Blowing Agent (blowing + agent)

Distribution by Scientific Domains

Kinds of Blowing Agent

  • chemical blowing agent
  • physical blowing agent


  • Selected Abstracts


    Use of Nitrogen as a Blowing Agent for the Production of Fine-Celled High-Density Polyethylene Foams,

    MACROMOLECULAR MATERIALS & ENGINEERING, Issue 10 2006
    John W. S. Lee
    Abstract Summary: While many experiments have been performed to examine the effects of administering CO2 as a blowing agent in the foaming process, very few studies have investigated the use of N2 for this purpose. In this study, foaming experiments were conducted in extrusion using HDPE as a polymeric material and N2 as a blowing agent. Talc was used as a nucleating agent, and three different pressure-drop rates were applied to study the effects of pressure-drop rates on HDPE foams. The experimental results revealed that the void fraction of high-density foams blown with N2 was not affected by the die temperature, contrasting the situation in low-density foams. Surprisingly, it was the cell density which determined the void fraction of high-density foams. It was also found that the use of talc significantly increased the cell density and the void fraction of the foams and minimized the role played by the pressure-drop rate in cell nucleation. Effect of N2 content on the cell density of HDPE foams. [source]


    Effect of rheological behavior of epoxy during precuring on foaming

    JOURNAL OF APPLIED POLYMER SCIENCE, Issue 2 2008
    Osamu Takiguchi
    Abstract In this study, the effect of rheological behavior of epoxy during precuring on foaming was investigated. Dynamic time sweep test of epoxy/curing agent (100/1, w/w) was conducted. The viscosities as a function of time showed extremely rapid increase from the order of 102,103 to 106Pa · s at a certain time, followed by slow increase of the viscosities. Dynamic frequency sweep test of precured epoxy with curing agent was conducted at 90°C. The critical gelation time was obtained by using rheological criterion proposed by Winter and Chambon. We found that the slopes of G,(,) and G,(,) decreased with increasing precuring time. Correspondingly, tan , showed a change from negative to positive slope at a critical time. By using the results, the critical gelation time was determined as t = 895,935 s. Samples of epoxy/curing agent/blowing agent (100/1/0.5) were precured for 960,1620 s. And then precured samples were foamed at 230°C for 300 s to decompose chemical blowing agent. The formed bubble size distribution becomes sharp with increase of the precuring time. There are roughly two sizes of bubbles when precured for relatively short time (t < 1080 s) before foaming: large bubbles (>100 ,m) and small ones (,30 ,m). On the other hand, foams precured for long time (t > 1200 s) before foaming, large bubbles disappear, and the average diameter of the bubble becomes small while the porosity is low. © 2008 Wiley Periodicals, Inc. J Appl Polym Sci, 2008 [source]


    Visualization of the foaming mechanism of polyethylene blown by chemical blowing agents under ambient pressure

    ADVANCES IN POLYMER TECHNOLOGY, Issue 4 2007
    Remon Pop-Iliev
    Abstract Understanding the fundamental mechanisms that govern the foaming process is the most essential universal prerequisite for developing effective processing strategies for fabricating high-quality foamed plastic products using any type of foaming technology. Despite chemically blown foaming of thermoplastics under atmospheric pressure has been successfully implemented in rotational foam molding over the last decade, the related open literature does not provide substantial research addressing the fundamentals of this unique foaming mechanism. The present study focuses on clarifying the fundamental foaming mechanisms that govern the successful manufacture of thermoplastic foams using a chemical blowing agent under low-pressure (atmospheric) conditions. The presented research is mainly based on observing a series of visualization experiments conducted using a custom-made visualization system including an optical microscope and a computerized CCD camera imaging system, which was utilized for investigating the behavior of foamable polyethylene samples prepared by using the compression-molding method. © 2008 Wiley Periodicals, Inc. Adv Polym Techn 26:213,222, 2007; Published online in Wiley InterScience (www.interscience.wiley.com). DOI 10.1002/adv.20102 [source]


    Development of an extrusion system for producing fine-celled HDPE/wood-fiber composite foams using CO2 as a blowing agent

    ADVANCES IN POLYMER TECHNOLOGY, Issue 4 2004
    H. Zhang
    Abstract This paper presents an innovative design of a tandem extrusion system for fine-celled foaming of plastic/wood-fiber composites using a physical blowing agent (PBA). The plastic/wood-fiber composites utilize wood-fibers (WF) as a reinforcing filler in the plastic matrix and are known to be advantageous over the neat plastics in terms of the materials cost and some improved mechanical properties such as stiffness and strength. However, these improvements are usually accompanied by sacrifices in the ductility and impact resistance. These shortcomings can be reduced by inducing fine-celled or microcellular foaming in these composites, thereby creating a new class of materials with unique properties. An innovative tandem extrusion system with continuous on-line moisture removal and PBA injection was successfully developed. The foamed composites, produced on the tandem extrusion system, were compared with those produced on a single extruder system, and demonstrated significant improvement in cell morphology, resulting from uniform mixing and effective moisture removal. The effects of WF and coupling agent (CA) on the cell morphology were studied. An increase in the WF content had an adverse affect. The cell morphology and foam structures were improved when an appropriate CA was added. © 2004 Wiley Periodicals, Inc. Adv Polym Techn 23: 263,276, 2004; Published online in Wiley InterScience (www.interscience.wiley.com). DOI 10.1002/adv.20016 [source]


    Rotational foam molding of polypropylene with control of melt strength

    ADVANCES IN POLYMER TECHNOLOGY, Issue 4 2003
    Remon Pop-Iliev
    Abstract Polypropylene (PP) has not been used extensively in rotational foam molding because it has been traditionally considered as nonfavorable for foaming applications because of its relatively weak melt strength and melt elasticity at elevated temperatures. However, because of the unique end-use properties of PP, PP foams have recently grown in importance. An experimental study was conducted to identify feasible processing strategies for producing PP foams with satisfactory morphologies in dry-blending-based rotational foam molding. The obtained results revealed that cell coalescence plays a key role in the production of PP foams in rotational foam molding. If it is efficiently suppressed, the cell morphology of the PP foams improves dramatically. To suppress cell coalescence, it would be necessary to preserve the melt strength of PP during processing. One way of doing this is maintaining the temperature of the PP melt as low as possible. This can be accomplished by either lowering the decomposition temperature of the chemical blowing agent by using an activator such as zinc oxide and/or reducing the temperature of the oven. © 2003 Wiley Periodicals, Inc. Adv Polym Techn 22: 280,296, 2003; Published online in Wiley InterScience (www.interscience.wiley.com). DOI 10.1002/adv.10056 [source]


    Rotational molding of two-layered polyethylene foams

    ADVANCES IN POLYMER TECHNOLOGY, Issue 2 2001
    Shih-Jung Liu
    Rotational molding of polyethylene foams has increasingly become an important process in industry because of its resultant thicker walls, low sound transfer, high stiffness, and good thermal insulation. This report assesses the rotomoldability of two-layer polyethylene foamed parts. The polymeric material used in this study was linear low-density polyethylene and the foaming material was an endothemic chemical blowing agent. Two different molding methods, by powder and by pellet, were used to mold the multilayer foamed parts. Rotational molding experiments were carried out in a laboratory scale uniaxial machine, capable of measuring internal mold temperature in the cycle. Characterization of molded part properties was performed after molding. Optical microscopy was also employed to determine the bubble distribution in foamed parts. The final goal of this study was to investigate how the blowing agent and processing conditions can influence the process of rotational molding and the final product quality. It was found that the rotational molding of two-layer polyethylene foams produced parts of better impact properties, as well as fine outside surfaces. In addition, rotational molding of foamed parts by pellets saves the cost of powder grinding, but is counteracted by uneven inner surfaces. © 2001 John Wiley & Sons, Inc. Adv Polym Techn 20: 108,115, 2001 [source]


    Effect of rheological behavior of epoxy during precuring on foaming

    JOURNAL OF APPLIED POLYMER SCIENCE, Issue 2 2008
    Osamu Takiguchi
    Abstract In this study, the effect of rheological behavior of epoxy during precuring on foaming was investigated. Dynamic time sweep test of epoxy/curing agent (100/1, w/w) was conducted. The viscosities as a function of time showed extremely rapid increase from the order of 102,103 to 106Pa · s at a certain time, followed by slow increase of the viscosities. Dynamic frequency sweep test of precured epoxy with curing agent was conducted at 90°C. The critical gelation time was obtained by using rheological criterion proposed by Winter and Chambon. We found that the slopes of G,(,) and G,(,) decreased with increasing precuring time. Correspondingly, tan , showed a change from negative to positive slope at a critical time. By using the results, the critical gelation time was determined as t = 895,935 s. Samples of epoxy/curing agent/blowing agent (100/1/0.5) were precured for 960,1620 s. And then precured samples were foamed at 230°C for 300 s to decompose chemical blowing agent. The formed bubble size distribution becomes sharp with increase of the precuring time. There are roughly two sizes of bubbles when precured for relatively short time (t < 1080 s) before foaming: large bubbles (>100 ,m) and small ones (,30 ,m). On the other hand, foams precured for long time (t > 1200 s) before foaming, large bubbles disappear, and the average diameter of the bubble becomes small while the porosity is low. © 2008 Wiley Periodicals, Inc. J Appl Polym Sci, 2008 [source]


    Porous Cellulose Acetate Butyrate Foams with a Tunable Bimodality in Foam Morphology Produced with Supercritical Carbon Dioxide

    MACROMOLECULAR MATERIALS & ENGINEERING, Issue 4 2008
    Leon J. M. Jacobs
    Abstract Porous cellulose acetate butyrate foams with a bimodal cell size distribution were produced using supercritical carbon dioxide as a blowing agent. It is demonstrated that the cell size distribution is tunable, due to the semi-crystalline nature of the polymer. The resulting morphology will either be homogeneous or bimodal, depending on the depressurization rate. Mercury intrusion porosimetry shows that the produced cellulose acetate butyrate foams possess an open cellular structure. [source]


    Effect of Sample Configuration on the Morphology of Foamed LDPE/PP Blends Injection Molded by a Gas Counterpressure Process

    MACROMOLECULAR MATERIALS & ENGINEERING, Issue 6 2007
    Georgi Kotzev
    Abstract Blends of isotactic poly(propylene) and low-density polyethylene with different composition ratios were prepared through direct melt compounding on a twin-screw extruder. The specimens with various geometric configurations were injection-molded using a gas counterpressure process, using blends to which 0.5 wt.-% of a blowing agent was added. The influence of blend composition and specimen geometry on the structure and morphology of the samples was investigated by SEM and WAXS. The thermal behavior of the blends was analyzed by DSC. It was found that the morphology of each region depended on the composition ratio and specimen geometry. [source]


    Use of Nitrogen as a Blowing Agent for the Production of Fine-Celled High-Density Polyethylene Foams,

    MACROMOLECULAR MATERIALS & ENGINEERING, Issue 10 2006
    John W. S. Lee
    Abstract Summary: While many experiments have been performed to examine the effects of administering CO2 as a blowing agent in the foaming process, very few studies have investigated the use of N2 for this purpose. In this study, foaming experiments were conducted in extrusion using HDPE as a polymeric material and N2 as a blowing agent. Talc was used as a nucleating agent, and three different pressure-drop rates were applied to study the effects of pressure-drop rates on HDPE foams. The experimental results revealed that the void fraction of high-density foams blown with N2 was not affected by the die temperature, contrasting the situation in low-density foams. Surprisingly, it was the cell density which determined the void fraction of high-density foams. It was also found that the use of talc significantly increased the cell density and the void fraction of the foams and minimized the role played by the pressure-drop rate in cell nucleation. Effect of N2 content on the cell density of HDPE foams. [source]


    Using Chitosan as a Nucleation Agent in Thermoplastic Foams for Heavy Metal Adsorption

    MACROMOLECULAR SYMPOSIA, Issue 1 2009
    Milton O. Vázquez
    Abstract Thermoplastics/chitosan-powder composite foams were prepared by extrusion using azodicarbonamide (ACA) as chemical blowing agent. The effect of chitosan content on morphology (cell size, nucleation density and foam density) of the foams was studied. Chitosan particles are located on the bubbles periphery. Morphological quantification showed that foam cell size decreased and cell population increased with addition of chitosan into polymeric matrix from 1 to 10%. Further, optimum chitosan content was obtained for each polymer. Polymers foamed with chitosan were tested as a chelating resin to adsorb chromium (Cr VI) from different concentration solutions. [source]


    Dynamics of Foaming of Polystyrene Particles

    MACROMOLECULAR SYMPOSIA, Issue 1 2006
    Gabriela Salejova
    Abstract September 24, 2006 Summary: In this work, we address the industrially relevant problem of the foaming of expandable polystyrene (PS) impregnated by pentane as a traditional down-stream processing in the suspension polymerization of styrene. Once the polystyrene foam is formed by means of a proper foaming agent, e.g., pentane or fluoro- or chloro-hydrocarbons, the blowing agent diffuses out from the cellular structure. Environmental efforts call for the reduced consumption of blowing agents. The dynamics of foaming of polystyrene particles was recorded video-microscopically in our laboratory as the sequence of images of expanding particle located in the small pressure cell placed under the microscope with sufficient depth of focus. The amount of pentane sorbed in PS was controlled by the length of the impregnation period and was determined independently by gravimetric measurements. Strong dependence of the structure of the produced foam and of the foaming dynamics on the amount of sorbed pentane, temperature and particle size is reported and explanations for some observed foaming phenomena are provided. [source]


    The effect of recycling on LDPE foamability: Elongational rheology

    POLYMER ENGINEERING & SCIENCE, Issue 1 2008
    Eddy Twite Kabamba
    The purpose of this work was to investigate changes in the elongational rheology of low density polyethylene (LDPE) when recycled. Both foamed and unfoamed LDPE were submitted up to 10 generations in a closed loop using constant extrusion conditions and azodicarbonamide as a chemical blowing agent. For both foamed and unfoamed polymers, decreasing elongational properties in terms of strain hardening was observed, indicating progressive loss of foamability with the number of time the polymer is recycled. It was also found that the elongational properties of the foamed polymer decreased more rapidly than its unfoamed counterpart. It is believed that higher mechanical degradation of polymer may be the result of higher deformation rates (biaxial) associated with foaming and the accumulation of blowing agent residues limiting polymer chain mobility and entanglement. POLYM. ENG. SCI., 48:11,18, 2008. © 2007 Society of Plastics Engineers [source]


    Expansion mechanisms of plastic/wood-flour composite foams with moisture, dissolved gaseous volatiles, and undissolved gas bubbles,

    POLYMER ENGINEERING & SCIENCE, Issue 7 2003
    G. M. Rizvi
    The large quantity of moisture in wood-flour may lead to the deterioration of the cell structure of foamed plastic wood-flour composites in terms of cell size, non-uniformity, and poor surface quality. Since these anomalies can cause poor mechanical properties of the foamed composites, the removal of the moisture from wood-flour becomes a critical issue with respect to the improvement of these properties. The wood-flour in this experimental study was first oven-dried at different temperatures and then subjected to acetone extraction and thermogravimetric analysis (TGA). The oven-dried wood-flour was blended with plastic and then subjected to extrusion foaming. The results obtained from the TGA studies indicate that most volatiles were released from the extractives. Conversely, a comparative experimental study of the foaming behavior of these plastic/wood-flour composites versus that of undried wood-flour composites confirms that removal of the adsorbed moisture from wood-flour results in a better cell morphology. However, it seems that some gaseous emissions released from wood-flour are soluble in plastic and thereby favorably contribute to the development of the cell morphology. This paper describes the expansion mechanisms of wood-flour composite foams resulting from the adsorbed moisture and dissolved gaseous emissions as well as resulting from the finely dispersed undissolved gas bubbles released from a chemical blowing agent. [source]


    Continuous extrusion of microcellular polycarbonate,

    POLYMER ENGINEERING & SCIENCE, Issue 7 2003
    Richard Gendron
    Extruded microcellular foams have been obtained from mixtures of polycarbonate (PC) and n-pentane. Cell diameters were in the range of 2 to 5 ,m and the foam densities varied between 400 and 700 kg/m3. Although two types of PC have been investigated, one linear and one branched, the presence of side branchings did not modify the extruded foam characteristics. Use of carbon dioxide as the blowing agent was also attempted, and cell sizes below 10 ,m have been successfully obtained. One prerequisite for microcellular foaming was believed to consist in a concentration of the blowing agent close to its limit of solubility as that defined under the actual processing conditions of pressure and temperature. This hypothesis was validated from the observation of extrusion of regular PC foams (intermediate to low densities and cell sizes ranging between 100 ,m and 1 mm) using moderate concentrations of blowing agents, and from solubility and viscosity measurements on similar polymer/blowing agent systems. [source]


    Foaming of PS/wood fiber composites using moisture as a blowing agent

    POLYMER ENGINEERING & SCIENCE, Issue 10 2000
    Ghaus Rizvi
    This paper presents an experimental study on foam processing of polystyrene (PS) and high-impact polystyrene HIPS/wood-fiber composites in extrusion using moisture as a blowing agent. Wood-fiber inherently contains moisture that can potentially be used as a blowing agent. Undried wood-fiber was processed together with PS and HIPS materials in extrusion and wood-fiber composite foams were produced. The cellular morphology and volume expansion ratios of the foamed composites were characterized. Because of the high stiffness of styrenic materials, moisture condensation during cooling after expansion at high temperature did not cause much contraction of the foamed composite and a high volume expansion ratio up to 20 was successfully obtained. The experimental results showed that the expansion ratio could be controlled by varying the processing temperature and the moisture content in the wood fiber. The effects of a small amount of a chemical blowing agent and mineral oil on the cell morphologies of plastic/wood-fiber composite foams were also investigated. [source]


    Melt viscoelasticity of polyethylene terephthalate resins for low density extrusion foaming

    POLYMER ENGINEERING & SCIENCE, Issue 3 2000
    uintans
    The rheological properties of conventional polyethylene terephthalate (PET) resins are not particularly suitable for low density extrusion foaming with physical blowing agents; as a result, chemically modified resins through chain extension/branching reactions are often used. Such resins have overall higher melt viscosity and higher melt strength/melt "elasticity" than unmodified materials. In this work, following a review of the prior art on PET chemical modification, an unmodified and a chemically modified resin were selected and characterized for their melt viscoelastic properties including shear and dynamic complex viscosity over a broad shear rate/frequency range, storage and loss modulus, and die swell. Certain rheological models were found to provide better fits of the entire viscosity curve for the unmodified vs. the modified resin. Foamed extrudates having variable densities (from about 1.2 to 0.2 g/cc), were prepared by carbon dioxide injection in monolayer flat sheet extrusion equipment. Foams with increasingly lower density, below 0.5 g/cc, were obtained by increasing gas pressure only in the case of the chemically modified resin. The effects of variables such as concentration of the physical blowing agent, resin rheology, resin thermal properties and choice of process conditions are related to product characteristics including density, cell size and crystallinity. [source]


    Visualization of the foaming mechanism of polyethylene blown by chemical blowing agents under ambient pressure

    ADVANCES IN POLYMER TECHNOLOGY, Issue 4 2007
    Remon Pop-Iliev
    Abstract Understanding the fundamental mechanisms that govern the foaming process is the most essential universal prerequisite for developing effective processing strategies for fabricating high-quality foamed plastic products using any type of foaming technology. Despite chemically blown foaming of thermoplastics under atmospheric pressure has been successfully implemented in rotational foam molding over the last decade, the related open literature does not provide substantial research addressing the fundamentals of this unique foaming mechanism. The present study focuses on clarifying the fundamental foaming mechanisms that govern the successful manufacture of thermoplastic foams using a chemical blowing agent under low-pressure (atmospheric) conditions. The presented research is mainly based on observing a series of visualization experiments conducted using a custom-made visualization system including an optical microscope and a computerized CCD camera imaging system, which was utilized for investigating the behavior of foamable polyethylene samples prepared by using the compression-molding method. © 2008 Wiley Periodicals, Inc. Adv Polym Techn 26:213,222, 2007; Published online in Wiley InterScience (www.interscience.wiley.com). DOI 10.1002/adv.20102 [source]


    Development of poly(vinyl chloride)/wood composites.

    JOURNAL OF VINYL & ADDITIVE TECHNOLOGY, Issue 2 2004
    A literature review
    Poly(vinyl chloride)/wood fiber (flour) composites are currently experiencing a dramatic increase in use. Most of them are used to produce window/door profiles, decking, railing, and siding by using conical counterrotating intermeshing twin-screw extruders. Heat stabilizers, processing aids, impact modifiers, lubricants, and pigments are still important for PVC/wood composite formulations. Poly[methylene(polyphenyl isocyanate)] (PMPPIC), ,-aminopropyltriethoxysilane, maleated polypropylene (MAPP), and copper metallic complex have proved to be effective coupling agents for this composite system. Mechanical properties of PVC/wood composites can be enhanced by combining wood with mica or glass fibers to form hybrid reinforcements. Ultraviolet light resistance and weathering dimensional stabilities of PVC/wood composites are superior to those of natural wood. Density reduction can be achieved through the microcellular foaming technique by using chemical blowing agents, such as azodicarbonamide and sodium bicarbonate, or physical blowing agents, such as carbon dioxide. J. Vinyl Addit. Technol. 10:59,69, 2004. © 2004 Society of Plastics Engineers. [source]


    Dynamics of Foaming of Polystyrene Particles

    MACROMOLECULAR SYMPOSIA, Issue 1 2006
    Gabriela Salejova
    Abstract September 24, 2006 Summary: In this work, we address the industrially relevant problem of the foaming of expandable polystyrene (PS) impregnated by pentane as a traditional down-stream processing in the suspension polymerization of styrene. Once the polystyrene foam is formed by means of a proper foaming agent, e.g., pentane or fluoro- or chloro-hydrocarbons, the blowing agent diffuses out from the cellular structure. Environmental efforts call for the reduced consumption of blowing agents. The dynamics of foaming of polystyrene particles was recorded video-microscopically in our laboratory as the sequence of images of expanding particle located in the small pressure cell placed under the microscope with sufficient depth of focus. The amount of pentane sorbed in PS was controlled by the length of the impregnation period and was determined independently by gravimetric measurements. Strong dependence of the structure of the produced foam and of the foaming dynamics on the amount of sorbed pentane, temperature and particle size is reported and explanations for some observed foaming phenomena are provided. [source]


    Modeling the phase behavior in binary mixtures involving blowing agents and thermoplastic resins,

    POLYMER ENGINEERING & SCIENCE, Issue 2 2010
    Pedro F. Arce
    The thermophysical properties of mixtures of thermoplastic resins and blowing agents, together with the knowledge of the solubilities of these components, are the basis for the manufacturing of plastic foams. In this work, the solubilities of blowing agents trichlorofluoromethane, dichlorodifluoromethane, chlorodifluoromehane, and 1,2-dichloro-1,1,2,2-tetrafluoroethane in thermoplastic resins poly(styrene), high density poly(ethylene), low density poly(ethylene), poly(propylene), poly(vinyl chloride), poly(carbonate) and poly(propylene oxide) were modeled by using the Perturbed Chain-Statistical Associating Fluid Theory (PC-SAFT) and the Sánchez-Lacombe equations of state (EoS), fitting a single temperature-dependent binary interaction parameter. PC-SAFT is a theoretically based equation of state with three pure component parameters that describe efficiently the thermodynamics of complex systems. Earlier works with this EoS have already predicted the phase coexistence properties of various refrigerants and higher order alkane series compounds, along with their mixtures. The pure component parameters for the blowing agents were obtained by regression of vapor pressure and liquid density data, while the pure component parameters for the thermoplastic resins were obtained by regression of pure liquid PVT data. The parameter estimation was performed by using a modified maximum likelihood method. The solubility results obtained with both EoS have been compared; the results from PC-SAFT showed a higher accuracy in terms of solubility pressure deviations. POLYM. ENG. SCI., 2009. © 2009 Society of Plastics Engineers [source]


    Conventional and nanometric nucleating agents in poly(,-caprolactone) foaming: Crystals vs. bubbles nucleation

    POLYMER ENGINEERING & SCIENCE, Issue 2 2008
    Carlo Marrazzo
    The aim of this article was to investigate the nucleating ability of different nucleating agents for the foaming of poly(,-caprolactone), a biodegradable, semicrystalline polymer. In particular, the efficiency of the nucleating agent in inducing the formation of the gaseous phase has been compared to the efficiency in inducing the formation of the crystalline phase. In effect, in foaming of semicrystalline polymers, bubble nucleation and crystal nucleation are concurrent and somehow interacting phenomena. Here, these two aspects have been evidenced and clarified. Foams were prepared by using a batch process with the pressure quench method, with nitrogen and carbon dioxide as the blowing agents. Conventional and novel nucleating agents were used: talc has been compared to several novel nanometric particles of different geometries and dimensions, such as titanium dioxide and alumina powders, exfoliated and intercalated clays, and carbon nanotubes. Foam densities and morphologies, in terms of number of cells per initial unit volume, were measured and found to depend both on crystalline phase nucleation and gaseous phase nucleation. In fact, the different nucleating agents, depending on shape, dimension, and surface functionalization, selectively nucleated the crystallites and/or the bubbles, affecting, respectively, bubble growth (and, hence, final foam density) and bubble nucleation (and, hence, cell number density,morphology). POLYM. ENG. SCI., 2008. © 2007 Society of Plastics Engineers [source]


    Long-term performance of environmentally-friendly blown polyurethane foams

    POLYMER ENGINEERING & SCIENCE, Issue 3 2005
    M. Modesti
    We studied the long-term performance of new environmentally-friendly blowing agents for polyurethane foams. Several blowing agents, hydrofluorocarbons, hydrocarbons, and a possible hydrochlorofluorocarbon substitute (dimethoxymethane), as well as hydrochlorofluorocarbons, were analyzed. The determination of effective diffusion coefficients (knowledge of which is required to study long-term performance) was performed by means of a classical gas chromatographic technique and by a new method based on infrared spectroscopy. The reliability of the experimental procedure used is showed by comparing experimental and predicted aging, as the slope of the aging curve (i.e., thermal conductivity vs. time) depends only on effective diffusion coefficients. Our study of long-term performance of foams blown with alternative blowing agents shows that hydrofluorocarbons represent a proper alternative to hydrochlorofluorocarbons, as the foams show similar initial thermal conductivity and a slower aging rate (i.e., better long-term performance). POLYM. ENG. SCI. 45:260,270, 2005. © 2005 Society of Plastics Engineers. [source]


    Continuous extrusion of microcellular polycarbonate,

    POLYMER ENGINEERING & SCIENCE, Issue 7 2003
    Richard Gendron
    Extruded microcellular foams have been obtained from mixtures of polycarbonate (PC) and n-pentane. Cell diameters were in the range of 2 to 5 ,m and the foam densities varied between 400 and 700 kg/m3. Although two types of PC have been investigated, one linear and one branched, the presence of side branchings did not modify the extruded foam characteristics. Use of carbon dioxide as the blowing agent was also attempted, and cell sizes below 10 ,m have been successfully obtained. One prerequisite for microcellular foaming was believed to consist in a concentration of the blowing agent close to its limit of solubility as that defined under the actual processing conditions of pressure and temperature. This hypothesis was validated from the observation of extrusion of regular PC foams (intermediate to low densities and cell sizes ranging between 100 ,m and 1 mm) using moderate concentrations of blowing agents, and from solubility and viscosity measurements on similar polymer/blowing agent systems. [source]


    Melt viscoelasticity of polyethylene terephthalate resins for low density extrusion foaming

    POLYMER ENGINEERING & SCIENCE, Issue 3 2000
    uintans
    The rheological properties of conventional polyethylene terephthalate (PET) resins are not particularly suitable for low density extrusion foaming with physical blowing agents; as a result, chemically modified resins through chain extension/branching reactions are often used. Such resins have overall higher melt viscosity and higher melt strength/melt "elasticity" than unmodified materials. In this work, following a review of the prior art on PET chemical modification, an unmodified and a chemically modified resin were selected and characterized for their melt viscoelastic properties including shear and dynamic complex viscosity over a broad shear rate/frequency range, storage and loss modulus, and die swell. Certain rheological models were found to provide better fits of the entire viscosity curve for the unmodified vs. the modified resin. Foamed extrudates having variable densities (from about 1.2 to 0.2 g/cc), were prepared by carbon dioxide injection in monolayer flat sheet extrusion equipment. Foams with increasingly lower density, below 0.5 g/cc, were obtained by increasing gas pressure only in the case of the chemically modified resin. The effects of variables such as concentration of the physical blowing agent, resin rheology, resin thermal properties and choice of process conditions are related to product characteristics including density, cell size and crystallinity. [source]