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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Broadening of the foam processing window of polypropylene in extrusion foaming via the incorporation of CO2-philic nanofibers.
Tensile stress growth during extensional flow is enhanced in linear polypropylene (PP) via the incorporation of chemically modified polytetrafluoroethylene (PTFE) nanofibers which demonstrates strong affinity for carbon dioxide (CO2). Foam extrusion of the PP nanocomposite using CO2 as the blowing agent reveals a three orders of magnitude increase in cell density, a ten-fold increase in expansion ratio, and a marked broadening of the foaming window with respect to when no nanofibers were added. The improvement in foaming ability is attributed to the increase in strain-induced hardening and the ability of the nanofibers to act as a reservoir of the blowing agent and facilitate the foaming process.
Solid-State Batch Processing and Structure of Nano-cellular Thermoplastic Polyurethane foams
Two step solid-state batch foaming of TPU/Clay nano-composite as well as melt processed neat TPU was conducted by using CO2 as the physical blowing agent. Nanoclay was dispersed into the TPU by using a twin screw extruder in order to promote cell nucleation. The samples were saturated under CO2 pressures of 30 MPa at room temperature. Subsequently, the solid state foaming step was carried out by immersing the saturated samples in a silicone oil bath at different temperatures around the first thermal transition of the considered nanocomposites assigned by differential scanning calorimetry. A scanning electron microscopy was used to examine the structure of the foams. Depending on the combination of processing parameters, a wide range of cellular structures was achieved. The cell size ranged between 10 ?m and 400 nm and the cell density was between 109 to 1013 cells/cm3. An optimum foaming time and temperature were found wherein the smallest cell size with highest cell density could be produced. This CO2-TPU/Nanoclay system provides a unique frame in which the bulk properties of nano-cellular and microcellular structures can be compared.
Structure-Property Relationships in a New Family of Bio-Based, Compostable Blown Films
This paper is concerned with the influence of processing conditions on microstructure development and performance of a new family of biobased and compostable blown film products based on Mirel? PHB copolymers (product referred to as B5009). The unique combination of performance attributes of B5009 blown films including biobased carbon content and compostability, along with an excellent balance of tear propagation resistance, puncture toughness and tensile strength will be highlighted. The potential applications of the subject film, that has similar to superior mechanical properties compared to LLDPE, will be reviewed. The synergistic advantages that can be garnered with multi-layer film structures (through coextrusion with other polymers) will also be discussed.
Electrical Properties of Polypropylene Composite Foams Reinforces with Long Stainless Steel Fibers
Conductive thermoplastic composite foams are a novel class of materials that can be an excellent candidate for producing cost-effective and lightweight products. In this work, electrically conductive polypropylene (PP) foams of various densities filled with varying contents of long stainless steel fibers (SSF) were successfully fabricated. The foaming of composites was achieved using a batch process and supercritical CO2 as the environmentally benign physical blowing agent. The PP-SSF foams maintained high level of electrical conductivity over a wide range of density reduction, depending on the initial loading of SSF. To better understand the conductivity behavior of solid and foamed composites, statistical percolation analysis was conducted. The analysis showed that the conductivity change with the foam density followed the percolation power law. The critical SSF concentration, calculated based on the sample’s final volume was 0.37 and 0.28 vol.% for the solid and foamed composites, respectively. In the current PP-SSF system, foaming decreased the weight up to ~70-80 % and lowered the percolation threshold by about 25%.
Determination of Specific Aluminum Flake Characteristics in Injection Molded Plastic through Colour and Effect Measurement
An attractive alternative to painting plastic parts with formulations that include metallic pigment has become the inclusion of metallic flake directly in the resin. One of the challenges associated with including metallic flake directly in the resin is that current molding technology limits our ability to control flake distribution during the manufacturing process and achieve a uniform appearance. For many end use applications including automotive interiors, a low-quality appearance is not acceptable; thus, the economic benefits of this method have historically remained out of reach. As a first step towards achieving a uniform finish in an injection-molded part with embedded flake, a method must be established to evaluate the uniformity of colour and flake effect in the end product. Recent developments in colour and effect measurement technology now allow for quantitative characterization of both metallic colour and flake effect. With this method in place, it is possible to begin optimizing all those parameters that affect flake distribution and quantify the customer’s visual impression. This paper describes this measurement method and demonstrates the method’s ability to discriminate between different effect pigments.
High Throughput Methodology for Mechanical Testing of Polymeric Films
Assessment of mechanical properties of thin polymer films under high speed impact is often nontrivial. Standard dart drop tests are not suitable for thin samples, nor does it provide information on stress- strain relationship under load. Other techniques such as tensile/flex and nanoidentation testing can only be performed at relatively low strain rates. A High Throughput Methodology for Mechanical Testing (HTMECH) of freestanding thin films under high speed loading is used in this work. The main advantages of this technique are the high instrumental sensitivity, ability of rapid screening, and simplicity of data analysis. Toughness properties of thin films were measured by HTMECH and compared with dynamic mechanical analysis (DMA) data. The correlation between the two techniques has been established and discussed.
The Effect of Hydroxyl-functionalization on the Structure and Properties of Polypropylene
Hydroxyl-modified polypropylenes (PPOH) with side chains containing OH groups were synthesized by the copolymerization of propylene with undecenyl-oxytrimethylsilane monomer. Copolymers with OH concentration ranging from 1.3 to 3.9 mol% were produced and their properties compared with unmodified polypropylene. The presence of intermolecular H-bonding between the OH groups affected the base polypropylene structure as well as its thermal and rheological properties. As predicted by Flory’s theory of melting point depression in copolymers, the melting point reduced with increasing [OH]. While the crystal structure remained unaffected, the crystal size reduced by approximately 15%. Crystallinity for PPOH polymers was also reduced by as much as 40% because of the hindrance to the ordered packing of backbone chains into the lamellar structure. On the other hand, the rheological properties such as the melt strength and the elasticity increased for the PPOH polymers. PPOH with only 3.9 mol% OH groups displayed a gel-like rheological behavior suggesting the formation of a weak elastic network in the melt.
Slow Crack Growth in High-Density Polyethylene Part 1: Experimental Observations
This paper aims to simulate slow crack growth in high-density polyethylene by using Crack Layer Model. We first derived the analytical approximations of stress intensity factor and crack opening displacement for finite geometries using close form solution of a semi-infinite crack and the numerical solutions for corresponding geometries. We then use the approximate solutions to assess the size of the process zone accompanying the crack, slow crack growth rate and mechanisms as well as the lifetime in brittle fracture of high-density polyethylene.
Virtual Prototyping in Rubber Seal Manufacturing and Testing
This case study highlights the entire design and testing process, virtual prototyping, of an extruded automotive aluminum reinforced rubber seal. First, the expected deformation of two similar shapes of the rubber seal will be analyzed. The design that will provide the required deformation, contact pressure, and reaction force, and hence better sealing performance, will be chosen for production. Two rubber material models are considered for the non-linear plain stress analysis, one being rate dependant (more realistic) and one is rate independent. The difference in behavior of the seal due to the material model used is highlighted. Then, to obtain the required extrusion die profile that will be used to manufacture that seal shape, the process of inverse die design will be implemented. In this procedure, the final seal cross section is used to obtain what the required die lip shape should be so that after die swell the final profile is obtained. Finally, to verify the entire die performance, detailed flow analysis is carried on the entire extrusion die and the flow balance is verified.
Constant Temperature Embossing (CTE): Process Analysis
The goal of this paper is to analyze the Constant Temperature Embossing (CTE) process by constructing a process model to determine the change in material parameters during the process. The process model is developed by combining the non-isothermal crystallization kinetics and suspension based rheological models. A shift factor is determined from the non-isothermal crystallization kinetics to predict the crystallization behavior at temperatures where the properties are difficult to measure. A suspension based rheology model is chosen to represent the change in viscosity of the polymer during the process as the increase in particle concentration. The thermal and rheology models are then merged by considering certain key assumptions, and a process model to determine the change in material properties during the CTE process is constructed.
Impregnation Process for Fiber Hybrid Braided Reinforcement Thermoplastic Plastic
The purpose of this study was to clarify the process of impregnation for hybrid braided FRTP. First, intermediate material was made and investigated. Second, braided fabric with some structure was made and by these braided fabric, moldings with some molding time were molded. After investigation of impregnation-property and mechanical property, it was clarified that essential molding time and the gradient of decreasing in un-impregnation ratio to molding time of BY and MEY were different according to the materials and to reduce un-impregnation area was important to improve mechanical property.
Friction Coefficient Measurements Using a Timoshenko and Van Karman Device: Bulk Polymers
In this paper, an alternative method to using the pin-on-disk tribometer was used to measure the kinetic friction coefficient of polymers. This method is based on the principle of the Timoshenko and Van Karman device . Compared to the pin-on-disk tribometer, this method is more cost effective and does not require precise manufacturing. Experiments were conducted to measure directly the period of oscillations from which the friction coefficient can be evaluated. Period is measured by IR timing device and Laser Vibrometer (LV). Three materials are tested, namely polyacetal (POM), Acrylonitrile butadiene styrene (ABS), and Polymethyl methacrylate (PMMA). The effects of normal force and sliding speed on the friction coefficients of these polymeric contacts are studied. Results show that both the normal force and the rotation speed of the rollers influence the friction coefficients. These observations conflict with the classical laws of friction.
Comparison of the Flow Performance Between Internal and External Deckling in Flat Film Die Systems
Deckles are devices useful to adjust the slot width of extrusion dies, and hence the extruded product width. There are basically two types of deckles: (i) internal deckles are made of components placed inside the die flow channel to block the flow channel to a specified width upstream the die lips, and (ii) external deckles typically comprise blockage devices positioned directly on and external to the die lips, at the exit orifice. To understand the fundamental differences in flow performance between the two technologies, 3D Computational Fluid Dynamics (CFD) models were built. A comparison of the original die width to the internally and externally deckled dies is carried out by evaluating the flow characteristics such as velocity uniformity at the die exit and Residence Time Distribution (RTD) in the die flow channel. The flow models show that the performance of an internally deckled die is close to that of a non-deckled die, while the external deckle system results in non-uniform flow distribution and broad RTD due to the occurrence of a large stagnation area upstream of the external deckle.
Decrosslinking of crosslinked HDPE via ultrasonically aided extrusion
Decrosslinking of crosslinked HDPE (XHDPE) at various processing conditions is performed by means of ultrasonic single and twin screw extruders. Without the imposition of ultrasound the high flow rate in the single screw extruder was impossible to achieve due to an excessive torque. Gel fraction, crosslink density, dynamic properties and mechanical properties of the virgin HDPE and XHDPE and decrosslinked XHDPE and is measured. Significant decreases of gel fraction and crosslink density of decrosslinked XHDPE was observed indicating the occurrence of decrosslinking. A universal linear relation between the normalized gel fraction and the normalized crosslink density is found, regardless of the type of extruders and processing conditions. The decrosslinking effect induced by ultrasound increased with the ultrasonic amplitude. The increase of amplitude led to a decrease of the complex viscosity and storage modulus and increase of the loss tangent of decrosslinked XHDPE. The viscosityfrequency curves were well described by a power-law model with the consistency and power law indices linearly increasing and decreasing with crosslink density, respectively. The dynamic characteristics of sol indicated an increase in polymer chain branching due to decrosslinking effect, as detected by an increase of the activation energy of viscous flow. The mechanical properties of decrosslinked XHDPE showed a strong dependence on the type of extruder and a no trend on processing conditions due to molecular complexity of the decrosslinked XHDPE.
Morphological Aspects of Injection-Molded Polypropylene with Metallic Pigments
Innovation, design freedom, cost and weight reduction are some factors for the replacement of metals by plastics. Plastics continue to offer attractive solutions for design engineers. The metallic effect obtained by incorporation of metal particles in polymers by injection molding has the advantage of eliminating post processing techniques such as painting or metallization. Moreover, it reduces production costs and time to get a superior part quality. Nevertheless, undesired defects in the final appearance of parts are common, such as flow lines and weld lines. These defects occur due to inhomogeneous orientation and anisotropy of the metal particles. Very few studies are reporting the influence of metallic particles on the morphology development of PP parts. This study focus on the production of composite materials made of PP/metallic pigments (aluminium, bronze and cooper) by injection moulding and on the influence of the metallic particles on the aesthetic and morphological properties of the parts.
A Safe and Low-Odor Organic Peroxide Formulation Designed for the Rotational Molding of Crosslinked Polyethylene
The rotational molding industry has experienced safety, hygiene and quality issues when using 2,5- methyl-2,5-di(tbutylperoxy) hexyne-3 (referred to as P-H3 in this paper). P-H3 at >93% assay is the traditional organic peroxide crosslinker for the rotational molding of crosslinked HDPE. P-H3 is classified as a subsidiary explosive based upon United Nations and USA safety testing. Furthermore P-H3 exhibits undesirable air and skin hygiene issues during the manufacturing and handling of crosslinked parts due to the primary skin irritants that are created when P-H3 decomposes to crosslink the HDPE. These low molecular weight triple bond by-products are also responsible for the discoloration of the crosslinked HDPE. The under-cure and general “inconsistency of cure” quality issues are traced to the incompatibility and volatility of P-H3 in the HDPE molding powder. Years of safety testing and R&D culminated in the development of Luperox® MIX (referred to as P-MX in this paper), specifically designed for the safe and reliable rotational molding of crosslinked HDPE. P-MX is a homogeneous blend of m/p-di(t-butylperoxy)diisopropylbenzene, triallyl cyanurate and a free-radical trap. The data in this technical paper demonstrates how P-MX addresses certain safety, hygiene and quality issues of P-H3. P- MX is a homogeneous solid at room temperature, with a 45°C melting point.
The Application of Rheological Techniques in Selecting Plasticizers for PVC Processing
This paper focuses on three different rheometric techniques to analyze how dibenzoate and other plasticizers affect flexible polyvinyl chloride (PVC) processability. Both plastisol and melt compounds will be considered. This analysis includes the use of a research rheometer in an oscillatory mode to evaluate plastisols. A torque rheometer was used to evaluate melt compound formulations. New dibenzoate plasticizers and a new monobenzoate have been introduced and the nature of the solvator class of these new benzoates will be evaluated.
Thermal Stability of Castor Oil Derived Polyurethanes
Polyurethanes synthesized using both unmodified and epoxidized, ring opened castor oil as a polyol were prepared and their thermal properties tested using thermogravimetric analysis and differential scanning calorimetry. Chemical changes upon degradation were investigated using Fourier transform infrared spectroscopy. The kinetics of degradation were elucidated using the Flynn-Wall and Flynn procedures. Epoxidized castor oil produces a rigid polyurethane exhibiting glassy behavior at ambient temperatures. All methods to determine activation energy of degradation indicate that, in a nitrogen environment, polyurethanes from unmodified castor oil are more thermally stable than those from modified castor oil. The appearance of peaks corresponding to amines, amides, and esters in FITR analysis of degraded samples suggests that the initial degradation step of the polyurethanes studied is the breaking of the urethane bond.
Effects of Glycerin Antifreeze on CPVC
There are multiple applications where chlorinated poly(vinyl chloride) (CPVC) may come in contact with glycerin. One common application is in fire suppression systems that could be subjected to subfreezing temperatures. Chlorinated poly(vinyl chloride) is increasingly being used for these systems in place of metal because of its many advantages, including the ease of installation, weight reduction, cost benefits and chemical resistance. When CPVC piping is used in an area that has the potential to freeze, an antifreeze solution must be used in the fire suppression systems to suppress the freezing temperature of the water and reduce possibility of failure of the piping system. Glycerin is a commonly used antifreeze for this application. The following article discusses the effects of using glycerin with CPVC piping and presents a case study of the use of bio-derived glycerin as an antifreeze agent. In general, it was found that glycerin from the bio-diesel industry had adverse effects on the CPVC.
Fabrication and Characterization of Polyvinyl Alcohol (PVA)/Nanofibrillated Cellulose (NFC) Filaments
This paper presents a new process to fabricate single polyvinyl alcohol (PVA)/nanofibrillated cellulose (NFC) filament and its tensile properties at various ratios (0.5 ~ 3 wt %) of NFC. The fabrication process generally contains four steps: NFC isolation, preparation of PVA/NFC solution, gel spinning and drying, and filament stretching. The ultimate strength of PVA/NFC increased by almost 2 times, compared with stretched neat PVA filament. In order to ensure that the NFC fibers disperse well in PVA solution, high shear processing was employed. To study the possible degradation of PVA caused by high shear, the parallel plate rheometer was used to investigate the viscosity of PVA/NFC solutions. The PVA crystal orientation in PVA/NFC filament was also characterized by wide angle x-ray diffraction (WAXD).
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