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.
The unequal flow of polymer, through a die, is a common problem in industry. This imbalance in flow is due to a non-uniform flow path resulting in different velocities at different points in the die. This problem is commonly fixed by adjusting the die or pin position to compensate for the uneven flow. In complex die shapes, compensating for uneven flow cannot be done as easily. Simulation software was used in a verification study to ensure that the results from the software matched the experimental results. This will be useful in industry's determining of the validity of such software.
EWI has developed a concept of simultaneous butt and lap double-secure beadless joints for tubular plastic components and tested it experimentally on high-purity (HP) polyvinylidene fluoride (PVDF) and high-density polyethylene (HDPE) pipes. The technique is based on through-transmission infrared (TTIR) welding method and uses an IR energy source placed outside of the joint area, so pre-assembled parts can be welded. The original joint design incorporates two welds: the lap and butt welds. The lap weld, which utilizes a straight coupling, provides structural strength to the joint. The butt weld between the pipe ends, while contributing to the overall strength, seals the gap without any bead, and forms a smooth transition from one pipe to another.Butt/lap joints offer considerable advantages, such as strength and security, absence of the internal bead, and inspectability, and while this project demonstrated that it is possible to produce such joints, further work is needed before the process will be fully developed and refined for specific applications.
A new approach to determining the molecular weight distribution of metallocene (mPE) and conventional polyethylenes using a single capillary rheometer technique is reported here. The melt flow properties of a range of 17 mLLDPEs and 4 conventional LLDPEs with different MFIs, densities and co-monomer types (butene, hexene, octene), from six different suppliers were investigated using this technique. The results show a direct correlation between melt flow rate ratio and molecular weight distribution (MWD,) measured by Gel Permeation Chromatography: MWD = (2.34 x MFRR) - 5.14. A direct correlation between weight average molecular weight (Mw) and melt flow index for the resins was also determined: Mw = 1.09 x 105 MFI-0.26.
This paper demonstrates how the rotational foam molding process can be employed for the manufacture of plastic articles that have a distinct layer of non-foamed skin surrounding a foamed core or layer. It is focused on the single-step processing principle the main feature of which is the simultaneous introduction of both the foamable and non-foamable resin into the cavity of the mold at the beginning of the cycle. Although this advanced concept eliminates the need for process interruptions and the use of drop boxes or plastic bags, it requires an appropriate processing strategy that would assure that the execution of the adhesion of the non-foamable thermoplastic resin to the internal surface of the mold always takes place prior to the activation of the foamable resin.
Rotational molding is used to produce hollow plastic parts. The polymer, usually in powder form, is loaded into a mold. The mold is then heated and rotated biaxially. During the heating process, the tumbling powder gradually melts and sticks on the mold surface. Heating is continued after the powder has melted until complete densification is achieved. The mold is then cooled and the molded part is removed. As the powder particles adhere to the mold surface, pockets of air are trapped within the melt and form bubbles. The presence of bubbles is an inherent drawback in a finished molded part. It impairs the aesthetic value and the mechanical strength of the product. The polymer sintering phenomenon plays a major role in both the molding cycle and the properties of the final parts.This work is part of a research program whose objective is to examine the sintering behavior of ethylene copolymers under conditions related to the rotational molding process and to determine the relative effects of the polymer molecular structure on the sintering process. It is also expected that in addition to the polymer molecular structure, the preatreatment imposed on the resins during the pulverization process also influences sintering behavior. The magnitude of these effects is, however, difficult to quantify. Experiments using both powder particles and cylindrical particles are conducted in this work to obtain a general overview of the effect of pulverization on the sintering process.
Previous work in flow simulation and runner system balancing has demonstrated the impact that small changes in gate size have on cavity filling. Gate wear affects shear rate and in turn, the viscosity of the melt. The flow of glass filled material has long been identified as a factor in tool wear. As part of the long-term wear studies of copper alloys and tool steels at Western Michigan University, careful scrutiny was given to wear of edge gates due to the flow of molten plastic. Certain hard coatings and alloys were shown to demonstrate superior resistance to wear.
Interest in polypropylene (PP) nanocomposites has increased considerably recently, especially in the automotive industry where PP comprises the main constituent in rubber modified PP blends for exterior and interior applications. The potential for increasing the mechanical properties with small reinforcement concentrations has driven much of this interest. However, it has been known that PP exhibits prominent skin-core effects. Here it is investigated this effect for nanocomposites using transmission electron microscopy, X-ray diffraction and thermal analysis. Further tensile and fracture toughness measurements are done as a function of concentration. Real time Infrared thermal wave imaging coupled to the mechanical testing is used to examine plasticity changes.
Significant developments in finite element modelling of the thermoforming process have been observed in the recent years. The large deformations of the sheet that occur during sagging and forming have traditionally been modelled using membrane or shell type elements. This paper proposes a 3D solid finite element approach for improving the part wall thickness predictions. A 27-node brick element with incompressibility constraint is presented for modelling large viscoelastic deformations of the sheet. An experimental validation on a vacuum formed part with three different sheet thicknesses is presented. A comparison with the membrane formulation is also provided.
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.
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.
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.
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.
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.
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.
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.
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.
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.
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.
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.
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.
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