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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Rheological Response of Polystyrene/Ortho-Terphenyl Solutions
The linear and nonlinear viscoelastic responses of concentrated solutions of polystyrene in ortho-terphenyl are being investigated. Three aspects of behaviour are being addressed: 1) the time-temperature and 2) the time-concentration dependence of this material system and 3) the time-strain separability of the response in the non-linear regime. Linear viscoelastic responses are being measured using an ARES rotary rheometer and the non-linear response will be investigated using an RMS7200 where both the torque and normal force response in torsional deformations will be measured. The polymer is a commercial specimen having a weight average MW of 192,000 g/mol. Concentration is being varied between 0.2 and 0.7 mass fraction of polystyrene. Since time-strain separability is fundamental to the tube theory of reptation, the non-linear response will be discussed in the reptation framework.
Swelling as a Method of Discriminating among Strain Energy Functions
The swelling of cross-linked elastomers is generally treated with the Flory-Rehner[I] theory. One aspect of the common use of the theory is the simplification of the form of the elastic strain energy function such that it appears as the shear modulus G(?) in the swelling equilibrium equations. A more general form of the relevant equations would be to use ??A(?)/?(?1/3) where A is the Helmholtz free energy of the network, ? is the volume fraction of polymer in the swollen system. Here we examine the limitations put on the form of the strain energy density function (A) when the shear modulus is observed to scale as ?1/3.
Isotropic Residual Stresses in Thermosetting Resins: Modeling and the Effects of Resin Modification Properties
Recently, we extended a thermo-viscoelastic model  to describe the development of isotropic residual stresses for a commercial thermosetting material during cure . In this paper, we extend this model to study residual stresses in novel thermosetting resin systems, such as spiro orthocarbonate/bismaleimide (SOC/BMI) which are under consideration by the Air Force for use as polymer matrix composites. In these systems, cure shrinkage and isotropic residual stresses are reduced through a ring-opening reaction which occurs independently of the addition reaction. The modeling effort includes a parametric analysis of the effects of various parameters, including the volume changes involved in the reactions, the relative rates and orders of the reactions, and the dependence of the glass transition on the network formed.
Large Deformation Response of Polycarbonate: Time-Temperature and Time-Strain Superposition
Data are presented from tests of the stress relaxation response of a glassy polycarbonate under torsional deformations. Tests were performed on samples over a range of strains from 0.0025 to 0.07 and at temperatures from 30 EC to 135 EC, all at a fixed aging time of 64800 s. Individual data sets at each strain and temperature could be described using a stretched exponential form relaxation function. Over the range of temperatures studied the data at each strain could be superimposed using conventional time-temperature superposition. For strains up to the yield strain the data at each temperature could also be superimposed to form a master curve following the principle of time-strain superposition. Interestingly, the master curves found from time-strain superposition at each temperature did not have the same form. Similarly, the master curves found from time-temperature superposition at each strain did not have the same form.
Comparative Study of Structure and Property of Ziegler-Natta and Metallocene Based Linear Low Density Polyethylene in Injection Moldings
Linear low density polyethylenes (LLDPE's) polymerized using metallocene and Ziegler-Natta catalyst were used to study the shear-induced crystallization in injection moldings. The gapwise distributions of crystallinity, spherulite size and thickness of the shear-induced crystallization layer in moldings were measured along with the mechanical properties of the moldings. The effects of processing conditions on these properties were determined. Metallocene based LLDPE shows higher thickness of skin layer, lower spherulite size and higher degree of crystallinity than Ziegler-Natta based LLDPE.
Biaxial Orientation of Blown Films Using an 80/20 LLDPE/LDPE Blend
The Hermans orientation function and the White-Spruiell biaxial orientation factors [1, 2] of blown films of blends constituted of linear low density polyethylene (LLDPE) and low density polyethylene (LDPE), with 90%  and 80% of LLDPE, were calculated by infrared spectroscopy and differential scanning calorimetry. These films were produced by using a industrial equipment, controlling the following processing conditions: BUR=Rf/Ri, where Rf and Ri are the final and initial radius of the blown films, the temperature and the thickness of the sample.
Phenomenological and Morphological Characterization of Shear Induced Crystallization of Isotactic Polypropylene
The Flow Induced Crystallization (FIC) of polypropylene was studied in a slit die coupled to a twin screw extruder in several ranges of temperature and flow rate. FIC layers were measured and characterized and fitted to the Janeschitz-Kriegl model (1). A morphological investigation using TEM, SEM and WAXS were also done. Morphological results showed that the FIC layers are composed by extended lamellae in the ? phase. The ? phase was observed in the neighborhood of FIC layer generated probably by a transcrystallization effect.
Quantitative Evaluation of Feeding Different Physical Forms of Stabilizers
The principles of feeding dry materials and a mathematical correlation to rank their ease of flowing (flowability) or ease of creating feeding problems (floodability and archability) were first explained by Ralph Carr in 1965. These same principles applied to powders of antioxidants explain the feeding challenges associated with handling such materials. Granular and non-dusting forms of the same additives improve these handling characteristics. This model helps explain how appropriate feeder designs can alleviate the problem, while inappropriate ones can create a massive problem.
Viscosity Regulation for Polymer Extruders
This paper introduces the viscosity regulation problem for polymer extruders, through viz breaking of polypropylene with injected peroxide. A simple, physically motivated model dependent on plant operating conditions is presented, the sensors used are characterized, and the results of experiments demonstrating the disturbance rejection capacity of the control system are shown. Low frequency disturbances, that is, disturbances with volume scale greater than the filled volume of the extruder, are of primary interest. The dynamic behavior of the plant varies as a function of the operating condition, and together with the sensor create significant if structured uncertainty. For this reason, adaptive control is applied.
Preparation and Mechanical Properties of Epoxy-Clay Nanocomposites. Influence of Core-Shell Rubber Particles Addition to Epoxy-Clay Nanocomposites
Polymer nanocomposites consist of highly purified inorganic material with at least one dimension in the nanometer scale and with an organic surface treatment to help their dispersion into a polymer matrix. The interest for the production of such materials has been growing because they exhibit greatly improved properties, even with a small addition of nanoclays. This work deals with the epoxy-clay nanocomposites. The state of dispersion and the fracture behavior of the system are studied. Core-shell rubber (CSR) particles are used to improve the toughness of such a system and found to be effective.
Application of Chemo-Rheology to Establish a Process Window for a New Solventless System to Manufacture Pre-Pregs and Laminates for Electronic Applications
The most common commercial processes for manufacturing pre-pregs for electronic applications use solvent-based epoxy systems. Solvents are environmentally unfriendly and contribute to voids in the pre-preg and laminate. Voids cause product variability, which is a major source of scrap in board shops. In this paper, we use chemo-rheological and kinetic measurements to identify a potential epoxy-based resin system for a solventless process, based on injection pultrusion. DSC and rheological data show that the candidate system does not react appreciably without catalyst to temperatures of 170°C or with catalyst at temperature below 110°C. The system solidifies below 105°C. It was found that the overall viscosity of the resin system is dependent upon the temperature, degree of cure, and filler content. Kinetic rate and viscosity rise expressions to be used in process modeling and optimization have been developed. A preliminary process window for the process has been established.
Optimizing Injection Gate Location and Cycle Time for the In-Mold Coating (IMC) Process
The standard practice when compression molding Sheet Molding Compound (SMC) panels is to in-mold coat (IMC) the parts, when surface appearance is important. Thus IMC needs to be considered an integral part when improving the process. Selecting the proper injection gate location is key to obtaining a defect free coating. In the present work, we present an optimization method to select the injection gate location that minimizes the potential for surface defects. We will also describe a process for the optimization of cycle time by minimizing curing time by either increasing the mold wall temperature or adding more catalyst. The approach is illustrated for typical IMC coating material.
Interfacial Interactions and Structure Development in Injection Molded HDPE/Hydroxyapatite Composites
This paper investigates the structure development in conventional molding and shear controlled orientation in injection molding (SCORIM) of HDPE/hydroxyapatite (HA) composites. The effect of a zirconate and a titanate coupling agents aimed to improve the interfacial interaction between the filler and the matrix is also described. The mechanical characterization of the composites included tensile testing and microhardness along the part thickness. The structure variation of the composites across the molding thickness was inferred from X-ray diffraction patterns. The tensile fracture surfaces and interfaces between the filler and the matrix were observed by scanning electron microscopy (SEM).
Decorating Polyolefins: The Color of Change
Processability, performance and cost make TPO’S a popular choice in various applications. Decorating polyolefins is still a challenge, but the advantages can out weigh the disadvantages if engineered with care.
Property Separation Based on Inversion of Micro-Mechanics
An inverse method to separate the matrix thermo-mechanical properties from the fiber-filled composite properties is suggested. The Tandon-Weng micro-mechanics model  and an orientation averaging method with orthotropic closure are used for the calculation of the anisotropic, heterogeneous properties on both a layer and element basis, then a combination of Newton's and least square methods are employed to solve the inverse problem. In comparison with a previously used separation method based on pvT model, the inverse method gives more accurate and reliable results.
Transfer Efficiency - Issues & Methods
Many manufacturers of industrial coating application equipment often cite efficiencies of their spray equipment in terms of transfer efficiency (TE). While useful in comparing different types of equipment (conventional, HVLP, airless, etc.), its value as a tool in evaluating real-world situations is questionable. This article is not intended to be a full discussion of the methods for testing spray equipment efficiency. More at heart is what are the primary methods of testing and what are the issues.
Non-Conventional Processing of Short Fibre Reinforced Composites
This communication describes a preliminary study based on the use of carbon (C) fibers as reinforcement of a HDPE matrix, using a non-conventional processing approach that integrates compounding and injection molding during the processing cycle. The mechanical performance of the short fiber reinforced composites produced was assessed by tensile tests and compared with the respective structure development and fiber orientation and length properties. Composites based in HDPE and C fibers with high stiffness were developed. Nevertheless, the mechanical performance is limited by fiber length degradation and final fiber orientation pattern across the molding thickness.
Determination of Condensable Volatiles during Polymer Processing Using an Analytical Extruder
It is well known that a certain amount of volatile material can be produced during polymer extrusion or compounding operations. Even with proper venting of the equipment, volatiles can still collect and condense in unwanted areas of the equipment causing vent plugging, die drip and buildup on chill rollers. In an effort to control these problems, laboratory methods for studying the kinetics and composition of the volatiles produced during extrusion have been developed. These methods include thermal gravimetric analysis (TGA), low temperature pyrolysis and other thermal techniques. The main disadvantage of these techniques is that the sample is subjected to thermal conditions in a static manner during analysis. In an extruder, the volatiles are produced while the polymer is in a dynamic melt state subjected to both heat and shear. This paper will focus on methods developed for the trapping and analysis of volatiles during extrusion. The main advantage of these methods is that the volatiles collected are a function of the heat and shear of the extrusion process providing a more realistic assessment of the composition and quantity of the volatiles. Other advantages of these techniques are increased sensitivity of analysis, the option of analyzing for a broader molecular weight range of the volatiles and the ability to use larger, more representative samples.
One-Step-Sandwich-SMC: A New Method for the Production of Lightweight Vehicle Parts
In respect of weight reduction an increasing request for light weight materials exists in the automotive industry. The compression molding of sheet molding compounds (SMC) has been established as a cost-efficient and widely applied process for semi-structural automotive components, especially in commercial vehicles. The deficiency of this material is the relatively low Young's modulus, which prevents these materials from being used in loaded structures. Therefore the idea was to increase the performance of these materials by forming a sandwich, but in principle use the same fast and cost-effective process of conventional SMC. The principle of this new technology is based on a one-step process using one sheet containing a blowing agent disposed between two conventional SMC sheets in the mold. By closing the mold the three layers are compressed and heated up until the expansion of the core material starts. The foaming process resulting from the expansion of the core material is controlled by a defined opening motion of the mold according to the requested sandwich height. After the foaming process the curing of the part is completed. The result is a rigid lightweight sandwich structure. The advantages of the One Step Sandwich-SMC in comparison to typical sandwiches are the decrease in production cost and the recycling properties, since no separation of the single layers is required (single material system) and since additionally the core layer may contain a high amount of SMC scrap material. The developing process of this technology was conducted by the simultaneous integration of fundamental research (material development, testing, processing technology) and by the development of the structural part (part conception/design). This demonstrator component is the front hood of a commercial vehicle, the Mercedes-Benz Actros, which was produced with optimized processing parameters. For the demonstrator chosen a cost potential of 30 % and a weight reduction potential of 10-1
Competition of Phase Dissolution and Crystallization in Poly(?-Caprolactone)/Poly(Styrene-Co-Acrylonitrile) Blend
Blend of poly(?-caprolactone) (PCL) and poly(styrene-co-acrylonitrile) (SAN) containing 27.5 wt% of acrylonitrile was studied. The PCL/SAN blend having LCST (lower critical solution temperature) phase boundary above the melting point Tm of PCL offered an excellent opportunity to investigate the competition of liquid-solid phase transition (crystallization) and liquid-liquid phase transition (phase dissolution). A blend with critical composition (80/20 PCL/SAN) underwent a temperature-jump above LCST to proceed spinodal decomposition, yielding a regularly phase-separated structure (SD structure). Then, it was quenched to the temperatures below Tm, at which both the crystallization and the phase dissolution could occur. By transmission electron microscopy it was found that during isothermal annealing after quenching to high temperatures close to Tm (e.g., 51°C), the SD structure gradually disappeared, and then the crystallization started from a single-phase mixture to yield normal crystalline structure similar to that from neat crystalline polymer. At lower temperatures (e.g., 40°C), crystallization quickly occurred and the SD structure was preserved, implying that the crystallization prevailed over the dissolution yielding a bicontinuos structure consisting of amorphous (SAN-rich) and crystalline (PCL-rich) regions. At intermediate temperatures (e.g., 45°C), the phase dissolution competed with the crystallization, resulting in a bicontinuos structure with longer periodic distance and broad boundary having a gradient in composition of amorphous region between PCL crystal lamellae. Light scattering analysis quantitatively revealed a competition of the crystallization and the phase dissolution in terms of the crystallization rate (from Hv scattering) and the apparent diffusion coefficient for dissolution (from Vv scattering).
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