Residual Solvent Content Research Articles

Control of encapsulation efficiency and morphology of poly(lactide-co-glycolide) microparticles with a diafiltration-driven solvent extraction process

The removal of organic solvents during the preparation of biodegradable poly(D,L-lactide-co-glycolide) (PLGA) microparticles by an O/W- solvent extraction/evaporation process was investigated and controlled by diafiltration. Emulsification and steady replacement of the aqueous phase were performed in parallel in a single-vessel setup. During the process, the solidification of the dispersed phase (drug:PLGA:solvent droplets) into microparticles was monitored with video-microscopy and focused beam reflectance measurement (FBRM) and the residual solvent content was analyzed with headspace gas chromatography (organic solvent) and coulometric Karl-Fischer titration (water). Microparticles containing dexamethasone or risperidone were characterized with regard to particle size, morphology, encapsulation efficiency and in-vitro release. Diafiltration-accelerated solvent extraction shortened the process time by accelerating solidification of dispersed phase but reduced the residual dichloromethane content only in combination with increased temperature. Increasing the diafiltration rate increased particle size, porosity, and the encapsulation efficiency of risperidone. The latter effect was particularly evident with increasing lipophilicity of PLGA. A slower and more uniform solidification of end-capped and increased lactide content PLGA grade was identified as the reason for an increased drug leaching. Accelerated solvent extraction by diafiltration did not affect the in-vitro release of risperidone from different PLGA grades. The initial burst release of dexamethasone was increased by diafiltration when encapsulated in concentrations above the percolation threshold. Both porosity and burst release could be reduced by increasing the process temperature during diafiltration. Residual water content was established as an indicator for porosity and correlated with the burst release of dexamethasone.

Accelerated removal of solvent residuals from PLGA microparticles by alcohol vapor-assisted fluidized bed drying

The removal of residual solvents from biodegradable poly(D,L-lactide-co-glycolide) (PLGA) microparticles by fluidized bed drying was investigated. Microparticles were prepared by the O/W solvent extraction/evaporation method and the influence of various process and formulation parameters on the secondary drying was studied. PLGA microparticles and films were characterized for residual organic solvent and water content, recrystallisation, surface morphology, drug loading and in-vitro release of the drugs dexamethasone and risperidone. While alcohol-free fluidized bed drying decreased the residual dichloromethane content only from about 7 % (w/w) to 6.4 % (w/w) (18 °C) or 3.2 % (w/w) (35 °C) within 24 h, 140 mg/L methanol vapor in purge gas facilitated almost complete removal of dichloromethane or ethyl acetate from microparticles (0–0.11 % (w/w) after 6 h). By controlling the alcohol concentration and temperature of the purge gas, the alcohol absorption and complete removal was controlled. Risperidone increased the methanol absorption enhancing the plasticization. A high initial residual water content was identified to promote aggregation and was eliminated by starting fluidized bed drying without alcohol. Alcohol vapor-assisted fluidized bed drying accelerated microparticle manufacturing without affecting the redispersibility, the drug loading and the in-vitro release of risperidone and dexamethasone.

Acceleration of Final Residual Solvent Extraction From Poly(lactide-co-glycolide) Microparticles.

The removal of the residual solvent dichloromethane from biodegradable poly(D,L-lactic-co-glycolic acid) (PLGA) microparticles was investigated by aqueous or alcoholic wet extraction or vacuum-drying. Microparticles were prepared by the O/W solvent extraction/evaporation method. The solidified microparticles were separated by filtration and the effect of subsequent drying and wet extraction methods were investigated. The residual solvent content was analysed with gas chromatography (organic solvents) and Karl Fischer titration (water). The effect of extraction conditions on microparticle aggregation, surface morphology and encapsulation of the drugs dexamethasone and risperidone was investigated. Residual dichloromethane was reduced to 2.43% (w/w) (20°C) or 0.03% (w/w)(35°C) by aqueous wet extraction. With vacuum-drying, residual dichloromethane only decreased from about 5% (w/w) to 4.34% (w/w) (20°C) or 3.20% (w/w) (35°C) due to the lack of the plasticizing effect of water. Redispersion of filtered, wet microparticles in alcoholic media significantly improved the extraction due to an increased PLGA plasticization. The potential of different extractants was explained with the Gordon-Taylor equation and Hansen solubility parameters. Extraction in methanol: or ethanol:water mixtures reduced residual dichloromethane from 4 - 7% (w/w) to 0.5 - 2.3% (w/w) within 1 h and 0.08 - 0.18% (w/w) within 6 h. Higher alcohol contents and higher temperature resulted in aggregation of microparticles and lower drug loadings. The final removal of residual dichloromethane was more efficient with alcoholic wet extraction followed by aqueous wet extraction at elevated temperature and vacuum drying of the microparticles.

Non-Invasive, Continuous, Quantitative Detection of Solvent Content in Vacuum Tray Drying

A non-invasive capacitance instrument was embedded in the base of a vacuum-drying tray to monitor continuously the residual amount of solvent left in a pharmaceutical powder. Proof of concept was validated with Microcrystalline Cellulose laced with water, as well as water/acetone mixtures absorbed in a spray-dried Copovidone powder. To illustrate the role of impermeability of the base, we derive a model of vapor sorption that reveals the existence of a kinetic limit when solids are thinly spread, and a diffusion limit with greatly diminished effective diffusivity at large powder thickness. By monitoring the residual solvent content of powders, this new in situ technique offers advantages over indirect methods like mass spectrometry of vapor effluents, but without complications associated with probe fouling. To prescribe design guidelines and interpret signals, we model the electric field shed by the probe when a powder holds variable solvent mass fraction in the vertical direction.Graphical abstract

New Surface Modification of Hydrophilic Polyvinyl Alcohol via Predrying and Electrospinning of Hydrophobic Polycaprolactone Nanofibers.

Despite the excellent oxygen barrier and biodegradability of polyvinyl alcohol (PVA), its poor physical properties owing to its inherent hydrophilicity limit its application. In this paper, we report a novel surface modification technique for PVA films, involving the control of the predrying conditions (i.e., amount of residual solvent) of the coated PVA film and adjusting the electrospinning process of hydrophobic polycaprolactone (PCL) nanofibers onto the PVA films. The residual solvent of the coated PVA film was varied by changing the predrying time. A shorter predrying time increased the residual solvent content significantly (p < 0.05) and the flexibility of the coated PVA film. Moreover, scanning electron microscopy depicted the improved physical binding of hydrophobic PCL nanofibers to the hydrophilic PVA surface with increased penetration depth to the PVA film with shorter drying times. The PVA/PCL composite films with different predrying times and electrospun PCL nanofibers exhibited an apparent increase in the contact angle from 8.3° to 95.1°. The tensile strength of the pure PVA film increased significantly (p < 0.05) from 7.5 MPa to 77.4 MPa and its oxygen permeability decreased from 5.5 to 1.9 cc/m2·day. Therefore, our newly developed technique is cost-effective for modifying the surface and physical properties of hydrophilic polymers, broadening their industrial applications.

Optimization of Red Ginger (Zingiber officinale var. Rubrum) Extraction Using Microwave Assisted Hydrodistillation Method

Red ginger is a spice plant that has high economic and social value. One of the uses of red ginger is to process it into a product, namely essential oil. This study aims to determine the optimization of the extraction process conditions on solvent volume, time, and extraction power that can produce optimum yield and residual content of red ginger essential oil solvent. The extraction was carried out with the help of microwaves. The research method is experimental design and optimization process with Response Surface Methodology (RSM) type Box-Behnken Design (BBD). The results showed that the optimum yield was at 700 mL solvent volume, 1 min extraction time, and 10% power (69.9 watts) with the equation Y = 0.2076 + 0.0262A – 0.0300B – 0.0013C and the concentration conditions the optimum remaining solvent with the equation Y = 4.98 – 1.0000A + 4.56B + 5.44C. The optimal yield of red ginger essential oil was 0.205%, with a residual solvent content of 3.8%, specific gravity 0.885, acid number 1.399, refractive index 1.485. The results of the optimum residual solvent content of -6.023%. Based on the results obtained, the yield value with the help of microwaves is higher than that without the help of microwaves. Keywords: Essential oil, Microwave, Residual solvent content, Response surface methodology (RSM), Yield.

Investigating Nano-Sized Dispersity and High Crystallinity of Perfluoro-Sulfonic Acidionomer in Polymer Electrolyte Fuel Cell Electrodes Via Electrospray Deposition

Polymer electrolyte fuel cells (PEFCs) hold great promise for mitigating the worldwide climate crisis by tapping into the potential of producing clean energy from renewable sources. However, widespread commercial adoption of PEFCs requires addressing the challenges associated with PEFC performance and durability, particularly concerning electrode materials and design. The PEFC electrode is a crucial component of PEFC performance, with the ionomer playing a vital role as both an electrode binder and proton conductor. Nano-sized dispersity and high crystallinity of the ionomer are vital properties that are crucial for achieving enhanced performance and durability. However, existing methods for fabricating PEFC electrodes have been unable to attain these desirable ionomer characteristics. In this work, we propose a novel approach to fabricating PEFC electrode architectures with ionomers possessing nano-sized dispersity and high crystallinity using the electrospray deposition (ESD) technique. In the ESD process, a precursor solution is atomized into charged droplets, while evaporating the solvent, and results in the formation of advanced electrode with vertical architecture that exhibits high crystallinity of ionomer, in contrast to much lower crystallinity of those fabricated by conventional decal methods. The ionomer characteristics significantly impact the overall fuel cell performance and durability. Therefore, controlling the residual solvent content during the ESD process is a crucial aspect that is vital for achieving the desired ionomer characteristics. The residual solvent content is tuned by investigating the initial mixed solvent ratio, substrate temperature, and distance between the nozzle to substrate. By fine-tuning the residual solvent content and optimizing the deposition parameters, the ESD technique can overcome the limitations of traditional fabrication methods, resulting in PEFC electrodes that offer enhanced performance, increased durability, and improved energy efficiency. The electrospray deposition (ESD) technique provides precise control over the amount of residual solvent required for deposition, making it a scalable technique. This work shows that the residual solvent content of PEFC electrodes significantly impacts the ionomer crystallinity and the electrode architecture using a well-controlled and optimized electrospray technique, without the use of any additives or special ionomer. In summary, this work demonstrates a novel approach to fabricating PEFC electrode architectures with ionomers possessing nano-sized dispersity and high crystallinity using the electrospray deposition technique. This approach provides precise control over the residual solvent content, allowing for enhanced performance and increased durability of PEFC electrodes due to the high-crystallinity of the ionomer. These findings have important implications for the development of sustainable energy technologies and contribute to the ongoing efforts towards mitigating the worldwide climate crisis.

Structure, Thermal, and Mechanical Behavior of the Polysulfone Solution Impregnated Unidirectional Carbon Fiber Yarns.

The paper is devoted to the study of thermal and mechanical behavior and structural features of the polysulfone solution impregnated unidirectional carbon fiber yarns depending on fabrication conditions and appearance for optimum production method of the composites. The effect of producing conditions, such as polysulfone solution concentration, drying and post-heating temperatures, and the residual solvent content on the structure, mechanical, and thermal properties of the carbon fiber-reinforced composites was studied. The polysulfone solution impregnated carbon fiber yarns show relatively high mechanical properties, realizing up to 80% of the carbon fibers' tensile strength, which can be attributed to good wettability and uniform polymer matrix distribution throughout the entire volume of the composites. It was found that the composites impregnated with 40 wt.% of the polysulfone solution showed lower porosity and higher mechanical properties. The results of a dynamic mechanical analysis indicate that residual solvent has a significant effect on the composites' thermal behavior. The composites heated to 350 °C for a 30 min showed higher thermal stability compared to ones dried at 110 °C due to removal of residual solvent during heating. The impregnated carbon fiber yarns can be used for the further producing bulk unidirectional composites by compression molding and the proposed method can be easily transformed to continuous filament production, for example for further use in 3-D printing technology.

Rapid assessment of residual solvent content in the TEGDN dual-base propellants by near-infrared reflectance spectroscopy

Excessive residual solvent (RS) levels in triethyleneglycol dinitrate (TEGDN) dual-base propellants can significantly impair combustion performance. This work aimed to develop a rapid and accurate model for detecting the RS content in the TEGDN dual-base propellants using near-infrared (NIR) spectroscopy in the reflectance mode. The optimal wavelength range for modelling, spanning from 1124.9−1230.2 nm and 1335.5–1527.5 nm, was identified based on absorption peaks characteristic of TEGDN dual-base propellant samples and RS. To enhance the quality of the data, we determined optimal window sizes for pre-processing methods: derivative pre-processing and Savitzky-Golay (S-G) smoothing pre-processing. After evaluating the performance of different pre-treatment methods, we found that the model employing multiple scattering corrections (MSC) in conjunction with first-order derivative (FD) pre-processing demonstrated superior results. The partial least squares (PLS) method was used to build the RS model with an optimal number of factors of 6. For the developed RS model, the root mean square error of calibration (RMSEC) and the root mean square error of cross-validation (RMSECV) were 0.019 and 0.024, respectively. The determination coefficient of calibration (Rc2) and the determination coefficient of cross-validation (Rcv2) were 0.968 and 0.952, respectively. In assessing the validation set using the developed model, we observed a root mean square error of prediction (RMSEP) of 0.025 and a determination coefficient of prediction (Rp2) of 0.958. Importantly, the relative error between the predicted values obtained through the NIR method and the measured values from the reference method consistently remained below 2 % under all circumstances. Consequently, the NIR-based RS model developed in this study offers a rapid and efficient means of detecting RS content in TEGDN dual-base propellants, facilitating judgment regarding the qualification of RS content.

Pollen allergen products: current standardisation issues

Scientific relevance. Pollen allergen medicines are in high demand, and their therapeutic benefits directly correlate with their standardisation. Better diagnosis and treatment of allergic diseases require state-of-the-art procedures for assessing the allergenic activity of pollen allergen products using reference standards and physicochemical testing methods.Aim. The study aimed at developing methodological approaches to the standardisation of pollen allergen products in order to shift to measuring their potency in allergenic activity units (AAU) and bring their quality in line with the requirements of the State Pharmacopoeia of the Russian Federation.Materials and methods. The study used pollen allergen reference standards by Microgen, the WHO International Standard for timothy grass (Phleum pratense) pollen extract, a gel filtration standard kit of molecular weight markers ranging from 1.35 to 670 kDa, bovine serum albumin, serum samples with specific IgE obtained from donors sensitised to the study pollen allergens, labelled anti-human IgE antibodies, and reference standards for determining residual volatile solvents by gas chromatography. The identification of in-house reference standards for the potency of pollen allergens involved Western blotting (for allergenic components). The total protein content was determined by Bradford’s assay. In addition, the authors used high-performance liquid chromatography to study protein fractions and gas–liquid chromatography to determine the content of residual organic solvents.Results. To substitute the existing method of non-specific characterisation of allergenic activity in protein nitrogen units (PNU), the authors developed and tested a new method to control allergenic activity in allergenic activity units (AAU) based on an in vitro competitive enzyme-linked immunosorbent assay (ELISA) procedure developed and validated in this study. Furthermore, the authors developed and certified 15 primary in-house reference standards with allergenic activity established in AAU/mL using skin tests in vivo. The experimental data were analysed to standardise the allergenic activity of the pollen allergens manufactured by Microgen. The authors developed physicochemical methods for the certification of in-house reference standards and validated these methods in accordance with the State Pharmacopoeia of the Russian Federation. The study involved selecting chromatographic separation conditions for residual organic solvents (acetone and diethyl ether) and establishing system suitability criteria for the chromatographic system. The allergenic activity of secondary in-house reference standards was certified against that of primary in-house reference standards using competitive ELISA. Thus, the authors managed to shift to the standardisation of pollen allergen products in vitro.Conclusions. The authors developed their competitive ELISA-based method to standardise pollen allergen products by comparing the inhibition of immune responses to a product and a standard. The study demonstrated the feasibility of substituting allergenic activity quantification (in AAU) for protein nitrogen content determination (in PNU) and showed the first example of using AAU for the certification of in-house reference standards. Additionally, the authors developed and validated an analytical procedure for determining the content of residual organic solvents in pollen allergen products by gas–liquid chromatography.

Development of Delayed Release Oral Formulation Comprising Esomeprazole Spray Dried Dispersion Utilizing Design of Experiment As An Optimization Strategy.

Solid dispersion (SD) technology is one of the most widely preferred solubility enhancement methods, especially for Biopharmaceutics classification system class II and IV drugs. Since the last decade, its application for the dual purpose of solubility hike and modified release using novel carriers has been in demand for its added advantages. Spray drying is a commercially accepted technique with high aspects of scalability and product characteristics. The current study used spray-dried dispersion to design delayed release capsule for the proton pump inhibitor esomeprazole. The SD carrier hydroxypropyl methylcellulose acetate succinate-medium grade (HPMCAS-MF) enhanced solubility, inhibited precipitation of saturated drug solutions, and allowed enteric release owing to its solubility above pH 6. The proposed approach avoided compression, coating with enteric polymers, and the development of multi-particulate pellet-based formulations, improving manufacturing feasibility. The formulation was optimized using Box-Behnken design, considering significant formulation variables like HPMCAS-MF proportion and critical process parameters like feed flow rate and inlet temperature. The optimized spray-dried dispersion were characterized based on Fourier transform infrared spectroscopy (FTIR), differential scanning calorimetry (DSC), powder X-ray diffraction (PXRD), and scanning electron microscopy (SEM) and also evaluated for solubility, in vitro drug release, residual solvent content, and stability testing. Response surface methodology optimization anticipated that formulation variables affected solubility and release profile, whereas CPPs affected yield. The design space was developed via overlay plot based on constraints specified to attain the desired response and validated using three checkpoint batches with desirability 1. FTIR showed active pharmaceutical ingredient-polymer compatibility. Particle size and SEM studies showed spherical particles with an average Z-value of 1.8 µ. DSC and PXRD confirmed SD's amorphous nature. The drug release investigation and release kinetics prediction utilizing DD-solver software showed a 2-h lag time with > 90% cumulative drug release up to 4h for the DR formulation. ESM SDD were prepared by spray drying technique using the novel solid dispersion carrier HPMCAS-MF to serve the dual purpose of solubility enhancement and delayed release. The ratio of API:carrier and process variables like feed flow rate and inlet temperature were varied using the Box-Behnken Design to determine the design space of optimized product to procure the desired characteristics of solubility improvement compared to crystalline API and delayed release of PPI to avoid the degradation in the gastric environment. The developed formulation represents several benefits over the already existing marketed products.

Synthesis of highly stable encapsulated astaxanthin/β-cyclodextrin microparticles using supercritical CO2 as an antisolvent

Although astaxanthin has promising physiological functions, its practical applications are limited by poor stability. Herein, astaxanthin was encapsulated in β-cyclodextrin (βCD) using CO2 as a supercritical antisolvent (SAS). The effects of process conditions, including temperature (313–333 K), pressure (12–18 MPa), solution concentration (3–5 wt%), solution flow rate (0.8–1.2 mL min−1), and astaxanthin-to-βCD mole ratio (1:50, 1:25, or 1:10), on the encapsulation efficiency, particle morphology, and residual solvent content were investigated. Astaxanthin–βCD complex spheres with an average diameter of 0.44 ± 0.08 µm were produced at 313 K and 15 MPa with a solution concentration and flow rate of 5 wt%, and 1.0 mL min−1, respectively. Under these optimal conditions, almost complete encapsulation (99.6% encapsulation efficiency) and residual organic solvent removal (0.22 ppm in the complex) were achieved. Density functional theory analysis of the configuration of the astaxanthin–βCD complex indicate that the hydroxyl hydrogen atoms on an ionone ring of astaxanthin interact with the oxygen atoms of βCD, but the ionone ring does not fit deeply within the βCD cavity. Notably, the astaxanthin–βCD complex exhibits higher thermal stability and antioxidant activity than free astaxanthin. The findings suggest that βCD encapsulation via the SAS process can produce astaxanthin microparticles with potential utility for food and pharmaceutical applications.

Evaluation of Solvent Compatibilities for Headspace-SIFT-MS Analysis of Pharmaceutical Products

Procedures for determination of the residual solvent and volatile impurity content in pharmaceutical products usually rely on dissolution in a solvent, followed by headspace-gas chromatography (HS-GC) analysis. Whereas chromatographic systems can utilize a wide variety of solvents, direct-injection mass spectrometry (DIMS) techniques have fewer solvent options, because elimination of the chromatographic column means that the instrument is more susceptible to saturation. Since water has the lowest impact, it has almost always been the default solvent for DIMS. In this study, selected ion flow tube mass spectrometry (SIFT-MS)—a DIMS technique—was applied to the systematic evaluation of the proportion of solvent that can be utilized (with aqueous diluent) without causing instrument saturation and while maintaining satisfactory analytical performance. The solvents evaluated were N,N-dimethylacetamide (DMAC), N,N-dimethylformamide (DMF), 1,3-dimethyl-2-imidazolidinone (DMI), dimethyl sulfoxide (DMSO), methanol, and triacetin. All solvents are compatible with headspace-SIFT-MS analysis at 5% (min) in water, while DMI, DMAC, and DMSO can be used at higher concentrations (50, 100, and 25%, respectively), though suffering substantial diminution of the limit of quantitation for non-polar analytes at higher proportions of non-aqueous solvent. Analytical performance was also evaluated using linearity, repeatability, and recovery measurements. This work demonstrates that organic solvents diluted in water can be utilized with headspace-SIFT-MS and provide an approach for evaluation of additional diluent solvents.

Effect of Residual Solvents on Properties of Composite Solid Electrolytes

Solid-state electrolytes (SSEs) can stabilize lithium (Li) metal anodes and achieve high energy density. However, they often suffer from solvent residues during the preparation. The residual solvent will affect the performance of SSEs. In this paper, we take Li1.5Al0.5Ge1.5P3O12 (LAGP)/Poly(propylene carbonate) (PPC) composite solid electrolyte (CSE) as an example, the content of the solvent residue of CSE prepared by the solution casting method and its effect on performance are investigated. The result reveals that the solvent content decreases with the increase of drying time. It still contains more than 5 wt % solvent even after vacuum drying for 48 h. The presence of residual solvent promotes the binding of lithium ions (Li+) and carbonyls, which is conducive to the transfer of Li+. When the residual solvent content is high, SSE has high ionic conductivity, cycling capacity, and excellent cycling stability. When the solvent content decreases, the electrochemical window becomes wider. This result is of great significance for the future regulation of SSE solvent content.

Intranasal spray of cubosomal tizanidine hydrochloride for brain targeting: in vitro and in vivo characterisation

Tizanidine HCl (TH) is used as first-line therapy for the treatment of muscular spasm. The intranasal cubosomal delivery system of TH for site-specific delivery, i.e. CNS was developed. Cubosomes of TH were prepared using glyceryl monooleate (GMO) as a lipid, poloxamer 407 as stabiliser, and ethanol and polyethylene glycol 200 as co-solvent. Optimised cubosomes of TH were characterised for vesicle size, zeta potential, % drug entrapment, and mucin binding efficiency, which were found to be 50.22 nm, −6.39 mV, 69.28%, and 42.12%. It is also evaluated for CRYO-FESEM, CRYO-TEM, SAXS, residual solvent content, and in vitro drug release. Ex vivo permeation was also conducted at 7.4 and it indicates that almost 93.66% drug was diffused from a formulation in 6 h. Histopathological study of the optimised TH cubosomes suggests that the prepared formulation is non-toxic to the nasal mucosa. Pharmacokinetic and brain distribution study indicates targeted action of the formulated TH cubosomes.

Potential of The Tyrosinase Enzyme Inhibition by Standardized Ethanol Extract And Ethyl Acetate Fraction of Bengkoang Peel (Pachyrhizus erosus L.)

This study examined the tyrosinase inhibitory potential of bengkoang peel standardised ethanolic extract and ethyl acetate fractions. 450 g of bengkoang peel powder (Pachyrhizus erosus L.) was macerated with 96% ethanol for 2 x 24 h, filtered, and concentrated till viscous. Extract standardisation uses specific and non-specific parameters. Microplate colorimetric tyrosinase inhibition assays were performed. The result of plant determination identified the bengkoang peel as Pachyrhizus erosus (L.) Urb. The organoleptic test revealed a brownish-yellow viscous extract, fresh smell, and bitter taste. Ethanol-soluble extract was 47.60% and water-soluble 22.42%. Bengkoang peel ethanolic extract includes alkaloids, flavonoids, saponins, tannins, and steroids. The non-specific parameters showed loss of drying (9.71%), water content (7.28%), total ash (9.91%), acid-insoluble ash (3.68%), no residual solvent content, lead content (-0.2324±0.1729), cadmium content (-0.0841±0.3418), TPC of 1 x 101 CFU/g, and TYMC of 2.26 x 102 CFU/g. The ethanol extract (103.9263) and ethyl acetate fraction (81.8606) IC50 values of bengkoang peel decrease tyrosinase enzyme activity compared to control (25.1235 ppm). These results show that the ethanol extract met both particular and non-specific quality standards. Bengkoang peel ethyl acetate inhibited tyrosinase.

Solvent transport dynamics and its effect on evolution of mechanical properties of nitrocellulose (NC)-based propellants under hot-air drying process

Appropriate drying process with optimized controlling of drying parameters plays a vital role in the improvement of the quality and performance of propellant products. However, few research on solvent transport dynamics within NC-based propellants was reported, and its effect on the evolution of mechanical properties was not interpreted yet. This study is conducted to gain a comprehensive understanding of hot-air drying for NC-based propellants and clarify the effect of temperature on solvent transport behavior and further the change of mechanical properties during drying. The drying kinetic curves show the drying time required is decreased but the steady solvent content is increased and the drying rate is obviously increased with the increase of hot-air temperatures, indicating hot-air temperatures have a significant effect on drying kinetics. A modified drying model was established, and results show it is more appropriate to describe solvent transport behavior within NC-based propellants. Moreover, two linear equations were established to exhibit the relationship between solvent content and its effect on the change of tensile properties, and the decrease of residual solvent content causes an obvious increase of tensile strength and tensile modulus of propellant products, indicating its mechanical properties can be partly improved by adjustment of residual solvent content. The outcomes can be used to clarify solvent transport mechanisms and optimize drying process parameters of double-based gun propellants.

Effects of residual dimethyl sulfoxide on the storage performance of nano-TATB

The stability of nano-TATB in an environment of long-term storage or service is currently one concern since it will affect the reliability of weapon systems. To explore the effects of the residual dimethyl sulfoxide (DMSO) solvent generated during synthesis on the storage performance of nano-TATB, this study proposed a new strategy that utilized solvent atmosphere induction to simulate the effects of residual solvents for the first time and quantified the residual solvents using the equilibrium adsorption capacity (Qe) obtained from the pseudo-first-order adsorption kinetic model. Moreover, this study investigated the storage performance of nano-TATB in the DMSO atmosphere using techniques of scanning electron microscopy (SEM), X-ray diffraction (XRD), Raman spectroscopy (Raman), and infrared (IR) spectroscopy. The results show that the residual DMSO can induce nano-TATB growth more significantly than stimuli in a hot and humid environment. After aging at 60 ​°C for 1 ​d in the DMSO atmosphere, a large number of particles with relatively a regular shape and a particle size of about 1 ​μm were generated in the DMSO atmosphere, with a Qe of DMSO of (1.045 ​± ​0.026) mg·g−1. After aging for 5 ​d, some nano-TATB particles grew and had a particle size of up to 5–6 ​μm, and the average density and cohesive strength of nano-TATB greatly increased. As shown by the analysis of the growth mechanism of nano-TATB in the DMSO atmosphere based on the above experimental results, the main reason for the self-assembly of nano-TATB is the surface DMSO induction caused by the interactions between nano-TATB and DMSO molecules. These results show that the key to improving the storage stability of nano-TATB is to reduce the content of residual solvents.

Role of Draw Rate and Molecular Weight when Electrospun Nanofibers are Post‐Drawn with Residual Solvent

AbstractThe postdrawing process is poorly understood for polymer nanofibers due to the difficulty of manipulating nanofiber structures. Here, an angled track system facilitates postdrawing of individual nanofibers with control of parameters including molecular weight, draw rate, draw ratio, and solvent evaporation time. In this study, the effects of molecular weight, draw rate, and relative residual solvent content on final nanofiber properties are investigated. Molecular weight is first investigated to clarify any influence polymer chain length can have on drawing in facilitating or hindering chain extensibility. Polyacrylonitrile nanofibers with 50 and 150 kDa molecular weights behave similarly with postdrawing resulting in reduced diameters and enhanced mechanics. Since solvent quantity during drawing is a time sensitive component it is meaningful to assess the impact of draw rate on the chemical and structural makeup of postdrawn fibers. Chemical bond vibrations and chain orientation are sensitive to draw rate when polycaprolactone nanofibers are dried for 3 minutes prior to postdrawing, but this dependency to draw rate is not observed when fibers are postdrawn immediately upon collection. These findings demonstrate that the amount of retained solvent at collection is relevant to this postprocessing approach, and highlights the dynamics of solvent evaporation during postdrawing.

Precision-aiming tuning of membranes prepared by NIPS and its performance enhancement

An industrially developed non-solvent induced phase separation (NIPS) for porous membranes is still being studied to improve performances and expand application fields. The work introduces a novel strategy to tune the structures of porous membranes via the combination of glass transition temperatures (T g ) and external stimulations . T g was adjusted by the content of residual solvents and additives. Heat and air blowing for higher T g porous membranes than 100 °C were efficient strategies to improve the surface porosity to 65%, the water flux to 600 LMH/bar, and the BSA rejection to 99.8%. Heat and vacuum for lower T g membranes than 100 °C could melt the surface pores and becomes a pier-like structure with the water flux of 2.4 LMH/bar and Na 2 SO 4 rejection of 95.6%. The method could hold great potential for achievable tuning of main characteristic parameters such as structure, performance, porosity, pore size, and molecular weight cut-off.