Electrokinetic and rheological behaviors of sepiolite suspensions in the presence of poly(acrylic acid sodium salt)s, polyacrylamides, and poly(ethylene glycol)s of different molecular weights

Assessing the Impact of Sepiolite-Based Bio-Pigment Infused with Indigo Extract on Appearance and Durability of Water-Based White Primer

The objective of this study is to evaluate how two varying amounts of sepiolite-based powder, infused with indigo extract, affect the appearance and durability of a water-based, white primer. To examine the influence of this eco-friendly pigment on the coatings' overall appearance, assessments were performed for color, gloss, and surface roughness. Additionally, the coatings were investigated through optical and electron microscopic observations, to evaluate the distribution of the pigment within the polymer matrix. The effect of the pigment on the coating's durability was assessed through accelerated tests, including exposure in a salt spray chamber and a UV-B chamber. These tests aimed to evaluate the emergence of defects and changes in the appearance of the samples over time. Furthermore, the impact of different quantities of sepiolite-based powder on the coating's ability to act as a barrier was assessed using liquid resistance tests and contact angle measurements. These evaluations aimed to understand how the coating responded to various liquids and its surface properties concerning repellency or absorption. In essence, this study underscores the considerable influence of the eco-friendly pigment, demonstrating its capacity to introduce unique color and texture variations in the paint. Moreover, the inclusion of the pigment has enhanced the coating's color stability, its ability to act as a barrier, and its overall durability when exposed to harsh environments.

Physicochemical properties of electrostatically crosslinked carrageenan/chitosan hydrogels and carrageenan/chitosan/Laponite nanocomposite hydrogels

In this work physical carrageenan/chitosan (Car/Chit) hydrogels are prepared by electrostatic complexation between the two oppositely charged polysaccharides. The hydrogels have storage moduli in the order of 5-10 kPa and swelling ratios in the order of 5000-6000 %. At conditions where both polysaccharides are highly charged (pH 5) the swelling ratios are lower than the ones at conditions of lower dissociation i.e., at pH 2 and 7 and the opposite trend is found for the storage modulus. Chit appears to act as a crosslinker for Car as increasing its concentration the swelling ratio decreases and the moduli increase. The hydrogels can incorporate the nanoclay Laponite (Lap) and form hybrid nanocomposites where the intercalation by the two biopolymers leads to exfoliation of the clay nanoplatelets in the presence of both Car and Chit. The composite hydrogels retain the mechanical properties of the Car/Chit hydrogels at the studied pH range (pH 2 to pH 7). This shows the prepared hydrogels can be potentially used as multifunctional biomaterials for drug delivery, tissue engineering and bone regeneration applications.

The seepage flow characteristics of hydrophobically associated polymers with different aggregation behaviours in porous media

The polymer solution for oil displacement is subjected to strong shear action in practical application, and this action will affect its percolation characteristics in porous media. The effects of mechanical shearing on the solution properties and seepage characteristics of modified hydrophobically associated polymers and dendrimers with two different aggregation behaviours were studied. The results showed that mechanical shearing did not affect hydrophobic microzones. Polymers can re-associate to restore part of the network structure, thereby improving shear resistance (dendritic hydrophobically associating polymers > hydrophobically modified partially hydrolysed polyacrylamide). Polymers with 'cluster' aggregation behaviour enhanced solution performance, enabling them to establish higher resistance coefficient (RF) and residual resistance factor (RRF) in porous media but also bringing about injection difficulties. Increasing the injection rate would increase the injection pressure, but the established RF and RRF showed a downward trend. Mechanical shear pretreatment effectively improved the injectability of the polymer. To achieve polymer injection and flow control, pre-shearing polymer solution and low-speed injection can be used in field applications.

Optimization of methylparaben degradation by sonocatalysis

Sonocatalytic degradation of methylparaben (MPB) in the presence of a low-cost clay mineral (sepiolite) was optimized using a multivariable center composite design protocol based on response surface methodology (RSM). Using the data generated with varying MPB concentrations, pH, frequency and catalyst dose, two semi-empirical expressions were developed to describe the relation between the apparent reaction rate constant of the parent compound and the most significant control variables. It was found that ultrasonic power, pH, sepiolite dose and its interactions with time and pH were the most significant parameters influencing the rate of MPB decay under high frequency ultrasound. The models also showed that the rate constant was a convex function of time, as it decreased during the first 35-min of sonolysis and increased thereafter, indicating the formation and depletion of competing oxidation byproducts. Finally, the models predicted that the rate of MPB decay was a maximum either at alkaline pH and a high sepiolite dose (k = 1.68 × 10^-1 min^-1), or at acidic pH and a considerably lower dose of the mineral (k = 1.48 × 10^-1 min^-1).

Methylene Blue Adsorption Study on Microcline Particles in the Function of Particle Size Range and Temperature

In this paper, the adsorption process of methylene blue has been investigated on microcline particles as a function of particle size and temperature. The characterization of microcline in the particle size ranges of 1−71 μm and 71−315 μm gained by sieving was proved using X-ray diffraction (XRD) and scanning electron microscopy combined with energy-dispersive detector (SEM-EDS) in powder form, over laser diffraction measurements in aqueous suspension. The optimum dosage of adsorbent was 13.5 g/L in dye adsorption and the adsorption isotherms on both microcline size fractions were determined at this adsorbent concentration. The maximum adsorption capacities were in the range of 1.5–3.1 mg g−1 on microcline particles with supplementing evaluation of isotherms using the Langmuir model. Considering the problems of linearization of equations, the non-linear least-squares estimation can be strongly recommended for modeling adsorption-equilibrium. The adsorption isotherm determined at elevated temperature of 60−65 °C represents a breakpoint at around 20 mg L−1 of equilibrated dye concentration due to performing of a potential process of dye self-association. According to our experiments, the increase in temperature has an adverse effect on adsorption.

Highly fluorescent hybrid pigments from anthocyanin- and red wine pyranoanthocyanin-analogs adsorbed on sepiolite clay

Flavylium cations serve as models for the chemical and photochemical reactivity of anthocyanins, the natural plant pigment responsible for many of the red, blue and purple colors of fruits and flowers. Likewise, pyranoflavylium cations serve as models of the fundamental chromophoric moiety of pyranoanthocyanins, molecules that can form from reactions of grape anthocyanins in red wines during their maturation. In the present work, hybrid pigments are prepared by the adsorption of a series of five synthetic flavylium cations (FL) and five synthetic pyranoflavylium cations (PFL) on sepiolite clay (SEP). The FL are smaller in size than the PFL, but both can in principle fit into the tunnels and/or external grooves (with dimensions of 3.7 × 10.6 Å) of SEP. Measurements of the fluorescence quantum yields of the adsorbed dyes indicate that they are at least as fluorescent as in acidic acetonitrile solution, and in a few cases substantially more fluorescent. The observation of biexponential fluorescence decays is consistent with emission from dye molecules adsorbed at two distinct sites, presumably tunnels and grooves. These hybrid materials also have improved properties in terms of stability of the color in contact with pH 10 aqueous solution and resistance to thermal degradation of the dye. SEP thus appears to be a promising substrate for the development of highly fluorescent flavylium or pyranoflavylium cation-derived hybrid pigments with improved color and thermal stability.