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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Conductivity of Inherently Conductive Polymer and Conductive Particle Composites
The electrical properties of blends of thermoplastic polymer, inherently conductive polymer (ICP) and metallized carbon fiber were studied. Both electrical resistance and electromagnetic shielding effectiveness were measured. These results were compared with the data for blends of thermoplastic polymer and metallized carbon fibers. The electrical resistance of the blends with ICP was much lower than that of the blends without. Additionally, the magnitude of the shielding effectiveness for the blends with inherently conductive polymer was higher than the blend without. The shape of the curves was different, as well, particularly at lower frequencies.
In-Situ Cavity Pressure Monitoring in Micro-Injection Molding
Cavity pressure has been found to be a reliable process indicator in injection molding for both part quality and process monitoring. Specifically, it has been found to provide real-time detection of part and process deviation. As such, cavity pressure measurement holds potential for monitoring part quality in micro-injection molding where direct part inspection is difficult due to part handling issues and microscopic feature sizes. The goal of this study is to determine the feasibility and robustness of using cavity pressure for process and quality monitoring of a molded hollow cylindrical cap. Although the processing window for micro-injection molding was smaller, the different shapes of cavity pressure curves showed that the pressure was able to respond differently to different molding conditions.
Effects of Surface Texture and Surface Roughness on Polymer Scratch Behavior
Surface texture/roughness is necessary for various engineering applications of plastics. Their effects on scratch performance have to be examined. Random animal skin surface was studied and compared against the smooth surface counterpart. It is found that of the animal skin surface can delay the onset visibility. To study the effect of surface roughness on scratch resistance, samples with controlled surface roughness were prepared to compare against the smooth and random animal skin surface samples. Rougher surfaces exhibit a lower friction coefficient and a better scratch performance. Approaches for improving scratch resistance of polymers via control of surface texture/roughness are discussed.
Development of Renewable Polymers from 1,3-Propane Diol and Malonic Acid
The goal of this research is to develop biodegradable copolymers from biomass-derived starting materials. The monomers, 1,3-propane diol and malonic acid, were selected based on the presence of reactive functional groups and availability of these materials in biomass. The effects of varying catalyst and temperature on polymer yield were determined. FTIR spectroscopy and nuclear magnetic resonance (NMR) were used to confirm polyester synthesis. The polymerization yields, using aluminum chloride, tin(II) chloride, and iron(III) chloride as the catalyst, ranged from 18-58%, 20- 43%, and 32-47%, respectively, over the 125-175 ºC reaction temperature range.
Case Studies: Innovative Products and Improved Polymer Materials Created via Electron Beam Irradiation
The electron beam irradiation of polymers can bring about various property improvements. The interaction between energized electrons and materials result in valuable reactions, the two most important reactions being crosslinking and chain scission. These modifications to the molecular structure of the materials are characterized by improvements to the mechanical and physical properties of the materials. A number of case studies have been completed involving the electron beam irradiation of various materials and the creation of innovative products. The paper will discuss the various studies and present the associated data.
Effect of Thermal Conductive Fillers and Hardness Thermal Conductivity of Silicone Elastomers
The effect of thermally conductive particles on the thermal properties of silicone rubber was studied. Different sized aluminum oxide was blended with addition cured silicone resin at various crosslink densities and filler loading levels. Thermal impedance of each sample was measured. Statistical analysis of the experimental data showed that hardness was not affected by filler type/size or filler amount; however, the amount of crosslinker was statistically significant with respect to hardness.Thermal impedence was affected by crosslinker and filler amount in a statistically significant way. As the filler particles are more conductive than the polymer, the greater the amount of filler present, the higher the composite conductivity. Deformation of the material during the test was found to influence the results of the testing.
Advancements in Laser Marking and Engraving Using Integrated, Through-The-Lens Vision
Laser marking and engraving for the automotive industry poses many challenges to the plastic mold manufacturer. In the past, laser-marking systems have not been intuitive in confirming part identification or part positioning. Inaccurate placement of the mark due to a part misalignment or the engraving of incorrect marking information due to a lack of part identification results in waste parts and reduces product profitability in a highly competitive market.This paper describes the procedure for laser marking using a through-the-lens vision process, Integrated Mark Positioning (IMP), and data compiled comparing marking with and without IMP. Results show that a mark placement accuracy of 0.03 mm with a part placement variation of 4 mm or larger can be achieved. System configuration, operation and benefits of integrated vision are also covered.
Analysis of the Effect of Nanoparticles on Mold Filling in a Vacuum Assisted Resin Transfer Molding System
In this paper, a novel manufacturing method was used to prepare the hybrid composite, wherein nanoparticles were sprayed and bonded onto fiber mats instead of mixing them in polymer resin. The effect of nanoparticles on the mold filling characteristics in a vacuum assisted resin transfer molding system was investigated. This study seeks to understand the flow of resin through the porous fiber bed, consisting of the long fibers and nanoparticles. A simplified model was used to predict the mold filling time. It was found that the dispersion and loading of the nanoparticles affected the permeability and porosity of the reinforcement system, and hence the mold filling time.
Influence of Temperature on Micro-Feature Replication at Ambient Pressure in Micro-Molding
This study assesses micro-feature replication at elevated mold temperature and ambient pressure using a variety of polymers and commonly used mold surfaces. In order to more fully explore the micro molding processing window, the effect of one end of processing condition i.e application of only high temperatures was studied. Molding trials were performed on micro and nano featured mold surfaces at elevated mold temperatures and ambient pressure. Feature replication was analyzed quantitatively using an atomic force microscope, comparing the attained depth of the polymers for different aspect ratio features. A qualitative and dimensional analysis was also performed by field-emission scanning electron microscope. Crystallinity of the polymers in the molded parts was attained by X-Ray Diffractometer. While feature detail was well replicated for all the polymers, the moldings exhibited poor dimensional accuracy due to high shrinkage in the parts. In general, polymers with low crystallinity showed the best feature replication.
A Designed Experiment Approach to Optimizing the Performance of Benzoate and Phthalate Blends in Flexible Vinyl
Plasticizer blends are commonly utilized to develop the desired processing and performance properties in flexible vinyl. To increase processing speeds, high solvating phthalates are typically included in these blends. Benzoate esters are high solvating plasticizers that can also be utilized for this purpose. However, the benzoate esters are not drop-in replacements for phthalates and other properties can be affected. An example of this is the increased viscosity commonly experienced in plastisols. The purpose of this paper is to demonstrate the use of designed experiment software to optimize the composition of general purpose and high solvating benzoate plasticizer blends to obtain all desired properties. A resilient flooring plastisol formulation was selected as the model. The following properties were measured on the plastisol: degassing, plastisol viscosity over a range of shear rates, viscosity stability of the plastisol and gelation/fusion characteristics. Stain resistance and tensile properties were evaluated on the fused vinyl film. The data will demonstrate the use of DOE software to develop an optimized plasticizer package that will deliver the desired balance of properties in an efficient and timely manner.
Isothermal Thermogravimetric Analysis to Study Oxidation Kinetics of Polypropylene
The oxidation kinetics of unstabilized polypropylene (PP) was analyzed by isothermal thermal gravimetric analysis (iTGA). Oxygen incorporation led to an initial weight gain before a dramatic decrease in weight as confirmed by Fourier Transform Infrared Spectroscopy (FTIR). The weight loss was attributed to the release of low molecular weight oxidation products. The time until the onset of weight gain as a function of temperature was used to determine the activation energy for the oxidation reaction. For PP the activation energy was determined to be 155kJ/mole. Literature values differ from this number from -28% (1) to 55%(2).
Controlling Morphology in Cocontinuous Polymer Blends
Cocontinuous morphologies, distinguished by the mutual interpenetration of two polymer phases, allow for enhanced mechanical properties, static charge dissipation, and barrier properties. Compatibilizers, e.g. block copolymers (bcp), are often added to hinder phase coarsening in blends of immiscible polymers and can improve adhesion at interfaces. We have studied the effect of bcp on the cocontinuous morphology of polystyrene (PS)/polyethylene (PE) and PS/poly (methylmethacrylate) PMMA model blends using scanning electron microscopy (SEM) with image analysis, 3D synchrotron x-ray microtomography, mercury porosimetry, solvent extraction, and rheology. We have shown that an optimal bcp suppresses coarsening in these blends and widens the range of cocontinuity.
The Impact of Shear Rate on Warpage with a Focus on Shear Imbalances in Neat and Filled Materials
Shear induced variation effects have been shown to cause imbalances in filling patterns in both single and multi-cavity molds. These effects, however, extend beyond just the way a cavity fills and can attribute to the way a part cools and warps. Neat and filled materials vary in shrinkage and warpage properties but both are affected by shear induced melt variations developed in the runner section. Using the somewhat opposite" shrinkage properties of a neat and fiber filled material will allow for an in depth understanding of how shear variations will affect materials with and without fillers during and after molding."
The Morphology-Actuation Relationships in Ionic Polymer-Metal Composite (IPMC) Membranes Cast with an Ionic Liquid
Ionic Polymer-Metal Composites or IPMCs, are one type of electroactive polymers that display remarkable shape-altering properties. Most IPMCs are made up of a polymer membrane contained within metal electrodes, which are typically gold or platinum. When an IPMC is hydrated, counter-ions can move freely away from stationary anions toward an electrode when an electric current is induced. This is due to the hydrating liquid’s effect of solvating the cation. The result is the IPMC’s deflection toward the anode. IPMC membranes have advantages over traditional actuators in the fact that they lack moving parts and require very small voltages to operate.
Polymer Clay Nanocomposites with Improved Melt Strength
Melt strength or strain hardening of the melt in elongational flow is important for a variety of polymer processing operations. The effect of varying surface treatment on the montmorillonite was investigated in composites prepared with 5 wt% of differently treated clays and a functionalized polypropylene alone as the matrix. The strain hardening behavior in extensional flow was evaluated with the EVF attachment on the TA-ARES rheometer. While the dispersion was better with the primary amine treated montmorillonite, the nanocomposite with the two alkyl tail quaternary ammonium ion showed dramatically improved strain hardening.
Micromechanical Analysis of Interfacial Shear Strength of Aramid Fibre Reinforced Thermoplastic Elastomers
For the majority of composites and their intended applications, the transfer of stress from the point of application throughout the remainder of the composite structure is by a shearing mechanism. The interface between fiber and matrix therefore, plays a major role. This paper examines the drawbacks from conventional micromechanical testing of model composites and introduces the benefits of fragmentation testing of aramid fibers in a thermoplastic elastomer matrix using Raman spectroscopy. Accurate and precise measurements of the interfacial shear strength between fibers and matrix are attainable.
Tg in Polymer/Oligomer Athermal Blends
The glass transition behavior of poly(?-methyl styrene), its tridecamer, and an athermal blend with its hexamer is investigated using differential scanning calorimetry. The glass transition, Tg, of the blend is found to become broader than that of the pure materials. However, the absolute heat capacity of the blend remains unchanged. The length scale of the cooperatively rearranging regions of the samples, as well as previously studied pentamer, polymer, and blends, is estimated from Donth's fluctuation model. The broadening of Tg is found to accompany a decrease of the length scale. In addition, the correlation between Tg, fragility, and the length scale of CRR is also examined.
Crystallization of Shape Memory Polymer Blends
Shape Memory Polymers (SMP) blends are of particular interest because they are easily processible, commercially available and recyclable. In this paper we study blends of PVDF (semi-crystalline, Tg=-35 °C, Tm=173 °C) and PVAc (amorphous, Tg=33 °C) which are miscible at all blending ratio (presence of a single Tg). Effects of composition as well as thermal histories on crystallization were investigated via differential scanning calorimetry (DSC), parallel plate rheology and polarizing optical microscopy (POM). For the first time, evidence for two distinct crystalline forms was observed in a blend with PVAc and PVDF crystallized for all blending ratios. Rheological measurements show that the rubber plateau of the blend decreases with lower PVDF content because of lower density of physical crosslinks. Surprisingly, in the case of 30:70 PVDF:PVAc the highest rubber plateau was achieved by isothermal crystallization at temperature close to, but above, the crystallization point measured by DSC. Comparing rheological and optical results for crystallization kinetic, it can be inferred that PVDF crystallizes faster near a solid interface than in the bulk.
Investigation of Reversed Shear Induced Melt Imbalances in Injection Molds
It has been proven that shear induced melt variations cause both cavity to cavity and intra-cavity filling imbalances. Cavity to cavity imbalances have been shown to result from the shear induced melt variations becoming separated in a runner branch. The high sheared outer laminates will follow the inside corner side of a branching runner and the low sheared material will follow along the opposite side of a branching runner. Unsupported theories suggest that these imbalances are a result of the local shear at the corner itself. This paper presents a study which shows that there is an additional phenomenon that occurs at the corner of a runner which is unrelated to either of the above mentioned theories, and that the effects are opposite. These opposite effects can be significant and are shown to cause filling imbalances of over 20%.
Multilayer Coextrusion of Polypropylene Nanocomposite Materials
A multilayer coextrusion die was used to create polypropylene (PP) / organoclay nanocomposites and to study the stress effects on clay dispersion. Nanocomposites contained 5 wt% maleic anhydride grafted PP compatibilizer and 1 – 5 wt% organoclay. Nanocomposite layers were extruded opposite talc filled PS before being separated. Individual PP nanocomposite layers were tested for improvements in mechanical, thermal and barrier properties and were compared to theoretical predictions in order to determine an aspect ratio for the organoclay. Aspect ratios from theory were compared to those measured directly through TEM. A PP nanocomposite / elastomer system was also considered.
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