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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Stress Corrosion Cracking of Nylon 6,6
Following a head-on car accident in which one driver was seriously injured, the cause was established by police as a leaking diesel return pipe on a recovery vehicle. Examination showed that the pipe had been cleaved across radially, and the Forensic Science Service attributed the failure to vandalism. Closer inspection revealed a brittle fracture which showed several growth phases, the first being initiated by stress corrosion cracking of the nylon connector in the pipe. The junction was immediately below the battery and it is likely that a drop of acid spilled onto it, starting the crack. It then grew at each successive start-up until final breakage. ESEM inspection showed fatigue-like striations and EDAX revealed the presence of sulphur. The injured driver was awarded substantial damages.
Stress Field in Extruded Cables Due to Cooling Process
During the cooling process of cables a complex temperature distribution appears in the polymer layer. A stress field is formed due to the temperature inhomogenity. A cooling and stress distribution mopdell have been developed and investigated. The material parameters (heat conduction coefficient, specific heat, density and heat expansion coefficient) depend on the temperature, the shear modulus depends on the temperature and loading time. In the model regression equation were used to describe the material parameters. An air and a water cooling processes were investigated. The cooling speed has a significant effect on the radial stress formed in polymer layer during the cooling.
Structural and Dynamic Investigation of Amorphous Solids by NMR
The real strength of solid state NMR spectroscopy reveals itself mainly if it is applied to amorphous materials, where the absence of translational order limits the usefulness of scattering techniques, and in the study of dynamic processes. Advanced multidimensional solid-state NMR techniques are capable of quantifying molecular order and packing in amorphous organic solids with high accuracy and specificity. In this paper, some recent results on the global and local orientational order that develops in Bisphenol-A Polycarbonate under plastic deformation are presented. and their implications for the (still unknown) underlying mechanism of plastic deformation is discussed.
Structural Characterization of Silane-Crosslinked Polyethylenes
LDPE, HDPEs and metallocene polyethylenes (MPOs) were grafted with vinyl triethoxy silane in co-rotating twin screw-extruders. Afterwards, the materials were crosslinked in water. Peroxide modified materials were also made. Degrees of crosslinking were measured by determining their gel contents after extraction of the soluble component in xylene and orto-dichlorobenzene. Dynamic rheological experiments were carried out for all materials at different temperatures. Five different catalysts were studied. The degree of crosslinking achieved for the PEs employed after curing follows the order HDPE1 > HDPE2 > LDPE. The degree of crosslinking achieved for the MPOs used after 24 hours of curing time was very similar. The crystallinities of modified HDPEs and LDPE are greatly affected by the crosslinking processes. However, the lamellar thickness distribution of the silane-crosslinking MPO materials is less affected.
Structural Recovery of Glass-Forming Polymers: Novel Temperature Perturbation Experiments
The phenomenology of structural recovery observed for glass-forming materials below their glass transition temperature is well understood. However, mathematical models of structural recovery are unable to simultaneously describe experiments performed over a wide range of thermal histories. We have developed a new experimental technique that uses intermittent temperature perturbations during volume recovery in order to obtain quantitative information concerning the evolution of the characteristic relaxation time (?p) for volume during structural recovery. The experiments are analogous to the intermittent creep experiments developed by Struik. Using an automated capillary dilatometer and a polystyrene sample, the timetemperature history dependence of the characteristic relaxation time for volume was investigated. For the set of temperature down jumps and memory experiments explored, the characteristic relaxation time appears to depend only on the instantaneous state of the material. However, the results suggest that the relationship between ln(?p) and the departure from equilibrium ?, may not be linear as is assumed in most models of structural recovery.
The Structure and Property Control of EPDM Rubber Using High Power Ultrasound
High power ultrasound treatment of ethylene propylene diene monomer (EPDM) rubber in extrusion process was found to affect its structure and properties. In comparison with the original EPDM rubber, the ultrasonically treated samples contained some amount of gel with sol having a higher molecular weight, possibly due to chain branching. Gel fraction and dynamic properties of the ultrasonically treated samples and their vulcanizates were measured as a function of processing conditions. Measurements of the stress-strain characteristics, dynamic properties and hardness of EPDM vulcanizates prepared after treatment indicated a possibility to control their properties by varying processing parameters.
Structure Development in Fiber Extrusion of Isotactic Polypropylenes of Varying Tacticity
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.
Structure Development of Extrusion Cast PET/PEN Blend Films in Biaxial Stretching Process
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.
Studies of the Process- Property Interaction of the Micromoulding Process
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.
A Study of Blown Film Nanocomposites Consisting of Polycaprolactone and Montmorillonite Clay
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.
Study of Flow Marks during Injection Molding
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.
Study of Polypropylene/ Polyamide 6 Blends by Raman Microspectroscopy
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 Study of the Foaming Process of Polyethylene with High Pressure CO2 in a Modified Extrusion System
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.
Study of the Parameters of Influence in the Mold that Vary the Roughness of Molded Parts
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.
Study of the Relationship between Crystal Size and Nano-Hardness in Ultra High Molecular Weight Polyethylene
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.
Study of Weld-Line Strength and Microstructure of Injection Molded Microcellular Parts
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.
Study on the Characteristic of New Type Screw Element in Co-Rotating Twin Screw Extruders
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.
Studying Additive Migration in LLDPE and Pop Films Using Synchrotron-Based FTIR Microspectroscopy
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.
Subinclusion Morphologies in HDPE/PS/PMMA Ternary Blends Prepared by Twin Screw Extrusion
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.
Sulfonated Block Copolymer Ionomers for Use in Direct Methanol Fuel Cells
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.
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