Foam Expansion Ratio Research Articles

A Facile and Efficient Method for Preparing Chain Extended Poly(lactic acid) Foams with High Volume Expansion Ratio

In recent years, poly(lactic acid) (PLA) foams have drawn considerable attention worldwide due to their environmental friendliness and excellent biocompatibility. However, it was a big challenge to prepare PLA foams with high volume expansion ratio owing to their poor crystallization properties and melt strength. In this work, the random copolymer of ethylene and glycidyl methacrylate as an efficient chain extender (CE) was chosen and employed to improve the crystallization behaviors and foamability of PLA. The chain extension reaction between PLA and CE was proved by torque curves, Fourier transform infrared spectra, gel fraction, and intrinsic viscosity measurements. Differential scanning calorimetry results and polarized optical microscope images showed that the crystallinity and spherocrystal number of various PLA samples increased notably as well as their spherocrystal size decreased with the CE content increasing. The viscoelasticity of various PLA samples was improved by the increment in the CE content. Various PLA samples were foamed by a batch foaming method at different foaming temperature with supercritical CO2 to research the influence of crystallization behaviors and/or rheological properties on the foaming behaviors of PLA. At the high foaming temperature, the cell density and volume expansion ratio (VER) of various PLA foams were affected by rheological properties significantly and their highest VER could reach to 42.41 ± 0.01 times. At the low foaming temperature, the cellular morphology of various PLA foams was improved notably, due to the increased melt strength induced by the cooling and the generation of crystallization region.

Impact of Additives on the Foamability of a Road Paving Bitumen

Because of the needs for the increased efficiency and environmental concerns that now emerge environmentally friendly techniques are more sought for and more commonly utilized in the road paving industry. Typical asphalt mixes are produced in temperatures exceeding 150˚C depending on the type of asphalt binder used, but new techniques are being developed, permitting decreased production and paving temperatures. One of the most effective techniques that are being studied are the Warm Mix Asphalt and Half Warm Mix Asphalt methods utilizing water based bitumen foaming that allow production of asphalt mixes at temperatures as low as 100˚C. Due to the extremely low processing temperatures, it is often difficult to obtain satisfactory results regarding the physical and mechanical properties of the resulting mixes, specifically the resistance to moisture the damage and resistance to the permanent deformation being in concern. As these issues were found to be originating in the inadequate coating of aggregates, a surface active agent in amounts of 0, 2% - 0, 6% and synthetic wax in amounts of 1, 0% - 2, 5% were added to 50/70 paving bitumen to improve its foamability and coating potential. Foaming characteristics were established in terms of bitumen foam expansion ratio ER and its half-life HL as a function of foaming water content ranging from 1, 5% to 4, 0%. It was found that the addition of surface active agent in the amount of 0, 6% resulted in the most favourable foaming performance at 2, 5% foaming water content, resulting in a doubling in expansion ratio and more than a 2, 5 times increase in half-life compared to the base bitumen. It is believed that the improved foaming characteristics of the bitumen would significantly benefit the performance of a subsequent warm or half-warm asphalt mix.

Classification of foam and foaming products for EPB mechanized tunnelling based on half-life time

During tunnel excavation with Tunnel Boring Machines (TBMs) and earth pressure balance (EPB) technology, conditioning agents are commonly used to modify the physical and mechanical properties of soils so that they are appropriate for the application of the front-face support pressure during excavation. The consistency of the conditioned soil must be stable during the time necessary to advance and install the lining. Hence, a stability analysis of the injected foams is an important aspect. To assess the stability of a foam a classification is proposed based on the results of a standard foam generation procedure and on half-life tests using products from the main suppliers. A further classification of the foaming agents used according to their ability to produce a stable foam in terms of Foam Expansion Ratio is also proposed.

Experimental research on gel-stabilized foam designed to prevent and control spontaneous combustion of coal

The gel-stabilized foam was prepared successfully by forming gel structure in the bubble film using thickening agent (TA) and crosslinking agent (CLA). The viscosity characteristic, foamability, stability, and microstructure of gel-stabilized foam were investigated systematically. The formation of gel structure reduced the foamability of foaming solution due to the increased viscosity, whereas it increased the foam stability significantly. By comprehensively considering foam expansion ratio >5 and half-life >120 h, the effective component range of gel-stabilized foam was determined as 3.4–5.5 g/L for TA and 2.1–4.0 g/L for CLA. Microstructure and liquid drainage kinetics analysis indicated that gel-stabilized foam demonstrated the smaller average bubble size, lower growth rate of bubble size and drainage rate compared to the traditional aqueous foam, mainly ascribing to the thickened bubble film and the formation of a viscoelastic shell on the bubble surface. The simulation experiment of spontaneous combustion of coal indicated the better inhibition efficiency of gel-stabilized foam to spontaneous combustion of coal than that of traditional foam, as evidenced by higher crossing point temperature, lower emission of carbon monoxide and ethylene for treated coal by gel-stabilized foam, which revealed its better water-retaining property to retard the oxidation of coal. Moreover, gel-stabilized foam will form a complete film on the surface of coal particles to isolate coal from the oxygen to inhibit spontaneous combustion.

The study of the stability of aqueous three-phase fire-resistant foam in typical liquidus hydrocarbons

The utilization of solid particles in aqueous foam has a great potential in improving fire fighting efficiency. In this study, aqueous foam supported by micro fly-ash (FA) was prepared and its stability in a specific type of oil was characterized. Firstly, different amount of FA was added to study the influence of FA concentration on foamability. It showed that within a specific extent, foam expansion ratio increased with the increasing of FA concentration. And compared with conventional foams, oil resistance of FA stabilized foams, which was investigated by analyzing drainage rate and evolution process with a self-made apparatus, was remarkably improved when FA concentration exceed 4.8wt.%. Secondly, SiO2 and Al2O3 particles with different median sizes were used to study the effect of particle size on stability. However, the smaller hydrophilic particles didn’t behave better as expected. Moreover, the foam stability in three hydrocarbons was evaluated in the same way. The results indicated that the short chain hydrocarbons had much stronger detrimental effect to both two-phase foam and three-phase foam. But overall, the three-phase foam stabilized by FA exhibited much better oil resistance, so it can be used as a promising material for pool fire extinguishing and prevention.GRAPHICAL ABSTRACT

13X zeolite as Difunctional nucleating agent regulating the crystal form and improving the Foamability of blocked copolymerized polypropylene in supercritical CO2 foaming process

Comparing with solid counterpart, plastic foams exhibit many merits, such as lightweight, excellent energy absorption, good thermal insulation and sound absorption properties. Blocked copolymerized polypropylene (PPB) is a kind of foamable polymer, but it is challenging to obtain the PPB foam with high expansion ratio, uniform cell structure and good toughness. In this study, 13X zeolite was used as nucleating agent for both crystallization process and foaming process. During the crystallization process, 13X zeolite used as β-nucleating agent not only improved the crystallization behavior but also induced the β-form crystal, thereby improving the toughness of PPB. During the foaming process, 13X zeolite used as cell nucleating agent improved the foamability of PPB by increasing the content of CO2 dissolved in PPB melt due to its porous structure. The experiment results revealed that when the content of 13X zeolite was 0.5 wt%, the relative content of β-crystal (kβ), the crystallization temperature (Tc) and the impact strength of PPB were greatly increased from 0.17, 114 °C, 838.9 J/m to 0.64, 122 °C, 952.9 J/m respectively. Moreover, at that content, the expansion ratio (Rv) of PPB foam reached the maximum value of 41 times under the optimal foaming temperature and pressure.

Strategy to control CO2 diffusion in polystyrene microcellular foaming via CO2-philic additives

The introduction of suitable CO2-philic additives, enabling high CO2 concentration retained in the polymer matrix, might be a promising strategy to obtain foams with small cell size and large volume expansion ratio. The effect of molecular weight (Mn) (2000–17000 g/mol) of CO2-philic additives (PDMS and PVAc) on the diffusion of supercritical CO2 into and out of polystyrene (PS) was investigated via experiments and dissipative particle dynamics simulations. The CO2 diffusion coefficient increased with the presence of additives especially with PDMS (2000 g/mol, from 1.2 × 10−9 m2/s to 2.8 × 10−9 m2/s). Meanwhile, the saturation solubility of CO2 increase with the incorporation additives. Compared with high Mn additives, the slower CO2 desorption rate with additives with Mn of 2000 g/mol enabled higher amount of CO2 retained in PS, resulting in higher cell density. The incorporation of PDMS (2000 g/mol) decreased the cell size (from 11.67 to 7.57 μ m) and increased volume expansion ratio of PS foams.

Enhanced dispersion, flame retardancy and mechanical properties of polypropylene/intumescent flame retardant composites via supercritical CO2 foaming followed by defoaming

The broad technological exploitation of polypropylene (PP)/intumescent flame retardants (IFR) composites with outstanding flame retardancy and mechanical properties is stifled by the lack of effective methods to improve the IFR dispersion, since the opposite polarity between PP and IFR would result in poor compatibility and uneven dispersion. In this work, we have demonstrated an industrially viable and efficient approach for the fabrication of PP/IFR composites with more uniform dispersion by combining the advantages of supercritical CO2 (scCO2) plasticization and biaxial bubble stretching through the scCO2 foaming technique followed by defoaming, and the increasing of the foam expansion ratio could lead to the better IFR dispersion of the final defoamed solid PP/IFR composites due to stronger bubble stretching force. Moreover, the improved IFR dispersion could result in the greatly enhanced flame retardancy and mechanical properties in comparison with those of uneven dispersed ones. We believe that the approach here can be used to guide the future design of high-performance materials on inorganic/organic hybrid polymer composites with homogenous dispersion.

Properties of potato flour-based loose-fill foams

Abstract Potato flour-based foams were made as loose-fill packaging materials. The different potato flour moisture contents of 10 to 16% (dry basis) were used and extruded using a single screw extruder. The water was employed as a blowing agent in this work. The water solubility index (WSI), compressive strength, foam appearance, expansion ratio and foam cell structure were evaluated. WSI of foams ranged between 48 and 67%. Increasing the moisture contents of potato flour tended to increase rigidity and irregular surfaces of foams. However, the expansion ratio and cell size of foams decreased as the moisture contents of potato flour increased.

Combustion of foamed emulsion prepared via bubbling of oxygen-nitrogen gaseous mixture through the oil-in-water emulsion

One of the perspective types of hydrocarbon fuels on the water base is the foamed emulsion. Foamed emulsion represents a multiphase system consisting of the gaseous bubbles filled with an oxidizer and dispersed in the oil-in-water emulsion. This paper considers for the first time the peculiarities of combustion of the foamed emulsion prepared via bubbling of gaseous oxidizer (air or the oxygen-nitrogen mixture) through the emulsion. In the process of emulsion preparation hexane, heptane, dichloroethane and petroleum ether were used as oil. The experimental data for the flame speed in the foam are obtained for various compounds of the gaseous phase, types of hydrocarbons, concentrations of oil, foam expansion ratios and tube diameters. It is established that the flame speed in the foam can be changed by several orders of magnitude due to the variation of gaseous phase content. Herewith, the foam expansion ratio causes the ambiguous effect on the flame speed.

Role of chain extension in the rheological properties, crystallization behaviors, and microcellular foaming performances of poly (butylene adipate‐co‐terephthalate)

ABSTRACTCurrently, the fabrication of microcellular semicrystalline polymer foam using supercritical CO2as a blowing agent constitutes a worldwide interest. In this work, a facile approach of chain extension and batch foaming was proposed to prepare microcellular semicrystalline poly (butylene adipate‐co‐terephthalate) (PBAT) foam using CO2as a physical blowing agent. With the introduction of chain extender (CE), the weight‐average molecular weight and gel fraction of PBAT samples increased; their crystallization temperature increased from 74.2 to 86.9 °C and their viscoelasticity was improved greatly. Microcellular PBAT foams with the cell size <4 μm and the cell density more than 1010cells cm−3were fabricated successfully. With increasing concentration of CE, the cell density and volume expansion ratio (VER) of various PBAT foams increased from 3.4 × 1010to 8.7 × 1010cells cm−3and from 1.5 to 2.0 times, respectively. With increasing foaming temperature, the cell size and VER increased and the cell density decreased. © 2018 Wiley Periodicals, Inc. J. Appl. Polym. Sci.2019,136, 47322.

In-situ cooling of adsorbed water to control cellular structure of polypropylene composite foam during CO2 batch foaming process

The fixation stage of cellular structure during polymer foaming process is difficult to control due to difficult removing of internal heat, especially for crystalline polymers such as polypropylene (PP). In order to control cellular structure in the fixation stage, we established an universal method by introducing water as an in-situ internal cooling agent during the foaming process of PP. Particularly, hydrophilic fillers were added into the high melt flow index polypropylene (HMI-PP) with poor foaming ability to study the effect of adsorbed water on the foaming process of PP/filler composites during sc-CO2 batch foaming process. Compared to pure HMI-PP, HMI-PP/hydrophilic filler composites showed increased adsorption amount for water and melt viscosity. The water within the composites played a key role in the foaming process, which not only served as a physical foaming agent to increase the volume expansion ratio of PP composite foam, but also showed the function of rapid cooling foam proved by thermal imaging technology. As a result, the presence of some hydrophilic fillers within HMI-PP matrix significantly improved the foaming properties of HMI-PP, including preventing internal bubble collapse and significantly increasing the volume expansion ratio of the foam. The applicability of this method was validated using other PP materials besides HMI-PP, including high molecular weight PP (HMW-PP), high melt strength PP (HMS-PP).

Foaming ability and stability of silica nanoparticle-based triple-phase foam for oil fire extinguishing: experimental

ABSTRACTThe triple-phase foam has been widely used in oil fire extinguishing, and its two key parameters for application are the foaming ability and stability. We present a comprehensive study on the foam expansion ratio (FER) and drainage time, where factors such as the foam morphology, zeta potential of particles, foam mixing homogeneity, surfactant concentration, particle mass percentage, and specific surface area of the particle are investigated in detail. The dependence relationship curves of FER and drainage time with respect to the latter four variables are given through experiments, and optimal parameter values are selected. Moreover, the scaling laws correlating these variables are in agreement with the experimental results, and some necessary parameters are obtained by data fitting. These analyses are beneficial to better understand the foaming ability and stability mechanism of the triple-phase foam and to prepare materials of high performances for oil fire extinguishing.

Cutter-disc consumption during earth pressure balance tunnelling in mixed strata

The wear of excavation tools is considered to be one of the critical factors affecting the scheduling of shield tunnel construction. There is presently no effective countermeasure to prevent severe wear of excavation tools during tunnelling operations in complex geological formations. In addition, such wear is likely to lead to other problems, such as face instability and an unfavourable rate of tunnel advancement. The study reported in this paper analysed the various factors that affected the wear and performance of excavation tools during earth pressure balance machine tunnelling at the Ma-Lian section of line 9 of the Guangzhou metro, China. It was found that tunnelling in mixed ground conditions (upper soft and lower hard strata) led to severe wear of the cutter discs, resulting in additional costs and schedule delays. The foam expansion ratio, concentration of foaming agent and the foam injection ratio were measured to be 20, 2·5% and 40% respectively. Pre-grouting and effective soil conditioning were also found to prevent excessive wear of the cutter discs and surface collapse incidents caused by face instability.

Investigation on the performance and application of a new design of foam generator used for fire extinguishment in underground coal mines

ABSTRACTMine fire is a serious threat to workers’ health and safety production of coal mines. Foam is used as an efficient extinguishment method in underground coal mines. A new design of foam generator was proposed to solve the drawbacks caused by the complicated operation of conventional foam technology. Experimental results show that the intake air pressure of the new foam generator increases with the foam liquid pressure linearly. The foam production quantity and foam expansion ratio reach maximums at the foam liquid flow of 3.5–4.5 m3/h. The intake air pressure increases sharply with the outlet pressure especially at a larger foam liquid flow. It is essential to keep the foam generator outlet pressure less than a critical value to get an optimal foam production quantity. The new foam generator has the advantages of simple structure, convenient operation and compact size that is very suitable for fire extinguishment in underground coal mines. The foam technology using the new device makes a good foaming effect in the field and ensures the safety operation of dismantling hydraulic supports from the working face, creating significant economic benefits for underground coal mines.

SYNTHESIS AND STUDY OF PROPERTIES OF SURFACTANTS BASED ON FAT ACIDS OF PALM OIL AND METHANOL

A new product was obtained with the use of methyl alcohol and fatty acids of palm oil. The series of experimens were performed to reveal its composition and properties with the use of modern devices and methods. The results of IR-spectroscopy have approved the presence of specific functional groups: hydroxylic, ester, carboxylic and sulfonate ones. The results of studies have shown that the synthesized substance posesses the surfactant properties: wetting, foaming, detersive; and it has a relatively low surface energy. It belongs to the group of high-despersity and mono-dispersity systems and takes an intermediate position between micro- and nano-particles. It was shown, that the contact angle of the water solution of the surfactant under study equals to at least 90 degrees and practically does not depend on the nature of wetted surface (eather hydrophylic or hydrofobic). It was founded that the foam expansion ratio and its stability are high and lay in direct relation with the substance concentration. It was found that relating to the protein composition, the detergent power of the surfactant is higher (up to 90 %) than regarding to pigment-and-oil contamination. Measuring the values of surface tension by Willhelm plate-bearing method allowed defining the critical concentration of micelle formation of 4.0 g/dm3, at which the maximum wetting is achieved. It was found that the synthezised product have a low emulsifying power towards the motor, machine oil and animal fat. Besides, the highest stability of emulsion was observed towards the machine oil (at concentration of synthesized product of 2.0 g/dm3). The emulsion stability can be increased by making compositions including the non-ionogenic surfactants. Moreover, it was found that the product under study is characterized by the high aggregative stability, since the achieved values of zeta-potential are in the range of 30 mB< ζ < -30 mB. The developed product belongs to the anionic surfactants, with рН of water solution of 7-8. It has a good water solubility. According to results of the hydrophylic-and-lipophylic balance, the synthesyzed surfactant belongs to detergents.Forcitation:Lutfullina G.G., Guseva K.S., Grishin P.B., Khairutdinova R.I. Synthesis and study of properties of surfactants based on fat acids of palm oil and methanol. Izv. Vyssh. Uchebn. Zaved. Khim. Khim. Tekhnol. 2018. V. 61. N 6. P. 88-95

Impact of low viscosity grade bitumen on foaming characteristics

The construction of highway infrastructure requires large quantities of construction materials and is an energy-intensive activity. Issues like scarcity of construction materials, increasing cost of materials, increasing cost of construction processes, and the emphasis on less polluting construction procedures have led to advancements in pavement construction practices. One such example is foamed bitumen technology. In this process, cold water is injected into a hot bitumen medium, which leads to drastic expansion of bitumen, forming a fine mist or foam. The performance of foam bitumen mixtures is influenced by the bitumen properties, as well as by the foaming process. This paper deals with research on the rheology of three different types of binders having low viscosity (in the range of 500 to 3 000 Poise at 60°C) on foaming characteristics. The water content and temperature also have significant effects on foam decay and the expansion ratio of foam. Results show that a low viscosity bitumen consumes less energy during the foam process compared to high viscosity bitumen. The conclusion drawn from this study is that the expansion ratio and half-life of foam bitumen depend on the rheology of the bitumen, as well as on the chemical composition of the bitumen. It was concluded that, with an increase in carbonyl and sulphoxide compound, the expansion ratio decreases and the half-life increases.

Microcellular foaming of polysulfones in supercritical CO2 and the effect of co-blowing agent

The microcellular foaming of two kinds of polysulfones, polyphenylsulfone (PPSU) and polysulfone (PSU), were investigated in supercritical CO2. The expansion ratio, which ranges from 1.10–2.45 for PPSU and 1.10–3.72 for PSU obtained under different conditions, is not sufficient due to the limited solubility of CO2. To improve the porosity of foams, the effect of co-blowing agents on foaming was studied by molecular modeling and foaming experiments. Ethanol has a more favorable interaction with CO2, followed by water, acetone and ethyl acetate. Additionally, ethanol significantly increases the interaction of CO2 with polymer chains. The expansion ratio of foams has an evident increase, and the foaming temperature window expands upon the addition of co-blowing agents. Consistently, the addition of ethanol has the highest expansion ratio, 5.02 for PPSU and 6.54 for PSU. Meanwhile, it broadens the foaming temperature dramatically, decreasing the value by 50 °C for PPSU and 70 °C for PSU.

Fluorinated and fluorine-free firefighting foams spread on heptane surface

The application of fluorinated firefighting foam has been restricted due to its serious environmental hazard. Thus, new fluorine-free firefighting foam formulations must be urgently developed. In this work, fluorinated and fluorine-free firefighting foams are synthesized. The spreading of the two foams on the surface of liquid fuel is achieved by using a circle stainless steel tray. Variation in the instantaneous spreading area of the foams versus time is analyzed. In addition, the effect of foam flow rate and expansion ratio (ER) on foam spreading is studied. Results indicate that an aqueous film on the heptane surface is observed during fluorinated foam spreading but not during fluorine-free foam spreading. At the same foam flow rate and ER, fluorinated foam shows faster spreading than fluorine-free foam. The foam spreading rate (FSR) increases with the increasing foam flow rate and decreases with the increasing ER. The high surface tension and great viscosity of fluorine-free foam solution are significant factors resulting in its slow spreading. Therefore, fluorine-free foam can spread on the heptane surface as fast as fluorinated foam by increasing the foam flow rate and lowering the ER.

Foam property tests to evaluate the potential for longwall shield dust control.

Tests were conducted to determine properties of four foam agents for their potential use in longwall mining dust control. Foam has been tried in underground mining in the past for dust control and is currently being reconsidered for use in underground coal longwall operations in order to help those operations comply with the Mine Safety and Health Administration's lower coal mine respirable dust standard of 1.5 mg/m3. Foams were generated using two different methods. One method used compressed air and water pressure to generate foam, while the other method used low-pressure air generated by a blower and water pressure using a foam generator developed by the U.S. National Institute for Occupational Safety and Health. Foam property tests, consisting of a foam expansion ratio test and a water drainage test, were conducted to classify foams. Compressed-air-generated foams tended to have low expansion ratios, from 10 to 19, with high water drainage. Blower-air-generated foams had higher foam expansion ratios, from 30 to 60, with lower water drainage. Foams produced within these ranges of expansion ratios are stable and potentially suitable for dust control. The test results eliminated two foam agents for future testing because they had poor expansion ratios. The remaining two foam agents seem to have properties adequate for dust control. These material property tests can be used to classify foams for their potential use in longwall mining dust control.