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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Micro-Graphite Enhanced Extrusion Foaming of PET Resin
Extrusion foaming of neat and recycled polyethylene terephthalate (PET) resins are difficult due to their high melting temperature and low melt strength. Chemical crosslinking modification of the PET resins is the most widely used method to solve this problem. However, the modified resins are expensive and difficult to be re-used. In this work, micro-graphite or nanoclay particulates were added to PET to adjust its melt viscosity and strength and to serve as a nucleation agent to facilitate cell growth during extrusion. Micro-graphite is an excellent infrared attenuation agent (IAA) that may provide enhanced thermal insulation to PET foams. Using our small lab extruder, the foamed micro-graphite/PET composite extrudates could reach a low density of 0.21 g/cm3, close to that achieved by chemical crosslinking modified PET resins, using injected hydrofluorocarbon (HFC) as a blowing agent in extrusion. Properties of the PET foam including density, cell size, and crystallinity depend on particulate type and processing conditions.
Mechanical Properties and Thermal Characteristics of Poly(lactic Acid) and Paraffin Wax Blends Prepared by Conventional Melt Compounding and Sub-Supercritical Gas-Assisted Processing (SGAP)
In this study, poly(lactic acid) (PLA)/paraffin wax (PW) blends containing different amounts of PW were investigated. The blends were prepared by a twin-screw extruder in two ways: conventional melt compounding extrusion and sub-supercritical gas-assisted processing (SGAP). Then, these blends and the neat PLA were injection molded into ASTM 638 Type V tensile bars for evaluation. To observe the effects of the different melt compounding processes and the amounts of PW on the blends, the thermal stability and mechanical properties of the tensile bars were characterized. The results showed that the addition of paraffin wax changed the fractural mechanism and yielded tremendous improvements in elongation compared to neat PLA. In addition, samples made by the sub-supercritical gas-assisted processing (SGAP) extrusion exhibited better and more consistent results.
Micro Organic Pollutants Removal Using a Foam Filter through Rationally Selected Hydrophilic Media
Here, we present an interesting and new application of cellular foams to separate stable oil/water emulsions for large scale water treatment. The hydrophilic polyester polyurethane foam with large pores measuring hundreds of microns can effectively adsorb micro-oil droplets from stable oil/water emulsions. The foam, when configured in a flow-through filter, operates at low pressure, low mass transfer resistance, and high flow rate. The cellular polymers are promising new class of filtration media for practical oil/water separation that minimize the use of coagulants, are cost effective, and are energy efficient. The foam-based filtration technology has the potential to be a game changer in advanced water treatment.
3D Printed Highly Elastic Strain Sensors of Multiwalled Carbon Nanotube/Thermoplastic Nanocomposites
3D-printable, flexible, and electrically conductive thermoplastic-based material was successfully developed for strain sensing applications. Thermoplastic polyurethane/ multiwalled carbon nanotube (TPU/MWCNT) nanocomposites were compounded, their filaments fabricated, and sensor samples 3D printed using fused deposition modeling (FDM). Mechanical, electrical, and piezoresistivity behaviors for bulk and 3D printed TPU/MWCNT nanocomposites were investigated under monotonous and cyclic loadings. The results revealed very modest decreases in the printed nanocomposites moduli (~14.4%, compared to those of bulk counterparts), indicating excellent interlayer adhesion and performance. Electrical conductivity was largely preserved after printing and piezoresistivity gauge factors for the printed and bulk samples were found to be similar, indicating no decay in the printed samples under applied strains as large as 100%. Furthermore, a highly repeatable resistance-strain response was observed under cyclic loadings. The results demonstrate TPU/MWCNT nanocomposites as excellent piezoresistive feedstock for 3D printing.
Cell Nucleation in High-Pressure Foam Injection Molding
Manufacturing polymeric foams with high cell densities with injection molding is of great interest to industry, primarily because of the flexibility and cost-effectiveness of the technology. Foams manufactured from high-pressure foam injection molding processes, in general, possess relatively uniform cellular morphology. When used in conjunction with the mold-opening technique, high-pressure foam injection molding would also enable the manufacture of foams with higher void fractions. This work undertook an experimental approach to study the difference in cell nucleation and growth behavior in high-pressure foam injection molding with and without implementing the mold-opening technique.
Aligned Nanocomposites from Cellulose Nanocrystals by Electrospinning with a Soluble Polymer Followed by Thermoset Impregnation
A two-step procedure for preparing vinyl ester nanocomposites containing aligned, cellulose nanocrystals (CNCs) was investigated. First, aligned, continuous fibers of poly(ethylene oxide) (PEO) and CNCs were electrospun. Then the aligned mats were impregnated by a vinyl ester resin in which the PEO was readily soluble. Preparation of aligned, electrospun fibers with a CNC content of up to 50% by weight were possible. The CNCs formed an aligned network with sufficient integrity to maintain its structure during impregnation with a vinyl ester resin and curing. The resulting aligned CNC composites showed different optical and mechanical behavior than randomly aligned CNC composites.
Revisions to ASTM D7310 "Standard Guide for Defect Detection and Rating of Plastic Films Using Optical Sensors"
Gels are a critical-to-quality defect in plastics, and the measurement of gels is a routine part of product quality assurance for resin suppliers as well as film producers. Early gel test methods were based on visual counting of gel defects in a film sample. An industry standard method was issued as ASTM D3351 “Standard Test Method for Gel Count of Plastic Film” in which gels in a film were counted by observing the image obtained when light is projected through the film. With the development of suitable cameras and digital image analysis software, automated optical analysis of films using cameras has become the analysis technology of choice with turn-key systems available from several vendors, including Optical Control Systems (OCS) and Brabender. In addition to eliminating the subjectivity of human visual inspection, another key advantage is that these systems can be implemented in at-line configuration to provide continuous product quality monitoring. ASTM D3351 was withdrawn in 2000, and a new guidance document ASTM D7310 “Standard Guide for Defect Detection and Rating of Plastic Films Using Optical Sensors” was issued in 2007, and revised in 2011. Unlike ASTM D3351, ASTM D7310 is not a test method, but rather a guide that provides general equipment information along with operational recommendations, troubleshooting tips, and suggested reporting. It is fairly general and insufficient to fully describe how to achieve a result that is reproducible across different laboratories/installations. Therefore, there is no uniform measurement scale for comparing materials from different resin suppliers, and customers must establish acceptable performance based on “fitness for use” with each supplier independently. Additionally, no precision and bias information is included. This is in contrast to other critical-to-quality polymer properties (melt index, density, yellowness index, etc.) where the industry has adopted standard test methods promulgated by external standards organizations (ASTM and ISO), and external proficiency programs are available for assessing the consistency of results between different laboratories. A cross industry task group has been working to propose revisions to ASTM D7310 with the intent to move the document from an ASTM guide toward an ASTM practice by adding the following elements: • Protocol for establishing extruder conditions • Protocol for determining appropriate camera settings for defect detection • Camera calibration and verification procedures • Description of information that should be recorded in a manner that is traceable to reported results • Initial Interlaboratory Uniformity Study results for precision statement
Modelling and Validation of a Direct-Write 3D Printed Track
Additive manufacturing (AM) is of great interest since complex, designer materials can be developed for a multitude of applications based on the performance criteria. However, consistency and repeatability of manufactured items must be ensured. A model that can satisfactorily estimate the specifications of interests such as the dimensions and geometry with the change in the operating conditions and the change in the dimensions of the AM hardware can be very useful not only for optimal design, but also for controlling the operating conditions so that materials of desired specifications can be manufactured reliably. While a detailed model can be useful for design, a reduced model that is reasonably accurate and can be run real-time is needed for real-time control of the robotic deposition process. With these incentives, a detailed model and a reduced model of a fluid track created by a direct-write 3D printer is developed in COMSOL Multiphysics software and MATLAB, respectively. Model results are compared with the experimental data.
Biopolymer Compounds for Applications Requiring Marine Degradation
The tremendous production and consumption of plastics in various industries has led to some serious environmental concerns. The persistence of synthetic polymers in the environment poses a major threat to natural ecological systems. Therefore, some people believe that the use of biodegradable plastics is the only way to significantly reduce the environmental pollution due to plastic waste because biodegradable polymers can be environmentally friendly. Biopolymers or bioplastics are plastics which include living microorganisms in their production process. Bioplastics have the biochemical advantage of being totally or partially produced from renewable materials such as vegetable oils, sugar cane, and cornstarch, and can be biodegradable into carbon dioxide, methane, water, and inorganic compounds. Research studies have been performed to better understand the degradation of different degradable polymers in marine environments. Typically, these studies are performed on single polymers and not blends of polymers. In various applications, however, blends of different polymers are needed to fulfill the requirements of the application. This study was initiated to understand the biodegradation of biopolymer compounds made from blends of different biopolymers. Specifically, the mechanisms of the degradation and how the different mechanisms affect the use of the compounds in a marine environment were investigated. The specific application of netting for oyster bed rebuilding was the focus.
Foam Injection-Molding Process Designed to Produce Sub-Micron Cells
Significant progress has been made in recent years towards the production of low density foams with cell size around 100 nm. However, the process commonly used is batch foaming with high pressure CO2, which is not easily scalable and ill-suited for the production of larger specimen with controlled dimensions necessary for reliable property testing. A new approach to generate sub-microcellular foams with expansion ratio up to 4 by a modified injection-molding process is presented. Homogeneous polymer/CO2 mixtures produced by an extrusion foaming line are injected under controlled pressure into a variable thickness mold, which can then be opened at a controlled speed to adjust cell morphology. Foams with cell size below 500 nm were made by this process.
Melt-Mastication of Isotactic Polypropylene for Improved Thermal and Physical Properties
Herein a new polymer processing method called Melt-Mastication (MM) is demonstrated as a method to fabricate Isotactic Polypropylene (iPP) with improved thermal and mechanical properties. Melt-Mastication is a low temperature mixing technique that subjects molten iPP to chaotic flow under simultaneous cooling, promoting flow induced crystallization (FIC). The resulting materials demonstrate an unusual crystal morphology that is highly crystalline by thermal calorimetry (57% crystallinity), melts at a temperature 10.3 K higher than conventionally processed iPP, and demonstrates melt memory after annealing at 200 °C. The crystal morphology by polarized optical microscopy and atomic force microscopy appears to be comprised of largely disorganized lamellae, with possible ordering in local regions. Melt-Masticated iPP demonstrates improved mechanical properties in compression, specifically compressive modulus (+77%) and strength (+40%). The enhanced mechanical properties are attributed to aspects of the crystal morphology produced by MM.
A Comparative Study of the Tensile Properties and Failure Behavior of Glass/ Polyethylene Terephthalate (PET) Mat Composites
This paper focuses on the effects of time and temperature in hot press molding on the tensile properties of three different types of composites with glass mat and polyethylene terephthalate (PET) mat. Failure behavior and mechanical properties of three composites were investigated and evaluated through tensile tests. The results showed that the best molding conditions established to produce composites of optimum mechanical properties are the compaction temperature of 284°C and time of 5 min. Composite A (fabricated by hot press molding prior to needle punch) exhibited better tensile properties than other two composites due to the enhancement of glass fibers in thickness direction introduced by needle punch system, followed by composite C with PET film molded by PET mat. Composite A showed the oblique fracture mode after tensile tests, while composite B (fabricated by hot press molding directly) and C (fabricated by hot press molding prior to molding PET mat into PET film) exhibited the restively flush mode.
Flexural Behavior of Needle Punch Glass/Jute Hybrid Mat Composites
In this research, creation of higher mechanical natural fiber mat composites was proposed. The hybrid mat with jute and glass mat was fabricated by needle punching system, in which jute mat was placed on glass mat. The ratio of jute and glass mat layers was set to be 1:0,1:1,1:2 and 2:1, respectively. The composites were fabricated by hand-lay up method with unsaturated polyester resin after needle punching process. Three-point bending test was carried out in order to obtain flexural behavior of different composites. The results show that flexural strength obtained for JF was approximately 37 MPa. Whereas similar flexural strength were achieved in JF/GF and JF/GF/GF, that exhibited about respective 61.7 % and 62.0 % higher than the values of JF. However, JF/JF/GF exhibited a lower value at around 38 MPa due to lager thickness of specimens than others. Finally, morphological analysis was carried out to observe fracture behavior using scanning electron microscope.
Rapid Evaluation of Surface Properties of Medical Tubing for Process Development and Quality Assurance
Important surface properties of medical tubing, such as wettability, adhesion, antithrombogenicity, and biocompatibility depend on the chemical composition and structure of the uppermost 2-3 nanometers of the material. This region that corresponds to only a few molecular layers. Control of the properties and consistency of this layer is a critical part of medical device manufacture. Surface chemical composition and structure is typically evaluated using surface sensitive analysis techniques such as attenuated total reflectance infrared spectroscopy (ATR-FTIR) and X-ray photoelectron spectroscopy (XPS). Evaluating biologic properties such as antithrombogenicity may require even more unwieldy tests such as uptake of radiolabeled reagents. While these tests can provide excellent and detailed information for process development and process trouble shooting, they are impractical to deploy as routine quality assurance techniques. Surface free energy is another material property that is very sensitive to subtle changes in surface composition and structure as well as properties. It is a potential quality assurance tool for medical device manufacture, but its use has been hampered by a lack of techniques suitable for rapid and convenient deployment in a manufacturing environment. This presentation discusses the rapid measurement of surface energy of small diameter medical tubing via ballistic deposition of sub-microliter drops of water. Contact angles determined using this method were correlated to surface chemical composition and thrombogenicity for treated and untreated surfaces, and represent a potentially fast and easily deployed quality assurance assay that is practical for medical device manufacture.
Extrudate Mass Flow Rate Analysis in Fused Filament Fabrication (FFF): A Cursory Investigation of the Effects of Printer Parameters
In the Fused Filament Fabrication (FFF) process, a nozzle deposits a polymer melt through an extrusion process to create the end-use part. Four significant parameters influence this process: the nozzle diameter, print speed, layer height and the nozzle temperature. The results suggest that these parameters must be all considered to ensure actual extrusion rates equal software specified values. As expected, the results indicated there is an ideal nozzle temperature range for each combination of the other three parameters. Surprisingly, this temperature window varies from as low as 180°C to over 250°C for the polylactic acid (PLA) resin that was tested. This suggests that the buildup of nozzle pressure varies widely due to the volumetric flow rate and nozzle temperature and must be accounted for if under extrusion is to be avoided both to improve quality and to remove this as a convoluting factor for other FFF research.
Analysis of Surface Properties of Polyethylene Caps and Closures with Erucamide
The surface concentration, distribution, and performance of erucamide on the surface of high-density polyethylene caps depend on integral properties of erucamide and the physicochemical interaction between erucamide and polyethylene. The migration of erucamide, its surface morphology, polyethylene properties and storage condition influence the surface characteristics. The high-density polyethylene caps loaded with erucamide were stored at 4 °C, 23 °C, 38 °C and 50 °C and the surface was analyzed at different times. Contact angle, IR-spectra of the carbonyl group of amide, surface concentrations, and torque of erucamide were examined to determine the change in surface property and performance induced by erucamide. The surface distribution of additive was also observed at different temperature and time under optical and atomic force microscope. The surface concentration and torque increased rapidly to an optimum level at 38 °C and 50 °C within 105 h of incubation while they remained unchanged for lower temperature. Erucamide formed flat plates like structure at similar time and temperature. These little flat plates can slide over each other and provide the slip required to decrease the torque. The increase in contact angle demonstrated that the hydrophobic C-chain was oriented towards the air interface. This study enables optimization of storage and confirmation of migration required for production-line.
Injection Molding with an Additive Manufacturing Tool
This study attempts to determine the viability of additively manufactured injection molding tools by assessing the quantity and quality of molded parts. Plastic tools were made by using PolyJet® and Fused Deposition Modeling® out of Digital ABS, FullCure 720, and Ultem 1010 materials. The test tools were then compared to the standard P20 metal tool by molding acetal, polycarbonate, and polypropylene in each tool type. The molded parts were analyzed for processing effects on part shrink, physical, and mechanical properties. Testing concluded that parts molded with additive manufacturing tools performed comparably to parts made on a P20 tool. The quantity of molded parts made from acetal and polycarbonate were consistent with the literature at 10-100 parts. Conversely, molding with polypropylene suggested that processing with additive manufactured tools could exceed 250 parts.
Surface Roughness and Energy on Slip of Polymer Melts
Effect of surface topology and energy on slip velocity of high-density polyethylenes (HDPEs) was studied using treated and non-treated smooth and patterned slit dies. In order to examine the effect of surface roughness, laser ablation method was utilized to micro/nano-pattern the surface of dies. Moreover, effect of surface energy on slip was investigated by applying fluoroalkyl silane-based coatings on smooth and patterned substrates. It was found that slip velocity is decreased for rough dies, due to high friction and penetration of polymer melt into the cavities of the substrates. In addition, silanization increases the slip velocity of polymers extruding from smooth die, but has negligible effect on patterned dies.
Effect of Nucleating Agent and Two-Stage Expansion on the Morphology and Mechanical Properties of Microcellular Injection Molded Thermoplastic Polyurethane
Improved rebound resilience while lowering bulk density is desirable in several sport-wear applications. While rebound resilience properties generally deteriorate with reduction of the bulk density of the foam, a method of increasing rebound resilience by improving the control on microstructure is explored in this study. Low density thermoplastic polyurethane (TPU)/clay nanocomposite foamed parts were prepared using twin-screw extrusion compounding followed by microcellular injection molding. Samples with two densities were created by microcellular injection molding and an optional cavity expansion at a preset time during cooling. Scanning electron microscopy, rheological analysis, uniaxial compression tests, and rebound resilience tests were conducted on both of the non-expanded and expanded samples. Presence of well dispersed nanoclay in the TPU matrix acting as a nucleating and melt strengthening agent, coupled with cell growth at lower temperature helped achieve better microstructures, especially at high density reductions. The expansion of TPU at lower temperatures with directional second-stage expansion also helped to increase the rebound resilience, while achieving softer foams and lower hysteresis loss ratios at lower densities.
Development of a Three-Stage Process to Achieve Customizable Densities, Microstructures, and Mechanical Properties in Thermoplastic Polyurethane Foams
A three-stage expansion process was developed to manufacture thermoplastic polyurethane (TPU) into foams of varying local density in the same microcellular injection molded part. Two stages of cavity expansion and a third expansion in a separate mold at elevated temperature were able to achieve this, with density varying from 0.25 g/cm3 to 0.42 g/cm3 and varying mechanical properties as well. Cyclic compressive strengths and hysteresis loss ratios together with the microstructure were characterized and reported.
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