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.
The Flat gating system evolved from a controlled study of gate size optimization when applying Hot Runner pinpoint gating techniques. A major objective of the study was to maximize gate cosmetics when applying these gating techniques to a variety of plastic resins, each with their own distinct characteristics. The size of the gate was determined by the type of plastic resin used. A flat diameter was established at the downstream end of a pinpoint gating tip. The size of the flat was determined by the volume of resin required to fill the part. The results of the study produced a technique that allows for the calculation of specific gate sizes. The technique can be used to achieve a minimal gate vestige while maintaining optimum flow performance. The Flat System technique is independent from tip design geometry, and can be used with most resins (filled or unfilled) without regard for material viscosity. A second study was initiated to determine the direct wear characteristics (shear effect) of pinpoint tips when processing plastic resins with abrasive fillers. In recent years, the industry has used harder steel alloys (carbide) for tip construction in an effort to combat tip erosion (wear). The second study resulted in a new Non-Turbulent" design that maintains laminar flow along the pinpoint tip. The new design minimizes shear that is produced by "turbulence rather than trying to resist it. This allows for tips made of softer steel alloys with increased life expectancy. Applying these new concepts to pinpoint tip construction results in improved molded part quality, improved gate cosmetics and reduced tip maintenance requirements.
A rigid PVC formulation was optimized for processing window and cost using sequential simplex techniques in combination with desirability functions. This optimization was performed on seven of the ten ingredients from a 'standard' siding compound with a relatively limited number of experiments. The processing window contour mapping technique was used to evaluate the effects of formulation changes. This was combined with the formulation cost using desirability functions to give an overall response for the simplex to optimize. The basic mechanics of sequential simplex and desirability functions will be described along with the results of the optimization.
In terms of the process sequence, laser butt welding corresponds to contactless heated tool welding. The difference lies in the heating phase in which the joining zones of the semi-finished products are periodically scanned by an Nd:YAG-laser beam at a high speed (Fig. 1). Tests carried out with laser butt welds with a meltpool, in which the joining zone is plasticised more deeply in the middle than in the outer areas, have shown parameter-independent high weld strengths over a wide range of heating time and joining displacement. Welds without a meltpool, however, showed short-time welding factors of 1. The reason for this strength behavior in contrast to heated tool and radiant heater welding must be seen in the temperature distribution in the joining zone. Different cooling processes as well as the state of internal stresses may provide an explanation for this.
CAE applied to injection molding is a relatively well known technology, which dates back to the early 80's. Its use in simultaneous engineering design is, in principle, recognized as one of the key factors for optimizing the quality of new products with the highly sought after goal of reducing the time-to-market. In spite of its potential, the use of this technology is far from being widely accepted in all cases where it can prove advantageous. The paper identifies the problems at the root of this situation and focuses on the likely evolution of the mold making industry, with particular attention to the make-or-buy decision regarding the engineering of part design prior to mold construction.
The shear and extensional rheology of three polyethylenes(PE's) synthesized using metallocene catalysts are compared. One of the PE's is linear i.e. no long-chain branches (LCB), while the other two have different amounts of long chain branching. The shear viscosity of the linear PE is reflective of the narrow molecular weight distribution of metallocene catalyzed PE's while the apparently branched PE's exhibit a higher viscosity and an earlier onset of shear thinning. The linear polymer exhibited lower activation energy than the branched PE with similar MW. The linear PE does not show stress-strain hyesteresis while the branched polymer does. All of them show supercooling behavior.
Film casting is one of the major commercial film manufacturing processes. Although various investigators have studied the process, no comprehensive set of data is available. In this study, film casting experiments of a LDPE polymer melt are conducted. The rheological properties of the melt, the film tension, the velocity profile, and the film width profile due to necking in will be presented. The thickness profile of the solidified film and the edge bead profile will also be reported. These experimental data will be useful for process analysis and verification of film casting simulation.
The curing process of an epoxy-fiber composite prepreg is a multistep process involving polymerization, gelation, crosslinking, and vitrification. Optimization of industrial processing requires knowledge of how each step is affected by time and temperature. This is usually facilitated by construction of a time-temperaturetransformation (TTT) diagram.1,2,3 Since the overall epoxy conversion reaction is exothermic, the rate and degree of conversion can be studied isothermally using differential scanning calorimetry (DSC), by comparing the change in enthalpy with the total change in enthalpy of the reaction4. An alternative method for determining the degree of conversion is by measuring the shift in Tg between Tg0 and Tg?, which will be proportional to the degree of conversion.3 The Tg can be measured by a variety of techniques, the most common being DSC, dynamic mechanical analysis (DMA) and thermomechanical analysis (TMA).5 Although DSC can detect both exothermic change and Tg, the two events are displayed on one signal and the two events are often found to overlap, making both signals difficult to quantify. Dynamic DSC allows the separation of reversing, in-phase events like glass transitions, from non-reversing, out-of-phase events like curing and enthalpic relaxations.6-12 However, both enthalpic change and Tg shift are unable to detect the gelation point, since it is not a rate effect. They can detect vitrification, since a drop in the rate of conversion occurs at this point. Gelation, being a molecular weight effect, is only seen in viscosity or chain mobility studies. The two most common techniques for determination of the gelation point are DMA (or rheology) and dielectric analysis (DEA). There are a variety of DMA techniques available for measuring the modulus and viscosity of epoxies, the most common being torsional braid analysis (TBA), parallel plate (or cone and plate), and three point bending. Several methods, most commonly DSC and DMA, can detect vitrif
The effects of polypropylene type, impact modifier type and level, talc filler, and injection speed on the properties of TPO blends were examined. Polypropylene impact copolymers drastically reduced stiffness while increasing impact strength. Talc significantly increased stiffness, but decreased impact strength. Higher molecular weight polypropylene homopolymer produced smaller decreases in tensile modulus, elongation, and impact strength. Increasing the amount of impact modifier slightly increased moduli, but decreased impact strength. The impact modifier type only influenced impact strength. Injection speed had no significant effects on the bulk properties of the blends.
For encapsulating solenoids, sensors, motor components and most recently integrated circuit (IC) modules, manufacturers are increasingly choosing engineering thermoplastics and injection molding technology over traditional thermoset resins and processing methods. After reviewing the cost and performance advantages of thermoplastic encapsulation technology, this paper reports on recent advances that are taking the technology into new areas. The advances include improved adhesion between encapsulated object and the encapsulating plastic, new coils that can withstand high voltage surges and the encapsulation of electronic circuitry to produce new kinds of speed sensors and novel devices for data storage and information retrieval.
A new technique has been developed allowing the quantification of self-diffusion and mutual diffusion at polymer/polymer interfaces using rheometry. The technique consists of measuring the dynamic moduli as a function of time for a multilayer sandwich-like assembly in molten state. The technique was tested on PS/PS and PS/PVME systems sheared in oscillatory mode under small amplitudes of deformation for different times of welding. Based on the reptation and double reptation theories [1,2], an analytical expression for the self-diffusion and mutual diffusion coefficients as a function of polymer rheological material functions was derived.
A critical issue for extruded polymer products is the up of these processes benefit from a complete knowledge effect of residence time, thermal history, and shear history of residence time distribution. on the physical properties of the extrusion product. Unfortunately, residence time data are rarely used in the In this report, a simple technique for measuring design and scale-up of compounded products. A reason residence time distributions in polymer processing for this is the time, complexity, and specialized equipment equipment is introduced. The residence time measurement required to generate these data. In this work, the literature technique was illustrated on a lab scale twin-screw and discuss a quick, simple technique for collecting extruder, but can be used equally well to characterize residence time distribution data are reviewed. A flows in laboratory or production scale single-screw colorimeter, of the variety found in most plastics lab, is extruders, injection molding machines, and other polymer used to measure the color of the pelletized extrudate.
We have used an optical fiber sensor for in-situ monitoring of product shrinkage during injection molding. The sensor, consisting of a bundle of optical fibers with a sapphire window at its end, is positioned in the ejector pin channel of the mold so that the sapphire window sits flush with the inside cavity wall. When the molded product shrinks, it separates from the wall and sapphire window, and establishes the geometry of a Fabry-Perot interferometer. During the molding of polystyrene, polypropylene and polyethylene, we observed optical interference fringes, and by counting fringes, a measurement of shrinkage was made.
The growing needs of the electronics and computer industries for plastic enclosures capable of providing electromagnetic interference (EMI) shielding can be met by molding enclosures from inherently shielding plastics. Such commercial materials mostly consist of conductive fibers in an electromagnetically inert polymer matrix. Surface or volume resistivity measurement, widely used to characterize the EMI shielding effectiveness (SE) of highly conductive coatings, is inadequate for low and moderately filled systems: Resistivity, which only accounts for the fibers that create continuous, conducting paths in the material, is only a good indicator of the ability of the material to dissipate static charges. The determination of SE of filled systems is more difficult because EMI shielding involves the reflection and absorption (scattering) of electromagnetic waves passing through the material by each fiber in the plastic matrix. SE estimates based on resistivity measurements on planar carbon-filled Polycarbonate are compared with a direct determination of SE by measuring the attenuation of a TEM wave passing through the material.
This is an update of a paper written for the 1996 CAD RETEC. The original paper considered the effects three different Infrared reflecting black pigments have on weatherable R-PVC. They were evaluated both as individual pigments and when formulated in typical vinyl siding shades. The effects measured included: % infrared reflection, heat build-up properties, and weathering characteristics - 1 year South Florida. The paper will primarily focus on the three year South Florida weathering results and look further at the possible effect free Iron is having on the weathering performance. 1 Additionally, a new weathering study has been initiated to look at variations in both the pigments and the R-PVC compounds to more fully understand the interaction of all factors.
This work investigates the morphology of several mechanically alloyed (MA) polymer blends which have been shown to produce immiscible blends by conventional blending techniques. Solid binary blends of Vectra® B950 liquid crystalline polymer (LCP)/Polyetheretherketone (PEEK), LaRC-TPI® /PEEK, and Vectra® B950 LCP/LaRC® -TPI were produced via mechanical alloying in a vibratory ball mill at ambient temperature. Processing similar blends at cryogenic temperatures will be completed in the near future. The thermal properties of these blends were investigated, and a morphology study of the blends in both powder and film form is ongoing.
No single rheological model is capable of reasonable prediction of observed behavior in cases where shear and extensional flows exit and neither can be neglected. Cogswell's approach was used to determine shear and extensional viscosities using the end-pressure drop method. The data was fitted by the Bird-Carreau model to predict shear and extensional viscosities. An expression for extensional viscosity is postulated based on shear viscosity plus only one other parameter. Determination of all parameters using the converging cone capillary rheometer is demonstrated for two common polymers. The model prediction agrees well with isothermal experimental data. For the first time, to our knowledge, a simple model for extensional viscosity that agrees with experimental data is presented, useful for engineering purposes.
The recyclability of any thermoplastic will be influenced by a large number of variables. One factor that influences recyclability of a thermoplastic is the material formulation itself. This is particularly true when additives such as reinforcements are incorporated into the base resin. Reinforcements such as glass fiber are widely used to enhance the stiffness, dimensional stability and elevated temperature capabilities of thermoplastics. It could be said that these reinforced thermoplastics are somewhat less recyclable than their neat counterparts due to the fiber degradation that occurs during processing and regranulation. Mineral filled thermoplastics can be an alternative to reinforced thermoplastics in some of these applications. While mineral filled compounds are not equivalent to the fiber reinforced formulations, they are more recyclable since minerals tend to retain there physical form during processing and regranulation. In this study, the effect of recycle history on the properties of neat, mineral filled, reinforced, and fiber I mineral hybrid nylon 6 has been evaluated. The neat, mineral, and hybrid materials have been shown to exhibit better property retention than the glass reinforced nylon when subjected to multiple recycle histories.
A highly accurate numerical technique for the simulation of resin infusion in composite preforms using a transient, 3-D, non-isothermal, two-phase analysis is presented. An adaptive finite element method is used to solve the equations. The uniqueness of the present approach is that resin infusion is modeled as a weakly compressible, two-phase flow in a porous media. VARTM processes can be solved by accurately specifying air properties based on the vacuum conditions. The results presented indicate the usefulness of the model.
Blends of Polypropylene (PP) and a PLC (Polymer Liquid Crystal) with the formula PET/ 0.6 PHB, where PET= poly(ethylene terepthalate) and PHB=p-hydroxybenzoic acid, 0.6 is the mole fraction of the liquid crystalline PHB, were used as interlayers between layers of PP comingled with glass fibers. 4-point bending tests were performed following the ASTM D790 standard. The results indicate that replacing a glass mat layer by PP+PLC blend layer can provide superior mechanical property of the composite at a lower weight. The performance also depends on the location of the blend layers with respect to the outer layers of the composite.
Amorphous poly(ether ether ketone)(PEEK) plasticizes and/or crystallizes in the presence of common organic solvents. In-situ Dynamic Mechanical Analysis techniques have been employed to study the effects of solvent-induced crystallization on the storage modulus (stiffness) of amorphous PEEK. Preliminary results indicate that the Tg of PEEK is depressed below 20°C allowing for room temperature crystallization. Real-time immersion at room temperature shows the competing effects of plasticization and crystallization on the mechanical response of PEEK.
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ANTEC 2016 - Indianapolis, Indiana, USA May 23-25, 2016. [On-line].
Society of Plastics Engineers
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