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.
In this work a methodology to automatically balance the flow in profile extrusion dies is used. For this purpose a computational code, based on the finite-volume method, was developed and used to perform the required three-dimensional numerical simulations of the flow. The methodology is illustrated using two case studies, each one leading to the adoption of a different constructive solution (with and without flow separators). In order to evaluate the quality of the automatically generated die geometries, an objective function, that takes into account the flow balancing and the ratio L/t of the parallel zone, is proposed.
The reinforcement of thermoplastics with short glass fibers is a common way for obtaining composites with high strength and stiffness. These materials are amenable for welding by the hot plate method, although a drop in the mechanical strength is observed. In this paper 20% glass reinforced polypropylene (GRPP) was injection molded in mono-material and bi-material (PP/GRPP) ISO-type tensile testing specimens and welded using the hot-plate technique. Morphological analysis and mechanical testing were used to investigate the effect of the processing parameters and type of molding on the weld behavior. It was found that the welds made with PP/GRPP moldings are stronger than if only GRPP is used in the moldings.
The design of a screw for polymer extrusion based on scientific principles is still a challenging task, which has received relative little attention in the literature. Prior to the definition of the geometric parameters of the screw, the designer has to decide about general features, such as the type and location of mixing zones, which is mainly based on empirical knowledge. Once the main process criteria are identified (e.g., pressure generation capability, mixing efficiency, power consumption), the design is then carried out on a trial-and-error basis. In the present work we consider screw design as an optimisation problem where the aim is to maximise the value of an objective function that describes quantitatively the process performance. A design methodology incorporating this approach is presented. The relevance of the solutions and the sensitivity of the method to changes in the criteria considered are demonstrated with various examples.
Die deposit (sometimes known as die drool, die lip build-up, etc) occurs in melt extrusion of polyolefins. It is an undesirable build-up of material, normally on the lip or open faces of extrusion dies. In commercial scale polyethylene extrusion processes (e.g. blown or cast film, fibre spinning, etc), die deposit can have a significant influence on productivity, through the need to shut down processing line periodically to clean the die, and on the end-product quality. There are a wide range of factors or sources that lead to the formation of die deposit as its mechanism is not understood, these include low molecular weight species and volatiles, die swell, die design and polymer structure. This paper investigates, through laboratory-scale extrusion and rheology evaluations, some of the key relationships in the die deposit formation process. A deposition mechanism is thus proposed from these studies, with some suggestions for its reduction.
Solid state microcellular foaming technology was employed to investigate the influence of impact modification on the foamability of neat rigid PVC and rigid PVC/wood-flour composite samples. The effects of impact modifier types (crosslinked versus uncrosslinked) and concentrations on the void fraction of foamed samples were examined. The influence of impact modification on the sorption behavior of CO2 in the samples was also studied. The experimental results indicate that impact modification accelerates the rate of gas loss during foaming process, which impedes the growth of nucleated cells, independent of modifier type. Due to this accelerated gas loss, impact modification inhibits the potential of producing foamed samples with void fractions similar to those achieved in unmodified samples. Consequently, impact modifiers are an unnecessary ingredient in the formulation of foamed neat rigid PVC and rigid PVC/wood-flour composites.
The effects of chemical foaming agent types (endothermic versus exothermic) and concentrations, as well as the influence of all-acrylic processing aid on the density and cell morphology of extrusion-foamed neat rigid PVC and rigid PVC/wood-flour composites were studied. Regardless of the CFA type, the density reduction of foamed rigid PVC/wood-flour composites was not influenced by the CFA content. The cell size, however, was affected by the CFA type, independent of CFA content. Exothermic foaming agent produced foamed samples with smaller average cell sizes compared to endothermic counterparts. The experimental results indicate that the addition of an all-acrylic processing aid in the formulation of rigid PVC/wood-flour composite foams provides not only the ability to achieve density comparable to that achieved in the neat rigid PVC foams, but also the potential of producing rigid PVC/wood-flour composite foams without using any chemical foaming agents.
A new molding technology is described which makes use of blends of thermoplastic polymers and reactive monomers (thermosetting polymer). In this way the viscosity is reduced and a low pressure processing is achieved. Due to polymerisation of the monomer during molding phase separation occurs with the thermoplastic polymer as the continuous phase in order to retain the desired properties of the thermoplastic. The behavior of such hybrid blend systems needs to be understood before an industrial process can be established. Here the reaction and diffusion kinetics of blends of epoxy and amine in PMMA are investigated. It is found that the reaction is slowed down initially by the presence of PMMA. In the second stage, after phase separation, the reaction rate increases in the polymer-poor dispersed phase. Since in the molding process the reaction is started by mixing the blends of polymers containing the respective monomers, diffusion has to establish a stoichiometric balance in the matrix after a certain extent of distributive mixing. By FT-IR microscopy in layered systems the diffusion coefficients are determined in the absence of reaction and concentration distributions are determined in the case of reaction. It is concluded from the model systems that in layers of 100 µm thickness stoichiometric balance is not achieved due to limited rate of diffusion.
Mass Transfer between a slender bubble and a Newtonian liquid in a simple extensional and creeping flow has been theoretically studied. The liquid is a solvent-polymer solution, having a variable diffusion coefficient, which depends exponentially on the solvent concentration. Assuming a thin concentration boundary layer thickness and applying the method presented by Levich for a constant diffusion coefficient, the differential binary mass balance was transformed into an ordinary differential equation, which was numerically solved. The final result was also compared with an approximated analytical solution developed by Polyanin and Dil'man.
The use of differential scanning calorimetry (DSC) fractionation techniques as a possible alternative to temperature rising elution fractionation (TREF) and/ or crystallization analysis fractionation (CRYSTAF) technique for the determination of comonomer distribution in polyethylene has been a topic of enduring interest in the polymer literature over the last ten years. In this paper, we demonstrate a surprisingly good correlation between CRYSTAF and the two most popular DSC fractionation techniques, the segregated fractionation technique (SFT) and the successive self nucleation and annealing (SSA) Technique for metallocene based polyethylenes.
The model preparation for the current mid-plane shell element type flow/pack/shrinkage/warpage and cooling analysis is time consuming and tedious. Many attempts have been made to automate the process, but most have proven to be inadequate. The obvious solution of moving to solids based analysis programs was limited by unacceptably long calculation times. This paper describes the results of three years of experimentation, to develop a proprietary technique to quickly and easily create a user controlled hexahedral mesh from STL files and reduced the solid model calculation times.
This paper is an attempt to analyze, in the limits of available space, the existing situation and development tendencies of the plastics food packaging, i.e. raw material resources, market structure and forecast for seven former Soviet influence zone states from Eastern Europe, not enough known to the American plastics market. Also presented here are the opportunities for American and Western European investors, with emphasis on the small and medium size production units already in place, benefiting from skilled work force, low production costs and increased market demand. Recommendations for changes in the western trade policy are also made.
The thermo-rheological properties of lower critical solution temperature (LCST) poly(styrene-co-maleic anhydride) (SMA)/polymethyl methacrlylate (PMMA) blends, with varying amounts of maleic anhydride (MA) content (8%, 14% and 32% by weight) in the SMA component have been investigated, using differential scanning calorimetry and small amplitude dynamic oscillatory rheological methods. The effect of MA content on the phase behavior of SMA/PMMA blends has been determined. The resulting phase diagrams have been modeled using Flory-Huggins theory.
Treated silica particles with different silane chain lengths were compounded in ethylene-propylene-diene terpolymer (EPDM) using an internal mixer, and their viscosity, agglomerate sizes, and extrudate swell were investigated and compared to carbon black filled systems. The treated silica compounds exhibited lower viscosity, smaller agglomerate size, and lower swell reduction than untreated silica compound after equivalent mixing times. The silica treated with shortest aliphatic chain length silane exhibited smallest agglomerate size compared to other silane treated systems. Silane acted as dispersing and processing aids in silica/EPDM compounds. Treated silica systems exhibited higher agglomerate size and viscosity than carbon black filled systems.
The pressure fluctuations that occur during the reactive twin-screw extrusion of polymers that contain solvents or solvent-borne reactants can be suppressed by closing off the reaction zone with low-pitch, reverse (so-called left-handed") screw elements. We suspect that the average down-channel velocity of the melt inside these screw elements is so high that the destabilizing effects of melt foaming occur only after the pressure is reduced. The time elapsing between the pressure drop below the boiling pressure and the end of the left-handed screw elements is the crucial parameter for controlling the stability of the process."
It has been known for many years that the rheology of linear single phase polymer melts depends strictly upon their molecular weight and molecular weight distribution. Recently, theoretical relationships have been developed that permit transforming rheological data into molecular weight information. Rheology has several advantages over GPC or LC in determining the molecular weight distribution of linear polymers. For one, rheology is highly sensitive to the high molecular weight tail, which is usually excluded in chromatographic separations. These fractions dominate the elasticity of the polymer melt, which greatly affects processing behavior. Generally, in order to determine the entire molecular weight distribution of a polymer, the rheological data must characterize the complete range of relaxation times between the plateau and terminal regions. In practice, such measurements are very tedious and time consuming, and can involve multiple tests run at several different temperatures, with different sets of conditions. A solution to this problem has been developed by Mead et. al. that allows incomplete rheological data to be combined with appropriate mathematical models to produce the molecular weight distribution curves. This paper reports on the transformation of the frequency dependent viscoelastic material functions to molecular weight and molecular weight distribution curves of LLDPE samples using this method. These results are compared with the molecular weight distribution curves obtained from GPC.
The rheology of polytetrafluoroethylene (PTFE) pastes has been studied using an Instron capillary rheometer. Four different grades of PTFE have been tested. Three of them had a homopolymer structure with different molecular weights. The fourth polymer had a slight degree of branching due to the incorporation of less than 0.5% by weight of another perfluorinated monomer. The investigated parameters included those related to the die design (contraction angle, capillary diameter and length to diameter ratio), extrusion conditions (temperature, and extrusion speed) and the molecular weight and structure of PTFE. It was found that these parameters significantly affect the capillary extrusion pressure, which is important in the creation of fibrils during paste extrusion. Quantification of fibrils in the extrudate has been attempted by the use of Raman microscopy. An attempt has also been made to correlate the degree of fibrillation with the tensile strength of the extrudate.
The plastication of solids in the reciprocating screw of an injection molding machine is a transient process, and consists of two phases. During the stationary phase of the screw, melting takes place mainly by conduction heat transfer from the barrel. The melting during the screw rotation phase of the molding cycle is similar to that of an extrusion screw, however the screw undergoes translation. Starting from the relationship for conduction melting and extending it to include a simplified model for the extrusion melting, a set of equations which can be easily solved for the solid bed profile in the reciprocating screw is derived. Using this extended model, simulations of the effect of the barrel temperature, screw speed, screw rotation time, screw geometry and resin properties on the melting performance of the screw are presented. Predictions of the model agree well with the experimental observations in practice. The easy applicability of the model is illustrated by worked-out examples.
Packaging is the largest application of polymers, in all countries, at all levels of development, 30 to 40 % of total plastics consumption, boosted by very strong facts and trends. Past present and forecast figures show diversified plastics growth in packaging, and new competition between plastics. The narrow link of packaging with food products makes packaging a stronghold of resistance, even in recession. The fast development of emerging countries generates demand for improvement of the food supply and packaging; Research goes on, for smarter, simpler, thinner packaging, of higher performance and easier on the environment.
Waste management is gradually becoming a priority within an integrated approach to nature conservation. Croatia has taken a number of good steps during the recent years. The first life-cycle and economy analyses in Croatia were made for managing of glass waste in 1997, but no serious study of plastic waste was made until recently. Among all types of plastic waste, only PET-bottles are collected in Zagreb (within the OHO system - Croatian Recycling System), so it was logical to make the first life-cycle analysis of PET-bottle. The results have shown the evaluation of PET-bottles' impact on the environment and the critical points" of PET-recycling were pointed out."
With the aim to establish some guidelines in the use of injection molding simulation programs as a predictive tool when designing a mold, an experimental validation of an injection mold was performed. Amorphous and semicrystalline materials were injection molded, and their corresponding process windows were established. C-Mold software was employed to simulate the experimental conditions. It was found that the software temperature predictions agree very well with the experimental results, but pressure predictions do not. The material properties seem to be strongly influencing the simulation results. Filling and packing times could be extrapolated from the simulation, but shrinkage predictions should be considered carefully.
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