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.
We investigated the effects of tacticity on structure development in melt spinning isotactic polypropylene (iPP). The fibers were characterized using wide-angle x-ray diffraction (WAXD), birefringence and differential scanning calorimetry (DSC).The melt-spun fibers exhibited generally the monoclinic ?-crystalline form and sometimes mesomorphic form. The mesomorphic structure was formed more readily in lower tacticity fibers. We also found some hexagonal ?-crystalline form in all of the ?-form fiber samples. The amount was generally negligibly small, but lower tacticity fibers spun at high draw-down ratios exhibited significant amounts of the ?-form crystal.At low spinline stress levels, some of lower tacticity fibers exhibited lower birefringence and chain orientation than high tacticity fibers due to a less perfect crystal structure. At certain high stress levels, lower tacticity fibers exhibited higher birefringence and crystalline chain-axis orientation. This is attributed to a significant reduction in epitaxial lamellar branching. However, the extent of lamellar branching in lower tacticity fibers would seem to increase again at higher stress levels. This led to a significant decrease in birefringence and crystalline orientation.
The development of crystalline structure and orientation of extrusion cast poly(ethylene terephthalate) (PET) / poly(ethylene-2,6-naphthalate) (PEN) blend films in the biaxial stretching process was studied by means of Differential Scanning Calorimetry (DSC), Abbe Refractometer, and Wide Angle X-ray Diffraction (WAXD). All PET/PEN blends having different compositions (100/0, 75/25, 50/50, 25/75, and 0/100) were extruded into transparent films showing excellent miscibility. The extrusion cast films were successfully biaxially stretched up to stretch ratio of ?MDx?TD=4x4. Stretching operation involved crystallization and orientation. Highly stretched films of these blends crystallized into triclinic unit cells during stretching operation. The d-spacings of the lateral reflections about the c-axis, which were calculated from the WAXD patterns, indicated that the crystal structures of blends were different from those of pure polymers. In the biaxially oriented pure and blend films, flat phenyl ring and naphthalene groups of PET and PEN, respectively, were preferentially aligned parallel to the film surface. The chain orientation of crystalline and amorphous regions was found to be dependent on the stretch ratios.
Activities in MEMS and biomedical applications are placing increasing demands on industry for product miniaturisation. In turn, this is leading to developments in materials processing. In this context the micro-injection moulding ( micromoulding ) of polymers and composites has evolved as a technology for the manufacture of intricate components of mass less than 0.001g. However, some fundamental issues need addressing for the process, and especially its products, to gain wider acceptance by the manufacturing sector. In particular, during the injection process polymers and composites are often exposed to severe processing conditions. For example, simple analysis of the injection rates reveals that melts can be subjected to shear rates > 1*106 s-1 on flow through the feed system in micromould tools. Such severe processing conditions may have a detrimental affect on the polymer properties and adversely affect the functionality and longevity of the final component. Studies conducted within our laboratory are focused on enhancing the understanding of polymer processing-property interaction, and especially the effects of micro-scale processing on the rheological and mechanical properties of polymers and composites. Our studies will investigate the effects of micro-scale processing on engineering and commodity polymers, nanocomposites, metal and ceramic injection moulded feedstock and biomaterials. In this paper we present the findings of some initial studies on moulded rectangular plaques of a miniature moulding scale. Surface micro-morphology and mechanical properties of mouldings are investigated using SEM and atomic force microscopy using contact and tapping modes.
The shrinkage is determinant on the final dimensions of technical parts. This feature of the injection moldings is dependent on the processing setup, namely the holding pressure and the molding temperature.In this paper results are presented on studies made on a semi-crystalline material and an amorphous material that were molded in planar and tubular moldings. The shrinkage was directly measured and related to the frozen-in orientation of the part. The orientation was indirectly quantified by the across-thickness variation of the birefringence.
Nanocomposite blown films of polycaprolactone (PCL)/montmorillonite clay were investigated to determine the influence of processing conditions on the polymer-clay interaction. PCL and clay at various loadings (2, 3 and 5%) were processed using a twin-screw extruder with various screw speeds, barrel temperatures, and feed rates. The interaction of the polymer and clay was determined by x-ray diffraction and transmission electron microscopy. Exfoliation was optimized with slower screw speeds and feed rates. The thermal and mechanical properties of the films were examined. The transition temperatures of PCL did not change significantly in the nanocomposites, but tensile strength and modulus increased as a result of increasing the feed rate or reducing the screw speed during processing.
In this paper, alternate and synchronous dull and glossy flow marks are studied. The effect of rheology, flow front velocity, mold geometry, melt temperature, mold temperature, and mold surface coatings on flow marks was studied. For the alternate flow marks, it was found that the flow marks did not occur at high injection speeds. The generation of the flow marks is explained by entry viscoelastic instability. For the synchronous flow marks, it was found that coating these surfaces could not prevent the occurrence of the flow marks, although it could alleviate them. Slip is not the cause of the generation of the synchronous flow marks.
Binary blends of polypropylene (80 and 60 weight %), polypropylene grafted with diethyl maleate and polyamide 6 were prepared in a Leistritz co-rotating twin-screw extruder at 230ºC, 90 rpm and 9 Kg/h of mass flow rate. Scanning Electron Microscopy (SEM) combined with Raman Microspectroscopy (RM) in samples previously tested in an Instron tensile equipment showed the effect as interfacial agent of the functionalized PP. In fact, when the PP-g-DEM was used an homogeneous dispersion with smallest and elongated particles was found. Tensile properties and heat distorsion temperature were also determined.
A conventional single screw extruder is used to process polymeric materials (HDPE, LDPE) in the presence of high pressure CO2. The extruder has been modified to allow for high pressures created by the injection of high-pressure CO2 into the system. The redesign includes a modified feed section that allows a given mass of polymer to interact with a metered amount of CO2 prior to the extrusion process. A variety of extrudate morphologies are obtained as a consequence of the inherent shear mixing and the presence of high-pressure CO2. Some of the relevant parameters in the foaming process of HDPE and LDPE during extrusion are analyzed and related to the processing conditions.
The research project to study the influence of the mold roughness in the roughness of molded parts (PA 6.6/6 reinforced with glass fibres) was the result of collaboration between the University of Vigo and the University of Minho.The design of experiments was applied to studing the behavior of the roughness of molded parts. The material with glass reinforcement was considered and the same plastic in a neat (no reinforcement added) condition. Different shapes of test molded parts were also considered.Finally a model was obtained relating the different parameters of the mold and the roughness of the molded parts.
Gamma radiation was used to induce chemical modifications in ultra high molecular weight polyethylene. UHMWPE specimens were compression molded and gamma irradiated in an inert atmosphere at dosages of 75 and 150 kGy. The surface hardness and modulus were characterized by nano-indentation. The effect of the gamma irradiation treatment on the surface properties was determined to a depth of 20,000 nm. The surface modulus and hardness exhibited a dependence on radiation dosage. The UHMWPE sample irradiated at 150 kGy exhibited the highest surface hardness and modulus. Both the modulus and hardness show a direct dependence on crystal thickness.
Microcellular injection molding (also known as MuCell process) can produce parts with excellent dimensional stability using lower injection pressure, shorter cycle time, and less material. This study is aimed at understanding how the process conditions affect the weld-line strength and microstructure of microcellular injection molded parts so that the advantages of the process can be fully realized. A design of experiments (DOE) was performed to produce polycarbonate tensile test samples with four systematically varied process conditions. It has been found that the weld-line strength increases with increasing melt temperature, injection speed, and shot size and is weakly dependant on the supercritical fluid level. This paper also presents the microstructure of the molded samples at various cross-sections.
In order to meet the development towards higher speed and efficiency of co-rotating twin screw extruders, we designed and manufactured a new type screw element of co-rotating twin screw extruder, it has linked together left and right hand flights and large pitch, i.e. similar to inner mixer rotor. After carrying out flow field simulation of this element, we carried out a lot experiments to verify the calculating results. The calculating and experimental results indicate that this new screw element is possessed of better plasticating and mixing ability, lower melt temperature and lower energy consumption than the conventional screw elements and FAMME.
The migration of additives in thick (~500 ?m) single layer and multilayer films has been characterized using FTIR microspectroscopy [1,2]. The objective of this research was to investigate additive migration and concentration profiles in single-layer and coextruded bilayer films of industrially relevant thicknesses. In particular, the investigation focused on the migration of an erucamide slip agent in 50-?m thick extruded films of linear low-density polyethylene (LLDPE) and a polyolefin plastomer (POP). Erucamide concentration profiles were successfully mapped using synchrotron-based FTIR microspectroscopy. The synchrotron radiation helped to achieve a higher spatial resolution for the thin films. A meticulous sample preparation was needed to map the thin film samples. Results with FTIR microspectroscopy showed that the additive-concentration profiles were relatively uniform across the multilayer-film thickness irrespective of the intended initial additive distribution. Results also showed that more erucamide migrated to the surface of a POP layer than an LLDPE layer.
Ternary blends of PS and PMMA in a PE matrix were prepared by twin screw extrusion to investigate the effect of viscosity ratios, sequence of addition and composition on the core/shell encapsulation phenomenon. The morphology was observed by SEM after selective extraction of either PS or PMMA. Composite droplet morphologies were observed with PS encapsulating PMMA as predicted by spreading coefficient theory. Processing and material viscosity effects are discussed. Good agreement was found between the obtained morphology and those expected from the theory of spreading coefficient.
Optimizing the efficiency of direct methanol fuel cells (DMFCs) requires the use of polymer electrolyte membranes the exhibit high proton conductivity and are resistant to methanol crossover (1). Figure 1 shows a schematic of how methanol crossover takes place. To accomplish this, a novel class of self-assembled block copolymers have been developed and investigated. The novel polymers are comprised of tri-blocks of polystyrene-polyisobutylene-polystyrene (PS-PIB-PS). The major component of the copolymer is PIB lending low temperature flexibility to the material and good barrier properties (2). When the PS monomers are chemically modified via sulfonation, the microphase-segregated morphology provides pathways for ion conductivity through the polymer film, while preventing methanol diffusion.In this study, the proton conductivity and methanol permeability of a series of sulfonated (PS-PIB-PS) polymer membranes have been examined. The polymers were sulfonated at various levels ranging from 0 – 40 % by weight in PS and compared to Nafion 117, a polymer currently utilized in fuel cell applications. Results reveal that these membranes show improved resistance to methanol permeability while providing sufficient ion conductivity to be used in fuel cells.
Proton exchange membrane (PEM ) fuel cells represent an attractive alternative to conventional power plants, especially the internal combustion engines (ICEs) used in motor vehicles. They are inherently more efficient than ICEs, which results in better fuel economy and lower fuel costs, have no moving parts, have lower CO2 emissions and do not emit common air-pollutants such as SO2, NOx and unsaturated hydrocarbons. A polymer electrolyte membrane is a crucial component of the PEM fuel cell. The membrane serves both as the electrolyte and as a separator to prevent direct physical mixing of the hydrogen at the anode and the oxygen at the cathode.
Global regulatory agencies are implementing strict guidelines associated with Transmissible Spongiform Encephlopathies (TSE). Medical manufacturers need to certify that their products are free of bovine derived products. In order to comply with these mandates, medical manufacturers must identify and address sources of their starting materials including active ingredients, excipients and reagents. Some additives utilized in the thermoplastic industry have bovine components.The following system allows a medical manufacturer to systematically search their processes and identify potential issues with meeting regulatory mandates.
Crosslinked rubbers and ground tyre rubber (S-GTR) have been treated using a surface grafting process allowing the incorporation of carboxyl and epoxy groups onto the polymer surface. The rubber were functionalised with glycidyl methacrylate (GMA) or methacrylic acid (MA) by photoinitiated grafting. The grafting degree of the rubber was determined by attenuated total reflectance Fourier-transform infrared (FTIR-ATR) spectroscopy. The grafted GTR can well be incorporated in various thermoplastics and thermosets. The surface grafting strongly enhances also the glueing ability of rubber sheets.
Polypropylene (PP) containing terminal unsaturation was modified with a hydride terminated polydimethylsiloxane (PDMS) through a catalytic hydrosilylation reaction in the melt phase at various temperatures. This paper presents a comprehensive study of the surface characteristics of these hydrosilylated polypropylenes (SiPP) using the axisymmetric drop shape analysis - profile (ADSA-P) technique and atomic force microscopy (AFM). Static and dynamic contact angle experiments were carried out using ADSA-P. The results of contact angle measurements show that the lower the reaction temperature, the larger the static/advancing contact angle, the smaller the permeability coefficient, and the more hydrophobic the surface. Surface topographic and compositional features were investigated using lateral force mode of AFM. All sample surfaces were rough on a micrometer scale and two different compositional domains were found to exist on the sample surfaces. The results show that decreasing the reaction temperature increases the amount of incorporated PDMS.
Mold release compounds can be transferred to molded parts and interfere in downstream painting, decorating, and bonding operations. These agents also accumulate on tool surfaces necessitating periodic cleaning which disrupts productivity and can involve the use of caustics or solvents. This study reports the promising results of using short duration exposures to UV irradiation to remove mold release compounds from both metals and non-metallic materials, such as plastics and polymer composites. In this study assorted materials were intentionally contaminated with heavy amounts of industrial mold release agents. The surfaces were rapidly and efficiently cleaned following exposure to high intensity UV light as demonstrated by a significant reduction in the water contact angle. UV treatments provide an environmentally benign alternative means to remove mold release compounds from tool or molded part surfaces.
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