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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Rheological Modeling of Plug-Assist Thermoforming
Solving problems for thermoforming processes in production of axisymmetric thin walled plastics is investigated in this research work. A non-linear viscoelastic rheological model with a new strain energy function is suggested for improvement of physical properties of final product. For model validation, a quantitative relation between stress and technical parameters of plug-assist thermoforming is determined by comparison of theoretical and experimental results. This process with the proposed rheological model could be suggested for prevention from some technical defects such as wall thickness variations, physical instability during inflation-shrinkage, and warpage exhibited in the final part of a polymeric sheet thermoforming.
New Modification Technology for Polymer Composites
Using a unique reactive gas modification technology, new families of polyolefins can be manufactured that have highly oxidized and water-wetable surfaces (figure 1). These functionalized polyolefin particles can be used as performance additives in both thermoplastic and thermoset composites. The unique and highly modified surfaces enable non-polar polyolefins to become compatible with polar polymers. This is seen when the functionalized particles are used in melt blending with engineering plastics, when used as a dispersed solid phase in a thermoset such as polyurethane or epoxy, and when used in a latex paint formulation. When the polyolefin particle integrity is maintained, polymer-polymer composites are formed, which have unique physical properties that often have commercial value.The process of functionalizing the surface of polyolefin particles using reactive gases has many advantages. The process can be done at any scale and in batch or continuous configuration without many of the concerns associated with other unit operations, such as melt phase grafting or liquid processes. Further, the process of using highly reactive gas atmosphere processes, such as those using elemental fluorine initiation, are amenable to modifying most polymers except those that are already highly fluorinated, such as PTFE.
A Review On: 'Stack Mold'
A mold's efficiency is determined by its cores, cavities and levels. Each cavity in a mold forms a single plastic product during each cycle" made by an injection-molding machine.A mold level (or "face") is the flat surface area of the mold containing the cavity. The simplest form of mold is a single-cavity single-level mold where the injection-molding machine injects plastic directly into the single cavity in order to form a molded plastic product. The single cavity can be extended to a multi-cavity layout which increases the number of plastic products molded in each cycle.Multi-cavity molds represent certain engineering challenges which are not present when molding products with a single-cavity mold. In order for the mold to work correctly plastic must be injected into each cavity at exactly the same time. As a result multi-cavity molds require hot runners a system of channels with manifolds designed to deliver molten plastic to each cavity at exactly the same moment. "Although stack molds are not new to injection molding industry they are still surrounded by myths and misconceptions regarding their applications benefits and requirements. The fact is stack molds can meet a variety of molding demands because they are available in configurations that can help users achieve the optimum tooling solution for their application.""
Study of the PTFE Rheology During Paste Extrusion Process
Polytetrafluoroethylene (PTFE) is a remarkable membrane material. Due to its high melting point, PTFE fine powder cannot be processed using conventional molding methods. Instead, techniques involving paste extrusion, rolling and sintering have to be employed. This research builds a simple PTFE capillary rheometer system, with accurate extrusion speed and extrusion pressure control, and investigate the rheology of PTFE paste during extrusion process. Due to the lower constant speed, the density variation of PTFE extrudate decreases from 1.75 g/cm3 (± 5.8%) to 1.68 g/cm3 (± 0.48%). In addition, different lubricant content (18 wt%, 20 wt%, and 22 wt%) was used to monitor the pressure drop at different extrusion speeds (0.5 mm/s, 1 mm/s, 2 mm/s) and reduction ratios (RR=26.47, 47.06, 80.06). It was found that higher lubricant content and high reduction ratio result in lower pressure drop. Lower extrusion speed also results in a better performance in extrudate formation.
Linear Viscoelastic Behaviors of Polypropylene
Polypropylene-layered silicate nanocomposites modified with different levels of maleated polypropylene (PPgMA) compatibilizers were prepared through melt compounding. Above a threshold loading the storage modulus G’ was shown to display a low-frequency plateau. The threshold loading level was found to be strongly correlated with the exfoliation of layered silicates. The samples with higher degree of exfoliation exhibited lower threshold loading level. Such threshold behavior is attributed to the existence, in the quiescent state, of mesoscopic domains composed of correlated silicate layers. Finally, melt rheology also demonstrated that the stress level imposed during melt compounding played an important role in clay exfoliation.
Extrudate Surface Tearing in Extrusion of Wood Plastic Composites
In previous publications from this laboratory it was shown that the phenomenon of wall slip occurs with HDPE filled with rice hulls and HDPE filled with wood flour. In the present work, metallocene polypropylene (mPP) was used as a thermoplastic matrix to investigate the extrudate surface tearing of wood plastic composites (WPC). Maple wood flour, mesh 100, was predried and used as filler at 50 wt.% loading. Maleated syndiotactic metallocene polypropylene and a thermoplastic silicon elastomer (TPSE) were employed as coupling agent and polymer processing aid (PPA) respectively to investigate their influence on the extrudate surface tearing.At loadings of 50 wt.% wood flour in the mPP the extrudates come out of the die with significant tearing and surface roughness. Addition of the coupling agent results in considerable improvement of the extrudates appearance, especially at high output rates. At low throughputs, however, the extrudate surface is still rough. It was found that TPSE at low concentrations (1- 3 wt.%) in the coupled 50% filled mPP composite was able to reduce or even completely eliminate the tearing at all throughputs. Likely, the low viscous PPA forms a lubricating layer on the extrudate surface initiating slip at the wall leading to plug-like flow of the melt flowing through the die. Increasing the screw rotation as well as the concentration of the additive yielded better results.
Isolation of True Runner System Behavior in Simulation Tools for Injection Molding
Obtaining accurate results from simulation tools requires that runners be modeled with mesh details that can identify melt variations in critical, high-gradient regions of the diameter. Modeling runners as beam elements or with inadequate refinement across the diameter may not represent the highly sheared outside laminates as they make their way through the runner system into the molded part. As a result, these simulations fail to identify imbalances in fill which occur in even naturally balanced layouts. In this paper, coarse and refined simulations are compared with runner throughput from an injection mold with a balanced layout to verify the ability to obtain accuracy in simulation, identifying concerns encountered in the process.
Parametric Study to Optimize the Processing Parameters and the Physical Properties of Porous PLGA 85/15 Scaffold
This study investigates the effects of the processing parameters on the scaffold physical properties. Porous scaffolds of PLGA 85/15 were prepared using a gas foaming/salt leaching technique. The processing parameters included: gas saturation pressure, gas saturation time and NaCl/polymer mass ratio. The physical properties considered were the density and porosity of the scaffold. The average pore size and pore density inside the scaffold were also studied. The results showed that for the samples made of NaCl/polymer mass ratio of 1, leaching all the NaCl was impracticable, and the percentage of open pores was relatively low. It was also found that for the samples made of NaCl/polymer mass ratio of 10 and 15, both the saturation time and saturation pressure did not affect the physical properties of the scaffold. However by varying the size or amount of the NaCl particles into the sample, the physical properties of the scaffold can be tailored.
Cure Kinetics of an Epoxy-Amine Adhesive System by Means of Differential Scanning Calorimetry
The cure kinetics of a medical grade epoxy-amine adhesive is studied under dynamic conditions by means of differential scanning calorimetry (DSC), and analyzed using a generalized autocatalytic model of chemical reaction. It is established that the model can be used to determine the degree of conversion, rate of conversion, and the exothermic heat of cure during any curing process with the use of the classical fourth-order Runge-Kutta numerical method. Also, the cure experiments under various quasi-isothermal conditions have been performed and the heat flows of cure measured as functions of cure times, which are then compared with the model calculations. The above numerical approach, coupled with convenient calorimetric cure measurements under dynamic conditions, provides a convenient and reliable tool for developing an oven-curing schedule of the adhesive in medical device industry.
Using TGA to Determine Carbon Fiber Content in Novel Polymer Composites
The objective of this work is to use a TGA (Thermogravimetric Analysis) method to quantify carbon fiber in a novel polymer composite such as PEEK (Polyetheretherketone). Other methods, such as electric muffle furnace, acid digestion, FTIR, and GC-MS are either incapable of detecting carbon fiber content from the composite, time consuming, inaccurate, or very expensive.The role of TGA in plastics industry to identify polymer(s) and filler(s) ratio is not widely used. However its importance has grown. Using TGA to quantify the filler that has similar chemical characteristics as the base polymer is always a challenge. This study applies a modified TGA method to determine the ratio of carbon fiber to polyetheretherketone within +/- 2% accuracy.
Rheological Studies on Radiation Modified Polyethylene Resins
Radiation modification of polyethylene resins prior to end product conversion has brought about significant improvement of various properties of the resins and products made from them using extrusion based processes where the products are formed in the melt phase at different shear rates and extensional rates. Rheological characterizations including Rheotens measurements, capillary viscosity and melt flow stability were carried out on radiation modified HDPE and LLDPE resins and their un-irradiated base resins. It is shown that electron beam irradiation of the resins has significantly enhanced the melt strength due to long chain branching. This effect would be very beneficial to the processability of the radiation-modified resins for applications that demand higher melt strength.
Ranking of PE Pipe Grades by Cyclic Crack Growth Tests with Cracked Round Bar Specimens
It is well known that resistance against slow crack growth is important for the lifetime of pressurized polyethylene (PE) pipes. As a result several methods have been proposed to evaluate the long-term performance of PE using fracture mechanics. It is generally believed that this leads to results more quickly compared to internal pressure tests. In the presented research work a method was implemented using fatigue loading of cracked round bar (CRB) specimens to characterize crack growth resistance. The method was applied to 6 commercially available PE pipe materials and the results were compared with the full notch creep test (FNCT). With both methods the same ranking was found, but it was obvious that FCG experiments were faster by up to two magnitudes, especially when characterizing modern (bimodal) PE types.
Shear-Induced Crystallization of Natural Fiber-Polypropylene Composites
Comparative study of shear-induced crystallization among injection molded polypropylene (PP) composites from vetiver grass, rossells, and sisal were examined. Shear viscosity among PP composites from vetiver grass, rossells, and sisal were investigated. Results indicated that the vetiver grass-PP composite had lower Tc, than those of rosells-PP, and sisal-PP composites. The %crystallinity of vetiver grass-PP was higher than those of rossells-PP and sisal-PP composites. However, the normalized thickness of the skin layer in vetiver grass-PP, rossells-PP, and sisal-PP composites showed insignificantly differences. In addition, the effect of fiber content on the normalized thickness of skin layer was elucidated. It was found that an increase of fiber contents led to a decrease in normalized thickness of skin layer and degree of crystallinity of the composites.
The Evolution of Slender Bubbles in an Extensional Flow: Inertial Effects
The influence of a small amount of external inertia on the evolution of a slender bubble in an extensional flow has been theoretically studied. The unsteady problem is governed by two parameters: The capillary number and the Reynolds number for the external flow. The unsteady shape of the bubble, described by a single partial differential equation, was transformed into a system of ordinary differential equations which was numerically solved. Contrary to the case where inertia is absent and breakup is not possible, a small amount of external inertia, above some critical level, can cause the bubble to break. We found the breakup mechanism to be that of center pinching.
Gradient Libraries of Surface-Grafted Polymers: Combinatorial Tools for Surface Functionality
We have developed new fabrication tools that enable us to study optimal properties of grafted polymers. These methods employ microfluidic technology to deliver well-defined mixtures and sequences of monomers to an initiator-functionalized surface. The resulting grafted polymer libraries exhibit gradual, systematic changes in composition, chain length and architecture. Gradients of grafted block copolymer prepared via these techniques reveal composition regimes that switch" their surface properties in response to solvent exposure. Moreover our unique ability to prepare statistical copolymer composition gradients provides comprehensive maps of complex surface chemistry that were previously impossible."
Toward Hydrophilic Polypropylene-Film Surfaces Using Migratory Additives
Linear and branched hydrophilic additives of various molecular weights and functional group densities were added to polypropylene (PP) as surface modifiers to make blend films through solution drop coating and heat pressing from melt-blended mixtures. Water contact angles on the film surfaces were measured over time to investigate the additive migration behavior. In particular, PP-additive blend films made through melt blending exhibited lower water contact angles than those made through solution drop coating. Ciba® IRGASURF HL560, linear polyethylene glycols (PEGs) and multi-arm polyethylene oxides (PEOs) were found to generate favorable wettability on the PP films, and all showed loss of durability when immersed in water.
Use of Semihyperbolic Die to Extrude High-Strength Polypropylene Rods
Present work deals with manufacturing and studying of self-reinforced thick-walled isotactic polypropylene products. Self-reinforcement based on flow-induced crystallization was achieved by continuous extrusion under particular flow and processing conditions - high percentage of elongational flow, high pressure and low temperature. The structure and resulting properties of extrudates were subsequently studied. Fibrous and highly oriented morphology, outstanding storage modulus in wide range of temperatures and reasonable thermal stability were found.
The Plastics Engineer as an Expert Witness
Business and patent laws of the United States are enforced by the criminal and civil courts at both the state and federal levels. The legal process utilizes technical experts such as qualified plastics engineers serving as expert witnesses to help resolve these disputes.This paper is divided into two parts. The first part notes some of the basic responsibilities and qualifications of expert witnesses and the second covers some case histories including the Gore vs. Bush election trial that took place in 2000 in Florida, where a SPE member was an expert witness.There are over a million references on “google.com” to the words ‘federal expert witness qualifications’. Many of the current laws about expert witnesses are based on a 1993 Supreme Court case1, and subsequent court rulings.
A Solution for Warpage in Polymeric Products by Plug-Assist Thermoforming
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.
Identification of Composite Beam Delamination Parameters
Identification of the delamination in fiber-reinforced composites, often used as aerospace and civil structures, is critical for structural health monitoring. It is well known that such a delamination affects the spectral characteristics (natural frequencies or mode shapes) of these structures. This study aims at developing numerical detection tools for identifying a single delamination in composite beam from its spectral data. The proposed mathematical models of delaminated composite beams will lead to the solutions of novel inverse transcendental eigenvalue problems (ITEP). Numerical techniques are developed here to solve such ITEP. It is demonstrated here that successful identification of damage parameters can be realized with finite number of spectral data set.
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