Halloysite Content Research Articles

Novel polymer/halloysite composites with high halloysite content and remarkable mechanical strength

Facilitated by interfacial H-bonding interactions, polymer/halloysite composites with high halloysite content and significantly enhanced mechanical properties have been achieved.

Nanocomposites based on halloysite nanotubes and sulphated galactan from red seaweed Gloiopeltis: Properties and delivery capacity of sodium diclofenac

We developed novel composite films based on biocompatible components, such as halloysite clay nanotubes and sulphated galactan (Funori) from red seaweed Gloiopeltis. The filling of the nanotubes within the sulphated galactan matrix was carried out by a green protocol (aqueous casting method) assuring that Funori/halloysite nanocomposites can be totally considered as sustainable materials. The amount of halloysite in the composites was systematically changed to explore the effects of the nanofiller concentration on the mesoscopic properties of the films. We observed that the halloysite content significantly affects the initial water contact angle and the light attenuation coefficient of the Funori based films. These results were interpreted according to SEM images, which showed that the surface morphologies of the nanocomposites depend on the halloysite amounts filled within the polymeric matrix. The mechanical characterization of the nanocomposites was conducted by tensile experiments performed using a linear stress ramp. Moreover, tensile tests were conducted in oscillatory regime at variable temperature to investigate the viscoelastic properties of the nanocomposites.Finally, we filled the biopolymeric matrix with halloysite nanotubes containing sodium diclofenac. The drug release kinetics from the nanocomposites at variable halloysite contents were studied to evaluate their suitability as oral dissolving films for pharmaceutical applications.

One-pot synthesis of siliceous ferrihydrite − coated halloysite nanorods in alkaline medium: Structure, properties and cadmium adsorption performance

The application of amorphous ferrihydrite (Fh) for Cd(II) removal is restricted by its unstable and easily transformable nature. Although doping with silicates stabilized ferrihydrite, its product siliceous ferrihydrite (SiFh) again suffered from the disadvantage of spontaneous agglomeration. Herein, ferrihydrite was hybridized with halloysite nanotubes (HNTs) to prepare a novel siliceous ferrihydrite − coated halloysite nanorods (SiFh@HNTs) in alkaline medium, to break through the current barriers. The characterization results showed that SiFh@HNTs could simultaneously overcome the defects of easy phase transformation of ferrihydrite and easy aggregation of SiFh nanoparticles (NPs). Meanwhile, the optimal SiFh@HNT40 with halloysite content of 40 % formed a well-developed mesoporous structure and exhibited the desired surface properties: a high specific surface area of 303.4 m2/g, an isoelectric point as low as pHiep = 4.5, and rich functional Fe − OH groups. The formation mechanism of such excellent sturcture–properties of SiFh@HNT40 were mainly attributed to two factors: the generation of smaller (∼5 nm) SiFh NPs induced by the integration of halloysite-derived SiO44- into ferrihydrite, and the dispersion of SiFh NPs on clay nanotubes. Furthermore, the adsorption capacity of SiFh@HNT40 for Cd(II) was up to 137.8 mg/g at 30 °C and pH 6, which was much higher than that of aggregated ferrihydrite (11.2 mg/g), halloysite (18.8 mg/g) and goethite (49.4 mg/g). The adsorption thermodynamics study revealed the adsorption of Cd(II) on SiFh@HNT40 was clearly chemisorption with a (ΔHads)q of 43.3 kJ/mol. Characterization results of XPS and FTIR confirmed that the rich Fe − OH groups on SiFh@HNT40 was the main adsorption sites, and Cd(II) was specifically adsorbed by inner-sphere surface complexation. In addition, SiFh@HNT40 had application potential in the mixed-metal wastewaters treatment. Cyclic regeneration experiments showed that SiFh@HNT40 had good regeneration performance and could be reused many times.

Green nanocomposite gels based on binary network of sodium alginate and percolating halloysite clay nanotubes for 3D printing

Alginate hydrogels with embedded rigid percolating network of halloysite clay nanotubes were evaluated as a novel ink for 3D printing. Hydrophilic alginate macromolecules adsorbing on halloysite stabilize the network of the nanotubes and form their own network of interlaced polymer chains. The effect of halloysite content on the structure and properties of the hydrogels was studied by rheometry, thermogravimetric analysis, FTIR-spectroscopy, dynamic light scattering, transmission electron microscopy, and 3D cryo-electron microscopy. Hydrogels demonstrate a very pronounced shear-thinning at extrusion and rather quick viscosity recovery after extrusion assigned to rapid rearrangement of the network structure promoted by mobile alginate chains. Even at low volume fractions (up to 0.054) the nanotubes reinforce the hydrogel increasing its storage modulus up to 650 Pa and inducing the appearance of yield stress. These properties make the alginate/halloysite hydrogels promising for the application in 3D printing for fabrication of green and sustainable nanocomposite materials made from natural components.

Durability assessment of soft clay soil stabilized with halloysite nanotubes

In this study the compressive strength and durability of soft clay soil stabilized with halloysite nanotubes are investigated. Halloysite nanotubes are novel 1D natural nanomaterials which are widely used in reinforcing polymer, pollution remediation, and as nanoreactors for biocatalyst. The wide use of halloysite nanotubes is due to their high aspect ratio, appropriate mechanical strength, high thermal stability, nature-friendly and cost-effectiveness. However, the use of halloysite nanotubes as a stabilizing agent for improving the durability of soil is not clear. In this research, halloysite nanotubes was used in the amounts of 2%, 5% and 10% by the weight of dried soil. Unconfined compressive strength, wet/dry cycles and freeze/thaw cycles tests were performed to evaluate the strength and durability of stabilized soft clay soil. Experimental results showed that halloysite nanotubes considerably improves the compressive strength and durability of soft clay soil. The optimum amount of halloysite nanotubes for soil stabilizing in terms of compressive strength and durability was 5%. The compressive strength of soft clay increased as much as 129% by applying 5% halloysite nanotubes. Also, the specimen containing 5% halloysite nanotubes showed the least strength loss after wet/dry and freeze/thaw cycles. The soil sample containing 5% halloysite nanotubes lost 20% of its initial compressive strength after 8 cycles of freezing and thawing, while the soil sample without any halloysite content lost 100% of its compressive strength after the same number of freezing and thawing. Based on the obtained results, the use of halloysite nanotubes in order to enhance the strength and durability of soft clay is strongly recommended.

Poly-ε-Caprolactone/Halloysite Nanotube Composites for Resorbable Scaffolds: Effect of Processing Technology on Homogeneity and Electrospinning.

Polycaprolactone (PCL)/halloysite composites were prepared to compare the effect of homogenization technology on the structure and properties of the composites. Halloysite content changed from 0 to 10 vol% in six steps and homogeneity was characterized by various direct and indirect methods. The results showed that the extent of aggregation depends on technology and on halloysite content; the size and number of aggregates increase with increasing halloysite content. Melt mixing results in more homogeneous composites than the simple compression of the component powders or homogenization in solution and film casting. Homogeneity and the extent of aggregation determines all properties, including functionality. The mechanical properties of the polymer deteriorate with increasing aggregation; even stiffness depends on homogeneity. Strength and deformability decreases drastically as the number and size of aggregates increase. Not only dispersed structure, but also the physical state and crystalline structure of the polymer influence homogeneity and properties. The presence of the filler affects the preparation of electrospun fiber scaffolds as well. A part of the filler is excluded from the fibers while another part forms aggregates that complicates fiber spinning and deteriorates properties. The results indicate that spinning is easier and the quality of the fibers is better if a material homogenized previously by melt mixing is used for the production of the fibers.

Kinetics of methylene blue dye adsorptive removal using halloysite nanocomposite hydrogels

Abstract In the present work, halloysite nano-clay (HNTs) based hydrogel was fabricated and their efficiency for the removal of methylene blue dye was studied. The hydrogel films were prepared with varying amount of halloysite nano-clay via facile solution casting method. Effect of halloysite clay on adsorption performance of composite was investigated. The hydrophobic thermoplastic synthetic polymer, polylactic acid (PLA) was blended with hydrophilic polymer polyvinyl alcohol (PVA) and HNTs to synthesize hydrogels. Swelling behavior and antimicrobial efficiency was also evaluated. The halloysite incorporating films showed excellent antibacterial activity. Swelling capacity of hydrogel with increased halloysite content was reduced due to increased crosslinking among polymer chains. Halloysite incorporated hydrogel exhibited higher adsorption ability as compared to film comprising of only PVA and PLA and dye removal followed pseudo first order kinetics. Film with 0.03 g HNTs rapidly attained adsorption-desorption equilibria and removed the dye completely within 30 min. Results confirmed that synthesized film could be potentially used for the removal of cationic dye and fabricated hydrogel film have promising potential for wastewater treatment since a higher adsorption capacity was observed for halloysite nano-clay incorporated hydrogel.

The formation of desilication products in the presence of kaolinite and halloysite – The role of surface area

A great deal of effort has been dedicated to improve the fundamental understanding of the mechanism of desilication product crystallization under Bayer process refinery conditions. Differences in the mineralogy of the reactive silica found in bauxite could change the kinetics and possibly the formation pathways of the desilication product. In this work, halloysite was investigated and compared to kaolinite, which is commonly found in bauxite. Different ratios of kaolinite and halloysite were used to form desilication product and the solids formed were characterized thoroughly to determine the impact the presence of the clay had. In addition, differences in dissolution rate due to the presence of halloysite was determined. The results show that the presence of halloysite led to a faster dissolution rate of the clay overall, which can be attributed to the total specific surface area of the reactive silica source. Thus, the crystallinity of the clay was found to have limited impact. The presence of halloysite also increased the measured maximum solution [SiO2] in solution, which in turn increases the driving force for the formation of desilication product. The increase in halloysite content thus results in desilication product being observed at an earlier stage and, overall, leads to an enhanced rate of desilication product formation.

Pickering Emulsions Based on Wax and Halloysite Nanotubes: An Ecofriendly Protocol for the Treatment of Archeological Woods.

A novel green protocol for the consolidation and protection of waterlogged archeological woods with wax microparticles has been designed. First, we focused on the development of halloysite nanotubes (HNTs) based Pickering emulsions using wax as the inner phase of the oil-in-water droplets. The optimization of the preparation strategy was supported by both optical microscopy and scanning electron microscopy, which allowed us to show the morphological features of the prepared hybrid systems and their structural properties, i.e., the distribution of the clay at the interface. Also, the dependence of the overall dimensions of the prepared systems on the halloysite content was demonstrated. Microdifferential scanning calorimetry (μ-DSC) was conducted in order to assess whether the thermal properties of the wax are affected after its interaction with HNTs. Then, the Pickering emulsions were employed for the treatment of waterlogged wooden samples. Compared to the archeological woods treated with pure wax, the addition of nanotubes induced a remarkable improvement in the mechanical performance in terms of stiffness and flexural strength. The proposed protocol is environmentally friendly since water is the only solvent used throughout the entire procedure, even if wax is vehiculated into the pores at room temperature. As a consequence, the design of wax/halloysite Pickering emulsions represents a promising strategy for the preservation of wooden artworks, and it has a great potential to be scaled up, thus becoming also exploitable for the treatments of shipwrecks of large size.

Fabrication of a water-retaining, slow-release fertilizer based on nanocomposite double-network hydrogels via ion-crosslinking and free radical polymerization

A new type of water-retaining, slow-release fertilizer (WSF) based on double-network hydrogels was fabricated via the ion-crosslinking of sodium carboxymethyl cellulose and the free radical polymerization of polymerizable β-cyclodextrin (MAH-CD), polyethylene glycol dimethacrylate (PEGDA), acrylamide (AM), and acrylic acid (AA) with urea-loaded halloysite as an additive. The effects of the AM to AA monomer ratio, the halloysite content, the AlCl3 content and the MAH-CD content on the swelling ratio were studied. Fourier transform infrared spectroscopy (FTIR), scanning electron microscopy (SEM), and thermogravimetric analysis (TGA) were applied to characterize the structure and properties of the WSF. The swelling behavior and water retention capacity of the fertilizer were investigated using a classic gravimetric method. The experimental results indicated that the presence of halloysite nanotubes clearly adjusted the swelling and release properties of the WSF. Kinetic modeling indicated that the swelling mechanism and slow release behavior were consistent with a Fickian diffusion mechanism. Form the considerations of its properties and raw materials, the fertilizer developed here has a good prospect of application and extension.

Introducing Porosity in Colloidal Biocoatings to Increase Bacterial Viability.

A biocoating confines nongrowing, metabolically active bacteria within a synthetic colloidal polymer (i.e., latex) film. Bacteria encapsulated inside biocoatings can perform useful functions, such as a biocatalyst in wastewater treatment. A biocoating needs to have a high permeability to allow a high rate of mass transfer for rehydration and the transport of both nutrients and metabolic products. It therefore requires an interconnected porous structure. Tuning the porosity architecture is a challenge. Here, we exploited rigid tubular nanoclays (halloysite) and nontoxic latex particles (with a relatively high glass transition temperature) as the colloidal "building blocks" to tailor the porosity inside biocoatings containing Escherichia coli bacteria as a model organism. Electron microscope images revealed inefficient packing of the rigid nanotubes and proved the existence of nanovoids along the halloysite/polymer interfaces. Single-cell observations using confocal laser scanning microscopy provided evidence for metabolic activity of the E. coli within the biocoatings through the expression of a yellow fluorescent protein. A custom-built apparatus was used to measure the permeability of a fluorescein sodium salt in the biocoatings. Whereas there was no measurable permeability in a coating made from only latex particles, the permeability coefficient of the composite biocoatings increased with increasing halloysite content up to a value of 1 × 10-4 m h-1. The effects of this increase in permeability was demonstrated through a specially developed resazurin reduction assay. Bacteria encapsulated in halloysite composite biocoatings had statistically significant higher metabolic activities in comparison to bacteria encapsulated in a nonoptimized coating made from latex particles alone.

Effects of halloysite content on the thermo-mechanical performances of composite bioplastics

The aim of this study is the design and preparation of Mater-Bi/halloysite nanocomposite materials that could be employed as bioplastics alternative to the petroleum derived products. The biocomposite materials at variable halloysite content (from 0 to 30 wt%) were prepared by using the solvent casting method. We investigated the mechanical behaviour and the thermal properties of the prepared nanocomposites in order to estimate their suitability as biocompatible packaging materials. The thermo-mechanical characteristics were correlated to the nanocomposites' morphologies, which were studied by Scanning Electron Microscopy (SEM). As a general result, the physico-chemical performances of Mater-Bi were improved by the presence of small amounts of nanotubes, which evidenced a homogenous distribution in the polymer matrix. The strongest enhancements of the thermal stability and tensile properties were achieved for Mater-Bi/halloysite 10 wt%. A further addition of nanotubes determined the worsening of both thermal stability and mechanical behaviour.The attained knowledge represents the starting step for the development of packaging films composed by Mater-Bi and halloysite nanotubes.

Characterization and Hydrogen Storage Performance of Halloysite Nanotubes.

Here we report on the structural characterization and the hydrogen storage performance of naturally derived halloysite nanotubes (HNTs). HNTs were mined from different deposits in Australia and purified with different processes including crushing, blunging, reblunging, sedimentation and filtration. The clay materials were characterized by different techniques such as powder XRD, TGA, XPS, FTIR spectroscopy, SEM, TEM, and N₂ sorption. Characterization results revealed that they are highly porous in nature with tubular morphology and exhibited excellent thermal stability. Among the halloysite materials studied, HNT1 which is having higher halloysite content and less kaolinite exhibited hydrogen uptake of 0.5 wt.% at 1 bar and -196 °C, which is increased to 1.33 wt.% when the pressure raised to 48 bar. High hydrogen uptake was linked with the high surface area, hollow tubular aluminosilicate structure and the large interlayer spacing of the HNTs as they favour physisorption of hydrogen. It was also demonstrated that HNT1 is considered to be better material than some of the materials reported so far in terms of their cost-effectiveness and environmental safety for the hydrogen storage.

Synergistic effect of chitosan and halloysite nanotubes on improving agar film properties

Agar-based nanocomposites at different halloysite loadings, with and without chitosan as an ingredient and modifier, were prepared by solution casting. The morphology of the nanocomposites was studied by field-emission scanning electron microscopy, and results showed that chitosan partly promoted halloysite dispersion in the nanocomposites. The synergetic effect of chitosan and halloysite on the mechanical properties, water resistance and transparency of the obtained nanocomposites was evaluated. Results indicated that with increased chitosan and/or halloysite content, the tensile strength and elongation at the break of nanocomposites increased significantly. When added 40% chitosan and 8% halloysite into agar matrix, the tensile strength and elongation at the break of agar/chitosan/halloysite composite was improved from 35.03 MPa to 14.79% to 48.29 MPa and 22.62%, respectively. With increasing chitosan content from 0 to 60%, the water-swelling degree of the obtained composites decreased from 409.8% to 34.7%. In addition, well-dispersed halloysite in the polymer matrix decreased the moisture uptake, water solubility and water-swelling degree of the composites. All the agar/chitosan/halloysite nanocomposite films showed >70% transparency in the visible-light region (400–800 nm), indicating that the light transmittance of the obtained nanocomposites was slightly affected by chitosan and halloysite.

Multiple polarization loss and permittivity adjusting of halloysite/BN Co-doped carbon/cobalt composites

Halloysite hybridized B-N co-doped C/Co composites (HNT/BNC/Co) for microwave absorption were prepared via a one-step pyrolysis method. The results indicate that the samples are consisted of halloysite nanotubes (HNT), cobalt nanoparticles and B-N co-doped carbon nanotubes (CNTs). Benefiting from unique hollow tubular structure and the polarization between multiple components, the 0.15HNT/BNC/Co composites with 40 wt% in wax matrix exhibit remarkable microwave absorption properties. A maximum reflection loss up to −40.86 dB with the thickness 1.51 mm at 17.12 GHz, and an effective absorption bandwidth (<−10 dB) up to 4.8 GHz (in the range 12.16–16.96 GHz) can be achieved in this sample. The unique hollow tubular morphology of halloysite and CNTs make it possible to obtain suitable complex permittivity when the sample doping content is 40 wt.%. Furthermore, it was found that the halloysite can be used to adjust complex permittivity of the composites, which were derived from the electromagnetic parameters of composites with different contents of halloysite and the changed doping amounts in paraffin-wax hybrids. This study can provide a new strategy for designing novel carbon and halloysite hybridized microwave absorption materials.

Halloysite nanotubes: Novel and eco-friendly adsorbents for high-pressure CO2 capture

Abstract Naturally available halloysite nanotubes (HNTs) and HNTs/Kaolin mixtures obtained from different locations in South Australia were processed and purified to varying degrees by crushing, blunging and reblunging, sedimentation followed by filtration. The microscopic and adsorption results revealed that the samples are highly porous in nature and exhibited tubular morphology with a high specific surface area. It was found that the halloysite content in the samples obtained from different locations was quite different although the processing steps make a slight difference in the final halloysite content in the samples. Out of the several materials characterized, HNT1, halloysite from Camel Lake, has a higher quantity of halloysite content (88%) and exhibits a specific surface area of ca. 50.8 m2/g. It was found that the halloysite nanotube HNT1 exhibited a CO2 adsorption capacity of 3.4 mmol/g at 25 °C, which increased to 6.1 mmol/g at 0 °C. Interestingly, CO2 adsorption per unit surface area of the studied HNT1 was estimated to be 120 μmol/m2 which is relatively higher than that of the existing halloysites and other well-known commercial materials such as activated carbon, mesoporous silica and carbon nitride materials. The higher adsorption capacity of HNT is mainly attributed to the excellent surface and tubular morphology with small pores and free hydroxyl groups present at the inner and outside surface of HNT, which play a significant role in the CO2 adsorption process.

The crystallization of polypropylene/halloysite fibers

The halloysite (HNT) in the form of nanotubes was used as an agent for the improved mechanical, thermo-mechanical as well as surface properties of polypropylene (PP) fibers. The halloysite is the nanoadditive that can affect differently the crystallization of PP in the non-oriented and oriented systems. The structure and mechanical properties of PP and PP/HNT fibers depended on the crystallinity and crystallization kinetics of PP at the fiber preparation. The Avrami method on the determination of isothermal crystallization kinetics parameters as well as an estimation of melting and crystallization temperatures and melting and crystallization enthalpies was used for the study of thermal behavior of polypropylene/halloysite non-oriented and oriented blends and fibers. Morphological structure, mechanical and thermo-mechanical properties of polypropylene/halloysite fibers were observed. An influence on all assessed properties was evaluated from the point of halloysite content in the PP and/or PP fibers. The increased HNT content in the non-oriented PP/HNT blends at the isothermal crystallization increases the rate crystallization (decreased t1/2 and free energy σe, increased K) of PP in comparison with the pure PP. The crystallinity of PP in the oriented PP/HNT fibers is not primarily affected by addition of the HNT content 3 mass% and does not change their mechanical and thermo-mechanical properties. 5 mass% HNT increases the crystallinity of PP in PP/HNT fibers expressing mainly the decrease in tenacity at the break, Young’s modulus and shrinkage.

Fluorescent nanotubes in PHEMA hydrogels: Visualizing aggregation and distribution by confocal fluorescence microscopy

In this work, physical hydrogels of poly(2-hydroxyethyl methacrylate) loaded with fluorescein-labelled halloysite nanoparticles were synthesized. The nanoparticles were first functionalized with amino groups and subsequently labelled with fluorescein isothiocyanate (FITC). Hydrogels were then synthesized by in situ polymerization using different contents of halloysite. The thermal properties of the resulting hydrogels were studied by differential scanning calorimetry and thermogravimetric analysis, the mechanical properties were examined by dynamic mechanical analysis, and the distribution of nanoparticles was determined by confocal microscopy. The results indicated that the addition of nanoparticles lowered the glass transition and decomposition temperatures of the hydrogels. Mechanical tests showed that the addition of 0.5 wt% nanoparticles led to an increase in the compression and relaxation moduli and a decrease in the relaxation time when the polymer was subjected to stress relaxation assays. Finally, the two- and three-dimensional distributions of nanoparticles in the hydrogel were examined by confocal microscopy and showed the formation of agglomerates with sizes in the range of 1–30 μm, where larger agglomerates formed with larger contents of nanoparticles, which was correlated to the measured mechanical properties.

Nanocomposites of Polypropylene and Halloysite Nanotubes Prepared by a Novel Vane Mixer

Halloysite nanotubes (HNTs) were used to prepare polypropylene (PP) nanocomposites through a novel vane mixer. The effects of melt blend time and halloysite content on properties of composites were investigated. SEM analysis was performed to show that HNTs were well dispersed in PP matrix with the increase of mixing time. DSC showed both the degree of crystallinity and crystallization temperature increased due to the introduction of HNTs into PP, which indicating a potential nucleation effect induced by the nanotubes. TGA illustrated that the presence of HNTs had two opposite effects on the thermal behavior. A surface catalytic action of the halloysite speeded up thermal degradation of PP. However, this effect was reduced with improved HNTs dispersion. Rheological investigations revealed that rheological properties were significantly increased by the addition of low fraction of halloysite to PP. The 2 wt% HNTs nanocomposites reached maximum tensile strength because HNTs dispersed evenly in PP.

Modification of gellan gum films by halloysite: physicochemical evaluation and drug permeation properties

The aim of this study was to determine the potential of gellan gum (GG) and halloysite (HS) dispersions at different mixing ratios and to investigate the potential of GG-HS dispersions in film formation. To this end, the dispersions and films were characterized. The dispersions formed films with large particles ranging from 3 to 4 μm in size, with a zeta potential of ∼−35 mV. The GG-HS films were fabricated using a solvent-casting technique, which generated films with a white opaque appearance and rough surface. The GG-HS films were formed via hydrogen bonding and electrostatic interactions at the inner cavity and outer surface, as confirmed by ATR-FTIR spectroscopy and X-ray diffractometry. The %water uptake and erosion of the GG-HS film decreased with increasing HS content, whereas both puncture strength and elongation were increased in the GG-HS ratios of 1:0.4 and 1:1.2. Moreover, addition of HS into the GG films could possibly decrease drug permeability coefficient when using higher HS ratio in acidic and neutral media. These results suggested that HS modifies the characteristics of the GG used to coat modified-release tablets.