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This review addresses the current potential of two-dimensional (2D) transition metal dichalcogenide (TMD) nanomaterials for multi-functional polymeric nanocomposites. The properties of TMDs, characterization techniques, the applicability of different synthesis methods along with the surface treatment/modification of TMDs, are comprehensively examined by largely focusing on TMD/polymer nanocomposite preparation. Moreover, a vast range of nanocomposite properties, including mechanical/tribological properties, thermal stability/flame retardancy, and electrical/electronic properties, was investigated. The incorporation of TMDs in both thermoplastic and thermoset matrices can lead to the improvement of the aforementioned properties as reported by many studies in the literature. TMDs can thus possibly be considered not only as a liable reinforcement for polymers to induce multi-functionalities to nanocomposites but also a good hybridizing agent for other types of nano reinforcements. Potential opportunities offered by TMDs in composites/nanocomposites have opened up new horizons in a vast range of applications in different fields, including transportation, electrical/electronic, filtration and biomedical. This review has also compiled publications on the research and developments of TMDs and TMD composites/nanocomposites, from 1970 to the present, with the special focus on molybdenum disulfide (MoS2) and tungsten disulfide (WS2).

The combination of egg white proteins (W) and hypophosphorous acid (HA) was used for developing a flame retardant coating for cotton fabrics by adopting the layer-by-layer assembly technique. This has resulted in a novel phosphorous-nitrogen-based assembly due to strong electrostatic interactions between W and HA. Coated cotton fabrics were characterized by using a variety of microscopic, analytical and thermal/combustion tests. Flammability properties of the fabrics were evaluated as per widely recognized standards like BS EN ISO 15025:2016 for protective clothing and ASTM D6413 for flame resistance of textiles. Coated cotton fabric showed self-extinguishing property with significant but fragile residual char structure, whereas uncoated fabric completely burnt with a little ash as residue. Thermogravimetric analysis revealed that decomposition temperature of coated fabric was lowered compared to control fabric, but char residue increased at 800 °C. Forced combustion cone calorimeter tests on the coated and uncoated fabrics showed that peak heat release rate, total heat released, and average rate of heat emission values reduced by 80%, 38%, and 40%, respectively, for coated fabrics as compared to control fabric. Even the mass loss rate value of the coated fabric has reduced significantly (from 514 g/m2.s for the uncoated fabric to 2 g/m2.s for coated fabric). Wash durability of the coated fabrics, though showed a slight reduction in flame-retardant properties as a consequence of ~ 9.7 wt% coating loss during soaking, yet there was no after-glow.

Microencapsulated phase-change material (ME-PCM) employing octadecane as a core material has been practiced for thermal-energy-storage (TES) applications in buildings. However, octadecane as a hydrocarbon-based PCM is flammable. Herein, silica-shelled microcapsules (SiO2-MCs) and poly(urea-formaldehyde)-shelled microcapsules (PUF-MCs) were successfully prepared, loaded with octadecane/tributyl phosphate (TBP) as hybrid core materials, which not only exhibited good TES properties but also high-effective flame retardancy. SiO2-MC (ΔHm = 124.6 J g-1 and ΔHc = 124.1 J g-1) showed weaker TES capacity than PUF-MC (ΔHm = 186.8 J g-1, ΔHc = 188.5 J g-1) but better flame retardancy with a lower peak heat-release rate (HRRpeak) of 460.9 W g-1 (556.9 W g-1 for PUF-MCs). As compared with octadecane (38.7 kJ g-1), the reduction in total heat release (THR) for SiO2-MC was up to 22% (30.1 kJ g-1) with combustion time shortened by 1/6. SiO2-MC had a typical diameter of 150-210 μm, shell thickness of ∼6.5 μm, and a core fraction of 84 wt %. SiO2-MC showed better thermal stability with a higher initial evaporation/pyrolysis temperature than PUF-MC. The thermal decomposition of MCs with its mechanism of flame retardancy was significantly studied using thermogravimetric analysis/infrared spectrometry (TG-IR). The strategy presented in this study should inspire the development of microcapsules with PCMs/flame retardants as hybrid core materials for structural applications. Agency for Science, Technology and Research (A*STAR) Ministry of National Development (MND) The authors would like to acknowledge financial support from the Agency for Science, Technology and Research (A*STAR) -- Ministry of National Development (MND), Singapore (SERC132 176 0014).

Polypropylene (PP) fibers are commonly used for the prevention of thermal spalling of ultra-high performance concrete (UHPC). In this work, the effect of fiber distribution on permeability and spalling resistance is investigated and an analytical model for permeability at 150 °C is proposed. This model, considering the parameters like fiber dimensions, dosage, and percolation, is based on Kozeny-Carman equation. It was found that the percolation of the interconnecting fiber network resulted in a significant increase in permeability of UHPC. X-ray tomography data on the three-dimensional spatial distribution of fibers reiterated that fiber aspect ratio and dosage (and fiber number density) were critical in increasing the fiber connectivity (percolation). It was also found that a vapor permeability of larger than 0.6 × 10⁻¹⁶ m² at 150 °C could eliminate spalling. Further, based on a semi-empirical approach, aspect ratio between 300 and 600 was recommended for spalling prevention with a fiber dosage of 0.3–0.4 vol%. Ministry of National Development (MND) National Research Foundation (NRF) This research work is supported by the Singapore Ministry of National Development and National Research Foundation under L2 NIC, Award No. L2NICCFP1-2013-4.

Material-scale tests involving milligrams of samples are used to optimize fire-retardant coating formulations, but actual applications of these coatings require them to be assessed with structural-scale fire tests. This significant difference in the scale of testing (milligrams to kilograms of sample) raises many questions on the relations between the inherent flammability and thermal characteristics of the coating materials and their &ldquo, performance&rdquo, at the structural scale. Moreover, the expected &ldquo, requirements and the definition of &ldquo, varies at different scales. In this regard, the pathway is not established when designing and formulating fire-retardant coatings for structural steel sections or members. This manuscript explores the fundamental relationships across different scales of testing with the help of a fire-protective system based on acrylic resin with a typical combination of intumescent additives, viz. ammonium polyphosphate, pentaerythritol, and expandable graphite. One of the main outcomes of this work dictates that higher heat release rate values and larger amounts of material participating in the pyrolysis process per unit time will result in a rapid rise in steel substrate temperature. This information is very useful in the design and development of generic fire-retardant coatings.

It has been established that the addition of synthetic fibers like polypropylene (PP) to ultra-high performance concrete (UHPC) enhances the latter's thermal spalling resistance. The key for this is the thermal mismatch between embedded fibers and matrix as a result of the expansion of PP fibers with temperature. This paper explores the effect of natural fibers (replacing traditional PP fibers) on compressive strength, hot permeability, and spalling resistance of UHPC. Different dosages (3, 5 and 10 kg/m3) of jute fibers are used for this purpose. The findings are critical as they oppose the mechanism of thermal spalling resistance established for synthetic fibers in UHPC. Natural fibers swell by absorbing water (during the casting of UHPC and during their service life) and shrink upon exposure to warm and high temperatures. The deswelling and shrinkage of natural fibers at high temperatures create spaces between fibers and matrix, which could influence permeability at those temperatures. This suggests that percolation of fibers is critical in the case of jute as opposed to PP fibers. It was found that a dosage of 10 kg/m3 of jute fibers is required for eliminating spalling of UHPC as opposed to 3 kg/m3 for PP fibers. Additionally, preliminary efforts are put in to investigate the short-term durability of the samples and changes in properties of UHPC with jute fibers. Ministry of National Development (MND) National Research Foundation (NRF) This research/work is supported by the Singapore Ministry of National Development and National Research Foundation under L2 NIC, Award No. L2NICCFP1-2013-4.

Cheetah skin carbon nanotube, a novel periodically patterned nanocarbon on CNT synthesized as a highly effective filler for fabrication of high performance composites. The advantage of newly developed morphology lies in the fact that the size of nanocarbon on CNT and their distance can be fully controlled based on the application requirements. Cheetah skin CNT shows an excellent thermal stability and dispersibility in a high density polyethylene (HDPE) compared to pristine CNT/HDPE composite, making cheetah skin CNT a suitable candidate for fabrication of high performance HDPE based composite. The addition of cheetah skin CNT into HDPE resulted in a composite with improved thermomechanical properties. Compared with the pure HDPE and HDPE/pristine CNT, storage modulus and loss modulus of HDPE/cheetah skin CNT improved significantly at low temperatures even with very low content of cheetah skin CNT. Also, the thermal stability of the cheetah skin CNT/HDPE was found to be significantly higher than that of pristine CNT/HDPE composite in both isothermal and non-isothermal degradation performed for composites.

In this Research Article, we report on the development of water-based flame retardant coating based on phospho-nitrogen combination for cotton fabrics. A one-step spray-on process was employed to coat the fabrics by taking advantage of the spontaneous reaction between para-phenylenediamine (PDA) and tetrakis (hydroxymethyl) phosphonium chloride (THPC) resulting in an instantaneous precipitation of poly[1,4-diaminophenylene-tris(dimethyl hydroxymethyl)phosphine] (PApP) on the fabric surface. The effectiveness of PApP in improving the flame retardant properties like ignition resistance and lateral flame spread were evaluated in accordance with ASTM D6413 and BS EN ISO 15025 flammability tests. Despite the early (thermal) decomposition onset for coated fabrics under both oxidative and pyrolytic conditions, remarkably, self-extinguishing behavior (

This work explores the importance of varying the ratio of conventional flame-retardant additives and the scale of testing on the thermal and flammability/fire performance of acrylic-based coatings. Ammonium polyphosphate (APP), pentaerythritol (PER), and expandable graphite (EG) are used as intumescent additives by varying their ratios as 1:1:3 or 1:3:1 or 3:1:1. APP, PER and EG are used as acid source, carbonising agent and blowing agent, respectively. Despite the different roles of APP, PER, and EG, in all the compositions, the physical mechanism of exfoliation of graphite played an important role in offering the fire protection. With higher loadings of EG, the fire-resistance time was higher. However, there were clear differences in the protection extent when tested in a furnace under one-dimensional heat transfer conditions (bench-scale) as opposed to three-dimensional large-scale testing. Parameters that are not intrinsic to the coating system like char cohesion, cracking, delamination from the substrate, rapid and non-directional expansion, and even higher heat fluxes experienced by the edges of the I steel section affect the fire performance. Ministry of National Development (MND) Nanyang Technological University National Research Foundation (NRF) This material is based on research work supported by the Singapore Ministry of National Development and National Research Foundationunder L2 NIC Award No. L2NICCFP1-2013-4 and JTC through NTU-JTC I3C (RCAs 16/277 and 17/365).

Carbon nanotubes have considerable potential for use as reinforcements in high-performance polymer composites, but their large-scale application has been hindered by their poor processability. Here, we report an extremely simple and scalable method for the chemical treatment of single-wall carbon nanotubes (SWNTs) to enable easy dispersion in an epoxy matrix. The treatment involves stirring SWNTs in a concentrated solution of sodium hydroxide in ethanol. The chemicals used can be recovered and re-used. The treated SWNTs show greater ease of exfoliation into organic solvents without the need for high-intensity ultrasonic probe treatment. Raman spectroscopy shows that the treatment does not create any noticeable defects or functional groups on the SWNT walls. As a result of the treatment, the SWNTs could be dispersed in epoxy with minimal, low-power ultrasonic treatment. The resulting composites showed increased fracture toughness and tensile strength at SWNT loadings as low as 0.5 weight percent, when compared with neat epoxy. The enhancement in properties of the composites does not decrease with increased SWNT loading, implying that the SWNTs do not re-aggregate.

Simultaneous improvement of flame retardancy and physiological comfort of clothing fabrics has not been studied before. One of the probable reasons for this is the complexity of dynamic processes involved. This work is a preliminary effort to understand various parameters involved in combining these two facets of fabrics. For this purpose, polyester fabrics are coated with branched polyethylenimine (BPEI) and sodium montmorillonite (smectite clay) via electrostatic self-assembly approach. The effect of their concurrent presence in different concentrations (variation of number of bilayers) on thermo-oxidative properties and flame retardancy behavior as well as physiological comfort (in terms of wicking, moisture management, and air permeability) of polyester has been assessed. The obtained results have shown the efficiency of the electrostatic self-assembly process in improving both facets. This work provides the foundation and knowledge for further development of effective coating systems with a multi-functional approach in the textile industry. Keywords: Flame retardant textiles, Electrostatic self-assembly, Moisture management, Montmorillonite

It has been a common practice to use polymer fibers to reduce susceptibility of explosive spalling in ultra-high performance concrete (UHPC). However, to-date, despite the proposition of different mechanisms through which polymer fibers enhance gas permeability and reduce explosive spalling, there are many unanswered questions and unjustified claims on the proposed mechanisms. Therefore, the major emphasis of this work is to thoroughly re-examine and understand the exact role of polymer fibers in the prevention of explosive spalling of UHPC. A range of analytical and microscopic tools are used to realize this objective. It is concluded that melting of polymer fibers and creation of empty channels are not required for enhancing the permeability of gases or water vapor through concrete. In fact, it is the thermal mismatch between embedded fibers and matrix that is critical in obtaining an interconnected network of cracks in the matrix. This occurs even before melting of polypropylene (PP) fibers. The network of cracks is responsible for enhancing permeability, thereby reducing the susceptibility of explosive spalling of UHPC.

A key parameter influencing ignition, heat of combustion and charring of polymer/clay (montmorillonite, MMT) nanocomposites during combustion is the catalytic activity of clay. This work explores the effect of metal ions (MIs) like Mg2+, Al3+ and Fe3+ that are inherent to clay in altering the kinetics of degradation of organic modifier, hexadecyltrimethylammonium bromide (HDTMA-Br). Based on Brønsted and Lewis acid characteristics associated with these metal ions, their catalytic activity varied; Brønsted acidity affected initial stages of organic modifier degradation, while Lewis acidity influenced oxidation stability of carbonaceous residue beyond dehydration temperatures. For example, OMgMMT yielded delayed peak degradation temperature for HDTMA+, while Fe3+ ions from OFeMMT significantly lowered the oxidation stability of carbonaceous content. Knowing the effect of each metal ion separately, correlation between clay structural chemistry and organic degradation onset has been established. Degradation mechanism for alkyl fragment (from organic modifier) was provided adding fundamental knowledge to the field that will help in the design and development of polymer/clay nanocomposites with superior fire retardancy. MOE (Min. of Education, S’pore) Accepted version

This article reports the preparation of nylon 6/stacked-cup carbon nanofiber (CNF) nanocomposites via in situ anionic ring-opening polymerization partially initiated from caprolactam-functionalized CNFs. As a result of the successful functionalization of CNF surface, good dispersion of the CNFs was observed by transmission electron microscopy (TEM). Moreover, with the addition of a very small amount of CNFs, significant enhancements in tensile modulus and yield strength were achieved together with slightly improved impact resistance. The enhanced stiffness may be attributed to effective filler–matrix stress transfer induced by interfacial covalent bonds. On the other hand, SEM micrographs provided evidence for the possible unraveling of the stacked-cup CNF, which may allow the CNFs to bridge the matrix during crack propagation, hence resulting in the toughening of the nanocomposites. ASTAR (Agency for Sci., Tech. and Research, S’pore)

The article elucidates the mechanisms of formation of varying degrees of surface pores/pits on polylactic acid (PLA) fibers during electrospinning. The role of a combination of different parameters in governing pore formation was demonstrated. They include solvent vapor pressure (pv), solvent miscibility/interaction with water, solubility parameter, and relative humidity (RH) within the spinning unit. Our results indicated that traditional mechanisms like thermally induced phase separation (TIPS) and vapor induced phase separation (VIPS) were not responsible in the generation of surface porosity/pits. Instead, higher RH (water vapor, a non-solvent of the polymer), and its miscibility/interaction with solvent(s) were concluded to be relatively more important than the simple presence of a high pv solvent or a combination of high pv and low pv solvent system. Further, content of high pv solvent in solution determined the spherical or elliptical nature of pores/pits by affecting the level of saturation of nearby region of the interface between jet and air during the electrospinning process. Accepted version

Solvothermally reduced and functionalized graphene (SRFG) was obtained by refluxing graphene oxide in dimethyl formamide at 140 °C. The resultant simultaneous nitrogen-doping and presence of dangling bonds on SRFG prompted us to study the evolution of structural changes with refluxing time. It is shown that the removal of oxygen-containing functional groups leaves dangling bonds during the solvothermal reduction, which are responsible for the nitrogen-doping with longer refluxing time. The relationship between the defects of SRFGs and their lithium ion storage performances are also discussed.

Inspired by the radical scavenging function of melanin-like materials and versatile adhesive ability of mussel-adhesion proteins, dopamine-modified clay (D-clay) was successfully incorporated into polypropylene (PP) using an amine-terminated PP oligomer as the compatibilizer. Although the PP/D-clay nanocomposites exhibit intercalated morphology, the incorporation of D-clay greatly improves the thermo-oxidative stability and UV resistance of PP owing to the strong radical scavenging ability of polydopamine (PDA) and large contact area between PP and the PDA coating on clay mineral. Moreover, the reinforcement effect brought by D-clay is fairly significant at very low clay loadings probably owing to the strong interfacial interactions between the layered silicates and the compatibilizer as well as that between the compatibilizer and the PP matrix. The work demonstrates that D-clay is a type of promising nanofiller for thermoplastics used for outdoor applications since it stabilizes and reinforces the polymers simultaneously.

Novel clay/waterborne polyurethane (WPU) nanocomposites were synthesized in which the clay was acidmodified with hydrochloric acid. The molecular motion of nanocomposites was investigated using high resolution solid state 13C NMR technique. Addition of clay drastically decreased the molecular mobility of waterborne polyurethane in hard segment; but little in soft segment. Two-leg trouser studies revealed that introducing clay into waterborne polyurethane significantly enhanced the tearing toughness of the nanocomposites. Refereed/Peer-reviewed

Combustion and thermo-oxidative properties of polyamide 6 (PA6)/montmorillonite (MMT) clay nanocomposites are studied with emphasis on the catalytic role of metal ions (Mg2+, Al3+ and Fe3+) present in MMT. Each metal ion uniquely influences condensed phase reactions (mechanism and/or kinetics) depending on its concentration in metal ion exchanged MMT, its ability to form metal-organic complexes, and confinement effect as determined by eventual dispersion of MMT in the matrix. Presence of Al3+ accelerated kinetics of PA6 decomposition during initial stages, Mg2+ rich composite displayed good thermo-oxidation stability and char yield, and Fe3+ prominently altered the chemical composition of condensed phase ultimately producing highest amount of smoke. Possible PA6 decomposition reaction mechanisms have been identified that are susceptible to metal ion catalysis in the presence of oxygen. These results provide important progress towards the understanding of widely reported yet poorly understood phenomena of catalyzing effect of clay during the combustion of polymer. The results are a definite step towards the realization of stand-alone clay based nanocomposites with superior fire retardancy. NRF (Natl Research Foundation, S’pore) MOE (Min. of Education, S’pore) Accepted version

Graphene oxide (GO) was reduced with biocompatible glucose and polyvinylpyrrolidone (PVP) and incorporated in polylactic acid (PLA). The thermal reduction of GO during the compression molding of PLA was also studied to delineate the reduction efficiencies from thermal and chemical processes. Results indicate that glucose is more effective in the reduction of GO (rGO-g) with a much higher electrical conductivity than PVP and thermally treated GO. Even rGO-g was also highly efficient in improving the electrical conductivity of PLA. The composite with ∼1.25 vol.% of rGO-g exhibited a high conductivity of ∼2.2 S/m due to the chemical reduction of GO with glucose and the thermal reduction of rGO-g during the compression molding process.

Functional polypropylene (PP) nanocomposites were prepared by melt compounding with multiwalled carbon nanotubes (MWNT) as the electrically conductive component and barium titanate (BT) spherical nanoparticles as the ferroelectric component. To make PP electrically conductive, more than 3 wt.% MWNT is required. Surface modification of either MWNT or BT with titanate coupling agent further improves the electrical conductivity of the PP/MWNT/BT ternary nanocomposites. Interestingly, by modifying both MWNT and BT, 2 wt.% MWNT are sufficient to make the ternary nanocomposite electrically conductive. In addition, the incorporation of MWNT greatly increases the dielectric permittivity of PP/BT nanocomposites. However, to retain a low dielectric loss, the MWNT loading should be slightly less than the percolation threshold of the nanocomposites. The improved electrical conductivity and dielectric properties make the ternary nanocomposites attractive in practical applications.

This paper deals with a novel concept of induction of well-distributed submicrometer voids in polypropylene (PP) and PP/CaCO3 nanocomposites during processing to alleviate their brittleness without sacrificing Young’s modulus and yield strength. The role of these voids in initiating/participating in the plastic deformation processes during tensile and double-notch four-point-bend (DN-4-PB) tests is investigated. It is shown that the voids act in a similar way as the cavitated rubber particles in rubber-toughened polymer systems; that is, plastic growth (of the pre-existent voids) in the PP matrix occurs upon deformation and subsequently triggers large plastic deformation of the surrounding matrix in the form of isolated and domainlike craze structures.

This study focuses on achieving high stiffness/strength and high fracture toughness in nylon 6/organoclay nanocomposites prepared via melt compounding by incorporating a maleic anhydride grafted polyethylene–octene elastomer (POE-g-MA) as a toughening agent. Mechanical test results indicated that the ternary nanocomposites exhibited higher stiffness than nylon 6/POE-g-MA binary blends at any given POE-g-MA content. More importantly, the brittle–ductile transition of nylon 6/POE-g-MA blends was not impaired in the presence of organoclay for the compositions prepared in this study. TEM analysis shows that organoclay layers and elastomer particles were dispersed separately in nylon 6 matrix. In the binary nanocomposite, no noticeable plastic deformation was observed around the crack tip. In the ternary nanocomposites, the presence of organoclay in the matrix provided maximum reinforcement to the polymer, while their absence in the elastomer particles allowed the latter to promote high fracture toughness via particle cavitation and subsequent matrix shear yielding. The partially exfoliated clay layers also delaminated and hence, adding to the total toughness of the nanocomposites.

Two contrasting approaches have been adopted in the current study to obtain environmental benign and superior flame retardant polymer nanocomposites. In the first approach, polyhedral oligomeric silsesquioxane (POSS) is incorporated as an additional filler in polyamide 6/clay nanocomposite to improve the homogeneity of the ‘physical’ barrier, since POSS transforms to a glassy material upon fire and enhances the coupling of silicate layers to each other. In the second approach, fire response of an intumescent system, polyamide 6/graphite oxide (GO), is compared to polyamide 6/clay systems. The intention of using GO as a flame retardant is to benefit from its layered structure (‘physical’ barrier mechanism) and intumescent/blowing effect (‘chemical’ mechanism). Considerable insight and physical knowledge on the roles of different fillers in the combustion process have been obtained, which would provide useful guidance for the development of a new generation of nanocomposites. Besides the obvious contrasting differences in the flame properties of different materials, the incorporation of various fillers, depending on their nature, has both advantages and disadvantages from the viewpoint of flame retardancy. Accepted version

The primary focus of this work is to elucidate the location and extent of exfoliation of clay on fracture (under both static and dynamic loading conditions) of melt-compounded nylon 66/clay/SEBS-g-MA ternary nanocomposites fabricated by different blending sequences. Distinct microstructures are obtained depending on the blending protocol employed. The state of exfoliation and dispersion of clay in nylon 66 matrix and SEBS-g-MA phase are quantified and the presence of clay in rubber is shown to have a negative effect on the toughness of the nanocomposites. The level of toughness enhancement of ternary nanocomposites depends on the blending protocol and the capability of different fillers to activate the plastic deformation mechanisms in the matrix. These mechanisms include: cavitation of SEBS-g-MA phase, stretching of voided matrix material, interfacial debonding of SEBS-g-MA particles, debonding of intercalated clay embedded inside the SEBS-g-MA phase, and delamination of intercalated clay platelets. Based on these results, new insights and approaches for the processing of better toughened polymer ternary nanocomposites are discussed.

The fracture toughness of a series of nylon 6/organoclay/maleic anhydride grafted polyethylene-octene elastomer (POE-g-MA) ternary nanocomposites with different compositions of clay and POE-g-MA was evaluated using the J-integral method. The fracture toughness of the ternary nanocomposites increased with POE-g-MA content at a fixed loading of organoclay. In contrast, increasing the loading of organoclay in nylon 6/POE-g-MA (70/30) blends reduced the toughness of the ternary nanocomposites. Transmission electron microscopy (TEM) with single-edge-double-notch four-point-bend (SEDN-4PB) specimens revealed the internal cavitation of POE-g-MA particles leading to effective relief of crack-tip tri-axial stress along with craze-like damage features consisting of line arrays of expanded voids in both un-reinforced and organoclay reinforced nylon 6/POE-g-MA blends, followed by very severe matrix plastic deformation at the crack-tip region. It is this plastic work that mainly contributes to the drastic enhancement of fracture toughness of the ternary nanocomposites, besides the energies absorbed in cavitation and stretching of rubber particles as well as delamination of clay layers.

The nanoscratch behavior of nylon 66/SEBS-g-MA/clay ternary nanocomposites produced by different blending protocols with contrasting microstructures is studied by using atomic force and transmission electron microscopy. A standard diamond Berkovich indenter is used for scratching and a low load of 1 mN, along with a low sliding velocity of 1 μm s −1 , are employed for this purpose. It is shown that in order to resist penetration it is more important to have exfoliated clay in the continuous nylon matrix during nanoscratching than to have the clay in the dispersed soft rubber domains. The results obtained also explain the preferred usage of ternary nanocomposites compared to binary nanocomposites, particularly nylon 66/exfoliated clay nanocomposites. This research extends current basic knowledge and provides new insights on the nature of nanoscale processes that occur during nanoscratching of polymer nanocomposites. Critical questions are raised on the relationships between the penetration depth and material deformation and damage left behind the moving indenter.

The primary aim of this paper is to provide an insight on the effect of the location of organoclay on the micro- and nano-scale deformation processes in melt-compounded nylon 66/organoclay/SEBS-g-MA ternary nanocomposites prepared by different blending sequences. In addition, the deformation processes of the ternary nanocomposites were compared to the binary nanocomposites (nylon 66/organoclay and nylon 66/SEBS-g-MA) and neat nylon 66. The incorporation of SEBS-g-MA particles toughened nylon 66 markedly; but the flexural modulus and strength were both reduced. Conversely, the use of organoclay increased the modulus but decreased the fracture toughness of nylon 66. Nylon 66/SEBS-g-MA/organoclay ternary nanocomposites exhibited balanced elastic stiffness and toughness. Stress-whitening studies of the fracture surfaces in terms of gray level were also performed and an attempt was made to correlate the optical reflectivity characteristics with fracture toughness. It was concluded that the capability of SEBS-g-MA particles to cavitate was decreased by the presence of organoclay in the SEBS-g-MA phase, resulting in reduced toughening efficiency. The best micro-structure for toughness and other mechanical properties is thus to maximize the amount of exfoliated organoclay in the nylon 66 matrix rather than to have it embedded in the finely dispersed SEBS-g-MA particles.

A novel strategy to prepare zirconium phosphate/Nafion nanocomposite proton exchange membrane (PEM) from exfoliated zirconium phosphate and Nafion solution was proposed and investigated. It was found that zirconium phosphate could be well-dispersed and disorderly exfoliated in the membrane. Compared to neat Nafion 117 thin film, methanol permeability was reduced by 77% while the proton conductivity only decreased by 7% in the nanocomposite membrane with 3 wt % zirconium phosphate. Results obtained also showed that the addition of zirconium phosphate could increase the thermal stability of the nanocomposite PEM.

Knowledge of the nature of molecular processes occurring during melt compounding of nanomaterials and polymers is crucial in determining the ultimate performance of polymer nanocomposites. In this paper, we demonstrate for the first time with detailed transmission electron microscopy, the parameters that affect the microstructure of polymer nanocomposites by varying the blending sequence. Nylon 66/organoclay/SEBS-g-MA ternary nanocomposites prepared by four different blending sequences exhibited distinct microstructure and mechanical properties. It was concluded that the best microstructure for toughness and other mechanical properties is to have the maximum percentage of the exfoliated organoclay in the nylon 66 matrix rather than to have it in the dispersed SEBS-g-MA phase. The presence of organoclay in the SEBS-g-MA phase reduces the latter's ability to cavitate, resulting in reduced toughening efficiency.

To obtain a balance between toughness (as measured by notched impact strength) and elastic stiffness of poly(butylene terephthalate) (PBT), a small amount of tetrafunctional epoxy monomer was incorporated into PBT/ [ethylene/methyl acrylate/glycidyl methacrylate terpolymer (E-MA-GMA)] blends during the reactive extrusion process. The effectiveness of toughening by E-MA-GMA and the effect of the epoxy monomer were investigated. It was found that E-MA-GMA was finely dispersed in PBT matrix, whose toughness was significantly enhanced, but the stiffness decreased linearly, with increasing E-MA-GMA content. Addition of 0.2 phr epoxy monomer was noted to further improve the dispersion of E-MA-GMA particles by increasing the viscosity of the PBT matrix. While use of epoxy monomer had little influence on the notched impact strength of the blends, there was a distinct increase in the elastic stiffness. SEM micrographs of impact-fracture surfaces indicated that extensive matrix shear yielding was the main impact energy dissipation mechanism in both types of blends, with or without epoxy monomer, and containing 20 wt. or more elastomer.

The paper describes the effect of wollastonite and talc on the scratch deformation behavior of low and high crystallinity polypropylenes under identical test conditions. The vertical resolution of atomic force microscopy and lateral resolution of scanning electron microscopy is utilized to examine the characteristics of scratch damage. Contrary to the expectations that high crystallinity and stiffness of polypropylene composites should increase resistance to scratch deformation, the susceptibility to mechanical deformation depends on bonding of mineral particles to the polymer matrix. Scratch deformed regions in neat polypropylenes were free of voids and grooves, while reinforced-polypropylenes exhibited voids and debonding/detachment of filler particles. The severity of plastic deformation in reinforced polypropylenes is a function of debonding/detachment of mineral particles, which is comparatively more for talc-reinforced polypropylenes than wollastonite-reinforced polypropylenes because of the layered structure of talc that encourages delamination. Usage of coating and coupling agents improved the resistance to scratch deformation by promoting adhesion and bonding between the reinforcement and matrix.

The paper describes the micro-scale response, mechanism, and susceptibility to stress whitening during tensile straining of polybutene-5 wt% clay nanocomposites, and its comparison with unreinforced neat polybutene utilizing electron microscopy observations. Polybutene-5 wt% clay nanocomposites exhibit increased tensile modulus, significantly reduced susceptibility to stress whitening, and are characterized by lower optical gray level in the plastically deformed stress whitened zone. Furthermore, crystallization studies suggest that the reinforcement mineral increases the rate of nucleation, accelerating the crystallization process. The reinforcement of polybutene with 5 wt% clay alters the primary micromechanism of stress whitening from stress relaxation of the 'fish-scale psiloma' containing tiny voids and subsequent transformation to ridge tearing at high plastic strains to nucleation and growth of large size voids in polybutene-clay nanocomposites. The final fracture in neat polybutene occurs by a mixed mode (brittle and fibrillation), while brittle deformation is the predominant fracture mode in polybutene-5 wt% clay nanocomposites.

The work presented here describes the effect of wollastonite and talc on the micromechanisms of surface deformation and subsequent propagation into the bulk of low and high crystallinity polypropylenes during tensile straining. The potential of high resolution electron microscopy is utilized to examine deformation processes, and develop deformation mechanism maps. While mineral-reinforced polypropylenes exhibited an increase in tensile modulus, yield strength remained unaffected. Crystallization behavior indicated that the reinforcement minerals increase the rate of nucleation with consequent increase in percentage of bulk crystallinity. The reinforcement of polypropylene with wollastonite or talc alters the primary micromechanism of deformation from deformation bands/crazing in neat polypropylenes to wedge/ridge tearing in mineral-reinforced low crystallinity polypropylene composites. However, wedges were absent in high crystallinity polypropylene composites. The final fracture in reinforced polypropylene occurs by a mixed mode consisting of fibrillation and brittle mode, while crazing–tearing and brittle deformation are fracture modes for neat polypropylenes.

The micromechanism and susceptibility to stress whitening during tensile straining of micrometric wollastonite mineral-reinforced polypropylenes is studied by electron microscopy and compared with unreinforced neat polypropylenes. Mineral-reinforced polypropylene composite exhibit significantly reduced susceptibility to stress whitening, and are characterized by lower gray level in the plastically deformed stress whitened zone. This behavior is attributed to the effective reinforcement of polypropylene by wollastonite that acts in concert increasing the tensile modulus of the composite and restricts plastic deformation of the matrix. The increase in tensile modulus is explained in terms of a three-phase model involving matrix, particle, and interface zone. Furthermore, isothermal crystallization indicated that the reinforcement mineral increases the rate of nucleation with consequent increase in % bulk crystallinity. The reinforcement of polypropylene alters the primary micromechanism of stress whitening from deformation bands/crazing in neat polypropylenes to wedge/ridge-tearing in mineral-reinforced polypropylene composites. The final fracture in reinforced polypropylene occurs by a mixed mode consisting of fibrillation and brittle mode, while crazing-tearing and brittle deformation are fracture modes for neat polypropylene.

The strain rate sensitivity of neat polypropylene (PP) and wollastonite-mineral filled polypropylene (PP-W) and concurrent microstructural evolution is investigated. Both the materials are strain rate sensitive and the change in strain rate sensitivity index parameter with strain reflects the change in micromechanisms of deformation and modes of fracture. Deformation processes in neat polypropylene involved craze-tearing and brittle mode of fracture, while wollastonite-filled polypropylene composite was predominantly characterized by wedge, ridge-tearing, fibrillation and brittle fracture. The dependence of yield stress of neat polypropylene (PP) and wollastonite-filled polypropylene (PP-W) with strain rate follows Eyring’s equation and yield similar activation volume implying similarity in the onset of plastic deformation.

Scratch deformation characteristics of neat and wollastonite-containing polypropylenes under identical test conditions are examined by electron microscopy and atomic force microscopy techniques. The study indicates that the severity of plastic deformation during scratch deformation in filled polypropylenes is a strong function of the debonding/detachment of wollastonite mineral particles from the polypropylene matrix. Scratch resistance is evaluated in terms of scratch hardness, scratch depth, average scratch roughness, thickness and density of the scratch tracks. Atomic force microscopy suggests the presence of a localized region surrounding the reinforcement particle that is characterized by enhanced crystal nucleation in which the local chain conformation and kinetics are likely to be different from regions that are a significant distance away from the mineral particle.

The strain rate sensitivity of thermoplastic materials namely high density polyethylene (HDPE), homopolymer polypropylene, and high isotactic homopolymer polypropylene and concurrent microstructural evolution is investigated. Strain rate sensitivity index followed the sequence, HDPE>homopolymer polypropylene>high isotactic homopolymer polypropylene. The strain rate sensitivity index parameter of the examined polymeric materials is consistent with the micro-mechanisms of deformation and modes of fracture. Deformation processes in HDPE involved fibrillation and craze-tearing, while homopolymer polypropylene and high isotactic polypropylene were predominantly characterized by craze-tearing and brittle modes of fracture.

The tensile flow behaviour and deformation processes during uniaxial loading of high isotactic (high crystallinity) polypropylenes have been investigated at various strain rates. The strain rate sensitivity index indicated that long chain high isotactic (high crystallinity) polypropylene (iPP-L) is relatively less sensitive to strain rate than short chain high isotactic (high crystallinity) polypropylene (iPP-S). Deformation bands formed at low strain contributed to the separation of fibrils/microfibrils, and on subsequent increase in tensile strain, the deformation bands developed into an array of closely spaced crazes that multiplied with an increase in strain and strain rate, and grew inwards. Three fracture morphologies were identified in iPP-L: brittle fracture, crazing - tearing, and brittle fracture with ductile pulling of fibrils/microfibrils (quasi-cleavage). In iPP-S, the predominant mode of failure at all displacement rates was brittle fracture. However, at lower displacement rates, smo...

The paper describes tensile flow behaviour and related microstructural aspects of injection moulded polyethylene. The flow stress increased with increase in strain rate indicating that the tensile flow behaviour is sensitive to strain rate. Also, the yield stress exhibited a linear relationship with strain rate and followed the thermal activation concept with the activation volume consistent with the thickness of the lamellar crystallite. The behaviour of mechanically induced surface damage on polyethylene was studied by SEM. At low strain rates, the deformation process was characterised by features that looked like deformation bands. With increase in strain rate and strain, the deformation bands developed into a distinct array of crazes and grew inwards, followed by tearing. Also, with increasing strain rate the crazes multiplied and secondary crazes were generated that were at an angle to the tensile axis. The examination of the morphology of the fracture surface of polyethylene at various stra...

Surface microstructural modification during tensile deformation in polypropylenes has been studied by atomic force microscopy (AFM) operated in tapping mode and Raman spectroscopy. The atomic force micrographs revealed differences in microstructures of undeformed and deformed polypropylenes that were used to predict the deformation characteristics of the two polypropylenes, designated as PP-L and PP-R. The undeformed surface of the two polypropylenes was characterised by differences in arrangement of fibrils depending on their melt flow conditions. PP-L is a polymer with longer chains and with restricted flow, and PP-R has shorter chains obtained by controlled rheology. The microfibrils in undeformed PP-L bend, forming raised surface features of height ~10 - 50 nm, whereas microfibrils in undeformed PP-R exhibit surface features of relatively lower height (10- 20 nm). 30 × 30 nm scan AFM images provided details of microfibrils containing chains of molecules of ~0.5 nm wide. The large scan AFM micr...

Atomic force microscopy (AFM) in tapping mode has been used to characterise surface damage on deformed polypropylenes induced during a scratch test. Atomic force micrographs revealed differences in microstructures that could be used to predict the deformation resistance of two different types of polypropylene. The undeformed surface of the two types of polypropylene (identified as polypropylene-L and polypropylene-R) was characterised by differences in arrangement (regular or irregular) of fibrils depending on their melt flow conditions. Polypropylene-L is a polymer with longer chains and with restricted flow, whereas polypropylene-R has shorter chains obtained by controlled rheology. The microfibrils in undeformed polypropylene-L bend, forming raised surface features of height in the region of 10- 50 nm. In comparison to polypropylene-L, the microfibrils in undeformed polypropylene-R exhibited surface features of relatively lower height (10 - 20 nm). 30 × 30 nm scan AFM images provided details of...

Surface characteristics of laser surface engineered iron oxide coatings on a cast aluminium alloy developed for improved wear performance have been studied by atomic force microscopy (AFM) in association with microhardness measurements. An attempt is made to relate the grain size and surface roughness of FeO and Fe3O4 based coatings to wear performance determined by block-on-disk dry sliding wear testing. Fe3O4 based coating exhibits finer grain and smoother surface in comparison to FeO coating. However, FeO displays superior wear performance even though the Knoop microhardness of both coatings was comparable.

The surface damage induced during tensile deformation of polyethylene at different strain rates was studied by atomic force microscopy (AFM) operated in tapping mode, before and subsequent to uniaxial tensile plastic deformation. Atomic force microscopy revealed striking differences in the deformed microstructures up to the nanoscale range. The surface of undeformed polyethylene was characterised by ribbonlike fibrils of width 0·25 νm and surface features of height about 20–60 nm. Fibrils were considered to consist of microfibrils of width 0·03–0.04 νm. Small scan (30 × 30 nm) AFM images provided details of microfibrils containing chains of molecules of ~ 0·5 nm wide. Tensile deformation in the plastic region involved stretching of fibrils and microfibrils resulting in the formation of surface openings. The ability of the ribbonlike surface fibrils and microfibrils to stretch, merge, and acquire an oriented and flat structure increased with increase in strain rate in the uniaxial tensile test. Als...

Three dimensional (3D) graphene aerogel was prepared by in situ reduction-assembly method. Paraphenylene diamine (PPD) was used as reducing and functionalizing agent of graphene oxide in an aqueous medium with ammonia. The synthesized 3D graphene-PPD aerogel has highly porous structure, low density, high electrical conductivity and good mechanical properties. Further, epoxy/aerogel composites were prepared by vacuum-assisted impregnation process, which exhibited good electrical conductivity and compressive properties. Accepted version

Fabricating carbon nanotube-based composites requires high degree of dispersion of carbon nanotubes into a polymer matrix. The widely used approaches reported in open literature for such a purpose are usually complicated and high-cost. Herein, we found that Chinese ink could be used to prepare composites composed of multi-walled carbon nanotubes (MWCNTs) and polyvinyl alcohol (PVA). The Chinese ink acted as a solvent and a dispersant. The MWCNT-ink-PVA ternary composite possessed both high flexibility and high electrical conductivity, with an optimized electrical conductivity of 8.17 S cm−1. This simple method is believed to be applicable to other nanosacle carbon materials. Accepted version

Regenerated silk fibroin solutions from Bombyx mori were tested for electrospinning. Simple and reproducible tensile tests were performed on threads of aligned fibers to obtain information about their mechanical performance at the fiber level. The binary solvent formic acid/chloroform (10:1, v/v) rendered unbeaded thinner fibers with increased extensibility before failure when compared with pure formic acid. A remarkable improvement in strength was induced by immersing length-restricted fibers into ethanol for 5 min. Conformational changes of the protein chains were studied by solid-state NMR.

A simple method for synthesizing Cu2S nanocrystals with different sizes and shapes via solution-phase thermolysis of a copper alkyldithiolate polymer precursor was developed. Monodisperse Cu2S nanodisks can self-assemble into novel corncoblike structure of stacked disks. This solution-phase thermolysis approach provides a facile technique for synthesizing new anisotropic metal chalcogenide nanostructures.

We prepared non-woven electrospun polylactic acid (PLA) membranes containing functionalized sepiolite fibrillar particles (5 wt%). Biocidal activity was achieved by functionalizing sepiolite fibers with Ag (26 wt%) and Cu (26 wt%), which were embedded in the fiber surface. Sepiolite particles were negatively charged in all cases, with zeta potential in the range of −15 to −37 mV, increasing their negative charge with pH. The membranes were biofouled in a cross-flow filtration device using model biofoulants, cultures of Saccharomyces cerevisiae (pH 4.5) and Pseudomonas putida (pH 7.5), which were pumped across the membrane for 24/48 h. The assessment of active biomass was performed by measuring the concentration of adenosine-5′-triphosphate (ATP) in used membranes. The results showed a significant decrease in the amount of surface ATP for PLA loaded with Ag and Cu functionalized sepiolite. The effect was particularly intense for Ag-sepiolite in contact with Saccharomyces cerevisiae , where the reduction amounted to 85% compared to neat PLA (control). This was attributed to the differences in ion availability as a function of pH and to the presence of chloride ions in solution. Pristine sepiolite (without functionalization) did not show any noticeable effect.