Surface Modification of Nanoclays with Styrene-Maleic Anhydride Copolymers

This study presents the modification of surfaces of nanoclays, halloysite nanotubes (HNT) and sepiolite (SEP), with styrene-maleic anhydride copolymers (SMA) via esterification reaction between hydroxyl groups of the nanoclays and anhydride groups of SMA. The structural, thermal, and morphological analyses of the modified nanoclays were performed by Fourier transform infrared spectroscopy (FTIR), X-ray diffraction analysis (XRD), thermal gravimetric analysis (TGA), and field emission scanning electron microscopy (FESEM). All of these results suggested that the expected modification of HNT and SEP surfaces were performed. Although XRD patterns of HNT containing samples showed that the basal spacing shifted to higher distances, it was found that those of the crystalline structure of SEP remained unchanged. Thermal gravimetric analysis exhibited that SMA copolymers were grafted onto the surfaces of nanoclays varying amounts between 15 and 43 wt. % depending on the types of nanoclays and SMA copolymers. This modification indicates that these nanoclays can be added to the polystyrene matrix without any compatibilizers.

Effect of Reactive Nanoclays on Performances of PMMA/Reactive Nanoclay Nanocomposites

PMMA/reactive nanoclay nanocomposites were prepared by emulsion polymerization using two different reactive nanoclays. X-ray diffraction（XRD） and thermogravimetric analysis（TGA） results confirmed that the reactive nanoclays, kaolinite and montmorillonite, were obtained by the silylation reaction and the double bonds were grafted onto the edges and surfaces of the nanoclays. The presence of reactive nanoclays could increase the average molecular weights, the glass transition temperatures（Tg） and improve the thermal properties of nanocomposite. The tensile properties, Young＇s modulus, and the aging properties of the nanocomposite films were also enhanced while the light transmittance decreased. Furthermore, the nanocomposites with the reactive kaolinite presented better performances than that with the reactive montmorillonite. Finally, the action mechanism of the reactive nanoclays to the performances of PMMA/reactive nanoclay nanocomposites was proposed.

Biofabrication of nanocomposite-based scaffolds containing human bone extracellularmatrix for the differentiation of skeletal stem and progenitor cells

Autograft or metal implants are routinely used in skeletal repair.However,they fail to provide long-term clinical resolution,necessitating a functional biomimetic tissue engineering alternative.The use of native human bone tissue for synthesizing a biomimeticmaterial inkfor three-dimensional(3D)bioprintingof skeletal tissueis anattractivestrategyfor tissueregeneration.Thus,human bone extracellular matrix(bone-ECM)offers an exciting potential for the development of an appropriate microenvironment for human bone marrow stromal cells(HBMSCs)to proliferate and differentiate along the osteogenic lineage.In this study,we engineered a novel material ink(LAB)by blending human bone-ECM(B)with nanoclay(L,Laponite®)and alginate(A)polymers using extrusion-based deposition.The inclusion of the nanofiller and polymeric material increased the rheology,printability,and drug retention properties and,critically,the preservation of HBMSCs viability upon printing.The composite of human bone-ECM-based 3D constructs containing vascular endothelial growth factor(VEGF)enhanced vascularization after implantation in an ex vivo chick chorioallantoic membrane(CAM)model.The inclusion of bone morphogenetic protein-2(BMP-2)with the HBMSCs further enhanced vascularization and mineralization after only seven days.This study demonstrates the synergistic combination of nanoclay with biomimetic materials(alginate and bone-ECM)to support the formation of osteogenic tissue both in vitro and ex vivo and offers a promising novel 3D bioprinting approach to personalized skeletal tissue repair.

Effects of Synthetic and Processing Methods on Dispersion Characteristics of Nanoclay in Polypropylene Polymer Matrix Composites

This work presents the effect of synthetic procedures (extrusion and casting) on the dispersion characteristics of nano layered silicate clay particles in the polypropylene (PP) polymer matrix. Three different molecular weights PP samples are taken and filled with nanoclay of 1 wt% and 3 wt%, and these nanocomposites were synthesized by using an extrusion or casting methods. The X-ray diffraction (XRD) and Transmission Electron Microscopy (TEM) is used to characterize the structure and morphology of nanocomposites. Rheological and mechanical results show that the extruded products are better than that of cast products. The outcome of this work is discussed in this paper.

Synthesis,characterization and evaluation of polyacrylamide graft starch/clay nanocomposite hydrogel system for enhanced oil recovery

In this paper the suitability of a graft polymer nanocomposite hydrogel system for enhanced oil recovery was examined using polyacrylamide graft starch/clay nanocomposite(a laboratory synthesized product) and chromium(III) acetate(crosslinker). X-ray diffraction analysis,Fourier transform infrared spectrometry analysis, field-emission scanning electron microscopy and transmission electron microscopy were carried out to reveal the laboratory synthesized product as a nanocomposite. The effects of various parameters like salt concentration, p H, temperature, polymer concentration and crosslinker concentration on the properties of the developed gel system were systematically evaluated.The thermal stability of the nanocomposite gel and the conventional gel system were also determined by thermogravimetric analysis. The graft polymer nanocomposite gel system exhibited acceptable gel strength, gelation time and gel stability compared with the conventional gel system. The nanocomposite gels prepared using a low crosslinker concentration showed higher gel strength and required longer gelation time than the conventional gel which is more desirable properties for the effective placement of gel during enhanced oil recovery operations. In addition, sand pack flooding experiments show that the graft polymer nanocomposite gels had better plugging capacity than the conventional gel systems under reservoir conditions. Hence, this gel system may be suitable in the water shutoff treatments required for enhanced oil recovery from oilfields.

Evaluation of self-healing properties of inhibitor loaded nanoclay-based anticorrosive coatings on magnesium alloy AZ91D

This study emphasizes on the evaluation and comparison of the anticorrosive properties of sol-gel coatings with and without inhibitor loaded nanocontainers.In this case,naturally available clay nanotubes(halloysite)were loaded with cationic corrosion inhibitors Ce 3+/Zr 4+.These nanocontainers were dispersed in hybrid organic-inorganic sol-gel matrix sol.Coating was applied on magnesium alloy AZ91D using the sols containing modified and unmodified nanocontainers employing the dip coating method and cured at 130℃for 1 h in air.Corrosion resistance of coated/uncoated substrates were analyzed using electrochemical impedance spectroscopy,potentiodynamic polarization and weight loss measurements after exposure to 3.5 wt%NaCl solution for varying time durations between 24 h to 120 h.Self-healing ability of coatings was evaluated by micro-Raman spectroscopy after 120 h exposure to 3.5 wt%NaCl solution.Coatings generated after dispersion of corrosion inhibitor loaded clay in hybrid sol-gel matrix have shown more promising corrosion resistance when compared to just the sol-gel matrix coatings,after prolonged exposure to corrosive environment.

Effect of organo-modified montmorillonite nanoclay on mechanical,thermal and ablation behavior of carbon fiber/phenolic resin composites

The mechanical,thermal and ablation properties of carbon phenolic(C-Ph)composites(Type-I)reinforced with different weight percentages of organo-modified montmorillonite(o-MMT)nanoclay have been studied experimentally.Ball milling was used to disperse different weight(wt)percentages(0,1,2,4,6 wt.%)of nanoclay into phenolic resin.Viscosity changes to resin due to nanoclay was studied.On the other hand,nanoclay added phenolic matrix composites(Type-II)were prepared to study the dispersion of nanoclay in phenolic matrix by small angle X-ray scattering and thermal stability changes to the matrix by thermogravimetric analyser(TGA).This data was used to understand the mechanical,thermal and ablation properties of Type-I composites.Inter laminar shear strength(ILSS),flexural strength and flexural modulus of Type I composites increased by about 29%,12%and 7%respectively at2 wt.%addition of nanoclay beyond which these properties decreased.This was attributed to reduced fiber volume fraction(%Vf)of Type-I composites due to nanoclay addition at such high loadings.Mass ablation rate of Type-I composites was evaluated using oxy acetylene torch test at low heat flux(125 W/cm^(2))and high heat flux levels(500 W/cm^(2)).Mass ablation rates have increased at both flux levels marginally up to 2 wt.%addition of nanoclay beyond which it has increased significantly.This is in contrast to increased thermal stability observed for Type-I and Type-II composites up to 2 wt.%addition of nanoclay.Increased ablation rates due to nanoclay addition was attributed to higher insulation efficiency of nanolcay,which accumulates more heat energy in limited area behind the ablation front and self-propagating ablation mechanisms triggered by thermal decomposition of organic part of nanoclay.

Resistance of Nanoclay Reinforced Epoxy Composites to Hyperthermal Atomic Oxygen Attack

Due to outstanding mechanical properties, heat resistance, and relatively facile production, nanoclay reinforced epoxy composites (NCRE composites) have been suggested as candi- date materials for use on external surfaces of spacecraft residing in the low Earth orbit (LEO) environment. The resistance of the NCRE composites to bombardment by atomic oxygen (AO), a dominant component of the LEO environment, has been investigated. Four types of samples were used in this study. They were pure epoxy (0 wt% nanoclay con- tent), and NCRE composites with di erent loadings of nanoclay|1 wt%, 2 wt%, and 4 wt%. Etch depths decreased with increasing nanoclay content, and for the 4 wt% samples it ranged from 28% to 37% compared to that of pure epoxy. X-ray photoelectron spectroscopy (XPS) indicates that after AO bombardment, relative area of C-C/C-H peak decreased, while the area of the C-O, ketones peaks increased, and the oxidation degree of surfaces increased. New carbon-related component carbonates were detected on nanoclay contain- ing composite surfaces. Scanning electron microscopy indicates that aggregates formed on nanoclay-containing surfaces after AO bombardment. The sizes and densities of aggregates increased with nanoclay content. The combined erosion depths, XPS and SEM results indi- cate that although all the studied surfaces got eroded and oxidized after AO bombardment, the nanoclay containing composites showed better AO resistance compared to pure epoxy, because the produced aggregates on surface potentially act as a physical “shield”, e ectively retarding parts of the surface from further AO etching.

Crosslinking as an Efficient Tool for Decreasing Moisture Sensitivity of Biobased Nanocomposite Films

Chitosan-nanoclay bio-hybrid films were successfully crosslinked with glutaraldehyde, genipin and glyoxal. Moisture sensitivity of films decreased as a result of crosslinking which led to improved barrier properties against water vapor and oxygen. Films containing chitosan (6.6 g/m2) with genipin (3.3 g/m2) and nanoclay (6.6 g/m2) had water vapor transmission rate of 72 g × 100 μm/(m2 × 24 h) which was 34% lower as compared to pure chitosan and 30% lower as compared to chitosan/nanoclay without crosslinkers. Glyoxal induced crosslinking resulted in 92% reduction in oxygen transmission rate at 80% relative humidity as compared to pure chitosan films. Oxygen transmission through glyoxal (3.3 g/m2) treated chitosan/nanoclay film was 2.8 cm3 × 100 μm/(m2 × 24 h) which was 53% lower as compared to chitosan/nanoclay without crosslinkers. In addition, nanoclay and especially glyoxal crosslinking prevented the water vapor sorption of chitosan considerably. Crosslinking may be used as an efficient tool for enhancing the exploitability of naturally hydrophilic biopolymers towards new high-value applications, such as food packaging.

Dynamic and buckling analysis of polymer hybrid composite beam with variable thickness

This work deals with a study of the dynamic and buckling analysis of polymer hybrid composite(PHC) beam. The beam has variable thickness and is reinforced by carbon nanotubes(CNTs) and nanoclay(NC) simultaneously. The governing equations are derived based on the first shear deformation theory(FSDT). A three-phase HalpinTsai approach is used to predict the mechanical properties of the PHC. We focus our attention on the effect of the simultaneous addition of NC and CNT on the vibration and buckling analysis of the PHC beam with variable thickness. Also a comparison study is done on the sensation of three impressive parameters including CNT, NC weight fractions, and the shape factor of fillers on the mechanical properties of PHC beams,as well as fundamental frequencies of free vibrations and critical buckling load. The results show that the increase of shape factor value, NC, and CNT weight fractions leads to considerable reinforcement in mechanical properties as well as increase of the dimensionless fundamental frequency and buckling load. The variation of CNT weight fraction on elastic modulus is more sensitive rather than shear modulus but the effect of NC weight fraction on elastic and shear moduli is fairly the same. The shape factor values more than the medium level do not affect the mechanical properties.

Environmental Stress Cracking Resistance of Halloysite Nanoclay-Polyester Nanocomposites

The environmental stress cracking resistance of halloysite nanoclay-polyester nanocomposites was investigated using fracture mechanics approach. The incorporation of halloysite nanoclay was found to improve the environmental stress cracking resistance of the nano-composites. The storage modulus of nano-composites measured by dynamic mechanical analysis increased remarkably as a function of halloysite nanoclay content. At 0.7 wt% nanoclay, the Tg improved from 72°C to 76°C. The fracture toughness increased up to 33% and time to failure improved 155% with the addition of 0.7 wt% of halloysite nanoclay. The maximum microhardness was found 119% higher for the same nano-filler concentration compared to monolithic polyester. The reinforcement with 1 wt% showed lower fracture toughness due to agglomerations of nanoclay which act as flaws. The presence of agglomerates weakened the bond between nano-particles and matrix hence reduces the environmental stress cracking resistance by halloysite nanoclay reinforcement.

UHMWPE/Nanoclay对改性沥青流变性能的影响

探讨由超高分子量聚乙烯和纳米黏土组成的聚合物纳米复合材料对沥青流变性能的影响。采用动态剪切流变仪和弯曲梁流变仪分别测定了中、高温和低温条件下纳米复合材料对沥青的改性效果。结果表明,纳米复合材料的使用,特别是4%的用量(按沥青的重量计算),提高了抗车辙疲劳开裂的能力,改性沥青的低温抗裂性能优于基质沥青。

Highly degradable chitosan-montmorillonite (MMT) nanocomposite hydrogel for controlled fertilizer release

Fertilizer consumption is increasing drastically along with the rapid expansion of farming in response to the ever-growing population. However, a significant portion of the nutrients in traditional fertilizers is lost during leaching and runoff causing economic loss and environmental threats. Polymer-modified controlled-release fertilizers provide an opportunity for mitigating adverse environmental effects and increasing the profitability of crop production. Here, we present a cheap and easy-to-fabricate controlled-release fertilizer excipient based on hydrogels scaffolded by safe and biodegradable chitosan and montmorillonite (MMT) nanoclays. By introducing elastic and flexible physical crosslinking induced by 2-dimensional (2D) MMT nanoflakes into the chitosan hydrogel, highly swellable and degradable chitosan-MMT nanocomposites were fabricated. The addition of MMT into the chitosan hydrogels enhanced the total release of phosphorous (P) and potassium (K), from 22.0 % to 94.9 % and 9.6% to 31.4 %, respectively, compared to the pure chitosan gel. The chitosan-MMT nanocomposite hydrogel achieved a well-controlled overall fertilizer release in soil. A total of 55.3 % of loaded fertilizer was released over 15 d with a daily release of 2.8 %. For the traditional fertilizer podwer, 89.2 % of the fertilizer was washed out during the first irrigation under the same setup. In the meantime, the nanocomposites improved the water retention of the soil, thanks to its excellent water absorbency. Moreover, the chitosan-MMT nanocomposite hydrogels exhibited high degradation of 57 % after swelling in water for 20 d. Such highly degradable fertilizer excipient poses minimal threat to the long-term fertility of the soil. The engineered Chitosan-MMT biopolymer scaffold as a controlled-release fertilizer excipient provides a promising opportunity for advancing sustainable agriculture.

Antifouling nanocomposite polymer coatings for marine applications:A review on experiments,mechanisms,and theoretical studies

Marine fouling is a worldwide challenge with huge damages on industrial structures,side effects on economics of industries,and environmental and safety-related hazards.Different approaches have been used for combating fouling in the marine environment.Meanwhile,nanocomposite polymer coatings are a novel generation of antifouling coatings with merits of toxin-free chemical composition and ease of large-scale application.Nanomaterials such as nano-metals,nano-metal oxides,metal-organic frameworks,carbon-based nanostructures,MXene,and nanoclays have antibacterial and antifouling properties in the polymer coatings.Besides,these nanomaterials can improve the corrosion resistance,mechanical strength,weathering stability,and thermal resistance of the polymer coatings.Therefore,in this review paper,the antifouling nanocomposite coatings are introduced and antifouling mechanisms are discussed.This review explicitly indicates that the antifouling efficiency of the nanocomposite coatings depends on the properties of the polymer matrix,the inherent properties of the nanomaterials,the weight percent and the dispersion method of the nanomaterials within the coating matrix,and the chemicals used for modifying the surface of the nanomaterials;meanwhile,the hybrids of different nanomaterials and appropriate chemical agents could be used to improve the antifouling behavior of the prepared nanocomposites.Moreover,the theoretical studies are introduced to pave the way of researchers working on theantifouling coatings,and the importance of the theoretical studies and computational modeling along with the experimental research is notified to develop antifouling coatings with high efficiency.

INVESTIGATION INTO MORPHOLOGY, MICROSTRUCTURE AND PROPERTIES OF SBR/EPDM/ORGANO MONTMORILLONITE NANOCOMPOSITES

Rubber compounds based on styrene-butadiene rubber/ethylene propylene diene monomer blends of different compositions （60/40, 70/30, 80/20, 90/10, 100/0） reinforced with 1 wt%, 3 wt%, 5 wt% and 7 wt% organoclay （Cloisite 20A） were prepared on a two roll mill via a vulcanization process and characterized by several techniques. Results of X-ray diffraction showed expansion of the inter-gallery distance, and transmission electron microscopy （TEM） micrographs confirmed that the prepared nanocomposite samples have intercalated and partially exfoliated structures. Cure characteristics showed that, organoclay not only accelerates the vulcanization reaction, but also gives rise to a marked increase of the torque, indicating crosslink density of the prepared compounds increases at the presence of organoclay. Mechanical properties of samples received markedly increase by clay loading due to the good interaction established between nanoclay particles and polymer matrix as it was evidenced by SEM photomicrographs. At the same time, rheological properties showed that addition of nanoclay could improve storage modulus as well as complex viscosity of SBR/EPDM samples. The results of ozone test revealed that the ozone resistance of samples significantly increases as nanoclay or EPDM content increases.

Intercalated 2D nanoclay for emerging drug delivery in cancer therapy

Natural two-dimensional （2D） kaolinite nanoclay has been incorporated into an emerging drug delivery system. The basal spacing of the kaolinite nanoclay was expanded from 0.72 to 4.16 nm through the intercalation of various organic guest species of different chain lengths, which can increase the efficiency in drug delivery and reduce the toxicity of doxorubicin （DOX）. Original kaolinite （Kaolin） and the Kaolin intercalation compounds exhibited a high level of biocompatibility and very low toxicity towards cells of pancreatic cancer, gastric cancer, prostate cancer, breast cancer, colorectal cancer, esophageal cancer, and differentiated thyroid cancer. However, lung cancer and hepatocellular cancer cells need more strict compositional, structural, and morphological modulations for drug delivery carriers. DOX-Kaolin and the DOX-Kaolin intercalation compounds showed dramatically faster drug release in moderately acidic solution than in neutral condition, and exhibited enhanced therapeutic effects against ten model cancer cell cultures in a dose-dependent manner. The use of 2D nanoclay materials for a novel drug delivery system could feasibly pave a way towards high-performance nanotherapeutics, with superior antitumor efficacy and significantly reduced side effects.

EFFECTS OF CHEMICAL MODIFICATIONS AND MMT NANOCLAY ADDITION ON TRANSPORT PHENOMENA OF NATURALLY WOVEN COCONUT SHEATH/POLYESTER NANOCOMPOSITES

Studies on the behavior of molecular transport properties such as thermal conductivity, gas permeability, volume and surface resistivity have been carried out for the naturally woven coconut sheath （CS） fiber reinforced composites with the addition of nanoclay and chemical treatment of fiber. The compression molding technique was used to fabricate the coconut sheath/clay reinforced hybrid composites. The morphological studies such as X-ray diffractogram （XRD）, transmission electron microscopy （TEM） and scanning electron microscopy （SEM） have been carried out for polyester nanocomposites and coconut sheath fiber. The decreased gas permeability, thermal conductivity and volume and surface resistivity have been observed with increasing the weight percentage of nanoclay in polyester matrix. In chemical modifications, the alkali and silane treated coconut sheath reinforced composites have shown great influence on the transport properties due to the increasing hydrophilic nature by the topographical changes at the fiber surface. Dielectric strength has also been reported in this paper for all types of composites. Infra-red （IR） spectra have also been taken to study the physical and chemical structural changes of treated coconut sheath.

Rheological and tribological approaches as a tool for the development of sustainable lubricating greases based on nano-montmorillonite and castor oil

This study investigates the development of novel montmorillonite/castor oil blends to formulate sustainable lubricating greases to promote the replacement of petrochemicals industry-derived materials by substances obtained from renewable sources.Specifically,the effect of the thickener concentration on the rheological,chemical,thermal,tribological properties,and atomic force microscopy(AFM)microstructure of these systems were studied.The results showed that the C20A nanoclay content could be used to modulate the viscosity values,the linear viscoelastic functions,and tribological properties of these montmorillonite dispersions.In general,these gel-like dispersions exhibited remarkable lubricant properties;the samples showed values of the friction coefficient and wear scars similar or lower than those obtained with model bentonite grease.

Accelerating Role of Clay in Photo-Oxidation of Polypropylene/Clay Multifilament Yarns

Photo-oxidative degradation of polypropylene/clay multifilament yarns containing different amounts of clay was investigated. These samples and pure polypropylene （PP） multifilametns were exposed to long wavelength radiations （λ〉 300 nm） under atmospheric condition of constant temperature and relative humidity. The photo-oxidative stability was studied using FTIR spectroscopy, tensile testing and microscopy. The results indicate that the addition of clay particles decreases the stability of PP/clay composites to photo-oxidative degradation according to comparison with pure PP. From FTIR study and tensile properties, it was also found that the multifilaments with higher clay loading reveals a faster loss of mechanical properties, higher photo-oxidative product formation and more reduction in the induction time of photo-oxidation. Moreover, the crack formation on surface of irradiated filaments corresponds well to the conclusions in tensile properties and FTIR characterization.

Mechanical, thermal and fire nanoclay/vinylester retardation behaviours of nanocomposites

The dispersion of montmorillonite （MMT） in vinylester for preparing nanoclay/vinylester gel coat was reported. Two sets of MMT/vinylester specimens, namely Type I and Type 2, were prepared for comparative studies. Type I specimens were prepared using ultrasonication only, and Type 2 specimens were prepared using both ultrasonication and twin-screw extrusion. According to XRD and TEM results, Type 2 specimens showed lower levels of nanoclay agglomeration and higher levels o! exfoliation. DSC results showed that the glass transition temperatures of Type 2 specimens are higher than those of Type 1 specimens. TGA results showed that the residual weight of 4 wt.% MMT/vinylester of Type 1 was 7.38%, while the corresponding value of Type 2 was 13,5%, indicating lower thermal degradation in the latter. MMTt vinylester/glass and MMT/vinylester/carbon specimens were fabricated and tested for mechanical and fire retardation behaviours. Type 2 based nanocomposite laminates showed greater values of ultimate tensile strength, flexural strength, interlaminar shear strength, impact strength, horizontal burning rate, and vertical burning rate than Type 1 based laminates. SEM images of tensile fractured surfaces revealed that Type 2 based laminates have no or less agglomeration of nanoclay than Type 1 based laminates.