Polymethylmethacrylate (PMMA) sub-microparticles produced by Supercritical Assisted Injection in a Liquid Antisolvent

A recently developed supercritical assisted process, called Supercritical Assisted Injection in a Liquid Antisolvent (SAILA) is proposed to produce polymer micro and nanoparticles in water stabilized suspensions. Polymethylmethacrylate (PMMA) has been selected as the model polymer for a systematic study of the influence of the SAILA operating parameters on particle morphology and diameter. The effect of expanded liquid injection pressure on particle size and distribution was studied and different expanded liquid temperatures and compositions were also explored. Successful precipitation of the polymer in a water stabilized suspension was obtained and narrow particle size distributions were obtained using 70 and 90 bar injection pressures. PMMA particles controlled diameter were produced ranging between 0.2 ± 0.04 μm and 0.9 ± 0.2 μm. Particles are formed from the expanded liquid solution as a consequence of very fast supersaturation produced by spraying it the liquid antisolvent.     

Use of solvent mixtures in supercritical antisolvent process to modify precipitates morphology: Cellulose acetate microparticles

In the supercritical antisolvent precipitation (SAS), the jet fluid dynamics is characterized by two-phase mixing at subcritical conditions, and by one-phase mixing at completely developed supercritical conditions. The amplitude of the pressure range, in which binary systems organic solvent/scCO₂ exhibit the transition between two-phase to one-phase mixing, depends on the organic solvent that is in contact with supercritical carbon dioxide (scCO₂) and conditions the morphology of the microparticles produced by SAS. When this pressure range is wide, as in the case of dimethylsulfoxide (DMSO), solutes solubilized in the organic solvent can be precipitated as microparticles by atomization, droplets formation and drying; when this pressure range is narrow, as for acetone, gas mixing prevails and only nanoparticles are generally observed. Therefore, generally speaking, solutes that are soluble only in solvents exhibiting gas mixing in scCO₂, do not exhibit microparticles morphology and this fact is a limitation for several industrial applications.In this work, a model compound, cellulose acetate (CA), that is slightly soluble in DMSO and freely soluble in acetone, was processed by SAS using mixtures of the two solvents that exhibit intermediate behaviors between the two pure solvents, to extend two phase mixing and produce CA microparticles. Using different DMSO/acetone mixture percentages, the effects of the polymer concentration in the liquid solution and of the pressure were studied. A mixture of DMSO/Acetone 50/50 (v/v), at a pressure of 85 bar and a concentration of the liquid solution equal to 40 mg/mL, efficiently produced non-coalescing CA microparticles with a mean diameter of 0.42 μm and a standard deviation of about 0.15 μm, demonstrating that this SAS strategy can be successful.     

Crystallization of silibinin from organic solutions using supercritical and aqueous antisolvents

Silibinin, an anticancer drug, was crystallized from organic solutions using supercritical and aqueous antisolvents. Silibinin was dissolved in acetone and ethanol at concentration range of 0.01–0.04 g/mL, and the drug solutions were placed in contact with two different antisolvents, carbon dioxide and water. The mixing of the drug solutions and antisolvents led to the prompt precipitation of silibinin in a solid crystal form. The experimental variables, such as temperature, solution concentration, mixing rate and solution/antisolvent volume ratio were manipulated. When the experiments were conducted with a supercritical antisolvent, the effects of external additives on the crystal habit were examined. α-d-Glucose penta acetate, triton X-100 and urea were added to the solution at concentration range of 0.001–0.003 g/mL as external additives. The temperature increase of 20 °C induced 25% increase in particle size. As the solution concentration was increased from 0.01 to 0.04 g/mL, the average particle size decreased from 35.5 to 22.0 μm in supercritical antisolvent experiments, while the particle size increased from 8.9 to 30.4 μm in aqueous antisolvent experiments. The use of different kinds of external additives resulted in different modifications of the particle shape and structures.     

Production of silica aerogel microparticles loaded with ammonia borane by batch and semicontinuous supercritical drying techniques

Silica aerogel microparticles were prepared by supercritical drying and used as support for hydrogen-storing ammonia borane (AB). The formation of aerogel microparticles was done using two different processes: batch supercritical fluid extraction and a semicontinuous drying process. Silica aerogel microparticles with a surface area ranging from 400 to 800 m²/g, a volume of pores of 1 cm³/g, and a mean particle diameter ranging from 12 to 27 μm were produced using the two drying techniques. The particle size distribution (PSD) of the microparticles was influenced by shear rate, amount of catalyst, hydrophilic–hydrophobic solvent ratio and hydrophobic surface modification. In particular, irregular aerogel particles were obtained from hydrophilic gels, while regular, spherical particles with smooth surfaces were obtained from hydrophobic gels. AB was loaded into silica aerogel microparticles in concentrations ranging from 1% till 5% wt. Hydrogen release kinetics from the hydride-loaded aerogel was analyzed with a volumetric cell at 80 °C. By stabilization of AB into the silica aerogel microparticles, an improvement of the release rate of hydrogen from AB was observed.     

A kinetic study of organic compounds (acetone,toluene, n-hexane and n-decane) adsorption behavior on activated carbon under supercritical carbon dioxide conditions at temperature from 313 to 353 K and at pressure from 4.2 to 15.0 MPa

Adsorption kinetics of four volatile organic compounds (VOCs) (acetone, toluene, n-hexane and n-decane) on activated carbon under supercritical carbon dioxide (scCO₂) conditions was studied. Breakthrough curve measurements of VOCs in scCO₂ were performed with a fixed bed method for activated carbon (ca. mean particles diameter: 100 μm, specific surface area: 1300 m²/g and mean pore diameter: 0.687 nm, respectively). The measured breakthrough curves could be correlated with a kinetic model by using only one fitting parameter (effective diffusion coefficient in pore) within 10% of average relative deviation. The determined effective diffusion coefficient decreased with decreasing temperatures and increasing pressures at all conditions. Additionally, a generalized model of the determined effective diffusion coefficients was developed, and the proposed model could satisfactorily describe temperature and pressure dependence at all VOCs conditions.     

Effect of particle size on the mechanical properties of reaction bonded boron carbide ceramics

In the present communication, effect of boron carbide particle size on the mechanical properties such as hardness, fracture toughness and flexural strength of reaction bonded boron carbide (RBBC) ceramics were investigated. RBBC composites were produced by the reactive infiltration of molten silicon into porous preform containing boron carbide and free carbon. Boron carbide powders with mean particle size of 18.65 μm, 33.70 μm and 63.35 μm were chosen for the RBBC composites. The experimental results show that hardness increases from 1261.70±64.74 kg/mm² to 1674.90±100.00 kg/mm² and fracture toughness drops from 5.76±0.26 MPa m^1/2 to 3.4±0.37 MPa m^1/2. However, flexural strength decreases from 403.41±5.70 MPa to 256.15±25.05 MPa with the increase in particle size. Indentation induced cracks in RBBC are mainly median type and number of cracks increase with the increase of starting particle size.     

Manipulating the size,the morphology and the polymorphism of acetaminophen using supercritical antisolvent (SAS) precipitation

The supercritical antisolvent technology is used to crystallize paracetamol particles. Supercritical carbon dioxide (scCO₂) is used as antisolvent. Ethanol, acetone and mixtures of ethanol and acetone are used as solvents. The initial concentration of paracetamol in the solution was varied between 1 and 5 wt%, the composition of the ethanol/acetone solvent mixture between 50 and 90 wt% of ethanol and the operation pressure between 10 and 16 MPa at a temperature of 313 K. The most important finding is that the polymorph of paracetamol crystals can be adjusted between monoclinic and orthorhombic by varying the content of ethanol in the solution. The second important finding is that the occurrence of primary and secondary crystal structures can be explained solely by the overall supersaturation during the crystallization process. While X-ray diffraction was used to analyze the polymorph of the particles, their morphology was analyzed using scanning electron microscopy.     

Carbon fibers from dry-spinning of acetylated softwood kraft lignin

An acetylated softwood kraft lignin was dry-spun into precursor fibers and successfully processed into carbon fibers with a tensile strength exceeding most values reported in prior studies on lignin-based carbon fibers. Limited acetylation of lignin hydroxyl groups enabled dry-spinning of the precursor using acetone (solvent) followed by thermo-oxidative stabilization. Resulting carbon fibers (∼7 μm diameter) displayed a tensile modulus, strength, and strain-to-failure values of 52 ± 2 GPa, 1.04 ± 0.10 GPa, and 2.0 ± 0.2%, respectively. Because of solvent diffusion during dry-spinning, fibers displayed a crenulated surface that can provide a larger specific interfacial area for enhanced fiber/matrix bonding in composite applications.     

Foaming strategies for bioabsorbable polymers in supercritical fluid mixtures. Part II. Foaming of poly(ɛ-caprolactone-co-lactide) in carbon dioxide and carbon dioxide + acetone fluid mixtures and formation of tubular foams via solution extrusion

This paper reports on the foaming of poly(ɛ-caprolactone-co-lactide) in carbon dioxide and carbon dioxide + acetone mixtures. Experiments were carried out in specially designed molds with porous metal surfaces and fluid circulation features to generate foams with uniform dimensions at 60, 70 and 80 °C at pressures in the range 7–28 MPa. Depending upon the conditions, foams with pores in the range from 5 to 200 μm were generated. Adding acetone to carbon dioxide improved the uniformity of the pores compared to foams formed by carbon dioxide alone. In addition, a unique high-pressure solution extrusion system was designed and used to form porous tubular constructs by piston-extrusion of a solution from a high-pressure dissolution chamber through an annular die into a second chamber maintained at controlled pressure/temperature and fluid conditions. Long uniform porous tubular constructs with 6 mm ID and 1 mm wall thickness were generated with glassy polymers like poly(methyl methacrylate) by extruding solutions composed of 50 wt% polymer + 50 wt% acetone, or 25 wt% polymer + 10% acetone + 65% carbon dioxide at 70 °C and 28 MPa. Pores were in the 50 μm range. The feasibility of forming similar tubular constructs were demonstrated with poly(ɛ-caprolactone-co-lactide) as well. Tubular foams of the copolymer with interconnected pores with pore sizes in the 50 μm range were generated by extrusion of the copolymer solution composed of 25 wt% polymer + 10 wt% acetone + 65 wt% carbon dioxide at 70 °C and 28 MPa. Reducing the acetone content in the solution led to a reduction of pore sizes. Comparisons with the foaming behavior of the homopolymer poly(ɛ-caprolactone) that were carried out in the molds with porous metal plates show that the foaming behavior of the copolymer is more akin to the foaming behavior of the caprolactone homopolymer component.     

TiO2 photocatalysis in cementitious systems: Insights into self-cleaning and depollution chemistry

The present work offers a general overview about application of titanium dioxide (or titania), TiO₂, photocatalysis to concrete technology in relation to enhanced aesthetic durability and depollution properties achieved by implementing TiO₂ into cement. Chemistry of degradation of Rhodamine B (RhB), a red dye used to assess self-cleaning performances of concretes containing TiO₂, as well as oxidation of nitrogen oxides (NOx), gaseous atmospheric pollutants responsible for acid rains and photochemical smog, is investigated using two commercial titania samples in cement and mortar specimens: a microsized, m-TiO₂ (average particle size 153.7 nm ± 48.1 nm) and a nanosized, n-TiO₂ (average particle size 18.4 nm ± 5.0 nm). Experimental data on photocatalytic performances measured for the two samples are discussed in relation to photocatalyst properties and influence of the chemical environment of cement on titania particles. Impacts on applications in construction concrete are also discussed.     

Effects of mono-dispersed PMMA micro-balls as pore-forming agent on the properties of porous YSZ ceramics

Porous yttria-stabilized zirconia (YSZ) ceramics were successfully fabricated by the dry pressing method with different size (1.8–20 μm) and amount (2–60 vol.%) of mono-dispersed poly methyl methacrylate (PMMA) micro-balls. Different PMMA additions with different size and amount were investigated to achieve optimal thermal and mechanical properties. With increases of the amount of PMMA, the porosity of porous YSZ ceramics ranges from 7.29% to 51.6%, the flexural strength increases firstly and then decreases, and the thermal conductivity decreases continuously. With decreases of the diameter of PMMA micro-balls, the mean pore size and thermal conductivity of porous YSZ ceramics decrease, and the flexural strength of porous YSZ ceramics with same porosity increases firstly and then decreases. The porous YSZ ceramics with a higher porosity (18.44 ± 1.24%), the highest flexural strength (106.88 ± 3.2179 MPa) and low thermal conductivity (1.105 ± 0.15 W/m K) can be obtained when the particle diameter and the amount of PMMA are 5 μm and 20 vol.%, respectively.     

Exfoliation/delamination of kaolinite by low-temperature washing of kaolinite–urea intercalates

The effects of short milling (2 × 10 min) of two fractions of kaolinite (< 5 μm (S5) and 5–45 μm (S)), previously expanded by intercalation with 20 wt.% and 40 wt.% urea (U) and exfoliated/delaminated using low-temperature procedures, were studied. Untreated and treated kaolinite samples were examined by X-ray powder diffraction (XRPD), and their specific surface area (SSA), particle size distribution (PSD) and Fourier-transform infrared (FTIR) spectra were measured and interpreted. Samples intercalated with different concentrations of urea and subsequently exfoliated during thermal or low-temperature washing exhibit a variable intensity of the 001 diffractions of kaolinite (K) and interstratified intermediate kaolinite (H) with randomly interstratified layers of grafted urea and water. Low-temperature washing procedures yield H structures interstratified with layers grafted with urea and water with a mean d₀₀₁ = 8.168(50) Å. After thermal washing procedures, H structures form with a mean d₀₀₁ = 8.322(60) Å, apparently as a result of prevailing interstratifications of water over grafted layers of urea. The H/K peak intensity ratio for exfoliated/delaminated samples S and S5 previously intercalated with 20% U is significantly higher than for those intercalated with 40% U. After all washing procedures, fine fraction S5 increases its SSA from 20.2 m²/g to 25–35 m²/g, whereas the grain-size diameter remains approximately constant, with a mean M_D = 2.80(20) μm. Exfoliated/delaminated coarse kaolinite of the S fraction not only increases its SSA from 9.4 m²/g to SSA between 12.5 m²/g and 20.5 m²/g, but also decreases its M_D from 12 μm to between 8.73 μm and 5.60 μm due to the breaking of particles. This procedure is quicker than milling and thermal washing operations reported and used so far, and, moreover, it yields SSA values comparable to those obtained for exfoliated/delaminated kaolinite.     

Supercritical antisolvent micronization of PVP and ibuprofen sodium towards tailored solid dispersions

The supercritical antisolvent technology is used to precipitate polyvinylpyrrolidone (PVP) particles and crystallise ibuprofen sodium (IS) crystals separately and in the form of solid dispersion together. Supercritical carbon dioxide (scCO₂) is used as antisolvent. For PVP particle generation, ethanol, acetone and mixtures of ethanol and acetone are used as solvents. The initial concentration of PVP in the solution was varied between 0.5 wt% and 1.5 wt%, the operation pressure between 10 MPa and 30 MPa and the composition of ethanol/acetone solvent mixtures between 100 wt% and 0 wt% of ethanol at a constant temperature of 313 K. Furthermore, the mean molecular weight of the polymer was varied between 40 kg mol⁻¹, 360 kg mol⁻¹ and 1300 kg mol⁻¹. An increase of the content of the poor solvent acetone in the initial solvent mixture as well as the usage of PVP with a higher molecular weight, leads to a significant decrease in mean particle size. At all the investigated parameters always fully amorphous PVP powder precipitates. For IS, only ethanol was used as the solvent, the initial IS concentration in the solution was varied between 1 wt% and 3 wt% and the operation pressure between 10 MPa and 16 MPa. A variation of these parameters leads to a manipulation of the size and the morphology of the crystallised IS crystals. Irrespective of the parameters used, always the same polymorphic form of ibuprofen sodium is produced. The solid dispersions were generated at different compositions of PVP to IS and with two different molecular weights of PVP at otherwise constant conditions. Fully amorphous solid dispersions consisting of IS and PVP together were generated at different ratios of PVP to IS.The mechanisms that control the final particle properties are discussed taking into account two different models for “ideal” and “non-ideal” solutes. Furthermore, the study of the “unconventional” SAS parameters, molecular weight and solvation power of the solvent shows that these parameters qualify to tailor polymer particle properties via SAS processing. Next to the investigation into the behaviour of both solutes separately, fully amorphous solid dispersions consisting of IS and PVP together were generated. While X-ray diffraction was used to analyze the crystalline structure of the particles, respectively, solid dispersions, their morphology was analysed using scanning electron microscopy (SEM).     

Precise micromachining of yttria-tetragonal zirconia polycrystal ceramic using 532 nm nanosecond laser

High quality micro-sized steps and blind hole structures without microcracks, chips or spatter deposition were machined on yttria-tetragonal zirconia polycrystal (Y-TZP, 3 mol% yttria) by nanosecond laser (wavelength=532 nm, pulse width ~6 ns). The diameter of blind hole is 500 μm and each step is 500±10 μm wide and 100±5 μm deep. The 1.35 mm³/min removal rate and the smooth machined surface with Ra=2.824 μm roughness depicting the high precise and efficient processing were achieved. The ablation characteristics of nanosecond laser process of Y-TZP ceramic were also studied. Based on the study, a reasonable design of the processing path for micromachining of a finer embedded step with 24±2 μm width (smaller than the 60 μm focused spot size) around the inner-wall of a 2×2 mm² cavity was developed. These results and discussion offer new possibilities in the manufacturing of bio-ceramic products by nanosecond laser with high processing quality and efficient.     

Processing naproxen with supercritical CO2

Naproxen has been processed with supercritical fluids in order to improve the dissolution rate and bioavailability. Microparticles of naproxen have been obtained by a Rapid Expansion of Supercritical Solutions (RESS) process in which carbon dioxide has been used as a solvent and methanol as a cosolvent. The influence of extraction pressure (200–300 bar) and extraction temperature (60 °C and 100 °C) on the naproxen precipitation has also been investigated. In general, the morphology of the precipitated particles improved and particle size (PS) decreased in comparison to the raw material. Lower extraction pressure and higher extraction temperature led to a smaller particle size. On the other hand, a supercritical antisolvent (SAS) process has been applied due to the relative medium solubility values of naproxen in supercritical carbon dioxide, with precipitation obtained successfully in all cases. The initial concentration of the solution and the solvent effect has both been analysed. Morphologies and mean diameter ranges have been analysed by scanning electron microscopy (SEM) and the influence on crystallinity of both supercritical processes has been evaluated by X-ray diffraction (XRD) measurements.     

Preparation of monodisperse PEG hydrogel microparticles using a microfluidic flow-focusing device

A microfluidic assisted preparation method of nearly monosized poly(ethylene glycol) (PEG) microparticles has been described. Three types of microfluidic flow-focusing devices with different geometries were fabricated using polydimethylsiloxane (PDMS). Microdroplets of PEG hydrogel were successfully prepared in the microfluidic flow-focusing devices by adjusting the flow rates of the continuous phase, namely, mineral oil, and the dispersed phase, viz., hydrogel solution. Then, the microdroplets of PEG hydrogel were cured by UV irradiation. Various experimental conditions pertaining to the geometry of the microfluidic flow-focusing device, flow rates of the dispersed and continuous phases, and concentration of PEG hydrogel solution were investigated and optimized to fabricate monosized PEG hydrogel microparticles. The prepared PEG microparticles were nearly monosized in the range of 40 μm to 200 μm in diameter according to the above experimental conditions. Then, PEG hydrogel particles laden with microbeads of 6 μm diameter were fabricated using the microfluidic flow-focusing devices with the optimized conditions.     

Pressurized liquid extraction and low-pressure solvent extraction of carotenoids from pressed palm fiber: Experimental and economical evaluation

In this work, a comparison of Soxhlet extraction (LPSE–SOX), percolation (LPSE–PE) and pressurized liquid extraction (PLE) for the recovery of carotenoid-rich extracts from pressed palm fiber (PPF) was carried out in terms of yield, carotenoid profile and economic viability to evaluate the methods’ industrial applicability. An optimization study was performed for each extraction technique with ethanol at a solvent/feed ratio of 20. The independent variables were temperature (35–55 °C), pressure (0.1–8 MPa) and flow rate (1.6, 2.4 g/min). The results showed that the global extraction yield obtained using LPSE–SOX (96 ± 4 mg extract/g PPF d.b.) after 6 h was higher than that obtained using LPSE–PE (74 ± 5 mg extract/g PPF d.b., 35 °C, 2.4 g/min) or PLE (44 ± 3 mg extract/g PPF d.b., 55 °C, 4 MPa, 2.4 g/min) after dynamic extraction time of 17 min under optimized conditions. On the other hand, the carotenoid yield obtained using PLE (305 ± 18 μg α-carotene/g extract and 713 ± 46 μg β-carotene/g extract) was higher than the obtained by LPSE–SOX (142 ± 13 μg α-carotene/g extract and 317 ± 46 μg β-carotene/g extract). PLE technique showed the highest selectivity for carotenoids than LPSE techniques. The lowest cost of manufacturing (COM) were obtained for LPSE–PE and PLE with values of US$13.4 and US$29.2/kg extract for a 0.5 m³ vessel capacity.     

Micronization of fenofibrate by rapid expansion of supercritical solution

Micronization of fenofibrate was investigated using rapid expansion of supercritical solution (RESS) process. Effects of pressure, temperature and nozzle on particle size were optimized using Taguchi's orthogonal array and analyzed using XRD, DSC, FT-IR, SEM, laser diffractometer and dissolution testing. Processed fenofibrate retained crystalline structure and has a similar chemical structure with unprocessed fenofibrate. The average particle size of fenofibrate was reduced from its original 68.779 ± 0.146 μm to 3.044 ± 0.056 μm under the optimum condition (T at 35 °C, P at 200 bar and nozzle diameter at 200 μm). The processed fenofibrate showed an enhanced dissolution rate by 8.13 times.     

Mesoporous MgO synthesized by a homogeneous-hydrothermal method and its catalytic performance on gas-phase acetone condensation at low temperatures

Mesoporous MgO micro-particles (20–80 μm) with crystalline phase framework wall were synthesized through a simple hydrothermal homogeneous precipitation route using urea as precipitating reagent. It possesses high specific area (278 m²/g), pseudo parallel pore and wall arrangement and large amount of basic sites and exhibits excellent catalytic activity for acetone condensation to mesityl oxide and isophorone even at low temperatures (< 200 °C).     

Synthesis of 5-Fluorouracil nanoparticles via supercritical gas antisolvent process

The micronization of an anticancer compound (5-Fluorouracil) by supercritical gas antisolvent (GAS) process was investigated. 5-Fluorouracil was dissolved in dimethyl sulfoxide (DMSO) and subsequently carbon dioxide as an antisolvent was injected into this solution thus, the solution was supersaturated and nanoparticles were precipitated. The influence of antisolvent flow rate (1.6, 2 and 2.4 mL/min), temperature (34, 40 and 46), solute concentration (20, 60 and 100 mg/mL) and pressure (9, 12 and 15 MPa) on particle size and particle size distribution were studied. Particle analyses were performed by scanning electron microscopy (SEM) and Zetasizer Nano ZS. The mean particle size of 5-Fluorouracil was obtained in the range of 260–600 nm by varying the GAS effective parameters. The High performance liquid chromatography (HPLC) and Fourier transforms infrared spectroscopy (FTIR) analyses indicated that the 5-Fluorouracil nanoparticles were pure and the nature of the component did not change. The experimental results indicated that increasing the antisolvent flow rate and pressure, while decreasing the temperature and initial solute concentration, led to a decrease in 5-Fluorouracil particle size.