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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Continuous Dispersion of Carbon Nanotubes in Polymers Using Ultrasound Assisted Extrusion Process
The unique morphology and strong intertube attraction between carbon nanotubes (CNTs) makes the dispersion of CNTs a big challenge and hence limits its effective use. A novel method for the continuous dispersion of carbon nanotubes in a polymer matrix for manufacturing high performance nanocomposites was developed using an ultrasonically assisted twin screw extrusion process. The effect of ultrasound on die pressure, electrical conductivity, rheological, morphological and mechanical properties of polyetherimide filled with 1-10 wt% MWNT was studied. Ultrasonic treatment caused a reduction in die pressure with a permanent increase of viscosity of treated samples.
A Feasibility Study for Sub-100 Nm Polymer Injection Molding
In this work, silicon mold manufacturing is considered to evaluate polymer replication at the nanoscale. The molds are made via e-beam lithography and deep reactive ion etching. Amorphous cyclic olefin copolymer is processed with optimized molding conditions. Characterization of the molds and replicas is carried out with atomic-force and scanning-electron microscopy. We find that the dose exposure is a critical parameter to observe for proper exposure of the mask and that low surface energy plasma polymerized films can be utilized as anti-adhesion layer during injection micro/nano-molding. We have fabricated structured molds and replicated features as small as 55 nm. We also demonstrate that the resolution of injection molded COC products is at least 5 nm.
Effect of Die Land Length on Die Pressure during Foam Extrusion – Part I Experimental Observations
Entrance pressures are determined experimentally for foam extrusion dies of constant cross section. These pressures are affected by the rheological properties of the polymer matrix, by the plasticizing effect of the blowing agent, and by the cell nucleation and growth. While the pressures change linearly with die land length during extrusion of pure polymer, this relation becomes nonlinear during extrusion of polymer/blowing agent mixtures. It is found that the degree of nonlinearity depends on the amount of premature cell growth and by the processing conditions, including temperature, pressure drop rate, and blowing agent content.
A Finite Element Model of Non-Isothermal Viscoelastic Flow in the Cast Film Process
The goal of this work is to develop a model which accurately predicts variation in shape, temperature, stress, velocity, and ultimately structure for a polymer cast film between the slit die and the chill role. The mathematical model is similar to that used in the work of Sollogoub, et al. (Jrnl. non-Newtonian Fl. Mech., 2006). Our approach varies from that effort in the treatment of the free surface and the choice of viscoelastic constitutive model. After describing the mathematical model and the solution procedure, comparisons of simulation results with previous results will be provided.
Processibility and End-Use Properties of Polypropylene Clarified by a High Efficiency Clarifier
Since the mid 1980's, clear polypropylene (cPP) has been available, mainly on account of sorbitol-based clarifiers. Recently, a novel, high efficiency clarifier, based on a new chemistry platform, has become commercially available. The weaknesses of the sorbitols, such as low thermal and chemical stabilities, have been overcome while the requirements for a melt sensitive clarifier are maintained. The high efficacy and thermal and chemical stabilities of the high efficiency clarifier provide advantages with regard to melt processibility and end-use properties of cPP.
Synergistic Biodegradable and Bio-Based Blends and Nanocomposites Created Using Pulverization
Well-dispersed biodegradable and bio-based blends and nanocomposites have been successfully created by solid-state shear pulverization. Pulverization of granular starch and polyethylene (PE) resulted in damaged starch granules. This altered granule morphology led to improved oxygen barrier properties and tensile modulus in PE/starch blends. High levels of dispersion were also achieved in polymer/clay nanocomposites using poly(caprolactone) as the matrix. Varying levels of clay exfoliation were achieved by altering processing conditions during pulverization. These materials also had improved barrier properties.
Isoconversion Analysis of the Glass Transition
Various aspects of the glass transition kinetics have been well described by phenomenological models of the glass transition, such as the TNM and KAHR model. An important assumption in these models is that the apparent activation energy, which describes the temperature dependence of the relaxation time, does not vary through the glass transition process. Some recent reports suggest that the activation energy decreases significantly from the glassy to the liquid state. In this work we apply an isoconversion analysis to data in the glass transition region which was obtained on cooling from capillary dilatometry and from differential scanning calorimetry (DSC) in order to determine whether the apparent activation energy changes through the glass transition.
Process Selection for Microfluidic Device Manufacturing
The emerging demand for microfluidic devices is driving decisions for product and manufacturing development. Three potential categories for microfluidic device manufacturing are hot embossing, injection molding, and liquid resin molding. We review the first two, along with two sub-categories of liquid resin molding: polydimethylsiloxane (PDMS) casting and UV embossing. We address the processes' strengths and weaknesses with respect to cost, material selection, tooling, temperature requirements, pressure requirements, feature sizes, aspect ratios, and rates. Based on the strengths, weaknesses, and processing parameters of these four micro replication techniques, we provide a table to aid in proper process selection.
Effect of Multiple Shear Histories on Rheological Behavior and Devolatilization of Poly(Ether Ether Ketone)
The effect of shear history on the properties of poly(ether ether ketone) (PEEK) was investigated by processing it through a twin screw extruder 20 times. Samples were taken at various stages in the recycling sequence for testing. The melt rheological behavior, solid mechanical properties, and total outgassing performance were monitored to evaluate the degradation of the PEEK as a function of processing history.The results of rheological testing suggest that degradation is initially dominated by chain scission with cross-linking becoming more significant with more reprocessing cycles. The rheological and mechanical behavior shows similarities to liquid crystalline polymers and filled polymer systems. The results of outgassing testing showed that the total amount of volatiles decreased with increasing processing cycles.
Single-Step Through-Hole Punching by Hot Embossing
Hot micro-embossing is a promising manufacturing technique for replicating millimeter to nanometer scale features, including fluidic channels, in thermoplastic parts. Complex microfluidic devices will require multiple functional layers as well as interlayer vias. We demonstrate a mated aluminum tool pair with integrated punch and die features. The punched hole diameters are approximately 500 µm, 740 µm, 1.0 mm, and 2.0 mm. The embossed through-holes were punched in PMMA at 120 *C with a velocity of 0.5 mm/min. The tool set also demonstrates the feasibility of forming channels on both sides of the part and producing interface ports and interlayer vias in a single step.
Experimental Studies of Polypropylene Extrusion Instability
A fundamental experimental study is conducted to investigate the extrusion stability characteristics of a homopolymer polypropylene in a lab scale extruder. An instrumented 2.5' single screw extruder is used with capability of measuring the pressure profile along the screw at a high sampling rate and the melt temperature of the extrudate. The effect of screw design (metering vs. barrier screw) on extrusion stability is investigated. For the processing conditions tested, the metering screw shows extrusion instability (surging) as manifested by high pressure variability along the screw and solid-bed break-up, while the barrier screw yields considerably more stable extrusion performance. The barrier screw is also found to be more efficient in terms of output rate and power consumption than the metering screw.
Impact Fracture Behavior of PP/EPR Blends
The impact fracture behaviors of two commercial polypropylene/ethylene-propylene rubber (PP/EPR) blends were investigated. The morphology and interfacial characteristics were directly characterized by transmission electron microscopy. The effects of EPR composition on phase morphology, interface and impact fracture behavior were systematically studied. The toughening mechanisms were examined using the double-notch four-point-bending technique. It is found that crazing and shear banding are the two dominant energy dissipation mechanisms in the impact PP/EPR blends investigated. Possible approaches for optimizing the impact strength of PP/EPR blends are also discussed.
Novel Self-Assembling Morphologies in Multicomponent Polymer Blends
Structured multicomponent polymer blends are an important class of next generation materials. In this work, HDPE/PP/PS blends modified with a SEB diblock copolymer were studied as a function of SEB content and annealing time. SEM observations show that the PS droplets, in unmodified blends, are located in the PP phase with some tending to locate at the HDPE/PP interface, as predicted by the spreading coefficient theory. This tendency is also observed for blends modified with SEB. However, after annealing, virtually all the PS droplets rapidly migrate to the HDPE/PP interface and reorganize themselves to form a highly ordered pearl-necklace structure at the interface. Remarkably, these PS droplets at the interface, even in this close-packed structure, do not coalesce and maintain a stable size with annealing time.
Polymeric Plasticizer Developments
Polymeric plasticizers are specialty types that are used in PVC formulations when extraordinary migration and extraction resistance are required. While different chemical classes of polymeric plasticizers are used, the most common type in the PVC market are liquid or near liquid polyester adipates. Typically, these polymeric plasticizers are in the 1000 to 13,000 molecular weight range (MW). While polymeric plasticizers have been used in PVC compounding for many years, developments continue. New polymeric plasticizers were developed for improved printing with waterborne inks and improved processing characteristics. This paper focuses on two new products and how they provide the required printability and processing characteristics.
Scientific Description and Industrial Interest of Laser Surface Treatment of High Temperature Thermoplastic Polymers
The interest of laser surface treatment of technical polymers is detailed. First experimental results concern polyetherimide exposed to Nd:YAG laser beams in different gaseous atmospheres. Depending on the nature and the pressure of the gas, the incidence and the intensity of the laser beam, the surface affinity of the polymer with a liquid can be increased or reduced as revealed by contact angle measurements. Polymer structural changes are identified by FTIR-ATR. The extension of this approach to several polymers permits the identification of the mechanisms involved by the laser treatment. Ultimately, the benefits of this technical solution to applications in railway industry are presented.
Foaming Behaviour of Cellulose Fibre Reinforced High Density Polyethylene Composites
This paper investigated foaming behaviour of cellulose fibre reinforced high density polyethylene composites. Two types of fibres were used in this study, similar in thickness and width, but differing in length. Extrusion foaming of the composites was conducted with a physical blowing agent, N2. The results suggested that fine-celled structure was obtained in the composites without a blowing agent. Addition of small amount of N2 further improved the cell morphology of the composites, namely, increase in the cell number and slight decrease in the cell size. However, addition of maleated high density polyethylene, which improves the interface between the fibre and polymer matrix, decreased the cell number in the composites.
Biaxial Constitutive Response of PET during Hot Drawing: Experimental Study and New Implications for Constitutive Modelling
A study was made of hot drawing of an amorphous isotropic poly(ethylene terephthalate) (PET) under biaxial stress, in the temperature and strain rate regime prevalent in injection stretch blow molding and biaxial film drawing. The constitutive response was mapped out more thoroughly than hitherto, as functions of temperature and strain rate, for constant width and equi-biaxial drawing. The data suggest multiple Eyring type flow activation volumes at lower drawing temperatures. Also the flow activation volume appears to decrease with increasing strain level, possibly attributed to entanglement slippage and intrinsic anisotropy of the flow process. The former observation would have a significant implication for current constitutive modelling approaches based on single shear and pressure activation volumes. The implications for refinement of the model are discussed.
Effect of Secondary Processing Conditions on Morphology of Thermoplastic Olefin Blends
Properties of thermoplastic olefin (TPO) blends are to a large extent determined by the morphology, (i.e., the size, shape and distribution), of the dispersed phase. Key factors that affect the morphology include: blend composition, the viscosity ratio between the matrix and the dispersed phase, interface interaction, and processing conditions during initial melt blending. For some blend compositions, however, the final morphology may also be affected due to secondary processing steps, such as injection molding or extrusion. This study investigated the stability of the elastomer dispersion during injection molding for TPO blends and established some preferred processing conditions.
Online Orientation during Polyethylene Blown Film Extrusion Using Polarized Raman Spectroscopy
Online Raman spectroscopy was used in this study to measure the orientation development during blown film extrusion of low-density polyethylene (LDPE). The analysis is valid for uniaxial symmetry of the structural units with the chain axis. The trans C-C stretching vibration of PE at 1130 cm-1, whose Raman tensor is coincident with c-axis of the orthorhombic crystal, was used to solve a set of five intensity ratio equations. Crystalline orientation (P2) was found to increase along the axial distance in the film line. The P2 values also showed an increasing trend with crystalline evolution during extrusion
Development of Laminated Oriented PE Film Light Weight Armor Material and a Device for Testing its Ballistic Characteristics
The effect of the number laminated oriented PE film (Tyvek) for use in the development of light weight armor and a device for testing its ballistics characteristics were evaluated. The study showed that Tyvek is oriented in the longitudinal direction ± 45° along the X-axis. The number of laminates appears to be critical ballistic characteristics. The higher the number of layers the shallower the penetration of the dart. For example with 6 layers, the penetration was 0.003 m for the long tube, and 0.001m for the short tube. This is because Tyvek is oriented in the longitudinal direction, and also the manner in which the layers are compression molded: biaxial or parallel has an effect on the ballistic characteristic.
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