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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High Temperature Issues for Polymer-Based Solar Thermal Systems
Use of polymer technology for solar thermal systems is perhaps the best strategy to achieve radical cost reduction. However, polymer materials durability is a key barrier to polymer-based systems, including affect of high temperatures. It is shown that stagnation temperatures in glazed flat plate collectors will rapidly degrade or melt commodity plastics, and overheat protection (OHP) must be employed. Normal operation and stagnation temperature frequency distributions are given, as needed for creep and other analyses. It is shown that venting-type OHP can reduce temperatures of the occasional stagnation events to below 100 C, which could allow successful commodityplastics- based solar thermal.
Correlations of Tensile Modulus for Polyethylene Blown Films with Microstructural Parameters
A series of blown films were produced by varying three key parameters: take-up ratio (TUR), blow-up ratio (BUR), and frost line height (FLH). The tensile properties of the resulting films were investigated in relation to their microstructure characteristics. The orientation parameters of the films were measured by XRD and birefringence. They were determined for both crystalline and amorphous phases. The crystalline content, the lamellar thickness and crystal sizes were obtained from DSC and WAXS pole figure technique. The SAXS technique was used to find the average length of the crystal and amorphous layers. A model for the tensile modulus was proposed and correlated to some structural parameters including crystalinity, orientation factors for crystalline c-axis and amorphous phase, lamellar thickness and crystal size. The measured modulus and calculated one were compared and a reasonable agreement was found between them.
Breakdown of the Cox-Merz Rule and Instability of Polymer Solutions in Viscometric Flows
There has been considerable interest in recent years concerning the instability of polymer melts and solutions in viscometric flows. Here we examine the flow instability in a polybutadiene solution and in NIST SRM 2490. The instability manifests itself as a deviation from the Cox-Merz rule that relates steady shear viscosity vs. shear rate with dynamic viscosity vs. frequency. We find that in all instances of deviation from the Cox-Merz rule investigated the fluid undergoes edge fracture and the deviations can be related to the edge fracture rather than to changes in constitutive behavior.
Correlation of Electrical Resistance and Electromagnetic Shielding for Thermoplastic Composites
Several commercially available electromagnetic interference (EMI) shielding thermoplastic materials were evaluated for electrical resistance and EMI shielding. International Electrical and Electronics Engineers (IEEE) test method 299 and ASTM D4395 shielding tests were performed as far field shielding tests. A ladder box configuration was used to evaluate near field shielding. Electrical resistance was measured along the surface and through the parts.It was found that type and fit of the correlation between shielding effectiveness and electrical resistance varied across the frequency sweep. Generally, it was found that through resistance provides a better correlation than surface resistance for all shielding tests. This may be due to the increased within test variability of surface resistance compared to through resistance.
Effect of Processing Parameters on Electrical Properties of Electrically Conductive Composites
The effect of injection molding parameters on electrical resistance and electromagnetic interference (EMI) shielding was examined for two commercially available grades of electrically conductive polycarbonate/acrylonitrile butadiene styrene (PC/ABS). A Box-Behnken design of experiments (DOE) was utilized for the variables of mold temperature, barrel temperature and back pressure. Surface resistance was measured to evaluate electrical conductivity. International Electrical and Electronics Engineers (IEEE) test method 299 was used to evaluate shielding effectiveness.Neither EMI shielding or surface resistance was changed in a significant way over the processing condition examined. A very weak trend is seen for one of the materials with mold temperature.
Comparative Study of New Generation Thermoplastic Elastomers and Polyester-Polyester Thermoplastic Elastomers
New generation thermoplastic Elastomers (Elastollan® HPM**) & Polyester-Polyester thermoplastic Elastomers (COPE) are block copolymers of hard and soft segments. The hard segments are semi-crystalline thermoplastic that act as physical cross-links which ties the amorphous elastomeric soft segments together. On one hand, the hard segment should have regular structure to promote crystallinity. On the other hand, the soft segment would have irregular structure and low glass transition temperature to promote low temperature flexibility. The melting point of the hard segment would influence the upper use-temperature of TPE, whereas, the glass transition temperature of the soft segment would influence the lower use-temperature of TPE.In this work HPM, are compared to traditional TPU and COPE. Several testing methods are used to compare the flow parameter, and physical & thermal properties of these materials. Melt-viscosity, tensile, tear, compression set, and long-term properties exemplified in hydrolysis resistance & oven aging are discussed and compared.
Long Term Performance of Polymers for Solar Hot Water Applications
Polymer materials used in domestic hot water heating systems must maintain mechanical properties in the working fluid over their target lifetimes. In potable water, chlorine and pH combine to create an oxidative environment, characterized by the oxidative reduction potential (ORP) that can chemically attack a polymer, resulting in permanent loss of mechanical strength and increase in creep compliance. Polymer morphology data and mechanical property data are presented for polysulfone (PSU), polybutylene (PB), polypropylene random copolymer (PP-r) and polyamide 6/6 (PA66) specimens that had been exposed to an aqueous oxidative environment. The data obtained after up to 1500 hours exposure in hot potable chlorinated water (ORP ranging from 550 mV to 825 mV), show that PSU and the polyolefins with antioxidant additives (PB and PP-r) maintain their mechanical properties, while PA66 degrades significantly.
A Mathematical Model for the Heat Sealing of Linear, Semi-Crystalline Polymers
A mathematical model and computer simulation describing the heat sealing process for linear, semi-crystalline polymer films has been developed. Accounting for the effects of conduction heat transfer with phase change, interfacial melting, and polymer chain scaling relationships based upon reptation theory to describe chain diffusion and strength development at the bonding interface during the transient, non-isothermal heat sealing process, the model demonstrates that interfacial melting, wetting, and chain interdiffusion are all important contributions to the development of the seal strength during rapid heat sealing. The model has been used successfully to compute the time dependence of interface strength development during the heat sealing process for linear polyethylene copolymers.
Polypropylene-Wood Plastic Composites Reinforced with Different Amounts of Wood and Organoclay
In this study, wood-plastic composites (WPCs) were made by compounding 10, 20, 30 and 50 wt% wood flour (WF) with a polypropylene (PP) / clay nanocomposite matrix using a co-rotating twin-screw extruder. A PP/clay master batch was diluted to give polymer nanocomposite (PNC) pellets having varying percentages of clay, and these pellets were then compounded with WF and a fixed amount of polypropylene grafted with maleic anhydride (PP-g-MA) that acts as coupling agent between wood and PP. The WPC pellets were finally injection molded into test specimens whose thermal and mechanical properties were measured and whose fracture surfaces were examined with the help of a scanning electron microscope (SEM). Results obtained were compared with results on WPCs containing additional WF but no clay. It was found that the addition of clay to PP enhanced the modulus of both the base polymer and the injection-molded WPCs. Also, the peak mass release temperature (PMRT) in TGA increased with wood and organoclay content.
The Effect of Pigment on Rotomoulded Polyethylene Powder and Micropellets
This paper presents the results from investigations into the differences in the rotational moulding and mechanical properties between pigmented polyethylene powder and micropellets. Both high shear and low shear pigment blending methods were examined, as were a range of pigment addition levels. This was followed by a series of mechanical and analytical tests on the rotomoulded articles to determine properties. Whilst micropellets tended to produce a different surface porosity than powder, few bubbles were evident within the wall thickness for both high shear and low shear blending. For high shear blending, with pigment addition levels up to 0.05%, similar impact properties were noticed for both powder and micropellets. Low shear blending resulted in more inconsistent impact values. There were also more visual inconsistencies in articles produced from powder.
Analysis of Die Drool Phenomenon for Metallocene Based Linear Polyolefins
Die drool phenomenon, occurring as a result of the viscoelastic behavior during the flow of the polymer melts, has been experimentally investigated for metallocene based LLDPE on the specially designed annular extrusion die with the capability to control the stress state at the end of the die by the help of specific type of cooling system. With the aim to understand the die drool phenomenon in more detail, the flow at the end of the die has been analyzed theoretically by the Finite Element Method (FEM) employing modified White-Metzner model as the constitutive equation. It has been revealed that the negative pressure occurs at the die lip area which seems to be driving factor for the die drool phenomenon.
A CO2 Assisted Nanoimprinting and Cold Embossing
A CO2 assisted nano-imprinting and embossing scheme was developed. The polymer surface was plasticized by dissolving CO2 in a newly developed high pressure mold stamping machine and the nanometer-scale fine pattern on the mold stamper was transferred to the plasticized polymer surface within few minutes at lower temperature than the glass transition temperature of the polymer. The pattern could be transferred to the surface of poly(methyl methacrylate)(PMMA) at 35 °C with in 1.5 minutes and to the surface of polycarbonate (PC) at 100 °C within 5.5 minutes without deforming the overall shape of the product. The transferable pattern structure as well as the processing time could be controlled by the degree of plasticization i.e., the pressure level of CO2 and processing temperature.
Rheological Modeling of Warpage in Polymeric Products Under High Temperature
Thermoforming process is one of the most popular techniques in the polymer processing. Wide applications of thermoforming are due to its high performance, simplicity, compactness and relatively low-cost equipment. The fundamental defect inherent to the thermoforming technology is warpage of the products during their application which becomes particularly apparent under high temperatures. The warpage defect is understood as the process of non-uniform (heterogeneous) change of the geometric dimensions of products in time resulting in a change (distortion) of their original form. The results of this work allow us to find out the causes of this warpage and ascertain the conditions that give rise to this defect, thereby making it possible to work out valid recommendations for its partial and, in some cases, complete elimination.
Recycling and Reuse of Vinyl Wallpaper
Vinyl wallpaper has two principal materials of natural and synthetic origin used in its manufacture: Thermoplastic polymer (PVC) Polyvinyl chloride combined with cellulose fibre. The present paper will follow an interdisciplinary approach aimed at producing strategies for the recovery and reuse of these materials, thereby minimising the level of wallpaper waste entering landfill. Consideration will be given to preparation, characterisation and properties of the compounded and moulded recyclate. A range of techniques used to characterise these materials will be discussed, including image analysis, thermo gravimetric analysis, compressive strength, impact and recovery measurements.
Numerical Simulation of Stress on the Mold in Beads Expansion Process and Thickness of Foam Product in the Recovery Process
The expanded polypropylene foam beads (EPP) production process, which consists of steaming, depressurizing, cooling and ageing processes, was simulated by a mathematical model. The model was developed by extending Yang and Lee's ageing model of extrusion foam products in terms of fundamental aspects of evaporation, condensation of blowing agents and heat conduction phenomena during the steam chest molding. The governing equations were established by coupling the mass transfer equation of steam and air at the interfoam cell walls, constitutive equation of evaporation and condensation in each cell, equation of heat conduction from the mold to foams, with mechanical force balances equation on the cell walls. The model could simulate the stress exerted to the foaming mold and expansion behavior of the cells in the EPP foam board.
Nonisothermal Crystallization Kinetics and Crystalline Structure of Nylon 6/Functionalized Multi-Walled Carbon Nanotube Composites
Nylon 6/functionalized multi-walled carbon nanotube (f-MWNT) composites were prepared by mixing the nylon 6 and carboxylic group containing MWNT in formic acid solution. DSC and XRD have been used to investigate the nonisothermal crystallization kinetics and crystalline behavior of nylon 6/f-MWNT composites. DSC data shows that the activation energy (Ea) drastically increases with the presence of 0.25 wt% f-MWNT in nylon 6/f-MWNT composites and then slightly increases with increasing f-MWNT content. These results indicate that the addition of 0.25 wt% f-MWNT into nylon 6 significantly reduces the transportation ability of polymer chains during crystallization process. By adding more f-MWNT into nylon 6 probably induces the heterogeneous nucleation in which the Ea slightly increased. XRD results indicate that the addition of f-MWNT favored the formation of the thermodynamically stable ? crystalline structure at various cooling rates, compared to that of pure nylon 6 matrix.
Study on the Weld Line Strength of Thin-Wall Molded Nanocomposites
Current study investigates tensile strength of Nylon6/ Fluoromica nano-composites (Unitika®), injection molded parts at different molding conditions such as melt temperature, mold temperature, packing pressure, and injection speed. Experimental results indicate that the tensile strengths of 1.0mm injection molded specimens (with weldline or without weldline) are stronger than that of 2.5mm. The tensile strength of weldline becomes significantly weak as compared to the non-weldline. As melt temperature, mold temperature, packing pressure, and injection speed increases the weldline and non-weldline tensile strengths of molded nanocomposites also increase.
Ultra-Thin Polymer Films: Elastic Response in the Rubbery Regime
Using a novel microbubble inflation technique developed within our laboratory, we are able to measure the absolute biaxial compliance of polymer films as thin as 13 nm. Experiments performed on both poly(vinyl acetate) (PVAc) and polystyrene (PS) films show that large reductions in the glass transition temperature at the nano-scale are nonuniversal, viz., the PVAc shows no reduction even for the thinnest films while the PS shows a significant reduction at a thickness below approximately 80 nm. More surprisingly, the rubbery plateau region for both materials shows dramatic stiffening (>300 times), perhaps due to surface pinning of the entanglement network. The compliance increases as approximately the square of film thickness.
Comparative Study of Organic and Inorganic Impact Modification of PVC
We have developed an inorganic material based on synthetic amorphous silicon dioxide with an average primary particle size of 150 nm and a specific surface area of 20 m2/g, called SIDISTAR®.These spherical particles can be optimally dispersed throughout the polymer matrix and will dissipate the impact energy over their particle surface so that in any direction the transmitted energy value is smaller than necessary for crack initiation or propagation.TEM (transmission electron microscopy) investigations prove that on impact the particles create a space between them and the surrounding polymer matrix thus avoiding energy transmittance.
Structure-Properties Relationship in Methylphenylsiloxane - Modified Epoxy Systems
The fracture resistance of epoxy resins was significantly improved through a new molecular toughening mechanism without sacrificing the desired thermal and mechanical properties. A liquid diglycidyl ether of bisphenol-A type epoxy resin (DGEBA) was modified with various methylphenyl siloxane (MPS) modifiers and then cured with two types of amine curing agents, meta-phenylenediamine (mPDA) and polyoxypropylene diamine (POPDA). The effects of such variables as the modifier type and concentration, and the curing agent type and curing cycle on the properties and the morphologies of the MPS-modified DGEBA systems were investigated. The glass transition temperatures (Tg) of the siloxane-modified DGEBA/mPDA systems were well-maintained. Chemically modified DGEBA samples by various MPS modifiers demonstrate greater enhancements in both the fracture toughness (KIc) and the fracture energy (GIc) compared with the unmodified epoxy system. With an increasing siloxane content, both the values of KIc and GIc increase. The improvement of fracture toughness can be attributed to shear band formation, crack path deflection, trans-particle fracture, particle tearing and localized plastic deformation.
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