Foaming Conditions Research Articles

A simple method for preparation of microcellularPLA/calcium carbonate nanocomposite using super critical nitrogen as a blowing agent: Control of microstructure

AbstractA simple method was used to prepare microcellular foams of poly(lactic acid) (PLA) and its nanocomposites to improve its shortcomings such as low impact resistance and high cost. The batch foaming process of purePLAandPLAfilled with Nano calcium carbonate (NCC) was conducted using supercritical nitrogen (N2) as a blowing agent. The effect ofNCCon crystallization ofPLAis discussed as a remarkable parameter in foaming of semicrystalline polymers. Differential scanning calorimetry (DSC) was used to optimize the process temperature. The effect of foaming conditions (temperature, pressure, and cooling rate) and nanoparticle content on the foam microstructure ofPLAand its nanocomposites were investigated using scanning electron microscopy (SEM). Foams were obtained in the range of macro‐ and microscale (different cell sizes) using different foaming conditions. The results revealed that nanoparticles show excellent nucleation performance onPLAfoaming. Results of dynamic mechanical thermal analysis (DMTA) also showed significant influences ofNCCon foamed and prefoamed samples to different foaming structures.

Features of the motion of gel particles in a three-phase bubble column under foaming and non-foaming conditions

Fil: Salierno, Gabriel Leonardo. Consejo Nacional de Investigaciones Cientificas y Tecnicas; Argentina. Universidad de Buenos Aires. Facultad de Ciencias Exactas y Naturales. Departamento de Industrias; Argentina

Effect of matrix−nanoparticle supramolecular interactions on the morphology and mechanical properties of polymer foams

AbstractIn this study, we report the fabrication of supramolecular polymer nanocomposite foams with a uniform cell structure, high cell density and high expansion ratio using a soft matrix of poly(methyl acrylate‐co‐2‐hydroxyethyl methacrylate) and silica nanoparticle fillers, both functionalized with ureido‐pyrimidinone (UPy) supramolecular groups. Microcellular structures were formed using a batch foaming process at 90 °C under a 9 MPa nitrogen atmosphere. Nanocomposites were characterized and compared before and after the foaming process to investigate the effect of supramolecular interactions on the thermomechanical properties and morphology of the foams. TEM images revealed that while strong inter‐filler supramolecular interactions do not have a positive effect on their dispersion state, matrix−filler interactions derived from hydrogen bonding UPy motifs result in a rather uniform distribution of nanoparticles. Competing filler−filler and matrix−filler supramolecular interactions can be balanced and optimized by adjusting UPy populations along the chains and on the surface of nanoparticles. At a given chain functionality, increasing the nanoparticle loading up to an optimum concentration improves the mechanical properties and formability of the system. Above such concentration strong interactions between fillers, which are not compensated by the matrix, result in large aggregates and consequently undermine the material performance. Supramolecular polymer foams illustrate a similar thermal and viscoelastic behavior to that of neat samples but after foaming, due to the formation of a cellular structure and rearrangement or dissociation of UPy dimers under the foaming conditions, the elastic modulus is reduced. © 2018 Society of Chemical Industry

Inertial Sensor-Based Assessment of Central Sensory Integration for Balance After Mild Traumatic Brain Injury.

Optimal balance control requires a complex integration of sensory information from the visual, vestibular, and proprioceptive systems. The goal of this study is to determine if the instrumented modified Clinical Test of Sensory Integration and Balance (mCTSIB) was impaired acutely after mild traumatic brain injury (mTBI) when postural sway under varying sensory conditions was measured with a wearable inertial sensor. Postural sway was assessed in athletes who had sustained a mTBI within the past 2-3 d (n = 38) and control athletes (n = 81). Postural sway was quantified with a wearable inertial sensor (Opal; APDM, Inc.) during four varying sensory conditions of quiet stance: (1) eyes open (EO) firm surface, (2) eyes closed (EC) firm surface, (3) eyes open (EO) foam surface, and (4) eyes closed (EC) foam surface. Sensory reweighting deficits were computed by comparing the postural sway area in eyes closed versus eyes open conditions for firm and foam condition. Postural sway was higher for mTBI compared with the control group during three of the four conditions of instrumented mCTSIB (EO firm, EC firm, and EC foam; p < 0.05). Sensory reweighting deficits were evident for mTBI individuals compared with control group on foam surface (EC firm vs EO firm; p < 0.05) and not on firm surface (EC firm vs EO firm; p = 0.63). The results from this study highlight the importance of detecting postural sway deficits during sensorimotor integration in mild TBI individuals.

Silk fibroin porous scaffolds by N2O foaming

Silk fibroin has acquired increasing interest for biomedical applications, and namely for the fabrication of scaffolds for tissue engineering, because of its highly positive biological interaction and the possibility to adapt the material to several application requirements by adopting different fabrication methods, in order to make films, sponges, fibers, nets or gels with predictable degradation times. For tissue engineering, in most cases porous scaffolds are required, in some cases possibly in situ forming and therefore fabricated in mild body-compatible conditions. In this work, we present a novel one-step method for the preparation of silk fibroin foams starting from water solutions and using low-pressure nitrous oxide gas as foaming agent. This foaming technique allows preparing fibroin porous scaffolds with easily tunable porosity, in mild processing conditions with the use of a relatively inert foaming agent saturating a fibroin water solution, that could be occasionally injected through a thin needle in the implantation site where expansion and foaming would occur. Optimal foaming processing conditions have been investigated, and the prepared foams have been characterized with Fourier Transform Infrared Spectroscopy (FTIR) compressive mechanical and rheological properties measurements, and by scanning electron microscopy and microCT.

The Effects of Foaming Conditions on Plasticized Polyvinyl Chloride Foam Morphology by using Supercritical Carbon Dioxide

This research studies the effects of foaming conditions by using supercritical (scCO2) as a physical blowing agent on plasticized polyvinyl chloride (PVC) foam morphology. Foaming conditions were foaming temperature of 40, 60, and 80 oC, foaming pressure of 120, 150, and 170 bar at constant soaking time of 30 min. Depressurization was employed to activate nucleation and samples were cooled at room temperature about 30 oC for stabilization, which cause shrinkage behavior. PVC foam samples were calculated percentage of shrinkage (Sh) by using density at before and after aging process at 30 oC for 12 h to make sure for completely permeation of air into foam structure. PVC foam by using scCO2 as a physical blowing agent reveal uniform closed bubble and regular foam structure with thin bubble wall (less than 5 µm). At high solubility of scCO2, PVC foam samples contain bubble diameter with less than 20 µm and high bubble density within the range of 108 - 1011 bubbles/cm3. PVC foam samples at low solubility foaming conditions display a large bubble diameter (more than 140 µm) and lower bubble density (106 bubbles/cm3). These foam samples are be able to reduce the density about 75% when compared with unfoamed sample but it structure highly shrink with Sh more than 50%.

Asphalt foaming quality control model using neural network and parameters optimization

Industrial asphalt foaming is a process of mixing, transferring heat and phase transition of multi-phase multi-component flow in the expansion chamber, including a series of complex problems such as difficult analysis and observation. In the context of this research, asphalt foaming quality control model using neural network was constructed to map the pertinent parameters (asphalt temperature, water content and air pressure) into the foaming properties (maximum expansion ratio and half-life time). In addition, Particle swarm optimization was adopted to avoid the local infinitesimal defect and slow constringency in the traditional BP algorithm. The prediction error of Shell 60/70 quality control model indicates that the asphalt foaming quality control model using PSO-BP neural network is effective, and this provides a novel idea for studying of the foam asphalt, which has practical significance for the design of asphalt foam equipment. Finally, a parameter optimization model with the maximization of the foaming index was proposed based on the quality control model to improve the foaming performance of the asphalt foaming equipment. With the analysis of a parameter optimization model of Shell 60/70 asphalt, the better foaming properties are the maximum expansion ratio of 12.28 times and half-life time of 11.02 s at the foaming condition of asphalt temperature of about 168 °C, the water content of about 1.5 wt% and the air pressure of about 1 bar. The method proposed in this paper is of important reference significance for the engineering with difficult analysis and observation.

The influence of supercritical foaming conditions on properties of polymer scaffolds for tissue engineering

Abstract The results of experimental investigations into foaming process of poly(ε-caprolactone) using supercritical CO2 are presented. The objective of the study was to explore the aspects of fabrication of biodegradable and biocompatible scaffolds that can be applied as a temporary three-dimensional extracellular matrix analog for cells to grow into a new tissue. The influence of foaming process parameters, which have been proven previously to affect significantly scaffold bioactivity, such as pressure (8-18 MPa), temperature (323-373 K) and time of saturation (1-6 h) on microstructure and mechanical properties of produced polymer porous structures is presented. The morphology and mechanical properties of considered materials were analyzed using a scanning electron microscope (SEM), x-ray microtomography (μ-CT) and a static compression test. A precise control over porosity and morphology of obtained polymer porous structures by adjusting the foaming process parameters has been proved. The obtained poly(ε-caprolactone) solid foams prepared using scCO2 have demonstrated sufficient mechanical strength to be applied as scaffolds in tissue engineering.

Mechanized Tunneling in Soft Soils: Choice of Excavation Mode and Application of Soil-Conditioning Additives in Glacial Deposits

The history of the formation of the alpine region is affected by the activities of the glaciers, which have a strong influence on underground works in this area. Mechanized tunneling must adapt to the presence of sound and altered rock, as well as to inhomogeneous soil layers that range from permeable gravel to soft clay sediments along the same tunnel. This article focuses on past experiences with tunnel-boring machines (TBMs) in Switzerland, and specifically on the aspects of soil conditioning during a passage through inhomogeneous soft soils. Most tunnels in the past were drilled using the slurry mode (SM), in which the application of different additives was mainly limited to difficult zones of high permeability and stoppages for tool change and modification. For drillings with the less common earth pressure balanced mode (EPBM), continuous foam conditioning and the additional use of polymer and bentonite have proven to be successful. The use of conditioning additives led to new challenges during separation of the slurries (for SM) and disposal of the excavated soil (for EPBM). If the disposal of chemically treated soft soil material from the earth pressure balanced (EPB) drive in a manner that is compliant with environmental legislation is considered early on in the design and evaluation of the excavation mode, the EPBM can be beneficial for tunnels bored in glacial deposits.

Manufacturing process of AA5083/nano-γAl2O3 localized composite metal foam fabricated by friction stir processing route (FSP) and microstructural characterization

The aluminum alloy AA5083 is a technologically important structural alloy as it is lightweight, with outstanding weldability and formability, moderate corrosion resistance and strength, making it suitable for a wide range of marine and transportation applications. In the present study, AA5083/nano-γAl2O3 composite metal foam was fabricated using a friction stir processing route (FSP). More precisely, the paper presents a first attempt to use grooves for the integration of the foaming and stabilizing agent on the metal foam precursor by FSP. The implementation of grooves allows to control the amount of foaming, integrates the stabilizing particles within the precursor and permits the production of localized metal foams. Unlike the commonly used manufacturing processes, only one plate is required for the production of the precursor sample in the proposed process. Therefore, this process can be easily implemented in the industrial sector. Furthermore, γ-Al2O3 nanostructured reinforcement, which is characterized by increased interfacial energy, was utilized as a stabilizing agent. The precursor specimens were manufactured by mixing blowing agent powder (0.4% w/w TiH2) and stabilization agent nanopowder (2% w/w γ-Al2O3) into the 5083 aluminum alloy matrix using FSP. The effects of the number of FSP passes and the foaming conditions (holding temperature and time) on the pore density, morphology and distribution were investigated. The microstructure and porosity evolution of the so-obtained metal foam was also examined and analyzed. Results indicate that, following the foaming procedure, a porosity of 60% and an equivalent pore diameter ranging from 0.2 to 3.3 mm can be achieved. Moreover, the microstructure was found to be closely related to microhardness distribution perpendicular to the traversing direction of the FSP tool for both precursor and foamed specimens.

The influence of microstructure on abrasive wear resistance of selected cemented carbide grades operating as cutting tools in dry and foam conditioned soil

WC cemented carbides are used extensively as cutting and drilling tools in the cutter heads of the full face Tunneling Boring Machines (TBMs).This paper describes the effects of microstructural properties of selected cemented carbide grades, operating as cutting tools in dry and foam conditioned soil, towards abrasive wear resistance. The work was carried out with the purpose of identifying the most promising cemented carbide microstructural formulation against abrasive wear and of defining the possible changes induced on the wear mechanisms by conditioning agents.Microstructures of six commercial grades of cemented carbides with different Co content and WC grain size were characterized. The wear tests were carried out using a testing device simulating the working environment of TBM cutter heads both in dry and conditioned soil.According to all experimental findings, wear resistance of the investigated cemented carbides strongly decreases as the grain size and mean binder free path increase, regardless of the test conditions. Furthermore, the carbides distribution, hereinafter called Delaunay distance, plays a crucial role on wear behavior, having a linear relation with the specific volume loss. Moreover, the optimal microstructural features to promote wear resistance are here described. Finally, foam conditioning of soils was found to strongly influence the wear resistance, by reducing binder ploughing and WC microcracking.

The effects of foaming conditions on plasticized polyvinyl chloride foam morphology by using liquid carbon dioxide

This research studies the effects of foaming conditions by using liquid carbon dioxide (CO2) as a physical blowing agent on plasticized polyvinyl chloride (PVC) foam morphology. Foaming conditions were soaking time of 6, 10, and 12 h, foaming temperature of 70, 80, 90 °C for 5 s, at constant soaking temperature of -20 °C and pressure of 50 bar. Instantaneously increasing temperature was employed in this process for making foam structure. PVC foam samples were calculated percentage of shrinkage (Sh) by using density at before and after aging process at 30 °C for 12 h. When PVC samples were activated to form foam by using liquid CO2 as a physical blowing agent, it reveal bimodal foam structure with a thick bubble wall (10-20 μm). Bubble diameter of PVC foam at longer soaking time is in the range of 40-60 μm and its at shorter soaking time reveal a large bubble that is in the range of 80-120 μm. Foaming condition slightly affected to bubble density that was in the narrow range of 106-108 bubbles/cm3. PVC foam reveal reduction of density up to 65% when compare with PVC and Sh is less than 10%.

Estimation of Input Pump Pressure in Conditions of Low Foaming Gas-Content Oil Pumping

Objectives: The core intention is to estimate input of submersible electric pump pressure in producing wells with using correlation during pumping gas-liquid mixture under oil low foaming conditions. Methods/Statistical Analysis: Known methods for calculating input pressure pump of high gas-content oil in well annulus are low-information and have poor accuracy. Based on the comparison and generalization of the data of comprehensive wellhead and deep well studies, we developed correlation dependencies for determining the density of a gas-liquid mixture taking into account the specific features of oil foaming in wells of the Upper Kama fields. Findings: Research results proved the influence of the content of high molecular compounds (resins and asphaltenes) determining the oil viscosity as well as gas-content on foaminess; wherein oil foaming properties decrease with increasing gas content. We developed equations for estimation relative density liquid mixture into the well annulus from pump submersion under dynamic level and oil foaming for mentioned above fields are obtained for the first time. These equations are based on the analysis of deep and estuarine well testing. It is shown that the oil gas-content affects the density of low foaming oil more than foaminess. According to the result to representativeness estimation of the obtained equations noted as accuracy sufficient for practical results to determine the density of the mixture in annulus and the input pump pressure. Application/Improvements: The basic field of application for the proposed approach is associated with exploitation of oil production wells. The results can be used for optimization of pump working in wells. Keywords: Foaminess, Gas, Input Pump Pressure, Oil, Well Production

Shedding new light on polyurethane degradation: Assessing foams condition in design objects

A new insight into the degradation of polyurethane (PUR) slabstock foams is suggested by studying historical design objects and PUR references submitted to natural ageing. PUR foams are segregated structures comprising hard and soft domains, as well as chemical and physical crosslinking (H-bonds). H-bonds have been commonly followed in polymerisation studies of PUR foams by monitoring carbonyl bands in the infrared. Their fundamental role in PUR physical properties has been stressed; however, their liability to natural ageing has been poorly focused, with few studies suggesting their vulnerability to high temperature and humidity. As PUR has a short lifespan, and many objects show severe degradation signs (yellowing, crumbling and brittleness), the in-depth analysis of PUR foams behaviour upon natural ageing, as well as the monitoring of H-bonds over these processes is discussed in this paper. References of PUR slabstock foams (ether-based polyols and toluene diisocyanates) were produced; and infrared micro-spectroscopy and optical microscopy (under darkfield, polarised light and UV light) were selected to assess PUR ageing. A visual (micro level) and molecular pathway for PUR natural ageing is suggested, and deterioration signs (yellowing, micro holes, pitting and cracks) on PUR cell buns were translated into specific infrared fingerprints (assigned to N–H, C–H and C=O stretching absorptions). As the C=O band at c. 1640 cm−1 (indicator of PUR hard domain ordered structure) showed considerable changes upon PUR ageing, this study confirms H-bonds as liable to natural ageing, and proposes this band as marker of ether-based PUR slabstock foam condition.

Influence of foaming technology on fibre breakage in long fibre-reinforced polypropylene composites parts

ABSTRACTIt is generally believed that the residual fibre length is one of the most important factors influencing on the mechanical properties of fibre-reinforced polymer matrix composites. In this study, long-glass fibre-reinforced polypropylene (LGFRPP) with initial fibre lengths of 12 mm was prepared and then moulded into parts via conventional injection moulding (CIM) and foamed injection moulding (FIM). The design of experiment (DOE) based on the Taguchi method was first used to determine the optimised processing conditions to increase the residual fibre length of the LGFRPP. The results indicated that foaming conditions have a substantial influence on the residual fibre length of the foamed samples. Based on the DOE, a set of optimised processing condition was selected, and two representative samples of CIM and FIM were carefully investigated using dynamical mechanical analysis, scanning electron microscopy, optical microscopy, etc. The experimental results further showed that the residual fibre length and the mechanical properties of the LGFRPP FIM components were better than those of the CIM components. It was also determined that there is a close relationship between the fibre breakage and the mechanical performance.

Calcium alginate beads motion in a foaming three-phase bubble column

Calcium alginate beads are frequently used to immobilize enzymes or microorganisms for fermentations carried out in agitated or pneumatic reactors. In this work, the well-known Radioactive Particle Tracking (RPT) technique is used to non-invasively extract relevant information of the motion of calcium alginate beads within a three phase bubble column under foaming conditions, which frequently appear in bioreactors operation. Special care is taken to produce a radioactive tracer that perfectly matches the features of the other particles in density and size. In addition, the tracer has the same texture and wettability since the adherence of gas to particles in foaming systems is crucial in determining the solid motion. Particles distribution, solid residence time, velocity fields, dispersion coefficients, shear stress and turbulence kinetic energy are determined from the radioactive tracer trajectories. Compared to previous works in non-foaming systems with denser particles, a relatively strong inward flow and less definite descending motion of the solid near the column wall is found. Turbulence intensities and shear stress are high in the disengagement zone, particularly for the churn-turbulent flow regime. However, since the biocatalyst damage would also depend on the actual exposure to harsh regions, the frequency of visit at different location was calculated to estimate maps of exposure risks as the product of turbulence stresses and these frequencies. Considering the particles motion, the region of largest risk for hydrodynamic damage is close to the gas entrance zone.

Effects of compatibility on foaming behavior of polypropylene/polyolefin elastomer blends prepared using a chemical blowing agent

ABSTRACTPolypropylene (PP) exhibits poor foaming property because of its low melt strength arising from its linear chains and relatively narrow molecular weight distribution. To fabricate a PP foam without crosslinking, PP should be blended with polyolefin elastomers (POEs) using chemical blowing agents. In this study, the effects of POE types and contents in a PP matrix were studied by analyzing the melt flow index, morphology, and thermal and dynamic viscoelastic properties. Furthermore, the POE type/content and foaming conditions (i.e., foaming temperature and oven residence time) were optimized by investigating the volume expansion ratio (VER), cross‐sectional morphology, and hardness of the PP/POE foams. We focused on how the foaming behavior and foaming conditions were affected by the compatibility and POE content in the PP/POE blend. The results demonstrated that the optimal VER of ∼9 was obtained at 30 wt % POE and foaming conditions of 220 °C for 9 min. © 2017 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2017, 134, 45201.

Preparation and mechanical properties of thermosetting epoxy foams based on epoxy/ 2-ethyl-4-methylimidazol system with different curing agent contents

Epoxy/2-ethyl-4-methylimidazol system with different curing agent content was completely cured for foaming, and the effect of a systematic variation in 2-ethyl-4-methylimidazol content on the crosslinking density of cured epoxy resins was investigated. It was found that the crosslinking density of completed cured epoxy reduced as the 2-ethyl-4-methylimidazol content increased in certain range of contents (10–50 mol%). Then the precursors were foamed by a batch foaming process with supercritical carbon dioxide. The cellular morphologies of foamed epoxy resins were analyzed by scanning electron microscopy. The results revealed that the reduced crosslinking density would improve the foamability of cured epoxy resin. The microcellular epoxy foams could be obtained by maintaining a moderate crosslinking density, which can be controlled by varying 2-ethyl-4-methylimidazol content. For the completely cured epoxy with different curing agent content, when the crosslinking density of epoxy resin was 232.40 mol m–3 (the 2-ethyl-4-methylimidazol content was 35 mol%) or lower, microcellular structure was obtained by adjusting the foaming conditions. The effects of foaming on the mechanical properties were also discussed. The results indicated that microcellular epoxy foams had higher impact strength but lower tensile strength and tensile modulus, validating that the introduction of microcellular structure in epoxy matrix was conducive to the improvement of the ductility of epoxy foams.

Continuous Prediction of the Gas Dew Point Temperature for the Prevention of the Foaming Phenomenon in Acid Gas Removal Units Using Artificial Intelligence Models

Acid gas removal (AGR) units are widely used to remove CO2 and H2S from sour gas streams in natural gas processing. When foaming occurs in an AGR system, the efficiency of the process extremely decreases. In this paper, a novel approach is suggested to regularly predict the gas dew point temperature (GDPT) in order to anticipate the foaming conditions. Prediction of GDPT is advantageous because the conventional methods of measuring GDPT such as: (i) using a chilled mirror device is time consuming; and (ii) the use of gas chromatograph for composition determination combined with the equation-of-state calculations involve column retention time and is expensive. New hybrid modeling algorithms based on the artificial neural network (ANN) combined with either the imperialist competitive algorithm (ICA) or particle swarm optimization (PSO) are employed to model the process. The models can then be used to prevent the foaming phenomenon. The proposed algorithms combine the local searching ability of ANN with the global searching abilities of ICA and PSO. ICA and PSO are used to optimize the initial weights of the neural networks. The resulting ICA-ANN and PSO-ANN combined algorithms are then applied to model the occurrence of foaming in the AGR plant based on a simulation data set acquired from the 6th refinery of the south Pars gas complex in Iran. The performances of the ICA-ANN, PSO-ANN and conventional ANN models are then compared against each other. It was found that the accuracies of the ICA-ANN and PSO-ANN models are better than that of the conventional ANN model. In addition, the PSO-ANN model outperformed the ICA-ANN model.

Stability analysis of tannin-based foams using multiple light-scattering measurements

Liquid foams were prepared by whipping aqueous solutions based on natural polyphenols, surfactant and crosslinker. The destabilisation mechanisms of such thick, opaque and viscous liquid foams were investigated for the first time with a light-scattering detection method using an optical analyser. The technique allowed separating processes such as drainage, coalescence and coarsening, and sedimentation, so that each of them could be investigated independently as a function of whipping time, surfactant amount, and temperature. The corresponding average bubble diameters could also be determined as a function of time. It was shown that this kind of optical analysis is quite relevant for optimising formulations and foaming conditions with the aim of recovering rigid foams after polymerisation, having a given homogeneous structure that might be useful for various applications such as thermal insulation or acoustic absorption.