Benzothiazole sulfide compatibilized polypropylene/halloysite nanotubes composites

Clay-philic benzothiazole sulfide, capable of donating electrons, is grafted onto polypropylene (PP) backbones when N-cyclohexyl-2-benzothiazole sulfonamide (CBS), a commonly used accelerator in the tire industry, is included in the processing of PP/halloysite nanotubes (HNTs) composites. CBS decomposes at elevated temperature and yields benzothiazole sulfide radicals, which react with the PP polymeric free radicals generated during the processing of the composites. On the other hand, the benzothiazole group of CBS is reactive to HNTs via electron transferring. The compatibilization between HNTs and PP is thus realized via interfacial grafting and electron transferring mechanism. The interfacial interactions in the compatibilized systems were fully characterized. Compared with the control sample, the dispersion of HNTs and the interfacial bonding are enhanced substantially in the compatibilized composites. The significantly improved mechanical properties and thermal properties of benzothiazole sulfide compatibilized PP/HNTs composites are correlated to the enhanced interfacial property. The present work demonstrates a novel interfacial design via interfacial grafting/electron transferring for the compatibilization of PP/clay composites.     

Styrene-butadiene rubber/halloysite nanotubes nanocomposites modified by sorbic acid

Sorbic acid (SA) was used to improve the performance of styrene-butadiene rubber (SBR)/halloysite nanotubes (HNTs) nanocomposites by direct blending. The detailed mechanisms for the largely improved performance were studied by X-ray photoelectron spectroscopy (XPS), X-ray diffraction (XRD), differential scanning calorimetry (DSC), porosity analysis and crosslink density determination. The strong interfacial bonding between HNTs and rubber matrix is resulted through SA intermediated linkages. SA bonds SBR and HNTs through grafting copolymerization/hydrogen bonding mechanism. Significantly improved dispersion of HNTs in virtue of the interactions between HNTs and SA was achieved. Formation of zinc disorbate (ZDS) was revealed during the vulcanization of the composites. However, in the present systems, the contribution of ZDS to the reinforcement was limited. Effects of SA content on the vulcanization behavior, morphology and mechanical properties of the nanocomposites were investigated. Promising mechanical properties of SA modified SBR/HNTs nanocomposites were obtained. The changes in vulcanization behavior, mechanical properties and morphology were correlated with the interactions between HNTs and SA and the largely improved dispersion of HNTs.     

Preparation and characterization of large-size halloysite nanotubes particles by a combined technique of interfacial polymerization and condensation polymerization

To granulate halloysite nanotubes (HNTs) into large-size particles, interfacial polymerization and condensation polymerization were combined. The former was used to form surface layer of particles and the latter was used to improve particle strength. Polyethylenimine (PEI) and terephthaloyl chloride were chosen, respectively as hydrophilic monomer and hydrophobic monomer in interfacial polymerization. Condensation polymerization was carried out between PEI and glycerol polyglycidyl ether (GPE). The results show that HNTs particles have sphere shape and its diameters range from 1.7 to 2.5 mm and vary with preparation condition. SEM images show that particles have typical core–shell structure with dense surface layer and porous inner structure and single nanotube is completely encapsulated by polymer material. The characterization of BET shows that because of dense surface layer and encapsulation of nanotubes, the specific surface area of particles determined decreases dramatically.     

Structure and Properties of Poly(vinyl chloride)/Halloysite Nanotubes Nanocomposites

Poly(vinyl chloride)(PVC)/halloysite nanotubes (HNTs) nanocomposites were prepared by melt blending. The effects of HNT content on the mechanical properties, morphology, and rheological properties of the nanocomposites were investigated. The results showed that HNTs were effective in toughening and reinforcing PVC nanocomposites. The notched impact, tensile and flexural strength, and flexural modulus of the nanocomposites were remarkably increased compared with those for the pure PVC. Scanning electron microscopy (SEM) results illustrated the ductile behavior of the nanocomposites, with a possible cavitation mechanism. Transmission electron microscopy (TEM) results showed that HNTs were uniformly dispersed in the PVC matrix. Interfacial interaction of hydrogen bonding between the HNTs and PVC matrix was substantiated. The plasticization times of PVC/HNTs nanocomposites were found to be shorter and the equilibrium torque was higher than that for the pure PVC.     

Silver nanoparticle supported on halloysite nanotubes catalyzed reduction of 4-nitrophenol (4-NP)

The silver nanoparticles with about 10 nm diameter were immobilized onto the halloysite nanotubes (HNTs) via the in situ reduction of AgNO₃ by polyol process. The silver nanoparticles supported halloysite nanotubes (Ag/HNTs), with Ag content of about 11%, were used for the catalyzed reduction of 4-nitrophenol (4-NP) with NaBH₄ in alkaline aqueous solutions. The effect of the reduction of 4-NP catalyzed by the catalysts in the presence of variable concentration NaBH₄ was investigated. It was found that the reduction rate increased with the increasing of the amounts of NaBH₄. And the larger amounts of NaBH₄ reduced the induction time.     

Preparation,Properties and Applications of Chitosan-Based Biocomposites/Blend Materials: A Review

Taking inspiration from many published chitosan (Cs)-based biocomposites, this article is written to highlight the significant effect of reinforcing and/or blending Cs polymer with the different constituents to increase various properties (mechanical, hydrophilic, thermal, adsorption ability and stability) of Cs without sacrificing any of its positive properties. It is concluded that the properties of Cs biocomposites with a synthetic constituent have contributed to its rigidity since only mechanical interaction occurred at the interfacial region. Instead of physical interactions, the addition of an organic constituent also promoted the chemical interactions at the interfacial region of the Cs biocomposites. This consequently produced Cs biocomposites with synthetic constituents with relatively low strength and stiffness but high resistance to fracture, whereas the ones with an organic constituent have high strength and stiffness but are very brittle. This review also screens the current applications of Cs-based biocomposites in the field of drug delivery, tissue engineering, antibacterial, food packaging, biomedical, metal adsorption and dye removal.     

Halloysite nanotubes grafted hyperbranched (co)polymers via surface-initiated self-condensing vinyl (co)polymerization

Halloysite nanotubes (HNTs) grafted hyperbranched polymers were prepared by the self-condensing vinyl polymerization (SCVP) of 2-((bromoacetyl)oxy)ethyl acrylate (BAEA) and the self-condensing vinyl copolymerization of n-butyl acrylate (BA) and BAEA with BAEA as inimer (AB*) respectively, from the surfaces of the 2-bromoisobutyric acid modified halloysite nanotubes (HNTs-Br) via atom transfer radical polymerization (ATRP) technique. The halloysite nanotubes grafted hyperbranched polymer (HNTs-HP) and the halloysite nanotubes grafted hyperbranched copolymer (HNTs-HCP) were characterized by elemental analysis (EA), Fourier transform infrared (FTIR), thermogravimetric analysis (TGA), X-ray diffraction (XRD), and transmission electron microscope (TEM). The grafted hyperbranched polymers were characterized with Nuclear magnetic resonance (NMR) and the molecular ratio between the inimer AB* and BA in the grafted hyperbranched copolymers was found to be 3:2, calculated from the TGA and EA results.     

Improving of the adsorption capacity of halloysite nanotubes intercalated with dimethyl sulfoxide

Algerian halloysite intercalated with dimethyl sulfoxide (DMSO) was prepared. The starting (H) and resulting (H-DMSO) materials were characterized by X-ray powder diffraction, Fourier transformed infrared spectroscopy, thermal analysis, transmission electron microscopy, pore-size distribution analysis, and employed as crystal violet (CV⁺) adsorbents from aqueous solutions. Intercalation reaches a rate of 95% and increases the basal spacing to 11.2 Å. (CH₃)₂SO interacts with the inner surface hydroxyls of halloysite through new hydrogen bonds with the S=O groups. The release of DMSO occurs in two phases: a partial elimination at 195 °C and a second part due to the DMSO combustion at 277 °C. The TEM image of H-DMSO reveals halloysite nanotubes (HNTs) polydisperse in length and diameter. A heterogeneous distribution in the nanotube size was highlighted with pore diameters of 10–11, 20.6, 28.6, and 37.0 nm, in correlation with transmission electron microscopy. The Redlich–Peterson equation describes efficiently the CV⁺ adsorption onto the modified sample. H-DMSO adsorbs 93.6 against 50.9 mg g^?1 for the starting material. This improving of the adsorption capacity of DMSO-intercalated HNTs, was explained via the behavior of the intercalated DMSO molecules. Intercalation constitutes a key procedure for developing new nanocomposites, attractive in technological applications, such as effective adsorbents.     

Controlling surface plasmon excitation of pair arrays of metallic nanocylinders

The polyvinyl alcohol (PVA)/halloysite nanotubes (HNTs) solution were prepared with the aid of ultrasonic treatment. The composite films were prepared through casting or coagulating the PVA/HNTs solution. The coagulation process was employed to obtain a composite film without aggregation of HNTs. It is shown that the particle size and distribution of HNTs in the PVA/HNTs solution is independent of the ratio between HNTs and PVA. It is also revealed that the aggregation of HNTs takes place during the drying process of the as cast film. Compared with the film by coagulation method, the HNTs in the as cast film show less profound effect on the nucleation of the crystallization of the PVA. The crystallization temperature initially increases with HNTs loading and overloading of HNTs tend to depress the improvement in the crystallization temperature. The glass transition temperature (T_g) of the composite film decreases with HNTs loading and the aggregation process shows practically no effect on the T_g. Inclusion of HNTs greatly depresses the decomposition of the PVA backbone, while it is not effective for improving the resistance to the abstraction of the side groups. The aggregation process at low concentration of HNTs has more significant effect on the thermal decomposition of composite films compared with that at high concentration. PACS 61.82.Pv; 61.46.Fg; 61.46.-w; 68.37.Lp; 67.80.Gb     

Adsorption of Ionic Liquid onto Halloysite Nanotubes: Mechanism and Reinforcement of the Modified Clay to Rubber

An ionic liquid (IL), 1-butyl-3-methyl-imiazolium hexafluorophosphate [BMIm]PF₆, was coated onto halloysite nanotubes (HNTs) in tetrahydrofuran–water mixture. The IL layers on the HNTs were confirmed by thermogravimetric analysis, diffuse reflectance infrared Fourier transform spectroscopy, determination of contact angle, and porosity analysis. The interaction between IL and HNTs, proposed to be hydrogen bonding, was verified by various spectral results such as Raman spectroscopy, nuclear magnetic resonance and X-ray photoelectron spectroscopy. Because of their interaction, the crystallization behavior of IL in the presence of HNTs was found to be changed, as indicated by the results of differential scanning calorimetry. The IL-coated HNTs (m-HNTs) were used as reinforcement for styrene–butadiene rubber. Compared with the compounds with uncoated HNTs, the uncured compounds with m-HNTs showed faster curing, and the resulting vulcanizates showed substantially higher tensile strength and much lower hardness. The unique changes in the compounds are correlated to the changes in filler dispersion and interaction between IL and HNTs.     

Templated synthesis of plate-like MoS<Subscript>2</Subscript> nanosheets assisted with HNTs and their tribological performance in oil

Two-dimensional MoS₂ nanosheets were synthesized by using halloysite nanotubes (HNTs) as template under the hydrothermal synthesis. The structure and morphology of the as-synthesized MoS₂ nanosheets were determined by a series of characterizations. The results showed that the as-synthesized MoS₂ nanosheets were of the plate-like structure with about five layers, and the basal spacing was about 0.63 nm. It was demonstrated that HNTs played a crucial template role in the formation of the plate-like MoS₂ nanosheets. The formation mechanism was proposed. Furthermore, the tribological performance of the as-prepared MoS₂ nanosheets in oil was intensively examined on the ball-on-ball wear tester. The testing results verified that the as-prepared MoS₂ nanosheets as additive could significantly improve the friction performance of oil, which exhibited the good antifriction, antiwear, and load-carrying properties.     

Kenaf/polypropylene biocomposites: effects of electron beam irradiation and alkali treatment on kenaf natural fibers

Thermal and dynamic mechanical properties of kenaf natural fiber reinforced polypropylene (PP) biocomposites were examined to compare the effects of natural fiber treatment by electron beam irradiation (EBI) and alkalization. The alpha cellulose contents, the functional groups on the surfaces and the thermal stability of the untreated and treated kenaf fibers were studied. Kenaf fiber/polypropylene(PP) biocomposites were fabricated by means of a compression molding technique using chopped kenaf fibers treated with electron beam (EB) dosages of 100, 200, 500 kGy or with NaOH concentrations of 2, 5, 10 wt%, respectively. The thermal stability, the dynamic mechanical and the interfacial properties of untreated and treated kenaf/PP biocomposites were also investigated through a thermogravimetric analysis, a dynamic mechanical analysis and a fractographic observation, respectively. The results show that the characteristics of kenaf fibers and biocomposites depended on the different treatment level with the EB dosages or on the NaOH concentrations used. In this study, the modification of kenaf fiber surfaces at 200 kGy EBI and treatment with 5 wt% NaOH was most effective for improving the performance of kenaf/PP biocomposites. This study suggests that EBI can be used for modification of natural fiber as an environmentally friendly process and contribute to an improvement in the performances of kenaf/PP biocomposites.     

Henequen/poly(butylene succinate) biocomposites: electron beam irradiation effects on henequen fiber and the interfacial properties of biocomposites

Henequen natural fiber-reinforced poly(butylene succinate) biocomposites were prepared through a resin microdroplet formation on a single fiber and also fabricated by a compression molding technique using chopped henequen fibers, surface-treated with electron beam irradiation (EBI) at various dosages. The effect of EBI treatment on the surface characteristics and dynamic mechanical properties of henequen fibers was investigated using SEM, XPS and DMA methods, respectively. Also, the interfacial behavior of biocomposites was explored through a single fiber microbonding test and fracture surface observations. The result indicates that the interfacial shear strength (IFSS) of biocomposites greatly depends on the EBI treatment level on the henequen fiber surface. This study also suggests that appropriate modification of natural fiber surfaces at an optimum EBI dosage significantly contributes to improving the interfacial properties of biocomposites.     

Novel Jute/Polycardanol Biocomposites: Effect of Fiber Surface Treatment on Their Properties

In the present study, novel biocomposites with chopped jute fibers and thermosetting polycardanol were prepared using compression molding technique for the first time. Prior to biocomposite fabrication, jute fiber bundles were surface-treated at various concentrations using 3-glycidoxypropyltrimethoxy silane (GPS) and 3-aminopropyltriethoxy silane (APS), respectively. The interfacial shear strength, flexural properties and thermal properties of jute/polycardanol biocomposites reinforced with untreated and silane-treated jute fibers were investigated by means of single fiber microbonding test, three-point flexural test, dynamic mechanical analysis, thermogravimetric analysis and thermomechanical analysis. Both GPS and APS treatments played a role in improving the interfacial adhesion, reflecting that the organofunctional groups located at the end of silane coupling agents may contribute to linking between jute fibers and a polycardanol resin. As a result, it gave rise to increased interfacial shear strength of the biocomposites. Such interfacial improvement also led to increasing the flexural strength and modulus, storage modulus, thermal stability and thermomechanical stability.     

Preparation of Halloysite Nanotubes/Polystyrene (HNTs/PS) Core‐shell Particles via Soap‐less Microemulsion Polymerization

Halloysite nanotubes/polystyrene (HNTs/PS) inorganic/organic core‐shell particles were prepared via a convenient soap‐less microemulsion polymerization. The inorganic cores were pre‐treated with allyl alcohol (AA) and the polymer shells were prepared successfully by the facile soap‐less microemulsion polymerization of styrene (St) with the allyl alcohol‐modified halloysite nanotube (AA‐HNT) nanoparticles as seeds, and potassium persulfate (KPS) as initiator in water. The products were characterized by Fourier transform infrared spectroscopy (FTIR) and thermogravimetric analysis (TGA). The morphologies of the HNTs/PS core‐shell particles were characterized by transmission electron microscopy (TEM). The mechanism of the nucleation is also mentioned.     

Thermal and Tensile Properties of Epoxy Nanocomposites Reinforced by Silane-functionalized Multiwalled Carbon Nanotubes

Epoxy nanocomposites with unmodified multiwalled carbon nanotubes (u-MWCNTs) and silanized multiwalled carbon nanotubes (si-MWCNTs) were prepared by a cast molding method. The effects of 3-aminopropyltriethoxysilane functionalization of MWCNTs on thermal, tensile, and morphological properties of the nanocomposites were examined. The nanocomposites were characterized by thermogravimetric analysis, dynamic mechanical thermal analysis, and tensile testing. The results showed that epoxy composites based on si-MWCNTs showed better thermal stability, glass transition temperature, and tensile properties than the composites based on u-MWCNTs. These results prove the effect of silane functionalization on the interfacial adhesion between epoxy and MWCNTs. This was further confirmed by morphology study of fractured surfaces of nanocomposites by field emission scanning electron microscopy.     

Mesoscale simulation of aggregation of imogolite nanotubes from potential of mean force interactions

The aggregation of colloidal clay mineral particles plays an important role in controlling the mechanical and transport properties of soils. Interactions and aggregation of plate-like montmorillonite particles were previously studied with the help of Molecular Dynamics (MD) simulation. This paper investigates the aggregation of cylindrical imogolite-like phyllosilicate nanotubes. Nano-scale MD simulations are carried out to find the potential of mean force between two nanotubes. This PMF is then used in a mesoscale simulation that represents interactions between elemental nanotubes through coarse-graining. We investigate the distribution of water molecules around the curved surfaces, and the effects of the surface charge density and tube length on aggregation. Shorter nanotubes were found to form larger stacks.     

Nanofilled Polypropylene/Poly(trimethylene terephthalate) Blends: A Morphological and Mechanical Properties Study

Polypropylene (PP) /poly(trimethylene terephthalate), (PTT), binary blends in the presence of two interfacial modifier as well as two organically modified nanoclay additives were studied in terms of mechanical and morphological characteristics. Scanning electron microscopy confirmed the incompatibility of the system which was solved to some extent through incorporating the nanoclay as well as functional compatibilizers. An evaluation of the specimens via static mechanical tests in tensile mode gave credence to the assumption that the higher the PTT content, the higher the mechanical performance would be. Furthermore, the compatibilizer-containing blends not only exhibited higher toughness, but also possessed enhanced stiffness when a maleated compatibilizer was added. The tensile modulus was promoted further in the presence of clay nanoparticles; however, toughness was somewhat sacrificed. The Barentsen as well as Halpin-Tsai models were found to describe the binary blends modulus. The reinforcing impact of the nanoclay was exploited to a greater degree in the presence of the compatibilizer.     

Cellulose-based biocomposites: comparison of different multiphasic systems

Biocomposites (biodegradable composites) are obtained by blending biodegradable polymers and fillers. Since the main components are biodegradable, the composite as a whole is also expected to be biodegradable. This paper presents various biocomposites that have been elaborated with cellulose or lignocellulose fibers from diverse sources, with different lignin contents. This paper is targeted on the analysis of 'fiber–matrix' interactions of two types of biocomposites based on agropolymer (plasticized wheat starch) and biopolyester (polybutylene adipate-co-terephthalate), named APB and BPB, respectively. Processing and main properties of both biocomposites are shown and compared. Polyolefin-based composite (PPC), which is known to present very poor 'fiber–matrix' interactions, is used as a reference. Through the Young's modulus, mechanical properties have shown that the reinforcement, by increasing fiber content, is much more significant for APB compared to BPB. The evolution of chains mobility, evidenced through shift of T _g values, according to the increase in fiber content and thence in interfacial area, have shown that the fiber–matrix interactions are higher for APB. BPB presents intermediate values, higher than PPC ones. These results are in agreement with the analysis of the composite morphologies performed by SEM on cryogenic fractures. Finally, by determining the theoretical works of adhesion and the interfacial tensions from contact angle measurements, it is shown that these parameters are partially able to predict the level of interaction between the fibers and the matrix. We could show that the perspectives of such work seem to be of importance to tailor new materials with a controlled end-use.     

Micromechanical Behavior of Carbon Nanotube-Covered SiC Fibers in Polymer Matrix Composites

The incorporation of nanotube-covered fibers in continuous fiber/epoxy composites has been shown to influence the mechanical, electrical, and thermal properties of the composite. Increased interlaminar shear stress, flexural strength and modulus have been reported in such composites over composites containing bare fibers. In this study, the microstructure and interfacial shear strength (ISS) of continuous silicon carbide fiber/epoxy composites with and without nanotubes grown from the SiC fiber surface were investigated with micro-Raman spectroscopy (MRS) and microscopy. The fibers with nanotubes grown from the surface were found to have a reduced ISS compared with the bare fibers. Electron microscopy showed good wetting of epoxy in the nanotube forests, but poor attachment of the nanotube forests to the fibers. These results suggest that the mechanism leading to improvements in bulk composite properties is not due to an improvement in the fiber/matrix ISS.