Phase change insulation for energy efficiency based on wax-halloysite composites

<p>Wax can be used as a phase change material in solar energy storage but has low thermal conductivity and cannot sustain shape at higher temperature (above 55 C). Introducing 50%  halloysite clay nanotubes into wax yields a stable and homogenous phase change composite with thermal conductivity of 0.36 Wm-1 K-1 and no leaking until 70 C (preserving layer-shape above the original wax melting point). Thermal conductivity of<br>wax/halloysite/graphite (45/45/10%) composite showed a six-fold conductivity increase to 1.4 Wm-1<br>K-1 compared to pure wax and had no liquid wax leakage until 81 C. Wax/halloysite/graphite/carbon nanotubes (45/45/5/10%) composite show thermal conductivity of 0.85 Wm-1 K-1 while maintaining the original shape until 91 C. Vectorial thermal energy transfer for double layers of different phase change materials demonstrated heat flux difference in the opposite directions differed by 25%. This variance in layer conductivity allows for smart building roof insulators with increased absorption during hot weather but limited thermal losses during periods of cooler temperatures. The new wax-nanoclay composite is a promising heat storage material due to good heat capacity, high thermal conductivity and ability to preserve its shape during wax melting.</p> <p> </p

Enlargement of Halloysite Clay Nanotube Lumen by Selective Etching of Aluminum Oxide

Halloysite clay tubes have 50 nm diameter and chemically different inner and outer walls (inner surface of aluminum oxide and outer surface of silica). Due to this different chemistry, the selective etching of alumina from inside the tube was realized, while preserving their external diameter (lumen diameter changed from 15 to 25 nm). This increases 2–3 times the tube lumen capacity for loading and further sustained release of active chemical agents such as metals, corrosion inhibitors, and drugs. In particular, halloysite loading efficiency for the benzotriazole increased 4 times by selective etching of 60% alumina within the tubes’ lumens. Specific surface area of the tubes increased over 6 times, from 40 to 250 m²/g, upon acid treatment

Interfacial Modification of Clay Nanotubes for the Sustained Release of Corrosion Inhibitors

Long-lasting anticorrosive coatings for steel have been developed on the basis of halloysite nanotubes loaded with three corrosion inhibitors: benzotriazole, mercaptobenzothiazole, and mercaptobenzimidazole. The inhibitors’ loaded tubes were admixed at 5–10 wt % to oil-based alkyd paint providing sustained agent release and corrosion healing in the coating defects. The slow 20–30 h release of the inhibitors at defect points caused a remarkable improvement in the anticorrosion efficiency of the coatings. Further time expansion of anticorrosion agent release has been achieved by the formation of release stoppers at nanotube ends with urea–formaldehyde copolymer and copper-inhibitor complexation. The corrosion protection efficiency was tested on ASTM A366 steel plates in a 0.5 M NaCl solution with the microscanning of corrosion current development by microscopy inspection and studying paint adhesion. The best protection was found using halloysite/mercaptobenzimidazole and benzotriazole inhibitors. Stopper formation with urea–formaldehyde copolymer provided an additional increase in corrosion efficiency as a result of the longer release of inhibitors

Nanodot-Loaded Clay Nanotubes as Green and Sustained Radical Scavengers for Elastomer

Radical-scavenging carbon nanodots (CDs) were loaded into the 50 nm diameter natural halloysite clay tubes to fabricate low toxic CD-delivery vehicles for elastomer composites with sustained antiaging functionality. Then, 2 nm diameter carbon nanodots released from the halloysite lumens interacted with reactive radicals, generated at the initial stage of oxidative processes, which significantly improved thermo-aging resistance of the elastomers. The antioxidative efficiency of these CD-delivery vehicles was further increased through the nanotubes’ surface modification with a thin grafted-silane shell, which allowed the slowing of the release rate, thus extending the protection. This nanoarchitectural design of the carbon dot-loaded clay nanotubes doped at 9 wt % into a rubber matrix allowed for sustained radical-scavenging and provides a new strategy for long-lasting elastomer protection. Our antiaging rubber nanoformulation based on a natural tubule clay and biocompatible CDs can decrease the environmental hazards of conventional petrol-derived antioxidants. Such clay core–shell systems may also be useful for biocompatible encapsulation of often-poisonous nanodots providing safe biomarkers

Antifouling Thermoplastic Composites with Maleimide Encapsulated in Clay Nanotubes

An antifouling ethylene-vinyl acetate copolymer (EVA) coating with halloysite clay nanotubes loaded with maleimide (TCPM) is prepared. Such antifoulant encapsulation allowed for extended release of TCPM and a long-lasting, efficient protection of the coated surface against marine microorganisms proliferation. Halloysite also induces the composite’s anisotropy due to parallel alignment of the nanotubes. The maleimide loaded halloysite incorporated into the polymer matrix allowed for 12-month release of the bacterial inhibitor preventing fouling; it is much longer than the 2–3 month protection when TCPM is directly admixed into EVA. The antifouling properties of the EVA-halloysite nanocomposites were tested by monitoring surface adhesion and proliferation of marine V. natriegens bacteria with SEM. As compared to the composite directly doped with TCPM-antifoulant, there were much less bacteria accumulated on the EVA-halloysite-TCPM coating after a 2-month exposure to seawater. Field tests at South China Sea marine station further confirmed the formulation efficiency. The doping of 28 wt % TCPM loaded halloysite drastically enhanced material antifouling property, which promises wide applications for protective marine coating

Natural Tubule Clay Template Synthesis of Silver Nanorods for Antibacterial Composite Coating

Halloysite is naturally available clay mineral with hollow cylindrical geometry and it is available in thousands of tons. Silver nanorods were synthesized inside the lumen of the halloysite by thermal decomposition of the silver acetate, which was loaded into halloysite from an aqueous solution by vacuum cycling. Images of individual ca. 15 nm diameter silver nanorods and nanoparticles were observed with TEM. The presence of silver inside the tubes was also verified with STEM-EDX elemental mapping. Nanorods had crystalline nature with [111] axis oriented ∼68° from the halloysite tubule main axis. The composite of silver nanorods encased in clay tubes with the polymer paint was prepared, and the coating antimicrobial activity combined with tensile strength increase was demonstrated. Coating containing up 5% silver loaded halloysite did not change color after light exposure contrary to the sample prepared with loading with unshelled silver nanoparticles. Halloysite tube templates have a potential for scalable manufacturing of ceramic encapsulated metal nanorods for composite materials

Highly Aging-Resistant Elastomers Doped with Antioxidant-Loaded Clay Nanotubes

A novel aging-resistant styrene–butadiene rubber (SBR) composite is prepared using the antioxidant <i>N</i>-isopropyl-<i>N</i>′-phenyl-p-phenylenediamine (4010NA) loaded inside of halloysite clay nanotubes and used as filler. Loading the antioxidant inside of halloysite allows for its sustained release for nine months in the rubber matrix. By utilizing modified halloysite, the antioxidant concentration in this rubber nanoformulation is tripled without causing “blooming” defects. Furthermore, the halloysite is silanized to enhance its miscibility with rubber. The aging resistance of SBR–halloysite composites is studied by comparing the mechanical properties before and after thermal-oxidative aging. A seven-day test at 90 °C shows preservation of mechanical properties, and no 4010NA blooming is observed, even after one month. Styrene–butadiene rubber with 27 wt % halloysite loaded with 4010NA shows marked increase in aging resistance and promising future of halloysite as a functional rubber filler

Electrospun Microfiber Membranes Embedded with Drug-Loaded Clay Nanotubes for Sustained Antimicrobial Protection

Guided tissue regeneration/guided bone regeneration membranes with sustained drug delivery were developed by electrospinning drug-loaded halloysite clay nanotubes doped into poly(caprolactone)/gelatin microfibers. Use of 20 wt % nanotube content in fiber membranes allowed for 25 wt % metronidazole drug loading in the membrane. Nanotubes with a diameter of 50 nm and a length of 600 nm were aligned within the 400 nm diameter electrospun fibers, resulting in membranes with doubling of tensile strength along the collector rotating direction. The halloysite-doped membranes acted as barriers against cell ingrows and have good biocompatibility. The metronidazole-loaded halloysite nanotubes incorporated in the microfibers allowed for extended release of the drugs over 20 days, compared to 4 days when directly admixed into the microfibers. The sustained release of metronidazole from the membranes prevented the colonization of anaerobic Fusobacteria, while eukaryotic cells could still adhere to and proliferate on the drug-loaded composite membranes. This indicates the potential of halloysite clay nanotubes as drug containers that can be incorporated into electrospun membranes for clinical applications

Sonication-Assisted Layer-by-Layer Assembly for Low Solubility Drug Nanoformulation

Sonication-assisted layer-by-layer (LbL) self-assembly is a nanoencapsulation technique based on the alternate adsorption of oppositely charged polyelectrolytes, enabling the encapsulation of low solubility drugs. In this work, a top-down LbL technique was performed using a washless approach and ibuprofen (IBF) as a model class II drug. For each saturated layer deposition, polyelectrolyte concentration was determined by titration curves. The first layer was constituted by cationic poly­(allylamine hydrochloride) (PAH), given the IBF negative surface charge, followed by anionic polystyrenesulfonate (PSS). This polyelectrolyte sequence was made up with 2.5, 5.5, and 7.5 bilayer nanoshells. IBF nanoparticles (NPs) coated with 7.5 bilayers of PAH/PSS showed 127.5 ± 38.0 nm of particle size, a PDI of 0.24, and a high zeta potential (+32.7 ± 0.6 mV), allowing for a stable aqueous nanocolloid of the drug. IBF entrapment efficiency of 72.1 ± 5.8% was determined by HPLC quantification. In vitro MTT assay showed that LbL NPs were biocompatible. According to the number of coating layers, a controlled release of IBF from LbL NPs was achieved under simulated intestinal conditions (from 5 h up to 7 days). PAH/PSS-LbL NPs constitute a potential delivery system to improve biopharmaceutical parameters of water low solubility drugs

Self-Healing Coatings Based on Halloysite Clay Polymer Composites for Protection of Copper Alloys

Halloysite clay nanotubes loaded with corrosion inhibitors benzotriazole (BTA), 2-mercaptobenzimidazole (MBI), and 2-mercaptobenzothiazole (MBT) were used as additives in self-healing composite paint coating of copper. These inhibitors form protective films on the metal surface and mitigate corrosion. Mechanisms involved in the film formation have been studied with optical and electron microscopy, UV–vis spectrometry, and adhesivity tests. Efficiency of the halloysite lumen loading ascended in the order of BTA < MBT < MBI; consequently, MBI and MBT halloysite formulations have shown the best protection. Inhibitors were kept in the tubes buried in polymeric paint layer for a long time and release was enhanced in the coating defects exposed to humid media with 20–50 h, sufficient for formation of protective layer. Anticorrosive performance of the halloysite-based composite acrylic and polyurethane coatings have been demonstrated for 110-copper alloy strips exposed to 0.5 M aqueous NaCl for 6 months