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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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.
Mechanism of the Operating Conditions on Dispersive Mixing and Humidity of Polymer in a Twin Screw Extrusion Process
Effective operational methodology of extrusion could impact pharmaceutical properties of polymer ranging from fundamental studies of mechanical and chemical mechanisms. Applied shear stress can regulate the polymer mixing as well as properties such as percentage of relative humidity. Polymer behavior differs in different operating conditions such as screw speed of extruder, specific throughput and barrel temperature. Combinations of such process parameters could directly affect the degree of polymer reaction in terms of percentage of breakup and water degradation. Yet, it is very complicated to determine the effective methodology for polymer extrusion process because the viscous drag pressure depends on some other parameters such as maximum temperature, screw design and the fill ratio. Here we present a novel approach to include barrel temperature and number of revolutions of extruder to correlate the pharmaceutical properties with the degree of combined mechanical mechanism. Design of Experiment (DOE) was being modified to determine property responses based on statistical significance. A 3-D Central Composite Design (CCD) grid was formulated to predict operational equation for percentage breakup and percentage of relative humidity.
Ultrasonic Joining of Through-the-Thickness Reinforced Ti-4Al-6V and Polyetherimide Hybrid Joints
Ultrasonic joining is an alternative direct-assembly joining technology to produce through-the-thickness reinforced hybrid joints between surface-structured metals and unreinforced or fiber-reinforced thermoplastics. As a result, joint damage tolerance can be improved. This paper presents a preliminary evaluation on the influence of joining energy on the joint formation, microstructure and mechanical performance of Ti-6Al-4V-Polyetherimide hybrid joints. Process-related microstructural changes and mechanical performance of optimized were assessed. The ultimate lap shear force of hybrid joints was six times higher (1860 ± 260 N) than the non-reinforced reference joints (292 ± 7 N). A considerable increase of ten times in displacement at break for ultrasonic joints was also achieved in comparison to reference joints. This is an indication that joint damage tolerance was increased due to an efficient load transfer by pin interlocking between the metal and polymer parts. Initial joint failure was by bearing – a non-catastrophic failure type – while shearing of the metallic pins was responsible for the final parts’ separation during lap shear testing.
An Overview on the Materials and Mechanical Behavior Used in Fused Deposition Modeling
Additive manufacturing offers significant opportunities for the production of final parts and products. Fused deposition modeling is a polymer additive manufacturing process widely used to build unreinforced and fiber-reinforced thermoplastic parts using the principle of extrusion. This work aims to review the state-of- the-art of fused deposition modeling by discussing the main advantages and limitations of the process. The building and processing parameters and their influence on mechanical behavior are addressed. A lack of understanding of these relevant parameters was identified. This literature review has shown that a deeper understanding of processing and material properties is needed to enable fused deposition modeling to become a standard manufacturing process in core industries.
Multilayer Polyethylene Films Having Grease Resistant Properties
Inter-material substitution and disruptive innovation continue to change the packaging world. The development of multilayer coextrusion lines have facilitated the transition from rigid containers to flexible packaging. A new family of barrier high density polyethylenes was discovered to have grease resistant properties. Unfortunately, only a few elementary methods exist for determining a package’s resistance to grease permeation. In addition, most grease permeation methods only provide a qualitative measure of grease penetration. As interest grows for incorporating recyclable plastic film structures into packaging for high fat content products, a simple technique is required for determining a film’s grease barrier properties and for ranking of different flexible film structures. Hence, a semi-quantitative method to measure grease/oil permeation through multi-layer films has been developed, and the results of several multilayer film structures are presented to delineate the efficacy of different film resins in improving the grease barrier properties of polyethylene multilayer films. The present study shows that it is now possible to develop cost effective and recyclable polyethylene film packaging structures with good grease barrier performance by utilizing certain single site catalyzed PE resin architectures.
Anisotropic Thermo-Viscous-Elastic Residual Stress Model for Warp Simulation of Injection Molded Parts
The residual stresses in injection molding process are developed due to the restriction of thermal contraction during the cooling, coupled with the frozen layer growth with the varying pressure history. The stress relaxation behavior of plastic materials also complicates the stress field. A thermo-viscoelastic model is a natural choice for predicting the residual stress in the injection molding process, but it is computationally very expensive and requires materials’ relaxation spectrum data which are not readily available in most of material databases. This study used a simplified anisotropic thermo-viscous-elastic model to calculate the residual stress development in three-dimensional simulation of injection molding process. The validation cases showed that the proposed model is able to predict the final shrinkage, warpage and molded-in residual stresses reasonably well.
Modification of LLDPE by UV-Irradiation
Linear low density polyethylene (LLDPE) is used widely in applications like lamination and agricultural films, as well as a modifier for low density polyethylene (LDPE) and high density polyethylene (HDPE). The melt strength of LLDPE is modified in this study by introducing long chain branching (LCB) and/or crosslinking to its backbone through UV initiated radical reactions. Benzophenone (BP) is added as a photo-initiator to form free radicals and a UV lamp is used to irradiate solid sheets of the molded LLDPE resin, at different time intervals and intensity, according to a design of experiments (DOE). This paper aims to study the effect of photo-initiation on material properties, using linear-viscoelastic (LVE) rheological measurements, and differential scanning calorimetry (DSC).
Elucidating the Cause of Surface Roughness in Melt Compounded PVC Plasticized by High-Solvators
High-solvating plasticizers, like dibenzoates, have shown marked success in their ability to plasticize PVC. This unique interaction has proven beneficial for formulators as dibenzoates are fast-fusing at lower temperatures, decreasing time and energy costs during processing. However, when plasticizers are used in processing conditions involving high shear, a characteristic surface roughness or, “nerviness” can be observed on a two roll mill . Using FTIR, gelation studies, tensile data and gloss measurements, this investigation aims to determine the cause of this morphology. The results indicate that secondary crystallite formation is likely the cause of the nerviness observed in flexible PVC. As well, nerviness was manifested formulations plasticized with DINP, and 1,2-cyclohexanedicarboxylic acid diisononylphthalate (DIDC), suggesting nerviness is an inherent phenomenon with PVC fusion that shifts to lower processing temperatures with high-solvating plasticizers.
Microencapsulation of Pamitic Acid with Polylactic Acid Shell for Thermal Energy Storage
Microencapsulation of vegetable-derived palmitic acid (PA) in bio-based polymer shell of polylactic acid (PLA) by solvent evaporation and oil-in-water emulsification was investigated. This study deals with the preparation and characterization of PLA-PA microcapsules. Chemical structures, morphology of microcapsules, and thermal properties were determined by Fourier transform inferred spectroscopy, scanning electron microscopy, and differential scanning calorimetry, respectively. In short, this work has demonstrated the possibility to fabricate 100% bio-based phase change material microcapsules for thermal energy storage applications.
Micro Components with Locally Different Properties Realized by Segmented Tempered Injection Molding
Influencing mold temperature during injection molding via dynamic tempering affects the melt’s cooling conditions and, therefore, can lead to a change in component properties. The current research presents an innovative dynamically tempered mold technology with different temperature zones within the cavity, which enables the production of micro components with locally different component properties. Results with iPP show that due to influencing internal component properties such as morphology and degree of crystallization, significant differences in mechanical component properties can be achieved.
Effect of Flow Lines on the Metallization of Laser-Structured Polymer Parts
Molded interconnect devices (MID) offer great potential for circuit board applications, especially regarding three-dimensional shaping and functional integration. Applying circuits to polymer substrates can be performed by means of laser patterning methods. In these, the matrix polymer is filled with a special metal additive, enabling laser activation and subsequent metallization. Important effects emerge during processing of the matrix polymer. In this work, the influence of the gate geometry and the resulting flow behavior during injection molding on the quality of the metallization is investigated.
Online Melt Viscosity Measurement during Injection Molding for New Control Strategies
Part quality and its reproducibility are crucial factors for the productivity of injection molding processes. While machine parameters can be reproduced with a high accuracy, disturbing influences may cause different processes regarding the melt state in the cavity and consequently production rejects. Fluctuations in the melt viscosity influence the pressure distribution within the cavity and have a strong impact on part quality. Therefore, viscosity fluctuations can cause differences in warpage or even under- or overpacked cavities. Fluctuations can occur due to differences in the residual moisture of the plastics material, the use of regrind material, batch variations or interruptions in the production process. To compensate the effects of different raw material viscosities onto the process, a determination of the current viscosity is required. Within this paper different concepts of viscosity measurement for polymer melts are reviewed with regards to applicability in an online control system for injection molding. The concepts range from machine based parameters to concepts using in-mold sensors. A new mold concept using pressure sensors within the hot runner manifold is presented. The feasibility is analyzed in numerical injection molding simulations. Finally, the simulation results are validated using practical injection molding trials.
Novel Interface-Modified Bionanocomposites with Improved Processability and Electricity
Novel interface-modified bionanocomposites with improved processability and AC conductivity was developed and examined in the experiments. The results indicated that the interface-modified bionanocomposites exhibited an approximately 2-fold decrease in complex viscosity and mechanically reinforced properties as compared to neat polylactic acid (PLA) and those without interfacial compatiblizer. Interface improvement from maleated PLA was observed on the fractured surface and also confirmed through the increased Young’s modulus and the improved thermal and electrical properties. The micromechanical models were applied to predict the mechanical properties of the bionanocomposites in the matrix. At 5~7 wt% GNPs loadings the electrical conduction path was achieved inside the PLA matrix through the formation of the effective three-dimensional conductive networks in these bionanocomposites. It was interestingly noted that above the percolation threshold the increasing graphene loadings resulted in lower but higher AC conductivity. The mechanisms in unusual decrease in AC conductivity above percolation threshold were discussed and elucidated.
Durability Evaluation to Residual Chlorine on Plastic Pipes
Recently, the polymer electrolyte fuel cells (PEFC) cogeneration systems with plastic pipes for hot water supply has been commercialized in Japan. The pipes for hot water supply are installed with bending from the polymer electrolyte fuel cell to inside a house without using fittings. However, it is expensive and hard to replace these plastic pipes. These pipes which installed with bending were not evaluated in the residual chlorine solutions for long term. Accordingly, it is important to evaluate the durability and to predict the lifetime of these bent pipes. This study intended to evaluate the bent pipes in the residual chlorine solutions early. The residual chlorine solution immersion test for the bent polybutylene (PB) pipes and the bent double-layer crosslinked polyethylene pipes (PEX2) was conducted at 80°C, 90°C and 98°C. In the residual chlorine solution immersion test, the concentration of the residual choline solution is 5 ppm and 10 ppm for 80°C, 5 ppm for 90°C and 5 ppm for 98°C. As a result, it took much time to get the results back from this immersion test beyond expectation. It was found that the bent polybutylene (PB) pipes had the cracks over for 36,000 hours at 5 ppm in 90°C, over for 40,000 hours at 10 ppm in 80°C and over for 44,000 hours at 5 ppm in 80°C. On the other hand, the bent double-layer crosslinked polyethylene pipes (PEX2) in the residual chlorine solution immersion test did not have the crack at all over for 47,000 hours.
Heat Sealing in Semicrystalline Polymer Films
This work investigates the non-standard microstructural aspects that might play a critical role in the heat sealing process of semi-crystalline polymer films. Two different ethylene-propylene copolymers having widely different Seal Initiation Temperatures (?SIT=18°C) but similar melting points (?Tm=2°C) were chosen for this study. The contribution of both the amorphous phase and the crystalline phase to heat sealing was investigated utilizing Dynamic Mechanical Analysis and Thermal Fractionation DSC respectively. Initial results indicate that the melting distribution of the thermally fractionated material plays a critical role in determining SIT. Other potentially contributing factors like isothermal crystallization kinetics, the kinetics of entanglement in the melt state are currently being investigated.
Preparation and Characterization of Thermoplastic Polyurethane (TPU) Foams with a Large Variety of Cell Sizes
In this study, thermoplastic polyurethane (TPU) foams were fabricated by batch foaming using supercritical carbon dioxide (ScCO2) at different foaming temperatures and saturation pressures. Experimental results revealed that lower saturation pressures would increase the sensitivity of cell sizes to varying foaming temperatures due to the different crystallization behaviours of TPU at different saturation pressures. As a result, lower saturation pressure seemed to provide more flexibility for researchers to develop multifunctional TPU composite foams by taking advantage of foaming-assisted alignment of fillers along their cell walls.
Thermally Insulated Bimodal Polystyrene/Multi-Walled Carbon Nanotube Nanocomposite Foams
We developed a bimodal polystyrene (PS)/multi-walled carbon nanotube (MWCNT) nanocomposite foam with a thermal conductivity of 30 mW/m-K without using any insulation gas. The MWCNTs were critical to the heat transfer because they decreased radiation significantly through the foams. A theoretical model has been proposed to analyze the thermal conductivity in nanocomposite foams. The proposed model verified the superior heat-blocking characteristics of the bimodal cellular morphology and the MWCNTs as follows: (1) The primary large cells acted to decrease the solid conduction; (2) The secondary small cells induced the Knudsen effect on gas conduction; and (3) The MWCNTs intensively blocked the IR transmission.
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