Editorial

4 pages, 172 KiB

Open AccessEditorial

Supercritical Fluid Processing of Polymers

by Stefano Cardea and Ernesto Reverchon

Polymers 2019, 11(10), 1551; https://doi.org/10.3390/polym11101551 - 24 Sep 2019

Cited by 8 | Viewed by 1700

The use of supercritical fluids instead of organic solvents has attracted the interest of numerous researchers, due to the unique peculiarities of supercritical fluids which are characterized by solvent powers comparable to those of liquid organic solvents, diffusivity comparable to those of gaseous [...] Read more.

The use of supercritical fluids instead of organic solvents has attracted the interest of numerous researchers, due to the unique peculiarities of supercritical fluids which are characterized by solvent powers comparable to those of liquid organic solvents, diffusivity comparable to those of gaseous substances and quasi-zero surface tension [...] Full article

(This article belongs to the Special Issue Supercritical Fluid Processing of Polymers)

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16 pages, 3361 KiB

Open AccessArticle

Foaming of Polycaprolactone and Its Impregnation with Quercetin Using Supercritical CO₂

by Ignacio García-Casas, Antonio Montes, Diego Valor, Clara Pereyra and Enrique J. Martínez de la Ossa

Polymers 2019, 11(9), 1390; https://doi.org/10.3390/polym11091390 - 23 Aug 2019

Cited by 16 | Viewed by 4222

Abstract

Foamed polycaprolactone impregnated with quercetin was carried out with a batch foaming technique using supercritical CO₂. The experimental design was developed to study the influence of pressure (15–30 MPa), temperature (308–333 K), and depressurization rate (0.1–20) on the foam structure, melting [...] Read more.

Foamed polycaprolactone impregnated with quercetin was carried out with a batch foaming technique using supercritical CO₂. The experimental design was developed to study the influence of pressure (15–30 MPa), temperature (308–333 K), and depressurization rate (0.1–20) on the foam structure, melting temperature, and release tests of composites. The characterization of the experiments was carried out using scanning electron microscopy, X-ray diffractometer, and differential scanning calorimetry techniques. It was observed that the porosity created in the polymer had a heterogeneous structure, as well as the impregnation of the quercetin during the process. On the other hand, controlled release tests showed a significant delay in the release of quercetin compared to commercial quercetin. Full article

(This article belongs to the Special Issue Supercritical Fluid Processing of Polymers)

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12 pages, 2225 KiB

Open AccessArticle

Purification of Polybutylene Terephthalate by Oligomer Removal Using a Compressed CO₂ Antisolvent

by Wen Yu, Jian-Hao Huang and Chung-Sung Tan

Polymers 2019, 11(7), 1230; https://doi.org/10.3390/polym11071230 - 23 Jul 2019

Cited by 2 | Viewed by 3938

Abstract

In this study, the cyclic oligomers in the highly chemically resistant polyester polybutylene terephthalate (PBT) were effectively removed using a compressed CO₂ antisolvent technique in which 1,1,1,3,3,3-hexafluoro-2-propanol (HFIP) was used as the solvent. In addition to the oligomers, tetrahydrofuran was completely removed [...] Read more.

In this study, the cyclic oligomers in the highly chemically resistant polyester polybutylene terephthalate (PBT) were effectively removed using a compressed CO₂ antisolvent technique in which 1,1,1,3,3,3-hexafluoro-2-propanol (HFIP) was used as the solvent. In addition to the oligomers, tetrahydrofuran was completely removed because of its low molecular weight and liquid state. The effects of the operating variables, including temperature, pressure, and the PBT concentration in HFIP, on the degree of removal of the oligomers were systematically studied using experimental design and the response surface methodology. The most appropriate operating conditions for the purification of PBT were 8.3 MPa and 23.4 °C when using 4.5 wt % PBT in HFIP. Under these conditions, the cyclic trimers and dimers could be removed by up to 81.4% and 95.7%, respectively, in a very short operating time. Full article

(This article belongs to the Special Issue Supercritical Fluid Processing of Polymers)

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14 pages, 4017 KiB

Open AccessArticle

Microstructural Changes of Aramid Fiber Due to Reaction with Toluene 2,4-diisocyanate under Tension in scCO₂

by Haijuan Kong, Qian Xu and Muhuo Yu

Polymers 2019, 11(7), 1110; https://doi.org/10.3390/polym11071110 - 01 Jul 2019

Cited by 11 | Viewed by 5092

Abstract

High modulus aramid fiber, such as Kevlar 49, is conventionally prepared by the heat annealing of high strength aramid fiber under a suitable tension at high temperature, especially higher than 500 °C. This enables the mobility of a rigid molecule chain to be [...] Read more.

High modulus aramid fiber, such as Kevlar 49, is conventionally prepared by the heat annealing of high strength aramid fiber under a suitable tension at high temperature, especially higher than 500 °C. This enables the mobility of a rigid molecule chain to be rearranged into a more perfect crystalline or orientation structure under tension. However, annealing decreases the tensile strength, since the thermal degradation of the molecular chain at high temperature cannot be avoided. Kevlar 49 fibers treated in supercritical carbon dioxide (scCO₂) under tension could improve their mechanical properties at a low temperature. The effects of the tension on the mechanical properties and structure of the Kevlar 49 fibers were studied by mechanical testing, wide-angle and small-angle X-ray scattering (WAXS, SAXS), and scanning electron microscopy (SEM). The results show that the mechanical properties, crystallinity and orientation of the fiber can be improved when the tension is less than 0.6 cN/dtex, which may be due to the increasing of the mobility of a rigid segment with the help of the plasticization of scCO₂ and re-arrangement of macromolecular chain into crystalline and orientation structure under tension. What’s more, the amorphous region also was enhanced by crosslinking reaction of toluene 2,4-diisocyanate (TDI) with the chain end groups of the macromolecules in the amorphous regions. However, a decrease of tenacity was found when the tension was higher than 0.6 cN/dtex, which is because the tension was so high that the microfibril was broken. The results indicated that treating the Kevlar 49 fiber in scCO₂ under a suitable tension with TDI as a crosslink agent can simultaneously improve both the tenacity and modulus of the fiber. Full article

(This article belongs to the Special Issue Supercritical Fluid Processing of Polymers)

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13 pages, 8558 KiB

Open AccessArticle

Study on Crystallization Behaviors and Properties of F-III Fibers during Hot Drawing in Supercritical Carbon Dioxide

by Xiaoma Ding, Haijuan Kong, Mengmeng Qiao, Zhifeng Hu and Muhuo Yu

Polymers 2019, 11(5), 856; https://doi.org/10.3390/polym11050856 - 10 May 2019

Cited by 7 | Viewed by 2884

Abstract

In order to obtain F-III fibers with high mechanical properties, pristine F-III fibers were hot drawn at the temperature of 250 °C, pressure of 14 MPa, tension of 6 g·d⁻¹, and different times, which were 15 min, 30 min, 45 min, [...] Read more.

In order to obtain F-III fibers with high mechanical properties, pristine F-III fibers were hot drawn at the temperature of 250 °C, pressure of 14 MPa, tension of 6 g·d⁻¹, and different times, which were 15 min, 30 min, 45 min, 60 min, 75 min, 90 min, and 105 min, respectively, in supercritical carbon dioxide (Sc-CO₂) in this article. All the samples, including the pristine and treated F-III fibers, were characterized by a mechanical performance tester, wide-angle X-ray scattering (WAXS), small-angle X-ray scattering (SAXS), and thermogravimetric analysis (TGA). The results showed that the thermal stability of F-III fibers was enhanced to some extent, and the tensile strength and modulus of F-III fibers had great changes as the extension of treatment time during hot drawing in Sc-CO₂, although the treatment temperature was lower than the glass transition temperature (Tg) of F-III fibers. Accordingly, the phase fraction, orientation factor f_c of the (110) crystal plane, fibril length l_f, and misorientation angle B_φ of all the samples were also investigated. Fortunately, the hot drawing in Sc-CO₂ was successfully applied to the preparation of F-III fibers with high mechanical properties. Full article

(This article belongs to the Special Issue Supercritical Fluid Processing of Polymers)

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17 pages, 3741 KiB

Open AccessArticle

A Phenomenological Approach to Study Mechanical Properties of Polymeric Porous Structures Processed Using Supercritical CO₂

by Antonio Tabernero, Lucia Baldino, Stefano Cardea, Eva Martín del Valle and Ernesto Reverchon

Polymers 2019, 11(3), 485; https://doi.org/10.3390/polym11030485 - 13 Mar 2019

Cited by 12 | Viewed by 2919

Abstract

This work proposes a modeling of the mechanical properties of porous polymers processed by scCO₂, using a phenomenological approach. Tensile and compression tests of alginate/gelatin and cellulose acetate/graphene oxide were modeled using three hyperelastic equations, derived from strain energy functions. The [...] Read more.

This work proposes a modeling of the mechanical properties of porous polymers processed by scCO₂, using a phenomenological approach. Tensile and compression tests of alginate/gelatin and cellulose acetate/graphene oxide were modeled using three hyperelastic equations, derived from strain energy functions. The proposed hyperelastic equations provide a fair good fit for mechanical behavior of the nanofibrous system alginate/gelatin (deviations lower than 10%); whereas, due to the presence of the solid in the polymer network, a four-parameter model must be used to fit the composite cellulose acetate/graphene oxide behavior. Larger deviations from the experimental data were observed for the system cellulose acetate/graphene oxide because of its microporous structure. A finite element method was, then, proposed to model both systems; it allowed a realistic description of observable displacements and effective stresses. The results indicate that materials processed using scCO₂, when submitted to large stresses, do not obey Hooke´s law and must be considered as hyperelastic. Full article

(This article belongs to the Special Issue Supercritical Fluid Processing of Polymers)

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11 pages, 3723 KiB

Open AccessArticle

Effect of Different Pressures of Supercritical Carbon Dioxide on the Microstructure of PAN Fibers during the Hot-Drawing Process

by Mengmeng Qiao, Haijuan Kong, Xiaoma Ding, Zhifeng Hu, Luwei Zhang, Yuanzhi Cao and Muhuo Yu

Polymers 2019, 11(3), 403; https://doi.org/10.3390/polym11030403 - 01 Mar 2019

Cited by 11 | Viewed by 3544

Abstract

The hot-drawing process of polyacrylonitrile (PAN) fibers is an important step during the production of PAN-based carbon fibers. In this study, supercritical carbon dioxide (Sc-CO₂) was used as one kind of media for thermal stretching of PAN fibers to study the [...] Read more.

The hot-drawing process of polyacrylonitrile (PAN) fibers is an important step during the production of PAN-based carbon fibers. In this study, supercritical carbon dioxide (Sc-CO₂) was used as one kind of media for thermal stretching of PAN fibers to study the effect of different pressures of Sc-CO₂ on crystallinity, degree of orientation and mechanical property of PAN fibers during the hot-drawing process. The changes of microstructure and mechanical properties in the PAN fibers were investigated by wide-angle X-ray diffraction, small angle X-ray scattering and monofilament strength analysis. The results showed that as the pressure increased, the crystallinity and degree of orientation of PAN fibers increased. Furthermore, when the pressure was 10 MPa, the crystallinity increased from 69.78% to 79.99%, which was the maximum crystallinity among the different pressures. However, when the pressure was further increased, the crystallinity and degree of orientation of the fibers were reduced. The test results of the mechanical properties were consistent with the trends of crystallinity and degree of orientation, showing that when the pressure was 10 MPa, the tensile strength of the fibers increased from 4.59 cN·dtex⁻¹ to 7.06 cN·dtex⁻¹ and the modulus increased from 101.54 cN·dtex⁻¹ to 129.55 cN·dtex⁻¹. Full article

(This article belongs to the Special Issue Supercritical Fluid Processing of Polymers)

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12 pages, 5578 KiB

Open AccessArticle

Study on the Changes of Structures and Properties of PAN Fibers during the Cyclic Reaction in Supercritical Carbon Dioxide

by Mengmeng Qiao, Haijuan Kong, Xiaoma Ding, Zhifeng Hu, Luwei Zhang, Yuanzhi Cao and Muhuo Yu

Polymers 2019, 11(3), 402; https://doi.org/10.3390/polym11030402 - 01 Mar 2019

Cited by 40 | Viewed by 4015

Abstract

Thermal pre-oxidation of polyacrylonitrile (PAN) fibers is a time-consuming and energy-consuming step in the production of PAN-based carbon fibers. In this paper, the effect of temperature on the structures and properties of PAN fibers cyclized in the supercritical carbon dioxide (Sc-CO₂) [...] Read more.

Thermal pre-oxidation of polyacrylonitrile (PAN) fibers is a time-consuming and energy-consuming step in the production of PAN-based carbon fibers. In this paper, the effect of temperature on the structures and properties of PAN fibers cyclized in the supercritical carbon dioxide (Sc-CO₂) medium was studied. The thermal behaviors of the PAN fibers were investigated by Fourier transform infrared spectra (FT-IR), X-ray diffraction (XRD), differential scanning calorimeter (DSC) and thermogravimetric analysis (TGA). The cyclization reaction was sensitive to the heating temperature and gas atmosphere. The FT-IR results of the PAN fibers treated in the Sc-CO₂ confirmed that the degree of cyclization increased with the increase of the cyclization temperature. Compared with the PAN fibers treated in the air, the PAN fibers treated in the Sc-CO₂ showed a higher degree of cyclization even at the same temperature. These findings might be related to the osmotic action of Sc-CO₂ causing the fibers to be further arranged in a regular manner, which was favorable for the cyclization reaction. Moreover, as one kind of high diffusion and high heat transfer media, the heat release during the cyclization of PAN fibers could be quickly removed by Sc-CO₂, which achieved the progress of the rapid-entry cyclization reaction. Full article

(This article belongs to the Special Issue Supercritical Fluid Processing of Polymers)

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11 pages, 6888 KiB

Open AccessArticle

Supercritical Assisted Electrospray: An Improved Micronization Process

by Lucia Baldino, Stefano Cardea and Ernesto Reverchon

Polymers 2019, 11(2), 244; https://doi.org/10.3390/polym11020244 - 02 Feb 2019

Cited by 43 | Viewed by 3798

Abstract

A new process is proposed that can largely improve classical electrospray (ESPR) atomization, thanks to the addition of supercritical CO₂ (SC-CO₂) to the liquid mixture, in which a polymer is dissolved, forming an expanded liquid. The consequent reduction of surface [...] Read more.

A new process is proposed that can largely improve classical electrospray (ESPR) atomization, thanks to the addition of supercritical CO₂ (SC-CO₂) to the liquid mixture, in which a polymer is dissolved, forming an expanded liquid. The consequent reduction of surface tension and viscosity allows the production of micrometric or nanometric particles of controlled size and distribution at a production rate up to one hundred times that of the traditional process. The new process was applied to particle generation from a very high molecular weight polyvinylpyrrolidone (PVP) and tested at different polymer percentages by weight and at different pressures. Repeatable microparticle diameters and distributions were obtained, ranging between 0.55 and 2.25 µm at PVP concentrations from 1 to 5% w/w and pressures between 80 and 120 bar. Full article

(This article belongs to the Special Issue Supercritical Fluid Processing of Polymers)

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16 pages, 5468 KiB

Open AccessArticle

Precise Dissolution Control and Bioavailability Evaluation for Insoluble Drug Berberine via a Polymeric Particle Prepared Using Supercritical CO₂

by Jingfu Jia, Kerong Zhang, Xue Zhou, Dan Zhou and Fahuan Ge

Polymers 2018, 10(11), 1198; https://doi.org/10.3390/polym10111198 - 26 Oct 2018

Cited by 12 | Viewed by 2836

Abstract

It is still controversial whether poor aqueous solubility is the most primary reason for the low oral bioavailability of insoluble drugs. Therefore, in this study, berberine-loaded solid polymeric particles (BPs) of varied dissolution profiles with β-cyclodextrin (β-CD) as carrier were fabricated using solution-enhanced [...] Read more.

It is still controversial whether poor aqueous solubility is the most primary reason for the low oral bioavailability of insoluble drugs. Therefore, in this study, berberine-loaded solid polymeric particles (BPs) of varied dissolution profiles with β-cyclodextrin (β-CD) as carrier were fabricated using solution-enhanced dispersion by supercritical fluids (SEDS), and the relationship between dissolution and berberine (BBR) bioavailability was evaluated. Dissolution property was controlled via particle morphology manipulation, which was achieved by adjusting several key operating parameters during the SEDS process. Characterization on BP using infrared spectroscopy, differential scanning calorimetry, and X-ray diffraction indicated that BBR was dispersed in amorphous form, while nuclear magnetic resonance spectroscopy showed that methoxy groups of BBR were included into the cavities of β-CD. In vivo pharmacokinetic studies showed that oral bioavailability increased by about 54% and 86% when the dissolution rate of BBR was increased by 51% and 83%, respectively. The entry speed of BBR into the bloodstream was also advanced with the degree of dissolution enhancement. It seemed that dissolution enhancement gave positive effect to the oral bioavailability of berberine, but this might not be the crucial point. Meanwhile, supercritical CO₂ technology is a promising method for pharmaceutical research due to its advantages in regulating drug-dosage properties. Full article

(This article belongs to the Special Issue Supercritical Fluid Processing of Polymers)

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