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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Analysis of the Effects of Flow Reorientation in Chaotic Mixing Flows on Coalescence in Blends of Polypropylene and Polystyrene
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.
Invesigations of Linear and Non-Linear Stress Optical Regimes during Uniaxial and Simultaneous Biaxial Stretching of Poly Lactic Acid Films by Real Time True Stress-Strain-Birefringence Technique
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.
Tensile Testing of Microtomed Sections from Molded Parts
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.
Synergistic Effect of Temperature and Stress During Stress Relaxation of LLDPE/EVA Coextruded Films
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).
Self-Reinforcement of High-Density Polyethylene
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.
Distribution of Glass Beads in Injection Molded Parts
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.
Injection Molding of a High Flow Polyetherimide-Polycarbonate Ester Blend
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.
Tensile Properties of the Gamma Phase of Isotactic Polypropylene with Small Particles
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%.
Forging Behavior of Nylon
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.
Plasticization of Epoxy Network in Epoxy-Nanoclay Systems Due to Stoichiometric Imbalance
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.
Specialty Additives Based on Controlled Architecture Material (CAM) Technology: Interfacial Modifiers in Blends, Foams and Composites
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.
New Chemistry for Manufacture of Improved Styrenic Plastics
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.
Nanocomposites of Polytrimethylene Terephthalate and Montmorillonite Clay
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.
On-Line Measurement of Dispersion in Nanocomposites
Properties of polymer-clay nanocomposites depend on the degree of dispersion of clay in the polymer matrix. Currently off-line techniques such as transmission electron microscope and x-ray diffraction are used to determine dispersion. This research aimed to determine a property that is affected by dispersion and has the ability to be measured on-line. Polypropylene and Cloiste 15A (nanoclay) were melt blended with the aid of maleic anhydride grafted polypropylene compatibilizer. The mechanical, electrical, optical, and rheological properties were measured for all the trials. Transmission electron microscopy was performed to evaluate the results. The capacitance of the nanocomposites varied with change in the degree of dispersion. The mechanical properties (tensile characteristics) did not show a significant change with dispersion. The rheological properties gave a good indication of exfoliation of clay layers at low shear rates. The visible color test could not give a definite indication of dispersion as compared to the other properties.
Structure and Property of Polyester Composite Fibers Reinforced with Thermotropic Liquid Crystal Polymer
The composite fibers based on melt blends of poly(ethylene 2,6-naphthalate) (PEN), poly(ethylene terephthalate) (PET), and a thermotropic liquid crystal polymer (TLCP) were prepared by a process of melt blending, and spinning to achieve high performance fibers with the improved processability. The tensile strength and modulus of the composite fibers can be significantly improved by both the reinforcement of the polymer matrix by the TLCP component and the TLCP fibrillar structure with their high aspect ratio. The increase in the apparent crystallite size with the spinning speed resulted from the development of larger crystallites and more ordered crystalline structure in the composite fibers. As the spinning speed was increased, the birefringence and density of the composite fibers were increased, indicating the improvement of the molecular orientation and the effective crystal packing.
Mechanical Morphology and Thermal Properties of Water-Crosslinked Wood Flour Reinforced Linear Low-Density Polyethylene Composites
Wood flour (WF) reinforced linear low-density polyethylene (LLDPE) composites were prepared. Water-crosslinking technique was used to improve the physical properties of composite. Composites compounded in a twin screw extruder and treated with a coupling agent (vinyltrimethoxysilane, VTMOS) and then be moisture-crosslinked. Composite after water-crosslinking treatment exhibited better mechanical properties than the non-crosslinked one because of the improved chemical bonding between the wood fiber and the polyolefin matrix. Scanning Electron Microscopy (SEM) of the fracture surfaces of water-crosslinked composites showed superior interfacial strength between the wood fiber and the polyolefin matrix. Thermal analyses of water-crosslinked composites indicate that thermal degradation temperature of composite increase with the increasing water-crosslinking time.
Study of High Abrasion Resistant UPR/SiO2 Nanocomposites Prepared by an In-Situ Polymerization Process
Abrasion-resistant nanocomposites, unsaturated polyester resin (UPR)/ silicon dioxide (SiO2), were prepared by an in-situ polymerization process. The effects of nano-SiO2 on the chemical-physical properties of UPR/ SiO2 nanocomposites were studied by performing thermal, morphological, and mechanical analysis, and the abrasion resistance has also been evaluated. The results show that UPR/ SiO2 nanocomposites have an average weight loss about half in comparison with that of neat UPR by adding only 2% of nano-particles. The glass temperature (Tg) of composite materials were measured by DSC. It is found that the Tg of composite materials is higher than that of UP resin, which is in agreement to the results of abrasion resistant properties. The in-situ UPR/SiO2 that reacts a good distribution of nano-SiO2 in the UPR has a better toughness and strength.
Flexural Properties and Morphology of Impact Modified Epoxy-Organoclay Nanocomposites
The flexural and impact properties as well as the morphology of epoxy-organoclay nanocomposites were investigated in this study. The epoxy matrix was impact modified with a polyol which formed an immiscible phase in the epoxy. X-ray Diffraction patterns showed that the interlayer spacing of the modified montmorillonite expanded from 1.83 nm to 3.82 nm when it was incorporated into the impact modified epoxy matrix. Synergistic effects in mechanical properties were observed in samples containing 1 wt % polyol plus 1 wt % organoclay. In these samples, the impact strength of the neat resin increased by 120 % with respect to the impact strength of the neat epoxy resin.
Study on Morphology Development for In-Situ Fiber Reinforced Composites by Blending Polypropylene and Polycaprolactone
In-situ fiber reinforced composites were prepared by blending of polyolefin and polycaprolactone. The dispersions in this blend materials were deformation into fibers using a polymer extrusion. Polymer processing conditions, such as drawing ratio, were measured to study its effect on elongation of dispersed phases. The dispersions have dramatically changed from spherical to spheroidal and filament shapes depending on drawing ratio. Reduced capillary number was used to characterize droplet deformation, thus giving us many informations on fiber formation of the dispersions.
Mechanical and Morphological Properties of Kevlar-Fiber Reinforced Polyamide 6,6 (PA66) Composites
The effects of fiber loading and surface treatment on the mechanical and morphological properties of nylon 6 (PA66)/Kevlar composites were studied. The effect of fiber surface treatment on modulus is not pronounced for 10% Kevlar fiber-reinforced composite (KFRC) but it succeeded in enhancing modulus in 24% KFRC. The reinforcement of PA66 by Kevlar fibers was indicated by the increase in tensile strength with increasing fiber content. However, there was no evidence to suggest that the surface treatments have any significant effect on the tensile strength of the composites. The failure surfaces of both surface treatments are similar to the untreated fiber as indicated by the massive fiber pulled out. However, less fiber splitting can be seen on the failure surfaces of the treated samples. Fiber breakage is also indicative of good interfacial bonding but the massive fiber pullout in high fiber content samples would complement the toughness and strength of the fibers itself.
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