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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In-Situ Monitoring of Product Shrinkage during Injection Molding Using an Optical Sensor
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.
EMI Shielding Effectiveness of Fiber-Filled Plastics - Material Testing Issues
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.
An Update on the Effect of Black Pigment Selection on Weatherable R-PVC
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.
Mechanical Alloying of High Performance Polymer Blends
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.
Predicting Pressure Drop in Mixed Shear and Extensional Flow Using Converging Cone Capillary Rheology
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 Effect of Recycle History on the Performance of Neat, Filled, and Reinforced Nylon 6
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.
Polymer Liquid Crystal (PLC) + Polypropylene Interlayers in Polypropylene + Glass Fiber Composites: Mechanical Properties
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.
Rapid Tooling: A Study of Different Cooling Techniques for Mold Inserts Used in the Direct AIM (Aces Injection Molding) Process
Direct AIM (ACES Injection Molding) is a rapid tooling process. In this process, shells of the core and the cavity inserts are built on the stereolithography machine. These shells are fitted into mold plates and backfilled with a supporting material. These mold inserts are then used to produce injection-molded prototype parts in the desired resin. The epoxy shell in the Direct AIM mold inserts has a glass transition temperature of 62°C (140°F). Plastic melt that is injected into the space between these mold inserts has a melt temperature of about 232°C (450°F). In order to maintain structural rigidity of the epoxy surface of these mold inserts, it is very important to cool the inserts quickly and evenly to below the glass transition temperature. The effect of epoxy shell thickness, the effect of different backfill materials and the effect of designed-in conformal cooling lines on the cooling ability of the Direct AIM mold inserts was studied. The study was divided into three sections: C-Mold analysis, Oil Bath experiments and Injection Molding. It was found that a thin epoxy shell improved the heat transfer from the shell surface to the backfill material. Also, it was found that the mold inserts backfilled with the low-melt metal alloy cooled faster than the mold inserts backfilled with aluminum powder filled epoxy. The cooling capability of the mold inserts with conformal cooling channels was found to be higher than the metal backfilled 0.100-inch thickness tool and slower than the metal backfilled 0.050-inch thickness mold insert. The results also showed that the addition of aluminum powder as a filler (39% by weight) did not significantly increase the thermal conductivity of the epoxy backfill material. However, the addition of carbon powder (12% by weight) to the epoxy backfill improved the heat transfer properties of this backfill material.
Biodegradable Bags Comparative Performance Study: Multi-Tiered Approach to Evaluating the Compostability of Plastic Materials
Modern municipal waste disposal strategies involve the development of integrated waste management systems in which the waste is disposed of in a safe, efficient, and cost effective manner. Such systems require alternative methods of collecting, handling, and processing solid waste according to the unique characteristics of the various fractions (ASTM, 1996). This includes composting of the biodegradable fraction of the organic waste including paper, food & yard waste, and new biodegradable" plastics. Indeed aerobic composting represents an attractive alternative to the disposal of solid wastes in landfills. Composting by biologically mediated oxidative decomposition produces highly stable organic matter that can be used for land applications or horticulture. However the degradation of plastics within a compost can affect the decomposition of materials enclosed in the plastic and the resulting composition and appearance of the composted material. From an environmental perspective biodegradable polymers offer an attractive alternative to traditional petroleum-based non-biodegradable polymers; i.e. they need not be landfilled will re-enter normal geochemical (natural) cycles with timeand many are derived from renewable (agricultural) resources. Nevertheless as a new generation of biodegradable products enters the marketplace questions regarding the long-term fate of these materials in the environment and their effects on the environment are being asked by industry government and consumer groups. In particular: how do specific materials degrade in different compost environments? and how well do standardized laboratory scale biodegradation tests predict a product's biodegradability in an actual full-scale compost environment?"
Biodegradable Bags Comparative Performance Study: Multi-Tiered Approach to Evaluating the Compostability of Plastic Materials
Modern municipal waste disposal strategies involve the development of integrated waste management systems in which the waste is disposed of in a safe, efficient, and cost effective manner. Such systems require alternative methods of collecting, handling, and processing solid waste according to the unique characteristics of the various fractions (ASTM, 1996). This includes composting of the biodegradable fraction of the organic waste including paper, food & yard waste, and new biodegradable" plastics. Indeed aerobic composting represents an attractive alternative to the disposal of solid wastes in landfills. Composting by biologically mediated oxidative decomposition produces highly stable organic matter that can be used for land applications or horticulture. However the degradation of plastics within a compost can affect the decomposition of materials enclosed in the plastic and the resulting composition and appearance of the composted material. From an environmental perspectivebiodegradable polymers offer an attractive alternative to traditional petroleum-based non-biodegradable polymers; i.e. they need not be landfilled will re-enter normal geochemical (natural) cycles with time and many are derived from renewable (agricultural) resources. Nevertheless as a new generation of biodegradable products enters the marketplacequestions regarding the long-term fate of these materials in the environment and their effects on the environment are being asked by industry governmentand consumer groups. In particular: how do specific materials degrade in different compost environments? and how well do standardized laboratory scale biodegradation tests predict a product's biodegradability in an actual full-scale compost environment?"
A New Approach for in-Mold Finishing: The Valyi Surface Finishing/Compression Molding Process
The Valyi SFC molding process for surface finishing/compression molding (SFC) provides an economical route to molding and Class A finishing of large thermoplastic parts in one step. In the Valyi Process, decorative film or fabric is placed over a mold cavity in a press. Plastic melt is then deposited onto the film which subsequently heats the film to a formable temperature. Positive air pressure may be supplied to support the film/molten plastic. The press is then closed to form the final finished part. The process is similar to the textile back molding process. The Valyi Process uses much lower pressures than conventional injection molding. Molding (cavity) pressures for the Valyi Process are <<10 MPa (1450 psi) as compared to conventional injection molding which is typically >30 MPa (4350 psi). The in-mold lamination of paint film achieves the paint appearance and protection without the environmental and cost impact of conventional painting. Also, heating the film using the heat from the deposited melt eliminates the pre-heating step in the in-mold injection molding process. This paper describes the Valyi SFC Molding Process and reveals the advantages such as the mechanical performance of the part, reduction in cost and reduction in paint pollution, which can be achieved over the conventional injection molding - painting process.
Dynamic Mechanical Thermal Analysis (DMTA) of Barrier Materials Immersed in Automotive Fuel Components
EC legislation has ordered vehicular hydrocarbon emissions to be drastically reduced by the year 2000. New polymeric materials must be used to manufacture fuel storage / delivery components. Such materials must offer increased barrier performance without loss of mechanical properties. Samples of poly butylene terephthalate (PBT), two types of poly vinylidene fluoride (PVdF) and THV, a terpolymer of tetrafluoro ethylene, hexafluoro propylene and vinylidene fluoride, were immersed in pure methanol, ethanol and toluene. The effect of the degree of solvation on the glass transition temperature (Tg) and the storage modulus (E') of each material were measured using dynamic mechanical thermal analysis (DMTA). Significant changes in Tg and E' were evident in each case, but behavioural differences were apparent between different polymers in a given solvent, and also for a given polymer in different solvents. In all cases, the Arrhenius activation energy changed on solvation.
Determination of Optimum Extrusion Conditions for Multilayer, Low Emission Plastic Fuel Line Systems Using Dual Capillay Rheometer Techniques
Multilayer co-extrusion of plastics is fast becoming a very cost effective method of improving the barrier properties of plastic products. In this process individual polymers are melted and conveyed by separate extrusion systems, into a common distribution block and through a forming die where the polymer melts merge to form an integral multilayer structure. Many of these polymers do not form a mutual bond in the melt and so specially formulated tie layers have been developed in order to facilitate melt bonding and so prevent delamination. Multilayer polymer tube structures have recently been developed for use in automotive fuel lines. These multilayer structures are proving difficult to extrude because of their widely different temperature profiles required during extrusion, and the fact that all the melts enter a common die which can only be maintained at one particular temperature. The melt rheological characteristics of a range of commercially available barrier materials, polyvinylidene fluoride (PVDF), a terpolymer of vinylidene fluoride, tetrafluoroethylene and hexafluoropropylene (THV), plasticised Nylons and tie layer materials have been studied using Dual Capillary Rheometric techniques. The relative change in shear viscosity with temperature, up to 270°C and shear rates up to 103 sec-1 have been investigated, for these materials, in order to determine optimum extrusion parameters during manufacture. The findings are confirmed by pilot plant tube extrusion trials using various multilayer structures. Arrhenius flow activation energies are also reported.
The Effect of Fuel Components and Standard Test Fuels on the Mechanical Properties and Glass Transition Temperature of Polymers Used in Mult-Layer Fuel Line Tubing
With the advent of more stringent legislation for fuel and fuel vapor emissions from vehicles, it has been necessary to introduce a barrier polymer into the fuel line as a means of reducing emissions. This paper investigates the changes in mechanical properties, such as tensile modulus, of a range of plasticized nylons, tie layer polymer systems and fluoropolymers which were immersed in various mixtures of fuel components and standard fuels at a temperature of 25°C. The percentage mass uptake and extent of swelling were also determined in addition to changes in glass transition temperature up to a period of 31 weeks.
Reactive Blends of Polyvinyl Chloride and Polyurethane
Effects of PVC resin and PVC stabilizer on thermoplastic polyurethane (TPU) polymerization kinetics are studied using DSC and adiabatic temperature rise measurements. Addition of PVC results in partial absorption of the unpolymerized polyester component of the TPU mixture resulting and lowers the rate of reaction. Thermal characterization of melt and reactive blends of PVC and TPU showed one glass transition indicating miscibility. However, SEM revealed that the PVC/TPU melt blend contained small PVC primary particulates dispersed in the TPU matrix. The PVC/TPU reaction blend exhibited no observable PVC particulates under the same magnification.
Influence of a Surfactant Additive on the Crystallization of Syndiotactic Polystyrene and Sulfonated Polystyrene
Syndiotactic polystyrene (sPS) was mixed with dodecylbenzene sodium sulfonate (DBSNa), benzene sodium sulfonate (BSNa) and dodecylbenzene (DB), to investigate the influence of these additives on the crystallization behavior of sPS. The crystallization of sPS containing DBSNa was significantly slower than that of sPS containing DB or BSNa. Since SAXS investigations indicated the presence of DBSNa aggregates within sPS/DBSNa samples, the observed decrease in the rate of crystallization is attributed to a slow expulsion of the bulky DBSNa aggregates from the crystalline growth front. In comparison, sulfonated syndiotactic polystyrene (SsPS)/DBSNa mixtures crystallized faster than SsPS, due to a disruption of the electrostatic crosslinks by DBSNa.
Flow Instability Reduction of PP through Blending of EVA
Flow instabilities are often encountered during extrusion of high molecular weight Polypropylene homopolymers. Traditional techniques of flow instability reduction such as addition of fluoropolymers or compatibilizers significantly increase the cost of the finished product. During this study it was found that blending small amounts of Poly (Ethyl Vinyl Acetate) EVA into the Polypropylene PP matrix eliminates melt fracture fonnation within a reasonable operating window, maintaining acceptable mechanical properties. A wide range of EVA concentrations was tested using capillary rheometry, microscopy and mechanical analysis. The acceptable operating window without instabilities was determined by analyzing the extrudate surface under the microscope.
Molecular Modeling Studies of the Molecular Components of Starch. I. an Atomistic Model of the Double Helical Structure of Amylose and Amylopectin
Starch is made of amylose and highly branched (amylopectin) ?-linked chains of D-anhydroglucose. A detailed atomistic model for the amylose and amylopectin components of starch was simulated using established molecular modeling methods. In particular, attention is paid to the formation of A and B amylose in the double helix configuration, and to the formation of the double helix configuration after the branch point in amylopectin. Molecular dynamics simulations are carried out over extended periods of time, and calculations suggest that the observed crystallographic parameters for the A and B forms of amylose can be reproduced with water molecules either inside the core of the double helix or with the core devoid of water. In both cases the strand repeat distance of ~2.14 nm is found. Models of the amylopectin macroscopic formation are described and speculation as to the molecular details of the amorphous high solvent and crystalline starch structure are made.
Use of a Hexafunctional Coupling Agent to Control Free Radical-Induced Molecular Weight Degradation during Reactive Processing of Polypropylene
Variable quantities of a hexafunctional coupling agent were reacted with polypropylene (PP) in a twin-screw extruder. An increase in the z-average molecular weight was observed, and attributed to the formation of PP crosslinks through the coupling agent, which tended to offset molecular weight degradation due to ?-scission. The mechanical properties and morphologies of the resultant extrudates were analyzed. Notched Izod impact and tensile strengths were enhanced over those of the control, which lacked added coupling agent. The presence of coupling agent crosslinks resulted in increased nucleation and growth rate during crystallization from the melt.
Fill Length Determination for a Non-Intermeshing Twin-Screw Extruder
This paper describes the effect screw speed and material throughput have on the filled regions in front of restrictive elements on a Non-Intermeshing Twin-Screw Extruder (NITSE). Fill length, operating conditions, material properties, and the pressure over the cylinders are all measured and compared to a model of pressu fill lengths can be predicted for a non-transparent barrel from geometric terms and material properties."re buildup in the screw elements of a NITSE. Experiments are performed over a range of operating conditions in a clear barrel ?0.8 NITSE. By determining the relationship between fill length and pressure across the cylinders
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