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.
In this study, we introduce the concept of in-situ nanofibrillation as an efficient, low-cost, and environmentally friendly tailored technique for the enhancement of polycarbonate (PC) properties. PC/ Ethylene Propylene Diene Monomer Rubber (EPDM)-fibril composites are prepared by a twin-screw extruder. Taking advantage of the crosslinked rubber phase as well as nanofibrillation processing play the main role in properties improvement. Modifications of the mechanical and rheological properties of PC via fiber-spinning of PC/EPDM are distinguished by elongation and crosslinked network of the second phase (EPDM) properly in the main matrix (PC). Morphological observations showed the well-dispersed fibrillar phase of EPDM with a high aspect ratio in the PC matrix. PC with nanofibrillated EPDM also improved the mechanical properties, especially the ductility and the toughness, while increasing the stiffness, in comparison with neat PC. The change in the tensile, Izod Impact and flexural properties was governed by the draw ratio. Hence, having stretched fibrils is an effective way to enhance the mechanical and rheological properties. Rheological investigations proved that PC with nanofibrillated EPDM has dramatically improved melt elasticity compared with neat PC. Linear viscoelastic behavior of small amplitude oscillatory shear measurements showed a strain-hardening, solid-like, behavior in the fiber-spun PC/EPDM, which was not observed in the neat PC or the melt-blended PC/EPDM.
Natural and synthetic polymeric foams display a variety of open and closed pores with diverse shapes, sizes, and degrees of anisotropy. In state-of-the-art foaming processes, microcellular anisotropy is generated by releasing confinement in one or more directions during the expansion of an initially isotropic melt or resin. As a result, the entire monolith foamed in this way exhibits cells aligned in the direction dictated by the confinement. This, in turn, results in a uniform deformational response that is dictated by the loading condition relative to the microcellular orientation. In this work, investigation was performed into generating a foamed morphology within an anisotropic medium (e.g. film or fiber) to understand how molecular orientation affects the resulting anisotropy in the microcellular structure. Additionally further investigation into the use of this strategy to generate complex microcellular hierarchical constructs was performed by using fibers and or films as templates to understand their effect on the corresponding deformation. Herein, results are presented to show how assemblies of fibers are woven or twisted with a bias or helical structure and then foamed using superheated water (shH2O) and/or supercritical carbon dioxide (scCO2) to manufacture complex microcellular structures. In addition, results from mechanical tests also show how the imposed bias in the foams result in complex deformation imposed by the bias. That is, foams generated to create a helical bias are shown to undergo torsional deformation commensurate wit h uniaxial deformation when compressed uniaxially. These concepts propose a technology to manufacture “smart foams” by assembling templates (films and/or fibers) that have locally different molecular orientations that ultimately create locally changing anisotropic microcellular patterns that govern complex deformational behavior under applied loads.
In the frame of polar, deep water, and exoplanet exploration, lightweight multifunctional materials with durability targeting extreme environments are highly sought. Specifically, mechanical strength and a high degree of thermal insulation are among the most critical properties of structural materials in these applications. Mechanical strength imparts the structural integrity needed to minimize damage to sensitive electronic components, while thermal insulation is needed to protect equipment in extreme temperature conditions. Herein, this work uses micro/nano-layered technology to fabricate film/foam alternating structures for an advanced structural architecture that combines the mechanical performance of multilayered materials with the thermal insulation properties characteristic of polymer foams. We used PC as the film layer, PMMA as the foam layer, and CO2 as the foaming agent. With respect to foam structure, our work demonstrates that due to the confinement effect of the film layers, samples expand only in the thickness direction with no noticeable expansion along the in-plane direction. The apparent expansion ratio in the thickness direction increases with increasing layer numbers (up to 513 layers), ranging from 2.3 to 11 times expansion. With respect to cell morphology, there is a clear decrease in cell size with increasing layer numbers, with a concomitant increase in cell density. Specifically, we obtain the highest cell nucleation density and smallest cell size, around 1.1×1013 cells/cm3 and 400 nm, respectively, from the 513-layer sample foam, when treated at 70 C and 20 MPa. This micro/nano-layered film/foam alternating system offers an outstanding combination of tensile strength (~33 MPa) and low thermal conductivity (~0.0297 W/m·K), in comparison to foams or aerogels with similar thermal conductivity and tensile strength of less than 1 MPa. The balanced tensile performance and insulation properties offered by this multi-tiered structure open the door for use in applications including the exterior layer of vehicles operating in extreme conditions.
Thermoplastic vulcanizates (TPVs) are highperformance polymeric materials classified as thermoplastic elastomers, and contain a continuous thermoplastic matrix with crosslinked elastomers as a dispersed phase. TPVs combine the high elasticity of crosslinked elastomers and the easy processability and recyclability of thermoplastics. The most widely produced TPV type is polypropylene (PP)/ethylene propylene diene monomer (EPDM), which is the focus of this study. In this study, polyhedral oligomeric silsesquioxane nanoparticles containing reactive side groups were used as coagents for PP/EPDM TPV system for the first time in the literature. The peroxide crosslinked PP/EPDM/POSS system was dynamically vulcanized in a lab-scale micro-compounder. The mechanical properties of samples were determined by tensile, hardness, and compression set analyses. Scanning electron microscope (SEM) and atomic force microscope (AFM) were used to evaluate the phase morphology. The results showed that nano-reinforced network structure improved the performance of the TPV materials.
High-density polyethylene (HDPE) exhibits poor melt strength which limits its widespread application especially where it is exposed to an elongational deformation flow in processes such as film blowing, melt spinning, and foaming. In this study, by taking advantage of in-situ nanofibrillation of thermoplastic polyester ether elastomer (TPEE) in HDPE matrix, we improved the rheological properties as well as the foamability of HDPE. TPEE consists of a hard crystalline segment of polybutylene terephthalate (PBT) and a soft amorphous segment of polyether. The polarity of these two groups causes TPEE to be thermodynamically incompatible with non-polar HDPE. Therefore, styrene/ethylene-butylene/styrene copolymer grafted maleic anhydride (SEBS-g-MA) as a compatibilizer was used for reducing the interfacial tension between two blend components. In the first step, a 10% masterbatch of HDPE/TPEE with and without compatibilizer was prepared employing a twin screw extruder. Next, to fabricate fiber-in-fiber composites, the 10% masterbatch was diluted and processed by spunbonding. Scanning electron microscopy (SEM) revealed that not only the spherical size of HDPE/TPEE decreased significantly after SEBS-g-Ma inclusion, but also a much smaller TPEE nanofiber size (60-70nm for 5%TPEE) was achieved. Moreover, the extensional rheological results showed strain-hardening behavior for both compatibilized and non-compatibilized stretched samples at earlier times, at a given extensional rate, compared to the unstretched counterparts. It is worth mentioning that the improvement of extensional rheological properties was more pronounced for compatibilized samples compared to the non-compatibilized ones. This can be attributed to smaller nanofiber size and consequently higher aspect ratio as well as a more robust 3D fibrillated network. Finally, batch foaming was conducted to investigate the foamability of fibrillated nanocomposites.
High density polyethylene (HDPE) is one of the most widely used materials in the pipe industry because of its several advantages such as low price, excellent productivity, light weight and high resistance to chemical degradation. For potable water pipes, their lifespans are supposed to be over 50 years, so it is essential to check their long-term performance in certain service conditions. The point is that potable water contains disinfectants including chlorine or chlorine dioxide which shortens the service time of water pipes. In addition to disinfectant, environmental conditions like internal pressure and temperature of media inside also cause deterioration of properties of plastic pipes. To understand the degradation mechanism by potable water, we focused on two parameters, the concentration of disinfectant and the temperature of the solution. In this study, specimens obtained from HDPE pipes were artificially degraded in 5 different kinds of chlorine dioxide solutions with various concentrations and temperatures. Micro-tensile tests were conducted to study the variation of mechanical properties of HDPE specimens. The Fourier transform infrared (FTIR) spectrometry and the gel permeation chromatography (GPC) analysis were also conducted to study the variation of chemical properties of HDPE according to exposure time to chlorine dioxide solutions.
Advances in nanotechnology and surface sciences have necessitated superior polymeric coatings with novel applications. Urethane-acrylate-based interpenetrating polymer networks are one such class of ultra-tough polymers being researched actively for their wide-ranging applications from bullet-proof vests to binders for super dewetting coatings. Urethane-based systems are well-known for undergoing side reactions which could result in instability of colloidal suspensions engendering gelation resulting in significantly reduced shelf life of synthesized formulations and coating inconsistencies over time. Consequently, it becomes crucial to examine and control the factors inducing gelation. In this study, we investigate two approaches to prevent the gelation of colloidal urethane-based suspensions. In the first approach, we tune the NCO:OH ratio, and in the second approach, urea groups were formed in the presence of water. It was observed that both approaches resulted in storage stable colloidal suspensions with more than six months of shelf life. Durability assessment of coatings however indicated that urea-containing formulation resulted in notably robust coatings as compared to NCO:OH tuned coatings which can be attributed to the presence of strong hydrogen bonding arising from bifurcated hydrogens of urea.
Nanocellular foam has attracted significant attention because of its superior physical and mechanical properties than microcellular foams. In this study, nanocellular foams were produced using the hot-bath and hot-press foaming methods. By lowering the saturation temperature (Tsat) to -30 ºC, the CO2 solubility was increased to 45.6%, and the cell size was reduced to less than 40 nm. Samples prepared by hot-bath exhibited smaller cell size, thinner solid skin, and transitional layer.
In the effort to alleviate climate change and energy consumption issues, thermally insulating polymeric foams can improve energy-management efficiency. we report a superior thermal insulation (~28.5 mW⋅m-1K-1) microcellular foam from ethylene-norbornene (NB) based cyclic olefin copolymers (COCs). Unlike the traditional carbon-filled approach, the incorporation of more NB segments (content from 33, 36, 51 and 58 mol %) in the COC structure greatly improved its ability to block thermal radiation without increasing its solid thermal conductivity. Using the supercritical CO2 and n-butane as physical blowing agents, we fabricated COC foams with tunable morphology. The void fraction of the foams ranged from 50 to 92%, and they demonstrated a high degree of closed cell content (>98%). In COC foams with given cellular structures (e.g. void fraction of 90%, cell size of 100–200 μm and cell density of ~107 cells/cc), their total thermal conductivity decreases from 49.6 to 37.9 mW⋅m-1K-1 with increasing NB content from 33 to 58%, which is attributed to high- NB COC’s strong ability to attenuate thermal radiation.
We report systematic studies on the foamability of our novel high-melt-strength long-chain branched polypropylene under supercritical CO2. Continuous foaming experiments were conducted using a tandem extrusion system and a set of filamentary dies with similar pressure drops but different pressure drop rates. The foam expansion was controlled by varying the temperature at the die exit. Under identical CO2 loadings, the expansion ratio plotted as a function of die temperature exhibited similar shapes across multiple pressure drop rates. However, the shape of the curve varied across different amounts of CO2, under which the highest achievable expansion ratio occurred at a lower die temperature with increasing CO2 content. The cell density displayed strong dependence on both the pressure drop rate and the amount of dissolved CO2. The effect of the latter became more apparent at lower pressure drop rates. The average cell size decreased with increasing CO2 loading but generally showed weak dependence on pressure drop rate except at the highest value.
Insoluble, high performance starch foams with high resistance to moisture were prepared by ZSK-30 twin screw extruder using additives such as chitosan, polyvinyl butyral (PVB) and sodium trimetaphosphate (STMP). Under the optimized extrusion conditions, water acted as a plasticizer and a blowing agent breaking up the hydrogen bonds within the starch granules and releasing the starch polymer chains without significantly reducing their molecular weight. The pressure drop at the die led to expansion and formation of closed cell foams. A screw configuration made up of 3 kneading sections was found to be the most effective for better mixing and foaming. The use of PVB was extremely effective in minimizing moisture sensitivity and made the foams hydrophobic and insoluble in water. Crosslinking of starch with STMP gave anionic mono and di-starch phosphates which formed an insoluble polyelectrolyte complex with cationic chitosan due to electrostatic attraction. This also increased the compressive strength of the foams by 3 times compared to the control foams. STMP also reduced the cell size and gave more uniform cell size distribution. It was found that properties like density, expansion ratio, compressive strength, resiliency, and cell size distribution of foams can be controlled by adjusting feed rates of starch, chitosan, and the crosslinking agent. These insoluble composite foams absorbed over 600% by weight water and formed a gel kind structure; a property which could be useful in hemostatic applications. Densities of foams were found to vary from 21 to 51 kg/m3 for different compositions studied. A maximum expansion ratio of 74.5 was obtained for the formulation containing 10% PVB and 4% chitosan.
In the past decade, the wireless communication technology has expanded rapidly over the globe, thus stipulating higher data rates and lower latency communication. The advancement in wireless technology has led to drastic increase in number of end users, demanding higher efficiency. To fulfil the requirement of data traffic, the unexplored millimeter wave frequency region is being studied which is recognized as the 5th generation of wireless communication system. This range of frequencies of millimeter waves can facilitate larger bandwidth, higher data rates, lower latency and can connect large number of devices. New technologies emerging for the foundation of 5G include massive MIMO, small cells, beamforming that plays an important role in revolutionizing the cellular network technology. Miniaturization, lightweight trends lead for utilization of thermoplastic materials being used for the antennas. The dielectric properties of thermoplastic materials are measured & used in building simulation models for antennas. A broadband dual polarized, injection moldable base station antenna with crossed dipoles, balun, feeding connectors and reflectors is designed to operate in the 5G spectrum at frequencies up to 10GHz. Sensitivity analysis is performed to examine the antenna performance and most efficient antenna design is chosen.
Crystallization and foaming behaviors of a semi-crystalline polymer in conditions comparable to those found in polymer processing, where the polymer melt experiences shear under elevated pressures, are key for modeling polymer processes and predicting the final structure and mechanical properties of polymer products. We investigate the crystallization behaviors of a newly developed high-melt strength polypropylene (PP) resin using a novel high-pressure visualization system. Overall crystallization kinetics can be easily controlled through the effect of induced-shear stress and the presence of pressurized CO2.
We have demonstrated the dynamics of bubble growth and collapse in the visual observation experimental and foam injection simulator in physical foaming of molten plastics. The modified Han and Yoo model can predict the bubble size for both the situation of bubble growth and collapsed. Our modified model is promising for the application of core-back foam injection molding.
Packing/holding stage as one of the most important stages during foam injection molding is often overlooked in the industry. It not only influences the part’s geometrical accuracy and stability, and the residual stress distribution but also has a significant impact on the production time, machine tonnage, etc. In this work, we attempted to predict the evolution of the cell size during packing using a previously developed model. The model predicted dissolution profile was then compared with measured cell size obtained from visualized high-pressure foam injection molding. Moreover, the use of the visualization mold granted us access to characterize the dissolution time for gate nucleated cells, thereby systematically study the efficiency of each individual packing parameters (i.e. gas concentration, packing pressure, and injection speed).
This study presents the recent development of three-dimensional prediction of cross-linked ethylene propylene diene monomer rubber (EPDM) with chemical blowing agent azodicarbonamide (ADCA) in transfer molding process. Plunger retraction is applied after transfer process is completed. The reaction kinetics model, density model, and viscosity model are applied to describe the complex foamed rubber system in the simulation study. The experimental investigation of material properties into EPDM/ADCA system are studied to make physical parameters in simulation model more realistic. The flow front behavior, the density of foamed rubber, the reaction behavior in foaming and curing conversion are examined to understand the dynamic behavior of the rubber material in both transfer and foaming stages. Furthermore, we study the effect of foaming and plunger retraction. Simulation results show that foaming effect make clamp force larger, however, plunger retraction effect make the back flow occur from cavity to pot to avoid high pressure in the cavity and therefore eliminate the mold clamp force. This study is of great relevance to light weighting application and should reduce the product-to-market cycle time by eliminating the need for the traditional trial-error method.
Thermoplastics have been blended with reactor-based and grafted-ethylene copolymers for over 50 years to improve room temperature and low temperature ductilityfor many applications, including those in the automotive, appliance, sporting goods industries. The compatibilityof the modifier with the thermoplastic matrix and the rheology of the blend components are key factors in controlling blend morphology. The amount of modifier used and the morphology obtainedaffect the balance of critical properties, including stiffness,impact toughness, and flow. Compatibility of the modifiers with the thermoplastic matrix can be controlled by composition of the modifier produced in-reactor, use of additional compatibilizers (such as diblock copolymers), and by in-situcompatibilization achieved through reactive blending. This paper reviews commercially practiced technologies for impact modification of various thermoplastics based on ethylene copolymers.
Highly porous and interconnected 3D structures are crucial elements for tissue engineering scaffolds since they can support the mass transport of cell nutrients and waste. Supercritical foaming technology is an environmentally-friendly and solvent-free way of manufacturing porous scaffolds. In this research, highly porous, interconnected poly(ɛ-caprolactone) (PCL) scaffolds combined with supercritical carbon dioxide (SCCO2) foaming and a polymer leaching process were fabricated by blending PCL with water-soluble poly (ethylene oxide) (PEO) as a sacrificial material. The effects of phase morphology of PCL/PEO blend on foaming behavior and pore morphology were investigated. The incorporation of PEO not only facilitated the foaming of PCL by increasing its viscosity, but also improved the porosity and interconnectivity of the post-leached PCL scaffolds. The fibrillated porous scaffolds with open-pore content up to 91% were obtained after the leaching process because of two different cell-opening mechanisms. Cell-opening on surface of scaffolds is difficult in preparing porous materials. In the end, a novel method for improving surface porosity and producing the so-called outer and inner porous PCL scaffolds is described. The information gathered in this study may provide a theoretical basis for research into porous tissue engineering scaffolds.
In foam extrusion, the blowing agent has a significant influence on the process parameters and the resulting foam properties. Low-density polystyrene foam sheets are usually produced with aliphatic hydrocarbons or alkanes as physical blowing agent. Due to the necessary safety precautions and the environmental impact, there is great interest in using alternative blowing agents such as carbon dioxide (CO2). The sole use of CO2 often leads to corrugation, open cells or surface defects on the foam sheet and therefore requires modifications to the process technology. The aim of this work is to investigate the effect of blowing agent mixtures of CO2 and organic solvents on the production of foam sheets. In particular, the interactions between the blowing agent formulation, the process parameters and the foam sheet properties are analyzed. The knowledge of the interactions can allow a systematic influencing of the foaming behavior without modifying the polymer itself. For a systematic evaluation, an existing process model for describing the melt flow in the extrusion die is extended and applied to an annular gap die. Based on the model, dimensionless numbers can be calculated to describe the foaming behavior. The characteristic numbers enable the direct comparison of different recipes, process settings and die geometries.
Industries that use polyurethane foam are looking for new sustainable and greener material to replace the petroleum-based polyols. Lignin produced as byproduct of pulp and paper and bioethanol industries is a suitable natural polymer to replace petroleum-based polyol in formulation of PUs. The emphasis was to study effect of different lignins obtained from different chemical processes and plant sources on the structural, mechanical and thermal properties of PU flexible foam and to achieve maximum lignin substitution. Additionally, we were interested to find correlation between lignin properties and performance of lignin-based PU foams to identify which lignin properties would affect the performance of developed lignin-based flexible PU foams and find the most suitable lignins for this application. It was seen that lignins isolated through organosolv process were better for PU fiexible foam applications. Overall, substitution of polyol with lignin increased compression strength, support factor, tear propagation strength and tensile strength of the developed PU foams.
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