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.
Environmental Protection Agency requirements for control of stormwater runoff are increasing the need to provide on-site stormwater storage as part of site development projects. Underground stormwater storage is one solution to this need. Open bottom thermoplastic chambers make use of profile design theories established for thermoplastic pipe and allow maximum area at the bottom for natural seepage of the stored water into the ground. This paper reports on analysis and testing of archshaped, open bottom, corrugated polypropylene stormwater storage chambers that have spans of 1270 mm (50 in.) and are supported on a flat, turned-out foot. Computer analysis included finite element, soil-structure interaction models of chambers with 450 mm (18 in.) and 2440 mm (8 ft) of fill with AASHTO HS20 design axle load. Field-testing included chamber installations at shallow cover from 150 mm (6 in.) to 600 mm (24 in.) with vehicle live loads and at deep cover with 3500 mm (11.5 ft) fill. Design calculations were based on the new AASHTO procedures for profile wall thermoplastic pipe. Using prescribed installation procedures, the factor of safety is greater than the required AASHTO factor for thermoplastic pipe of 1.95.
Devices that utilize chaotic advection to controllably form polymer blend morphologies or arrange solid additives into functional structures (i.e., smart blenders) have been demonstrated. In relation to this new technology, a numerical study has been performed with the aim of characterizing melt residence time distributions (MRTDs) in an idealized smart blender. A numerical model was constructed by the superposition of flows given by an analytical blinking rotlet model and a Poiseuille velocity profile through a cylindrical pipe. The use of analytical models reduced numerical error associated with tracing pathlines of individual particles while allowing general characterization of parametric effects. Since each particle could be tracked independently, the numerical model was implemented on a parallel computer to reduce computational times and give accurate results. Results are also generally applicable to related chaotic mixers that operate in a continuous flow mode where the focus is on mixing in lieu of controllable in situ structure development.
Chaotic mixing has been utilized in the past to produce an array of microstructures, such as lamella, fibrils, and droplets, in the blending of two immiscible polymers. In the present work, we studied the effect of nanoclay on morphology development in chaotic mixing of polyamide-6 (PA6) with polypropylene (PP). The organically modified nanoclay was first pre-compounded with PP and the PP-clay mixture was blended with PA6. All morphological forms, e.g. lamella, fibrils, and droplets were seen as in blends without clay. However, the following distinct observations were made: (1) Nanoclay particles migrated into PA6-phase throughout the mixing period, (2) The conversion of the PP-phase into droplets was delayed, and (3) the size of the PP droplets were much smaller than those obtained in absence of clay.
Most polymer blends are currently produced with machines intended to mix so the variety of obtainable blend morphologies has been constrained. The relation of structure (i.e., blend morphology) to properties at fixed compositions has as a consequence remained largely unknown. In this paper, a new smart blending technology (www.ces.clemson.edu/mmpl) that is based on chaotic advection has been implemented to assess the various types of morphologies producible in polypropylene (PP) - low density polyethylene (LDPE) blends for LDPE volume fractions of 10, 20 and 30%. Tensile properties of extruded films are related to morphologies and blend composition. Results indicate that morphologies other than droplet morphologies typically obtained with present compounding equipment can impart the best combined property enhancements.
The synthesis of polyamide-polyester based random block copolymers were carried out in a modular co-rotating twin screw extruder via reactive extrusion process. These random block terpolymers have not been previously polymerized in a twin-screw extruder and these copolymers are very limited in open literatures. We used ?-lauryllactam , ?-caprolactam, and ?-caprolactone as monomers for synthesis of copolymers in a twin screw extruder. We also used sodium hydride as an initiator and N-acetylcaprolactam as a coinitiator. Simultaneously two lactams with initiator systems to make random copolymer and subsequently added the lactone without initiator to form a random block copolymers. All formation of random-block copolymers were studied in a twin-screw extruder as a chemical reactor. The thermal, mechanical, rheological, and structural properties of new synthesized random block copolymers were investigated and compared with homopolymers and Pebax® (Atofina) which consist of polyamide12- PTMEG (polytetramethyleneglycol)-polyamide12 block copolymer. It has the properties of a thermoplastic eslastomer (TPE).
The self-similar lamellar structures produced by mixing of aromatic or aliphatic diisocyanates, polyol, and butanediol chain extenders were utilized in this study in carrying out rapid conversion of isocyanate groups in the formation of thermoplastic polyurethanes. Chaotic mixing helped produce TPUs with narrow molecular weight distribution in the same system when the time scale of reactions was shortened by the use of tin catalyst and matched with the time scale of mixing. In addition, chaotic mixing distributed the exothermic heat of reaction homogeneously and, thus, helped minimize the extent of side reactions.
A phenomenological model was developed to analyze the effects of flow reorientation on collision between droplets and drainage of fluids between colliding droplets in shear flows encountered in chaotic mixing devices. It was found that flow reorientation affects the possibilities of collision between the droplets depending on the local shear rate, reorientation frequency, and reorientation angle. It was found that the collision frequency is reduced due to time-periodic reorientation, with respect to unidirectional shear flows. The time-periodicity of chaotic flows also affects the drainage step, e.g., by increasing or decreasing the drainage rate depending on the local shear rate at the time of the collision. Experiments on coalescence using a blend of polypropylene and polystyrene carried out in a chaotic mixer consisting of a two-roll mill showed that the rate of coalescence reduced significantly. These results are of remarkable importance in establishing that chaotic mixing not only expedites the formation of fluid morphology in blends, it also reduces the rate of coalescence.
Polylactic acid(PLA) films are stretched in different modes at different rates. Development of birefringence and true stress of the film during stretching are measured on-line. Effect of stretching rate and modes on stress-optical behavior at different stage of stretching and microstructures formed in each stage were studied. The uniaxially constraint width stretched samples exhibit multistage linear and nonlinear stress optical behavior. The first regime I is a linear regime exhibiting a rate and mode independent stress-optical constant which is found to be 2.5GPa-1. If low rates of stretching are employed, a second stage appears with steeper positive slope associated with stress-induced crystallization before the final stage with a negative deviation in stress-optical co-efficient. If faster stretching rates are used, the first linear stage expands to higher stress and birefringence levels and the stress-optical behavior reach the final regime III with a negative deviation without showing the regime II. A one-dimensional mesophase ( nematic structure) can be observed in samples showing negative deviation in stress-optical behavior under high stretching rates. In simultaneous biaxial stretching mode, regime I and regime III are also clearly observable.
This paper describes a method to accurately measure the tensile properties of microtomed sections from molded parts. This technique has great utility in determining physical property changes from skin to core for a molded part. It can also be used to assess potential process-induced degradation. Microtomed sections are too thin for contact extensometer use. In this study, accurate modulus and strain measurements are obtained with the use of a non-contact video extensometer. This paper details the test methodology to accurately measure the tensile properties of microtomed sections from molded parts. It also compares tensile test results from microtomed sections to bulk sample results.
The morphology and stress relaxation of coextruded five layer LLDPE (linear low density polyethylene)/EVA (ethylene-vynil-acetate) copolymer films were studied. It was found that the increasing of VA (vinyl acetate) content in EVA causes the decreasing of shrink tension of the films which can be explained by a decrease in crystallinity amount. It was shown that the relaxation time spectrum of the coextruded crosslinked LLDPE/EVA films is similar to the relaxation time spectrum of crosslinked LLDPE film at room temperature. However, at the elevated temperatures the additional peak appears on the spectrum of coextruded film. The cause of this peak is temperature-stress induced recrystallization of EVA during the relaxation test (this recrystallization was observed with DSC and wide angle X-ray analysis).
Along with conventionally extruded rods, self-reinforced polyethylene rods were prepared using a conventional extruder equipped with a converging extrusion die. From the work it is apparent that self-reinforced rods showed elastic modulus nearly 4 times higher than that of conventionally extruded rods. Scanning electron microscopy revealed that the morphology of the self-reinforced samples was fibrous and that the fibrils were extended straight along the extrusion direction. Moreover, the self-reinforced samples melted at higher temperature than the samples which had been prepared conventionally.
As mechanically loaded construction parts are increasingly made from polymers, reinforced polymers are getting more and more important. To predict the mechanical properties of glass microbead filled construction parts it is necessary to determine the distribution of the fillers and correlate it to the molding parameters. Using optical methods and image processing it is possible to determine the distribution of glass microbeads in injection molded parts. The results of a set of experiments, varying the parameters melt temperature, injection rate and thickness of the injection molded plate are expressed.In order to improve the simulation of loaded construction parts the differing material parameters due to differing glass microbead distribution have to be taken into account.Calculated results are presented and compared for a construction part under stress with homogenous and inhomogeneous (real) distributed glass microbeads.
A high flow injection moldable Polyetherimide-Polycarbonate Ester blend resin has been developed for advanced lighting applications. The blend demonstrates a 45% improved flow length at 1.5 and 2.3 mm thickness as compared to a commercially available PEI/PCE blend. Cycle times are reduced with lower melt processing temperatures while maintaining equivalent thermal properties. The high flow blend still retains good practical impact and strength properties. Processing advantages of improved flow, faster cooling time, and reduced cycle time are discussed and compared with isopherone based high heat polycarbonates.
Mechanical properties of the pure ?-form of iPP have never been conducted at any level mainly due to difficulties in producing pure ? specimens. The mechanical properties of ? structure are very important because most processes are conducted at high pressures. This study provides an opportunity to investigate the effect of different crystal forms of iPP on the mechanical response. Wide angle X-ray diffraction (WAXD), differential scanning calorimetry (DSC), static tensile tests, were employed to characterize and compare the physical and mechanical properties of ? and ? phases. Several specimens of the pure ?-form were successfully prepared at 200 MPa and 177.5 °C and a number of the pure ?-form specimens were prepared at low pressure and 120 °C. The WAXD patterns confirmed that pure forms were produced. The average degree of crystallinity, as determined by DSC, was 41% and 43% for the ?- and ?- forms, respectively. The tensile results showed that the ?-form exhibits considerably higher elongation at break and small reduction in stiffness as compared to that of the ?-form. The average measured yield strength of the ? phase is higher than that of the ? phase by 8%.
Compared to molding processes, polymer solid phase forming has several advantages. Particularly, polymer forging is able to reduce cycle time for thick parts, process difficult-to-mold materials such as ultra high molecular weight polyethylene, and enhance mechanical performance through self reinforcing. Although much research has been carried out in the past forty years on solid phase forming, little has been done on polymer forging. This can be partially attributed to the lack of fundamental understanding of the process, e.g. lack of understanding on instantaneous recovery and viscoelastic recovery. In the present study, upsetting experiments were conducted to study the forging behavior of nylon. The nylon samples exhibited uniform deformation and little barreling. The instantaneous elastic recovery was found to be affected by the strain, the strain rate, the dwell time and the operation temperature. The overall recovery including both instantaneous recovery and time dependent recovery can be reduced by the application of a higher upsetting speed and an appropriate dwell time during forging.
It was recently found that the ratio G'/?* plays an important role in determining whether exfoliated or intercalated nanoclay structures can be obtained in epoxynanoclay systems; G' and ?* are the storage modulus and complex shear viscosity of crosslinking epoxy respectively inside and outside the clay galleries. In this study, the possible effects of quaternary ammonium ions on the values of G'/?* ratio were investigated. The first effect was that of plasticization of crosslinked epoxy networks inside the clay galleries by hydrocarbon chains of quaternary ammonium ions, which slowed down the growth of G'. Second, the quaternary ammonium ions derived from primary amines dissociated at elevated temperatures generating amines, which reacted with the epoxide groups, causing an imbalance in stoichiometry. This led to reduction of crosslink density and further plasticization by excess amines.
Controlled architecture materials (CAMs) (block copolymers, telechelic polymers, starbranched polymers) are being explored as specialty additives for a myriad of melt-processing related applications. These block copolymer-based additives provide interesting solutions to interfacial problems in areas such as blend compatibilization and polymer wood composites. In addition to providing enhanced physical properties and performance, these additives can also aid in the processibility of polymers under extrusion conditions.
Of the multitude of polymerization processes available for plastics manufacture, continuous free radical polymerization is preferred because it offers the lowest monomer to polymer conversion cost. However, free radical polymerization offers very poor control of polymer chain architecture because of the multitude of simultaneous termination processes. This leads to the formation of a broad polydisperse resin. In recent years there has been a large global research effort aimed at developing controlled radical polymerization (CRP) technology. CRP provides control of termination by the addition of a stable free radical to the polymerization process. The stable free radical reversibly couples with propagating polymer radicals thus virtually eliminating uncontrolled termination. CRP allows researchers to synthesize new polymers previously inaccessible by conventional polymerization chemistry. This discovery has led to a renaissance in polymer science and has resulted in the development of several new living polymerization processes. CRP technology has given polymer researchers the ability to synthesize advanced macromolecules with control over shape, size and functional group placement not possible using traditional free radical processes. However, to date there has been slow commercial implementation of CRP technology, especially in commodity polymer businesses requiring the lowest conversion cost possible, at the sacrifice of improved plastic performance. This paper describes our research probing the utility and limitations of CRP for the manufacture of improved styrenic resins.
Injection molded nanocomposites have been successfully fabricated from cellulose acetate (CA), triethyl citrate (TEC) plasticizer and organically modified clay. The effect of sequential mixing methods and plasticizing conditions on the performance of these nanocomposites has been evaluated. The mechanical and thermal properties of nanocomposites are correlated with the XRD and TEM observations. Cellulosic plastic-based nanocomposites with 75-minute pre-prasticized CA/TEC/organoclay showed the best exfoliated structure.
Polytrimethylene terephthalate (PTT), known as SORONA™, polymer is an example of a condensation polymer that can be made from 1, 3-propanediol and terephthalic acid. Nanocomposites of polytrimethylene terephthalate and organoclay were fabricated in microcompounding equipment. Injection molded samples of these materials were evaluated by mechanical and thermal analysis. To understand the role of clay platelets in the nanocomposites, the microstructure was observed using transmission electron microscopy (TEM) and wide angle X-ray scattering (WAXS). These nanocomposites showed improvement in properties and strong promise for further improvements through process optimization and material combinations.
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