Colloidal Silica Research Articles

Influence of colloidal silicon dioxide‑magnesium stearate interaction on flow and compaction behavior of an MCC-Lactose binary mixture

The amount of glidant and lubricant in a tablet formulation is driven by their primary functionalities of enhancing flowability and reducing particle-wall friction. However, their interaction can lead to undesirable outcomes. This study has examined the influence of this interaction on powder flow and compaction, using colloidal silicon dioxide as a glidant and magnesium stearate as a lubricant in a 50:50 w/w MCC:Lactose binary blend. The findings suggest that nano-sized CSD particles coat other particles in a blend. However, increasing CSD decreases exposed MgSt and reduces its lubricity, resulting in intriguing powder flow and compaction phenomena. CSD impacts powder flow more than MgSt. Increasing the CSD reduces exposed MgSt and increases particle-wall adhesion. Higher CSD concentrations decreased powder bed bulk density and permeability due to the formation of porous structures on primary host particles. A complex interplay between CSD and MgSt during tablet compaction affected tensile strength. CSD promoted tablet picking due to reduced exposed MgSt and increased tablet-punch adhesion. This is the first study correlating tablet picking with take-off force, and it was found that >5 N take-off force risked picking. Ejection force increased with CSD and decreased with MgSt, reaffirming CSD's impact on particle-wall adhesion.

Synthesis of colloidal silica nanofluid and assessment of its impact on interfacial tension (IFT) and wettability for enhanced oil recovery (EOR)

Ever-increasing global energy demand, from one hand and reduced oil initially in place in oil reservoirs due to production and reduced natural reservoir production capacity, on the other hand, has encouraged researchers to investigate different methods to improve and increase enhanced oil recovery (EOR) from oil reservoirs. One method is to employ nanotechnology in injected water, where nanoparticles could affect interfacial tension (IFT) between water and oil and wettability through properties, including high specific surface area and nanoparticle size. However, a major challenge in using nanoparticles in injected water is the instability of these particles in water, which ultimately reduces the efficiency of EOR. These particles cannot be stabilized through conventional methods at a large scale. In this study, stabilized silica nanoparticles were synthesized in the water phase using sodium silicate and sol–gel processes. The stability of this nanofluid was studied in seawater, and then its effect on IFT and changing wettability was examined. According to the results, seawater containing 40 times diluted nanofluid could obtain 41% reduced IFT and 40% alteration in wettability of carbonate core becoming more water-wet and ultimately 13.7% improved final oil recovery in secondary oil recovery and 8.3% improved final oil recovery in third EOR.

Colloidal Silica Production with Resin from Sodium Silicate and Optimization of Process

Colloidal silica is a stable and homogeneously dispersed form of amorphous silicon dioxide (SiO2) nanoparticles in water. Colloidal silica has been the focus of research due to large surface area, biocompatibility, low toxicity and chemical and thermal stability. It has been used in a wide variety of industrial applications, including pulp and paper, chromatography, electronics, foods, and colloids, as well as in the ceramics and glass industry. In this study, colloidal silica was produced using cationic resin and sodium silicate and process conditions were optimized. Temperature (50-80 °C), mixing speed (200-500 rpm) and time (20-120 min.), which significantly affect the particle size, were selected as parameters. Particle size distribution (PSD) analyzes of colloidal silica particles were performed to determine appropriate levels of the parameters. The most suitable process conditions are 50°C temperature, 40 min. and 300 rpm. The average particle size of colloidal silica produced in optimum conditions was measured as 80 nm.

Thermoresponsive hollow polymeric shell nano/microparticles with interconnected nanoholes

AbstractPNIPAAm‐grafted thermoresponsive hollow nano‐holed polymeric‐shell (HHPS) particles were fabricated from surface‐modified colloidal silica (CS) with poly(ethylene glycol) methyl ether‐3‐(triethoxysilyl)propyl isocyanate (PEGME‐IPTES) and 3‐(trimethoxysilyl) propyl methacrylate (MPS) as templates. The polymeric shells were then synthesized through a “grafting‐through” approach via surface‐initiated polymerization of N‐isopropyl acrylamide (PNIPAAm) using potassium persulfate (KPS) as an initiator, followed by the etching of CS with hydrofluoric acid to remove the CS core templates. CS nanoparticles and PEGME‐IPTES were presynthesized using tetraethoxysilane (TEOS) and distilled water in methanol with ammonia solution as a catalyst by the sol–gel method and using 3‐(triethoxysilyl) propyl isocyanate (IPTES) with poly(ethylene glycol) methyl ether (PEGME) in the presence of dibutyltin dilaurate. The chemical structures of bare and modified CS, PNIPAAm, PNIPAAm‐CS, and HHPS particles were characterized by FT‐IR and NMR spectroscopies. SEM and TEM images confirmed that the resulting HHPS particles had a significant number of interconnected nanoholes. To evaluate the LCST behaviors of HHPS particles, the transition of transmittance and the changes in particle diameter according to the temperature change were measured through UV‐vis spectroscopy, DLS, and microscopy.

Interparticle interaction-dependent jamming in colloids: insights into glass transition and morphology modulation during rapid evaporation-induced assembly.

Understanding the role of interparticle interactions in jamming phenomena is essential for gaining insights into the intriguing glass transition behavior observed in atomic and molecular systems. In this study, we investigate the jamming behavior of colloids with tunable interparticle interactions during evaporation-induced assembly (EIA). By manipulating the interaction among charged colloids using cationic polyethyleneimine (PEI) through electro-sorption and subsequent free polymer induced repulsion, we observe distinct jamming behavior in silica colloids during EIA, depending on the interparticle interactions. Silica colloids with strong repulsive interactions exhibit a repulsive colloidal glass state with a volume fraction of silica colloids in supraparticle ϕ ∼ 0.70. On the other hand, PEI-mediated attractive interactions among silica colloids lead to an attractive colloidal glass phase with a significantly lower ϕ ∼ 0.43. Free polymer induced repulsion of colloids at higher PEI concentration once again results in a repulsive glassy state with ϕ ∼ 0.61. Furthermore, we revealed that interparticle interactions not only influence the jamming behavior but also play a significant role in shaping the morphology of self-assembled structures during EIA, and the assembled structure undergoes a morphological reentrant transition from a doughnut-like shape to a spherical form and again back to a doughnut-like configuration. Jamming-dependent evolution of micropores and dynamics of the confined PEI have been probed using positron annihilation lifetime spectroscopy (PALS) and broadband dielectric spectroscopy (BDS). PALS reveals distinct variations in the micropores of the supraparticles with different PEI loadings, confirming the impact of jamming on the evolution of the micropores within the supraparticles. BDS measurements uncover non-monotonic dynamics of PEI molecules confined in the evolved pore network. It is revealed that the reentrant jamming behavior of colloids, modulated by PEI, holds profound significance for the long-term stability of supraparticles.

Sand and silt treatment with novel binders

An attractive approach to reduce the carbon footprint for ground improvement application is to replace Portland cementbased binders by non-cementitious binders for instance by geopolymers based on metakaolin in deep soil mixing applications or by colloidal silica and acrylates in permeation based applications. Safe design requires a good understanding of the mechanical and hydraulic properties of the improved ground but little is known about how soil is improved by these products. Besides, for permeation grouting applicability criteria are frequently set in terms of the host soil water permeability. However, for novel binders the threshold value is not known and published empirical basis for available criteria is relatively scarce. This paper summarizes results from a laboratory characterization campaign of soils of variable permeability improved with different novel binders, focusing on the effect on strength, stiffness and permeability. Observations relative to the effect of curing conditions are also provided, as well as the insight gained by examining the injection process outcomes with computed tomography. Results show how these novel products have the potential to significantly improve the mechanical properties and reduce permeability in a large range of soils.

Experimental study on the effect of colloidal nano silica in high strength self-compacting concrete containing ground granulated blast furnace slag

Self-compacting concrete (SCC) is profusely utilized in building construction due to its unique design and mechanism of flow without segregation by occupying the corners and preventing the voids to achieve better compaction and mechanical strength. This work addresses the effect of colloidal nano-silica (NS) of size 5-40nm with an active nano solids content of 32% on the high-strength SCC containing Ground Granulated Blast Furnace Slag (GGBFS) and Ordinary Portland Cement as binders in addition to NS. The liquid content of 68% in NS was added to the water content in the mix. The ratios of NS were evaluated at 0%,0.5%,1%,1.5%, 2% and GGBFS as 20% by weight of binder in concrete. The water to binder ratio was 0.33 with a water and binder content of 184kg/m3 and 557.58 kg/m3. The optimum mix was 1.5% NS based on the concrete’s slump and compressive strength at 28 days. The slump was reduced with a rise in NS beyond 1.5% due to the accumulation of NS particles causing the reduction in flowability. The density of SCC for all the mixes was satisfactory. The compressive strength of optimum SCC, M21.5NS20G was decreased by 5.88% and increased by 0.49% and 2.45% at 7, 28 and 91 days to that of the reference mix whereas its split tensile strength was risen by 31.13%, 9.27%, and 12.41% and flexural strength was risen by 5.8% and reduced by 8.17% and 4.06% to that of the reference mix at aforementioned durations. The SEM and XRD analyses were conducted on the optimum hardened SCC mix at 28 days in which the presence of Calcium silicate hydrate compounds of different crystalline structures, viz., Ettringite, and Portlandite were observed. The SCC designed in the work can be used for structural applications such as beam-column joints.

Nanopriming of Tomato (Solanum lycopersicum) Seeds Against Heavy Metal Stress During Germination and Seedling Formation

Abiotic stress can have a negative impact on plant growth. Heavy metal is one of the examples. One approach to overcome this issue is to use seed priming. The priming used in this study was nanopriming. We used colloidal silica nanoparticles (size of 10 nm) as the priming agent and copper (Cu) and barium (Ba) as the model heavy metals. This treatment was implemented for tomato (S. lycopersicum var. Momotaro) seed germination. The results showed that the presence of heavy metals during germination may lead to prolonging the germination time. The presence of Cu and Ba at 1 ppm could increase germination time by 28.38% and 26.9%, respectively, compared to control. When primed seeds were subjected to heavy metal stress, the use of silica nanopriming could reduce the germination time by 10.45% for Cu and 11.54% for Ba compared to the unprimed seeds. This evidence demonstrated that nanopriming could make seeds more resilient to heavy metal stress. We also found that heavy metal ions became less detectable in the seedlings when nanopriming was applied. This ion transport alteration essentially allowed seeds to cope with heavy metal stress. This method can be potentially used on various kinds of crops and heavy metals.

Assessing silica-based gel system for high-temperature water shut-off applications

Excessive water production in oil and gas wells poses a significant challenge for reservoir management, necessitating effective water shut-off solutions. This study focuses on the development and evaluation of a colloidal silica-based fluid system tailored for high temperature water shut-off applications in challenging reservoir conditions. The system comprises colloidal silica and an activating salt, characterized by its low viscosity, enabling deep penetration and effective treatment. The evaluation methodology employed in this study encompasses visual assessment of gelation time and precise viscosity measurements. Key findings include the influence of temperature, salt concentration, silica content, and activating salt concentration on gelation kinetics. Higher temperatures, increased salt concentration, and elevated silica content were found to significantly expedite gelation, impacting the system’s efficiency. Moreover, different activator ions exhibited varying effects on gelation, primarily attributed to their charge density and size, adding nuance to the gelation dynamics. The study also revealed the system’s sensitivity to even minor variations in salt concentration, particularly when exposed to elevated temperatures. Based on these findings, a practical application strategy is proposed. When deploying silica gels in formations characterized by high salinity formation water and elevated temperatures, the introduction of a low-salinity water preflush is advised. This strategic approach mitigates premature gelation, ensuring the effectiveness of water shut-off operations. Keywords: water shut-off; silica gel; gelation time; sandpack; high temperature.

Stem cutting: A novel introduction site for transporting water-insoluble particles into tomato (Solanum lycopersicum) seedlings

The introduction of exogenous particles into plants has promising applications in agriculture and biotechnology. Nanoparticles can be transported into plants through foliar application or root uptake. However, both methods have limitations in terms of the size of the particles (<40 nm) that can be transported due to the barriers of the cell wall and cuticle. In the present study, we proposed a novel method to deliver particles of up to 110 nm into plants by cutting the stem of tomato seedlings. We demonstrated for the first time, using water-insoluble silica colloids, that not only nanoparticles but also submicron particles can be transported toward the leaves when the plant stem is used as the entry point of particles. Thirty-five-day-old tomato seedlings were used as the target plants. When the cut stem seedlings were immersed in the colloidal particle suspension for up to 24 h, significant particle accumulation was observed in the nodes and leaves. The relatively low particle concentrations (10 mg/L) allowed effective transport throughout the plants. Silica particles with average diameters of 10 nm and 110 nm were both well transported and moved through the stem. Even after the particles entered the plant, adventitious roots were formed, resulting in the formation of whole plants with roots, stems, and leaves. This method can be applied not only to tomatoes but also to other food crops for various applications in plant biotechnology.

Silicon-Germanium on Insulator CMP Slurry Designed with Oxidant and Accelerator Heading an Amine Functional Group for Remarkably Enhancing Polishing Rate

High quality single crystal silicon-germanium-on-insulator (SGOI) has a potential to enable the next generationof photonic and electronic devices. However, to utilize an SGOI structure, a high SiGe-film polishing rate isnecessary (i.e., > 200 nm/min) for polishing the facet crystalline SiGe during the fabrication of SiGe on insulatorthrough epitaxial growth processes.In previous studies, amine-based chemicals as SiGe-film polishing rate accelerators have been reported, butthere were limitations in increasing the SiGe-film polishig rate by considering only the chemical reaction of SiGe-film surface. In this study, for the first time, both oxidant(i.e., H2O2) and accelerator with amine functional groups(i.e., triethanolamine) were designed, resulting in a surprising increase in the SiGe-film polishing rate of 270nm/min, as shown Fig. 1a.The SiGe chemical mechanical planarization (CMP) mechanism was clearly demonstrated by preciselyinvestigating both chemical properties(i.e., GeO2 spectra intensity via X-ray photoelectron spectroscopy) andmechanical properties(i.e., electrostatic repulsive force between colloidal silica abrasives and the SiGe-film viaelectrophoretic light scattering). The remarkable enhancement of the SiGe-film polishing rate for oxidant andtriethanolamine was the result of (i) minimizing the loss of degree of SiGe surface oxidation, as shown Fig. 2, (ii)enhancing degree of adsorption of the CMP slurry on the polished SiGe-film surface during CMP, and (iii)decreasing the electrostatic repulsive force between colloidal silica abrasives and the SiGe-film surface, as shownFig 1b. Finally, successful removal of the facets in SiGe on insulator wafers was achieved, securing excellentsurface roughness characteristics. SiGe-film polishing mechanism and the SiGe slurry characteristics will bepresented in detail. Figure 1

Sol-gel coatings for solar cover glass: Influence of surface structure on dust accumulation and removal

Soiling of solar cover glass is a major cause for efficiency loss of solar photovoltaic modules. Anti-soiling coatings can be used to reduce the rate of soiling and lower cleaning costs. The efficiency of these coatings has been demonstrated in laboratory and field tests, but the mechanisms and relevant parameters are still not well understood.In this article, we present a study on the influence of surface structure of hydrophilic sol–gel coatings on their anti-soiling performance in terms of both, dust accumulation and subsequent indoor tests for dust removal by wind. The surface structure of the films originates from the addition of colloidal silica particles of different sizes to the sols used for film preparation. In the dust deposition experiments, standardized test dust and dust collected from solar installations were used. Repeated tests were conducted under controlled humidity.In the case of dust deposition, the accumulation of dust particles larger than ∼10 µm is strongly reduced, in relation to bare glass, by the anti-soiling effect of all coatings regardless of their surface structure.For the dust removal via wind, coatings that bear a smoother surface structure are cleaned more easily than coatings with a rougher surface structure.Additionally, larger and rounder dust particles are removed more easily from coatings with a rougher surface structure (structure height over ∼40 nm), while smaller and more irregularly shaped dust particles are removed more easily from coatings with a smoother surface structure.

Production Methods Effect on Nanosilica Properties

This study explored nanosilica synthesis using colloidal silica, silica sand, and TEOS, utilizing rotary evaporator drying, sol-gel, and titration methods. It examined the influence of these techniques on silica’s functionalization and mechanical properties. Methacryloxypropyl trimethoxysilane was employed for silanation, with silica characterized using various analytical methods. Particle sizes from SEM images were 19 nm and 14 nm for rotary and sol-gel samples, respectively, while titration samples showed an irregular structure. Zetasizer analysis revealed larger particle sizes. The purity of silica powders ranged from 90% to 99%, and titration samples demonstrated the highest silanability. When used in dental composites, rotary-evaporated silica displayed promising suitability based on its mechanical and physical properties.

Prediction of Plastic Shrinkage Cracking of Supplementary Cementitious Material-Modified Shotcrete Using Rheological and Mechanical Indicators.

Plastic shrinkage cracking is a complex and multifaceted process that occurs in the period between placement and the final setting. During this period, the mixture is viscoplastic in nature and therefore possesses rheological properties. The investigation of the relationship between rheological behavior and its propensity to undergo cracking during the plastic phase presents an intriguing subject of study. However, many factors influence plastic cracking, and the corresponding interaction of its effects is complex in nature. This study aimed to evaluate the impact of rheological and physicomechanical properties on the occurrence of plastic cracking in high-performance shotcrete containing various supplementary cementitious materials. To achieve this, plastic cracking was evaluated employing the ASTM C 1579 standard and a smart crack viewer FCV-30, and the rheological parameters were controlled using an ICAR rheometer. In addition, a study was conducted to assess the strength development and fresh properties. Further, a relationship was established via statistical evaluation, and the best predicting models were selected. According to the study results, it can be concluded that high-yield stress and low plastic viscosity for colloidal silica mixtures are indicators of plastic cracking resistance owing to improved fresh microstructure and accelerated hydration reaction. However, earlier strength development and the presence of a water-reducing admixture allowed mixtures containing silica fume to achieve crack reduction. A higher indicator of yield stress is an indicator of the capillary pressure development of these mixtures. In addition, a series containing ultrafine fly ash (having high flow resistance and torque viscosity) exhibited a risk of early capillary pressure build-up and a decrease in strength characteristics, which could be stabilized with the addition of colloidal silica. Consequently, the mixture containing both silica fume and colloidal silica exhibited the best performance. Thus, the results indicated that rheological characteristics, compressive strength, and water-reducer content can be used to control the plastic shrinkage cracking of shotcrete.

Unveiling Enhanced Electrostatic Repulsion in Silica Nanosphere Assembly: Formation Dynamics of Body-Centered-Cubic Colloidal Crystals.

We demonstrate the effective establishment of long-range electrostatic interactions among colloidal silica nanospheres through acid treatment, enabling their assembly into colloidal crystals at remarkably low concentrations. This novel method overcomes the conventional limitation in colloidal silica assembly by removing entrapped NH4+ ions and enhancing the electrical double layer (EDL) thickness, offering a time-efficient alternative to increase electrostatic interactions compared with methods like dialysis. The increased EDL thickness facilitates the assembly of SiO2 nanospheres into a body-centered-cubic lattice structure at low particle concentrations, allowing for broad spectrum tunability and high tolerance to particle size polydispersity. Further, we uncover a disorder-order transition during colloidal crystallization at low particle concentrations, with the optimal concentration for crystal formation governed by both thermodynamic and kinetic factors. This work not only provides insights into assembly mechanisms but also paves the way for the design and functionalization of colloidal silica-based photonic crystals in diverse applications.

Synthesis of SAPO-34 Zeolite Membrane: Influence of Sources of Silica

The research described the production and characterization of various materials, particularly alpha-alumina ceramic supports, zeolite SAPO-34, and zeolite membranes. Ceramic supports were manufactured through dry uniaxial compaction. Sintering of the supports was carried out at 1300°C for 2 h. SAPO-34 zeolites and zeolite membranes were synthesized through a hydrothermal process involving two steps: a first step at 38°C for 24 h and a second step at 200°C for 24 h. The research aimed to determine how different silica sources, namely Aerosil 380, colloidal silica, and TEOS, influenced the outcome of the synthesis. The study identified that Aerosil 380 silica was the most suitable source for synthesizing SAPO-34 zeolites and membranes. Zeolite membranes (SAPO-34/alpha-alumina) displayed a uniform and homogeneous distribution of SAPO-34 phase zeolitic crystals. The absence of defects or cracks in these membranes confirmed the successful formation of the SAPO-34 zeolite membrane structure. This research has significant implications, particularly in materials science and applications utilizing zeolites and membranes. The choice of silica source plays a crucial role in determining the quality and properties of the synthesized materials, and the detailed characterization provides valuable insights into their performance in practical applications. Overall, the research contributes to the understanding and optimization of zeolite synthesis processes.

Influence of cation concentration and valence on the structure and texture of spray-dried supraparticles from colloidal silica dispersions

The structure and texture of supraparticles determine their properties and performance, thus playing a critical role in research studies as well as industrial applications. The addition of salts is a well-known strategy to manipulate the colloidal stability of nanoparticles. In this study, this approach is used to tune the structure of spray-dried supraparticles. Three different salts (NaCl, CaCl2, and AlCl3) were added to binary silica (SiO2) nanoparticle dispersions (of 40 and 400 nm in size) to change their colloidal stability by lowering the electrostatic repulsion or enhancing the cation bridging. Dependent on the cation valence of the added salt and the nanoparticle size, the critical salt concentration, which yields nanoparticle agglomeration, is reached at different salt amounts. This phenomenon is exploited to tune the final structure of supraparticles - obtained by spray-drying binary dispersions - from core-shell to Janus-like to well-mixed structures. This consequently also tunes textural properties, like surface roughness and the pore system of the obtained supraparticles. Our results provide insights for controlling the structure of spray-dried supraparticles by manipulating the stability of binary nanoparticle dispersions, and they establish a framework for composite particle design.

Kaolin-based stable colloidal nano-silica: Peptization factors and stability assessments via designed experiments

This study aims to synthesize stable colloidal silica via the peptization method as a green and low-cost route. It is crucial to adopt a proper synthesis procedure and choose an appropriate raw material. To achieve this purpose, kaolin was employed as a silica rich source that occurs abundantly in nature. The process involves synthesis of the wet gel through the succession of calcination, acid leaching, alkaline treatment, sodium silicate precipitation, and then peptization of the wet gel. Effect of the acid type on acid leaching was evaluated. Effective factors affecting the gel purity such ad acid concentration, pH of gelation, and temperature of alkaline treatment, were studied and optimized via a statistical design of the experiments. Subsequently, the influential parameters on stability and particle size of the obtained colloidal silica, including the temperature of the gel formation, pH of sol medium, concentration of silica gel, and type of stabilizing base, were investigated via one-facto-at-a-time. The samples were characterized by X-ray fluorescence analysis (XRF), dynamic laser light scattering analysis (DLS), X-ray Diffraction (XRD), Fourier transform infrared (FTIR), Brunauer–Emmett–Teller (BET), and Field emission scanning electron microscopy (FESEM) analyses. Results showed that under optimum conditions, ultra-pure silica gel with a silica content of 99.34 % was obtained. The colloidal sample with the highest stability (zeta potential of −75.6 mV), had nanoparticles showing sizes in the range of 21–66 nm.

Preparation and characterization of colorless and transparent semi‐alicyclic fluoro‐containing polyimide nanocomposite films with enhanced high‐temperature dimensional stability via incorporation of colloidal silica nanofillers

AbstractColorless and transparent semi‐alicyclic fluoro‐containing polyimide (PI) nanocomposite films with enhanced high‐temperature dimensional stability and sustained optical transparency were designed and prepared via incorporation of nano‐sized colloidal silica (SiO2) fillers into the PI matrix derived from hydrogenated pyromellitic dianhydride (HPMDA) and 2,2′‐bis[(4‐aminophenoxy)phenyl]hexafluoropropane (BDAF). The derived PI composite films, abbreviated as 6FCPI‐X in which X stands for the weight percent of the SiO2 in the composite films, exhibited superior thermal and comparable optical properties to the pristine 6FCPI‐0 (6FDA‐BDAF) matrix film. For example, as for the thermal properties, 6FCPI‐35 composite film showed a glass transition temperature (Tg) of 279.1°C and a residual weight ratio at 750°C (Rw750) of 66.1%, which were apparently higher than those of 6FCPI‐0 matrix (Tg = 272.2°C; Rw750 = 47.1%). More importantly, the 6FCPI/SiO2 nanocomposite films showed obviously lower linear coefficients of thermal expansion (CTE) values as compared with that of the 6FCPI‐0 matrix. 6FCPI‐35 composite film showed a CTE value of 36.1 × 10−6/K in the temperature range of 50–250°C, which was lower than half of that of the 6FCPI‐0 matrix (CTE = 77.9 × 10−6/K) in the same range of temperature. In addition, incorporation of nano‐sized colloidal SiO2 particles basically maintained the intrinsically good optical properties of the pristine 6FCPI‐0 matrix film. 6FCPI‐35 composite film showed the optical transmittances of 81.7%, 85.3%, and 87.2% at the wavelength of 400 nm (T400), 450 nm (T450), and 500 nm (T500), respectively, which were in the same level with those of the 6FCPI‐0 film (T400 = 84.0%; T450 = 86.3%; T500 = 87.6%). The 6FCPI series of nanocomposite films also exhibited similar CIE Lab color parameters, including the yellow indices (b*) lower than 2.0 and haze values lower than 1.0%.

Evaluation of available adsorbents for the dry washing of the wasted frying oil based crude ethyl esters

Russia's invasion of Ukraine strongly actualized the issue of liquid biofuels production. Ethyl esters biodiesel may be produced from widely available domestic Ukrainian oils and locally produced bioethanol. Dry washing with adsorbents is an advanced biodiesel purification technique. There is still a lack of information on the dry washing of alkaline ethanolysis products, especially concerning the removal of heavy contaminants, originating from partially polymerized waste oils. Current work deals with the investigation of available materials as adsorbents for the purification of crude ethyl esters (88% esters, 1.61% monoacylglycerols, 0.73% diacylglycerols, 0.19% tryacylglyceroles, 1.04% soaps, 0.12% fatty acids, 1.07% glycerol, and 0.17% ethanol). Esters were prepared via alkaline-catalyzed transesterification of wasted frying sunflower oil (2.46 mg KOH/g, 7.1% palmitic, 3.5% stearic, 27.7% oleic, and 59.3% linoleic acids). Activated anthracite, synthetic carbon Chemviron, colloidal silica, meta-kaolin, talc, and bentonite were evaluated as adsorbents. All samples provided the removal of the majority of soaps and glycerol, decreased the ethanol concentration, and, in most cases, acid value. Dry washing had almost no impact on the acylglycerols content. Activated carbons, characterized by a combination of developed micro- and mesoporosity, produced the greatest results, including a minor amount of monoacylglycerols removal. However, none of the adsorbents provided the removal of heavy oligomer contaminants, which is indirectly indicated by no higher than 90% esters content in treated samples. Improvement of these characteristics may be achieved by vacuum distillation.