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Abstract Accurate solute solubility measuring and modeling in supercritical carbon dioxide (ScCO2) would address the best working conditions and thermodynamic boundaries for material processing with this type of fluid. Theory- and data-driven methods are two general modeling approaches. Using theory-driven methods, the solubility is estimated based on the principles of thermodynamics, while data-driven methods are developed by training the algorithms. Despite acceptance of each of these methods, more experimental solubility data are still needed to promote modeling performances. In this study, for the first time, solubility of morphine sulfate is determined and modeled by a set of 13 semi-empirical (theory-driven) and random forest (data-driven) models. Using a laboratory system with an ultraviolet-visible (UV-Vis) spectroscopy, the experimental solubilities including 48 data points were obtained at different temperatures (308–338 K) and pressures (12–27 MPa). The minimum (0.806 × 10−5) and maximum (5.902 × 10−5) equilibrium mole fractions were observed at working pressures of 12 and 27 MPa, respectively, both at the same temperature of 338 K. It was indicated that random forest model (with AARD% of 1.29%) had an excellent predictive performance against semi-empirical models (with AARD% from 9.33 to 19.76%). The results showed that solute molecular weight had the highest effect on random forest modeling. Using modeling results from Chrastil and Bartle models, total and vaporization enthalpies of dissolution of morphine sulfate in ScCO2 were found to be 35.12 and 59.04 kJ/mole, respectively.

When the CO2 in a supercritical state (SCCO2) is released from deep coal seams, it reacts with minerals in coal, changing the porosity of coal, which in turn affects the effect of CO2 sequestration in coal seams and the effect of increasing methane production. In order to discover the influence characteristics of SCCO2-H2O-coal rock interaction on the porosity in coal, the experiments on the supercritical CO2 reforming coal under different water content conditions were carried out with coking coal as the research object. Based on the results of mineral composition and porosity measurements, the differences between the main minerals and the changes in pore cleavage at various scales in coal were compared, and the action mechanism of the SCCO2 fluid on the pore cleavage properties under various water content states was explored. The results show that: ① After the SCCO2 treatment, the surface of the coal body is rough and loose, some fissures are penetrated as a result of mineral dissolution, and the connectivity of micro fissure is improved. ② The SCCO2 fluid has a “pore-expanding”effect on coal, which is manifested by a decrease of the content of micro- and small pores, and an increase of the proportion of medium- and large pores, i.e., the conversion of micro- and small-sized pores to large pores, as well as the improvement of pore connectivity. Furthermore, it is discovered that the fractal dimension of the adsorption pores of the coal samples increases slightly in size and roughness, while the fractal dimension of the seepage pores decreases significantly, and the complexity and non-homogeneity are reduced. ③ The SCCO2 fluid has the best solubility on the carbonate minerals in coal, followed by clay minerals, and with the increase of water content, the proportion of carbonate minerals in the extracted coal first increases and then decreases. The SCCO2 fluid makes the carbonate minerals in the coal samples of the dry basal state and saturated water state dissolve significantly, which effectively improves the pore structure, and the effect on the coal samples of the saturated water state is better. After the air-dry basal coal samples were subjected to the SCCO2, the newly formed dolomite minerals gathered in the pore throats to cause the plugging effect, reducing the original large pore size, which is the main cause of the differential changes in the pore space of coals with different water content states.

Waterless dyeing of polyamide 6.6 using scCO2 (supercritical carbon dioxide) was investigated. PA (polyamide) fibers can be dyed with various dyes, including disperse dyes. The conventional aqueous dyeing process uses large amounts of water and produces polluted water. Considering these environmental issues, waterless dyeing of fibers is a forefront issue, and utilization of supercritical carbon dioxide (scCO2) is a commercially viable technology for waterless dyeing. This study tested PA6.6 (polyamide 6.6) dyeing in scCO2 at 100 °C 220 bar pressure for 45 min. Color measurements and color fastness tests were performed, as well as tensile strength, scanning electron microscope (SEM) analysis, and Fourier transform infrared spectroscopy (FTIR) analysis. PA6.6 fabrics yielded higher K/S (color strength, the Kubelka–Munk equation) values with larger molecular weight dye and almost the same color strength with medium and small-sized dyes, demonstrating the ability of dyeing in a supercritical environment without water as a more environmentally friendly dyeing option compared to conventional dyeing. [ABSTRACT FROM AUTHOR]

Abstract Osteoarthritis (OA) of the knee is a common degenerative articular disorder and is one of the main causes of pain and functional disability. Cartilage damage is frequently linked to elevated osteoarthritis incidence. Supercritical carbon dioxide (scCO2) decellularized cartilage graft produced from the porcine cartilage is an ideal candidate for cartilage tissue engineering. In the present study, we derived collagen type II (Col II) solution from the scCO2 decellularized porcine cartilage graft (dPCG) and compared its efficacy with hyaluronic acid (HA) in the surgical medial meniscectomy (MNX) induced post-traumatic osteoarthritis (PTOA) model. Dose-dependent attenuation of the OA (12.3 ± 0.8) progression was observed in the intra‐articular administration of Col II solution (7.3 ± 1.2) which significantly decreased the MNX-induced OA symptoms similar to HA. The pain of the OA group (37.4 ± 2.7) was attenuated dose-dependently by Col II solution (45.9 ± 4.1) similar to HA (43.1 ± 3.5) as evaluated by a capacitance meter. Micro‐CT depicted a dose-dependent attenuation of articular cartilage damage by the Col II solution similar to HA treatment. A significant (p

Osteoarthritis (OA) of the knee is a common degenerative articular disorder and is one of the main causes of pain and functional disability. Cartilage damage is frequently linked to elevated osteoarthritis incidence. Supercritical carbon dioxide (scCO2) decellularized cartilage graft produced from the porcine cartilage is an ideal candidate for cartilage tissue engineering. In the present study, we derived collagen type II (Col II) solution from the scCO2 decellularized porcine cartilage graft (dPCG) and compared its efficacy with hyaluronic acid (HA) in the surgical medial meniscectomy (MNX) induced post-traumatic osteoarthritis (PTOA) model. Dose-dependent attenuation of the OA (12.3 ± 0.8) progression was observed in the intra‐articular administration of Col II solution (7.3 ± 1.2) which significantly decreased the MNX-induced OA symptoms similar to HA. The pain of the OA group (37.4 ± 2.7) was attenuated dose-dependently by Col II solution (45.9 ± 4.1) similar to HA (43.1 ± 3.5) as evaluated by a capacitance meter. Micro‐CT depicted a dose-dependent attenuation of articular cartilage damage by the Col II solution similar to HA treatment. A significant (p < 0.001) dose-dependent elevation in the bone volume was also observed in Col II solution-treated OA animals. The protective competence of Col II solution on articular cartilage damage is due to its significant (p < 0.001) increase in the expression of type II collagen, aggrecan and SOX‐9 similar to HA. To conclude, intra‐articular administration of type II collagen solution and HA reestablished the injured cartilage and decreased osteoarthritis progression in the experimental PTOA model. [ABSTRACT FROM AUTHOR]

The exceptional mechanical properties of aramid fibers make them a popular choice for high‐performance materials; despite that, their potential is limited due to their surface properties bonding energy and interfacial bonding strength with matrix materials. The enhanced resistance of poly‐aramid fibers (AFs) to severe surroundings and improved interlaminar adhesion in sandwich compounds with admirable mechanical characteristics are becoming a great challenge for various chemical and physical surface treatment techniques. Supercritical carbon dioxide (scCO2) is a popular and sustainable approach that can effectively bond and homogeneously deposit functional groups or nanoparticles and exhibit the excellent performance of fibber modification. This article examines aramid fibers' surface modification advancements using scCO2‐assisted techniques, including monomer grafting, impregnation, and functionalization with various functional groups and nanoparticles. Additionally, the article discusses the challenges faced in scCO2‐assisted aramid fiber modification and what the future holds for this technology. [ABSTRACT FROM AUTHOR]

Waterless dyeing of polyamide 6.6 using scCO2 (supercritical carbon dioxide) was investigated. PA (polyamide) fibers can be dyed with various dyes, including disperse dyes. The conventional aqueous dyeing process uses large amounts of water and produces polluted water. Considering these environmental issues, waterless dyeing of fibers is a forefront issue, and utilization of supercritical carbon dioxide (scCO2) is a commercially viable technology for waterless dyeing. This study tested PA6.6 (polyamide 6.6) dyeing in scCO2 at 100 °C 220 bar pressure for 45 min. Color measurements and color fastness tests were performed, as well as tensile strength, scanning electron microscope (SEM) analysis, and Fourier transform infrared spectroscopy (FTIR) analysis. PA6.6 fabrics yielded higher K/S (color strength, the Kubelka–Munk equation) values with larger molecular weight dye and almost the same color strength with medium and small-sized dyes, demonstrating the ability of dyeing in a supercritical environment without water as a more environmentally friendly dyeing option compared to conventional dyeing.

The purpose of this study is to investigate the thermo-oxidative degradation behavior of polypropylene (PP) by comparing three types of pristine PP granules (consisting of homopolymer, random copolymer, and block copolymer) with their corresponding oxidized analogues. These analogues were intensely oxidized under oxygen at 90 °C for 1000 h by using the electron spin resonance (ESR) spin trapping method that can detect short-lived radical intermediates during the degradation. The degrees of oxidation could be evaluated by chemiluminescence (CL) intensity, which was related to the concentration of hydroperoxide groups generated in the PP chain. In the pristine PP samples, a small amount of hydroperoxides were found to be formed unintentionally, and their homolysis produces alkoxy radicals, RO•, which then undergo β-scission to yield chain-end aldehydes or chain-end ketones. These oxidation products continue to take part in homolysis to produce their respective carbonyl and carbon radicals. On the other hand, in the oxidized PP granules, because of their much higher hydroperoxide concentration, the two-stage cage reaction and the bimolecular decomposition of hydroperoxides are energetically favorable. Carbonyl compounds are formed in both reactions, which are then homolyzed to form the carbonyl radical species, •C(O)–. PP homopolymer produced the largest amount of carbonyl radical spin adduct; thus, it was found that the homopolymer is most sensitive to oxygen attack, and the presence of ethylene units in copolymers enhances the oxidation resistance of PP copolymers. [ABSTRACT FROM AUTHOR]

Epoxidized oils are commonly used in the plastics industry as additives in the formulation of polyvinyl chloride (PVC) and as monomers in the coating industry. They are produced from petrochemical feedstocks or by chemical epoxidation of natural oils. Currently, the synthesis processes of these materials are expensive, utilize volatile organic solvents and hazardous oxidants, which are unfavorable for the environment. There is a need to find natural epoxidized oils. Vernonia galamensis (ironweed) is a plant found in abundance in Ethiopia with no commercial value, but its seeds contain 40 wt% epoxide rich triglycerides. V. galamensis oil contains up to 80 wt% of vernolic acid (VA), a mono‐unsaturated fatty acid with an additional epoxide functionality. The presence of alkene and epoxide(oxirane) groups offers excellent opportunities to synthesize new building blocks for polymerisations. Here, we report a green and efficient extraction methodology (up to 80% of extraction‐efficiency) of the triglyceride vernonia oil from V. galamensis using supercritical carbon dioxide (scCO2). We then report the synthesis of a series of polymerisable monomers (conversion in monomers 64%–99%) based on the VA obtained from the saponification process. Finally, the novel monomers are polymerized into different polymers through polycondensation using a mixture of metal‐based and enzyme catalysts. [ABSTRACT FROM AUTHOR]

The purpose of this study is to investigate the thermo-oxidative degradation behavior of polypropylene (PP) by comparing three types of pristine PP granules (consisting of homopolymer, random copolymer, and block copolymer) with their corresponding oxidized analogues. These analogues were intensely oxidized under oxygen at 90 °C for 1000 h by using the electron spin resonance (ESR) spin trapping method that can detect short-lived radical intermediates during the degradation. The degrees of oxidation could be evaluated by chemiluminescence (CL) intensity, which was related to the concentration of hydroperoxide groups generated in the PP chain. In the pristine PP samples, a small amount of hydroperoxides were found to be formed unintentionally, and their homolysis produces alkoxy radicals, RO•, which then undergo β-scission to yield chain-end aldehydes or chain-end ketones. These oxidation products continue to take part in homolysis to produce their respective carbonyl and carbon radicals. On the other hand, in the oxidized PP granules, because of their much higher hydroperoxide concentration, the two-stage cage reaction and the bimolecular decomposition of hydroperoxides are energetically favorable. Carbonyl compounds are formed in both reactions, which are then homolyzed to form the carbonyl radical species, •C(O)–. PP homopolymer produced the largest amount of carbonyl radical spin adduct; thus, it was found that the homopolymer is most sensitive to oxygen attack, and the presence of ethylene units in copolymers enhances the oxidation resistance of PP copolymers.

Supercritical fluids (SCFs) are the materials formed at the values of temperature and pressure, above its critical point. Some supercritical fluids can replace the toxic industrial solvents. Unique properties of the supercritical fluids especially supercritical carbon dioxide (scCO2) provide the various opportunities in the field of polymerization. The supercritical carbon dioxide (scCO2) is used as a monomer, reaction medium and catalyst for the synthesis of polymers. Various processes for the polymer synthesis have been discussed in this review article such as homogeneous polymerization, step growth polymerization, emission polymerization, dispersion polymerization and electrochemical synthesis of conducting polymers. The polymers can be readily separated from the reaction mixture as the particles or drops, in the presence of supercritical carbon dioxide (scCO2) during the polymerization. In this review, some applications including impregnation and supercritical dyeing, purification of polymers, polymer modifications and particle production has been evaluated to study the efficiency of super critical fluids on the polymer production. This article also demonstrates the effects of various parameters on the process of polymerization such as pH, temperature and pressure. Generally, by increasing the values of pH or the reaction media, the viscosity of prepared polymers tends to increase. The characterization techniques such as Fourier Transform Infrared (FTIR) spectroscopy, X-Ray Diffraction (XRD), 1H Nuclear Magnetic Resonance (1HNMR) and Differential Scanning Calorimetry (DSC) are also discussed for the determination of chemical arrangement, structure of polymers and functional groups. [ABSTRACT FROM AUTHOR]

Large bone fractures with segmental defects are a vital phase to accelerate bone integration. The present study examined the role of supercritical carbon dioxide (scCO2) decellularized bone matrix (scDBM) seeded with allogeneic adipose-derived mesenchymal stem cells (ADSC) as bio-scaffold for bone regeneration. Bio-scaffold produced by seeding ADSC to scDBM was evaluated by scanning electron microscopy (SEM). Rat segmental femoral defect model was used as a non-union model to investigate the callus formation in vivo. Histological analysis and osteotomy gap closure in the defect area were analyzed at 12 and 24 weeks post-surgery. Immunohistochemical expression of Ki-67, BMP-2 and osteocalcin was evaluated to assess the ability of new bone formation scDBM. ADSC was found to attach firmly to scDBM bioscaffold as evidenced from SEM images in a dose-dependent manner. Callus formation was observed using X-ray bone imaging in the group with scDBM seeded with 2 × 106 and 5 × 106 ASCs group at the same time-periods. H&E staining revealed ASCs accelerated bone formation. IHC staining depicted the expression of Ki-67, BMP-2, and osteocalcin was elevated in scDBM seeded with 5 × 106 ASCs group at 12 weeks after surgery, relative to other experimental groups. To conclude, scDBM is an excellent scaffold that enhanced the attachment and recruitment of mesenchymal stem cells. scDBM seeded with ASCs accelerated new bone formation.

This review considers the recent advancements of using supercritical carbon dioxide (scCO2) in the synthesis and activation of metal-organic frameworks (MOFs). The first section outlines MOF synthesis by scCO2-based methods; pure scCO2 system, and also in conjunction with a co-solvent, auxiliary ligand, expandable solvent or an ionic liquid. This is followed by elaborating on MOF activation techniques that employed scCO2, be it independently or together with thermal activation. The third section considers the effects of scCO2 on MOF and polymer structures. To conclude, projections are made for current researchers in this area to better exploit scCO2 utilization. [ABSTRACT FROM AUTHOR]

Hexyl laurate is employed in several cosmetics having great demand. It could be synthesized catalytically like a "natural" perfume using a lipase. The use of mesocellular foam silica (MCF) for immobilization of lipases could be made using supercritical CO2 as a medium to enhance its activity in comparison with the normal techniques. Three different catalysts were supported on MCF such as Candida antractica B (CALB), Amano AYS, and Porcine pancreas (PPL), and their activity was evaluated in the preparation of hexyl laurate from lauric acid and hexyl alcohol. CALB@ MCF was the best among all. A systematic study was conducted to assess the effects of different operating parameters. It was ternary complex mechanism with inhibition by hexyl alcohol. The enzyme was reusable and the process is green. [ABSTRACT FROM AUTHOR]

In this study, the optimal setup of supercritical fluid extraction (SFE) was designed and developed, leading to the quantitation of 11 distinct cannabinoids (cannabidivann (CBDV), tetrahydrocannabivann (THCV), cannabidiol (CBD), cannabigerol (CBG) cannabidiolic acid (CBDA), cannabigerolic acid (CBGA), cannabinol (CBN), delta 9-tetrahydrocannabinol (Δ9-THC), delta 8-tetrahydrocannabinol (Δ8-THC), cannabichomere (CBC) and delta 9-tetrahydrocannabinol acid (THCA-A)) extracted from the flowers of medicinal cannabis (sp. Sativa). Supercritical carbon dioxide (scCO2) extraction was performed at 37 °C, a pressure of 250 bar with the maximum theoretical density of CO2 (893.7 kg/m3), which generated the highest yield of cannabinoids from the flower-derived extract. Additionally, a cold separator (separating chamber) was used and positioned immediately after the sample containing chamber to maximize the yield. It was also found that successive washing of the extract with fresh scCO2 further increased yields. Ultra-high performance liquid chromatography coupled with DAD (uHPLC-DAD) was used to develop a method for the quantification of 11 cannabinoids. The C18 stationary phase was used in conjunction with a two solvent system gradient program resulting in the acquisition of the well-resolved chromatogram over a timespan of 32 min. The accuracy and precision of isolated cannabinoids across inter-and intra-day periods were within acceptable limits (2, which holds promise in the development of well-characterized medicinal cannabis formulations. As to our best knowledge, this is the first study to report the uHPLC quantification method for the analysis of 11 cannabinoids from scCO2 extract in a single run with more than 1 min peak separation.

Graphical abstract Highlights • A novel simultaneous polyester dyeing and antimicrobial functionalization is developed using scCO2 dyeing route. • The efficiency and compatibility were analyzed by measuring the color strength, antimicrobial properties and durability. • An excellent color strength and fastness properties, improved wettability, and antimicrobial activity was achieved. • The proposed surface modification and anchoring mechanism improved antimicrobial durability and color intensity. Abstract In this study, a novel green approach was adopted to develop antimicrobial polyester fabric using sustainable biopolymers (chitosan/derivative) as eco-friendly antimicrobial agents via the resource efficient supercritical CO 2 (scCO 2) dyeing route in a single step. Polyester fabric was dyed with a small amount of dye (0.4% owf) in the presence of chitosan/derivative (3% owf) in scCO 2 at 120 °C, 25 MPa for 1 h. The success of chitosan/derivative impregnation was confirmed by Fourier Transform Infrared (FTIR), Zeta Potential (ζ), Scanning Electron Microscopy (SEM), and Water Contact Angle (WCA) measurements. According to the result, excellent color strength and fastness properties were obtained and the treated samples also reduced 75 − 93% of Escherichia coli (ATCC 25922) bacteria within one hour. This suggests that the dye and chitosan/derivative had no adverse effect on each other, proving compatibility. This new approach would help to reduce the cost of production and environmental pollution associated with the conventional textile finishing processes. [ABSTRACT FROM AUTHOR]

In this study, polytrimethylene terephthalate (PTT) and polybutylene terephthalate (PBT) samples were dyed n supercritical carbon dioxide (scCO 2) medium. Dianix Dry Blue XF2 and CI Disperse Blue 79 were used for dyeing. Pressure and time optimisation trials were conducted, maintaining the temperature constant based on the optimal results obtained from these trials. The color, fastness, and tensile strength values were assessed. For both PTT and PBT fabrics, the closest color values to conventional dyeing were achieved when dyed with CI Disperse Blue 79 at 85 °C and 25 MPa, and with Dianix Dry Blue XF2 at 70 °C and 25 MPa. Notably, when compared to conventionally dyes samples, darker colors were obtained in scCO 2 medium after 70 °C when dyeing with Dianix Dry Blue XF2 and after 85 °C when dyeing with CI Disperse Blue 79 compared to conventionally dyed samples. [Display omitted] • An environmentally benign and innovative dyeing process for PTT and PBT fibers. • Waterless dyeing in scCO2 medium at low temperature. • Uniformly and deep dyed PTT and PBT fibers with excellent dye fixation. [ABSTRACT FROM AUTHOR]

Polycaprolactone (PCL) scaffolds have recently been developed via efficient and green supercritical carbon dioxide (scCO2) melt-state foaming. However, previously reported gas-foamed scaffolds sometimes showed insufficient interconnectivity or pore size for tissue engineering. In this study, we have correlated the thermal and rheological properties of PCL scaffolds with their porous morphology by studying four foamed samples with varied molecular weight (MW), and particularly aimed to clarify the required properties for the fabrication of scaffolds with favorable interconnected macropores. DSC and rheological tests indicate that samples show a delayed crystallization and enhanced complex viscosity with the increasing of MW. After foaming, scaffolds (27 kDa in weight-average molecular weight) show a favorable morphology (pore size = 70–180 μm, porosity = 90% and interconnectivity = 96%), where the lowest melt strength favors the generation of interconnected macropore, and the most rapid crystallization provides proper foamability. The scaffolds (27 kDa) also possess the highest Young’s modulus. More importantly, owing to the sufficient room and favorable material transportation provided by highly interconnected macropores, cells onto the optimized scaffolds (27 kDa) perform vigorous proliferation and superior adhesion and ingrowth, indicating its potential for regeneration applications. Furthermore, our findings provide new insights into the morphological control of porous scaffolds fabricated by scCO2 foaming, and are highly relevant to a broader community that is focusing on polymer foaming.

High pressure in situ Fourier transfer infrared/near infrared technology (HP FTIR/NIR) along with theoretical calculation of density functional theory (DFT) method was employed. The solvation behaviors and the free radical homopolymerization of methyl methacrylate (MMA), methacrylate acid (MAA), trifluoromethyl methacrylate (MTFMA) and trifluoromethyl methacrylate acid (TFMAA) in scCO2 were systematically investigated. Interestingly, the previously proposed mechanism of intermolecular-interaction dynamically-induced solvation effect (IDISE) of monomer in scCO2 is expected to be well verified/corroborated in view that the predicted solubility order of the monomers in scCO2 via DFT calculation is ideally consistent with that observed via HP FTIR/NIR. It is shown that MMA and MAA can be easily polymerized, while the free radical polymerizability of MTFMA is considerably poor and TFMAA cannot be polymerized via the free radical initiators. The α trifluoromethyl group (−CF3) may effectively enhance the intermolecular hydrogen bonding and restrain the diffusion of the monomer in scCO2. More importantly, the strong electron-withdrawing inductive effect of −CF3 to C=C may distinctly decrease the atomic charge of the carbon atom in the methylene (=CH2). These two factors are believed to be predominantly responsible for the significant decline of the free radical polymerizability of MTFMA and the other alkyl 2-trifluoromethacrylates in scCO2.

To date limited work has focused on assessing the economic viability of scCO2 extraction to obtain waxes as part of a biorefinery. This work estimates the economic costs for wax extraction from maize stover. The cost of manufacture (COM) for maize stover wax extraction was found to be €88.89 per kg of wax, with the fixed capital investment (FCI) and utility costs (CUT) contributing significantly to the COM. However, this value is based solely on scCO2 extraction of waxes and does not take into account the downstream processing of the biomass following extraction. The cost of extracting wax from maize stover can be reduced by utilizing pelletized leaves and combusting the residual biomass to generate electricity. This would lead to an overall cost of €10.87 per kg of wax (based on 27% combustion efficiency for electricity generation) and €4.56 per kg of wax (based on 43% combustion efficiency for electricity generation). A sensitivity analysis study showed that utility costs (cost of electricity) had the greatest effect on the COM.

Tissue engineering scaffolds require a controlled pore size and structure to host tissue formation. Supercritical carbon dioxide (scCO2) processing may be used to form foamed scaffolds in which the escape of CO2 from a plasticized polymer melt generates gas bubbles that shape the developing pores. The process of forming these scaffolds involves a simultaneous change in phase in the CO2 and the polymer, resulting in rapid expansion of a surface area and changes in polymer rheological properties. Hence, the process is difficult to control with respect to the desired final pore size and structure. In this paper, we describe a detailed study of the effect of polymer chemical composition, molecular weight and processing parameters on final scaffold characteristics. The study focuses on poly(DL-lactic acid) (PDLLA) and poly(DL-lactic acid-co-glycolic acid) (PLGA) as polymer classes with potential application as controlled release scaffolds for growth factor delivery. Processing parameters under investigation were temperature (from 5 to 55oC) and pressure (from 60 to 230 bar). A series of amorphous PDLLA and PLGA polymers with various molecular weights (from 13 KD to 96 KD) and/or chemical compositions (the mole percentage of glycolic acid in the polymers was 0, 15, 25, 35 and 50 respectively) were employed. The resulting scaffolds were characterised by optical microscopy, scanning electron microscopy (SEM), and micro X-ray computed tomography (µCT). This is the first detailed study on using these series polymers for scaffold formation by supercritical technique. This study has demonstrated that the pore size and structure of the supercritical PDLLA and PLGA scaffolds can be tailored by careful control of processing conditions.

In this work, a methodology was studied for estimating the solubility of salsalate, an active pharmaceutical ingredient of non-steroidal anti-inflammatory drugs, in supercritical CO 2 (scCO 2) using the experimental data of its solubility in organic solvents and perturbed-chain statistical associating fluid theory (PC-SAFT)-based modeling. This type of modeling is more predictive than conventional semi-empirical correlation models and cubic-type equations of state. The PC-SAFT pure-component parameters of salsalate were determined by fitting its solubility data in organic solvents, which were newly measured in this work. The PC-SAFT parameters obtained thus were then applied to estimate the solubility of salsalate in scCO 2. This approach can adequately reproduce the experimental values of the isothermal and isobaric solubilities of salsalate in scCO 2 over a wide range of temperatures and pressures even when the binary interaction parameter (k ij) is set to zero. [Display omitted] • Solubility of salsalate (anti-inflammatory drug) in supercritical CO 2 (scCO 2) predicted using PC-SAFT. • PC-SAFT pure-component parameters derived from solubility data in organic solvents. • Extracted PC-SAFT parameters used to estimate the solubility of salsalate in scCO 2. • PC-SAFT reproduces experimental isothermal and isobaric solubilities of salsalate in scCO 2. [ABSTRACT FROM AUTHOR]

To date limited work has focused on assessing the economic viability of scCO2 extraction to obtain waxes as part of a biorefinery. This work estimates the economic costs for wax extraction from maize stover. The cost of manufacture (COM) for maize stover wax extraction was found to be €88.89 per kg of wax, with the fixed capital investment (FCI) and utility costs (CUT) contributing significantly to the COM. However, this value is based solely on scCO2 extraction of waxes and does not take into account the downstream processing of the biomass following extraction. The cost of extracting wax from maize stover can be reduced by utilizing pelletized leaves and combusting the residual biomass to generate electricity. This would lead to an overall cost of €10.87 per kg of wax (based on 27% combustion efficiency for electricity generation) and €4.56 per kg of wax (based on 43% combustion efficiency for electricity generation). A sensitivity analysis study showed that utility costs (cost of electricity) had the greatest effect on the COM. [ABSTRACT FROM AUTHOR]

The purpose of this study is to investigate the thermo-oxidative degradation behavior of polypropylene (PP) by comparing three types of pristine PP granules (consisting of homopolymer, random copolymer, and block copolymer) with their corresponding oxidized analogues. These analogues were intensely oxidized under oxygen at 90 °C for 1000 h by using the electron spin resonance (ESR) spin trapping method that can detect short-lived radical intermediates during the degradation. The degrees of oxidation could be evaluated by chemiluminescence (CL) intensity, which was related to the concentration of hydroperoxide groups generated in the PP chain. In the pristine PP samples, a small amount of hydroperoxides were found to be formed unintentionally, and their homolysis produces alkoxy radicals, RO•, which then undergo β -scission to yield chain-end aldehydes or chain-end ketones. These oxidation products continue to take part in homolysis to produce their respective carbonyl and carbon radicals. On the other hand, in the oxidized PP granules, because of their much higher hydroperoxide concentration, the two-stage cage reaction and the bimolecular decomposition of hydroperoxides are energetically favorable. Carbonyl compounds are formed in both reactions, which are then homolyzed to form the carbonyl radical species, •C(O)-. PP homopolymer produced the largest amount of carbonyl radical spin adduct; thus, it was found that the homopolymer is most sensitive to oxygen attack, and the presence of ethylene units in copolymers enhances the oxidation resistance of PP copolymers.

A method to estimate the solubilities of two non-steroidal anti-inflammatory drugs (NSAIDs), ibuprofen and ketoprofen, as active pharmaceutical ingredients (APIs) in supercritical CO 2 (scCO 2), was examined using perturbed-chain statistical associating fluid theory (PC-SAFT), which is more predictive than conventional methods that use cubic-type equations of state and semi-empirical correlation models. The values of the three PC-SAFT pure-component parameters of the API were adjusted to the solubility in organic solvents and determined. These parameters were then applied to estimate the solubility of the API in scCO 2. The PC-SAFT solubility calculations almost reproduced the experimental values over a wide pressure range, even when k ij (the binary interaction parameter) was set to zero. Furthermore, the isobaric solubility of scCO 2 was successfully described by PC-SAFT using the generalized k ij. [Display omitted] • Predictive PC-SAFT approach for API solubilities in scCO 2. • PC-SAFT parameters determined by fitting solubilities in organic solvents. • PC-SAFT approach reproduces API solubilities in scCO 2 without k ij. • Generalized k ij parameter improves calculated results of solubilities in scCO 2. [ABSTRACT FROM AUTHOR]

Highlights: [•] Supercritical CO2 MQL benchmarked against conventional aqueous flood coolants for tool wear. [•] ScCO2 MQL improves tool life under production level machining conditions. [•] ScCO2 MQL allows up to 40% increase in material removal rate (MRR) at comparable tool wear. [•] Roughly 70g/min of CO2 flow required for each kW of cutting power at the higher MRR. [•] Tools fail from crater wear and chip hammering in scCO2 MQL instead of notch formation. [ABSTRACT FROM AUTHOR]

Abstract: Biodiesel, an ideal alternative to fossil fuels, is very imperative for the sustainable development of mankind. Among its preparation technologies, biotechnological preparation is the most promising one. This study critically reviews the current progresses in biocatalysts (lipases), transesterifaction, feedstocks, and, particularly, the key aspects that have been neglected or have recently emerged. A complete summary of the development of stable and cost-effective lipases, ultrasonication and microwave-assisted treatment for biodiesel synthesis, solvent engineering, synergetics of different lipases, kinetics and reaction mechanism for enzymatic transesterification, potentially cheap feedstocks, and economic efficacy analysis has been provided. As a bulk commodity with low revenue, biodiesel production is strongly affected by the prices of oil feedstocks. Hence, value-added derivatives are highly significant. This topic has been highlighted and comprehensively addressed in this review for the first time. [Copyright &y& Elsevier]

Highlights: [•] Melt crystallization is a method of choice for separating isomeric long-chain aldehydes. [•] Separation problem caused by chemical instability of aldehydes solved with stabilizers. [•] Isomeric aldehydes with chain lengths of C11 to C13 form eutectic solid-liquid equilibria. [•] Measurement of growth rates and purities in a lab-scale layer crystallizer. [•] Precise mathematical description of sweating by improving a method from literature. [Copyright &y& Elsevier]

Abstract: Extractive distillation using ionic liquids (ILs) is a promising technology to separate the close-boiling mixture ethylbenzene/styrene. A proper solvent regeneration is crucial to obtain a technical and economic feasible process. In this work, several regeneration technologies were studied to recover styrene from the IL [4-mebupy][BF4] using Aspen Plus. Stripping with a hot gas (N2 or ethylbenzene), supercritical CO2 extraction, distillation by adding a co-solvent, and evaporation were investigated. It was found that the IL that was fed as solvent to the extractive distillation column should have a purity of at least 99.6wt% to maintain the purities of the top and bottom products from the extractive distillation column. This purity could not be obtained with an evaporator using mild conditions (T =130°C, T condenser ≥20°C). From the process models and the economic evaluation for a typical production capacity of 500,000mta, the conclusion can be drawn that evaporation using very low pressures (P <10mbar) and stripping with ethylbenzene are the most promising technologies to recover styrene monomer from the IL [4-mebupy][BF4]. [Copyright &y& Elsevier]

Poly (styrene-co-acrylonitrile)/fluorinated montmorillonite was successfully prepared in supercritical carbon dioxide (scCO2) by dispersion polymerization. In this study, a mixed stabilizer system was applied and investigated. Poly(styrene-r-acrylonitrile)-block-poly(1,1,2,2-tetrahydroperfluorooctyl methacrylate) (PSAN-b-PFOMA) was synthesized and investigated as stabilizer in scCO2. Fluorinated surfactant was used for the modification of the montmorillonite. The fluorinated montmorillonite (FMMT) applied in the polymerization was not only used as nanocomposite filler but also as a guest stabilizer. This study examined the stabilization roles of stabilizer and guest stabilizer respectively. The optimum dosages of both compounds were studied. The polymerization with mixed stabilizer resulted in high yield and high molecular weight. Moreover, a series of nanocomposites were characterized and the products showed excellent properties. It was found that the montmorillonite layer could be completely exfoliated using reasonable loading, and dispersed in the polymer matrix. In addition, the pressure of scCO2 was studied and the density of scCO2 was shown to be relevant to the stabilization of the reaction. The mixed stabilizer system made the polymerization more effective and the in-situ dispersion polymerization performed in scCO2 was shown to be a useful method for the nanocomposites preparation. [ABSTRACT FROM AUTHOR]

Abstract: Porous LiFePO4 particles have been investigated as cathode materials for lithium ion batteries by introducing supercritical carbon dioxide (scCO2). First we produced LiFePO4 through hydrothermal method. Then scCO2 was introduced to change the morphology of the particle. By controlling the experiment parameter, porous LiFePO4 was finally obtained. A solid-to-porous transformation mechanism was supposed based on the dissolution of LiFePO4. Electrochemical measurements showed that porous structure greatly improved the performance of LiFePO4. [Copyright &y& Elsevier]

An antisolvent processing technique by simultaneous compressed antisolvent precipitation and photopolymerization for cross-linked polymer microparticles formation was presented in this paper. In this process, photopolymerization of the homogeneous solution composed of methylene chloride, poly(ethylene glycol)600 diacrylate (PEG600DA) as monomer and diphenyl-(2,4,6-trimethylbenzoyl)-phosphine oxide (TPO) or 2,2-dimethoxy-2-phenylacetophenone (DMPA) as photoinitiator resulted to microparticle when it was sprayed into supercritical carbon dioxide (scCO2) and simultaneously exposed to initiating light. High miscibility of the solvent in scCO2 made methylene chloride quickly extracted from the dispersion phase, leaving very high concentrations of monomer (PEG600DA) dispersed in scCO2. The high monomer concentration combined with photo initiating polymerization facilitates rapid reaction rates and ultimately lead to polymer precipitation. Particle size and morphology were adjustable by changing the processing conditions, such as temperature and pressure. © 2012 Wiley Periodicals, Inc. J Appl Polym Sci, 2012 [ABSTRACT FROM AUTHOR]

Abstract: Supercritical carbon dioxide (scCO2), an environmentally friendly solvent, can change the fine structure of fibers depending on treatment temperature and pressure. Samples of partially oriented yarn (POY) PET fibers were uniaxially drawn below the glass transition temperature (T g) and then exposed to scCO2 under tension to induce morphological changes in them. The effects of draw ratio and scCO2 exposure on the structural changes and mesomorphic transitions were evaluated. For this purpose, thermal characteristics of the structure, especially the rearrangement of polymer chains in the amorphous phase induced by cold-drawing and exposure to scCO2, were evaluated by differential scanning calorimetry (DSC) and Fourier transform infrared (FTIR). The orientation factor of the fibers was measured using a polarizing microscope. The paracrystalline portion and the crystallite sizes of exposed samples were estimated by wide-angle X-ray diffraction. To evaluate the solubility of CO2 molecules in the samples, density and fractional free volumes were also measured. A good correlation was obtained between the results obtained from various measurement techniques. Results showed that cold-drawing of PET fibers leads to a strain-induced crystallization and that exposure to scCO2 changes the structure of the oriented PET samples. To investigate mesophase transitions, percentage of extended chains in the amorphous regions was calculated by analyzing the results of DSC and FTIR. Results showed that the amount of extended chains developing during cold-drawing in the amorphous regions decreased when exposed to scCO2. [Copyright &y& Elsevier]

Abstract: The porous structure of a scaffold determines the ability of bone to regenerate within this environment. In situations where the scaffold is required to provide mechanical function, balance must be achieved between optimizing porosity and maximizing mechanical strength. Supercritical CO2 foaming can produce open-cell, interconnected structures in a low-temperature, solvent-free process. In this work, we report on foams of varying structural and mechanical properties fabricated from different molecular weights of poly(dl-lactic acid) P dl LA (57, 25 and 15kDa) and by varying the depressurization rate. Rapid depressurization rates produced scaffolds with homogeneous pore distributions and some closed pores. Decreasing the depressurization rate produced scaffolds with wider pore size distributions and larger, more interconnected pores. In compressive testing, scaffolds produced from 57kDa P dl LA exhibited typical stress–strain curves for elastomeric open-cell foams whereas scaffolds fabricated from 25 and 15kDa P dl LA behaved as brittle foams. The structural and mechanical properties of scaffolds produced from 57kDa P dl LA by scCO2 ensure that these scaffolds are suitable for potential applications in bone tissue engineering. [Copyright &y& Elsevier]

Abstract: The three crude extracts including Oryza sativa (bran) from supercritical carbon dioxide fluid (scCO2) process which gave the highest unsaturated fatty acid contents and biological activities including the antioxidative, tyrosinase inhibition, stimulation index on human normal skin fibroblast were selected from ten edible plants to prepare the semi-purified fractions. Fraction No. 3 of the O. sativa bran crude extract gave the highest content of unsaturated fatty acids and 5α-reductase (type 1) inhibition activity (5AR). Its linoleic acid (LN) and total unsaturated fatty acid (TUC) contents were significantly positive and linear correlated to 5AR on DU-145 cell line (at r of 1.00, p <0.01). Its total phenolic contents and all biological activities also showed positive correlations to 5AR with r >0.9 (p <0.05). This study has demonstrated the potential of fraction No. 3 fractionated from the O. sativa bran crude extract prepared by scCO2 to be developed as anti-androgenic alopecia products. [Copyright &y& Elsevier]

Abstract: Amorphous poly(dl-lactic acid) (P dl LA) and poly(lactic acid-co-glycolic acid) (PLGA) polymers have been used to fabricate porous scaffolds for tissue engineering applications via a supercritical foaming technique. The chemical composition of the polymers and the morphology (pore size, porosity and interconnectivity) of the scaffolds are crucial because they influence cell filtration, migration, nutrient exchange, degradation and drug release rate. To control the morphology of supercritical foamed scaffolds, it is essential to study the interactions of polymers with CO2 and the consequent solubility of CO2 in the polymers, as well as the viscosity of the plasticized polymers. In this paper, we are showing for the first time that well known and useful biodegradable polymers can be plasticized easily using high pressure CO2 and that we can monitor this process easily via a high pressure attenuated total reflection Fourier transform infrared (ATR-IR) and rheology. High pressure ATR-IR has been developed to investigate the interactions of CO2 with P dl LA and PLGA polymers with the glycolic acid (GA) content in the copolymers as 15, 25, 35 and 50% respectively. Shifts and intensity changes of IR absorption bands of the polymers in the carbonyl region (∼1750 cm−1) are indicative of the interaction on a qualitative level. A high pressure parallel plate rheometer has also been developed for the shear viscosity measurements of the CO2-plastisized polymers at a temperature below their glass transition temperatures. The results demonstrate that the viscosities of the CO2-plasticized polymers at 35 °C and 100 bar were comparable to the values for the polymer melts at 140 °C, demonstrating a significant process advantage through use of scCO2. The data from the high pressure rheology and high pressure ATR-IR, combined with the sorption and swelling studies reported previously, demonstrate that the interaction and the solubility of CO2 in PLGA copolymers is related to the glycolic acid content. As the glycolic acid ratio increases the interaction and consequent solubility of CO2 decreases. The potential applications of this study are very broad, from tissue engineering and drug delivery to much broader applications with other polymers in areas that may range from composites and polymer synthesis through to injection moulding. [Copyright &y& Elsevier]

Abstract: Medium engineering for biocatalytic reactions is imperative approach for the synthesis of biologically active compounds. Biocatalytic reaction media holding water, organic solvent and supercritical fluids have become well established for commercial applications. Non-aqueous biocatalytic reactions carry significant advantages that non-polar substrate can be specifically reacted and/or product recovered efficiently. On the other hand, usage of conventional organic solvents as non-aqueous medium affects green chemistry aspects. Hydrophobic ionic liquids (ILs) provide desirable environment for many enzymatic reactions as conventional organic solvents do but without emission of volatile organic compound (VOCs). To extend hydrophobic ILs laboratory performance into commercial process requires the creation of a brief database for biocatalytic reactions. In light of the growing relevance of this theme, the current review intends to address the important biotechnological applications of the frequently employed hydrophobic 1-butyl-3-methylimidazolium hexafluorophosphate ([Bmim] PF6) IL. The review also attempts to describe the comparison of various whole cell biocatalytic reactions using supercritical carbon dioxide (scCO2) biphasic systems for product extraction with potentially competitive ILs and other conventional solvents. [Copyright &y& Elsevier]

The decellularization method efficacy varies depending on the tissue type. There are commonly used physical, chemical and enzymatic methods. Most of the methods affect the extracellular matrix properties that will in turn alter the cell fate when the biological scaffold is recellularised. We aimed to optimize the decellularization of ram cardiac via scCO 2 extraction to preserve the moisture and the components of the ECM during the decellularization procedure. In literature decellularization studies focus on heart vessels. In this study, we aimed to decellularize and recellularize ram cardiac tissue for the first time. Besides we obtained a decellularized tissue without cells on it with a mechanical strength similar to native ECM. Decellularized ram cardiac tissue is expected to be animal-based biomaterial for candidate biomedical applications in vitro and in vivo further studies. [Display omitted] [ABSTRACT FROM AUTHOR]

The optimization of the supercritical fluid extraction (SFE) of cannabinoids, using supercritical carbon dioxide (scCO2), was investigated in a fractional factorial design study. It is hypothesized that four main parameters (temperature, pressure, dry flower weight, and extraction time) play an important role. Therefore, these parameters were screened at predetermined low, medium, and high relative levels. The density of scCO2 was used as a factor for the extraction of cannabinoids by changing the pressure and temperature. The robustness of the mathematical model was also evaluated by regression analysis. The quantification of major (cannabidiol (CBD), cannabidiolic acid (CBDA), delta 9-tetrahydrocannabinol (Δ9-THC), delta 8-tetrahydrocannabinol (Δ8-THC), and delta 9-tetrahydrocannabinol acid (THCA-A)) and minor (cannabidivann (CBDV), tetrahydrocannabivann (THCV), cannabigerolic acid (CBG), cannabigerol (CBGA), cannabinol (CBN), and cannabichomere (CBC)) cannabinoids in the scCO2 extract was performed by RP-HPLC analysis. From the model response, it was identified that long extraction time is a significant parameter to obtain a high yield of cannabinoids in the scCO2 extract. Higher relative concentrations of CBD(A) (0.78 and 2.41% w/w, respectively) and THC(A) (0.084 and 0.048% w/w, respectively) were found when extraction was performed at high relative pressures and temperatures (250 bar and 45 °C). The higher yield of CBD(A) compared to THC(A) can be attributed to the extract being a CBD-dominant cannabis strain. The study revealed that conventional organic solvent extraction, e.g., ethanol gives a marginally higher yield of cannabinoids from the extract compared to scCO2 extraction. However, scCO2 extraction generates a cleaner (chlorophyll-free) and organic solvent-free extract, which requires less downstream processing, such as purification from waxes and chlorophyll. [ABSTRACT FROM AUTHOR]

A new polymerization procedure with the aid of reverse micelles in supercritical carbon dioxide (SCCO2) has been employed to synthesize polyaniline (PANI). Sodium bis(2-ethylhexyl)-sulfosuccinate (AOT) and polyether-modified polysiloxane (PeSi) were used as mixing surfactants. PANI with more favorable needle-like aggregation structure, higher crystallinity, more excellent conductivity (7.22 S cm- 1) and better dispersibility in ethanol has been obtained via the inverse emulsion polymerization in SCCO2, compared to the PANI synthesized in isooctane. These results were demonstrated by the analysis of Fourier Transform Infrared Spectroscopy (FTIR), Scanning Electron Microscope (SEM), Transmission Electron Microscope (TEM), X-ray diffraction patterns (XRD) and conductivity measurement. The new polymerization procedure was also employed to prepare polyaniline-fluorinated montmorillonite (PANI-FMMT) nanocomposites in SCCO2. The nanocomposites with highly concentrated (12 wt%-50 wt% loading to monomer), fully delaminated FMMT were successfully prepared. The intercalation of FMMT in SCCO2 was characterized by FTIR, XRD, TEM. Thermogravimetry Analysis (TGA) was performed to investigate the enhancement of thermal stability of PANI-FMMT nanocomposites. SCCO2 facilitate the synthesis of PANI with high performance and PANI-MMT with high MMT concentration. SCCO2 is not only an “alternative” solvent for its environmental-friendly characteristic, but also a more “effective” medium compared to some organic solvent (such as isooctane) to prepare PANI and its intercalated composite materials. [ABSTRACT FROM AUTHOR]