Partial Exfoliation Research Articles

High Density Polyethylene/Pistachio Shell Flour/Nanoclay Composites - Effect of Accelerated Weathering Conditions on Mechanical Properties, Relative Brightness and Total Colour Change

This study investigates the effect of the addition of nanoclay (Cloisite 20A) on some mechanical properties, % relative brightness (ΔLrel) and total colour change (ΔEab) of high density polyethylene (HDPE)/pistachio shell flour (PSF) composites when exposed to accelerated weathering conditions. X-ray diffraction (XRD) patterns of samples containing 3 and 6 per hundred composite (phc) of nanoclay indicated partial exfoliation and intercalation. The tensile modulus and tensile strength of HDPE/PSF composites (without nanoclay) decreased when the exposure time increased to 1500 h, while the tensile modulus and tensile strength increased. For samples with nanoclay, ΔLrel and ΔEab increased upon accelerated weathering conditions up to 500 h, and thereafter remained constant. But results show that ΔLrel and ΔEab increased significantly upon accelerated weathering exposure in HDPE/PSF samples up to 1500 h. Scanning electron microscopy (SEM) results after 1500 h exposure to weathering condition showed signs of the presence of cracks in samples without nanoclay, unlike the samples with nanoclay.

A new micromechanical approach for the preparation of graphene nanoplatelets deposited on polyethylene

An advantageous micromechanical technique to deposit large area graphene nanoplatelet (GNP) thin films on a low-density polyethylene substrate is proposed. This method is based on the application of shear-stress and friction forces to a graphite platelets/ethanol paste on the surface of a polymeric substrate; it allows us to obtain a continuous film of superimposed nanoplatelets mainly made of 13–30 graphene layers. X-ray diffraction (XRD), atomic force and transmission electron microscopy (TEM) measurements support the occurrence of a partial exfoliation of the graphite platelets due to shear-stress and friction forces applied during film formation. Scanning electron microscopy (SEM) observations point out that the surface of the polymer is uniformly coated by the overlap of GNPs, and TEM analysis reveals the tendency of the nanoplatelets to align parallel to the interface plane. It has been found that the deposited samples, under white light illumination, exhibit a negative photoconductivity and a linear photoresponse as a function of the applied voltage and the optical power density in the −120 ÷ 120 mV and 20.9 ÷ 286.2 mW cm−2 ranges, respectively.

Fluorinated exfoliated graphite as cathode materials for enhanced performances in primary lithium battery

Accordion-like graphites prepared by exfoliation of a low temperature graphite fluoride were fluorinated using F2 gas at various temperatures. The fluorinated exfoliated graphite exhibits unusual dual CF bonding, i.e. weakened covalent and covalent. This bonding allows the discharge potential at the beginning of the electrochemical processes to be increased. Moreover, the accordion-like texture avoids partial exfoliation and loss of the electrical contact for some parts of the electrode, and allows the growth of LiF particles in the opened macro-porosity.

Emulsion-mediated synthesis of hierarchical mesoporous-macroporous Al-Mg hydrotalcites

A new sol-gel method mediated by the use of paraffin emulsions is presented for the synthesis of hierarchical mesoporous-macroporous Al-Mg hydrotalcites. Prior to the synthesis, the construction of ternary diagrams for paraffin/surfactant/ethanol helped to identify the most suitable compositional synthesis domain. Two distinct regions, denoted L1 (transparent microemulsion) and L2 (opaque emulsion) were identified for low and high concentrations of paraffins, respectively. The ternary diagrams revealed some features: i) n-hexane (C6) had the smallest L2 region; ii) the high viscosity of n-octadecane (C18) did not allow control of phase separation, and iii) the most suitable paraffin for the use as the emulsifier was the intermediate-sized n-dodecane (C12). The use of paraffin in concentrations included in the L1 region did not contribute to the creation of pores, but the emulsion templating in the L2 region led to hierarchical porous hydrotalcites when were calcined up to 250 °C having enhanced textural properties and presenting mesopores and macropores with mean sizes of 0.02 and 1 μm, respectively. The slit-like shaped mesopores were caused by the partial exfoliation of hydrotalcite layers unordered packed around the emulsion droplets, while the macropores arose from voids left by the droplets after thermal treatment. The singular textural properties of the studied Al-Mg hierarchical porous hydrotalcites turns the emulsion mediated-synthesis a potential method to obtain more efficient catalysts to be used in process involving bulky molecules.

Photoinduced formation of thiols in human hair

Raman, scanning electron, and optical microscopy of hair and spectrophotometry of soluble hair proteins are used to study the effect of UV-vis radiation on white hair. The samples of a healthy subject are irradiated using a mercury lamp and compared with non-irradiated (control) hair. The cuticle damage with partial exfoliation is revealed with the aid of SEM and optical microscopy of semifine sections. Gel filtration chromatography shows that the molecular weight of soluble proteins ranges from 5 to 7kDa. Absorption spectroscopy proves an increase in amount of thiols in a heavier fraction of the soluble proteins of irradiated samples under study. Raman data indicate a decrease in the amount of SS and CS bonds in cystines and an increase in the amount of SH bonds due to irradiation. Such changes are more pronounced in peripheral regions of hair. Conformational changes of hair keratins presumably related to the cleavage of disulfide bonds, follow from variations in amide I and low-frequency Raman bands. An increase in the content of thiols in proteins revealed by both photometric data on soluble proteins and Raman microspectroscopy of hair cuts can be used to develop a protocol of the analysis of photoinduced hair modification.

Supercapacitors Based on Reduced Graphene Oxide Nanofibers Supported Ni(OH)2 Nanoplates with Enhanced Electrochemical Performance

Pseudocapacitive materials are critical to the development of supercapacitors but usually suffer from poor conductivity and bad cycling property. Here, we describe the production of novel graphene oxide nanofibers (GONFs) via a partial oxidization and exfoliation method and concurrently report that highly crystallized Ni(OH)2 nanoplates uniformly grow on reduced GONFs' outer graphene nanosheets through the hydrothermal method. Because of their unique structure with high electric conductivity, the rGONF/Ni(OH)2 composite exhibits superior specific capacitance (SC), favorable rate capability and enhanced cycling stability relative to other composites or hybrids, e.g., 1433 F g(-1) at 5 mV s(-1) scan rate, 986 F g(-1) at 40 mV s(-1), and 90.5% capacitance retention after 2000 cycles, and as-fabricated rGONF/Ni(OH)2//active carbon asymmetric supercapacitor (ASC) exhibits a remarkable energy density and a 85.3% high retention (44.1 Wh kg(-1) at 467 W kg(-1) and 37.6 Wh kg(-1) at 3185 W kg(-1)) with a wide potential window of 0-1.7 V. Therefore, this study shows that rGONFs offers an exciting opportunity as substrate materials for supercapacior applications and opens up a new pathway for design and manufacture of novel supercapacitor electrode materials.

Study of thermal, flammability and mechanical properties of intumescent flame retardant PP/kenaf nanocomposites

ABSTRACTDetrimental physical and mechanical properties are common problems for composites when their flame retardancy is improved through filler additions. An increased interest of the synergistic nanoparticle addition to improve the flame retardancy of natural fiber composites is the aim of this work. The paper investigates the synergistic effect of two different nanoparticles (halloysite nanotubes (HNTs) and montmorillonite (MMT) nanoclay) on the flame and mechanical properties in an intumescent ammonium polyphosphate (APP)-based polypropylene (PP)/kenaf composite system. First, the nature of nanoparticle dispersion in PP through X-ray diffraction (XRD) and transmission electron microscopy (TEM) reveals that under twin screw compounding process, the partial exfoliation and intercalation have taken place within the nanocomposites. An increase in the decomposition temperature was observed under thermogravimetric analysis (TGA), with the presence of HNT. However, MMT tends to lower the maximum decomposition temperature under inert atmosphere. The flammability analysis in an intumescent flame retardant (IFR) system shows that the suitable amount of high aspect ratio nanoparticles with their exfoliation characteristics effectively helps to reduce the sustained combustion. Even though, improved stiffness properties can be observed with the presence of increased filler content, particle agglomeration tends to reduce the mechanical strengths of these composites due to low compatibilization and crack propagation.

Rational design of three-dimensional nitrogen and phosphorus co-doped graphene nanoribbons/CNTs composite for the oxygen reduction

Abstract In the present work, we report nitrogen and phosphorus co-doped 3-D structured carbon nanotube intercalated graphene nanoribbon composite. The graphene nanoribbons are prepared via partial exfoliation of multi-walled carbon nanotubes. In the graphene nanoribbons/CNTs composite, carbon nanotubes play a role of skeleton and support the exfoliated graphene nanoribbons to form the stereo structure. After high temperature heat-treatment with ammonium dihydrogen phosphate, the unique structure reserves both the properties of carbon nanotube and graphene, exhibiting excellent catalytic performance for the ORR with excellent onset and half-wave potential, which is similar to commercial Pt/C electrocatalysts.

3D V3O7·H2O/Partially Exfoliated Carbon Nanotube Composites with Significantly Improved Lithium Storage Ability

Currently, transition metal oxides are widely explored as electrode materials for lithium ion batteries due to their remarkably large reversible capacities. However, these materials always suffer from poor conductivities and slow lithium ion diffusion in the lattice. Given this, a distinctive 3D porous network is developed through partial exfoliation of multiwall carbon nanotubes, which can function as not only superior conductive additive but also as an efficient 3D porous scaffold. By self‐assembling with V3O7·H2O nanowires, the hybrid electrode is demonstrated to achieve a significant boost in lithium storage when compared with pristine V3O7·H2O nanowires. This method can provide much inspiration in the construction of high‐performance metal oxides based electrodes.

Physico-chemical modification induced in PLGA/OMMT nanocomposite films by Li3+ ion beam

The swift heavy ions irradiation (SHI) effects on the optical, structural and morphological properties of poly(lactide-co-glycolide) (PLGA) nanocomposites containing organically modified nanoclay organo-montmorillonite (OMMT) (Cloisite®30B) has been studied over a range of fluences. Optical analysis of the polymer nanocomposites shows that both the cross-linking phenomenon is caused by swift heavy ion irradiation. The absence of peak of nanoclay in all irradiated nanocomposite samples in Fourier transfer Infrared (FTIR) spectrum demonstrates the formation of complete and/or partial exfoliation. The broadening of peak width of X-ray diffraction (XRD) spectra of irradiated nanocomposite implies an increase in the amorphous phase at higher fluences. Field emission scanning electron microscopy (FESEM) shows the formation of porous structure after irradiation. Presence of nanoclay is found to affect the properties of this degradable copolymer when subjected to ionizing radiation.

SnO2/reduced graphene oxide composite films for electrochemical applications

Abstract SnO2/GO (GO is graphene oxide) composite films with GO mass fraction wC ranging from 0.01 to 80% have been prepared using colloidal solutions. Heat treatment of SnO2/GO films in Ar atmosphere at 400 °C leads to GO reduction accompanied by partial exfoliation and decreasing of the particle thickness. SnO2/rGO (rGO is reduced GO) film electrodes demonstrate a high electrocatalytic activity in the anodic oxidation of inorganic (iodide-, chloride-, sulfite-anions) and organic (ascorbic acid) substances. The increase of the anodic current in these reactions is characterized by overpotential inherent to the individual rGO films and exchange current density grows linearly with rGO concentration at wC ≤ 10% indicating that the rGO particles in composites act as sites of electrochemical process. The SnO2/rGO composite films, in which the chemically stable oxide matrix encapsulates the rGO inclusions, can be considered as a promising material for applied electrochemistry.

Viscoelastic properties of poly(ε‐caprolactone)/clay nanocomposites in solid and in melt state

ABSTRACTViscoelastic properties in solid and in melt state of poly(ε‐caprolactone), PCL, nanocomposites with organomodified clays (Cloisite30B and Cloisite15A) are thoroughly investigated. Although WAXD is insensitive to the difference in the nanocomposites structure, the melt rheology reveals pronounced differences between the two series. Melt yield stress values, obtained from fittings by the Carreau–Yasuda model, are used as a measure of partial exfoliation of the clay. Temperature dependence of the shift factors, used for time–temperature superposition of the modulus curves, yields similar values of the flow activation energies for all the samples. Temperature dependences of the dynamic modulus and loss factor of solid nanocomposites were correlated to the structural differences deduced from the melt rheology. The increase in the storage modulus is compared to the theoretical predictions from the Halpin–Tsai model. The effective aspect ratio obtained from this comparison agrees reasonably with the value estimated from the melt rheology. © 2015 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2016, 133, 42896.

Organoclay nanocomposites of post-industrial waste poly(butylene terephthalate) from automotive parts.

Polymeric nanocomposites are novel materials of huge interest owing to their favourable cost/performance ratio with low amount of nanofillers, improved thermal resistance, flame retardancy and mechanical properties in relation to their matrices. In this work, composites based on post-industrial waste or primary recycled poly(butylene terephthalate) and 5 wt.% of organic modified montmorillonite clays were melt compounded using a twin-screw extruder. A 2(2) factorial experimental design was used to study the compounding and processing variables: Organic modified montmorillonite with one or two hydrogenated tallow (initial basal spacing) and screw speed of the extruder. X-ray diffraction and transmission electron microscopy suggest that a partial exfoliation of the organoclay in the recycled poly(butylene terephthalate) matrix was achieved for organic modified montmorillonite with lower initial basal spacing. On the other hand, formulations containing organic modified montmorillonite with higher initial basal spacing showed only intercalated structure. The recycled poly(butylene terephthalate)-organic modified montmorillonite nanocomposites did not drip flaming material during burning tests. Storage of dynamic-mechanical, tensile and flexural moduli of the recycled poly(butylene terephthalate)-organic modified montmorillonite were improved when compared with both virgin and recycled poly(butylene terephthalate)s, mainly for nanocomposites formulated at a lower initial basal spacing organoclay. This could be related to a better diffusion of polymer into organic modified montmorillonite layers compared with the higher initial basal spacing organoclay. The improvements on the physical properties of recycled poly(butylene terephthalate) showed the feasibility to add value to primary recycled engineering thermoplastics with a very small amount of organic modified montmorillonite.

Research on the Application Properties of Tpe/Ommt as Mold Materials

The aim of this work was to select one type of polymer as an alternative to room-temperature-vulcanizated silicone rubber (RTV) which was used in the preparation of rubber molds. Thermoplastic elastomer (TPE) and its organo-montmorillonite (OMMT) filled composites were chosen as candidates. Their structure and properties were researched and compared. The properties such as tensile strength, elongation at break, dimensional stability, and thermal stability were studied. The composite with 1 wt% OMMT showed the highest tensile strength and elongation at break, 10.9 MPa and 1313.6%, which was 172.5% and 30.3% higher than that of pure RTV. In addition, this TPE composite exhibited excellent thermal and dimensional stability. At room temperature, the coefficient of linear expansion (COLE) and coefficient of volume expansion (COVE) of the TPE/OMMT-1 wt% was 2.3×10−5 and 7.2×10−4, respectively. This was 87% and 86% lower compared to that of pure RTV, 1.7×10−4 and 5.1×10−3. This dimensional stability was superior to the pure RTV, indicating this composite can be used as an alternative to RTV as mold material to improve the texture fineness of the culture stone. X-ray diffraction (XRD) and scanning electron microscope (SEM) were used in the investigation of the microtopography of the TPE composites. It was revealed that the layered silicates exhibited partial exfoliation with the addition of 1 wt% OMMT in the matrix.

Aligned poly(ε-caprolactone)/graphene oxide and reduced graphene oxide nanocomposite nanofibers: Morphological, mechanical and structural properties.

A number of studies have demonstrated that the mechanical properties of electrospun polymeric nanofibrous scaffolds are enhanced with the incorporation of graphene and its derivatives, thus developing their applications in hard tissue engineering. However, our understanding of the relationship between the microstructure and properties of these fibrous scaffolds and how they are influenced by graphene oxide (GO) and reduced graphene oxide (RGO) loading is much more limited. Thus, in this paper, poly(ε-caprolactone) (PCL)/GO and RGO nanocomposite nanofibers containing 0, 0.1, 0.5 and 1wt.% GO and RGO were prepared using an electrospinning technique. With the addition of 0.1wt.% of GO and RGO nanosheets in PCL, the tensile strength of PCL scaffolds increased over ~160 and 304% respectively and elastic modulus increased over 103 and 163% due to the good dispersion of the nanosheets and their interaction with the molecular chains of PCL. These were supported by the parallel increase in relaxation time and molecular orientation of PCL chains at the presence of nanosheets with a loading of 0.1wt.%. The enhancement effect of the nanosheets was weakened with an increase in GO and RGO loading up to 1wt.% in which it is connected to a partial exfoliation of the nanosheets.

Effect of Artificial Weathering on PLA/Nanocomposite Molecular Weight Distribution

The reduction of polylactide acid (PLA) molecular weight for amorphous and semicrystalline grade nanocomposites with 5 wt% load of organomodified montmorillonite Cloisite30B (C30B) was investigated in periods of up to 360 h under artificial weathering. A correlation between artificial and natural weathering was established. The nanocomposites were prepared by mixing the C30B in PLA matrix using two stages of extrusion followed by injection molding. In addition, we also studied materials without C30B in PLA matrix prepared by a single stage of injection, as well as with two stages of extrusion followed by injection, in order to assess thermal effects. XRD (X-ray diffraction) and TEM (Transmission electron microscope) were used to determine the layer dispersion of the C30B within the PLA. An increase in the interlayer spacing of a sandwich structure corresponding to a partial exfoliation of the C30B was found, leading to the creation of small particles at nanoscale of one (1.29 nm) to eight (11.76 nm) platelets. Also, GPC (Gel permeation chromatography) was used to evaluate the molecular weight decay of neat PLA and its nanocomposites due to thermal processing and subsequent artificial weathering exposure. From thermal processing, a more significant decrease of polydispersity in amorphous PLA than in semicrystalline PLA counterparts could be observed. First order fitting of molecular weight decay of samples versus time of exposure under artificial weathering was found for all materials tested. It was observed that the addition of clay favored PLA degradation in amorphous PLA, in comparison with semicrystalline PLA in both thermal processing and artificial weathering. Moreover, a possible effect of C30B interactions with PLA chains under artificial weathering could be postulated.

Activation of few layer graphene by μW-assisted oxidation in water via formation of nanoballs – Support for platinum nanoparticles

The functionalization of carbon nanomaterials in controlled and selective manner and in order to stabilize small metal nanoparticles is of high interest particularly in the catalysis field. We present the μ-waves assisted few layer graphene (FLG) oxidation in water, which results in a partial sheets exfoliation and formation of oxygen functionalized carbon nanoballs, supported on highly graphitized graphene sheets. This double morphology material allows homogenous anchoring of Pt nanoparticles, while the advantages of planar and highly crystallized FLG are preserved. For comparison, acid treated FLG (conventional heating) exhibits highly hydrophobic and inert surface with carboxylic groups as anchoring sides localized at the FLG edges. Despite similar oxygen content, the performed physicochemical analyses depict different nature and localization of the oxygen/defects functionalities introduced in water (in μ-waves) and acid treated FLGs. Finally, the addition of FLG during the preparation of Pt particles-carried out by μ-wave assisted polyol method yields small nanoparticles with average size of 1nm.

Controlled partial-exfoliation of graphite foil and integration with MnO2 nanosheets for electrochemical capacitors.

Here we demonstrate a controlled two-step partial exfoliation method to synthesize functionalized exfoliated graphite substrates. Ultrathin and functionalized graphene sheets anchoring on the graphite provide a large conductive surface area for loading pseudo-capacitive MnO2 nanosheets. The functionalized exfoliated graphite/MnO2 electrode achieved an excellent areal capacitance of 244 mF cm(-2), corresponding to an estimated MnO2 based gravimetric capacitance of 1061 F g(-1), which is just slightly lower than its theoretical value of 1110 F g(-1). More importantly, the seamless integration of graphene sheets and the graphite substrate minimizes the contact resistance, and substantially improves the rate capability of pseudo-capacitive materials. The electrode retained 44.8% of its capacitance when the charging current density increased 50 times from 0.23 to 11.5 mA cm(-2). This novel functionalized exfoliated graphite substrate serves as a promising supporting material that could address the relatively low electrical conductivity of various pseudo-capacitive materials, and increase the mass loading and rate capability of pseudo-capacitors.

Production of montmorillonite/polypyrrole nanocomposites through in situ oxidative polymerization of pyrrole: Effect of anionic and cationic surfactants on structure and properties

Montmorillonite/polypyrrole (Mt/PPy) nanocomposites were prepared through in situ oxidative polymerization of pyrrole in aqueous dispersions of unmodified montmorillonite (Na+–Mt) with three different surfactants (dodecylbenzenesulfonic acid (DBSA), sodium dodecyl sulfate (SDS) and cetyltrimethylammonium bromide (CTAB)), using iron (III) chloride hexahydrate (FeCl3⋅6H2O) as an oxidant. In order to investigate the effect of the anionic and cationic surfactants used in the pyrrole polymerization, Mt/PPy nanocomposites were also prepared without surfactant. The anionic surfactants promoted the intercalation and partial exfoliation of the clay, while clay polymer nanocomposites (CPN) prepared with cationic CTAB (Mt/PPy.CTAB) and without surfactant (Mt/PPy.Cl) were partially intercalated. High electrical conductivity (10.8Scm−1) was observed for the Mt/PPy.SDS nanocomposites due to the highly site-specific interaction between the protonated PPy (N+) and the negatively-charged Si–O–Si groups of the Mt. Finally, the thermal stability of the CPN was higher than that found for the corresponding PPy samples, with the exception of the Mt/PPy.CTAB nanocomposite, due to the protective effect of the clay layers.

Preparation and enhanced properties of polyaniline/grafted intercalated ZnAl-LDH nanocomposites

The polymeric nanocomposites (PANI/AD-LDH) were prepared by in situ polymerization based on polyaniline (PANI) and decavanadate-intercalated and γ-aminopropyltriethoxysilane (APTS)-grafted ZnAl-layered double hydroxide (AD-LDH). FTIR and XRD studies confirm the grafting of APTS with decavanadate-intercalated LDH (D-LDH). The extent of grafting (wt%) has also been estimated on the basis of the residue left in nitrogen atmosphere at 800°C in TGA. SEM and XPS studies show the partial exfoliation of grafted LDH in the PANI matrix and the interfacial interaction between PANI and grafted LDH, respectively. The grafted intercalated layered double hydroxide in reinforcing the properties of the PANI nanocomposites has also been investigated by open circuit potential (OCP), tafel polarization curves (TAF), electrochemical impendence spectroscopy (EIS), salt spray test and TGA-DTA. The experimental results indicate that the PANI/AD-LDH has a higher thermal stability and anticorrosion properties relative to the PANI.