Physical Foaming Agent Research Articles

Preparation of high-performance thermal insulation composite material from alkali-activated binders, foam, hollow glass microspheres and aerogel

• Physical foaming, hollow glass microspheres and aerogel were used for AAB. • CMC minimized foam and slurry delamination and improved foaming effect. • KH550 treated hollow glass microspheres showed enhanced the interfacial bonding. • PE100-hydrophobic aerogel had extern hydrophilic and internal hydrophobic effect. Herein, a high-performance thermal insulation composite material was prepared by adding physical foaming agent (FA), hollow glass microspheres (HGMs) and aerogel (AG) with alkali-activated binders (AABs) as the matrix. The results of orthogonal experiments revealed that AG has the greatest effect on thermal conductivity, followed by the effect of FA and HGMs. The thermal conductivity value of AABs was reduced from 0.6057 to 0.0870 W/(m·K) at an AG dosage of 4 g (42.48 kg/m 3 ) in the single factor experiments. The effect of compressive strength followed an order of: HGMs < FA < AG. Under the temperature condition of 400–800 °C, the FA exacerbated the linear shrinkage of the sample, HGMs inhibited the linear shrinkage at 400 °C and 600 °C, and exacerbated it at 800 °C, while AG inhibited the linear shrinkage. X-ray diffraction and scanning electron microscopy analyses revealed that the sample maintained stable performance below 800 °C. Orthogonal experiment results concluded that the optimal level combination was 6 g FA, 6 g HGMs and 3 g AG (A6B6C3) and exhibited the minimal thermal conductivity (0.0434 W/(m·K)). The compressive strength of A6B6C3 at 30 °C was 0.38 MPa, which gradually increased with temperature, reaching the maximum of 0.79 MPa at 800 °C. This composite can meet the thermal insulation, mechanical and high temperature resistance properties. In addition, accredited to simple preparation process, short curing period, and low cost, this approach can be deemed of great significance for applications in composite thermal insulation materials in nuclear power plants and other key areas.

Effect of nano TiO2 on the cellular structure and mechanical properties of wood flour/polypropylene composite foams via mold‐opening foam injection molding

AbstractMicrocellular foamed wood‐plastic composites (WPCs) have shown good development prospects in environmentally‐friendly composites. Herein, the foamed wood flour (WF)/polypropylene (PP) composites were fabricated by mold‐opening injection molding using supercritical N2 as a physical foaming agent. The effects of nano TiO2 on the microcellular structure and mechanical properties of WF/PP composites were investigated, and the results show that nano TiO2 accelerates the crystallization rate and reduces the crystallinity of PP, which is beneficial to the formation of foamed homogeneous systems and cell growth in the WF/PP composites. This is mainly due to heteronucleation effect of nano TiO2, resulting in the refinement of crystal. Molecular chain movement of PP is limited with the introduction of nano TiO2, resulting in increased the melt elasticity of WF/PP composites, thereby reducing cell coalescence and collapse. With the addition of 5 wt% nano TiO2, the cell density was increased by 393.8%, the cell size was reduced by 54.4%, and the cell size homogeneity was clearly improved. In addition, impact strength increased by 33.3%. The improved foamability of WF/PP composites using nano TiO2 shows a great promise for the production and application of WPC foams, especially in automotive, packaging and building areas.

Fabrication of super-hydrophilic and highly open-porous poly (lactic acid) scaffolds using supercritical carbon dioxide foaming.

Porous poly (lactic acid) (PLA)-based scaffolds have been widely used as a promising product in tissue engineering. However, it is still a challenge to prepare the PLA-based scaffolds with high expansion ratio, good hydrophilicity, and excellent cytocompatibility by a green and cost-effective fabrication approach. Herein, we prepared porous PLA-based scaffolds using carbon dioxide (CO2) as the physical foaming agent. To improve the hydrophilicity and foaming behavior of PLA, poly (ethylene glycol) (PEG) was selected as a good additive to blend with PLA. It revealed that the introduction of PEG could improve the foaming behavior of PLA and promote the formation of opening cells via reducing the matrix strength of PLA. The obtained 3D PLA/PEG scaffolds exhibited high expansion ratio (9.1), high open-cell content (95.2%), and super-hydrophilicity (water contact angle 0°). Additionally, the mouse fibroblast NIH/3T3 cells with live/dead cell fluorescence staining assay was utilized to examine the biocompatibility of PLA/PEG scaffolds. The result demonstrated that the proliferation ratio of NIH/3T3 cells on the surface of PLA/PEG scaffolds was higher than that of PLA scaffolds, indicating that the highly interconnected cell structure was conducive to cell adhesion and attachment. Consequently, such hydrophilic open-cell structure obtained by adding PEG into PLA possesses great potential for use in tissue engineering.

ВЛИЯНИЕ ФИЗИЧЕСКОГО ПЕНООБРАЗОВАТЕЛЯ НА СВОЙСТВА ЖЕСТКИХ ПЕНОПОЛИУРЕТАНОВ

The article discusses the properties of rigid polyurethane foams (PU foams) obtained with the use of various environmentally friendly physical foaming agents - cyclopentane, cycloisopentane mixtures (CIP), methylal, methyl formate and methyl tert-butyl ether. No significant differences were noted in the use of various blowing agents during technological samples free foaming. In the course of further research, it was confirmed that the physical and mechanical properties of the finished foam significantly depend on the type of gas in the closed cells of the material. Foams obtained with the use of hydrocarbon blowing agents have a fine-meshed structure without defects, cavities and voids. It has been established that in the case of foaming with cyclopentane and cycloisopentane compositions, the introduction of isopentane provides an increase in the strength of the finished foams in compression in the horizontal direction in accordance with the direction of foam rise. It is also noted that materials foamed with methylal and methyl formate have the lowest compressive strength values. A slight difference was also noted in the thermal conductivity of the foamed products. The lowest values of thermal conductivity in the present study were noted for foams based on cyclopentane and cycloisopentane mixtures. It was also of interest to establish the change in the thermal conductivity of finished products based on cyclopentane and CIP over time. Experimentally found that after 500 days the thermal conductivity of the samples increased and reached equal values. This effect is due to the diffusion of the foaming component molecules through the walls of the foam cells, as a result of which air with a much higher thermal conductivity coefficient diffuses into the cells. It was shown in a comparative analysis that the mixtures of polyurethane foam components have good fluidity in the case of cyclopentane and cycloisopentane use, which contributes to uniform filling of the mold and reduction of losses during pouring. Based on the work done, cycloisopentane mixtures can be recommended as foaming components in the production of polyurethane foam insulation.

Experimental Study on Reducing the Heat of Curing Reaction of Polyurethane Polymer Grouting Material

Polyurethane polymer grouting material has been effectively applied and promoted in the repair of road damages in nonfrozen areas. However, this material undergoes an exothermic reaction in the curing stage, which can cause a thermal disturbance in the frozen soil subgrade. To minimize the influence of the thermal disturbance of the polyurethane polymer grouting material in the repair of the frozen soil subgrade, an experiment was conducted to reduce the heat of the curing reaction under the influence of different proportions of a foaming agent, high-boiling point solvent, catalyst, and prepolymer. According to these test results, a proportioning scheme for the low exothermic polymer grouting material was formulated. The results indicated that the curing reaction temperature threshold of the polyurethane polymer grouting material was negatively related to the proportion of physical foaming agent (HCFC-141b) and high-boiling point solvent and positively related to the proportion of water weight. In the three stages of rapid temperature rise, slow temperature rise, and constant temperature, the rate of the temperature rise of the low exothermic polymer grouting material was lower than that of the common polymer, and the curing temperature threshold was 30.34% lower at a value of 101°C. At a density of 80 kg/m3, the compressive strength and tensile strength of the low heat release polymer grouting material were lower than those of the common polymer grouting material, thereby ensuring the excellent performance of polyurethane foam and providing a theoretical reference for the rapid repair of frozen soil roadbed diseases.

Fabrication of Highly Interconnected Poly(ε-caprolactone)/cellulose Nanofiber Composite Foams by Microcellular Foaming and Leaching Processes.

In this study, microcellular polycaprolactone (PCL)/sodium bicarbonate (NaHCO3)/cellulose nanofiber (CNF) composite foams with highly interconnected porous structures were successfully fabricated by microcellular foaming and particle leaching processes. Supercritical CO2 (scCO2) served as a physical foaming agent, NaHCO3 was chosen as a chemical foaming agent and porogen, and CNF acted as a heterogeneous nucleating agent. The effect of scCO2, NaHCO3, and CNF on pore structures and the cofoaming mechanism were investigated. The results indicated that the addition of NaHCO3 and CNF increased the melt strength of the PCL matrix significantly. During the foaming process, the presence of CNF can form a rigid network due to the hydrogen bonding or mechanical entanglement between individual nanofibers, improving the nucleating efficiency but slowing down the cell growth rate. Additionally, due to the interaction of “soft” PCL matrix and “hard” domains in a PCL-based composite during the foaming process, together with the NaHCO3 leaching process, highly interconnected cell structures appeared. The obtained PCL/NaHCO3/CNF composite foams had a cell size of 15.8 μm and cell density of 6.3 × 107 cells/cm3, as well as an open-cell content of 82%. The reported strategy in this paper may provide the guidelines and data supports for the fabrication of a PCL-based porous scaffold.

Effect of silica‐coated TiO2 nanorods on the foamability of polypropylene and photostability of foamed polypropylene

Researches about the heterogeneous nucleation ability of nanorods and the weather resistance of polypropylene (PP) foams were very limited. In this study, the well‐defined rutile TiO2 nanorods with UV‐absorbing function were coated with silica and then calcined. The obtained nanorods (denoted as “TS”) could be uniformly dispersed in PP matrix by melt blending. The foaming behavior of linear PP and its composites was investigated by using supercritical carbon dioxide (scCO2) as a physical foaming agent. The results demonstrated that the addition of 5 wt% TS made PP/TS‐5% foam have higher cell density, regular cell structure and uniform cell distribution owing to the large numbers of nucleation sites provided by well‐dispersed TS nanorods. At the same time, the aging performance of PP foam samples was evaluated by the changes of macro or micro morphology, melting and crystallization behavior before and after UVB irradiation. It was intuitively found that the damage to the surface of PP foams caused by UV light, involving the erosion of surface, the collapse of cells and the degradation of PP chains could be significantly suppressed by the incorporation of TS nanorods. These findings indicated that TS nanorods could be used as multifunctional nanofillers to achieve the PP foams with improved foamability and photostability.

Boosting solubility performance of supercriticalCO2via ethanol toward fabrication of polyetherimide/carbon fiber composite foam with three‐dimensional geometry shape

AbstractThe demand for light‐weight, high‐performance polymeric foam material, and part soars to meet the requirements of the national economy and the high‐tech industries. Currently, foaming technologies are inadequate to fabricate these advanced materials. In this study, polyetherimide/carbon fiber (PEI/CF) foam was prepared by pressure‐induced batch foaming technology with the supercritical CO2(scCO2) and ethanol (EtOH) as the physical foaming agent and co‐foaming agent, respectively. The presence of EtOH was verified to enhance the solubility of scCO2and increase the interaction energies between PEI molecular chain and CO2/EtOH foaming agent, the expansion ratio of PEI pellets, as a result, was effectively improved from 1.3 to 7.5. Using the stainless mold‐assisted sinter molding, numerous PEI or PEI/CF pellets was simultaneously foamed and squeezed into three‐dimensional (3D) geometry shape. The cell morphology tests indicated that the CF, served as the nucleating agent, cannot only facilitate the formation of denser microcellular structure, but also improve the mechanical performance of the final foam product. As a model system, PEI/CF foam product with a density of 320 kg/m3was successfully obtained, the compression and tensile strength of which were 11.6 and 9.7 MPa, respectively, as proved by the mechanical performance measurements.

New amine adducts with carbon dioxide as blowing agents in the production of integral polyurethane foams

Blowing agents play an important role in the production of cellular polyurethanes. The traditional chemical blowing agent H2O/CO2 did not meet all application requirements. This led to the introduction of physical foaming agents in the 1950–1960s, which were subject to four further modifications due to climatic hazards. The recently introduced new generation of hydrofluoroolefins (HFOs) hydrocarbons is currently in the application assessment and meets the utility and climate requirements for now. Without waiting for a long-term final assessment of this blowing agent group, an attempt was made to introduce carbon dioxide in the form of adducts with aliphatic amines into the foaming process. As example compounds, CO2 adducts with aliphatic hydrocarbons containing also primary, secondary and tertiary nitrogen atoms in the same molecule were used. The synthesis of adducts was carried out by the absorption of carbon dioxide gas in a solution of amines in monoethylene glycol (MEG) and triethanolamine (TELA). The resulting solutions containing 12–16 wt % CO2 were next used in the application-oriented study. Amines regulating the foaming and gelation processes were used for the production of adducts, which allowed the elimination of organometallic gelling additives. Selected adducts were checked during the production of furniture chair seats on an industrial scale, obtaining integral foams in the range of density 190–294 kg/m3 and hardness 22–38 °ShA. In the production process of these foams carried out at PLASTPUR a double-stream foaming machine from Hennecke was used.

Effect of POE on mechanical properties and cellular structure of PP/Nano-CaCO3 composites in IMD/MIM process

Nano-CaCO3 can effectively improve the strength of foamed Polypropylene (PP), ethylene-octene copolymer (POE) can greatly enhance the toughness of PP, and PP-g-MAH can improve the compatibility of Nano-CaCO3 with PP. The supercritical fluid-nitrogen (N2) was used as physical foaming agent, and the PET film was selected to study the effect of POE content on the mechanical properties and cellular structure of PP/nano-CaCO3 blends during combined in-mold decoration and microcellular injection molding (IMD/MIM) process. The results showed that the addition of POE did improve the impact strength of PP/nano-CaCO3 composites, while the tensile strength and flexural strength decreased. On account of the characteristics of POE, the melt strength change of PP/nano-CaCO3 blend system after POE’s addition was studied. The melt strength of the blend system decreased at first and then increased. It can be found that POE distributed uniformly in PP, and POE particle size decreased with the increase of POE content. Besides, it was revealed that POE could improve the cellular structure of the vertical section and the parallel section. The mechanical properties and cellular structure were optimized when 10% POE was added.

Foaming behavior of poly(lactic acid) with different D-isomer content based on supercritical CO2-induced crystallization

Using supercritical carbon dioxide (sc-CO2) as a physical foaming agent, the effect of sc-CO2 on the formation of crystalline domains and subsequently on the foaming behaviors of the two grades of PLA with different D-isomer content were investigated in a wide foaming temperature range. The PLA’s final crystallinity is significantly increased with decreasing annealing temperature and by reducing the D-isomer content. Cellular structure results show that not only the crystallinity but also the crystalline morphology play an important role in cellular structure. A novel spherulite morphology including ringless and ring-banded morphology in the same spherulite was formed at lower foaming temperature, as a result, some entities were nonuniformly distributed in the PLA foams. Uniform and closed cellular structure were obtained when only the ring-banded spherulites were formed. An opened and interconnected cellular structure is tended to be formed because of the synergistic effect of high temperature and plasticization of CO2. Based on the crystallinity and morphology, a suitable foaming window as a function of temperature is proposed. It is found that PLA with 4.1% D-isomer content had much broader suitable foaming window range to produce homogeneous cellular structure.

Foaming of Poly(3-hydroxybutyrate-co-3-hydroxyvalerate) with Supercritical Carbon Dioxide: Foaming Performance and Crystallization Behavior.

Poly(3-hydroxybutyrate-co-3-hydroxyvalerate) (PHBV) samples were successfully foamed using supercritical carbon dioxide as a physical foaming agent. PHBV sheets were first saturated at 175 °C followed by a foaming process at different temperatures (145 to 165 °C) and different CO2 pressures (10 to 29 MPa). It was found that microcellular structures with average cell sizes ranging from 6 to 22 μm and cell densities ranging from 108 to 1.2 × 109 cells/cm3 could be controllably prepared by selecting suitable foaming conditions. To investigate crystallization behavior during the foaming process and explore the corresponding foaming mechanism, differential scanning calorimetry, wide angle X-ray diffraction, and small-angle X-ray scattering characterizations were carried out. Stretching behavior during the cell growth stage may increase the crystal nucleation rate, and the generated crystal nucleus accelerates the crystallization rate as well as thickens PHBV crystal lamellae.

Preparation of Polypropylene Foams with Bimodal Cell Structure Using a Microporous Molecular Sieve as a Nucleating Agent

A novel approach for fabricating polypropylene (PP) foam with bimodal cellular structure utilizing CO2 as a physical foaming agent was established by adding porous molecular sieve (PMS) as nucleati...

Natural fiber reinforced inorganic foam composites from short hemp bast fibers obtained by mechanical decortation of unretted stems from the wastes of hemp cultivations

The wettability of hemp fibers, to be applied in fiber-reinforced foams, can be improved with several chemical treatments. In this paper, a innovative treatment with sodium ascorbate was evaluated. Untreated and treated fibers have been characterized using FTIR spectroscopy and TGA measurements. Furthermore, the feasibility of treated fibers was evaluated preparing diatomite-based fiber-reinforced foams. These materials were finally characterized by mechanical compressive strength and thermal properties (thermal conductivity). The fiber-reinforced foams have been produced using a diatomite natural source as a matrix. A suitable amount of Si powder and vegetable surfactant were used as chemical and physical foaming agents while a polysilicate solution was used as reactive crosslinker. The foams highlight low density, around 350 kg/m3, and low thermal conductivity (0.06 W/mK).

Morphological evolution of PLA foam from microcellular to nanocellular induced by cold crystallization assisted by supercritical CO2

The use of physical foaming agents to form nanofoams in semicrystalline polymers is still a tremendous challenge. The change from microcellular to nanocellular bubbles (the micro/nano transition) in poly(lactic acid) (PLA) foam was investigated by adjusting the type of crystals induced in PLA during cold crystallization. The results showed that at saturation temperatures below the micro/nano transition temperature, α′ crystals formed; their coarser surfaces and higher crystallinity resulted in a higher cell nucleation efficiency, and thus a microcellular foam was converted to a high-cell-density nanofoam. After chain extension, the micro/nano transition temperature decreased, and the properties of the foam were improved at temperatures above the micro/nano transition temperature. A nanocellular foam with a cell density of 1015 cells/cm3 and a cell size of approximately 30 nm was obtained.

A Novel Hybrid Foaming Method for Low-Pressure Microcellular Foam Production of Unfilled and Talc-Filled Copolymer Polypropylenes.

Unfilled and talc-filled Copolymer Polypropylene (PP) samples were produced through low-pressure foam-injection molding (FIM). The foaming stage of the process has been facilitated through a chemical blowing agent (C6H7NaO7 and CaCO3 mixture), a physical blowing agent (supercritical N2) and a novel hybrid foaming (combination of said chemical and physical foaming agents). Three weight-saving levels were produced with the varying foaming methods and compared to conventional injection molding. The unfilled PP foams produced through chemical blowing agent exhibited the strongest mechanical characteristics due to larger skin wall thicknesses, while the weakest were that of the talc-filled PP through the hybrid foaming technique. However, the hybrid foaming produced superior microcellular foams for both PPs due to calcium carbonate (CaCO3) enhancing the nucleation phase.

Tuning cell structure and expansion ratio of thick-walled biodegradable poly(lactic acid) foams prepared using supercritical CO2

Thick-walled poly(lactic acid) samples are foamed using supercritical carbon dioxide as physical foaming agent over a wide saturation time range using a constant-temperature mode and a wide foaming pressure range using the constant-temperature mode and a varying-temperature mode. Using the constant-temperature mode, three regions with no-celled core and two regions with cells of different diameters appear on the fractured surfaces of the foamed samples prepared at 5 and 10 min saturation times, respectively, whereas a relatively uniform cellular structure is obtained at 20–180 min saturation times. Raising the foaming pressure can improve the cellular structure uniformity. Moreover, prolonging saturation time or raising foaming pressure results in rupture of more cell walls and so formation of open-celled structure to a certain extent. Using the varying-temperature mode, a bimodal cellular structure with stamen-like cells and a trimodal cellular structure with an extraordinarily high expansion ratio (76.2) are successively achieved during raising the foaming pressure (18–22 MPa). The formation mechanisms for the bimodal and trimodal cellular structures are analyzed based on the result of the foaming pressure effect on the cellular structure in the foamed poly(lactic acid) samples prepared using the constant-temperature mode.

Foamability and viscosity behavior of extrusion foamed PLA–pulp fiber biocomposites

ABSTRACTThis study addresses the effect of fiber reinforcement, chain extension, and physical foaming agent type on foam morphology and viscosity behavior of pulp fiber reinforced poly(lactic acid) (PLA) biocomposites. PLA reinforced with 0, 10, and 20 wt % of bleached kraft pulp fibers with and without chain extender were foamed using two different physical foaming agents (carbon dioxide and isobutane) by extrusion foaming. Densities, foam morphologies, and viscosities were systematically analyzed and compared from the produced foams. As a conclusion, low‐density foams are produced with both foaming agents and fiber levels, fiber addition limiting cell growth. Isobutane provides better dimensional stability with narrower cell size distribution, whereas carbon dioxide enables lower foaming temperature. Chain extension is essential to achieve foam with low density and good cell structure. Contrary to nonchain extended PLA, addition of fibers reduced the viscosity of chain extended PLA. © 2019 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2019, 136, 48202.

Characterizations of foamed asphalt binders prepared using combinations of physical and chemical foaming agents

The objective of this study is to characterize the foamed asphalt binders prepared using different combinations of physical and chemical foaming agents. The foamed asphalt binders were investigated using the Rotational Viscosity (RV), Dynamic Shear Rheometer (DSR) and expansion ratio tests. Asphalt binders were also evaluated after short-term and long-term aging conditions. During the asphalt binder’s foaming process, the preheated binder was formerly foamed using a physical foaming agent (either water or ethanol), followed by the addition of sodium bicarbonate (NaHCO3) to improve the bubbling and the stability of the foam. Theoretically, through this process, numerous bubbles are generated by the vaporized ethanol or water, and the gases are released by NaHCO3, which significantly increases the volume of foamed asphalt. All foamed asphalt binders were produced at the same temperature, 100 °C, to diminish the inconsistency of binder-aging conditions during the preheating process. Overall, the results indicated that ethanol has better characteristics in lowering the viscosity of asphalt binders at low temperatures and is expelled from the asphalt binder after continuous heating at temperatures higher than its boiling point (78 °C). Although the addition of NaHCO3 has slightly increased the foamed binder viscosity that may affect its workability, it substantially lowers the volatile loss of foamed binders, as well as significantly improves the expansion ratio and the resistance to rutting.

Effects of Nano-CaCO₃ Content on the Crystallization, Mechanical Properties, and Cell Structure of PP Nanocomposites in Microcellular Injection Molding.

Using supercritical nitrogen as the physical foaming agent, microcellular polypropylene (PP) nanocomposites were prepared in microcellular injection molding. The main purpose of this work is to study effects of content of nano-CaCO3 on the crystallization, mechanical properties, and cell structure of PP nanocomposites in microcellular injection molding. The results show that adding nano-CaCO3 to PP could improve its mechanical properties and cell structure. The thermal stability and crystallinity enhances with increase of nano-CaCO3. As a bubble nucleating agent, adding nano-CaCO3 to PP improves the cell structure in both the parallel sections and vertical sections. The mechanical properties increase first and then decrease with increase of nano-CaCO3. The mechanical properties are affected by the cell structure, as well. The mechanical properties and cell structure are optimum when the content of nano-CaCO3 is 6 wt %.