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Schematic of a Flory-Huggins thermodynamic model 127. Black circles and white circles represent polymer molecule chains and small solvent molecules, respectively.
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Over the last century, polymer processes involving a gas or supercritical fluid (SCF) have attracted significant attention. The attributes of a gas/SCF in polymers benefited many polymer processing applications. In polymer applications, the solubility and diffusivity of the gas/SCF in polymers are important parameters. This review discusses experim...
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... classical Flory-Huggins theory is based on a lattice model for describing polymer/solvent or polymer/polymer mixture systems. In a lattice model, all the cells are occupied with segments (i.e., solvent molecule or segment of a long polymer chain) as shown in Figure 2. The volume among different segments (segments of a long polymer chain or small solvent molecules) is assumed to be the same. ...
Citations
... Sorption and desorption tests of CO 2 were conducted to investigate the CO 2 sorption behavior of solid TPU samples and to analyze further the relationship between CO 2 solubility, diffusion coefficient, and gradient cellular morphology. The gravimetric method was employed to carry out the CO 2 sorption content measurements [44]. The highprecision electronic balance was used to weigh the initial weight of the prepared sample before the sorption experiments. ...
... As the temperature increases, the molecular chains become more mobile, which results in larger pores in the free volume [3], as well as stronger thermal movements of the CO 2 molecules, which in turn increases the diffusion capacity and diffusivity. TPU has a significantly higher CO 2 sorption diffusion coefficient than common polymers such as PET [56], PMMA [44], and PVC [57]. This can be attributed to the soft segment of TPU being the primary area impregnated with CO 2 [58], as well as the strong mobility of its molecular chains. ...
... where S denotes the solubility coefficient (mol/m 3 ·Pa), and p H is the partial pressure of hydrogen (Pa). The hydrogen permeability coefficient of a polymer is the product of the diffusion and solubility coefficients and is expressed as P e = D × S [44,45]. ...
Type IV hydrogen storage cylinders comprise a polymer liner and offer advantages such as lightweight construction, high hydrogen storage density, and good fatigue performance. However, they are also characterized by higher hydrogen permeability. Consequently, it is crucial for the polymer liner material to exhibit excellent resistance to hydrogen permeation. International organizations have established relevant standards mandating hydrogen permeation tests for the liner material of type IV on-board hydrogen storage cylinders. This paper provides a comprehensive review of existing research on hydrogen permeability and the hydrogen permeation test methods for the polymer liner material of type IV on-board hydrogen storage cylinders. By delving into the hydrogen permeation mechanism, a better understanding can be gained, offering valuable references for subsequent researchers in this field. This paper starts by thoroughly discussing the hydrogen permeation mechanism of the liner material. It then proceeds to compare and analyze the hydrogen permeation test methods specified by various standards. These comparisons encompass sample preparation, sample pretreatment, test device, test temperature and pressure, and qualification indicators. Then, this study offers recommendations aimed at enhancing the hydrogen permeation test method for the liner material. Additionally, the influence of test temperature, test pressure, and polymer material properties on the hydrogen permeability of the liner material is discussed. Finally, the influences of the test temperature, test pressure, and polymer material properties on the hydrogen permeability of the liner material are discussed. Future research direction on the hydrogen permeability and hydrogen permeation test method of the liner material of the type IV hydrogen storage cylinder has been prospected.
... We tried to avoid collecting isotherm tails exhibiting such behavior.2.Experimental methodology flaws are somewhat more difficult or even impossible to detect.We will define them broadly, including equipment malfunction, unjustified approximations made for data processing, misprints in a research paper, etc. A comprehensive review of the experimental methods and their pitfalls can be found elsewhere331,332 . We will only shortly comment on some typical cases, which include:-equipment malfunction or loose calibration, failure to collect the readings correctly, poor reagents quality, etc. ...
A twin convolutional neural network is proposed to predict the pressure and temperature-dependent sorption of gases, vapors, and supercritical fluids in amorphous polymers based solely on spatial electron density distribution. Quantum chemical data as 3D tensors (3D images) is derived from DFT calculations. A dataset of almost 15000 experimentally measured uptakes (0.01-50 wt%) of 79 gases in 102 different polymers under pressures from 1E-3 – 7E+2 bar range and temperatures from 233-508 K range is collected from over 250 literature sources. The dataset includes measurements on almost 500 solvent-polymer systems spanning from typical low-pressure sorption in membrane glassy polymers to high-pressure solubility of supercritical fluids in molten polymers. Irreducible mean absolute percentage error (MAPE) is approximately estimated to be ~20%. The sources of inherent data variability are briefly discussed. In 150 epochs, the model achieved 31% MAPE on a test set of 1600 experimental measurements concerning 22 polymers previously unseen by the model.
... Factors affecting the diffusion coefficient include free volume and gas permeation paths [49]. When the crystallinity is high, the molecular chains are tightly arranged, which leads to a decrease in the free volume fraction [50]. As for the gas permeation path, gas permeation in a polymer matrix can be described in terms of tortuosity [51], that is, the process by which gas penetrates the surface of the polymer material and passes around internal obstacles such as fillers, as shown in Figure 13b. ...
The rapid development of hydrogen fuel cells has been paralleled by increased demand for lightweight type IV hydrogen storage vessels with high hydrogen storage density, which raises the performance requirements of internal plastic liners. An appropriate manufacturing process is important to improve the quality of polymer liners. In this paper, DSC, WAXD, a universal testing machine and a differential pressure gas permeameter were used to investigate the effect of the cooling rate of the rotational molding polyamide 11 on the thermal, crystallization, mechanical and barrier properties. The cooling rate is formulated according to the cooling rate that can be achieved in actual production. The results suggest that two PA11 liner materials initially exhibited two-dimensional (circular) growth under non-isothermal crystallization conditions and shifted to one-dimensional space growth due to spherulite collision and crowding during the secondary crystallization stage. The slower the cooling process, the greater the crystallinity of the specimen. The increase in crystallinity significantly improved the barrier properties of the two PA11 liner materials, and the gas permeability coefficient was 2-3-fold higher than at low crystallinity. Moreover, the tensile strength, the tensile modulus, the flexural strength, and the flexural modulus increased, and the elongation at break decreased as the crystallinity increased.
... Fig. 2a-b present the effects of saturation pressure on pure CO 2 and N 2 solubility. It can be found that the relationship between the pressure and the solubility of pure gas was linear, agreed with Henry's law [33]: ...
Poly(butylene adipate-co-terephthalate) (PBAT) is considered one of the most promising environment-friendly polymers due to its recognized biodegradability and irreplaceable mechanical properties. Microcellular foaming can further endow PBAT with more functional performance, such as high elasticity, sound and thermal insulation. However, the preparation of PBAT foams generally exhibits serious shrinkage problems, which results in a low and unstable expansion ratio, poor performance, and dramatically limits its wide applications. In this work, the microcellular foaming with N2 & CO2 as co-blowing agents was designed to address the shrinkage problem effectively. Thanks to the N2 & CO2 co-blowing agents, PBAT foams with a high expansion ratio of 14.9-fold and a restricted shrinkage of less than 6% were produced by using microcellular foaming. The results indicate that introducing N2 & CO2 as co-blowing agents can not only stabilize the cellular structure but also restrict the shrinkage of cell walls. More importantly, the prepared PBAT foams exhibited outstanding compressive properties with a strength of 0.17 MPa, and superior resilience with an energy loss coefficient of 12%. Therefore, it is demonstrated that the microcellular foaming with mixed blowing agents provides a suitable strategy to solve the shrinkage of foams, thus exhibiting admirable prospects for the mass production of biodegradable polyester foams.
... In other words, to understand the applicability of the CAPC method, one needs to understand the plasticization of the polymers involved. CO 2 is known to easily dissolve into polymers, especially when dissolved in the amorphous part, by numerous viewpoints (reaction engineering of polymers in supercritical CO 2 [20], model calculations of CO 2 solubility [21], Polymers 2022, 14, 3724 2 of 14 determination of CO 2 solubility [22], and interaction between polymers and CO 2 [23]). The degree of crystallinity of the polymers greatly affects the formation of foams by influencing the solubility and diffusion of CO 2 [24]. ...
... In Equations (20)- (22), the exponential part of the function was fixed only for the untreated sample, whereas the exponential part of each of the remaining samples was used as the fitting parameter. The results are shown in Table 1 and Figure 9. ...
Carbon dioxide (CO2)-assisted polymer compression method is used for plasticizing polymers with subcritical CO2 and then crimping the polymer fibers. Given that this method is based on crimping after plasticization by CO2, it is very important to know the degree of plasticization. In this study, heat treatment was gently applied on raw material fibers to obtain fibers with different degrees of crystallinity without changing the shape of the fibers. Simultaneously, two types of sheets were placed in a pressure vessel to compare the degree of compression and the degree of hardness. Furthermore, a model was used to derive the relative Young’s modulus of porous materials composed of polymer fibers with different degrees of crystallinity. In the model, the amount of strain was calculated according to the Young’s modulus as a function of porosity and reflected in compression. Young’s modulus of porous polymers in the presence of CO2 has been shown to vary significantly with slight differences in crystallinity, indicating that extremely low crystallinity is significant for plasticizing the polymer by CO2.
... Fig. 2a-b present the effects of saturation pressure on pure CO 2 and N 2 solubility. It can be found that the relationship between the pressure and the solubility of pure gas was linear, agreed with Henry's law [33]: ...
Thermoplastic polyester elastomer (TPEE) is a high-performance polymer with high tear strength and excellent abrasion resistance, and microcellular TPEE foams exhibit low density and special mechanical properties. Nevertheless, shrinkage behavior of the TPEE foam is still a critical challenge which greatly limits its industrial application, and further, the shrinkage mechanism is rarely figured out. Herein, a novel strategy of implementing mixed CO2 & N2 as blowing agents in microcellular foaming was developed to stabilize cell structure. Thanks to the modest permeability of mixed blowing agents, TPEE foams with high stable expansion ratio of higher than 17-fold and recovery ratio of up to 77 % were fabricated, and it found that the ratio of mixed blowing agents could modulate the shrinkage behavior of TPEE foams. Moreover, the correlation between the mechanical properties and TPEE foams with different shrinkage behaviors was investigated. For TPEE foams with similar stable expansion ratios, decreasing the shrinkage helped to increase the maximum compressive stress by 100 % and to reduce the energy loss coefficient by 43 %. Overall, the developed microcellular foaming prepared with the mixed CO2 & N2 as blowing agents shows great promise in fabricating advanced elastomer foams with high expansion ratio, stable cell morphology and outstanding mechanical properties.
... CO 2 is the most favorable choice because it is inexpensive, nontoxic, and environmentally benign (zero Ozone depletion potential and 100-year global warming potential compared to 1300 years for HFC). Many challenges must be met to enable the use of CO 2 as a blowing agent: (1) The low solubility of CO 2 in most polymer melts; (2) CO 2 has a high diffusivity in the polymer melt due to its small size, while this ensures a fast mixing process, it also results in quick escape of gas from the foam after processing; (3) CO 2 has a higher gas thermal conductivity in comparison to that of HFC blowing agents [162]. ...
Everyone wants the lightest materials to their use. Lighter materials are the most important parameter for a dynamic system. This chapter describes all the types of latest ultralight materials having a density of <10 mg/cm³. Aerogel, aerographite, aerographene, 3D graphene, carbyne, microlattice, and foam come under ultralight material. Classification, fabrication, properties, and applications of each of the ultralight material has been described here extensively.
... Temperature as a vital factor in gas solubility should be kept constant. After introducing the gas to the sample the decreasing pressure as a function of time is measured until the gas sorption into the membrane is completed (rate of gas sorption and desorption become equal) [49]. ...
This study aimed to fabricate and investigate the nanocomposite membrane made of polyetherimide (PEI) and hydrophobic fumed silica as filler. Commercial nanosilica (0–20 wt%) was embedded into PEI (Ultem1000) to prepare PEI/Silica dense nanocomposite membranes. Permeability and solubility of H2, CO, and CO2, as the main gases in syngas mixture, was investigated at 2–6 bar and 25 ± 1 °C. The effect of feed pressure (2–6 bar) on the gas permeability and solubility was studied for the pure and nanocomposite membranes. The membrane characterization was examined by FTIR, XRD, DSC, SEM, and EDX analysis. It revealed that in the low percentage of nanosilica, the permeability increased and the selectivity decreased, as the permeability of H2 increased from 1.08 to 1.63 barrer at 6 bar, while H2/CO and H2/CO2 decreased from 19.6 to 15 and from 3.8 to 3.6, respectively. The SEM and EDX images showed that by the increase in nanosilica loading, the silica particles dispersed more uniformly in the polymer matrix and formed membranes without any defect. For the nanocomposite membrane containing 20 wt% nanosilica, in comparison with pure PEI membrane, the H2/CO selectivity increased by almost 350% and reached 66.4, while H2 and CO permeability reduced by 21% and 77%, respectively. Solubility and diffusivity obtained through gas sorption measurement experiments, confirmed these outcomes, as the hydrogen diffusivity increased by an increase in nanosilica loading but CO and CO2 diffusivity decreased.
... The porous materials prepared by this new method have been studied in porosity control [9], adhesion strength [10], gas permeability [11], drug release [12], mass production [13], and multilayering [14,15] studies. Past studies of plasticization by CO 2 have suggested that CO 2 impregnates the amorphous part of resins [16][17][18], but the relationship between the crystallinity of raw materials and their suitability for CAPC processes remains unclear. The combination of CO 2 and PLA has been considered as a suitable sustainable method [19,20]. ...
CO2-assisted polymer compression (CAPC) is an environmentally friendly processing method that uses CO2 to plasticize and crimp polymer fibers at room temperature, enabling low-energy processing within a short time. In this study, CAPC was applied to polylactic acid (PLA), a carbon-neutral polymer. To evaluate the relationships between CO2 plasticization and the crystallinity degree and plasticization of PLA, samples with different degrees of crystallinity were layered and simultaneously compressed to observe the most collapsed layer. The sample with lower crystallinity exhibited better crushing and higher plasticization than the crystallized samples. The PLA with high crystallinity developed cracks on the fiber surfaces with consequent loss of strength. Based on the results, CAPC is a potentially effective method for PLA with low crystallinity.
