength than the analogous solid fibers. In general, the polymer orientation in a hollow fiber was larger than the orientation in a solid fiber, even when the spinning speed for the latter was much larger. For a fixed outer diameter, increasing the hollowness improved fiber properties. However, as hollowness was further increased, fiber properties declined slightly. At a given percent hollowness, increased spinning speed increased modulus and tenacity.
Quick Tooling: New Software Applications Bring Power and Compatibility to the Toolmaking Process
With customers demanding shorter and shorter lead times to get their products to market, profitable moldmaking demands accurate quoting. Design problems that are unforeseen during the quoting process disrupt production and impact your margin. Quick Tooling delivers critical tooling information to salesmen, engineering and shop-owners for timely and informed decisions. This new technology enables moldmakers to compress the mold delivery cycle, elevate critical design variables early in the process, and eliminates repetitive manual tasks. The faster you can establish which constraints will cost you the largest engineering concerns in the tool delivery cycle, the more accurately you can quote, the better the bottom line. Quick Tooling adds value to the tooling development process by providing an environment in which expert tool engineering process knowledge is captured and analyzed, enabling the user to account for upstream constraints earlier in the tool design process. Simulation software enables users to digitally view the actions of the tool before committing engineering hours to the job.
Mixing Behavior of a Model Miscible Binary Polymer System Having Extremely Low Viscosity Ratio
It is well known in industry that production of multi-component compounds with an extremely low viscosity ratio is a very difficult undertaking. This paper describes an attempt to investigate factors affecting mixing of a model system having a viscosity ratio well below 0.001 using a batch internal mixer. Similar to the findings of Ratnagiri, Scott, Joung, and Shih (1, 2, 3) on morphological development during mixing of immiscible polymers, we have observed similar S-shaped torque profiles during mixing of miscible polymer systems of styrene-isoprene-styrene block copolymers with hydrocarbon oils. The time to reach the upper higher torque branch, i.e., the Phase Inversion (PI) time as defined by Ratnagiri and Scott (2), increased with the amount of low viscosity component in the binary composition. The data could be well represented using an exponential model. We also found the PI Time to be longer at equal shear rates and slightly longer at equal RPM using a larger mixer. We were surprised to find the miscible system also exhibited a similar S-shaped torque profile. A method to reduce the PI Time in blends with a high concentration of the low viscosity ingredient was explored. It was also shown that PI Time could be reduced significantly using a split low viscosity feed addition and that a 25% / 75% split had a shorter time to PI than a 50% / 50% or 75% / 25% oil distribution. This emphasized that a slight lowering of the major component viscosity with small additions of oil was the most advantageous process for decreasing total time for PI.
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