Foaming Conditions Research Articles

Electromagnetic shielding effectiveness of polycarbonate/graphene nanocomposite foams processed in 2-steps with supercritical carbon dioxide

The electromagnetic interference (EMI) shielding properties of polycarbonate/graphene composites foamed with supercritical carbon dioxide were investigated as a function of cellular morphology and graphene particle dispersion. The 2-step foaming method used was found to improve graphene dispersion and led to a different cellular structure compared to traditional 1-step foaming. Reflection was found to be the dominant EMI shielding mechanism and EMI shielding effectiveness was improved with large cell morphology that promoted isotropic/random orientation of graphene particles. A maximum EMI specific shielding effectiveness of ~78dBcm3/g was achieved in foams, which was more than 70 times higher than that of the unfoamed polymer (1.1dBcm3/g). The study shows that by controlling foaming process conditions and nanoparticle characteristics, it is possible to improve multiple properties while achieving lightweight materials suitable for various applications.

Batch foaming of carboxylated multiwalled carbon nanotube/poly(ether imide) nanocomposites: The influence of the carbon nanotube aspect ratio on the cellular morphology

ABSTRACTA series of microcellular poly(ether imide) (PEI) foams and nanocellular carboxylated multiwalled carbon nanotube (MWCNT‐COOH)/PEI foams were prepared by the batch foaming method. MWCNT‐COOHs with different aspect ratios were introduced into the PEI matrix as heterogeneous nucleation agents to improve the cell morphology of the microcellular PEI foams. The effect of the aspect ratio of the MWCNT‐COOHs on the cellular morphology, and gas diffusion is discussed. The results show that with the addition of MWCNT‐COOH, the sorption curve showed a slight reduction of carbon dioxide solubility, but the gas diffusion rate could be improved. The proper aspect ratio of MWCNT‐COOH could improve the cellular morphology under the same foaming conditions, in which m‐MWCNT‐COOH (aspect ratio ≈ 1333) was the best heterogeneous nucleation agent. When the foaming temperature was 170°C, the cell size and cell density of nanocellular m‐MWCNT‐COOH reduced to 180 nm and increased to 1.58 × 1013 cells/cm3, respectively. © 2015 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2015, 132, 42325.

Fabrication of highly insulating foam glass made from CRT panel glass

We prepared low-density foam glasses from cathode-ray-tube panel glass using carbon and MnO2 as the foaming agents. We investigated the influence of the carbon and MnO2 concentrations, the glass-powder preparation and the foaming conditions on the density and homogeneity of the pore structure and the dependence of the thermal conductivity on the foam density. The results show that the moderate foaming effect of the carbon is greatly improved by the addition of MnO2. A density as low as 131kgm−3 can be achieved with fine glass powder. The foam density has a slight dependence on the carbon and MnO2 concentrations, but it is mainly affected by the foaming temperature and the time. The thermal conductivity of the foam-glass samples is lower than that of commercial foam glasses with the same density. The lowest value was determined to be 42mWm−1K−1 for a foam glass with a density of 131kgm−3. A further improvement in the closed porosity could potentially decrease the thermal conductivity even further, and thus our approach has great potential in terms of a thermal insulation material.

Preparation of poly(propylene carbonate)/nano calcium carbonate composites and their supercritical carbon dioxide foaming behavior

ABSTRACTBiodegradable polymer foams are attracting extensive attention in both academic and industrial fields. In this study, an emerging biodegradable polymer, poly(propylene carbonate) (PPC), was compounded with nano calcium carbonate (nano‐CaCO3) and foamed via supercritical carbon dioxide for the first time. Four concentrations of nano‐CaCO3, 1, 3, 5, and 10 wt %, were used and the thermal properties of PPC/nano‐CaCO3 composites were investigated. The glass‐transition temperature and thermal decomposition temperature of the PPC/nano‐CaCO3 composites increased with the addition of nano‐CaCO3. The morphologies of the PPC/nano‐CaCO3 composites and the rheological results showed that homogeneous dispersions of nano‐CaCO3 and percolated nano‐CaCO3 networks were achieved at a nano‐CaCO3 content of 3 wt %. Therefore, the finest cell diameter (3.13 μm) and highest cell density (6.02 × 109 cells/cm3) were obtained at the same nano‐CaCO3 content. The cell structure dependences of PPC and PPC with a nano‐CaCO3 content of 3 wt % (PPC‐3) foams on the foaming pressure and temperature were investigated as well. The results suggested that the cell structure of PPC‐3 was more stable at different foaming conditions due to the networks of nano‐CaCO3. Moreover, the change in pressure was more influential on the cell structure than the temperature. © 2015 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2015, 132, 42248.

Graded porous polyurethane foam: A potential scaffold for oro-maxillary bone regeneration

Bone tissue engineering applications demand for biomaterials offering a substrate for cell adhesion, migration, and proliferation, while inferring suitable mechanical properties to the construct. In the present study, polyurethane (PU) foams were synthesized to develop a graded porous material-characterized by a dense shell and a porous core-for the treatment of oro-maxillary bone defects. Foam was synthesized via a one-pot reaction starting from a polyisocyanate and a biocompatible polyester diol, using water as a foaming agent. Different foaming conditions were examined, with the aim of creating a dense/porous functional graded material that would perform at the same time as an osteoconductive scaffold for bone defect regeneration and as a membrane-barrier to gingival tissue ingrowth. The obtained PU was characterized in terms of morphological and mechanical properties. Biocompatibility assessment was performed in combination with bone-marrow-derived human mesenchymal stromal cells (hBMSCs). Our findings confirm that the material is potentially suitable for guided bone regeneration applications.

Effect of polystyrene long branch chains on melt behavior and foaming performance of poly(vinyl chloride)/graphene nanocomposites

Several poly(vinyl chloride)-g-polystyrene graft copolymers (PVC-g-PS) with well defined molecular structures were synthesized via atom transfer radical polymerization (ATRP) from the structural defects of PVC. The effects of PS branch chains on the shear and extensional rheology as well as foaming properties were investigated. Compared to linear PVC, the introduction of PS branches results in increased complex viscosity, an elevated value of storage modulus at low shear frequencies, more pronounced shear-thinning behavior, more significant upshifted deviation from linear behaviour and a strain hardening phenomenon. Under the same foaming conditions, most of the resulting PVC-g-PS foams exhibit a closed cell structure, increased cell density and uniform cell size distribution while the linear PVC foam has serious cell coalescence. Moreover, graphene nanosheets could be well dispersed in the PVC-g-PS matrix due to the π–π stacking with PS relative to the PVC without PS branch chains. As expected, both the nucleation effect and increased melt viscosity from well-dispersed graphene sheets significantly improve the foaming behavior of PVC-g-PS/graphene nanocomposites, in comparison with the poor foamability of PVC/graphene composites due to the non-uniform dispersion of graphene.

Generation of nanocellular foams from ABS terpolymers

ABS nano-cellular foams have been produced using a gaseous CO2 foaming process. ABS materials have been investigated in this study because of their specific morphologies, which can increase the nuclei density by creating heterogeneous nucleation near the interfaces between acrylonitrile–styrene and butadiene phases during the foaming process. This study focuses on the foaming of different ABS materials with a batch process using gaseous CO2 and presents the influence of the initial microstructures of ABS materials on their final foam structures. In specific cases, depending on initial ABS microstructures and also on foaming conditions, nano-cellular materials have been produced with foam double structures and effective porosity with 100nm diameter open cells.

Biopolymer foaming with supercritical CO2—Thermodynamics, foaming behaviour and mechanical characteristics

Polymer foams, especially those based on biodegradable polymers, are in high demand for energy saving applications, for example as thermal insulations or packaging materials. To understand and predict the quality and material properties of polymer foams, concise knowledge of the factors influencing the foaming behaviour, especially pressure and temperature, is required. Therefore, three biodegradable polyesters, namely poly (lactide) (PLA), poly (butylene succinate) (PBS) and a blend of poly (lactide) and poly (hydroxy butyrate) (PLA-PHB), have been subjected to a direct foaming procedure using compressed carbon dioxide as blowing agent, studying the influence of saturation temperature (ranging from 95°C to 175°C) and applied pressure (ranging from atmospheric pressure to 30MPa) on the resulting foam material. As these results are strongly depending on the melting behaviour of the polymers, all three polymers were subjected to calorimetric analysis in a scanning transitiometer that allows for applying pressure levels of up to 45MPa. The created porous materials were characterized by determining their density, porosity and morphology, using SEM analysis. Their mechanical behaviour was investigated by using compressive strength tests. It is shown that the quality of the produced foam structures and its properties is strongly depending on the foaming conditions. In order to obtain foams with a high quality, the saturation temperature and pressure have to be adapted to the phase transition liquid–solid of the polymer–gas system. The results obtained via scanning transitiometer represent the SLG-line of the binary systems polymer and CO2, and their influence on the foaming behaviour enabled the identification of ideal foaming conditions for the three polymers regarded in this study.

A Novel Strategy for Achieving High Melt Strength Polypropylene and an Investigation of Its Foamability

A novel and feasible strategy for preparing high melt strength polypropylene (HMSPP) was developed by a melt grafting reaction in the presence of macro-monomer vinyl polydimethylsiloxane (VS), co-monomer styrene (St), and initiator benzoyl peroxide through a one-step reactive extrusion. The rheological behaviors, melt strength, and foaming ability of HMSPP were studied. The results showed that VS and St were successfully grafted onto polypropylene (PP), and the weight average molecular weight, molecular weight distribution, and melt strength of HMSPP were dramatically increased compared with those of the virgin isotactic polypropylene (iPP). Especially, the melt strength of HMSPP increased from 0.022 N for the virgin iPP to 0.29 N, which made the foamability of HMSPP significantly improved when supercritical carbon dioxide was used as the blowing agent. The foaming condition was optimized to 160°C and 14 MPa, for which HMSPP foams with a high expansion ratio of 66 times and a high cell density of about 5.8×107 cell/cm3 were obtained, while the virgin iPP did not yield foams with good cell structure. Moreover, the resultant HMSPP could be foamed in a remarkably wide temperature range from 145°C to 165°C, which would be of great significance for industrial application.

Cell structure and impact properties of foamed polystyrene in constrained conditions using supercritical carbon dioxide

To obtain cellular with small cell diameter, to control cell structure and to improve impact strength of foaming materials, the quick-heating method was applied for foaming polystyrene (PS) using supercritical CO2 (Sc-CO2) as physical blowing agent. Then, changes of cell structure and impact strength in microcellular foamed PS materials under constrained conditions were studied. The effects of foaming processing parameters, such as foaming temperature, saturation pressure and foaming time on the cell structure and impact strength of foamed PS in the constrained conditions were studied. The results showed that the Sc-CO2 solubility and nucleation density in the constrained conditions were not influenced compared with those under free foaming conditions. However, cells in constrained foaming process are mostly circular and independent with thick cell walls; the phenomenon of cell coalescence and collapse was effectively eliminated under constrained conditions. In addition, cell diameters in constrained foaming process decrease with increase in foaming temperature and increase with increase in the foaming time. Compared with that in free foaming conditions, the cell growth was restrained dramatically under constrained conditions which resulted in smaller cell diameter. Moreover, higher impact strength could be obtained for foamed PS as foaming time was prolonged, foaming temperature was increased or saturation pressure was enhanced.

Postural stability limits in manifest and premanifest Huntington’s disease under different sensory conditions

Increasing evidence indicates that Huntington’s disease (HD) produces postural control impairments even before the clinical diagnosis. It has been suggested that postural disorders of HD patients are explained by deficits in the processing and integration of sensory information, but this hypothesis has been under-explored. In the present study, we evaluated the amplitude of the center of pressure (COP) displacement during maximum leaning in four directions (forward, backward, rightward and leftward) and under three sensory conditions (eyes open, eyes closed and eyes closed standing on foam). We assessed the stability limits in 20 individuals with a positive HD genetic test (12 premanifests; eight manifests HD) and 15 healthy controls. The COP displacements were analyzed during the first and second phases of maintenance of the maximum leaning position. Manifest HD patients showed significantly greater COP ranges than healthy controls in both learning phases and all sensory conditions, but the greatest deterioration of their performance was found in the foam condition. In contrast, premanifest HD patients displayed larger COP ranges than controls only during the second phase of maximum learning, especially in the foam condition. Furthermore, both HD groups had significantly smaller limits of stability than healthy subjects during the second phase of maximum learning. However, their ability to maintain the maximum leaning position was degraded during both learning phases. Together, these findings demonstrate that HD reduces the limits of stability even before the clinical disease onset. Furthermore, our results indicate that dynamic postural tasks with high demand for sensorimotor integration and especially the use of proprioception are highly sensitive to early HD disease processes. This dynamic postural task may become a useful biomarker of HD progression.

Influence of expansion cooling regime on morphology of poly(ε‐caprolactone) foams prepared by pressure quenching using supercritical CO2

Creation of foam structures from hydrolytically degradable poly(ε‐caprolactone) (PCL) is a current task in biomaterial research. One example are degradable scaffolds. The thermodynamic and kinetic conditions in a supercritical CO2 (scCO2) supported foaming process of PCL can influence the resulting morphology of the foam. PCL foaming with scCO2 was systematically investigated in the pressure range from 78 to 200 bar at temperatures between 25°C and 50°C with the help of a view cell. PCL foams could be obtained at both conditions above the pressure dependent melting temperature as well as below this temperature, i.e. from supercooled melt states. Differential scanning calorimetry investigations of the PCL foam samples were used for the analysis of the relationship between pore morphology and foaming conditions. Three characteristic regions could be distinguished in the PCL/CO2 phase diagram. Only when the foaming was conducted above the critical temperature of CO2, a significant influence of the depressurization rate could be observed. Here, an increase in the quenching rate resulted in a decreasing pore size while the pore density was found to increase. Copyright © 2014 John Wiley & Sons, Ltd.

Optimization of Foaming Condition and Drying Behavior of White Button Mushroom (A garicus bisporus )

Foaming conditions of button mushroom (Agaricus bisporus) puree were optimized using response surface methodology with respect to cress seed gum concentration (0.3–0.6% w/w), mushroom puree to water ratio (1:0.5–1:2.5 w/w) and whipping time (2–8 min) for minimum foam density and foam drainage volume as response variables. Finally, optimized foam was dried at 50, 65 and 80C to an equilibrium moisture content using a hot air dryer, and values of effective diffusivities and activation energy were determined. The optimized conditions were found at cress seed gum concentration = 0.57% w/w, mushroom puree to water ratio = 1:0.5 and whipping time = 6.49 min. The predicted values of foam density and foam drainage volume were 0.58 g/cm3 and 2.9 mL, respectively. The effective moisture diffusivity of mushroom foam mats ranged from 4.765 to 10.42 × 10–9 m2/s. Practical Applications The white button mushroom is the most popular edible mushrooms with short shelf life. One approach intended to increase consumption of mushroom is to produce mushroom powder for using as an ingredient into instant soup, snacks, baby foods and other products. Foam mat drying is a novel, improved and economical method for drying liquid or semiliquid foods to obtain products with desired properties. Preparation of the stable foam plays major role in foam mat drying. In this context, foaming condition of white mushroom was optimized and drying behavior was studied.

Experimental study and modeling of nanofoams formation from single phase acrylic copolymers

Medium to low density thermoplastic nanofoams have previously been produced using nanoparticles as nucleating center. Here we show that by designing the molecular structure of the polymer matrix to achieve high CO2 solubility while controlling the glass transition temperature, it is possible to produce nanofoams with cell nucleation densities as high as 1016/cm3 without introducing nucleation aids. This was achieved by maximizing foam expansion without uncontrolled cell ripening for a series of acrylic copolymers, which were foamed under a set of standard conditions. To predict the role of foaming conditions on foam characteristics, a theoretical foaming model was built to simulate cell nucleation, growth and foam stabilization. Experimental or predicted properties of the polymer/carbon dioxide mixture were used as inputs. Despite simplifying assumptions, such as the use of classical nucleation equations, the semi-quantitative model provides insight into the foam expansion behavior and validates experimental observations.

Burning characteristics of microcellular combustible objects

Abstract Microcellular combustible objects for application of combustible case, caseless ammunition or combustible detonator-holding tubes are fabricated through one-step foaming process, in which supercritical CO 2 is used as foaming agent. The formulations consist of inert polymer binder and ultra fine RDX. For the inner porous structures of microcellular combustible objects, the cell sizes present a unimodal or bimodal distribution by adjusting the foaming conditions. Closed bomb test is to investigate the influence of both porous structure style and RDX content on burning behavior. The sample with bimodal distribution of cell sizes burns faster than that with unimodal distribution, and the concentration of RDX can influence the burning characteristics in a positive manner. In addition, the translation of laminar burning to convective burning is determined by burning rate versus pressure curves of samples at two different loading densities, and the resulting transition pressure is 30 MPa. Moreover, the samples with bigger sample size present higher burning rate, resulting in providing deeper convective depth. Dynamic vivacity of samples is also studied. The results show that the vivacity increases with RDX content and varies with inner structure.

Experimental Study on Foamed Asphalt Warm Mix Technology

Usually, foamed asphalt as cold recycling mixture binder, study on foamed asphalt warm mix technology was limited in China. Aimed at the asphalt foaming characteristic, the paper put forward the best asphalt foaming condition and carried out indoor and outdoor experiment to study the road performance of warm mixed asphalt mixture. The paper proposed the maturation curing time concept and its evaluation method. Results indicated that the warm mixed asphalt mixtures road performance can meet the HMA specification requirement in a lower temperature of construction, and low-temperature crack resistance was better than the tradition hot mix asphalt mixture so the warm mix foamed mixture has a remarkable economic and society benefit.

Features of the foaming of acrylamide-acrylic acid copolymers

The processes that occur during the processing and foaming of thermosetting composites based on a random copolymer of acrylamide and acrylic acid—softening, foaming, and curing of the copolymer—are studied with the use of methods of chemical kinetics, Fourier transform infrared spectroscopy, and thermomechanical analysis. The above processes are coordinated with respect to time and temperature; prognostic methods for calculating the dynamics of these processes and the properties of foam materials as functions of the composition of the original foam-forming composite and the foaming conditions are proposed.

Assessment of instream foam formation and quantification of foam in effluents

Although the foam formation on surface waters nowadays is not comparable with the foam "mountains" in the 1970s, it still is an issue of water quality concern. A drawback in the discussion is the lack of methods to assess instream foam formation and foam emitted by point sources. Foam formation on a transboundary river in Austria led to an intensive study resulting in two parameters to quantify instream and emitted foam. Foam potential is introduced as emission parameter that is defined as flow rate of river water, which can foam due to an effluent's discharge. The foam index (FI) represents a parameter to assess the foam on the river and allows a semi-quantitative differentiation between the varying foaming conditions. This publication will present the developed methods and show some results to prove their accuracy and applicability.

Extrusion foaming of PHBV

This paper reports work on extrusion foaming of poly(3-hydroxybutyrate- co-3-hydroxyvalerate) with a chemical blowing agent based on sodium bicarbonate and citric acid and calcium carbonate nucleation agent. It includes investigations in the effects of rheological behaviour of the polymer, blowing agent, nucleation agent and processing conditions on the foam density and morphology. The poly(3-hydroxybutyrate- co-3-hydroxyvalerate) is a natural biodegradable polyester with high crystallinity, low melt viscosity and slow crystallisation rate and high sensitivity to the thermal degradation at temperatures above its melting point, making it particularly difficult to control the foaming process. Use of negative gradient temperature profile was found beneficial to minimise the thermal degradation and achieve necessary melt strength to stabilise the cell structure. Solidification of the super-cooled polymer melt occurring at the die was discussed in relation to the selection of the temperature profile and rheological behaviour and solidification of the poly(3-hydroxybutyrate- co-3-hydroxyvalerate) characterised by rotational rheometry. In addition to extrusion foaming conditions, effect of the blowing and nucleation agents on rheology of the polymer, the cell refinement on foam density and morphology were discussed. The poly(3-hydroxybutyrate- co-3-hydroxyvalerate) was extruded with a twin screw extruder fitted with a strand die yielding up to 60% density reduction with uniform fine cell structure.

Optimization of Foaming Parameters and Investigating the Effects of Drying Temperature on the Foam-Mat Drying of Shrimp (Penaeus indicus)

In this study, foaming conditions of shrimp (Penaeus indicus) were optimized using response surface methodology (RSM) and the effect of drying temperature on drying behavior was investigated. The experiments were conducted according to face-centered central composite design for three independent variables: xanthan gum concentration (0.1–0.4% w/w), whipping time (2–6 min), and water : shrimp ratio (2:1–6:1 w/w) to minimize the foam density (FD) and the drainage volume (DV) as responses. Statistical analysis of results showed that linear terms of the models were significant (p < 0.01) except the linear term of whipping time in DV. Xanthan gum concentration 0.19% (w/w), water : shrimp ratio 4.5:1 (w/w), and whipping time 5.89 min were found to be the optimum foaming conditions. The effect of different drying temperatures (45, 60, 75, and 90°C) on drying behavior of optimized foam was then evaluated. The drying air temperature had a considerable effect on drying time and drying rate. As the temperature increased from 45 to 90°C, the drying time decreased to 90 min. Drying rate curves showed that foam-mat drying of shrimp principally occurred in the constant rate period. Different mathematical models were tested with the drying behavior of shrimp foam in the dryer. According to the results, the Weibull distribution model is superior to the other models for explaining the drying behavior. Effective moisture diffusivity was calculated and was between 1.114 × 10−8 and 3.951 × 10−8 m2/s within the studied temperature range. An Arrhenius relation with an activation energy value of 26.89 kJ/mol expressed the effect of temperature on diffusivity.