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The research advances in rubber/halloysite nanotubes (rubber/HNTs) nanocomposites are reviewed. HNTs are environmentally-friendly natural nanomaterials, which could be used to prepare the rubber-based nanocomposites with high performance and low cost. Unmodified HNTs could be adopted to prepare the rubber/HNTs composites with improved mechanical properties, however, the rubber/HNTs nanocomposites with fine morphology and excellent properties were chiefly prepared with various modifiers by in situ mixing method. A series of rubber/HNTs nanocomposites containing several rubbers (SBR, NR, xSBR, NBR, PU) and different modifiers (ENR, RH, Si69, SA, MAA, ILs) have been investigated. The results showed that all the rubber/HNTs nanocomposites achieved strong interfacial interaction via interfacial covalent bonds, hydrogen bonds or multiple interactions, realized significantly improved dispersion of HNTs at nanoscale and exhibited excellent mechanical performances and other properties.

In this study, transparent poly(vinyl alcohol) (PVA) and PVA/halloysite nanotubes (HNTs) bionanocomposite films were prepared by solution casting and glutaraldehyde (GA) crosslinking. The surface topography and chemistry of the films were characterized by atomic force microscopy (AFM) and attenuated total reflection Fourier transform infrared (ATR-FTIR) spectroscopy, respectively. Blending with HNTs induced changes in nanotopography and surface chemistry of PVA films. The mechanical properties of PVA were enhanced by the incorporated HNTs. The stain-induced crystallization was confirmed by DSC after tensile test. MC3T3-E1 osteoblast-like and NIH 3T3 fibroblast cells were cultured on neat PVA and PVA/HNTs films to evaluate the effects of surface nanotopography and composition on cell behavior. The observations indicated that MC3T3-E1 cell behavior strongly responded to surface nanotopography. On nanotube-dominant surface, cells exhibited a significantly higher level of adhesion than on neat PVA film, whereas neat PVA showed higher degree of osteoblast proliferation compared with PVA/HNTs. In vitro fibroblasts response demonstrated that both neat PVA and PVA/HNTs nanocomposite films were biocompatible and PVA/HNTs films favored to fibroblasts attach and growth below 7.5 wt % of HNTs incorporated. In summary, these results provided insights into understanding of PVA and PVA/HNTs bionanocomposite films in potential applications in bone tissue engineering and drug delivery systems., ((c) 2009 Wiley Periodicals, Inc.)

ABSTRACT In this study, nanosheets including graphene oxide (GO) and reduced graphene oxide (rGO), were incorporated into natural rubber (NR), to study the effects of substituting GO or rGO for carbon black (CB) on the structure and performance of NR/CB composites. The morphological observations revealed the dispersion of CB was improved by partially substituting nanosheets for CB. The improvements in static and dynamic mechanical properties were achieved at small substitution content of GO or rGO nanosheets. With substitution of rGO nanosheets, significant improvement in flex cracking resistance was achieved. NR/CB/rGO (NRG) composites has a much lower heat build-up value compared with NR/CB/GO (NG) composites at a high load of nanosheets. However, both GO and rGO tended to aggregate at a high concentration, which led to the poor efficiency on enhancing the dynamic properties, or even deteriorate the performance of rubber composites. © 2015 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2015, 132, 41832. [ABSTRACT FROM AUTHOR]

Many recycled plastics are the polypropylene (PP)/poly(ethylene terephthalate) (PET) blends with PET as the minor component. The modification of such kinds of PP/PET blends for higher performance is essential as PP and PET are not thermodynamically compatible. In this study, the elastomer, SEBS- g-MAH, and the inorganics, halloysite nanotubes (HNTs) are chosen as the modifiers for the modification of a model PP/PET blend (90/10). The mechanical performance of such blend is optimized by the selective dispersion of the nanotubular HNTs into the interfacial region of the blends via a two-step process. Compared with the control one, the overall mechanical properties of the blend are substantially improved. The crystallization of PP in the blend is also facilitated by the selective dispersion of HNTs and the folding surface free energy is substantially increased. The substantially improved mechanical performance is interpreted according to the formation of the unique morphology. This study provides new insight in improving the performance of polymer blends via selectively dispersing the nanosized inorganics in the blend. © 2012 Wiley Periodicals, Inc. J. Appl. Polym. Sci., 2013 [ABSTRACT FROM AUTHOR]

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. [ABSTRACT FROM PUBLISHER]

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. [ABSTRACT FROM AUTHOR]

Optically transparent composites containing nanotubular clay up to 65 wt%, prepared by a facile “one-pot” process, exhibited high mechanical strength and heat resistance. The attractive characteristics of the composites, in addition to their transparency, include use of low-cost and nontoxic raw materials, easy scaling-up, and possible petroleum independence. The properties of the composites were ascribed to the strong interfacial interactions and the excellent dispersion of nanotubular clay. [ABSTRACT FROM AUTHOR]

Abstract: The nucleating ability of halloysite nanotubes (HNTs) towards isotactic polypropylene (iPP) was investigated by differential scanning calorimetry (DSC), X-ray diffraction (XRD), polarized optical microscopy (POM) and scanning electron microscopy (SEM). HNTs are identified to have dual nucleating ability for α-iPP and β-iPP under appropriate kinetics conditions. The formation of β-iPP is dependent on the HNTs loading in the iPP/HNTs composites. The composite with 20phr of HNTs is found to have the highest content of β-iPP. Under non-isothermal crystallization the content of β-iPP increases with decreasing of the cooling rate. The maximum β-crystal content is obtained at cooling rate of 2.5°C/min. The supermolecular structure of the β-iPP is identified as β-hedrites with flower-cup-like and axialite-like arrangements of the lamellae. Under isothermal crystallization the β-crystal can be formed in the temperature range of 115–140°C. Outside the temperature range, no β-iPP can be observed. The content of β-crystal reaches the maximum value at crystallization temperature of 135°C. The formation of the β-iPP in the composites is correlated to the unique surface characteristics of the HNTs. [Copyright &y& Elsevier]

Abstract: 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. [Copyright &y& Elsevier]

Abstract: Non-isothermal crystallization and the polymorphism of the PA6 and the polyamide 6/halloysite nanotubes (PA6/HNTs) nanocomposites are studied by adopting differential scanning calorimetry (DSC) analysis, X-ray diffraction (XRD) analysis and polarized optical microscopy (POM) observations. HNTs act as nucleating agent and accelerate the crystallization. The kinetics analysis indicates that the fold-surface free energy of PA6/HNTs nanocomposites is larger than that of neat PA6. The increasing tendency of the fold-surface free energy of PA6/HNTs nanocomposites is restricted at higher HNTs loading. Interestingly, the crystallinity of the PA6/HNTs nanocomposites increases with cooling rate. HNTs content is found to have a significant effect upon the crystallinity of the PA6/HNTs nanocomposites, and the crystallinity reaches its maximum with 5phr of HNTs content. Moreover, the higher HNTs content is, the larger percentage γ-phase crystals take up. The crystallization behavior of the PA6/HNTs nanocomposites is correlated with the multiple roles of HNTs in the crystallization of PA6. [Copyright &y& Elsevier]

Abstract: 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. [Copyright &y& Elsevier]

Abstract: Methacrylic acid (MAA) was used to improve the performance of styrene–butadiene rubber (SBR)/halloysite nanotubes (HNTs) nanocomposites by direct blending. The detailed interaction mechanisms of MAA and the in situ formed zinc methacrylate (ZDMA) were revealed by X-ray diffraction (XRD), surface area and porosity analysis, X-ray photoelectron spectroscopy (XPS) together with crosslink density determination. The strong interfacial bonding between HNTs and rubber matrix is resulted through ZDMA and MAA intermediated linkages. ZDMA connects SBR and HNTs via grafting/complexation mechanism. MAA bonds SBR and HNTs through grafting/hydrogen bonding mechanism. Significantly improved dispersion of HNTs in virtue of the interactions between HNTs and MAA or ZDMA was achieved. Effects of MAA content on the vulcanization behavior, morphology and mechanical properties of the nanocomposites were investigated. Promising mechanical properties of MAA modified SBR/HNTs nanocomposites were obtained. The changes in vulcanization behavior, mechanical properties and morphology were correlated with the interactions between HNTs and MAA or ZDMA and the largely improved dispersion of HNTs. [Copyright &y& Elsevier]

The article presents a study which modified a natural clay halloysite, an aluminosilicate with a predominantly nanosized hollow tubular structure, by polymers achieving polymer-halloysite composite nanotubes. The composite nanotubes were developed to a core-shell coaxial structure after the interior cavity was covered by the polymer. Polymeric nanotubes and nanowires were derived after dissolution of the halloysite template.

Abstract: A co-coagulation process was utilized to prepare carboxylated butadiene–styrene rubber (xSBR)/halloysite nanotube (HNT) nanocomposites. The interfacial interaction, morphology, and the mechanical performance of the nanocomposites were investigated. Attenuated total reflection Fourier transform infrared spectroscopy (ATR-FTIR) and X-ray photoelectron spectroscopy (XPS) results indicate the formation of hydrogen bonding between xSBR and HNTs. Lower content of HNTs tends to delay the vulcanization of xSBR/HNT compounds, while higher HNT loading promotes the vulcanization. It is shown that HNTs are dispersed individually and uniformly in the matrix with strong interfacial bonding. The mechanical properties, especially the modulus and hardness, are significantly increased by the inclusion of HNTs. The significant reinforcing effects of HNTs are correlated to the co-coagulation process and strong interfacial interactions via hydrogen bonding. [Copyright &y& Elsevier]

Natural occurred nanotubes, halloysite nanotubes, were modified by silane and incorporated into epoxy resin to form nanocomposites. The morphology of the nanocomposites was characterized by transmission electron microscopy (TEM). Dynamic mechanical analysis (DMA) and thermogravimetric analysis (TGA) were performed on the nanocomposites. Flexural property and coefficient of thermal expansion (CTE) of the nanocomposites were also determined. Comparing with the neat resin, about 40% increase in storage modulus at glassy state and 133% at rubbery state were achieved by incorporating 12 wt% modified HNTs into the epoxy matrix. In addition, the nanocomposites exhibited improved flexural strength, char yield and dimensional stability. TEM examination revealed a uniform dispersion of the nanotubes in the epoxy resin. The remarkably positive effects of the HNTs on the performance of the epoxy resin were correlated with the unique characteristics of the HNTs, the uniform dispersion and the possible interfacial reactions between the modified HNTs and the matrix. [ABSTRACT FROM AUTHOR]

The article reports a research study of the construction of a filler network to reinforce crystalline plastics, through the use of a self-assembly process using hydrogen bonding. Naturally-occurring halyosite nanotubes and silica are used as inorganic hydrogen-bonding couplers (IHC), because they offer specific sites for unpaired electron exchange. Organic species used as organic hydrogen-bonding couplers (OHC) include melamine, melamine cyanurate, and diphenyl guanidine. Paired IHC and OHC form a strong inorganic network using hydrogen bonds.

Abstract: Naturally occurred halloysite nanotubes (HNTs) with hollow nanotubular structures were used as a new type filler for poly(propylene) (PP). Nanocomposites based on PP and HNTs were prepared by melt blending. Scanning electronic microscopy (SEM) results suggested HNTs were dispersed in PP matrix evenly at nanoscale after facile modification. Thermal stability of the nanocomposites was found remarkably enhanced by the incorporation of HNTs. Cone calorimetric data also showed the decrease of flammability of the nanocomposites. Entrapment mechanism of the decomposition products in HNTs was proposed to explain the enhancement of thermal stability of the nanocomposites. The barriers for heat and mass transport, the presence of iron in HNTs, are all responsible for the improvement in thermal stability and decrease in flammability. Those results suggested potential promising flame retardant application of HNTs in PP. [Copyright &y& Elsevier]

The exploitation of generic strategy for preparation of conductive elastomer composites with interconnected filler network is of significant scientific and technical interests. Herein, we report a novel, green and effective strategy to prepare conductive natural rubber (NR) composites with interconnected graphene network structure. It is found that the Pickering emulsion template is effective in constructing 3D interconnected graphene oxide (GO) networks while the thermal treatment during hot pressing step is able to convert GO to conductive thermal reduced graphene (TRG). This strategy does not rely on the toxic and corrosive reducing agents and the adopted solvents in Pickering emulsions can be recycled and reused, which makes the process environmentally friendly. As a result, interconnected graphene network is well constructed within NR matrix, which significantly enhances the electrical conductivity, mechanical properties and lowers the percolation threshold of the resulted composites. Specifically, with the incorporation of 1.90 vol% TRG, the electrical conductivity of NR composites with interconnected graphene network structure is more than 7 orders of magnitude higher than that of NR composites with uniform graphene dispersion. More intriguingly, this GO stabilized Pickering emulsion template strategy can also be used to realized the selective distribution of carbon nanotubes and assemble them into interconnected network structure, further facilitating the conductivity improvement of the resulted composites. Overall, we envision that the present work offers new insights into the design of conductive elastomer composites. [ABSTRACT FROM AUTHOR]

Abstract: In this contribution, halloysite nanotubes (HNTs), a kind of natural hydrophilic nanoclay, are incorporated into polypropylene (PP) for tailoring the surface microstructures of the composites prepared by solution casting. HNTs act as heterogeneous nuclei for PP, which leads to the change of phase separation process during drying of the composites and consequently the microstructures of composite surfaces. Micro-papilla like hybrid spherulites with nanostructures are formed on the PP/HNTs composite surfaces. The rough surfaces demonstrate superhydrophobicity with a maximum water contact angle as nearly 170° and sliding angle of about 2°. The spherulites size, surface roughness, and wetting property of PP can be tuned by HNTs. HNTs can significantly improve the thermal degradation behavior of the composites which is attributed to the well-dispersed HNTs and the improved interfacial interactions by the nucleation effect. The present work provides an alternative routine for preparing polymer superhydrophobic surfaces via tailoring the surface microstructures by adding nanoparticles in a solution process. [ABSTRACT FROM AUTHOR]