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.
Thermal residual stresses in freely quenched semi-crystalline polymer slabs were calculated based upon the modifications of the Indenbom theory for inorganic glasses and linear viscoelasticity. These modifications were introduced to include the influences of crystallization on the shear relaxation modulus of the polymer during free quenching. The non-isothermal crystallization kinetic model due to Nakamura et al. was employed to calculate the variations of crystallinity. In the case of the Indenbom theory, a polymer during crystallization due to quenching was assumed to undergo an abrupt transition from an ideal plastic state to an elastic state upon the completion of crystallization. In the case of linear viscoelasticity, the Morland-Lee constitutive equation was utilized with the effect of crystallization on the time-temperature dependent shear modulus taken into account. The Spencer-Gilmore equation of state was employed to model the specific volume changes during crystallization, and used to determine the local thermal loading that results in the thermal stresses. Based on the above theoretical work, numerical simulations of development of thermal stresses in the symmetrically-cooled slabs of isotactic polypropylenes (i-PP) under various cooling conditions were performed. The predicted thermal stresses in the slabs were then compared with the measurements.
Blends of polypropylene and polystyrene compatibilized with styrene-butadiene-styrene (SBS) and styrene-ethylene/butylene-styrene (SEBS) copolymers were studied. The morphology was studied by Scanning Electron Microscopy. Emulsion curves relating the average radius of the dispersed phase to the concentration of compatibilizer added to the blend were obtained. The rheological behavior of the blends was studied by small amplitude oscillatory shear, and correlated to the morphological observations. The interfacial tension between the components of the blends was evaluated from the rheological data.
The generation of low melting phosphate glasses has allowed the development of new processes for the manufacture of polymer-glass composites. The low Tg of these glasses allows the material to be deformable at conditions used to process many thermoplastics. These co-deformable composite systems could offer many advantages in processes requiring deformation such as injection molding, thermoforming and compression molding. This paper presents an overview of some the work that has been performed in analyzing the behavior of these composite systems for a variety of processing applications.
Reorganization is a process where improvements or perfections of the initial metastable crystal can occur. A molecular weight dependence on the rate of reorganization can be shown for poly(vinylidene fluoride) (PVDF). Additionally its reorganizational response is found to be intermediate between that of polyamide 12 and poly(p-phenylene sulfide). The addition of a noncrystallizable unit into the PVDF polymer chain should not only lower the melting temperature but also affect the reorganizational response. In effect, it should stabilize the zero-entropy production meltings way below the equilibrium melting temperature. The effect of the addition of hexafluoropropylene (HFP) in VF2/HFP copolymers is studied in this work through the use of multiple heating rates and temperature-modulated differential scanning calorimetry (TMDSC).
Carbon black is a form of elemental carbon. Over 90% of the world's production of carbon black is produced by the oil furnace process from liquid, aromatic hydrocarbons. As a key additive in many types of plastic resins, carbon black can impart a variety of desirable characteristics, such as opacity, color, electrical conductivity, protection from ultraviolet radiation, and in some cases, reinforcement. This broad range of effects requires many grades of carbon black varying significantly in fundamental properties. In choosing a carbon black for a specific application, key factors to consider are the particle size, structure, surface chemistry, and density of the grade. This paper will discuss the carbon black properties which control its behavior in plastic systems and to use those properties to guide formulators in selecting the most appropriate grade for a given end use application.
Samples of recycled plastic lumber constituted of a mixture of two different polyolefins and an inorganic glass were subjected to short-term stress relaxation tests. In addition, stress-strain tests were carried out at different rates of stress and strain for both full-sized lumber profiles and smaller samples machined from the larger pieces. The results from the short-term stress-strain tests were used in conjunction with a mathematical model to calculate values of stress as a function of time for the relaxation experiments. Calculated values are in good agreement with experimental stress relaxation data. The feasibility of extending this model to predict long-term time-dependent behavior is discussed.
Commercial epoxy resins have a wide range of average molecular weights and molecular weight distributions. The effect of the epoxy equivalent weight (EEW) on the cure kinetics was investigated in this study. The reactions to produce cured epoxy resins can be divided into two steps, adduct formation and etherification. The final product properties are dependent on the structures of the epoxy monomer and the curing agent. The cure kinetics is also influenced by the epoxy molecular weight distribution. The specific objectives of this work were to delineate the reaction mechanism of commercial epoxy resins (Epon 828, 825, 834, 836 and 1001) cured by 2- ethyl-4-methylimidazole(EMI-24), to determine the kinetics of the curing reaction, to construct a model for describing the effect of the epoxy average molecular weight, and to explore the influence of epoxy average molecular weight on the physical properties of the cured epoxies.
Thermal, optical, and mechanical properties of uniaxially stretched blends of PET/PEI films as a function of draw ratio were investigated. PET/PEI blends of compositions 0-30% PEI were prepared in a twin screw extruder, and cast into transparent amorphous films on a chilled roll fed by a single screw extruder. The DSC data showed a rapid rise in crystallinity followed by a much slower increase directly after the films reached the stress hardening point. The addition of PEI was found to hinder the formation of the crystalline lattice of PET and once formed, the crystallites were highly distorted. Also, PEI caused the onset of stress hardening to move to lower draw ratios. However, this influence on the stress-strain curves was not as a result of increased strain crystallizability but perhaps formation of a network that accelerated stress hardening in the presence of stiff and bulky molecules. This result clearly suggests that one can produce self leveled" films at lower draw ratios by the addition of a small amount of PEI."
Polymer sintering and heat transfer are fundamental phenomena in rotational molding. Sintering experiments have been performed with rotational molding grade resins. It was shown that the sintering process of two particles was not significantly affected by the sintering surface. Based on this result, the initial coalescence of powder in rotational molding is predicted using a two-particle sintering model. The sintering model is used together with a lumped parameter heat transfer model to predict the level of powder coalescence during the heating cycle. Results showed that as the oven temperature increases, the time required for all the powder to melt decreases but the level of sintering before the formation of bubbles decreases.
The microstructure of a new class of polypropylenes and co-ethylene-polypropylenes was examined by 13 C NMR spectroscopy. This new class of polypropylenes and coethylene-polypropylenes of controlled MFR (range 1.0 dg.min to 40 dg/min) and crystallinity (heat of fusion = 15 to 70 J/g) were prepared by a single catalyst system. The isotactic content was correlated with physical properties such as tensile and dynamic modulii. Most physical characteristics showed a strong correlation to developed crystallinity. In turn, crystallinity was shown to be dependent on isotactic content in homopolymers and measurement of impeifections in copolymers.
Loading of thermoplastics with CO2 results in a reduction of the polymer viscosity. When added in higher concentrations, carbon dioxide allows the production of foams. The addition of carbon dioxide can be realized during processing in the plasticizing unit of a special injection molding machine. However, in the present case the additive was given to the polymer within an autoclave prior to processing with a standard injection molding machine. Firstly, sorption and desorption measurements of carbon dioxide in the polymer were conducted using a magnet suspension balance. Finally, the influence of the process parameters on foam structure and density is tested.
To broaden the potential applications of resorbable polymers, a special process has been developed. The focus of attention is the use of a gaseous medium as a plasticizer added to the polymer prior to processing. This reduces the glass transition temperature of the polymer significantly. Within the applied process the resorbable polymer is processed to stents at 35 °C, primarily utilizing the plasticizing effect of carbon dioxide. This specific process allows the production of resorbable stents, the creation of microcellular structures as well as the incorporation of biologically active substances, which, due to their thermal sensitivity, could not be processed otherwise.
Due to the extensive use of polypropylene, the comprehension of its stability and degradation processes is essential. In particular, our interest was to distinguish the differences between thermal and thermooxidative effects on its properties. The influence of temperature and atmospheric conditions on the time dependent aging process of PP was investigated. By means of suitable analyses, it has been proved that inert conditions can significantly reduce the degradation of polypropylene both in use and while processing.
For short-time temperature stress as applied during soldering of MIDs there are no reliable temperature limits of plastics available. It is supposed, that many 3D-MID-applications are feasible with less thermally stable and cheaper plastics such as PA, PBT, PP and ABS. According to investigations heat deflection and physical ageing of plastics have a great influence on solderability of plastics. The physical ageing of polymers depends on their thermal pretreatment (processing) and determines most of the changes of the mechanical properties. The solderability of plastics is not only a material specific change of the short-time properties, it also depends on processing. The long time behaviour, which is determined mainly by chemical ageing is only scarely influenced by soldering.
The dependence of calcium carbonate (CaCO3) concentration on the mechanical properties of unsaturated polyester composites is essential to the prediction of the stress-strain and creep behavior of the composite. Experimental determinations of the mechanical response is compared to the predicted values with the use of known constitutive models. The models are then applied to predict the strain response to a step load profile with the use of the Boltzmann superposition principle. Comparisons between the model predictions and the experimental results show excellent agreement.
Threaded inserts or self-threading screws can be used to join different polymers or polymers to metal at high loads. In addition to static loads, joints are often subjected to dynamic loads as well as temperature variations. The essential parameter of the joint performance in highly loaded applications is the preload force and its time dependence, especially for joints with self-threading screws. In this paper, experimental results on the time dependence of the applied prestress force of threaded joints are investigated. In particular, the surrounding temperature and design parameters of the thermoplastic boss and self-threading screw will be shown and discussed.
Designers of thermoplastic products have always striven to find faster, more cost-effective and durable methods for marking plastic parts. Manufacturers are also looking for systems that allow the reduction of paint and eliminate VOC issues. With new quality mandates, permanent marks on parts must be durable, legible, and traceable to provide information for the lifecycle of the product. Color laser marking thermoplastics is a new marking method that meets these criteria. There are a number of factors to be considered when introducing laser marking into a manufacturing operation. First, is to plan for laser marking at the earliest stage of product development. Second, is to understand the physics and chemistries involved when the laser beam hits the plastic surface. Last, is the impact of using a computer-controlled laser for faster marking and rapid design changeover. Current commercial product case histories are included to illustrate this new technology. These issues and others will be discussed in this paper.
Testing of newly developed pipe is both time consuming and costly. Hydrostatic creep-rupture tests that measure hoop stress vs. time to failure can be used to rank systems and predict service lifetimes. This paper presents a fracture mechanics approach to ranking polymers and predicting lifetimes for long-term, slow crack-growth rate failures. Constant load three point bend tests have been performed on notched specimens to produce displacement vs. time data and calculate stress intensity (K1) vs. crack growth rate (da/dt) relationships. Very good repeatability has been demonstrated and da/dt has been found to be a unique function of K1 independent of the combination of load and crack length used to obtain it.
Most polymer/clay nanocomposites require the surface modification of the clay in order to render the clay compatible with the polymer. Two main methods for surface modification of smectites have been described in the literature. These methods include the more traditional ion exchange method utilizing onium ions and the more recently described ion-dipole method. With the large number of surface modifying agents available and the great variety of polymers, a rapid method of screening was needed. Computational modeling has proven to be just such a tool. A computational method has been developed that can predict very accurately the type of intercalate that will form with a given molecule but also yield quantitative x-ray d-spacings for the intercalated clay complex. The method also can be utilized to predict the energetics of exfoliation into a polymer to form a nanocomposite. This modeling method, as well as, specific examples will be described in detail.
Powder injection molding (PIM) is well established for net shape production of ceramic parts. However, the size of the molding is limited by economic efficiency due to the expensive powder. Moreover the wall thickness defines not only cooling time but rather the time required for debinding and sintering. For this reason the combination of PIM and gas-assisted injection molding is of interest. It provides more cost effectiveness through considerable savings for debinding and sintering time. The aim of IKV's investigations is to realize gas-assisted PIM" and to provide comprehensive knowledge about the spreading of the gas bubble."
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