Search

The study investigates the use of thermoplastic expanding microspheres (TEM) as a physical blowing agent in EPDM-based rubber foams. Thermal conductivity is a local, time and temperature dependent variable that is influenced by foam expansion and plays a crucial role in this foaming process. To model this interaction, Representative Volume Elements (RVE) are used to investigate how morphological parameters, such as porosity and pore size distribution, affect the thermal conductivity of the rubber foam. Experimental validation will be carried out on pure rubber and various rubber foam samples. The aim is to establish a method for the determination of the foam morphology dependent thermal conductivity, which will allow predictive process simulations. [ABSTRACT FROM AUTHOR]

The recognized selection of a product processing method is significant in improving the efficiency and suitability of polymer product applications. In this study, the compressive properties of polyethylene (PE) and ethylene vinyl acetate (EVA) foam mixture (PE/EVA) using compression and rotational molding method were investigated. The sample was prepared in two steps. Firstly, PE and EVA resins, zinc oxide (ZnO) as an accelerated agent, azodicarbonamide (ADC) as a blowing agent, and other additives were mixed using single screw extrusion to form pelletized products. Furthermore, pellets was processed by compression and rotational molding into a PE/EVA foam mixture sample. The results showed that the compressive strength and the density of the sample with rotational molding method were higher than compression molding method, with a value of 0.24 MPa and 0.258 g/cm3, respectively. However, the hardness value of both methods were not significantly different. To find the affected hardness value, morphology spectroscopy of the foam was observed using scanning electron microscopy (SEM) to measure the size and homogeneity of the foam cells. The results showed that the distribution of foam cells from both methods was not uniform with a random structure. Therefore, the properties of hardness, density, and compressive strength could be determined by the uniformity of the foam cell size. Based on the results of this research investigation, comparing the three parameters of compressive strength, density, and morphology, it can be concluded that the rotational method was better used in the PE/EVA foam manufacturing process. [ABSTRACT FROM AUTHOR]

One of the most important additive manufacturing plastic processes is selective laser sintering (SLS). Complex component geometries can be produced directly from the CAD model. A significant factor in the decision for or against the use of SLS is the availability of material. High demands are placed on the laser sintering powder in terms of size distribution, shape, and surface. Therefore, only a few materials have been able to establish themselves on the market so far. The process for producing laser sintering powder researched in this project is the PGSS process ("Particle from Gas Saturated Solutions"). In this process, polymers are plasticised with the help of a twin-screw extruder and applied with supercritical CO2. After the extruder, the plastic-gas mixture is conveyed through a melting pump into a dynamic mixer. Here the mixture is homogenised, and further supercritical CO2 is added. In the subsequent melt cooler, the fluid is mixed again and cooled to pre-expansion temperature before it can be sprayed through a nozzle into the spraying tower. Since the CO2 acts as a blowing agent, the viscosity of the polymer is reduced enormously. At the same time, the pump builds up the necessary pressure to push the polymer-gas mixture through the nozzle and thereby spray it. When the dispersion is sprayed, the supercritical CO2 returns to a purely gaseous state, causing it to expand and thus increase in volume. As a result, the gas dissolves out of the plastic phase and breaks it apart. The resulting particles form a sphere during the fall due to the surface tension of the polymer. At the same time, these spherical particles are strongly cooled and solidified by the Joule-Thomson effect that occurs during the expansion of a gas. The final result should be a laser sintering powder with ideally spherical plastic particles and consequently good flowability. [ABSTRACT FROM AUTHOR]

In the literature it is well known that foaming is a highly complex process which is influenced by e.g. the process parameters, the choice of polymer and its structure as well as by the blowing agent type and concentration. Due to the dependency of both, shear and elongational viscosity on such influencing factors, the melt viscosity is highly influenced during the foaming process. Thus, the viscosity is a crucial parameter for the foaming process. A collapse of single bubbles or even of the whole foam structure is often a result of a too low elongational viscosity and the associated melt strength. Therefore, polylactide (PLA) is difficult to foam. In this study the melt viscosity in shear and extensional flow, and the melt strength was increased by modifying PLA with dicumyl peroxide on a twin-screw extruder. Thus, the polymer chain structure was changed from linear to branched and strain hardening was observed during uniaxial viscosity measurements with a Sentmanat extension rheometer at different temperatures and Hencky strain rates. The uniaxial elongational viscosity of the modified PLA including the observed strain hardening was predicted at different temperatures and different Hencky strain rates with the molecular stress function model (MSF). Because of the good accuracy of the MSF model predictions in comparison to the uniaxial viscosity measurements, the equibiaxial viscosity was modeled as well since equibiaxial deformations mainly occur during the foaming process. Therefore, the elongational viscosity of modified polymers for foaming applications can be characterized and predicted. [ABSTRACT FROM AUTHOR]

We present the design of a technique that combines the simplicity of polymer foaming with the precision of 3D printing. In the context of polymeric cellular materials, foaming processes, either using physical or chemical blowing agents, are extensively operated in industry to produce pores, yet without a spatial control of the pore positioning. This intrinsic stochastic structuring may introduce imperfections, which reduces the overall mechanical properties of the material; thus, regular (e.g., periodic) structures are more desirable than stochastic ones. 3D printing is another technique to fabricate polymeric cellular materials and it allows to produce cellular materials with empty spaces in precise locations and with a well-defined periodic structure. To this end, very expensive 3D printers are required to achieve micron-resolution pores. Correspondingly, the production time increases dramatically, and becomes a bottleneck to the industrial scale-up. Herein, we show the design of a technique that combines the advantages of polymer foaming with the 3D printing, indeed, the resulting cellular materials have: a micron-controlled cell structure and can be printed at reasonable costs and time. The proposed approach is validated using a biobased and compostable polymer (i.e. polylactic acid) for application in biomedical, agriculture and chemical engineering fields. The resulting foamed strands are novel in terms of morphology with a controlled local porosity that opens up to an immense scenario of applications thanks to a possible cost-effective production of hierarchical structures with superior properties (e.g., scaffolds for bioengineering and advanced devices for energy storage or collection). [ABSTRACT FROM AUTHOR]

Biodegradabel foam is an alternative packaging as the subtitute of styro foam with the main raw material from starch so that the packaging can be naturally degraded. This study was conducted to find out the effect of blowing agent toward biodegradable foam charactgeristic produced from sago starch. The starch was used as modification raw materia, the acid used for acid-alcohol hydrolysis method were HCL and H2SO4. The blowing agent used was NaHCO3 and citric acid (1,3:1) with concentration variation of 0, 10, 12, 15, and 18% w/w of starch.baking process at the temperature of 125° was employed to produce biodegradable foam production. The analyses in biodegradable foam production were water absorbance, degradability, density, tensile strength and SEM (Scanning electron microscopy). The addition of blowing agent produces low density, low tensile strength, high degradability, and high water absorbance. The result of this study shows that biodegradable foam modified using H2SO4 has low density, low tensile strength, high water absorbance and high degradability compare to biodegradable foal modified using HCl. SEM analysis of sago starch modified using HCl and H2SO4 with the best addition of blowing agent of 12% modification of H2SO4 produce morphology shape with the bigger particle/cell size compare to modification using HCl. [ABSTRACT FROM AUTHOR]

The article discusses a study on the creation of new effective composite chemical flotation reagents - blowing agents and the study of their physicochemical and flotation properties. The foaming ability and foam stability of the developed flotation reagents are shown to be used in the process of flotation of non-ferrous and noble metal ores based on local raw materials and production wastes. The results of laboratory-production tests of the developed flotation reagents-blowing agents of the KСF-VS type at the processing plant of the central laboratory of new technologies in the conditions of JSC "Almalyk MMC" are presented. [ABSTRACT FROM AUTHOR]

The growing environmental awareness and natural resources scarcity various fully biodegradable polymer systems development and utilization initiates poly lactic acid (PLA) and copolymers biodegradable polymer, extensive attention as they biodegradability, numerous renewable sources, and excellent mechanical and thermal properties like advantages other polyester resins like PLA inherent chemical composition and molecular structures due to very poor fire resistance the aviation and electrical industry PLAs widespread use low thermal resistance, combustion and drip hampered flame retardant modification essential Combustion-type flame retardants polymer by physical means incorporated materials production convenient industry widely in used. Flame retardants certain chemical compounds polymers paralytic reactions slow or inhibit or combustion oxidative reactions They mainly halogen, phosphorus and metal hydroxides containing compounds Halogen flame retardant drawbacks metal components highlight ability combustion during hydrogen formed toxicity and some governments or organizations halogen controlled flame retardants use restrict proposed halogen-free flame-retardant additives indomethacin flame retardant (IFR) considerable attention and polypropylene (PP) and polyethylene (PE) such as polymers used their low smoke, no toxicity, and halogen absence benefits. and corrosive gas production In general an IFR system three basic components char-forming agent carbonization catalyst, and a blowing agent combustion during IFR multi-cellular structure combustible layer a physical that acts barrier gas and compressed between heat and mass transfer reducing reducing the burning melt in thermoplastic flame-retardant conversion is a particular problem. Drops melting burning surface area increase fire intensity increase faster fire spread viscosity Melting coal formation strong impact PLA, polyethylene terephthalate (PET), and poly butylenes succinct (PBS) like Linear polymers branched or thermo set polymers compared low melt viscosity burning test during serious melt dripping layered silicates thermal stability improve reduce filler concentration flammability low investigations found. [ABSTRACT FROM AUTHOR]

Recently, several research studies have been implemented using sodium bicarbonate (NaHCO3) as a blowing agent on rubber foams, yet none has been found in natural rubber latex foam (NRLF). The use of NaHCO3 as a blowing agent in NRLF prepared by the Dunlop process can potentially develop greener foaming processes and more environmentally friendly foam in the industry of latex foam. This novel method is designed to manage the reduction of harmful waste disposal associated typically in producing the NRLF product which is useful for industry purposes. Hence, this research is presented to investigate the physical properties of NRLF such as relative foam density, crosslink density, average cell diameter, and thermogravimetric analysis (TGA) based on the influences of different sulphur vulcanization systems via conventional vulcanization (CV) system and efficient vulcanization (EV) system. The relative density and crosslink density were increased with an increase in NaHCO3 concentration with the CV system exhibiting higher value than the EV system. For average cell diameter, the results showed a decrease in both systems with the EV system having higher value than the CV system. Thermal stability from the TGA results was also improved at higher NaHCO3 concentration and for the use of the CV system as a foaming approach, the CV system has higher thermal stability than the EV system. [ABSTRACT FROM AUTHOR]

Polymeric foam composites containing natural fibre is gaining attention for light-weight and environmental friendly engineering materials. In this works, physical and morphological characteristics of unsaturated polyester-based polymeric foam composites containing oil palm empty fruit bunches fibre (OPEFBF) were investigated. Sodium hydroxide treated-OPEFBFs (average diameter 0.3 mm, fibre length 3-5 mm) were loaded as fillers for unsaturated polyester-based polymeric foam composites, using polyurethane as blowing agent. It was found that increased content of the blowing agent decreased density of the composites. It was revealed that increased loading of the OPEFBF resulted on increase of mechanical characteristics, but also density of the composites. Optimum formulation of the polymeric foam composite was achieved using weight ratio: Polyester: OPEFBF: Polyurethane: MEPOX= 40: 40: 15: 5, with resulted characteristics: density: 990 kg/m³, foam content: 6.32 %, Modulus of Elasticity: 8460 MPa. Morphological investigation of the composites using SEM microscopy indicated finely distributed of OPEFBF and air pores within the bulk of the composites. [ABSTRACT FROM AUTHOR]

Injection foam molding provides the industry with advantages from production through to the life cycle of plastic components. Despite numerous applications, many questions regarding the fundamentals of this technology are fraught with uncertainty. One aspect of supreme importance is the relationship between the gas content during processing and its influence on the process and part performance. To refine the foaming technology and to comply with modern market requirements, it is crucial to understand this dependence, as proper process design and tailoring of mechanical properties require this knowledge. This work represents a thorough investigation of the influence of CO2 content on both the process and the produced components. Using talc filled polypropylene in a MuCell® process, initially the dynamic solubility limit, i.e. the ultimate amount of gas dispersible in the polymer melt during an injection molding process, was determined via a bulk modulus methodology. During this procedure, foamed plates were molded at different CO2 contents. Processing parameters, morphology and bending behavior of the produced plates were monitored and measured. The results show interesting mechanical behavior, especially close to the determined solubility limit. Based on these outcomes our experiments clearly argue for larger gas contents in physical foaming, which also benefit injection pressure/work or torque during processing. In contrast to these findings, trials with a chemical blowing agent (also yielding CO2) were carried out with the same material. The TGA of the blowing agent yielded an astonishing difference regarding gas concentration in the melt of one order of magnitude compared to physical foaming. In spite of the vanishingly small amounts of gas in chemical foaming, a fine morphology developed. This study provides novel insights into the complexity of injection foam molding, critically assesses gas contents during processing but also poses new questions.. [ABSTRACT FROM AUTHOR]

Sodium bicarbonate (NaHCO3) was used as a blowing agent in natural rubber latex foam (NRLF) in this study. At fixed vulcanization temperature and time in an air-circulating oven, the NRLF was prepared via the Dunlop method by whipping until frothing and adding NaHCO3 in latex compounds with different loading (i.e., 0, 3, 9 and 12 phr). An alternative formulation for the inclusion of NaHCO3 in NRLF was used. The effect of different blowing agent loading on the physical characteristics of NRFL such as relative foam density was investigated. Observation of cell diameter was performed using an optical microscope (OM). The result of NRLF's compression strength was also evaluated, which correlated with the foam's physical characteristics. The relative foam density was increased with an increase in the amount of NaHCO3. However, the average cell diameter was shown to decrease as the loading of the blowing agent increased. The outcomes of the NRLF's compression strength were also enhanced as the loading of the blowing agent increased following the physical characteristics of the foam respectively. [ABSTRACT FROM AUTHOR]

The thermal properties of polyurethane foams are important to meet the government mandated energy efficiency goals. Polyurethane foams blown by traditional blowing agents such as water, n-Pentane, and Methyl formate may not have the thermal and mechanical properties to meet the target of the manufacturer. Over the last few years, Forane (FBA) was introduced as the fourth-generation of blowing agents that provide excellent insulation properties for the rigid polyurethane foams. One of the obstacles of using HFCF blowing agents was the high values of global warming and ozone depletion potentials. The current research provides a study of the effect of various blends of FBA 1233zd and traditional blowing agents on the mechanical and thermal properties of rigid polyurethane foam insulation. Foam samples were blown by 0, 25, 50, and 100% blowing agent blends were studied and the results show that for which extent foam properties were changed. [ABSTRACT FROM AUTHOR]

Thermoplastic Elastomer Vulcanized (TPE-V) syntactic foams made by Thermo-Expandable Microcapsules (TEMs) are becoming of a large interest for automotive industry. TPE-Vs combine advantages of class rubber compound properties with an easier manufacture process and are recyclable. Therefore, TPE-Vs are more and more used to manufacture automotive sealing system by an extrusion process, which is the focus of this research. Due to the two-phase structure of TPE-V, classical extrusion foaming technologies, such as chemical and physical foaming, are complex to be controlled. Thus, TEMs show an outstanding ability to be effective and produce repeatable microstructure with standard extrusion equipment. TEMs consist in a mixture of liquid hydrocarbons, encapsulated by a gas-proof polymeric shell. Exposed to elevated temperatures, the internal pressure drives the dilation of the TEMs, as a result a TPE-V syntactic foam is produced. The aim of this study is to understand where the expansion occurs and how can it be affected by extrusion process parameters. Temperature is a well-known key parameter to control final expansion of TEMs. Hence, measurements at high pressure and temperature were done to find out the location of expansion during extrusion process. Additionally, we have designed three groups of three dies to apply different pressure drops, pressure drop rates and residence time, inside the die. Under these process conditions, density, cell microstructure and viscosity have been investigated. [ABSTRACT FROM AUTHOR]

Biodegradable plastics find more and more applications. In addition to biodegradable packaging, the number and type of products also being used in medical applications is increasing. The goal of the presented research is development technique for preparation of microcellular foams based on biodegradable polylactic acid (PLA) and its co-polymers for biomedical applications. The goal is to understand the influence of microblowing agents on the course and efficiency of microcellular process of injection molding biodegradable polymer compounds as well as on the properties of the obtained products. Polylactide (PLA) under the trade name NatureWorks Ingeo 2002D modified with chemical blowing agents having an exothermic and endothermic character of the distribution was used during the tests. The blowing agents used in the injection molding process were inserted into polymers processed in the following amounts: 0.5%, 1.5% and 3.0% wt. The article presents the characteristics of the process of injection of biodegradable plastics and the study of selected physical properties of the materials produced. The research on the structure of manufactured materials, density and the degree of porosity, mechanical strength, impact resistance and hardness are presented. It was found that as a result of the increased temperature in the plasticizing system, the blowing agents decompose and the resulting numerous microcells, due to pressure and surface development, immediately mix with the plastic. The resulting microcells are filled with both air and gases, increasing the volume of PLA. There was a change in the examined physical properties of the tested materials, mainly mechanical strength of the tested PLA compositions. [ABSTRACT FROM AUTHOR]

Ethylene vinyl alcohol (EVOH) was melt compounded with an organo-modified nanoclay (NC) at a loading level of 5% by weight in a twin-screw extruder (TSE) using a sub-critical gas-assisted process (SGAP). Carbon dioxide (CO2) and nitrogen (N2) were used as blowing agents to induce foaming inside of the barrel of the extruder and as the melt exits the die. Samples processed with SGAP demonstrated better dispersion of NC versus the traditional extrusion process due to the additional stresses that bubble expansion provides during foaming. [ABSTRACT FROM AUTHOR]

The traditional rotational molding process is the most widely implemented technology for low-cost fabrication of low-volumes of hollow/double-walled large-sized, seamless and virtually stress-free, single-piece plastic articles with complex shapes and/or moderate undercuts. However, demanding industrial end-use applications often require lightweight rotationally molded articles that could resist harsh environments while simultaneously demonstrating buoyancy, enhanced mechanical strength, thermal and/or acoustic insulative properties, as well as improved strength-toweight ratios. In response to this need, over the years, several design modifications of the traditional rotational molding process advantageously enabled the manufacture of rotationally foam molded cellular composites having a distinct integral solid-skin that is fully encapsulating a foamed inner core or layer. Although the resulting cellular composite moldings were attributed with significantly enhanced properties compared to their hollow non-foamed predecessors, the inherent disadvantages of the traditional parent process, such as the very lengthy and energy-intensive processing cycle times and the very limited means for real-time process control, were only further aggravated. This paper focuses on a recently patented process that alleviates these drawbacks by replacing the close interactions between foamable and nonfoamable polymeric resins to their effective independence. It is referred to as Rapid Rotational Foam Molding (RRFM). An experimental study in the domain of processing polypropylene (PP)-based integral-skin cellular composites using the RRFM technology is presented in details. In this context, by successfully decoupling (segregating) the skingenerating/article-shaping processing phase from the foamed-core-processing segment, RRFM proved to provide a viable solution to the common previously faced challenges in the manufacture of PP foams surrounded by an integral-solid-PPskin with a desired shape. [ABSTRACT FROM AUTHOR]

For the continuous production of foam products, the extrusion process is commonly used. Typical extrusion systems include an extruder for melting and mixing the thermoplastic material(s) as well as an extruder for cooling the melt. Both tasks can also be performed in one extruder. Between these extruders or extruder zones the blowing agent (e.g. CO2, N2) is injected into the melt with relatively high pressure. This study presents a foam extrusion process utilizing a twostage- screw in which the blowing agent is injected at a low-pressure range and extruded as a strand. The study uses PP as well as nitrogen and carbon dioxide as blowing agents which are widely used for foaming. The screw concept makes it possible to produce a blowing agent loaded polymer melt with the present pressure of a standard gas bottle (or other gas storage devices) thus eliminating the need for expensive gas cooling, dosing and pumping technology. The influence of melt temperature and gas injection pressure on foam quality (expansion ratio, cell structure) is investigated. The produced foam has a regular cell structure. [ABSTRACT FROM AUTHOR]

This paper presents the optimization of a continuous foam extrusion process to manufacture high impact polystyrene (HIPS) foams through a twin-screw extruder. The effects of chemical blowing agent type and content as well as; process parameters: e.g., die temperature profile and screw speed (RPM) were investigated. After determination of the optimum die temperature profile, effect of chemical blowing agent type and content (i.e., 1, 3, 5 wt. %) and screw RPM (i.e., 100, 150, 200, and 250) were investigated. Results show that; the best void fraction (around 22%), with the highest cell density (around 6 x 105 cells/cm³) obtained at die temperature profile of 150-145 °C. It was also observed that 100 RPM, revealed the highest void fraction (around 32%) with cell density of around 3 x 105 cells/cm³. The increase of chemical blowing agent, increased the void fraction from around 10% to 31% where the cell densities were also increased, respectively, from around 8 x 104 cells/cm³ to 2 x 107 cells/cm³. [ABSTRACT FROM AUTHOR]

The role of blowing agent in the manufacture of porous metal alloys is very important to produce the desired pore. The thermal stability and speed of foam formation have an effect on the resulting pore structure. In porous metal alloys, uniformity of size and pore deployment are the main determinants of the resulting alloys. The coating process of calcium carbonate (CaCO3) has been done using Sodium trisilicate solution by sol-gel method. Foaming agent was pretreated by coating SiO2 passive layer on the surface of CaCO3. This coating aims to produce a more stable blowing agent so that the foaming process can produce a more uniform pore size. The microstructure of the SiO2 passive was observed using Scanning Electron Microscope (SEM) equipped by Energy Dispersive X-Ray Spectrometer (EDS) mapping. The results showed coating CaCO3 using sodium trisilicate was successfully done creating a passive layer of SiO2 on the surface of CaCO3. By the coating process, the thermal stability of coated CaCO3 increased compared to uncoated CaCO3. [ABSTRACT FROM AUTHOR]

Foam injection molding uses physical blowing agents under high pressure and temperature to produce structural foams having a cellular core and a compact solid skin. This technology is particularly interesting for biodegradable polymers, which often present a very narrow processing window, with the suitable processing temperatures close to the degradation conditions. The addition of a supercritical gas can lead to the reduction of both the viscosity and the glass transition temperature of the polymer melt, which therefore can be injection molded adopting lower temperatures and pressures. In this work, the effect of different processing parameters on foam morphology of Poly(lactic) Acid, PLA, was studied. In particular, two commercial grades of PLA having different rheological properties were adopted to obtain foamed parts by injection molding process with nitrogen as a physical blowing agent. For both PLA grades, the effect of mold temperature on the crystallinity and the resulting cell morphology was assessed. [ABSTRACT FROM AUTHOR]

Thermoplastic elastomer SEBS foams were prepared by using carbon dioxide (CO2) as a blowing agent and the process is classified as physical foaming method. During the foaming process, the diffusivity of CO2 need to be controlled since it is one of the parameter that will affect the final cellular structure of the foam. Conventionally, the rate of CO2 diffusion was measured experimentally by using a highly sensitive device called magnetic suspension balance (MSB). Besides, this expensive MSB machine is not easily available and measurement of CO2 diffusivity is quite complicated as well as time consuming process. Thus, to overcome these limitations, a computational method was introduced. Particle Swarm Optimization (PSO) is a part of Swarm Intelligence system which acts as a beneficial optimization tool where it can solve most of nonlinear complications. PSO model was developed for predicting the optimum foaming temperature and CO2 diffusion rate in SEBS foam. Results obtained by PSO model are compared with experimental results for CO2 diffusivity at various foaming temperature. It is shown that predicted optimum foaming temperature at 154.6 °C was not represented the best temperature for foaming as the cellular structure of SEBS foamed at corresponding temperature consisted pores with unstable dimension and the structure was not visibly perceived due to foam shrinkage. The predictions were not agreed well with experimental result when single parameter of CO2 diffusivity is considered in PSO model because it is not the only factor that affected the controllability of foam shrinkage. The modification on the PSO model by considering CO2 solubility and rigidity of SEBS as additional parameters needs to be done for obtaining the optimum temperature for SEBS foaming. Hence stable SEBS foam could be prepared. [ABSTRACT FROM AUTHOR]

Compression and deformation behavior of partially open cell natural rubber (NR) foam produced from dry natural rubber (DNR), were investigated by performing compressive deformation at different strains and strain rates. Different concentrations of sodium bicarbonate as a blowing agent (BA) were utilized, from 4 to 16 phr in order to produce foams with range of cell size and morphology. Overall, increasing of blowing agent concentration had significantly changed relative foam density. Compression stress-strain curves of the foams exhibited that the compression behavior was directly correlated to the foam cells morphology and physical density. Pronounced changes were noticed for foams with bigger cells particularly at 4 phr concentration of BA where the compression stress at plateau region was greater compared to those with higher concentration of BA. Cell deformation progressive images confirmed that the foams demonstrated small degree of struts bending at 15% of strain and followed by continuous severe struts bending and elastic buckling up to 50% of strain. Compression test at different strain rates revealed that the strain rate factor only affected the foams with 4 phr of BA by causing immediate increment in the compression stress value when higher strain rate was applied. [ABSTRACT FROM AUTHOR]

An environmental-friendly blowing agent has been used to fabricate flexible polyurethane (PU) foam. Polyurethane foam was prepared from palm kernel oil-based monoester polyol (PKO-p) via prepolymerization method. Acetone has been used as solvent in this study. The developed polyurethane foam was characterized using tensile, differential scanning calorimetry analysis (DSC), thermogravimetric analysis (TGA), optical microscope and drop shape analyzer. The mechanical properties of the PU-reference (PU-R) and PU-NaHCO3 foam was analyzed by tensile using ASTM D 3574-01. From the results, the elongation of PU- NaHCO3 shows reduction to 26.3% compared to PU-R. The DSC showed two glass transition temperatures in all samples that belonged to the PU-R and PU-NaHCO3. TGA revealed that the incorporation of sodium hydrogen carbonate into the PU system did not show significant difference as compared to the control PU. The morphology of both PU was investigated using optical microscope. Contact angle has been measured to determine the hydrophobicity of the PU. The PUNaHCO3 exhibited an increase in contact angle (93.1°). [ABSTRACT FROM AUTHOR]

The structure of thermally expandable microcapsule (TEMs) is consisted of a thermoplastic shell which is filled with liquid hydrocarbon at core. The shell of TEMs becomes soft when the temperature is higher than boiling temperature of liquid hydrocarbon. The shell of TEMs is expanded under the high temperature because the inner pressure of TEMs is increased by vaporization of hydrocarbon core. Therefore, the TEMs are applicable for blowing agents and light weight fillers. In this research, we fabricated the polypropylene (PP) foam by using the TEMs and chemical blowing agents and compared to their physical properties. The density of the specimen was decreased when the contents of chemical blowing agents and TEMs were increased. In addition, the mechanical properties (i.e. tensile strength and impact strength) of specimens were deteriorated with increasing amount of chemical blowing agents and TEMs. However, PP foam produced with TEMs showed higher impact strength than the one with the chemical blowing agent. In order to clarify the dependence of impact strength of PP foam as the blowing agent, the morphology difference of the PP foams was investigated. Expanding properties of PP foams produced with TEMs was changed with TEMs content of PP foams. Processing conditions also influenced the mechanical properties of PP foam containing TEMs. [ABSTRACT FROM AUTHOR]

Polymer foams play an important role caused by the steadily increasing demand to light weight design. In case of soft polymers, like thermoplastic elastomers (TPE), the haptic feeling of the surface is affected by the inner foam structure. Foam injection molding of TPEs leads to so called structural foam, consisting of two compact skin layers and a cellular core. The properties of soft structural foams like soft-touch, elastic and plastic behavior are affected by the resulting foam structure, e.g. thickness of the compact skins and the foam core or density. This inner structure can considerably be influenced by different processing parameters and the chosen blowing agent. This paper is focused on the selection and characterization of suitable blowing agents for foam injection molding of a TPE-blend. The aim was a high density reduction and a decent inner structure. Therefore DSC and TGA measurements were performed on different blowing agents to find out which one is appropriate for the used TPE. Moreover a new analyzing method for the description of processing characteristics by temperature dependent expansion measurements was developed. After choosing suitable blowing agents structural foams were molded with different types of blowing agents and combinations and with the breathing mold technology in order to get lower densities. The foam structure was analyzed to show the influence of the different blowing agents and combinations. Finally compression tests were performed to estimate the influence of the used blowing agent and the density reduction on the compression modulus. [ABSTRACT FROM AUTHOR]

Foam injection molding uses environmental friendly blowing agents under high pressure and temperature to produce parts having a cellular core and a compact solid skin (the so-called "structural foam"). The addition of a supercritical gas reduces the part weight and at the same time improves some physical properties of the material through the promotion of a faster crystallization; it also leads to the reduction of both the viscosity and the glass transition temperature of the polymer melt, which therefore can be injection molded adopting lower temperatures and pressures. These aspects are of extreme interest for biodegradable polymers, which often present a very narrow processing window, with the suitable processing temperatures close to the degradation conditions. In this work, foam injection molding was carried out by an instrumented molding machine, able to measure the pressure evolution in different positions along the flow-path. The material adopted was a biodegradable polymer, namely the Poly(lactic acid), PLA. The effect of a physical blowing agent (PBA) on the viscosity was measured. The density reduction and the morphology of parts obtained by different molding conditions was assessed. [ABSTRACT FROM AUTHOR]

Thermoplastic cellulose acetate (CA) is a bio-based polymer with optical, mechanical and thermal properties comparable to those of polystyrene (PS). The substitution of the predominant petrol-based PS in applications like foamed food trays can lead to a more sustainable economic practice. However, CA is also suitable for more durable applications as the biodegradability rate can be controlled by adjusting the degree of substitutions. The extrusion foaming of CA still has to overcome certain challenges. CA is highly hydrophilic and can suffer from hydrolytic degradation if not dried properly. Therefore, the influence of residual moisture on the melt viscosity is rather high. Beyond, the surface quality of foam CA sheets is below those of PS due to the particular foaming behaviour. This paper presents results of a recent study on extrusion foamed CA, using a two-component physical blowing agent system compromising HFO 1234ze as blowing agent and organic solvents as co-propellant. Samples with different co-propellants are processed on a laboratory single screw extruder at IKV. Morphology and surface topography are investigated with respect to the blowing agent composition and the die pressure. In addition, relationships between foam density, foam morphology and the propellants are analysed. The choice of the copropellant has a significant influence on melt-strength, foaming behaviour and the possible blow-up ratio of the sheet. Furthermore, a positive influence of the co-propellant on the surface quality can be observed. In addition, the focus is laid on the effect of external contact cooling of the foamed sheets after the die exit. [ABSTRACT FROM AUTHOR]

We have prepared low density carbon foams from molten sucrose using aluminium nitrate and boric acid blowing agents. A comparative study of the oxidation resistance of the carbon foams prepared using the two blowing agents are reported in the present paper. Oxidation of the carbon foams was evaluated under isothermal and non-isothermal conditions in air atmosphere using thermogravimetric analysis (TGA). We have observed that the alumina produced from the aluminium nitrate blowing agent acts as a catalyst whereas the boron produced from boric acid inhibits the oxidation of the carbon foams. The oxidation resistance of carbon foams increases with boron concentration. The oxidation onset temperature for the carbon foams prepared using boric acid blowing agent was nearly 60°C higher than that prepared using aluminium nitrate blowing agent. Carbon foams prepared using aluminium nitrate blowing agent undergoes complete oxidation at temperature less than 700°C. Whereas that prepared using boric acid blowing agent leave ∼ 50 wt.% residue at 900°C. Further evidence is provided by the kinetic analysis of the TGA using Coats-Redfern (CR) equation. [ABSTRACT FROM AUTHOR]

In this work, variational principle based film blowing model combined with Pearson and Petrie formulation, considering non-isothermal processing conditions and novel generalized Newtonian model allowing to capture steady shear and uniaxial extensional viscosities has been validated by using experimentally determined bubble shape and velocity profile for LDPE sample on large scale film blowing line. It has been revealed that the minute change in the flow activation energy can significantly influence the film stretching level. [ABSTRACT FROM AUTHOR]