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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Melt Spinning of Syndiotactic Polypropylene: Structure Development and Implications for Oriented Crystallization
Stereoregular polypropylenes can be prepared using metallocene-based catalyst systems. The objective of this work is to investigate structure development during melt spinning of syndiotactic polypropylene. The fibers are well crystallized at low spinning speeds, but are only poorly crystallized at higher speeds. The helical nature of the preferred crystal form is responsible for the substantial differences in crystallization behavior of the syndiotactic PP compared to isotactic PP. Implications regarding crystallization kinetics in oriented systems with conformation-dependent crystallization are also addressed.
High Quality Flax Fibre Composites Manufactured by the Resin Transfer Moulding Process
In this work the use of high quality natural fibres as reinforcements was studied using the resin transfer moulding (RTM) processing technique. The fibres were unidirectional high quality ArcticFlax and the matrix was an epoxy resin. The mechanical properties of the composites were compared to conventional RTM manufactured glass fibre composites, traditionally retted UD-flax fibre composites and to the pure epoxy. The results from mechanical testing showed that the (50/50) high quality ArcticFlax/epoxy composite has a stiffness of about 40 GPa compared to the stiffness in pure epoxy of 3.2 GPa. The same composite has a tensile strength of 280 MPa compared to 80 MPa of the epoxy. RTM showed to be a suitable processing technique for natural fibre composites when high quality laminates are preferred.
Coextrusion Blow Molding with LCP
Because of their high barrier properties, high temperature capability, and resistance to chemicals, liquid crystal polymers (LCPs) are ideally suited for use in multilayer containers. This paper will describe a coextrusion die and process for orienting the LCP layer in a PET-tie-layer/LCP three-layer container with approximately 13 percent LCP, showing oxygen barrier properties over 10 times better than a PET container of equal volume and wall thickness. Low shrinkage after hot fill, and excellent resistance to flavor loss will also be demonstrated. The process is applicable to other thermoplastics with LCP, and applications for packaging of beverages, fragrances, solvents, and other chemicals will be discussed, along with comparison against alternative multilayer containers.
Relaxation Phenomena in Liquid Crystalline Epoxies
Liquid crystalline (LC) epoxies have been of great interest to academic and industrial communities because they combine the performance of epoxies with the anisotropic properties of LC polymers. In this study, we investigated the effect of structural changes on the frequency dependent dielectric relaxation in a series of aromatic thermotropic main chain LC epoxies by broadband dielectric relaxation spectroscopy and differential scanning calorimetry. Various polarization mechanisms were identified over a wide range of frequency and temperature. The molecular origin of these relaxations was assigned and dipole dynamics was described in terms of the location and intensity of relaxation spectrum.
Systemic Development Models of Polymer Mouldings and the Appropriate Injection Moulds
Many activities during the manufacturing of mouldings and the appropriate mould are carried out simultaneously. This proves the need to apply the basic principles of systemic technology theory to the development and production system of polymeric mouldings. The development of an appropriate mould for injection moulding can be regarded as a real sub-system of the development and production system of the mouldings. The planning of a systemic model in this case means defining of the exact sequence of activities during the mould development. Thus the guidelines for mould development are created, which can serve especially to inexperienced mould designers.
Joining of Nylon Based Plastic Components - Vibration and Hot Plate Welding Technologies
Previously we reported to SPE'96 the optimized mechanical performance of linear vibration welded nylon 6 and 66 butt joints. Under the optimized vibration welding conditions (amplitude, pressure, meltdown, thickness of interface), the tensile strength at the nylon butt joints was equal to or 14% higher than the tensile strength of the base polymer (matrix). H. Potente and A. Brubel presented to SPE'94 and SPE'98 an analysis of the welding performance in a family of amorphous and semi-crystalline thermoplastics including nylon 6 using hot-plate welding technologies. For hot-plate welded nylon 6 with a range of glass-fiber reinforcement from 0 to 40% (by weight), the tensile strength at the weld was 40-60% less compared to the tensile strength of the base polymer. We performed a comparative study of mechanical performance of welded nylon's butt joints. In this study we analyzed the efficiency of both widely used joining technologies: vibration welding and hot plate welding. Under the optimized hot plate welding conditions, tensile strength of both nylon 6 and 66 joints is close to or slightly higher than the tensile strength of the base polymers. Presented results will help plastic parts designers, material developers and manufacturers, by giving them alternatives when choosing types of nylon (6, 66, 66/6, 46, etc.) and welding technologies for a wide range of applications.
Direct Measurement of Slippage Induced by a Polymer Processing Additive
Flow profiles of a linear low density polyethylene (LLDPE) were measured in an optical slit die situated at the exit of a twin screw extruder. The velocities of tracer particles were measured as a function of position across the slit die at various flow rates. The results show that the presence of a PPA (Dyanmar) in the polymer melt induces slippage on the surfaces of the die. The occurrence of slippage indicates that the process improvements obtained with this high energy additive occur via migration to the polymer-metal surface and subsequent reduction in the effective friction" between the polymer and the wall."
Relaxation Processes in Polymer Networks by Dynamic Light Scattering and Dielectric Spectroscopy
Isothermal chemical reactions of network forming monomers or functional polymers produces a continuous increase in the systems Tg and the accompanying cooperative segmental relaxation time (? process). Both broad-band dipolar relaxation spectroscopy (DRS)-probing the ? process via dipolar reorientational mobility, and dynamic light scattering (DLS)-probing the ? process via correlation times of density fluctuations, were used to monitor the system in-situ (to our knowledge, the first study of its kind). An excellent agreement was found between DRS and DLS for the ? process characteristic parameters: relaxation time and KWW stretched exponential parameter (characterizing the relaxation breadth). It was concluded that the broadening of the ? process is due to a general phenomenon: the microscale heterogeneous nature of glass formers.
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) propose a methodology for evaluation of the kinetics of network formation, (3) describe the dynamics in terms of the location and intensity of relaxation spectrum, and (4) 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.
Binary Blends of Ziegler-Natta and Metallocene Catalyzed Polyethylenes: Rheological Properties
The rheological and morphological behaviors of three binary blends of polyethylenes regarding the melt index and density, one component made by Ziegler-Natta and the other by metallocene catalysts, have been investigated to elucidate miscibility and phase behavior. If the comonomer contents are similar, then the melt viscosity is weight average value, otherwise it shows different behavior: the FA+FM blend is miscible, but the RF+EN and RF+PL blends inform immiscible. The microtomed cutting surface indicates that all the blends are not homogenous regardless the density, melt index and cooling processes, and show banded spherulites.
Cure Monitoring of Phenolic Resins Using Dynamic Rotational Rheometry
The mechanical responses of two phenolic thermoset resins during curing were monitored as a function of time and temperature using dynamic rotational rheometry. The tangent of the phase angle tan ?, the ratio of elastic to viscous modulus, was used to characterize the reactions because of foaming and emission of by-products. For resole phenolic resins, gelation was interpreted as the cross-over of the storage and loss moduli, i.e. tan ?=1. This assumption proved to be reasonable, as activation energies derived thereby agreed with those found using in-line ultrasonic measurements. The gelation time of the novolac resin was successively assumed to be the first occurrence of tan ?=1 or the minimum of tan ?. The activation energies found using these assumptions were both significantly higher than those found using ultrasonic measurements. Resolution of this discrepancy may require a knowledge of the influence of the foam structure on tan ?.
The Analytical Models for the Warpage of Integrated Circuit Devices
This paper studies thin elongated packaging for large size silicon chips and its warpage caused by temperature changes during the packaging process. An integrated circuit device is composed of several materials with various different properties, of which, differences in the thermal expansion coefficients of the materials poses the largest influence on the resulting product. In the course of IC encapsulation, as the product goes through numerous processes, temperature will rise and fall and causes the composing materials to experience repeated thermal expansion and shrinkage. Since the material layers are under perfect adhesion, if two neighboring materials have different thermal expansion coefficients, the stress from the temperature change will cause the product to deform. Current IC warpage analytical models researches base mainly on Dr. Suhir's theory of the compatibility conditions for the interfacial strains. The analytical model in Dr. Suhir's theory is constructed upon four layers of two-dimensional materials. There are two sections in the model: one is the section comprising the silicon chip and one is the section without the silicon chip. The latter section is only roughly simulated with a single homogenous material and is unable to correctly simulate the geometric shape of an actual encapsulation component. This paper, extends Dr. Suhir's analytical model to possessing unlimited layers and consisting of many sections, thus not only increases the completeness and correctness of the analysis results but also resolves the problem of accommodating models with different geometric shapes.
Rapid Prototyping of Small Injection Molded Plastic Components for Critical Medical Devices
Mallinckrodt Inc is an international company serving markets in healthcare and specialty chemicals. The Advanced Process Development Lab supports the Critical Care Division. It is staffed by four individuals who each contribute a particular specialty. • The designer is an expert in the use of solid modeler software and is responsible for the engineering design and solid modeling. • The PLC/CNC programmer is a computer science graduate, and is responsible for programming automated machinery as well as operation of the CNC equipment. • The Tool and Die Maker has over 35 years experience, and is responsible for all conventional machining. • The Plastics Processing Technician has over 25 years experience in a wide range of plastics processing, and is responsible for establishing parameters for all new tooling and dies, as well as developing processes for new equipment.
In-Line Dielectric Sensor for Chemical Composition Measurements in Molten Polymers
Resin producers and compounders use additives to extend and modify the properties of their polymers, and they increasingly use rugged dielectric sensors to measure additive concentrations in-line for automatic process control and quality monitoring. They need to control the concentrations of the additives they use as processing aids and to modify properties in plastics, elastomers, fibers, adhesives and coatings. This helps them meet demanding product quality specifications and ensure strong prices and market shares. Theory and experiments described here indicate that dielectric measurements in melts can quantitatively determine individual or total additive concentrations with an accuracy that depends on electrical contrast and can exceed 0.1 volume percent (1000 ppm) with polymers and compounds having one or possibly two dominant additives. In-line measurements of additive concentration facilitate automatic process control, which helps maintain product quality and manufacturing efficiency. In multi-component mixtures the measurements indicate on-aim conditions, provide automatic quality monitoring and accelerate transitions.
Hierarchical Assembly of Fibrous Proteins
Fibrous proteins provide useful models with which to explore self-assembly processes from the molecular scale to the macromolecular scale. Silks and collagens are under study in an effort to understand the sequence of events involved in these assembly processes, as well as to explore options to direct this process toward different paths. Model peptides, the native proteins, and recombinant versions of these proteins are studied. Interfacial and bulk solvent environments are utilized in an effort to understand and direct these processes. The interplay between primary repeat sequence and solvent is essential in fostering a specific assembly pathway. Insights into these processes will be presented within the context of pattern formation in fibrous protein materials with implications for biomaterials and tissue engineering.
An Accurate Warpage Prediction for Injection Molded Part by Using Simulation Program
This paper describes the computerized injection molding simulation of filling, post-filling, cooling and shrinkage and warpage phase analyses for an injection molded fiber-filled reinforced frame part used in a laser printer. Using C-MOLD ® simulation program, the part warpage was separately predicted by non-uniform shrinkage, fiber orientation, and unbalanced cooing effects. In the study, the frame part, as an example, the displacement components induced by different factors were investigated. The predicted shrinkage and warpage of the part are compared to the measurements of an actual production part. It was in good agreement with the actual injection molded part.
Modification of Thermoplastics for Density and Gas Permeability through Additives and Reactive Processing
Transport properties of thermoplastics such as thermal conductivity and gas permeability are usually controlled through foaming and the formation of lamellar microstructures respectively. Production of low-density foams by extrusion in the presence of physical blowing agents requires materials with particular rheological characteristics. Reactor/post-reactor branching or controlled cross-linking is commonly carried out in the presence of multifunctional additives. Low vapor/gas permeability structures may be formed through the incorporation and subsequent orientation of impermeable lamellar fillers, or the in-situ formation of lamellar microstructures during processing of mixtures of immiscible polymers. Examples of available technologies in both areas and recent research results will be presented.
Visual Research of Melting Mechanism of Polymer Pellets in Intermeshing Co-Rotating Twin-Screw Extrusion
With visualization co-rotating twin-screw extruder, the transition of polymer from solid to melt can be investigated on-line. Based on different states of polymer pellets along the screw in the experiments, several melting sub-stages, such as conduction melting, particle deformation, inter-particle friction melting and viscous dissipative mix-melting, were divided and defined in order to fully understand the melting process. Function of every stage was deeply discussed. It showed that dissipative mix-melting was an efficient way to polymer pellets melting, which depended on not only screw configurations but operational conditions and polymer properties as well.
The Formation of Supermolecular Polycaprolactone (PCL) Spherulites in Polystyrene-Polybutadiene-PCL (PS-b-PB-b-PCL) Semicrystalline Block Copolymers
The morphological behavior of polystyrene (PS), polybutadiene (PB), and polycaprolactone (PCL) semicrystalline block copolymers as a function of annealing conditions is discussed. For this study, both bulk and thin films of (PS)0.35(PB)0.15(PCL)0.5 were cast from toluene solution and the morphologies were examined using transmission electron microscopy (TEM) and polarized light microscopy (PLM). The morphology of either as-cast or annealed bulk (1 mm) specimens is a lamellar-cylindrical morphology having PB cylinders at the interphase boundaries. The block copolymer thin film (5-10 µm) from fast solvent evaporation also shows a lamellar-cylindrical microphase-separated morphology without the formation of visible PCL spherulites using PLM. After the formation of the well-defined PCL spherulites by annealing, the micromorphology is no longer lamellar-cylindrical but instead the PCL lamellar crystals dominate the system.
Structure and Processing Control of Electrically Conducting Polymers
The electrical conductivity of doped conjugated polymers is very sensitive to their in-chain and interchain structure. We present results of an integrated study of the electrical and magnetic properties. Modifications examined include the role of oligomer length, substituent group, chirality of dopant and processing-induced orientation and crystallinity. The data show a systematic variation of the room temperature conductivity and its temperature dependence. The variation of magnetic behavior supports the important role of structural order and inhomogenity. New concepts such as the role of “fractal networks” in determining the electrical properties (and industrial applicability) of these polymers are introduced.
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