Polyurethane foaming with CO2 adducts from C8 alkyl grafted polyethyleneimines: Optimization of the grafting rate and application of the blowing agents

We previously explored a series of CO₂ adducts from alkylated polyethylenimines with C₄ to C₁₆ alkyl side chains, serving as climate-friendly blowing agents for polyurethanes (PUs). Among them, the polyethylenimine with C₈ alkyl (2-ethylhexyl) side chains demonstrated the highest foaming efficiency. In this study, we further changed the grafting rate of the C₈ alkyl, from 7 to 16%, and investigated the effects of the resulting blowing agents on the foaming process. For both foaming systems containing a castor oil-derived polyol (Polycin T-400) or a poly(propylene glycol) polyol (Polyether 4110), the CO₂ adducts with a grafting rate of 13% displayed the best foaming performance in terms of high dispersibility in the foaming systems, homogenous cellular morphology, and good mechanical properties. Moreover, the 13%-C₈-alkylated blowing agent demonstrated high suitability for the foaming systems from biomass-sourced polyols (like Polycin T-400). Therefore, the optimized CO₂-adduct blowing agent could replace the currently used climate-changing hydrochlorofluorocarbons and hydrofluorocarbons, as well as might contribute to the development of future renewable PU foams. © 2019 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2020 , 137, 48752.     

Carbon dioxide adduct from polypropylene glycol grafted polyethyleneimine as a climate-friendly blowing agent for polyurethane foams

A novel CO₂ adduct has been synthesised from a branched polyethyleneimine with polypropylene glycol (PPG) side chains and can serve as an alternative to traditional polyurethane blowing agents, such as hydrochloroflourocarbons and hydrofluorocarbons, which cause ozone depletion and/or global warming. The CO₂ adduction trapped 13.8 wt% of CO₂, forming alkylammonium carbamates in the main chains. Therefore, the prepared blowing agent is amphophilic, and can form micellae-like spheres in the mixture of polyurethane raw materials called the white component. Once this mixture is blended with isocyanate or the black component like in conventional foaming processes, the consequent exothermic polymerisation drives the release of the captured CO₂ from the micelles, serving as the foaming gas. Meanwhile, the blowing agent gradually restores its original polyamine structure, whose bulky PPG side chains can sterically inhibit the reaction between the restored amine groups and the isocyanate groups in the growing polyurethane chains. The resulting foam displays uniform cellular morphology with a much lower density than the control sample blown by trances of water from the raw materials. This is the first report using thermally instable CO₂ adduct to blow polyurethanes, which could pave the way for the next generation of climate-friendly polyurethane blowing agents.     

Carbon dioxide adducts from DOPO-grafted polyethylenimines as both blowing agents and flame retardants for polyurethanes

The high risk of flammability of polyurethane foams (PUFs) and the high global warming potentials of polyurethane (PU) blowing agents rank key problems to be solved in PUF industry. Herein, 9,10-dihydro-9-oxa-10-phosphenanthrene-10-oxide (DOPO)-grafted polyethylenimines (PEIs) are synthesized via Atherton–Todd reaction, with grafting rate ranging from 13.3% to 28.3%. The grafted PEIs further react with CO₂ to obtain corresponding CO₂ adducts (DOPO-PEI-CO₂s). On the one hand, these CO₂ adducts can disperse into PU foaming mixture to release CO₂ as a climate-friendly blowing agent. The resultant PUFs possess a density about 56 kg m⁻³ and a compressive strength over 200 kPa, suitable for some industrial applications. On the other hand, the DOPO grafting endows the PUFs with moderate flame retardancy, increasing the PUFs' limiting oxygen index value from 19.7 to 25 vol%, and decreasing the horizontal burning speed from about 360 mm min⁻¹ down to 130 mm min⁻¹. This study for the first time provides a type of polyurethane (PU) raw material that can serve as both blowing agents and flame retardants.     

A study of cell nucleation in the extrusion of polypropylene foams

An investigation has been performed of the cell nucleation and initial growth behaviors in the foam processing of polypropylene (PP) in both the linear and branched forms. These materials were foamed in extrusion with the two blowing agents, CO₂ and isopentane. The cell density generally increased with an increased content of the blowing agent, for both CO₂ and isopentane. The effect of processing pressure on the cell density was distinct when CO₂ was used, whereas no pressure effect was observed in the foam processing with isopentane. The cell morphologies for the two PPs were found to be significantly different. A slightly lower nuclei density was observed in the branched PP foams than in the linear PP foams. However, the phenomenon of cell coalescence was observed much less in the branched PP foams. Most cells in the branched PP foams were closed, whereas in the linear PP foams they were connected to each other. The experimental results indicated that the branched structure played an important role in determining the cell morphologies through its effects on the melt strength and/or melt elasticity.     

Modified polyurethane with a covalent bond of dye molecule

In this article, we have successfully synthesized polyurethanes (PUs) with a covalent bond of dye molecule via a coupling agent of epichlorohydrin. The structure is proven by infrared (IR) spectra, which exhibits the absorption peak of dye molecule, as we expected. The dye‐grafted polyurethanes were used to evaluate their inherent viscosity, mechanical, and thermal properties and, also, their dyeing behavior. For the inherent viscosity, the PUs with the grafting of the dye molecule demonstrate a lower value of viscosity than those without grafting of the dye molecule. The tensile strength is found to decrease with the grafting of the dye molecule due to the further separation of intermolecular distance of the grafted PUs. But the elongation at break is increased with the grafting of the dye molecule. In consideration of the thermal properties, PUs with the grafting of dye molecule exhibit higher T_gh than those without dye molecule. However, their T_gs and T_ms of soft segment between dyed and undyed PU seem to be similar. For dye migration property, the PUs with the grafting of dye molecule are proven to be much lower thermal migration values (Mp%) than those of simple mixing of PU and dyestuff. © 1999 John Wiley & Sons, Inc. J Appl Polym Sci 73: 245–253, 1999     

Foaming behavior of isotactic polypropylene in supercritical CO2 influenced by phase morphology via chain grafting

Polystyrene (PS) and poly(methyl methacrylate) (PMMA) grafted isotactic polypropylene copolymers (iPP-g-PS and iPP-g-PMMA) with well-defined chain structure were synthesized by atom transfer radical polymerization using a branched iPP (iPP-B) as polymerization precursor. The branched and grafted iPP were foamed by using supercritical CO₂ as the blowing agent with a batch method. Compared to linear iPP foam, the iPP-B foams had well-defined close cell structure and increased cell density resulted from increased melt strength. Further incorporating PS and PMMA graft chains into iPP-B decreased the crystal size and increased the crystal density of grafted copolymers. In iPP-g-PS foaming, the enhanced heterogeneous nucleation by crystalline/amorphous interface further decreased the cell size, increased the cell density, and uniformized the cell size distribution. In contrast to this, the iPP-g-PMMA foams exhibited the poor cell morphology, i.e., large amount of unfoamed regions and just a few cells distributed among those unfoamed regions, although the crystal size and crystal density of iPP-g-PMMA were similar to those of iPP-g-PS. It was found that the iPP-g-PMMA exhibited PMMA-rich dispersed phase, which had higher CO₂ solubility and lower nucleation energy barrier than copolymer matrix did. The preferential cell nucleation within the PMMA-rich phase or at its interface with the matrix accounted for the poor cell morphology. The different effect of phase morphology on the foaming behavior of PS and PMMA grafted copolymers is discussed with the classical nucleation theory.     

SBA-15 grafted with 3-aminopropyl triethoxysilane in supercritical propane for CO2 capture

Supercritical propane (SC-propane) was found to be a promising solvent for grafting (3-aminopropyl)triethoxysilane (APS) onto synthesized SBA-15 for CO₂ capture. The influence of operating conditions in SC-propane for CO₂ adsorption at different pressures (8.3–13.8 MPa), temperatures (85–120 °C), and periods of time (4–16 h) were evaluated. The CO₂ adsorption conditions under different partial pressures, temperatures and moisture were evaluated. The results showed a reduction in pore characteristics and an increased amount of grafted APS with increasing pressure and temperature after grafting. After grafting in SC-propane at 11.0 MPa and various temperatures for 16 h, a 3–20% increase in the amount of grafted APS and a 6–49% increase in the CO₂ adsorption capacity over the toluene refluxing was observed. The time required for grafting in SC-propane could be reduced while maintaining higher nitrogen content and CO₂ adsorption capacity compared with grafting in toluene refluxing.     

Stable CO2/water foam stabilized by dilute surface-modified nanoparticles and cationic surfactant at high temperature and salinity

CO₂ enhanced oil recovery and storage could see widespread deployment as decarbonization efforts accelerate to meet climate goals. CO₂ is more efficiently distributed underground as a viscous foam than as pure CO₂; however, most reported CO₂ foams are unstable at harsh reservoir conditions (22 wt% brine, 2200 psi, and 80°C). We hypothesize that silica nanoparticles (NP) grafted with (3-trimethoxysilylpropyl)diethylenetriamine ligands (N3), to improve colloidal stability, and dimethoxydimethylsilane ligands (DM), to improve CO₂-phillicity, combined with the cationic surfactant N¹-alkyl-N³, N³-dimethylpropane-1,3-diamine (RCADA), will develop viscous, stable CO₂ foams at reservoir conditions. We grafted NP with N3 and DM ligands. We verified NP stability at reservoir conditions with measurements of zeta potential, amine titration curves, and NP diameter. We measured NP water contact angles (θ_w) at the water–air and water–liquid CO₂ interfaces. In a high-temperature, high-pressure flow apparatus, we calculated the viscosity of CO₂ foams across a beadpack and determined static foam stability with microscope observations. Modified NP were colloidally stable at reservoir conditions for 4 weeks, and had higher θ_w in liquid CO₂ than in air. Addition of at least 0.5 μmol/m² DM silane (0.5DM) greatly improved foam stability. RCADA-only foam coarsening rates (dD_SM³/dt) decreased 16–17× after adding 1 wt/vol% 8N3 + 1.5DM NP, and 5–10× with a 0.1–1 vol/vol% increase in RCADA concentration (with or without NP). 1 vol/vol% RCADA foam exhibited coarsening rates of 900 and 2400 μm³/min with 1 and 0.2 wt/vol% 8N3 + 1.5DM NP, respectively. These results demonstrate impressive foam stabilities at harsh reservoir conditions.     

A new microcellular foam injection‐molding technology using non‐supercritical fluid physical blowing agents

A new foam injection‐molding technology was developed to produce microcellular foams without using supercritical fluid (SCF) pump units. In this technology, physical blowing agents (PBA), such as nitrogen (N₂) and carbon dioxide (CO₂), do not need to be brought to their SCF state. PBAs are delivered directly from their gas cylinders into the molten polymer through an injector valve, which can be controlled by a specially designed screw configuration and operation sequence. The excess PBA is discharged from the molten polymer through a venting vessel. Alternatively, additional PBA is introduced through the venting vessel when the polymer is not saturated with PBA. The amount of gas delivered into the molten polymer is controlled by the gas dosing time of the injector valve, the secondary reducing pressure of the gas cylinder and the outlet (back) pressure of the venting vessel. Microcellular polypropylene foams were prepared using the developed foam injection‐molding technology with 2–6 MPa CO₂ or 2–8 MPa N₂. High expansion foams with an average cell size of less than 25 μm were prepared. The developed technology dispels arguments for the necessity to pressurize N₂ or CO₂ to the SCF to prepare microcellular foams. POLYM. ENG. SCI., 57:105–113, 2017. © 2016 Society of Plastics Engineers     

Challenge to fortyfold expansion of biodegradable polyester foams by using carbon dioxide as a blowing agent

This paper presents a new foaming technology using supercritical carbon dioxide as a blowing agent to obtain large volume expansions of biodegradable polyester foams of over fortyfold. The basic approach for the promotion of a large volume expansion ratio with carbon dioxide was to prevent cell coalescence by using a branched material, to dissolve carbon dioxide completely in the melt by promoting convective diffusion under a high processing pressure, to reduce the diffusivity of gas by lowering the melt temperature, and to optimize the processing conditions in the die to maximize volume expansion. The desirable composition of the materials includes dehydrated branched biodegradable polyester (polybutylene succinate), CO₂ (blowing agent), and tale (nucleating agent). A single‐screw extrusion system was used for foam processing. A large volume expansion ratio of up to forty‐fivefold was achieved from the biodegradable polyester foams. The morphologies and volume expansion ratios of biodegradable polyester foams at various processing temperatures and pressures were studied.     

Dielectric response of conducting carbon‐black‐filled ethylene–octene copolymer microcellular foams

Dielectric response of conducting carbon‐black‐filled ethylene–octene copolymer microcellular foams has been investigated with variation of blowing agent and filler loading in the frequency range of 100 Hz to 5 MHz and temperature range from 30 to 100°C. With increase in blowing agent loading, the dielectric permittivity increases for both unfilled as well as carbon‐black‐filled microcellular foams. The experimental complex impedance plots were compared with model‐fitted plots obtained by taking an equivalent circuit of (CQR) (CR).The values of R_b (bulk resistance), R_gb (grain boundary resistance), bulk capacitance (C_b), and grain boundary capacitance (C_gb) at different temperatures were calculated and compared with experimental values. The relaxation time due to bulk effect (τ_b) has been calculated from relaxation frequency (f_r). The dc conductivity (σ_dc) decreases with rise in temperature indicating the existence of positive temperature coefficient of resistance in the material. The activation energy (E_a) calculated from the relaxation time due to bulk effect (τ_b) was found to be 0.446 eV, whereas it was 0.363 eV from the dc conductivity plot in the temperature range of 30–100°C. POLYM. COMPOS., 37:3398–3410, 2016. © 2015 Society of Plastics Engineers     

Extruded polystyrene foams with bimodal cell morphology

Extrusion foaming using supercritical carbon dioxide (CO₂) as the blowing agent is an economically and environmentally benign process. However, it is difficult to control the foam morphology and maintain its high thermal insulation comparing to the conventional foams based on fluorocarbon blowing agents. In this study, we demonstrated that polystyrene (PS) foams with the bimodal cell morphology can be produced in the extrusion foaming process using CO₂ and water as co-blowing agents and two particulate additives as nucleation agents. One particulate is able to decrease the water foaming time so both CO₂ and water can induce foaming simultaneously, while the other increases the CO₂ nucleation rate with little effect on the CO₂ foaming time. Our experimental results showed that a dual particulate combination of nanoclay and activated carbon provided the best bimodal structure. The bimodal foams exhibited much better compressive properties and slightly better thermal insulation for PS foams.     

Novel poly(aryl ether nitrile ketone) foams and the influence of copolymer structure on the foaming result

Novel poly(aryl ether nitrile ketone) foams were prepared through the batch foaming method with supercritical CO₂ as the blowing agent. Both temperature‐induced and pressure‐induced foaming methods were conducted to examine the influence of nitrile groups on the foaming result. The results indicated that nitrile groups influenced the foaming result by affecting both the viscoelasticity and CO₂ absorption of the polymers. In addition, the CO₂ solubility of the polymers increased with increasing CN content presumably because of the Lewis acid–base nature of the interaction between the CO₂ molecules and the nitrile groups. The cell growth process was assessed by analyzing the influence of foaming temperature and foaming time on the cell morphology. Nanocellular foams with a minimum size of 30–50 nm were achieved by the temperature‐induced foaming method. Moreover, highly expanded foams with a maximum expansion ratio of 23.6 were obtained by the pressure‐induced foaming method. © 2018 Society of Chemical Industry     

Copper (I) ion stabilized on fe3o4‐core ethylated branched polyethyleneimine‐shell as magnetically recyclable catalyst for ATRP reaction

Branched polyethyleneimine (bPEI) was used to modify the surface of Fe₃O₄ nanoparticles coated with silica layer, and then, it was treated with ethyl iodide to prepare Fe₃O₄@SiO₂@Ethylated‐bPEI. In the next step, the yolk–shell structure was gained by selectively etching the SiO₂ middle layer. Finally, copper(I) was introduced to the yolk–shell Fe₃O₄@Ethylated‐bPEI and the activity of the catalyst was evaluated for atom transfer radical polymerization (ATRP) of styrene, led to obtain the well‐defined polymer with relatively low polydispersity. The toxicity of the residual copper in the polymer product was a limiting issue for applicability of ATRP reactions especially for biological purposes. In this report, the copper content in the polymer was reduced to the excellent value of 1.1 ppm. Moreover, the magnetic isolation, recyclability, and remove the need for an external ligand were other advantages of the synthesized catalyst which makes it suitable for employing in ATRP reactions. © 2015 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2015 , 132, 42337.     

Mesoporous silica particles grafted with polystyrene brushes as a nucleation agent for polystyrene supercritical carbon dioxide foaming

In this study, spherical ordered mesoporous silica (s‐OMS) was applied as a new type of nucleating agent in polystyrene (PS) foaming with supercritical CO₂ as a blowing agent. These s‐OMS particles were modified by the selective grafting of PS brushes on the outside surface, by which the mesoporous structure inside particles could be maintained. Transmission electron microscopy, X‐ray diffraction, thermogravimetric analysis, Fourier transform infrared spectroscopy, and Brunauer–Emmett–Teller surface area analysis were used to characterize the structure of the original and modified particles; these indicated that the PS brushes were grafted on the outside surface and the inside porous structure were maintained. PS/s‐OMS–PS composites were prepared by a solution blending method, and the s‐OMS–PS particles could have been well dispersed in the PS matrix because of the surface modification. Subsequently, PS and composite microcellular foams were prepared by a batch foaming process, and the morphology characterization on these foams showed that the s‐OMS particles exhibited an excellent heterogeneous effect on PS foaming. The heterogeneous effect became more significant when the foaming temperature or saturation pressure was low. © 2013 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 130: 4308–4317, 2013     

Amine‐functionalized mesoporous silica: A material capable of CO2 adsorption and fast regeneration by microwave heating

The surface of ordered mesoporous (MCM‐48) silica has been subjected to covalent grafting with silane molecules containing one to three amino groups. The dielectric properties of the materials were studied in detail, and the functionalized materials were used for CO₂ adsorption at room temperature, followed by regeneration under either conventional heating or microwave irradiation. It has been found that, as the intensity of functionalization with amino groups increases (from mono‐ to tri‐amino silanes) both the CO₂ load and the dielectric response at microwave frequencies increase. In particular, functionalization with a tri‐amino silane derivative gave the highest CO₂ adsorption and the fastest microwave heating, resulting in a fourfold acceleration of adsorbent regeneration. The grafted material was fully stable for at least 20 adsorption‐regeneration cycles, making it an ideal candidate for microwave‐swing adsorption (MWSA) processes. © 2015 American Institute of Chemical Engineers AIChE J, 62: 547–555, 2016     

Preparation of open‐cell foams from polymer blends by supercritical CO2 and their efficient oil‐absorbing performance

This letter reports on the hydrophobicity and oleophilicity of open‐cell foams from polymer blends prepared by supercritical CO₂. A typical bulk density of the foam is measured to be 0.05 g/cm³. The contact angle of the foam with water is determined to be 139.2°. The foam can selectively absorb the diesel from water with the uptake capacity of 17.0 g/g. The foams are technologically promising for application of oil spill cleanup. © 2016 American Institute of Chemical Engineers AIChE J, 62: 4182–4185, 2016     

Aminating modification of viscose fibers and their CO2 adsorption properties

An adsorbent for CO₂ capture was prepared by the grafting of acrylonitrile (AN) onto viscose fibers (VFs); this was followed by amination with triethylene tetramine (TETA). The effects of the reaction conditions, such as the concentrations of the monomer, initiator, and nitric acid, on the grafting degree and grafting efficiency were studied. The adsorption performance of the adsorbent for CO₂ was evaluated by fixed‐bed adsorption. The highest dynamic adsorption capacity of the adsorbent for CO₂ was 4.35 mmol/g when the amine content of the adsorbent VF–AN–TETA reached 13.21 mmol/g. Compared with the polypropylene (PP)‐fiber‐based adsorbent (PP–AN–TETA), VF–AN–TETA with hydroxyl groups on the fibers facilitated the diffusion of CO₂ and water and led to a higher CO₂ adsorption capacity than that of PP–AN–TETA. The VF–AN–TETA adsorbent also showed good regeneration performance: its CO₂ adsorption capacity could still retain almost the same capacity as the fresh adsorbent after 10 adsorption–desorption cycles. © 2015 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2016 , 132, 42840.     

Foaming and defoaming properties of CO2-switchable surfactants

The present study is about the foaming and defoaming properties of the CO₂-switchable surfactant N,N-dimethyltetradecylamine (C₁₄DMA) and its advantages compared with the non-switchable counterpart tetradecyltrimethylammonium bromide (C₁₄TAB). In the absence of CO₂, C₁₄DMA is a water insoluble organic molecule without any surface activity thus being unable to stabilize foams. In the presence of CO₂, the head group becomes protonated which transforms the water insoluble molecule into a cationic surfactant. Comparing the surface properties and foamability of C₁₄DMA and C₁₄TAB one finds a very similar behavior. However, the foam stabilities differ depending on the gas. Foaming the two-surfactant solutions with CO₂ leads to very unstable foams in both cases. However, foaming the two surfactant solutions with N₂ reveals the switchability of C₁₄DMA: while the volume of foams stabilized with C₁₄TAB hardly changes over 1600 s, the volume of foams stabilized with C₁₄DMA decreases significantly in the same period of time. This difference is due to the fact that the surface activity, that is, the amphiphilic nature, of C₁₄DMA is continuously switching off since CO₂ is displaced by N₂ thus deprotonating and deactivating the surfactant.     

Cell evolution and compressive properties of styrene–butadiene–styrene toughened and calcium carbonate reinforced polystyrene extrusion foams with supercritical carbon dioxide

Polystyrene (PS) foams have been used in various fields, whereas its broader application is limited by its low mechanical strength and brittle features. In this study, styrene–butadiene–styrene (SBS) and calcium carbonate (CaCO₃) nanoparticles were melt‐blended with PS and extrusion‐foamed with supercritical carbon dioxide as a blowing agent to simultaneously toughen and reinforce PS foams. Under the same foaming conditions, the addition of SBS and CaCO₃ was shown to have a significant influence on the cell structure and the compressive properties of the composite foams. We found that the cell structure evolution was highly correlated with the system viscosity. When the rubbery‐phase SBS content was 20%, the cell diameter decreased by 20.7%, and the compressive modulus was enhanced by 289.5%. With the further addition of 5% rigid CaCO₃ nanoparticles, the cell diameter was further reduced by 72.2% and the compressive modulus was improved by 379.2%. © 2016 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2016 , 133, 43508.