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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Rheology and Crystallization in Fiber Optic Cable Jacket and Conduit Extrusion
Rheological tests measure melt-state polymer flow, delineating molecular structure and predicting extrudability. Rheology of compounds used in fiber optic (FO) cable jackets and in the conduits that contain such cables will be our focus. Polyolefin-based jackets strengthen the FO cable and protect internal components, while the conduit provides long-term strength and protects the cables against environmental stresses. High density polyethylene use in these applications is growing rapidly, spurred by FO cable growth. Important properties in both applications include melt-state processability, stress crack resistance and solid-state stiffness. Melt rheology directly influences processability, combining with crystallization behavior to dictate final solid-state properties.
Reinforced Plastic Design: Microstructure and Stiffness of Tensile Bars
The majority of mechanical property data reported for reinforced thermoplastics and available to a part designer is based upon testing end-gated injection molded tensile bars. ASTM Type I injection molded tensile bars were molded of ~30 wt% glass-filled polybutylene terephthalate, polycarbonate, and nylon-66. Detailed microstructural evaluations of the lengths and orientations of the glass-fibers were made. The experimental elastic moduli are predicted to within 4% using micromechanics. As a general observation, the simulations reveal that the modulus for a 30 wt% short glass fiber-filled thermoplastic tensile bar is 50 to 70% that expected from a composite of unidirectional fibers of infinite lengths.
Phase Morphology and Cure State Characterization of Soft Thermoplastic Vulcanizates (TPVs) by Using Atomic Force Microscopy (AFM)
AFM shows comparable capability to transmission electron microscopy (TEM) for characterization of TPV phase morphology. Phase imaging by tapping mode AFM scanning gives good contrast between the rubber phase, plastic phase, and filler in a TPV. In addition to TPV phase morphology characterization capability, it can quantitatively distinguish the cure state difference of the rubber in TPVs. A procedure for the analysis on phase imaging data is demonstrated and a good correlation is observed between AFM data, weight gain, and modulus at 100% elongation.
Tear Resistance of INSPiRE Performance Polymer Blown Films
Tear resistance is critical for Polypropylene (PP) blown film in packaging applications and has been widely evaluated by several ASTM standard test methods. However, for characterization and differentiation of the tear resistance of blown films, these factors should be considered: tear behavior, tear propagation trajectory, film thickness, and tear speed. The tear strength of several mono- and multi-layer INSPiRE performance polymer films was analyzed by several test methods in this paper. The effect of film orientation, loading speed, failure mechanism, and sample geometry on tear strength will be discussed. Some uniqueness of the tear behaviors and advantages of the INSPiRE performance polymer blown films will also be discussed.
Injection Molding Long Glass Fiber Reinforced Thermoplastic Composites
Long Glass Fiber Reinforced Thermoplastic (LGFRT) Composites are produced by a proprietary pultrusion process rather than conventional extrusion compounding. This pultrusion process provides a high level of fiber impregnation in the pellets with no fiber damage compared to conventional short glass compounding. The result is injection moldable pellets containing fully wetted fibers equal in length to the pellet, typically 11 mm. This longer, initial fiber length translates into improved properties in molded parts when processing with optimized molding equipment and conditions that preserve the higher aspect ratio. As a class, long fiber composites exhibit overall higher mechanical properties, better elevated temperature performance, lower wear, and improved creep and fatigue endurance. This paper will examine the advantages of long fiber composites, properties of long vs. short fiber, equipment, tooling and processing conditions to maximize fiber length in the molded part and resultant mechanical advantage. In addition, alternative processing techniques including structural foam, injection compression & gas-assist, types of thermoplastic materials used and typical applications will be discussed.
Dependence of Melting Behavior on Melt Index
The dependence of dissipative melting behavior of solid bed on melt index ([MI]) was studied experimentally for polystyrene (PS) and high density polyethylene (HDPE). Melting occurs primarily by the heat generated in the melt film in dissipative melting. The melting rate and the shear stress were expected to decrease with increasing [MI] because of decreasing viscosity. For PS, the shear stress decreased as expected but the melting rate increased with increasing [MI]. For HDPE, both the shear stress and the melting rate did not show a simple dependence on [MI]. HDPEs with very low [MI] values exhibited unstable melting mechanism and their melt did not coat the metal surface. Such unstable melting mechanism is probably responsible for high screw wear. Shear stress depends on the viscosity in the melt film. [MI] only indicates the viscosity at low shear rates, far below the shear rates in the melt film, and by itself cannot indicate the viscosity in the melt film. Melting rate depends on the viscosity and also the velocity profile in the melt film. The viscosity and the velocity profile in the melt film depend not only on the [MI] but also on the shear and the temperature sensitivities in a complex way.
3D Blow Molding Today, an Overview about Different Systems Which Are Established in the Market Today
3D-blowmolding was introduced some years ago. In the meantime a certain number of different systems became established in the market. Suction blowmolding, 3D-blowmolding with parison manipulation and a split mold, horizontal machine with vertically opening mold and a 6-axis-robot laying the parison into the cavity or a machine without a closing unit at all. All these systems can be combined with 6 or 7 layer coextrusion or with sequential coextrusion running hard-soft-hard resins one after the other. The paper gives an overview, production examples and an outlook to future developments.
Chain Extension of PA-6 and PA-6/66 copolymer via Reactive Extrusion with Triscaprolactamyl Phosphite (TCP)
Polyamide 6 (PA-6) homopolymer and copolymers have been chain extended from a low molecular weight feedstock into high molecular weight, high melt viscosity nylon products via a reactive extrusion process using a novel chain extender viz., triscaprolactamyl phosphite (TCP). The chain extension process involves an 'activated' polycondensation reaction between the endgroups of the nylon. In this paper we will discuss the effect of the chain extender concentration and the extruder process conditions on the chain extension efficiency with respect to molecular weight and rheological property benefits achieved.
New High Barrier, Oxygen Scavenging Polyamides for Packaging Applications
Honeywell International is currently developing high oxygen barrier polyamides based upon nylon 6 and blends of nylon 6 with amorphous nylons (PA6I,6T type). Significant improvements in oxygen barrier result from the introduction of a proprietary oxygen scavenger moiety (active barrier") and/or silicate nanoclays ("passive barrier"). The nanoclay is added during polymerization rather than in a melt compounding process which leads to improved barrier properties and lower haze levels in multi-layer films and bottles. These novel polyamides are suitable for use as high oxygen barrier layers in cast and blown film as well as for barrier layers in co-extrusion blow molded polyolefin based bottles and co-injection stretch blow molded PET bottles. They are part of a cost-effective multi-layer film/bottle solution for packaging oxygen sensitive products. When blended with nylon 6 amorphous nylon lowers the total crystallinity and may enhance adhesion to PET. These new high oxygen barrier nylons should meet the barrier requirements of many demanding packaging applications while continuing to offer desirable properties such as flavor barrier strength and toughness."
Time Dependence of Shear-Thinning of Polymer Melts
We analyze Non-Newtonian dynamic data of several polymer melts and find experimental evidence for the time dependence of shear-thinning. To summarize, viscosity is not just function of temperature, pressure and strain rate (or frequency), as is already well known, but also of time. We specify the experimental conditions to observe this phenomenon, and provide an analytical expression that fits the data very well. An interpretation of this time dependent behavior is presented. It is suggested that disentanglement" understood in terms of the dual-phase interactive model (EKNET theory) is responsible for the time dependence of viscosity. We stipulate that any desired amount of disentanglement can be induced in any polymer melt by the proper mechanical treatment specifically providing means to eliminate entropic mechanisms of melt deformation. This can be achieved by synchronizing the viscoelastic states of the dual phases for instance by a combination of the proper temperature rate and amplitude of shear deformation. It is shown that time dependence of shear-thinning can only occur below the temperature of stability of the network of interactive coupling interactions between conformers which we are able to associate with Tll Boyer's liquid-liquid transition. Practical applications to processing are discussed in a companion paper of this ANTEC meeting ."
Extrusion of Polymer Melts under Intensive Shear-Thinning Inducing Lower Pressure and Temperature Requirements
We have built an extension to an extruder line, which provides the means to submit polymeric melts, as they extrude out, to an intensive shear-thinning treatment by combining cross-rotational and shear vibration melt deformation. Experiments are conducted with two polymers, a highly entangled metallocene polyethylene and a general purpose extrusion grade polycarbonate. It is shown that, for both polymers, extrusion requirements for a given throughput, i.e. pressure and temperature, can be drastically reduced, by as much as 80°C for temperature, and, simultaneously by a factor 2-5 for pressure, when applying the new patented combined cross-rotational and vibrational means. We study the individual effect on shear-thinning of cross-rotation alone, and of cross-vibration alone, and also analyze their combined effect which results in drastically reducing pressure and temperature of extrusion at constant throughput. Applications are discussed, which range from the benefits of extruding melts and blends at lower temperature (when normal extrusion requirements would degrade one of the ingredients), or increasing throughput, to producing disentangled frozen-in resins, having much lower viscosity at given molecular weight, when extrusion under intensive shear-thinning is extended to much longer flow lengths.
Reduction of Viscosity of Polymer Melt by Shear-Thinning and Disentanglement : Rheological Criteria and Commercial Perspectives
Mechanical performance of polymers improves with molecular weight (MW). Unfortunately, melt viscosity and thus lack of processability also increases with MW. Recently, a method to temporarily reduce the melt viscosity without changing MW has been proposed . The method uses processing windows such that shear oscillation superposed on extensional flow at gradually increasing shear thinning amplitude are created by imposing conditions of strain, frequency and temperature that bring the melt (G'/G*) close to 0.75-0.85. The purpose of the present communication is to report results of a two-year research and development effort aimed at reducing the viscosity of several commercial resins using a pilot stage disentanglement machinery. The paper explores the commercial implications and answers the following questions: is it possible to shear-disentangle a large quantity of commercial resin at fast throughput, is it possible to process the disentangled melt before it regains its normal entanglement, and is it possible to speed-up the re-entanglement process after forming to regain mechanical benefits? From a laboratory and low throughput extrusion scale, the answer to all these questions is positive. The technology is presently being tested at a pilot pre-production scale to quantify the answers from a commercial perspective.
Measuring the Nonlinear Viscoelastic Material Properties of Thermoplastic Materials by Dynamic Mechanical Analysis (DMA)
As plastics are more and more used for high-performance application the design and material selection have to take into account the complex material properties. The lifetime of a product and the suitability of a raw material for a certain application can often only be estimated based on a huge data set of mechanical properties. Mechanical properties of thermoplastic materials are influenced by temperature, time and the level of loading. Thus, the engineer at least needs stress-strain-curves measured under varying temperatures and loading speeds to ensure an efficient product design. These measurement data are also required by software for simulating nonlinear visoelastic material behavior. Because of the costs of measurement the required data often are not available sufficiently. This paper describes first results of research aiming at generating the stress-strain-curves out of Dynamic Mechanical Analysis (DMA) measurement data. By help of DMA mechanical properties can be measured faster, more extensively and with lower costs than by tensile tests. prediction of product lifetime. Also it can reduce costs for product testing as models are able to simulate the effect of boundary conditions which in tests only can be realized with a lot of effort (e.g. changing temperatures, multi-dimensional stresses, changing loading speeds). However, material models base on measured material data. Every suitable model at least needs the data of several tensile tests.
Resistance to Erosive Wear by Copper Alloy Mold Components
Injection molds are increasingly making use of high strength, high thermal conductivity copper alloy mold components to reduce cycle time and improve dimensional accuracy. Molders are focused on the durability of these components. This paper is the first of a two-part discussion of erosive wear. Performance of standard copper alloys and tool steels was compared. Wear measurements were taken on a flat surface across from the gate, on the core side of the mold. Samples were run without release or lubrication aides, using 33% glass-filled nylon. Uncoated copper alloys were found to have comparable performance to that of pre-hardened tool steel.
Comparison of Various Hard Coatings to Protect Copper Mold Components from Erosive Wear
Demand for fast-cycle, dimensionally-consistent, thin wall parts molded from reinforced engineering thermoplastics continues to increase. The use of high strength, high thermal conductivity copper alloys has been limited by the perception that these alloys will not stand up to the wear of reinforced engineering resins. This is the second part of a discussion on the effects of erosive wear on copper alloy mold components. The ability of several chromes, electroless nickel, and titanium nitride to protect against erosion was tested. Several combinations of alloys and plating systems provided wear resistance that favorably compared to hardened H13 tool steel.
Environmental Stress Cracking of PC in Contact with Aqueous Solutions
The environmental stress cracking (ESC) behavior of some plastics is very well examined. Especially for polyethylene the mechanisms are nearly clear. For amorphous thermoplastics this mechanisms were examined in many researches, but are still not really clear. Especially for polycarbonat (PC) in contact with aqueous solutions systematic examinations of the ESC behavior are rare. In this paper examinations of the ESC behavior of PC in different aqueous solutions are presented. The tests were done by a medium-tensile-creep test. Different pH-values of water and a surfactant were examined about their influence on the ESC behavior. Also distinctive types of PC and their influence on the ESC behavior were examined. It is determined that the ESC of PC in contact with aqueous solutions is not only, like classical approach, controlled by physical effects. A large effect of chemical mechanism is also part of the failure mechanism.
The Effect of Pigment Type and Concentration on the Rheological Properties of Polypropylene
The rheological characteristics of a range of pigmented polypropylene (iPP) was investigated using dual capillary rheometry techniques, over the temperature range 190°C to 230°C and shear rate range of 10s-1 to 800s-1. The iPP was compounded with pigment masterbatch concentrations ranging from 0.2% to 3.0%, using a 38mm Killion compounding line. The pigment masterbatches investigated were iron oxide, titanium dioxide and phthalocyanine blue. The rheological data, showed that there were considerable increases in apparent viscosity of pigmented iPP even at relatively low pigment loadings. The increase in apparent viscosity was particularly evident over the lower shear rate range. Activation energies (Ea) calculated from the rheological data showed large increases in Ea for pigmented iPP especially at lower shear rates, suggesting crystallization of the iPP melt.
The Effect of Phthalocyanine Based Pigments on the Crystallinity and Mechanical Performance of Chill Roll Cast Polypropylene Extruded Sheet
The nucleating effect of phthalocyanine based pigments on the processing and properties of semi-crystalline polymers has been a challenge to polymer processors for many years. These effects are ever more pronounced during in-line, post extrusion processes such as elevated temperature drawing of polypropylene slit film tapes, for rope and twine applications. A range of polypropylene films containing levels of 2% phthalocyanine based pigments and inorganic iron (II) oxide based pigments were manufactured using the chill roll cast extrusion process, using a range of quench temperatures and die to chill roll gaps. Analysis of the tensile properties of the films showed significant increase in modulus for the phthalocyanine pigmented films by up to 25% in comparison to the iron (II) oxide pigmented and non pigmented films. DSC analysis showed the crystallinity of phthalocyanine pigmented films to be less affected by quench roll temperatures than the iron (II) oxide pigmented and non pigmented films. However polarized light microscopy analysis of the films showed the spherulite sizes for the phthalocyanine pigmented films to be significantly smaller than the iron (II) oxide pigmented films and non pigmented films.
Modeling of the Thermomechanical Behavior of Nonlinear Viscoelastic Materials under Multidimensional State of Stress
The thermomechanical behavior of nonlinear viscoelastic materials depends on time, temperature, loading rate and height of load. A model has been presented that allows the simulation of nonlinear viscoelastic materials under multidimensional state of stress. This 3-dimensional deformation model is built by parallel arrangement of a certain number of basic elements. Each basic element consists of an elastic Hookean element and a damper system (3D damper) to describe the viscous properties. The model is calibrated by isothermal strain rate controlled tensile tests at different temperatures. Along with suitable calculation algorithms, this model offers the ability to simulate any multidimensional load history caused by direct stresses and changing temperatures. The model allows the simulation both of quasi-static and dynamic loading at different temperatures . Building up on this model, modifications on the calculation algorithms are done to enable the simulation of thermally induced stresses in constrained geometries. For this reason the calibration of the model has to be extended. The thermal expansion coefficient is determined from non-isothermal zero stress experiments. Furthermore modifications on the biaxial testing device are started to be able to carry out non-isothermal, biaxial tests.
Failure Analysis of a Cracked Construction Vehicle Grille
Cracking occurred within grilles used on heavy construction equipment, without apparent cause. The cracking was observed to be sporadic and had initiated while the parts were being stored in a warehouse, prior to installation on the vehicles. The cracking was found adjacent to holes used to secure a logo nameplate in conjunction with metal bolts. The focus of this investigation was a timely determination as to the nature and cause of the failures. Of particular interest was whether the failure was primarily associated with material, design, processing, or environmental factors. This paper will document some of the testing performed to characterize the failure mode and identify the root cause of the cracking, in order to illustrate the failure analysis process.
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