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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Single-Step Through-Hole Punching by Hot Embossing
Hot micro-embossing is a promising manufacturing technique for replicating millimeter to nanometer scale features, including fluidic channels, in thermoplastic parts. Complex microfluidic devices will require multiple functional layers as well as interlayer vias. We demonstrate a mated aluminum tool pair with integrated punch and die features. The punched hole diameters are approximately 500 µm, 740 µm, 1.0 mm, and 2.0 mm. The embossed through-holes were punched in PMMA at 120 *C with a velocity of 0.5 mm/min. The tool set also demonstrates the feasibility of forming channels on both sides of the part and producing interface ports and interlayer vias in a single step.
Experimental Studies of Polypropylene Extrusion Instability
A fundamental experimental study is conducted to investigate the extrusion stability characteristics of a homopolymer polypropylene in a lab scale extruder. An instrumented 2.5' single screw extruder is used with capability of measuring the pressure profile along the screw at a high sampling rate and the melt temperature of the extrudate. The effect of screw design (metering vs. barrier screw) on extrusion stability is investigated. For the processing conditions tested, the metering screw shows extrusion instability (surging) as manifested by high pressure variability along the screw and solid-bed break-up, while the barrier screw yields considerably more stable extrusion performance. The barrier screw is also found to be more efficient in terms of output rate and power consumption than the metering screw.
Impact Fracture Behavior of PP/EPR Blends
The impact fracture behaviors of two commercial polypropylene/ethylene-propylene rubber (PP/EPR) blends were investigated. The morphology and interfacial characteristics were directly characterized by transmission electron microscopy. The effects of EPR composition on phase morphology, interface and impact fracture behavior were systematically studied. The toughening mechanisms were examined using the double-notch four-point-bending technique. It is found that crazing and shear banding are the two dominant energy dissipation mechanisms in the impact PP/EPR blends investigated. Possible approaches for optimizing the impact strength of PP/EPR blends are also discussed.
Novel Self-Assembling Morphologies in Multicomponent Polymer Blends
Structured multicomponent polymer blends are an important class of next generation materials. In this work, HDPE/PP/PS blends modified with a SEB diblock copolymer were studied as a function of SEB content and annealing time. SEM observations show that the PS droplets, in unmodified blends, are located in the PP phase with some tending to locate at the HDPE/PP interface, as predicted by the spreading coefficient theory. This tendency is also observed for blends modified with SEB. However, after annealing, virtually all the PS droplets rapidly migrate to the HDPE/PP interface and reorganize themselves to form a highly ordered pearl-necklace structure at the interface. Remarkably, these PS droplets at the interface, even in this close-packed structure, do not coalesce and maintain a stable size with annealing time.
Polymeric Plasticizer Developments
Polymeric plasticizers are specialty types that are used in PVC formulations when extraordinary migration and extraction resistance are required. While different chemical classes of polymeric plasticizers are used, the most common type in the PVC market are liquid or near liquid polyester adipates. Typically, these polymeric plasticizers are in the 1000 to 13,000 molecular weight range (MW). While polymeric plasticizers have been used in PVC compounding for many years, developments continue. New polymeric plasticizers were developed for improved printing with waterborne inks and improved processing characteristics. This paper focuses on two new products and how they provide the required printability and processing characteristics.
Scientific Description and Industrial Interest of Laser Surface Treatment of High Temperature Thermoplastic Polymers
The interest of laser surface treatment of technical polymers is detailed. First experimental results concern polyetherimide exposed to Nd:YAG laser beams in different gaseous atmospheres. Depending on the nature and the pressure of the gas, the incidence and the intensity of the laser beam, the surface affinity of the polymer with a liquid can be increased or reduced as revealed by contact angle measurements. Polymer structural changes are identified by FTIR-ATR. The extension of this approach to several polymers permits the identification of the mechanisms involved by the laser treatment. Ultimately, the benefits of this technical solution to applications in railway industry are presented.
Foaming Behaviour of Cellulose Fibre Reinforced High Density Polyethylene Composites
This paper investigated foaming behaviour of cellulose fibre reinforced high density polyethylene composites. Two types of fibres were used in this study, similar in thickness and width, but differing in length. Extrusion foaming of the composites was conducted with a physical blowing agent, N2. The results suggested that fine-celled structure was obtained in the composites without a blowing agent. Addition of small amount of N2 further improved the cell morphology of the composites, namely, increase in the cell number and slight decrease in the cell size. However, addition of maleated high density polyethylene, which improves the interface between the fibre and polymer matrix, decreased the cell number in the composites.
Biaxial Constitutive Response of PET during Hot Drawing: Experimental Study and New Implications for Constitutive Modelling
A study was made of hot drawing of an amorphous isotropic poly(ethylene terephthalate) (PET) under biaxial stress, in the temperature and strain rate regime prevalent in injection stretch blow molding and biaxial film drawing. The constitutive response was mapped out more thoroughly than hitherto, as functions of temperature and strain rate, for constant width and equi-biaxial drawing. The data suggest multiple Eyring type flow activation volumes at lower drawing temperatures. Also the flow activation volume appears to decrease with increasing strain level, possibly attributed to entanglement slippage and intrinsic anisotropy of the flow process. The former observation would have a significant implication for current constitutive modelling approaches based on single shear and pressure activation volumes. The implications for refinement of the model are discussed.
Effect of Secondary Processing Conditions on Morphology of Thermoplastic Olefin Blends
Properties of thermoplastic olefin (TPO) blends are to a large extent determined by the morphology, (i.e., the size, shape and distribution), of the dispersed phase. Key factors that affect the morphology include: blend composition, the viscosity ratio between the matrix and the dispersed phase, interface interaction, and processing conditions during initial melt blending. For some blend compositions, however, the final morphology may also be affected due to secondary processing steps, such as injection molding or extrusion. This study investigated the stability of the elastomer dispersion during injection molding for TPO blends and established some preferred processing conditions.
Online Orientation during Polyethylene Blown Film Extrusion Using Polarized Raman Spectroscopy
Online Raman spectroscopy was used in this study to measure the orientation development during blown film extrusion of low-density polyethylene (LDPE). The analysis is valid for uniaxial symmetry of the structural units with the chain axis. The trans C-C stretching vibration of PE at 1130 cm-1, whose Raman tensor is coincident with c-axis of the orthorhombic crystal, was used to solve a set of five intensity ratio equations. Crystalline orientation (P2) was found to increase along the axial distance in the film line. The P2 values also showed an increasing trend with crystalline evolution during extrusion
Development of Laminated Oriented PE Film Light Weight Armor Material and a Device for Testing its Ballistic Characteristics
The effect of the number laminated oriented PE film (Tyvek) for use in the development of light weight armor and a device for testing its ballistics characteristics were evaluated. The study showed that Tyvek is oriented in the longitudinal direction ± 45° along the X-axis. The number of laminates appears to be critical ballistic characteristics. The higher the number of layers the shallower the penetration of the dart. For example with 6 layers, the penetration was 0.003 m for the long tube, and 0.001m for the short tube. This is because Tyvek is oriented in the longitudinal direction, and also the manner in which the layers are compression molded: biaxial or parallel has an effect on the ballistic characteristic.
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.
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