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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Fractographic Examination of Failures in Polycarbonate and Polyacetal due to Impact, Tensile, Fatigue, and Creep Mechanisms
Fractography is a powerful tool in the failure analyst’s arsenal, allowing unknown conditions that led to a failure to be revealed by examination of a fracture surface. In this study, fractures generated by different failure mechanisms were examined by scanning electron microscopy (SEM) to discern key characteristics and distinguishing features. Amorphous polycarbonate (PC) and semicrystalline acetal homopolymer were fractured by impact, tensile overload, cyclic fatigue, and creep. SEM images are provided and discussed.
Impact Modification of PLA Using Biobased, Biodegradable Mirel PHB Copolymers
This work will focus on an approach to improve the impact toughness of poly (lactic acid) or PLA without compromising the biobased carbon content and compostability of PLA. Specifically, low-crystallinity and amorphous PHB copolymers were demonstrated to be very effective in improving the toughness of PLA at modest loading levels of 10-20 weight percent. This presentation will also compare the above approach with urethane, butadiene and acrylic impact modifiers along with the impact modification provided by other compostable polymers such as PBS and PBAT. Of particular significance is the extent of impact modification provided by an amorphous PHB copolymer (M4300 @ 10-20% loading) wherein the blend demonstrates a combination of mechanical properties that rival those of some engineering thermoplastics. Morphological considerations for the observed improvement in impact performance will also be highlighted.
The World's Highest Heat Melt-Processable Amorphous Thermoplastic
A new class of high performance amorphous thermoplastic polyimide (TPI) resin has been designed with a glass transition temperature exceeding 300°C while still being 100% melt-processable. Further, this novel material has been bestowed with the highest UL (Underwriter’s laboratory) RTI rating in the world for an unfilled thermoplastic. The polymeric material offers outstanding high temperature strength and dimensional stability which makes it attractive to be positioned in applications with an emerging need of such materials that are truly melt-processable while giving as-molded properties for end use.
Complex Fiber Orientation Distributions within Injection Molded End-Gated Plaques
The Method of Ellipses has been applied to short and long fiber polymer composites in order to quantify the fiber orientation distribution within the end-gated plaque. Short and long glass fibers with post- processing average fiber lengths of 0.364 and 3.90 mm, respectively, have been studied at multiple percentages of mold flow, including at the gate and entry region and near the advancing front. Additionally, orientation data has been acquired for short glass fibers at multiple locations of plaque width including near the side mold wall. Preliminary data suggests that the orientation of short and long glass fibers is similar along the centerline of the plaque, with both fiber lengths developing the predicted core-shell structure at moderate to high percentages of mold fill. However, short glass fibers exhibit a broad and relatively uniform orientation distribution in the regions of complex flow at high percentages of plaque width, with a substantial increase in flow-aligned fibers. Work is ongoing to complete analysis of long glass fibers in regions of complex flow near the side walls of the mold.
Material Optimization and Performance Evaluation of PolyVinyl Alcohol (PVOH) Films in Fresh and Salt Water for Decelerator Applications
Material optimization of biodegradable and water soluble polymers along with the influence of fresh and salt water conditions on the performance of polyvinyl alcohol-based films was examined for a U.S. Naval sonobuoy decelerator application. PVOH films of various thicknesses were produced on a manufacturing-scale lamination line using a solvent-based adhesive. Salt water and its temperature significantly influenced dissolution properties of the films. Mechanical properties of the as-received and laminated films were also examined and reported.
Effects of Biodiesel on Plastics
Many chemicals have the ability to attack on plastics as solvents and can lead to failure. In some cases, the source of the solvent is not well defined. In this study, the effect of biodiesel, a fatty acid methyl ester, on various plastics, namely polyamide 6 (PA 6), polycarbonate (PC), acrylonitrile-butadiene- styrene (ABS) and ABS/PC plastic blends was studied. Various feedstocks of biodiesel were also studied, including, soy bean oil (new and used), animal fat (tallow), corn oil as well as choice white grease. The plastics samples were tested under ASTM standard where a predefined strain is applied to the samples prior to exposure to the solvent (biodiesel). It was found that under the majority of combinations, other than PA 6, cracking was seen within 12 hours, and with ABS/PC and PC cracking was seen in minutes. Thus, it has been shown that biodiesel can be a degrading solvent for engineering plastics, such as PC, ABS and ABS/PC blends.
The Effect of Processing Flows on Polystyrene/Nanotube Nanocomposite Conductivity and Structure: 3D Visualization of Cluster Distributions
The electrical conductivity of polymer nanotube composites can be dramatically modified during processing steps. We examine the interplay between processing, the multi wall carbon nanotube (MWCNT) network structure and the resulting conductivity through 3D measurements of cluster size distributions and orientation. We discover that the nanotubes assemble into clusters whose mass distribution follows a classic power law with a slope of approximately -1. This mass distribution is relatively insensitive to the imposed flows over our accessible shear range, even though the conductivity changes by orders of magnitude. The orientation distribution of the MWCNTs within the clusters is strongly dependent on the flow type and its magnitude, but does not correlate with conductivity. These results point to the dominant role played by the nanotube –nanotube contact resistance as a determinate of composite conductivity.
Investigation of Cold-Runner Injection Molding Processing Parameters and Their Effects on Product Optical Properties
This paper describes current efforts to investigate and expand melt modulation capabilities to control the packing parameters of cold-runner based injection molding processes. Packing parameters, including packing pressure and packing time, have significant impact on the internal molecular orientations, mechanical properties and optical performance of injection molded polymeric products. The investigation focuses on manipulating and controlling packing parameters in order to produce molded parts with different optical properties in each injection molding cycle. Numerical simulations of common thermoplastic optical polymers, such as PMMA, PC, and PS and some experimental results are also presented.
Investigation of Fracture in Polymers Using a Cohesive Zone Model
Polymers are increasingly being used for engineering structures and medical devices because of their excellent corrosion resistance and low cost compared with metals. However, the lifetime of plastics used in severe environments is significantly reduced due to environmental stress cracking (ESC). Current understanding of ESC in polymers is mostly empirical. In this paper, a methodology for investigating ESC in polymers is presented. The proposed approach, based on the cohesive zone model (CZM), is capable to characterize the degradation in the fracture zone explicitly, independent from the bulk material. In our preliminary investigation, the fracture on an elastic-plastic material was simulated, and the results were compared to a published paper. The simulation outcome indicates that the CZM is an effective tool to study fracture propagation in polymers under ESC.
Effect of Ladder-like Polysilsesquioxane on the Surface and Thermomechanical Properties of Polyimide Based Block Copolymers
A novel type of polyimide (PI)-polyurea (PU) block copolymers containing polysilsesquioxane was successfully prepared by reacting ladder-like polysilsesquioxane (LPS) with poly(amide acid)-b-polyurea, followed solution film casting and thermal imdization. The LPS composed of mercapto and fluoride side groups was synthesized by using the sol –gel and monomer self-assembly methods. The resulting hybrid films have outstanding surface and thermomechanical properties. The dynamic contact angles (DCA) and dynamic mechanical thermal analysis (DMA) were used to study the surface energy and mechanical properties of the hybrid films. The presence of LPS containing fluoride and mercapto side groups dramatically increased in the degree of imidization by low temperature curing (150°C).
Specific Mold Filling Characteristics of Highly Filled Phenolic Injection Molding Compounds
The objective of the study is to analyze the influence of the mold filling behavior during injection molding of phenolic compounds on mechanical properties. Injection molding filling studies, mechanical testing and optical microscopy were done while varying mold geometry (injection gate and cavity height), mold temperature and injection rate during injection molding a highly filled phenolic compound. It was found that the mold filling behavior varies with changing the injection molding parameters as well as the mold geometry. In consequence of this the mechanical properties change according to the resulting reinforcement orientation.
Ultrasonic devulcanization of tire rubber of different particle sizes in twin-screw extruder
The present study is devoted to ultrasonic devulcanization of tire rubber particles of 10 and 30 meshes by means of a new ultrasonic twin-screw extruder. Ultrasonic amplitude and devulcanization temperature were varied at a fixed frequency of 40 kHz. The die pressure and ultrasonic power consumption during devulcanization were recorded. Degree of devulcanization was investigated by measuring the crosslink density, gel fraction and revulcanization behavior. Rubber of 30 mesh exhibited a lower die pressure and higher degree of devulcanization than those of rubber of 10 mesh. Due to the higher level of devulcanization and lower viscosity of devulcanized rubbers at higher amplitudes, the temperature of devulcanized rubbers at the die was reduced with an increase of the ultrasonic amplitude. Cole-Cole plots, crosslink density and gel fraction of devulcanized and revulcanized rubbers, revulcanization behavior, and modulus of revulcanizates separated in two distinct groups based on the level of devulcanization and effect on molecular structure of devulcanized rubber. Revulcanizates with a greater degree of devulcanization exhibited higher elongation at break, while those with a lower degree of devulcanization exhibited higher strength and modulus. Revulcanizates of rubber of 30 mesh exhibited a consistently higher elongation at break. The normalized gel fraction versus normalized crosslink density was described by a unique function independent of the processing conditions and rubber particle size.
Sustainable Materials for Horticultural Application
Bioplastic materials were compounded utilizing soy, poly-lactic acid (PLA) and poly-hydroxyalkanoate (PHA) biopolymers along with ethanol industry co-products and biomass additives to manufacture horticultural plant containers. Various formulations and processing conditions were studied to improve mechanical properties of the plastics. These materials were developed and compounded at Iowa State University and subsequently injection molded into 4.5 inch greenhouse pots at R&D/Leverage, Lee's Summit, Missouri. The bioplastic pots were evaluated for their performance by studying plant growth of vegetable and ornament crops grown in them under greenhouse and field conditions. The pots were also characterized for degradation and water retention. Commercial polypropylene pots, 4.5” green color, were used as the control treatment for the study. Comprehensive growth studies along with degradation results identified numerous bioplastic types that performed as well as or better than commercial polypropylene plant containers. Among the different material types, SPA-PLA, a blend of soy and PLA resins, was observed to produce the best results in terms of plant growth compared to polypropylene plastic pots during plant production. This is attributed to the slow release of fertilizing compounds during the degradation of soy protein. Certain bioplastic pot types were observed to retain soil moisture content over a longer time period than pots made from other environmentally friendly materials, such as paper or peat moss. Such properties are considered beneficial during the plant production cycle when using horticultural pots because they require less watering.
Film Casting of LLDPE/Clay Nanocomposites Without and With Compatibilizer with the Aid of Ultrasonic Treatment
One step process for ultrasonic compounding and film casting consisting of an ultrasonic extruder followed by a cast film machine was used to prepare cast films of linear low density polyethylene (LLDPE) and LLDPE/Clay 20A nanocomposites. Cast films of LLDPE, 90/10 LLDPE/compatibilizer, 95/5 LLDPE/Clay and 85/5/10 LLDPE/Clay/compatibilizer were prepared at take up speed of 1.524 cm/s (3 ft/min) and different ultrasonic amplitudes. The die pressure and ultrasonic power consumption were measured. X-ray patterns, NMR, FT-IR, thermal, and gas permeability properties of cast films were studied. The mechanical properties of the prepared films in the machine and transverse directions were measured. Cast films of LLDPE and 95/5 LLDPE/Clay nanocomposites were transparent, while cast films lost their transparency with addition of compatibilizers. The compatibilizer with higher maleic anhydride grafting showed better properties. The strength and oxygen permeability results improved significantly due to the addition of compatibilizer and ultrasonic treatments.
Mold Maintenance: A Strategy for Optimizing Mold Performance
All mold builders perform mold repair, usually on molds they built. But few strategize to also offer ongoing mold maintenance services. A system has been developed for training and certifying mold builders and to put in place a documentation software system that enables them to serve as an extension of molders' toolrooms, thus freeing up a molder's employees for only the most specialized on- site emergency mold repair work. This system, dubbed 'Certified Maintenance Provider', consists of training, software installation, and subsequent auditing, in order to position a mold builder to become a source for maintenance within the immediate region.
Approach to Fabricating Thermoplastic Polyurethane Blends and Foams with Tunable Properties
Thermoplastic polyurethane (TPU) has been widely used in many applications because of its broad property range. In this paper, twin screw extrusion was used to produce TPU blends with tunable properties; the foamed samples were produced by microcellular injection molding (a.k.a. MuCell). Multiple tests were performed to confirm the miscibility and tunability of the blends. Fourier transform infrared spectroscopy (FTIR) was used to verify the presence of soft and hard segments in the three blends. Differential scanning calorimetry (DSC) and dynamic mechanical analysis (DMA), combined with scanning electron microscopy (SEM), confirmed that soft and hard TPU were miscible at ratios of 2:1 and 1:2, but immiscible at a ratio of 1:1. Rigidity increased while the shape recovery rate decreased with increasing hard TPU content. The blend ratio influenced the foaming morphology as well as other mechanical properties of the foamed samples. Decomposition, as investigated by thermogravimetric analysis (TGA), and degradation, as measured in a phosphate buffered saline (PBS) solution, were also studied. It was found that TPU or blends with more hard segments decomposed and degraded faster.
Mold Alignment: Testing Engineered Options
Molds are exposed to harsh conditions, as molding presses typically have platen sag which causes mold misalignment. For decades, this misalignment has been countered by leader pins and bushings used to bring the mold halves “close” and interlocks mounted on the mold parting line to bring alignment “home”. With the amount of weight hitting at each mold cycle, often for millions of cycles, interlocks have been prone to wear, galling, and eventual failure. This paper will disclose the engineering route and analytical method, versus an anecdotal approach, used to develop an interlock that has exponentially surpassed performance of other configurations.
Manufacturing of Polypropylene/Ground Tire Rubber Thermoplastic Elastomers by Ultrasonically Aided Extrusion
Compounding ground tire rubber (GTR) with thermoplastic polyolefins, such as polypropylene (PP), is a possible way to manufacture thermoplastic elastomers and also to recycle waste tires, thus solving a major environmental problem. The effect of ultrasonic treatment on the mechanical, rheological and morphological properties of PP and PP/GTR (ground tire rubber) blends in an ultrasonic single screw extruder (SSE) and an ultrasonic twin screw extruder (TSE) were investigated. PP and GTR was fixed at a ratio of 50:50. The treatment was carried out under amplitude of 5, 7.5 and 10 ?m, and at a flow rate of 2 lbs/hr. Pressure and ultrasonic power consumption were measured. Mechanical and rheological properties of untreated and ultrasonically treated PP indicated that TSE provided more degradation than in SSE. For 40 mesh blends from SSE, the mechanical properties improved with increasing ultrasonic amplitude. The viscosity indicated very little dependence on ultrasonic amplitude, which is evidence a formation of covalent bonds between PP and GTR. Viscosity of 140 mesh blends was lower than that of 40 mesh blends from both SSE and TSE, indicating a larger degree of degradation of blends with smaller rubber particle size. In addition, with smaller rubber particle size, much better elongation at break is obtained which indicates better adhesion between PP and GTR.
Validation of an Analytical Method to Estimate the Bulk Melt Temperature from In-Mold Temperature Data
An analytical method for estimating the bulk melt temperature in the injection molding process by means of in-mold temperature sensors data has been validated. The method was evaluated for experimental data and data acquired with a computer simulation of the process. The simulation considered the heat flux and heat accumulation throughout the cycle in the mold. For the simulation, a full 3D model of the mold geometry was developed. Most trends correlated for both simulated and experimental data; however, the magnitude of the predictions varied due to the sensitivity of the analysis to the parameters.
Dynamic Uni-Layer Melting Model
Traditional screw design theory is based on formation of a solid-bed of resin between the screw flights. Melting the solid bed is primarily accomplished by shear heating in the screw compression zone. However, there are several problems related to controlling this melting method. The research here will show how removing the screw compression zone and preventing solid bed formation allows for; 1) eliminating melt over-heating from shear heating, 2) improves melting efficiency, 3) increases melt stability, and 4) reduces material residence time. This melting model has been applied to a wide range of plastic materials and has been implemented in both injection molding and extrusion.
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