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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Drying: A Closer Look
This paper will discuss the adverse effect on viscosity when polymers are excessively dried. Many processors are concerned exclusively with excessive moisture and give little consideration to the permanent detrimental effects from over-drying. As part size gets smaller in many applications, dryer throughput is lower. The result is extended exposure to the drying process. Thus, the viscosity of the material is increased and permanent loss of material properties occurs. This effect was observed as an actual manufacturing problem.
Blends of Poly(ethene-co-octene) Elastomers
Blends of polystyrene (PS), and polymethyl methacrylate (PMMA) with poly(ethene-co-octene) elastomer (POE) were investigated. The experiments were performed in a counter-rotating reactive twin screw extruder. The evaluation of mechanical properties and morphology were completed to determine stress-strain behavior, impact, domain size, and interfacial adhesion for the blends. The results of tensile strength, modulus of elasticity, and impact properties for the blends show that incompatible and synergistic behavior over a wide range. Morphology studies using scanning electron microscopy (SEM) indicate that the domain sizes of rubber phase in the blends are rang from 1 to 15 ?m and a variety of interfacial adhesion behavior. All the blends displayed phase-separated. The blends of polystyrene / poly(ethene-co-octene) elastomer with compatibilization illustrate that not only the domain size of the phase of elastomer can be reduced but also the interfacial adhesion can be enhanced. The mechanical properties of the blends using compatibilization , such as impact strength and tensile strength, can be improved.
Melt Temperature Considerations for Extrusion
Melt temperature measurement and control are important to understand when optimizing or studying extrusion systems. This extrusion parameter is not as simple to measure as it may seem. This discussion will include the devices that are typically used for the measurement and control of melt temperature and the methods of employing the devices to get meaningful results. Accurately knowing the melt temperature level of a given system allows an accurate comparator for possible improved equipment design. Adjusting melt temperature via altering machine parameters for optimized extrusion results requires that the measured value is a meaningful number. A general discussion of melt temperature in extrusion will be carried out for this tutorial and the measurement and control of this important parameter will be discussed.
Polydiacetelene Fiber Optic Pressure Sensors
Micro-opto-electro-mechanical sensors (MOEMS), where optics are integrated with micro-electro-mechanical systems (MEMS), are logical candidates for sensing flow, temperature and pressure in harsh environments. MOEMS offers small size, high frequency response, immunity to electromagnetic interference, and resistance to degradation from exposure to harsh environments. However, interfacing MEMS with fiber optics is quite challenging. Here we discuss the possibility of coating the fiber with a pressure sensitive polymer (polydiacetelene) to increase its coupling strength to a MEMS' deformable diaphragm. Interestingly, we noticed that the coated fiber, in this case, was itself sensitive to hydrostatic pressure and could be directly used as a pressure sensor. The sensitivity, reproducibility and the structure of this simple and inexpensive structure are discussed in this work.
Fiber-Optic Electric Field Sensors Using Polymer-Dispersed Liquid Crystal Coatings and Evanescent-Field Interactions
A simple evanescent-field fiber- optic electric-field sensor is reported. The sensor is constructed by coating the exposed fiber-optic core with a polymer-dispersed liquid crystal (PDLC). The effective refractive index of the liquid-crystal polymeric coating [poly(methyl methacrylate)(PMMA)/E7] has a large dependence on the direction and the magnitude of an any electric field present. This dependence was large enough to enable simple transmission measurements to detect the presence of an applied electric field. By coating a PDLC film onto the exposed core of the optical fibers, we are able to detect an electric field. The sensors showed good sensitivity and reproducibility and a polarity dependence was observed. The time response of the device is dominated by the RC time constant of the structure rather than the response of the PDLC and is approximately 3 minutes with 15-20 minute relaxation time. Using an electric circuit model of the device we also discuss how these response times can be improved by many orders of magnitude.
The Effect of Molecular Structure on the Extensional Melt Rheology of Conventional and Metallocene Polyethylenes
Extensional melt rheology and processing characteristics of conventional high pressure low density polyethylene (LDPE) and Ziegler-Natta linear low density polyethylenes (LLDPE) are compared with both narrow and broad molecular weight distribution (MWD), long chain branched (LCB) metallocene polyethylenes. The effects of MWD and LCB on the melt behaviour of these different types of polymers will be presented in terms of their dynamic linear viscosities and their strain-hardening behaviour from transient tensile stress growth experiments. Film processability properties will also be discussed.
Fluorescence Based Temperature Measurements and Applications to Real-Time Polymer Processing
Fluorescent dyes doped into polymer resins are used to monitor the true resin temperature during processing. Two examples of real-time process monitoring are presented: first, the effects of shear heating during extrusion are measured and second, the effects of poor temperature control during extrusion are observed.
Transient Viscoelastic Simulation of Coextrusion Flows in Coat-Hanger Dies
A 2-D transient finite element model of two-layer coextrusion has been developed with the Criminale-Erikson- Filbey (CEF) constitutive equation to study the problem of interfacial instability. Experiments were done with LDPE 132I™ (Dow Chemical Co.) in a coat-hanger die using two extruders, under well controlled temperature and flow conditions, where stable and unstable interface profiles were observed. Cross-sections of the frozen heel were taken and compared to transient simulations by quantitatively examining the position of the interface between the two layers.
Practical Guidelines for Predicting Steady State Cure Time during Sheet Molding Compound (SMC) Compression Molding
The longest part of the molding cycle during SMC compression molding is the curing stage. Thus it is extremely important to be able to predict its duration to estimate the cost of manufacturing a part. To avoid blistering, the cure time must be increased with consecutive moldings until a steady state value is achieved (tcss). In this paper, we present a series of charts that can be used to estimate the steady state cure time for new parts. These values can then be used to estimate the manufacturing cost.
Method to Estimate Vibration Behavior of Fiber Reinforced Thermoplastic Parts
Until now it has been difficult to estimate quantitatively the vibration behavior of FRTP parts using computer simulation. The reason was that the conventional simulation model did not express appropriately the damping properties of vibration (dependence on the temperature, amplitude, frequency and moisture content) and the orthotropic Young's modulus. Therefore, a new simulation model was proposed through measuring the damping factor of the specimen and the experimental modal analysis of the parts. Based on this model, the simulation result of the realistic vibration behavior on the FR-nylon product (e.g. air intake manifold) proved to be in good agreement with the experiment.
Crystalline Transitions in Nylon/Clay Nanocomposites
Nylon 6-clay hybrid is a molecular composite of Nylon 6 and uniformly dispersed silicate monolayers of synthesized saponite. Nylon 6 has two crystalline forms, ? and ?. The a phase is the thermodynamically most stable crystalline form but the ? phase is not. In this study, the nylon 6/synthesized saponite has prepared by the intercalation of e-caprolactam and then exfoliating the layered synthetic saponite by subsequent polymerization. The DSC thermal analysis and X-ray diffraction methods were used to investigate the crystal structure change of nylon 6/synthesized saponite. The results indicate the presence of crystalline transition in nylon 6 nanocomposites. The effect of thermal annealing on the crystalline structure of nylon 6 nanocomposites in the range between Tg and Tm is also discussed.
Characterization of the Interfacial Regions in Multilayer Coatings by NEXAFS Microscopy
Characterization of polymer interfaces is an important analytical need in many areas of technology. Many techniques, that provide the requisite spatial resolution, provide limited quantitative chemical information. On the other hand, techniques, that provide the desired level of quantitative chemical information, have limited spatial resolution. A relatively new analytical tool, Near-Edge X-ray Absorption Fine Structure (NEXAFS) microscopy [1- 4], provides a unique combination of chemical specificity and spatial resolution that is particularly well-suited for characterization of interfaces in polymer coating, blends and composites. In this paper, the application of NEXAFS microscopy to a multilayer polymer coating is discussed.
Rheological and Blown Film Characterization of Binary Blends of Metallocene-Catalyzed LLDPEs
The advent of metallocene catalyst technology has created several opportunities in the worldwide packaging film marketplace. In this work, we explore the effects of blending two metallocene-catalyzed LLDPEs of reasonably differing molecular weights. Specifically, the shear rheology, quiescent and shear-induced crystallization characteristics, and blown film performance were investigated as a function of blend composition. The presence of small amounts of longer molecules was found to have significant effects on the shear-induced crystallization kinetics and blown film orientation of the blends; this was explained in terms of an increasing number of extended chain nuclei for crystallization with increasing molecular weight. Lastly, the biaxial orientation features in the crystalline and non-crystalline phases of the blend blown films were also characterized and used in explaining the Elmendorf tear and dart impact performance of the blown films.
High Performance Rigid Flexible Combinations Made of Thermoplastic and Liquid Silicone Rubber
The injection molding of LSR represents a cost-efficient process for the production of high quality rubber parts for technical applications. Due to excellent material properties at extreme temperatures silicone rubbers offer various advantages for the production of soft/rigid combinations in comparison to thermoplastic elastomers. A new kind of LSR is presented which exhibits excellent adhesion properties to engineering thermoplastics. The process and the adhesion mechanism is designed in a way that no mold coating is required. A systematic analysis of the injection molding process points out suitable material combinations and indicates the influence of process parameters on adhesion strength.
Welding of Plastics: Introduction into Heating by Radiation
For welding of plastics, various procedures of heat transfer are presently in use. Non-contact heating by radiation allows heating e.g. without contamination of a heated tool and makes heating faster by volume-absorption of the material. Presently infra-red lamps and infra-red laser beams are in use for welding of plastics. This paper wants to give an introduction into the physical principles of heating by infra-red radiation, wants to divide between surface and volume absorption of different materials and wants to give a survey about the advantages and disadvantages of infra-red lamps and lasers.
Melt Rheological Properties of Natural Fiber-Reinforced Polypropylene
The melt viscosities and mechanical properties of 3 different natural fiber-polypropylene composites were investigated. Coir (coconut), jute, and kenaf fibers were compounded with polypropylene at 30% by weight content. A capillary rheometer was used to evaluate melt viscosity. The power-law model parameters are reported over a shear rate range between 100 to 1000 s-1. Effects on melt viscosity with the use of a coupling agent and different fiber types were also evaluated.
Injection Molding Tie Bar Extension Measurements via Strain Gauge Collars for Optimized Processing
The measurement of the clamping force in injection molding can give valuable insight for optimization of the process. Problems in production are often related to the level and the distribution of the clamping force. A novel measuring system that employs strain gauges that are clamped around the tie bars make a precise measuring method applicable in a rugged industrial environment. It was the objective of this work to evaluate the performance of the device in practical use.
Dielectric Relaxation Spectroscopy of Reactive Network-Forming Polymers
Dipole dynamics in network-forming polymers were investigated by broadband dielectric relaxation spectroscopy (DRS). The changes in reorientational dynamics during the advancement of reactions were used to (1) describe the molecular origin of various relaxation processes (?,?), (2) describe the dynamics in terms of the location and intensity of relaxation spectrum, and (3) advance an interpretation of network dynamics in terms of intermolecular cooperativity. The chemical state of network at various stages of cure was identified by simultaneous DRS and remote fiber-optic FTIR.
Simulation of the Filling and Curing Phase in Injection Molding of Liquid Silicone Rubber (LSR)
The injection molding of Liquid Silicone Rubber (LSR) represents a cost-efficient process for the production of high quality rubber parts. Due to the extreme thermal conditions in the mold and the very low material viscosity a precise subvolumetric filling of the cavity is required to avoid flash formation. Modeling flow properties, curing characteristics and as the pvT-behavior creates the basis for an unified simulation of the injection molding process. The implementation of these models into a process simulation software makes it possible to calculate the filling phase considering a subvolumetric filling and to simulate the course of cavity pressure during the heating phase.
Thin-Wall Injection Molding
A precision monitoring system for high speed thin-wall injection molding machine was build so that hydraulic pressure, nozzle pressure, injection speed, filling to packing switchover and cavity pressures can be monitored during the whole molding process. Tensile test specimens of 2.5 mm, 1.2 mm, 1 mm and 0.8 mm thick were molded. It was found that as part becomes thinner the pressure prediction of CAE simulation gets worse and the errors range from about 50% to more than 100%. Filling time, proper filling to packing switchover, gate size, holding pressure and mold temperature were found to be the critical factors to successful molding and part quality. When part becomes thinner, residual stress is higher and affects part strength more significantly. When molding industrial thin parts, the residual stress concentrates around gate area, bosses and area where part thickness varies. Thickness reduction for the housing of computer dictionary can be achieved without great reduction in structural performance when localized thinning design is implemented.
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