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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Solid State Polymerization of Recycled Poly(Ethylene Terephthalate) - The Influence of Process Conditions in the Increase of Molecular Weight and Thermal Properties
The solid state polymerization (SSP) of recycled PET from 2L bottles was investigated. The bottles were ground, washed, dried, crystallized and processed in a reactor under heating and nitrogen flow. The material was feed in the reactor as flakes and not in pellet form, so an extrusion step was eliminated. A systematic study of the influence of process conditions, like crystallization temperature, SSP temperature, reaction time and nitrogen flow rate was carried out. The weight-average molecular weight of the recycled PET were measured by SEC. Thermal properties and crystallinity were determined by DSC.
Spatially Controlled Growth of Polyelectrolyte Multilayer Islands
We are pursuing a new method for the rapid processing of polymeric multilayers with spatial resolution based on a combination of Electrostatic Self Assembly (ESA) and contact deposition using swollen hydrogel applicators. Thus far, we have demonstrated the build-up of multilayered polymeric structures (10-200 nm thick) by using separate applicators swollen with either a polyanion or polycation solution and pressing them upon a pristine substrate. The swelling response of the photopolymerized hydrogel is an important phenomenon. We find that the steady state swelling in water depends on the crosslink density while observations of the swelling behavior in polyelectrolyte solutions revealed a dependence on both ionization and concentration. We found that as more PAH (polyallylamine hydrochloride) is added to the solution, the degree of swelling decreases slightly and as the crosslink density is decreased, the percent swelling increases. PMAAc (polymethacrylic acid) has a contrasting effect on the swelling of the hydrogel; at full ionization, a slight amount of PMAAc surprisingly promotes swelling. Using Atomic Force Microscopy, we compared surface structures of ESA done by dipping with those created by stamping. The AFM from contact ESA showed favorable homogeneity, but some large features that are hypothesized to come from aggregates that form in the stamps.
Spectrum Determination for a Very Broad Molecular Weight Distribution Polyethylene
The relaxation spectrum of a very broad molecular weight distribution (MWD) high-density polyethylene (HDPE) was estimated using dynamic linear viscoelastic data. The spectrum, which does not cover a sufficiently broad time range to include all of the relaxation processes, does indicate that the material exhibits some extremely long relaxation times. A relaxation spectrum was also estimated from the molecular weight distribution using the sophisticated technique recently proposed by Leonardi et al.1. The measured and predicted spectra agree at short time scales but not at long time scales. The source of this discrepancy is elucidated.
Standard Reference Materials: Non-Newtonian Fluids for Rheological Measurements
The National Institute of Standards and Technology (NIST) develops Standard Reference Materials® for calibration, quality assurance and for research into improved measurements. Two fluids that demonstrate shear thinning and normal stresses typical of polymeric fluids have been developed as standards for rheological measurements. SRM 2490 is a solution of polyisobutylene dissolved in 2,6,10,14-tetramethylpentadecane. SRM 2491 is a poly(dimethylsiloxane) melt, with less temperature dependence than SRM 2490. NIST certifies the shear-rate dependence of the viscosity and first normal stress difference at 0 °C, 25 °C and 50 °C, and the linear viscoelastic behavior over the same temperature range.
Stearic Acid and Particle Shape Effects on Rheological Properties of Talc, CaCO3 and Talc/CaCO3 Filled Polypropylene Composites
The effect of stearic acid on the particles and the effect of the particle shape on the shear/dynamic viscosity have been investigated using uncoated and coated talc, calcite and mixed talc/calcite filled polypropylene composites. The viscosity of the stearic acid coated filler particles exhibited much less than the uncoated fillers. In addition, the effect of stearic acid was more significant on coated calcite than the coated talc system. The real yield value measured using a sandwich creep measurement exhibited lower than obtained from the extrapolation. The isotropic calcite seems to give less interfacial force and hydrodynamic resistance between the filler and the polypropylene matrix than the anisotropic talc at low shear rate/stress. The Cox-Merz relation fails between the complex and shear viscosity for the both uncoated and coated compounds.
Strength of Vibration Welds Made from Dissimilar Nylons
Vibration welding of dissimilar nylons is a promising joining technique for assembling complex components made of different polymers. The effects of pressure and meltdown on the tensile strength of nylon 6 (PA 6) to nylon 66 (PA 66) vibration welds were determined in this study through an experimental design on several weld geometries. All weld strengths were affected by weld pressure and meltdown. The weld strength was also shown to vary with the position of the lower melting material for T-welds. Using DSC and fracture surface analyses, it is concluded that for all geometries, higher weld strengths can be achieved when the both materials are melted.
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.
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