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.
We researched a novel simulation strategy that predicts bubble growth phenomenon tailored to high-pressure foam injection molding (HP-FIM) processes. This was done via systematic HP-FIM experiments using a visualization technique. The mathematical model that we developed was based on the well-known “cell model”. To improve the model’s robustness and accuracy, we used the Simha-Somcynsky equation of state for the PS/CO2 mixture, which in turn offers an accurate prediction of the initial bubble radius. Moreover, to capture the fluid flow and mass transport behavior during bubble growth, the transport and rheological properties (that is, its diffusion coefficient, surface tension, viscosity, and relaxation time) that were adopted in this work were functions of the temperature, the pressure, and the gas concentration. In this work, instead of solving the cavity temperature and pressure separately, the temperature and pressure profile inside the cavity were respectively simulated using MoldFlow and experimentally obtained. By inputting the initial gas concentration and the transient pressure and temperature profiles, the proposed model could accurately predict the bubble growth profile under different HP-FIM conditions. The proposed model was validated using experimental data obtained from a series of visualized HP-FIM trials. In both cases, qualitative and good quantitative agreements were achieved between the simulated and the measured bubble growth data.
Attached growth bioreactor process provides surface area to support the growth and attachment of bacteria, and thereby a means to biologically remove organics from wastewater. In this work, an open-cellular polyvinylidene fluoride (PVDF) foams consisted of macroporous structures were designed and fabricated to promote the efficiency of existing biofilm carriers for wastewater treatment. A manufacturing approach that integrated compression molding and particulate leaching was employed to fabricate the PVDF foams. Different contents of salt were used as leaching agent to fabricate PVDF foams with macroporous structures of different total protected surface areas. Experimental studies were conducted to elucidate the structure-to-performance relationships of these macroporous PVDF carriers in terms of bacteria-to-carrier interaction and organic removal efficiency.
This paper provides details on the topic of impact management and injury mitigation for playing surfaces, including Football Fields, Soccer Fields, Playgrounds and other playing surfaces both indoors and outdoors and the use of Expanded Polyolefin Particle Foam in their design and construction.The design and construction of sports surfaces plays an important role in playability, performance, injury reduction, and overall impact management and shock mitigation. Expanded Polyolefin Particle foams are being used to fulfill this role. The properties of Expanded Polyolefin Particle Foams allow for designs which take advantage of the isotropic nature of particle (bead) foams, the highly efficient energy management properties, and the ability to manage energy and mitigate impact with a combination of compression, flex and tension. The ability to shape mold the material allows for the most efficient three-dimensional and multi-axis design for energy management. It also allows further performance optimization through changes in geometry and changes in density.This paper will present recent sports surface design innovations and provide case studies vs. competitive technology. Other benefits of Expanded Polyolefin Particle Foam will be presented including 100% recyclability, water-resistance, chemical resistance, long term performance, and the ability to meet the ever increasing rigorous standards for restricted chemicals. This paper will also explore the latest development in the area of soft bead foam technology. New materials beyond the existing Expanded Polypropylene (EPP) such as advanced thermoplastic polyolefins, elastomers, vulcanizates, and polyurethanes are now being used to manufacture expanded particle foam which provide enhanced benefits in the area of energy management and safety. The benefits of these new materials, which include Expanded Thermoplastic Olefins (ETPO), Expanded Thermoplastic Urethanes (ETPU), Expanded Thermoplastic Elastomers (ETPE), Expanded Thermoplastic Vulcanizates (ETPV), and other expanded material blends will also be shown.
The strain hardening behavior of polymers has important roles in processing such as foaming, film formation, and fiber spinning. The most common method to enhance strain hardening is to introduce a long-chain branching structure on the backbone of a linear polymer, but this method is costly and challenging to tailor the behavior. We hypothesized that in situ shrinking fibers can increase the strain hardening of linear polymers, and the degree can be efficiently controlled. In this study, we show that heat-activated shrinking fibers compounded in linear polypropylene enhance strain hardening and foamability. Moreover, changing processing conditions, such as temperature, can amplify the degree of enhancement. Rheological measurements and physical foaming tests are shown to support our hypothesis.
Shear stress on polymers has been shown to have a strong effect on morphological and thus mechanical properties of the final structure. In this study, an in-situ visualization system was developed to i) visualize crystal nucleation and growth with high spatial and temporal resolutions and ii) have capability to measure the local shear stress and viscosity of a saturated polymer in isolated, simple shear. The system allows for easy control of experimental parameters: applied shear strain, shear strain rate, temperature, heating/cooling rate, pressure, polymer, and saturation gas. An early verification of the shear stress measuring capability was conducted of the This visualization/measuring system provides a reliable way of determining both rheological and optical properties of plastics simulated under dynamic conditions like that of industrial plastic processes.
Environmentally friendly thermal insulation and energy saving materials are in high demand for buildings, packaging, and other applications. Here, we report ultra-low density composite foam materials that are mainly composed of cellulose, an abundant degradable and recyclable green material. Nanocrystalline cellulose (NCC) was mixed with 0-20 wt.% polyvinyl alcohol (PVA) in an aqueous solution, followed by ice crystallization and freeze drying processes to fabricate the NCC/PVA cellular structures. Ultralight foams with densities as low as 0.026 g.cm-3 (porosities as large as 98.22%) were successfully prepared and their compression and thermal conductivity behaviors were characterized. The results revealed that the compressive stiffness and strength of NCC foams can be significantly enhanced (about an order of magnitude) by the introduction of 20 wt.% PVA as an elasticity enhancer. The thermal conductivity of NCC/PVA foams remained approximately unchanged with an increase in the PVA content and varied only between 0.037 and 0.041 W/mK, a range that is common for commercially available insulation materials. A relatively low thermal conductivity with enhanced mechanical properties of these NCC-based foams offers a potential bio-based material composition for insulation applications.
The relationship between Electromagnetic interference shielding effectiveness and void fraction of foamed PVDF polymer-based composites with 1 wt% MWCNTs is investigated in this paper. The specimens are prepared through the film casting, compression molding, and batch foaming processes. The composite is advantageous to EMI shielding when the foaming technique is incorporated to reduce weight. It is found out that a 0.62 ~ 0.96 g/cm3 composite achieves an overall EMI SE of 10.5 ~ 25.4 dB in the frequency range of 26 ~ 40 GHz, since increased interfacial surface area from internal gas bubbles contributes to a rise in EMI shielding via absorption.
When organic aerogel particles are polymerized, a complex three-dimensional (3-D) nano-network is generated. This network is composed of randomly assembled nanoparticles, which form many-branched nanoclusters with unique morphological features. The organic aerogels that result from this process have exceptional properties, which supersede those of the current materials used. We studied the morphological features of an organic aerogel (resorcinol-formaldehyde, RF) and correlated each feature to the sample thermal insulation properties. Several RF aerogels were synthesized with different morphological features and structural assemblies. This was done by changing the catalyst percentages and the void fractions at the polymerization stage. Then, each morphological feature was assessed and categorized using two scales: the macro scale and the micro scale. We found that the macro-features were independent of the catalyst percentages and depended only on the void fractions. However, the micro-features were highly sensitive to any changes during the polymerization process. These changes altered the samples’ three main structural factors: (i) The structural assembly, (ii) The porous structure, and (iii) The fractal parameters. Thus, we characterized and quantified each component within these areas. Then, we assessed the structure’s heat transfer modes and classified them as follows: (i) Solid conductivity through the solid particles, (ii) Gas conductivity through the gas molecules, and (iii) Thermal radiation. We identified the morphological features that governed each mode. For example, the samples’ solid conductivity was highly dependent on the fractal parameters of our structure; that is, the particles’ roughness, the structural complexity, and the structural homogeneity. For those samples with extremely rough particles and a complex structure, the solid conductivity reached the lowest possible point. We also found that the total thermal conductivity was mainly controlled by the micro-morphological features, and that the solid conductivity was the most dominant heat transfer mode.
In the conductive polymer composite (CPC) foams, the cell growth can make the rod-like conductive filler rotate and translate due to the force exerted on the polymer matrix. This may influence the percolation threshold of the fillers in CPC foams. This study explores a mathematic model to estimate the effects of cell growth on the percolation threshold.At first, the rod-like filler in the 3-dimensional Cartesian coordinate system was defined using six parameters (i.e., the three coordinates of the filler mid-point, filler length and the two angles between filler and two coordinate planes). The defined filler in 3-dimension was then converted into a 2-dimensional plane using the Euler angels. Then, the filler rotation and translation caused by a single cell growth on that 2-dimensional plane was calculated based on a previously developed mathematical model by our group (Compos Part A, 88). The filler after rotation and translation in 2-dimension was converted into the initial corresponding 3-dimensional Cartesian coordinate system using the Euler angels, again. Finally, with the initial and final filler coordinates before and after cell growth, we can use a Monte Carlo model to simulate the effects of cell growth on the filler percolation threshold.The single-cell-growth effects in a polymer foam containing MWCNTs was calculated as an example. Comparing to the solid system without foaming, in which the MWCNTs percolation threshold was also calculated by the Monte Carlo model, the foam system exhibited lower percolation threshold of MWCNTs. This indicates that foaming may have positive impact on the percolation threshold of conductive fillers in CPC foams.
It is well accepted that the microcellular structure can enhance electromagnetic interference shielding (EMI) properties due to the multiple reflection and scattering in the microcells. Moreover, the foams were proved to be the competitive materials owing to the savings of energy and raw materials. In this study, the poly(vinylidene fluoride)/ graphene nanoplatelets (PVDF/GnP) composite foams were successfully prepared through a facile home-made batching foaming avenue. The microcellular structure of PVDF/GnP foams can be tuned by the batching foaming temperature. We can notice that the void fraction of foams firstly increased and then decreased with increasing temperature. In addition, we also investigated the electrical conductivity and electromagnetic shielding properties of PVDF/GnP foams. The results revealed that the electrical conductivity and EMI properties can be effectively monitored, and the PVDF/GnP foam with low void fraction exhibited the high electrical conductivity and EMI properties. The optimal EMI values of PVDF/GnP foams with a thickness of 2.5 mm were 27.4 dB. An analysis of the shielding mechanism showed that the main contribution to the EMI shielding came from the absorption mechanism, and that the EMI shielding could be tuned by controlling the foams’ thickness. Thus, these PVDF/GnP foams could be considered as the high-efficiency EMI materials.
In Canada, the cleaning cost of 340 billion gallons of oil sands tailings ponds is estimated to be over $27 billion. There is a need for cost-effective technologies for removal and recovery of oil from these ponds. Previously, we reported foams application for absorption and adsorption of crude oil from water. This works aims to develop effective method for foam reuse and oil recovery to improve the benefits of the treatment process. The polyester polyurethane (PESPU) foam with pH-responsive wetting properties and crude oil were used to assess the effectiveness of mechanical compression, pH-swing method, and chemical wash method. The mechanical compression is a simple, environmental friendly, and easy to implement method. This process was effective in recovery of the absorbed oil, where the oil uptake mechanism is reversible superhydrophobic forces and pore filling. However, for adsorbed oil recovery it was less effective. According to pseudo-second-order kinetic model, the oil droplets were adhered to the sponge surface by physical forces. As a result, mechanical forces were weak in shearing-off the thin oil film. Based on pH-responsive wetting property, the oil adsorption was effective at acidic conditions. Therefore, the oil recovery was performed at basic conditions by introducing new “pH-swing” technique. This method produced minimal waste and sustainable, but materials reusability declined to ~70% within three cycles. Finally, chemical wash method was applied to recover the adhered oil from the surface. According to surface chemical displacement principles, a solvent with appreciably low surface tension than the foam and similar molecular structure the crude oil was used to wash the sponge at ambient conditions. Due to enhanced solubility and flowability, the crude oil was readily recovered from the foam surface. The cleaned foam as well exhibited over 99% efficiency over multiple reuses. Our finding show that the foam is a promising solution to remediate detrimental oil sands tailings and for recovery of the residual crude oil from water leading to environmental and economic benefits.
It is widely accepted that the manufacturing of high expansion PP foams with fine cell morphology is a challenging task due to the low melt strength and the weak rheological behavior of the linear polypropylene. In this study we present a novel method to manufacture high cell density, large expansion microcellular foam through nano-fibrilation PP/PET composites. Various studies have been conducted to improve the processability of linear PP foams. Until now, the most successful industrial approach is using the branching PP as it expressed the strain hardening response and the increased melt strength behavior. However, the commercial price of branching PP resins are still doubled or even tripled comparing with linear PP resins, which dramatically limits the branching PP’s applications. Inducing chemical cross-linking is proven to be another effective way to improve the melt strength of PP. However, the cross-linked structure causes difficulty in recycling PP resins. Furthermore, the cross-linking reaction is not evenly initiated throughout the matrix rendering non-uniform cell structure in the final foam product. Implementing inorganic/organic filler is another alternative route for enhancing the foamability. PP reinforced with those fillers has higher viscosity and better elasticity at melting state. Nonetheless, the well-recognized challenging issue is to achieve well distribution and dispersion of nano-size fibers inside the polymer matrix. Because of the large surface to volume ratio, the nano-fibers tend to agglomerate. The well-established methods usually requires complex experimental conditions and normally involves dealing with chemical hazards. By implementing nano-fibrillation technology, all above mentioned draw-backs were overcome. The nano-fibrillation technology is used to manufacture polymer-polymer fibril composite in this study. The nano-fibrillation technology can generate high aspect ratio nano-fibrils uniformly dispersed inside the polymer matrix. The processing can be briefly summarized as: (i) blending immiscible polymer matrix (A) and polymer reinforcement (B) to make polymer (B) dispersed in spherical shape (the melting temperature of polymer B should be at least 30oC higher than polymer A); (ii) applying large deformation on the polymer extrudate by either hot stretching or cold stretching; (iii) carefully choosing a temperature between the melting temperature of polymer A and polymer B to melt the composite without damaging the fibril morphology of polymer B. In this study, three kinds of PPs with different viscosity are reinforced with PET nano-fibrils via melt spinning. The study shows that the high viscosity PP is preferred to generate low diameter nano-fibrils (~200 nm) in a wide concentration range; while the diameter of fibrils in low viscosity PP decreased with raising PET concentration. The oscillatory shear behavior is studied by comparing the storage modulus (G’) and phase angle (tanδ) of the non-fibrillated and fibrillated samples. Differential scanning calorimetry and birefringence optical microscope were employed to study the crystallization kinetics of PP/PET fibril composites. The rheological properties and crystallization kinetics were significantly improved with the presence of PET fibrils. Crucially, benefit from the strengthened rheological behavior and crystallization kinetics, the batch foaming of PP/PET nano-fibril composite is able to product a high cell density polymer foams.
Due to their complex flow and curing behavior the quality of parts made from thermosetting molding compounds depends to a high degree on the reactive and viscous char-acteristics during their processing. In the study at hand a newly developed test procedure was applied to examine the dependence of these characteristics on the composition of the pourable molding compound, the amount of hard-ener, the present material humidity and the process pa-rameters. Three thermosetting molding compounds were purposefully impinged with high air moisture, the amount of hardener was partially increased and the resulting flow and curing behavior was determined with the implement-ed testing sensors. A distinct dependence of the flow re-sistance and the reaction kinetics on the tool temperature, the amount of hardener and the material moisture was detected. These results are discussed and the potential of the developed testing device is pointed out.
The present paper shows a rather simple but effective and useful method, namely, the spotwise painting of the mold wall surface to investigate slip of the phenolic melt on the cavity surface. For all processing conditions, it was found that there was a strong slip on the interface between the phenolic polymer and the mold wall surface. Furthermore, a differential scanning calorimeter (DSC) and a plate-plate rheometer are employed to measure degree of cure and viscosity of the phenolic injection molding compounds. In addition, a numerical methodology has been written to fit cure kinetics and reactive viscosity model based on experimental data. The fitted parameters were used to simulate the injection molding process for a phenolic component with slip boundary condition. A good agreement was found in comparison between simulation and experimental results.
The exploration of highly effective flame retardants takes an essential part in the fire-resistant enhancement of matrix. Herein, UP/APP/ATH composites were fabricated by blending ammonium polyphosphate (APP) and aluminum hydroxide (ATH) in various proportions into unsaturated polyester resin (UP) matrix at the curing process. Thermogravimetric analysis (TGA) indicates the UP/APP/ATH composites exhibit a favorable high-temperature stability and an enhanced char yield. The flame-retardant performances were conducted by UL-94 vertical combustion tests, limiting oxygen index (LOI), and microscale combustion calorimetry (MCC). The combination of APP and ATH demonstrates an excellent synergistic flame-retardant effect, UP/APP/ATH sample can reach V-0 rating and LOI values are raised to 33.5 %. SEM and thermogravimetric analysis/infrared spectrometry (TG-IR) tests represent that the formed compact and dense char layer can act as a physical barrier to inhibit the heat transfer, and the volatiles of combustible gases are reduced.
Conventional cross-linked polyurethane (PU) or PU networks are unable to be reprocessed in the melt state into reshaped, high-value recycled products. This is because of the irreversible nature of the cross-links in PU, a common feature of thermosets which prevents the cross-linked network or thermoset from ever returning to a melt state. We have recently discovered several chemical platforms for making cross-linked polymers melt-reprocessable by instilling a reversible nature to the cross-links as a function of temperature. Here, we describe our approach for making reprocessable polyhydroxyurethane (PHU) networks that exhibit full property recovery associated with cross-link density after multiple melt-state reprocessing steps. PHUs are a class of non-isocyanate-based polyurethanes (NIPUs) that can be synthesized via reaction of amines with cyclic carbonates; the PHUs contain urethane linkages with adjacent primary or secondary hydroxyl groups. In the presence of appropriate catalyst, we have synthesized PHU networks with robust properties at room temperature and many tens of degrees above room temperature. These networks containing appropriate catalyst can be effectively reprocessed at least three times at 140 degrees C leading to full recovery within error of rubbery-state plateau modulus and room-temperature tensile strength and strain at break.
This paper presents formulation details and initial property information for a new class of high-performance double-network glasses that are created through frontal polymerization of an initially formed gel. It is envisioned that this technology can be used for a variety of applications ranging from new adhesives to composite pre-pregs. Herein, we describe the creation of a new, one pot, liquid system consisting of miscible acrylates and epoxies. This system has the ability to undergo radical polymerization of selected acrylate monomers under long-wave ultraviolet radiation at room temperature. This polymerization produces a free-standing gel that can be incorporated as an adhesive or pre-preg in a composite system. The resulting gel can then undergo cationic, thermal frontal polymerization of the epoxy-based second network to form a cured high-performance resin. The stability of both the liquid mixture and the subsequent gel after the initial polymerization of the first network are discussed. The liquid system retains the capacity to undergo both the gelation and frontal polymerization steps after over and year and a half of storage. The ability to use sequential polymerization steps combined with the stability of the gelled state creates a system that shows promise for creating monolithic shapes, using frontal polymerization, from freestanding gels. Possible applications for this technology include 3D printing, electronics potting, and moldable adhesive films.
Exterior Rigid PVC products such as Siding, Cladding, Fencing, Decking and Window profiles are moving to more dark colors to enhance design features. Darker colors pose a challenge for Rigid PVC as infrared radiation absorbtion from the Sun can often raise the temperature high enough to exceed the Heat Distortion Temperature of the PVC causing distortion and sagging. Current technologies such as infrared non-absorbing pigments and coatings and additives, while minimizing the distortion, all have some problems in these exterior applications. Eastman is introducing a new material that solves many of these problems while increasing the Heat Distortion Temperature, enhancing ductility, and little effect on processing. This paper will discuss Eastman’s recent developments.
The layered double hydroxide ([Mg0.667Al0.333(OH)2](CO3)0.167·mH2O) (LDH) has found application as a heat stabiliser for PVC. Derivatives of this compound were synthesised using a hydrothermal method. Emulsion grade PVC was plasticised with 100 phr diisononyl phthalate and stabilised with 30 phr of the LDH filler additives. Heat stabilities were determined at 200 C. The dynamic heat stability tests were performed on the plastisols using the torque rheometer method. Static heat stability was evaluated on the fused compounds. It was evaluated from discoloration profiles of strips exposed for various lengths of time to heat in a Metrastat oven. The time dependence of hydrogen chloride evolution was followed with a Metrohm Thermomat instrument. The conventional LDH provided the best dynamic heat stability. However, partial replacement of the magnesium with copper significantly delayed the release of volatile HCl. If instead the replacement was done using zinc, better colour retention was achieved.
Accelerated weathering testing is used widely to evaluate the performance of outdoor polymeric materials. Test standards have been published by multiple international and other standards bodies for performing testing to simulate outdoor environments. These test methods apply ultraviolet (UV) light, high temperature, and water in the form of condensation, humidity, and spray. Control of temperature during accelerated weathering testing is critical for many plastic materials, both to control the rate of photochemical degradation and to avoid unrealistic failure modes from plastics softening or even melting. Unfortunately, maintaining proper specimen temperature during accelerated weathering testing can be challenging and is often not well-understood.
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