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.
Use of mixtures of blowing agents in thermoplastic foam extrusion has been an industrial practice for a long time. However it has gained renewed interest in the past few years due to the introduction of difficult-to-process alternative gases, targeted as potential replacement for the banned ozone-depleting blowing agents. Reasons for blending physical foaming agents (PFA) are numerous. The incentives may be economical, environmental or technical. With respect to that latter factor, blending suitable PFA’s is often regarded as providing a better control of processing conditions. For example, a specific PFA could be selected for its inflation performance and blended with other co-blowing agents chosen for their stabilizing role. Although considerable amount of work has been done in that area, very little information has been disclosed in open literature.Carbon dioxide (CO2) has been reported as an interesting candidate for low-density polystyrene (PS) foaming, although the required concentrations are associated with high processing pressure due to the low solubility of the gas. Thus stable processing conditions are difficult to achieve. This work studies the effect of blending CO2 with ethanol (EtOH) as a co-blowing agent for PS foaming. Extrusion foaming performance of this mixture will be discussed, with respect to its solubility (i.e. degassing conditions) and rheological behavior. The function of each blowing agent during the process will be analyzed with respect to the plasticization, nucleation, expansion and stabilization phases. Attention will also be paid to the interaction involving the two PFA components.
The use of simulation software to predict the thickness distribution in a blow molded part is becoming more widespread, thus saving considerable time and money in the product development process. For extrusion blow molding simulations, the ability to obtain an accurate final thickness prediction depends on starting with the correct parison thickness distribution. An extrusion simulation tool that incorporates the effects of parison programming, die swell and parison sag due to gravity is required to predict the correct parison thickness distribution. In this study, we compare the parison volume predicted by a finite element-based extrusion model with experimental measurements. The effects of different parison programs are investigated. The goal is to determine the level of accuracy and reliability of the extrusion model for predicting parison thickness.
Bulk polymer properties are altered when they are blended with an immiscible component. A glassy polymer, polymethylmethacrylate (PMMA) was blended with a semi-crystalline one, polypropylene (PP) via melt processing. The effect of blend structure and physical interactions between components on the Tg of the glassy component were studied. Modulated Differential Scanning Calorimetry (MDSC) was used to analyze the glass transition. Even though the components are immiscible, significant correlations between blend composition and glass transition temperatures were observed. Models which could explain this behavior are discussed.
The measurement of polymer melt viscosity can be difficult. The application of a parallel plate rheometer designed to operate with a sealed and pressurized sample chamber simplifies the measurement of viscosity. In addition, a robust transducer allows the measurement of the polymer transition from the melt phase to the solid phase. The use of directly heated dies permits better temperature control of the sample chamber and resolution of transitions within the polymer. The temperature at solidification and the rate of solidification are also measured. The effect of changes in a polymer formulation on the viscosity and the solidification process are now easily determined. Examples of these measurements are presented.
Blends of polypropylene (PP) and nanoclays were foamed by direct injection of carbon dioxide (CO2) in a twin-screw extruder. These nanocomposite foams were characterized according to their density, microstructure and mechanical properties. Foam density was easily reduced in the 100-200 kg/m3 range by adding very small amounts of CO2. No specific efforts were made to further decrease foam density, as the first objective of this work was to evaluate the mechanical performance of PP nanocomposite foams. No impacts of the clay addition have been observed on cell nucleation. The clay particles were shown to be mostly involved in aggregates and intercalated structures. Nevertheless, the nanocomposite foams produced were 30- 40% stiffer and 15-20% tougher than their neat, unfilled counterparts.
The feasibility of applying the single-charge rotational foam molding processing principle to the fabrication of integral skin polypropylene (PP) foams comprising a PP solid skin and a PP foamed core is investigated in this paper. A systematic process interruption and sample evaluation approach was used to quantify the experimental results and explore possibilities for improving the process control strategies to ultimately achieve a desired homogeneity and thickness uniformity of the solid PP skin layer that would be fully encapsulating the PP foamed core of a desired cell population density and average cell size. The experimental results revealed that this is quite a challenging task not only because of the well known intrinsically poor foaming nature of PP due to its low melt strength at elevated temperatures, but also because in single-charge rotational molding the processing parameters are often conflicting each other and therefore have to be optimized within a very narrow processing window. However, simultaneous, single-charge, quality PP integral skin and foamed PP core formation in rotational foam molding is feasible. Optimizing the heating profile, heating rate, heating time, and the mold rotational speed as well as careful selection of PP resins (or resin blends), chemical blowing agents (CBA), and their composition formulations is strongly recommended.
ABS and polycarbonate are renowned for their low temperature properties whereas their blends have enhanced flammability resistance and lower cost properties. The use of nanoparticles in combination with polymeric materials to create plastic nanocomposites (PNCs) is a current trend. The infusion of these nanoparticles in polymeric matrix is typically carried out via sonication. In this project, we explore the alternative but very viable process of extrusion as a nanoparticle infusion process, and present the results obtained for the mechanical and flammability resistance properties of nanoclay-infused ABS/PC blends. Torque Rheometry data indicate that processability is enhanced with small amounts of nanoclay up to the 4.0 PHR level. Optimal mechanical properties are attained at the 3.0 PHR nanoclay level whereas flammability resistance properties increase with increase in nanoclay level.
Pistons and cylinders in hydraulically systems are separated using composite wear rings, positioned in grooves of the piston. Metal-metal contact is a serious failure mode in hydraulic cylinders.Metal-metal contact can occur due to more elastic deformation than predicted, wear, exceeding tolerances and too high radial loads.The paper is about failure analysis of damaged hydraulic cylinders for levelling a construction. The failure was not expected because data about the stiffness of the wear rings in the brochure were very much in error.The design curve about “average bearing pressure – compression” of wear rings were suspected and have been accurately measured in a laboratory of Delft University of Technology.Although the data in the design brochure about the stiffness of the wear rings was very much in error, metal-metal contact could then not be explained.It was also assumed that during the setting of our experiments some plastic compression could have occurred. The additional compression should be just enough to explain metal-metal contact if “worst case” of tolerances should have occurred.It was decided to use a probabilistic approach to predict the probability distribution of the radial clearance. Monte Carlo method was applied to determine the probability density function of the radial clearance. From this approach we learned that the probability of metal-metal contact was very low. The only remaining explanation was exceeding of the radial forces on the wear rings.
The environmental regulations, societal concerns, and a growing environmental awareness have triggered the search for new products and processes that are compatible with the environment. Polyhydroxybutyrate (PHB) is a biodegradable polymer that has created significant interest recently because of its renewable resource-based origin. PHB shows susceptibility to fracture when subjected to high rates of deformation. This work investigates toughening mechanisms for PHB via incorporation of functionalizede lastomeric components into the PHB matrix. A compatibilizer was investigated to improve the interfacial adhesion between the incompatible elastomer and plastic phases. The toughened PHB was characterized through their thermo-mechanical, rheological and morphological analysis. The resulting toughened PHB showed more than5 times improvement in impact strength over virgin PHB with around 60 % loss in modulus. The loss of modulus was recovered to permissible extent through incorporation of titanate modified montmorillonite clay. The hydrophilic clay was modified by titanate-based treatment to make it organophilic and compatible with the polymer matrix. Nanocomposites with this modified clay exhibited more than 275% improvement in impact properties with around 40% reduction in modulus in comparison with the virgin PHB bioplastic.
Composite filtration technology can be implemented less expensively to prevent fossil fuel burning power plants and nonroad and highway heavy-duty engines from releasing green house gases and air pollutants directly into our environments. Carbon-carbon composites (CCCs) were investigated for CO2 filtration from flue gas streams and air pollution filtration such as nitrogen oxide and hydrocarbons from diesel fuel emission. The porous structure of CCC filters was made of chopped carbon fibers and phenolic resin going through curing, pyrolysis and activation. In this study, CCC filters were synthesized under different combinations of pyrolysis and activation times. The structural, physical as well as thermal properties of CCC filters were studied: Scanning Electron Microscopy (SEM) showed the porous structure of CCC filters. Sorption and thermal swing was used for the surface area and adsorption capacity measurements. From the thermal gravimetric analysis (TGA), the thermal properties of CCC filters were investigated. The gravimetric processing has been shown to impact significantly on the filtration performance of CCC filters.
Adhesion of (Poly)carbonate (PC) with a carbon fiber filled (Poly) ether ether ketone (PEEK) compound (SP3000) was evaluated for an insert molding application. Composite samples of PC and SP3000 were injection molded as a function of injection speed, packing pressure, nozzle and mold temperature. The composite samples were tested in tension. Modulus was invariant. Breaking stress showed the most change with process conditions. In general, injection speed and packing pressure had little effect on ultimate properties. Nozzle and mold temperature were the governing variables for adhesive strength.
In dynamic analysis of composite structures the characteristic polynomials, associated with the discrete model (FEM/FDM), lack the ability to approximate the transcendental functions (continuous systems) accurately and they introduce error in evaluating the higher eigenvalues. Due to such dissimilar asymptotic behavior of the eigenvalues, higher frequencies of the discrete models deteriorate the reconstruction process. A low-dimensional mathematical model is developed here such that the non-uniform composite beam is approximated by another beam with piecewise constant physical parameters. Such approximation preserves the spectral consistency between the asymptotic behaviors of the original system and approximated system. The solution of corresponding inverse transcendental eigenvalue problems is developed and small scale vibration tests are conducted. A finite number of experimental spectral data is used for the reconstruction of non-uniform composite beams.
Last year (ANTEC 2004) we presented a new class of highly efficient organic Near Infrared (NIR) absorbers with a unique performance profile especially suited for laser transmission welding and transparent heat management applications. In this paper we want to introduce novel perylene based high performance black pigments with extraordinary high NIR transparencies. Their excellent thermo- and photostabilities, in combination with a neutral hue, high transparency and color strength make them the ideal candidates for black laser weldable formulations and opaque heat management applications. We present models for the explanation of the unique thermostability and weatherability of this class of compounds, as well as recent advances in the synthesis of those materials, and examples for state-of- the-art plastics applications
Electron Beam irradiated high density polyethylene (HDPE) and ethylene tetra fluoro ethylene (ETFE) was studied using dynamic rheology. The objective of this work was to compare and critique different modes and methods of dynamic mechanical testing, determine the best method or test to characterize the structural changes, and verify the governing phenomenon for structural changes in irradiated injection molded HDPE and ETFE. The predominant response to radiation in HDPE and ETFE is that of cross-linking. The tests were conducted in tension, bending, and shear.This study is limited to comparing the response of electron beam irradiated materials to the aforementioned tests. Effects of radiation levels and aging are beyond the scope of this work.It was found that dynamic shear testing at temperatures above the melting point of the materials is the best mode and method to finger print the structural changes in radiated HDPE and ETFE. The flexure test modulus results were higher than that from the tensile test.
Biaxially oriented Poly (propylene) [BOPP] films are extensively used in food packaging industry primarily because of their good barrier properties, machinability and printability1. We investigated the effect of flexographic UV-cured acrylic inks on to BOPP films with a focus on permeability towards oxygen and moisture. Temperature dependence on mechanical properties of the printed films was studied. Instron tensile strength, Mocon permeability tests, and thermodynamic results were obtained that suggest that there is no appreciable change in the physical properties when the films are printed with UV curing inks.
The thermal properties and rheological behaviors of polystyrene (PS)-based thermoplastics bearing polyhedral oligosilsesquioxane (POSS) were investigated with variation of isobutyl (iBu)-POSS weight percentage. The incorporation of POSS-group significantly decreases the glass transition temperature and the rubbery plateau modulus. These findings are attributed to an influence of the nanometer-scale POSS pendant group on the microscopic topology of the host polymeric chains and negligible interactions between POSS and PS matrix.
The rheological and thermal behavior of a powder injection molding feedstock (highly filled polymer blend) was studied using rheometry, and thermal techniques. The feedstocks were prepared using two mixing schemes. In the first scheme, an internal mixer and a twin-screw extruder were used. In the second scheme the blends were prepared in a laboratory internal mixer. The filler material was stainless steel and its content in the samples is above 90 % by weight. The rheological behavior of the feedstock was studied in dynamic mode. The techniques used and the results obtained are presented.
A critical phase in fabricating microfluidic polymer chips is welding of a cover to a channel in order to produce tube type geometry. A possible method to weld such a cover is by through transmission laser welding of polymer components. The major issue in welding of microstructured parts is blockage of the flow path by molten polymer (flash) resulting from a typical welding process. In this study, a sacrificial material technique is developed, in which a water-soluble material is used as a mold material to prevent weld flash from being allowed to flow into the channels. In detail, a sacrificial mold remains in the embossed parts instead of being separated from the part (De-embossing) after molding. A cover or other embossed part is then welded to this part. In this study, through transmission laser welding was used to fabricate such parts. The sacrificial material was then removed by dissolution in an appropriate solvent. Different mold preparation methods are discussed and examples of welded structures are given here.
In this work, cell coarsening in polymer foaming was investigated through numerical simulation. Cell coarsening occurring on two adjacent bubbles of different sizes in a finite volume of polymer melt was considered to be representative of the whole foaming system. A quadratic triangle-based finite element analysis with an implicit scheme for time evolution was utilized to solve the governing diffusion equation in the axisymmetric coordinate system. The effects of the bulk gas concentration, the intercellular distance, and the initial bubble sizes on cell coarsening were estimated. Efforts were made to improve a fundamental understanding of cell coarsening in polymer foaming.
A technique is described to quantitatively assess mixing effectiveness. The technique utilizes infrared (IR) analysis of dissimilar polymer blends. The rheology of the blend system can be tuned through temperature to easily derive a spectrum of viscosity ratios. The technique has been applied to two common laboratory mixing apparatus, a batch mixer and a mini-twin screw extruder. Mixing effectiveness of these two devices will be described within both spatial and temporal considerations. The relative merits of the different mixing techniques will be additionally discussed.
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ANTEC 2016 - Indianapolis, Indiana, USA May 23-25, 2016. [On-line].
Society of Plastics Engineers
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