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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Model of Isothermic Laser-Sintering
In the product development of plastic components, increasing use is made of laser-sintering (LS) processes [1, 2, 3, 4]. To improve properties of prototypes, the main goals of development are reproducible density, to maintain edge sharpness, and to prevent uncontrolled shrink-age. Today, R+D mainly focuses on laser-technology, development of scan strategies, and LS process optimization.Another approach to make LS even more effective for product development is to identify the most important material properties of possible raw materials (polymer powder). The knowledge of significant material proper-ties could be an important tool for the choice of the correct material as well as for the development of new raw materials (structure- and chemistry synthesis).Thus, the current research of our group summarized in this paper mainly focuses on formulating requirements for LS raw materials . Therefore, the theoretic model of isothermic laser-sintering was developed. Based upon this model it can be shown that the most important requirements for raw materials refer to crystallization and melting behavior as well as surface tension and melt viscosity.
Model Studies in Enzyme Catalyzed Transesterification Reactions
Lipases are now known to also function as polyester synthases. In a previous report, we showed the ability of Lipase B from Candida antartica (Novozyme-435) to catalyze transesterification reactions between preformed polymer chains. To further study the kinetics and mechanism of these reactions, model reactions were performed using benzyl alcohol as the nucleophile and various aliphatic polyesters as substrates. Effects of the reaction temperature, time, nucleophile concentration, and the structure of the polymeric substrates on the rate of transesterification are reported. We also report the extent that these transesterification reactions occur with selectivity with respect to the site on chains that is cleaved.
Model-Based Control of Material Distribution in Thermoformed Parts
The thermoforming industry has achieved a good understanding of the process, which has been in large scale operation since the 1950's. Consequently, control of machine settings such as heater band temperatures, plug position, plug and mould temperatures is quite advanced. However, to date, little work has been done to address the control of state parameters describing material behaviour during processing, such as sheet temperature and material distribution in the part. Control of state parameters is essential as material property changes, environmental factors and machine operating drifts can significantly change the dynamic operating point of the machine.
Modeling of the Temperature Profile in Film Coextrusion
The question of temperature in film coextrusion is an important issue for the quality of the product. Since a direct measure of the temperatures in the melt is difficult, the modeling gives the values of the local temperatures, and the velocity profile as well. Important is the determination of the temperature at the interfaces of the layers, since this allows to compute the viscosities and the stresses at the interfaces. The ratio of the stresses is important in order to predict if the flow is stable, and to avoid instabilities. The knowledge of the temperature makes possible to avoid local overheating. We present a software running on a PC, a good tool to predict local peaks of temperature.
Modeling Peroxide Crosslinking in Polyolefins
By combining sol-gel analysis and curemeter testing with a Monte Carlo simulation, the 160°C dicumyl peroxide initiation efficiency and scission/crosslinking ratio of a metallocene catalyzed ethylene 1-octene elastomer was determined to be 48% and 0.24, respectively. Using a calibrated simulation analysis, the network structural evolution during crosslinking was determined. Commonly used methods of curemeter interpretation were found to be severely flawed due to the combined effects of nonlinear evolution of elastically active chains, trapped entanglements, and slowly relaxing chain structures. A framework for correct interpretation of cure behavior is described.
Modeling Stress-Strain of Glassy Polymers up to Yield
Based on a picture of a polymeric glass as a mosaic of nanoscale clusters of differing viscoelastic characteristics, we propose a new model for glassy polymers that accurately captures the stress-strain dependence at different rates and temperatures from small strain up to yield for polycarbonate. The model allows one to interpolate and extrapolate limited experimental data (it requires three stress-strain curves as input). The model also provides insight into the fundamental issue of glassformer fragility" in the glassy state and a practical means to assess dynamic inhomogeneities within polymeric glasses."
Modeling the Temperature Variation of Intrinsic Viscosity Using a Temperature Dependent Scaling Exponent
Intrinsic Viscosity measurements are usually analyzed using the empirical Mark-Howink-Sakurada equation, which gives a power-law dependence of the intrinsic viscosity to the molecular weight of the polymer. Variation of the scaling exponent, a" with temperature is only poorly understood necessitating individual measurements at each temperature for every polymer/solvent system. The temperature dependence of "a" is shown to fall on a single universal curve under appropriate rescaling of the temperature of the solution. A method to obtain "a" from the static exponent is also described."
Modification of High Flow Polypropylene by Ethylene/a-Olefin Elastomers Produced by Single Site Constrained Geometry Catalyst
The recent advent and commercialization of technology using single site, constrained geometry catalyst has made possible the introduction of unique ethylene/a-olefin elastomers with novel molecular architecture. These advances in elastomer technology have resulted in differentiated materials capable of impact modifying polypropylene polymers thereby offering new TPO blends with enhanced properties. This paper will explore high flow polypropylene blends modified with this distinct class of elastomers and will discuss the influence of elastomer comonomer choice, molecular weight and crystallinity along with discussions on the effect of dispersion, morphology and rheology.
Modification of Nylon-6,6 through Solid-State Polymerization in Supercritical CO2
The solid-state polymerization of nylon-6,6 has been studied in the presence of supercritical (SC) carbon dioxide (CO2 ) in a small autoclave. Experiments have been carried out under varying pressure and temperature conditions at several reaction times. In addition, experiments have been performed in the presence of nitrogen (N2) which is commonly used in commercial solid-state polymerization processes. The results indicate that the samples produced in the presence of CO2 have higher molecular weight and viscosity compared to those produced in the presence of N2 under the same reaction conditions. Furthermore, the polyamides produced in SC-CO2 have higher end group differences.
Modification of the PP/HDPE Blend and the PP/HDPE/Woodflour Composite Using Peroxide
The mechanical, thermal and rheological behavior and the morphology of a Polypropylene (PP)/high density polyethylene (HDPE) blend and of the PP/HDPE/Woodflour composite, both modified with peroxide, were evaluated. A decrease in the apparent viscosity of the blends with the increase in the content of peroxide was found. None of the peroxide modified samples showed significant variations in the melt and crystallization temperatures. The blend modified with 0.04 phr of peroxide showed the highest Young's modulus of all. The woodflour produced a significant increase in the viscosity and the Young's modulus of the composite.
Moisture as a Foaming Agent in the Manufacture of Rigid PVC/Wood-Flour Composite Foams
Relationships between the density of foamed rigid PVC/wood-flour composites and the moisture content of the wood flour, the chemical foaming agent (CFA) content, the content of all-acrylic foam modifier, and the extruder die temperature were determined using a response surface model (RSM) based on a four factor central composite design (CCD). The experimental results indicated that there is no synergistic effect between the CFA content and the moisture content of the wood flour. Wood flour moisture could be used effectively as foaming agent in the production of rigid PVC/wood-flour composite foams. Foam density as low as 0.4 g/cm3 was produced without the use of chemical foaming agents. However, successful foaming of rigid PVC/wood-flour composite with moisture contained in wood flour strongly depends upon the presence of all-acrylic foam modifier in the formulation and the extrusion die temperature. The lowest densities were achieved when the all-acrylic foam modifier concentration was between 7-phr and 10-phr and extruder die temperature was as low as 170°C.
Mold Design and Manufacture an Approach to Innovation and Sustained Development
The Portuguese mouldmaking industry has a driving force for competency and innovation. This attitude relies on the embodiment of the latest developments in science and technology. In 1999 the University of Minho was challenged to design a course to materialize that purpose.This idea sprung from one of the regular meetings of the Advisory Council to the Department of Polymer Engineering involving representatives of the Plastics and Moldmaking Industries and the University of Minho. As a result an MSc course is now running in cooperation with the industry.This initiative deserved the interest of the Agency for Innovation within the Ministry for Science and Technology, who meant it to be a stimulus and commitment to the joint initiatives towards the improvement of the know-how in the fields of molds and plastics, involving the government, the industry and the university.The course includes core subjects as Injection Molding or Manufacturing, and options as Communications Networks or Rapid Tooling Prototyping.The globalization of science and technology suggests this experience being open to other countries, for example developing an English version of the course with international cooperation of specialists.
Monitoring the Changing State of a Polymer Using Insitu Frequency Dependent Dielectric Sensors during Polymerization, Fabrication and Use
Essential to 'intelligent manufacturing' and 'smart materials' is the ability to monitor the state of a polymer resin as it is synthesized in a reactor, as it cures during fabrication and as it ages during uses in the field. Important aspects of this sensor monitoring capability are: in situ, on-line measurement; that the signal output be related to the relevant processing and use properties; sensitivity with long-term reliability in a manufacturing and field environment. This paper addresses how to successfully use in situ dielectric sensor measurements to monitor the changing state of a polymer resin during fabrication and/or use both in the laboratory, in an industrial plant, and during use in the field. The talk will address thermoset and thermoplastic materials as neat resins, composites and coatings.
Morphogloy Evolution of Binary Polymer Systems Using Microfabricated Samples
Binary polymer blends with well-defined initial structure were prepared by Computer Numerical Controlling (CNC) machining, photolithography and micro-embossing. Using the methods, we designed the size and distribution of the dispersed phase and the composition of the blends. Compatibilizer can also be easily placed at the interface of the two components during sample preparation. With the micro-fabricated samples, the dynamics of phase inversion and the morphology evolution of binary polymer blends were studied in simple shear flow under isothermal conditions. The effects of interfacial tension, viscosity rate, blend composition, and shear rate on rheology and morphology evolution were investigated.
Morphological Development and Mechanical Performance of Injection Molded Starch Based Composites
Conventional injection molding and Multiple live Feed Molding (MLFM) has been used to process starch based biodegradable composites aimed for load bearing bone replacement/fixation applications. Blends of starch with : (i) poly(ethylene vinyl alcohol) and (ii) cellulose acetate were studied. Both polymers were reinforced with bone-like ceramics (hydroxylapatite) in amounts up to 50 % wt.. The use of MLFM allowed for the inducement of molecular anisotropy into the moldings. However it was necessary to prevent material degradation associated to shear dissipation effects and to the longer residence times.
Morphological Studies on Poly (Trimethylene Terephthalate) (PTT) / Clay Nanocomposites
A series of intercalated Poly (trimethylene terephthalate)/ montmorillonite (PTT/MMT) nanocomposites were produced by a melt intercalation process. The PTT/MMT nanocomposites were shown to have similar d-spacing, about 3.1nm. More coherent stackings of silicate layers were observed at higher clay concentrations and shorter blending time. Compared to conventional PTT filled with MMT, the nanoscale dispersed MMTs are more effective nucleating agents and enhance the crystallization of PTT. The influence of nano montmorillonites on the crystallization and melting behavior becomes distinct when the concentration of MMT is greater than 1%.
Morphological Study of Polyamide-6/Polysyrene/Polyethylene Ternary Blends
The morphology of Polyamide-6 / Polystyrene / Polyethylene blends was predicted based on spreading coefficient of three components, and the predicted morphology was compared with the actual blending morphology. Without any treatment such as compatibilizers and changes in mixing sequence during the melt blending, it has been observed that PE domains are exclusively located in the PS phase in PA6 matrix, as expected by the spreading coefficient. In this study, trials to control the locus of the PE domains were also performed. It should be noted that the locus of the PE domains is successfully controlled. Thus, the PE domains can be dispersed in PS phase exclusively, in PA6 matrix exclusively or both in PA6 matrix and in PS phase. Effects of SMA and PS on the PA6/PE blending morphology were also investigated. It was found that SMA reduce the size of the disperse PE domains dramatically, in spite of no specific interaction expected between SMA and PE. This phenomenon was successfully explained by the spreading behavior of PS on PE in PA6 matrix. A small amount of PS added also affects the co-continuity of PA6/PE blend.
Morphology and Properties of Oriented mLLDPE Films
Cast films of a metallocene Linear Low Density Polyethylene (mLLDPE) have been cold-drawn along MD in two sequential steps to form ultra-oriented films. The initial films are cast under low shear conditions to form essentially isotropic films. The first draw yields oriented films, which display block-shear type morphology. Under controlled conditions, void formation occurs during the second draw and the ultradrawn films whiten and display a fine crystalline morphology. In their ultra-oriented state, the water vapor transmission of the films is equivalent to that of poly(vinylidenedichloride) (PVDC). Independent experiments show that this ~13x decrease in the WVTR is due to an increase in the degree of crystallinity and increase in tortuosity due to the blocky crystalline morphology. Additionally, it is hypothesized that an increase in the amorphous phase density also contributes to the decrease in permeability.
Morphology and Stress-Relaxation of Biaxially Oriented Crosslinked Polyethylene Films
In the present work the morphology and stress-relaxation of crosslinked polyethylene films were investigated. The stress-relaxation of crosslinked films was studied as a function of temperature and as a function of the irradiation dose applied. The relaxation time spectra of crosslinked films were observed to display additinal relaxation times. Irradiation dose and temperature were shown to influence the relaxation time spectrum of crosslinked and non-crosslinked films. The crystallization of crosslinked and non-crosslinked polyethylene was compared. It was shown that the lower mobility of the crosslinked molecules affects the final crystal size.
Morphology Development in I-PP Articles Moulded via Cryogenic Gas-Assisted Injection Moulding
The current experimental study investigates the development of the micro-morphology across the residual wall thickness and along the gas channel of specimens moulded via a recently developed cryogenic gas-assisted injection moulding process. This novel method was developed as an alternative to conventional gas-assisted injection process (GAIM), targeting cycle time reduction by improving the internal heat transfer from the polymer melt to the gas. The cryogenic GAIM process employs the injection of nitrogen gas at cryogenic temperature into the polymer melt stream and its controlled manipulation throughout the gas holding phase. The effects on the morphology induced by the injection of gas at cryogenic temperature are investigated using polarised light microscopy and the results compared with the structure produced at conventional GAIM temperatures. Differential interference contrast (DIC) is used to characterise the morphology of the internal surface.
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