Exploiting the Colloidal Stability and Solubilization Ability of Clay Nanotubes/Ionic Surfactant Hybrid Nanomaterials

Halloysite clay nanotubes are functionalized by exploiting the different charges between the inner positive and the outer negative surfaces; accordingly, a selective adsorption is pursued by employing anionic and cationic surfactants. The obtained hybrid materials dispersed in aqueous phase are studied from the physicochemical viewpoint to investigate the colloidal stability that is a crucial parameter for applications. It is demonstrated that the adsorption of anionic surfactant into the HNTs lumen increases the net negative charge of the nanotubes enhancing the electrostatic repulsions and consequently the dispersion stability. The solubilization capability of these functionalized nanotubes toward hydrophobic compounds is demonstrated. This paper puts forward an easy strategy to prepare hybrid materials, like inorganic micelles, that can be used in water for solubilization and delivery of a hydrophobic compound by taking advantage of the sustainable and biocompatible properties

Halloysite Nanotubes Loaded with Calcium Hydroxide: Alkaline Fillers for the Deacidification of Waterlogged Archeological Woods

A novel green protocol for the deacidifying consolidation of waterlogged archaeological woods through aqueous dispersions of polyethylene glycol (PEG) 1500 and halloysite nanotubes containing calcium hydroxide has been designed. First, we prepared functionalized halloysite nanotubes filled with Ca­(OH)₂ in their lumen. The controlled and sustained release of Ca­(OH)₂ from the halloysite lumen extended its neutralization action over time, allowing the development of a long-term deacidification of the wood samples. A preliminary thermomechanical characterization of clay/polymer nanocomposites allows us to determine the experimental conditions to maximize the consolidation efficiency of the wood samples. The penetration of the halloysite–Ca­(OH)₂/PEG composite within the wooden pores conferred the robustness of the archaeological woods based on the clay/polymer composition of the consolidant mixture. Compared to the archeological woods treated with pure PEG 1500, the addition of modified nanotubes in the consolidant induced a remarkable improvement in the mechanical performance in terms of flexural strength and rigidity. The pH measurements of the treated woods showed that the halloysite–Ca­(OH)₂ are effective alkaline fillers. Accordingly, the modified nanotubes provided a long-term protection for lignin present in the woods that are exposed to artificial aging under acidic atmosphere. The attained knowledge shows that an easy and green protocol for the long-term preservation of wooden artworks can be achieved by the combination of PEG polymers and alkaline tubular nanostructures obtained through the confinement of Ca­(OH)₂ within the halloysite cavity

Biopolymer-Targeted Adsorption onto Halloysite Nanotubes in Aqueous Media

Studies on the adsorption of biopolymers onto halloysite nanotubes (HNTs) in water were conducted. Three polymers with different chargesanionic (pectin), neutral (hydroxypropyl cellulose), and cationic (chitosan)were chosen. The thermodynamic parameters for the adsorption of polymers onto the HNT surface were determined by isothermal titration calorimetry (ITC). The experimental data were interpreted based on a Langmuir adsorption model. The standard variations in free energy, enthalpy, and entropy of the process were obtained and discussed. Turbidimetry was used to evaluate the stability of functionalized nanoparticles in water. The ζ-potential clarified the surface charge properties of functionalized nanotubes upon polymer adsorption. The interaction of modified nanotubes with polymers led to the formation of a colloidal system with tunable stability and surface properties, which offers different perspectives on new applications of these dispersions, such as carriers for substances to be released in response to external stimuli

Biopolymer-Targeted Adsorption onto Halloysite Nanotubes in Aqueous Media

Studies on the adsorption of biopolymers onto halloysite nanotubes (HNTs) in water were conducted. Three polymers with different chargesanionic (pectin), neutral (hydroxypropyl cellulose), and cationic (chitosan)were chosen. The thermodynamic parameters for the adsorption of polymers onto the HNT surface were determined by isothermal titration calorimetry (ITC). The experimental data were interpreted based on a Langmuir adsorption model. The standard variations in free energy, enthalpy, and entropy of the process were obtained and discussed. Turbidimetry was used to evaluate the stability of functionalized nanoparticles in water. The ζ-potential clarified the surface charge properties of functionalized nanotubes upon polymer adsorption. The interaction of modified nanotubes with polymers led to the formation of a colloidal system with tunable stability and surface properties, which offers different perspectives on new applications of these dispersions, such as carriers for substances to be released in response to external stimuli

Modified Halloysite Nanotubes: Nanoarchitectures for Enhancing the Capture of Oils from Vapor and Liquid Phases

We prepared hybrid halloysite nanotubes (HNT/sodium alkanoates) in which the inner cavity of the nanoclay was selectively modified. Physicochemical studies evidenced the interactions between HNT and sodium alkanoates, ruled out clay exfoliation, quantified the amount of the loaded substance, and showed an increase of the total net negative charge, allowing us to obtain rather stable aqueous nanoclay dispersions. These dispersions were exploited as inorganic micelles to capture hydrocarbon and aromatic oils in the vapor and liquid states and were revealed to be nonfoaming but very efficient in encapsulating oils. Here, we have fabricated biocompatibile and low-cost inorganic micelles that can be exploited for industrial applications on a large scale

Unveiling Carbon Fiber Reinforced Polyurea Composites Engineered through Vacuum Assisted Resin Transfer Molding: An In-depth Analysis of Mechanical, Thermal, and Degradation Performance

Carbon fiber reinforced polymer (CFRP) composites have attracted increasing attention in recent years as they exhibit excellent mechanical strength and are substituting metals in marine, automotive, aerospace, and construction industries. However, the brittleness of CFRP leads to low toughness, limiting its structural performance. In this work, for the first time, the utilization of super elastomeric polyurea as the matrix with carbon fiber via vacuum-assisted resin transfer molding is featured. This study revealed a direct correlation between the number of carbon fabric layers and the enhancement of the flexural load, stiffness, and resistance to mechanical indentation. The 8-layer laminate with a thickness of 2.5 mm showed flexural strength of 237 MPa at 5% flexural strain, flexural modulus of 93.4 GPa and hardness of 80 HD. Polyurea matrix demonstrated exceptional stress absorption and redistribution capabilities, preventing complete breakage up to 5% flexural strain, ultimately restoring the laminates’ position upon unloading. Field emission scanning electron microscopy analysis showed strong matrix-fiber interfacial adhesion that could be attributed to the interphase mechanical locking resulting in high storage modulus of 2441 MPa. An in-depth analysis of the laminates’ fracture morphology unveiled delamination predominantly within the compression zone, except for the 2-layer laminate, where fractures manifested simultaneously in both compression and tension zones due to the slender thickness. Furthermore, the degradation behavior of the polyurea composite laminates under exposure to 5% NaCl solution at a temperature of 60 °C highlighted an initial increase in flexural strength within the initial 28-day period, attributed to the plasticizing effect induced by moisture. However, at 63 days, a decline in flexural strength is observed, signaling the degradation and debonding of the matrix from the reinforcing fibers. This work opens the door for viscoelastic CFRP as an excellent absorbing composite material with high toughness that is suitable for marine environments

Nanohydrogel Formation within the Halloysite Lumen for Triggered and Sustained Release

An easy strategy to obtain nanohydrogels within the halloysite nanotube (HNTs) lumen was investigated. Inorganic reverse micelles based on HNTs and hexadecyltrimethylammonium bromides were dispersed in chloroform, and the hydrophilic cavity was used as a nanoreactor to confine the gel formation based on alginate cross-linked by calcium ions. Spectroscopy and electron microscopy experiments proved the confinement of the polymer into the HNT lumen and the formation of calcium-mediated networks. Biological tests proved the biocompatibility of the hybrid hydrogel. The nanogel in HNTs was suitable for drug loading and sustained release with the opportunity of triggered burst release by chemical stimuli. Here, we propose a new strategy based on inorganic reverse micelles for nanohydrogel formation, which are suitable for industrial and biological applications as well as for selective and triggered adsorption and/or release

Selective Functionalization of Halloysite Cavity by Click Reaction: Structured Filler for Enhancing Mechanical Properties of Bionanocomposite Films

Selective modification of the inner surface of halloysite nanotubes (HNTs) by the cycloaddition of azides and alkynes (click reaction) was successfully achieved. Fourier transform infrared spectroscopy and thermogravimetry confirmed that the modification involved only the HNT cavity. Morphological investigations evidenced that the functionalized nanotubes formed microfibers and clusters in the micrometer range. By means of the casting method, these nanomaterials were dispersed into biopolymeric matrixes (chitosan and hydroxypropyl cellulose) with the aim of obtaining nanocomposite films with tunable properties from the physicochemical viewpoint. For comparison purposes, we also characterized composite nanomaterials based on pristine halloysite. The mesoscopic structure of the nanocomposites was correlated with their tensile, thermal, and wettability properties, which were found to be strongly dependent on both the nature of the polymer and the HNT functionalization. The attained knowledge represents a basic point for designing new hybrid nanostructures that are useful in specific purposes such as biocompatible packaging

Effect of Morphology and Size of Halloysite Nanotubes on Functional Pectin Bionanocomposites for Food Packaging Applications

Pectin bionanocomposite films filled with various concentrations of two different types of halloysite nanotubes were prepared and characterized in this study as potential films for food packaging applications. The two types of halloysite nanotubes were long and thin (patch) (200-30 000 nm length) and short and stubby (Matauri Bay) (50-3000 nm length) with different morphological, physical, and dispersibility properties. Both matrix (pectin) and reinforcer (halloysite nanotubes) used in this study are considered as biocompatible, natural, and low-cost materials. Various characterization tests including Fourier transform infrared spectroscopy, field emission scanning electron microscopy, release kinetics, contact angle, and dynamic mechanical analysis were performed to evaluate the performance of the pectin films. Exceptional thermal, tensile, and contact angle properties have been achieved for films reinforced by patch halloysite nanotubes due to the patchy and lengthy nature of these tubes, which form a bird nest structure in the pectin matrix. Matauri Bay halloysite nanotubes were dispersed uniformly and individually in the matrix in low and even high halloysite nanotube concentrations. Furthermore, salicylic acid as a biocidal agent was encapsulated in the halloysite nanotubes lumen to control its release kinetics. On this basis, halloysite nanotubes/salicylic acid hybrids were dispersed into the pectin matrix to develop functional biofilms with antimicrobial properties that can be extended over time. Results revealed that shorter nanotubes (Matauri Bay) had better ability for the encapsulation of salicylic acid into their lumen, while patchy structure and longer tubes of patch halloysite nanotubes made the encapsulation process more difficult, as they might need more time and energy to be fully loaded by salicylic acid. Moreover, antimicrobial activity of the films against four different strains of Gram-positive and Gram-negative bacteria indicated the effective antimicrobial properties of pectin/halloysite functionalized films and their potential to be used for food packaging applications. \ua9 2017 American Chemical Society

Effect of Morphology and Size of Halloysite Nanotubes on Functional Pectin Bionanocomposites for Food Packaging Applications

Pectin bionanocomposite films filled with various concentrations of two different types of halloysite nanotubes were prepared and characterized in this study as potential films for food packaging applications. The two types of halloysite nanotubes were long and thin (patch) (200–30 000 nm length) and short and stubby (Matauri Bay) (50–3000 nm length) with different morphological, physical, and dispersibility properties. Both matrix (pectin) and reinforcer (halloysite nanotubes) used in this study are considered as biocompatible, natural, and low-cost materials. Various characterization tests including Fourier transform infrared spectroscopy, field emission scanning electron microscopy, release kinetics, contact angle, and dynamic mechanical analysis were performed to evaluate the performance of the pectin films. Exceptional thermal, tensile, and contact angle properties have been achieved for films reinforced by patch halloysite nanotubes due to the patchy and lengthy nature of these tubes, which form a bird nest structure in the pectin matrix. Matauri Bay halloysite nanotubes were dispersed uniformly and individually in the matrix in low and even high halloysite nanotube concentrations. Furthermore, salicylic acid as a biocidal agent was encapsulated in the halloysite nanotubes lumen to control its release kinetics. On this basis, halloysite nanotubes/salicylic acid hybrids were dispersed into the pectin matrix to develop functional biofilms with antimicrobial properties that can be extended over time. Results revealed that shorter nanotubes (Matauri Bay) had better ability for the encapsulation of salicylic acid into their lumen, while patchy structure and longer tubes of patch halloysite nanotubes made the encapsulation process more difficult, as they might need more time and energy to be fully loaded by salicylic acid. Moreover, antimicrobial activity of the films against four different strains of Gram-positive and Gram-negative bacteria indicated the effective antimicrobial properties of pectin/halloysite functionalized films and their potential to be used for food packaging applications