Non-polar Matrices Research Articles

Performance enhancement of silica filled natural rubber nanocomposites using organic deep eutectic solvent

Silica is an important filler of “green tires” while its dispersion in the aid of silane coupling agents emits volatile organic compounds during rubber compounding and its invariably agglomeration in nonpolar rubber matrices enhances strain softening. Herein a highly active deep eutectic solvent (DES), synthesized using stearic acid as hydrogen bond donor and tetrabutylammonium chloride as hydrogen bond acceptor, is used to tailor reinforcement and softening behaviors and to replace the silane coupling agents for preparing volatile organic compounds-free nanocomposites. The results show that DES can regulate the crosslinking network structure of rubber matrix and accelerate the vulcanization by reacting with non-rubber components in natural rubber (NR) and by improving the proportion of disulfidic linkage. Furthermore, DES is able to improve the dispersion of silica, crosslinking density of NR and the interfacial interaction between silica and NR, and slow down the thermo-oxidative aging behavior. It could also weaken the damping and softening accompanying Mullins effect for the nanocomposites vulcanizates at high strains. In comparison with silane, DES endows the nanocomposites with superior vulcanization and mechanical properties, providing guides to mediate the reinforcement and strain softening behaviors and manufacture high-performance “green tires” in an energy-efficient approach.

One-Component Nanocomposites Made from Diblock Copolymer Grafted Cellulose Nanocrystals.

Cellulose nanocrystals (CNCs) are bio-based, rod-like, high-aspect-ratio nanoparticles with high stiffness and strength and are widely used as a reinforcing nanofiller in polymer nanocomposites. However, due to hydrogen-bond formation between the large number of hydroxyl groups on their surface, CNCs are prone to aggregate, especially in nonpolar polymer matrices. One possibility to overcome this problem is to graft polymers from the CNCs' surfaces and to process the resulting "hairy nanoparticles" (HNPs) into one-component nanocomposites (OCNs) in which the polymer matrix and CNC filler are covalently connected. Here, we report OCNs based on HNPs that were synthesized by grafting gradient diblock copolymers onto CNCs via surface-initiated atom transfer radical polymerization. The inner block (toward the CNCs) is composed of poly(methyl acrylate) (PMA), and the outer block comprises a gradient copolymer rich in poly(methyl methacrylate) (PMMA). The OCNs based on such HNPs microphase separate into a rubbery poly(methyl acrylate) phase that dissipates mechanical energy and imparts toughness, a glassy PMMA phase that provides strength and stiffness, and well-dispersed CNCs that further reinforce the materials. This design afforded OCNs that display a considerably higher stiffness and strength than reference diblock copolymers without the CNCs. At the same time, the extensibility remains high and the toughness is increased up to 5-fold relative to the reference materials.

Evolution of the Microstructure of PP-LDHs Nanocomposites during Melt Compounding: A Simulation Approach.

In the context of polymer-based nanocomposites containing layered nanofillers, the achievement of good extents of dispersion and distribution of the embedded nanoparticles and, even more, the obtainment of intercalated and/or exfoliated structures through melt compounding still represents a persistent challenge, especially in the case of anionic layered double hydroxides (LDHs)-containing systems and non-polar polymeric matrices. In this work, a simulation approach is proposed to evaluate the influence of the processing conditions on the morphology of polypropylene (PP)-based nanocomposites containing organomodified LDHs. In particular, the effect of the screw rotation speed and the feed rate on the final microstructure of the materials formulated through melt compounding in a twin-screw extruder was assessed. The rheological and morphological characterizations demonstrated that a more homogeneous morphology was achieved when high levels of both exploited processing parameters are selected. The results coming from the simulation of the processing were used to establish some relationships between the flow parameters and the microstructure of the nanocomposites, demonstrating that low residence times coupled with high local shear rates are required to ensure the achievement of homogenous morphologies, likely involving the occurrence of intercalation phenomena.

Optimizing Acetic Anhydride Amount for Improved Properties of Acetylated Cellulose Nanofibers from Sisal Fibers Using a High-Speed Blender.

Acetylated cellulose nanofibers (ACNFs) have shown a great potential for strengthening non-polar polymer matrices and better dispersion which can improve composite properties. However, insufficient acetylation may cause inadequate nanofibrillation ACNF during the fibrillation process. The objective of this work was to evaluate the effect of different amounts of acetic anhydride (0, 45, 55, and 65 mL) on the degree of substitution (DS), morphology, crystalline structure, and thermal properties of ACNF obtained from sisal fiber produced using a high-speed blender. The attenuated total reflectance-Fourier transform infrared spectroscopy revealed the success of the acetylation process by the presence of the carbonyl signal around 1724 cm-1. Furthermore, the DS of ACNF was increased with the acetic anhydride amounts. X-ray diffraction analysis revealed that the crystalline structure of ACNF and non-ACNFs were cellulose I, and the crystallinity index of CNF was increased after acetylation treatment. Thermogravimetric analysis showed that the thermal stability of CNF was improved considerably after the acetylation process. The water contact angle of ACNF was higher than that of CNF, indicating that the structural property of CNF altered from hydrophilic to more hydrophobic after acetylation. In addition, the thermal resistance of CNF was improved significantly after acetylation treatment. The optimum amount of acetic anhydride was achieved in 55 mL of acetic anhydride (ACNF-55) which produced ACNF with a DS value of 0.5, a crystallinity index of 77%, a diameter of 87.48 nm, a maximum degradation temperature of 351 °C, and a contact angle of 37.7°. Overall, it was concluded that the obtained ACNF had great potential as reinforcement materials for nanocomposites based on non-polar polymeric matrices.

Rationalizing the Dependence of Poly (Vinylidene Difluoride) (PVDF) Rheological Performance on the Nano-Silica

Research on the rheological performance and mechanism of polymer nanocomposites (PNCs), mainly focuses on non-polar polymer matrices, but rarely on strongly polar ones. To fill this gap, this paper explores the influence of nanofillers on the rheological properties of poly (vinylidene difluoride) (PVDF). The effects of particle diameter and content on the microstructure, rheology, crystallization, and mechanical properties of PVDF/SiO2 were analyzed, by TEM, DLS, DMA, and DSC. The results show that nanoparticles can greatly reduce the entanglement degree and viscosity of PVDF (up to 76%), without affecting the hydrogen bonds of the matrix, which can be explained by selective adsorption theory. Moreover, uniformly dispersed nanoparticles can promote the crystallization and mechanical properties of PVDF. In summary, the viscosity regulation mechanism of nanoparticles for non-polar polymers, is also applicable to PVDF, with strong polarity, which is of great value for exploring the rheological behavior of PNCs and guiding the process of polymers.

Covalently functionalized cellulose nanocrystal-reinforced photocurable thermosetting elastomer for 3D printing application

Due to distinct advantages of 3D printing (3DP), multifunctional materials are swiftly finding their applications into diverse industries nowadays. Among the existing 3DP materials, polymers present vast and exciting opportunities but simultaneously face new challenges to satisfy certain specifications. Among the existing polymer classes, elastomers play an important role because of its wide range of applications in nearly every industry such as automotive, marine, aerospace, electronics, medical, and consumer. However, 3D printing of elastomers remains an exigent task because of the resulting weak mechanical properties that impede its proliferation to different industrial applications. In improving material properties, the use of nanofiller has been a widely accepted approach. In pursuit of global environmental sustainability, the trend nowadays is to identify a material from a biobased source. As a biobased filler with inherently high stiffness, high strength, and high aspect ratio, cellulose nanocrystal has the potential to impart high-performance reinforcement to 3D-printed elastomers and consequently satisfy end-use requirements. Notwithstanding its inherent characteristics, the inhomogeneous dispersion of CNC in an elastomeric matrix would cause detrimental effects on the structural integrity of the nanocomposite material. Earlier attempts of reinforcing stereolithography resins using CNC, pristine and modified, yield to a moderate increase in strength but greatly compromise the elongation at break of the composite material. Hence, this study first reports high toughness improvement of the 3D-printed photocurable elastomer via stereolithography using a covalently functionalized CNC. More so, it is interesting to note that percolation threshold of < 1 wt% has significant effects on the different mechanical properties of the new nanocomposite material. The morphological, thermal, and mechanical properties of the new nanocomposite material are delineated. The approach prescribed in this study presents an effective route to expand the utility of CNC to nonpolar matrices such as the thermosetting elastomer and to increase the biobased content of a 3DP material in achieving the global need for sustainable materials.

Ductile composite films of polyethylene and low grammage paper

To obtain high dispersion and good mechanical properties, the incorporation of cellulose in non-polar polymeric matrices is usually carried out with chemical modification of precursors or addition of compatibilizers. Despite the great advances in increasing stiffness, the resulting composites generally have their deformation compromised (dramatic decrease in ductility in comparison with neat polymer). Here, from polyethylene films and thin paper sheets, composites that combine high rigidity and high ductility were obtained by hot pressing, without additional steps or compatibilizers. The use of a structured reinforcement (low grammage paper) to prepare the composites allowed: (a) obtaining a good fiber distribution in the matrix; (b) achieve an architecture for composites that enables high deformation; (c) use of mild processing conditions; (d) obtaining via continuous processing by a heated cylinder system. The low grammage paper – PE composites exhibited a considerable increase in modulus (up to 90%) and high ductility. Therefore, as a consequence of the (i) rigidity and ductility, (ii) low price of precursors and (iii) possibility of processing by a simple and practical method, these composite films have potential industrial application (as in tarpaulins and geomembranes).

Preparation of Polyethylene Nanocomposites Based on Polyethylene Grafted Exfoliated α-Zirconium Phosphate

Polymer nanocomposites containing well-exfoliated nanoplatelets have been shown to possess greatly enhanced physical and mechanical properties. However, it is still a significant challenge to achieve adequate exfoliation of 2D nanoplatelets in polyolefin matrices due to poor compatibility and associated entropic penalty between 2D inorganic filler and nonpolar polyolefin matrices. Grafting polyolefin chains onto the surfaces of an already exfoliated nanoplatelet is a simple, yet effective solution to this problem. The grafted polyolefin chains on the nanoplatelets can entangle and cocrystallize with the polyolefin matrix, preventing agglomeration. In this study, polyethylene (PE) grafted α-zirconium phosphate (ZrP), ZrP-g-PE, was prepared and blended with the PE matrix. The graft density of ZrP-g-PE was designed to maintain ZrP exfoliation during subsequent blending with the PE matrix. It was found that PE confined crystallization formed in ZrP-g-PE, resulting in the formation of PE crystal orientation perpendicular to the ZrP nanoplatelets. The usefulness of this study for preparation of high-performance polyolefin nanocomposites is discussed.

Surface modification of the cellulose nanocrystals through vinyl silane grafting

Incompatibility of nanocellulose with non-polar polymer matrices disrupts the interfacial interaction and results in aggregation and phase separation. In this study a facile and environmentally friendly method was used to partially substitute the surface hydroxyl groups by attaching polysiloxane to impart hydrophobic properties. The silanization reaction proceeded with hydrolysis of triethoxyvinylsilane (TEVS) into reactive silanols followed by condensation to form the branched polymer. These polysiloxane oligomers were chemically grafted to form alkoxy silane bonds on the surface of CNCs. A suitable degree of hydrophilic-hydrophobic balance of the modified CNCs was achieved which improved their dispersion in hydrophobic matrix poly(butylene adipate-co-terephthalate) (PBAT). FTIR, NMR (13C and 29Si) and XPS demonstrated successful surface chemical modification and confirmed extent of silanization as a function of silane concentration. XRD showed successful grafting of the vinyl silane agent and confirmed polymorph structure of the nanocellulose was retained. The results from TEM and AFM demonstrated successful coating of nano whiskers at 5 wt% silane loading. The successful grafting of the silane agent with pendant vinyl groups improved surface hydrophobicity. These results show that this facile method produces adequately surface modified CNC which can be used as filler in hydrophobic matrices of bioplastics.

Evaluation and optimization of the influence of silver cluster ions on the MALDI-TOF-MS analysis of polystyrene nanoplastic polymers.

In the analysis of polystyrene nanoplastics (PSNs), a nonpolar polymer (NP), using matrix-assisted laser desorption/ionization time-of-flight mass spectrometry (MALDI-TOF-MS), silver salts were used as cationization reagents and simultaneously brought the potential problems of silver clusters that interfered with the PSN signal of MS. To detect PSNs, silver trifluoroacetate (AgTFA) and silver nitrate (AgNO3) were mixed with five polar matrices, namely 2-(4-hydroxyphenylazo) benzoic acid (HABA), dithranol (DI), sinapic acid (SA), trans-3-indoleacrylic acid (IAA), and 2,5-dihydroxybenzoic acid (DHB), and three nonpolar matrices, namely pyrene (PRN), anthracene (ATH) and acenaphthene (ACTH). The results showed that silver salt cluster ions were detected in the range of m/z 1000-4000. Five polar matrices with silver salts produced silver clusters, which interfered with the signals in the mass spectrum of PSNs, but the combination of these matrices with copper II chloride (CuCl2) salt did not produce copper-related clusters. However, the use of nonpolar matrices such as PRN, ATH or ACTH significantly decreased the signals of silver salt cluster ions, and this alteration of matrix types is considered a promising optimization approach for silver cluster ions. The nonpolar matrix conditions were optimized without producing silver cluster ions and the optimal detection conditions were found to be under nonpolar matrices (e.g., pyrene) with silver salts (e.g., AgTFA). The results suggest that when polar matrices, such as HABA, DI, SA, IAA, and DHB, are combined with silver salts in MALDI-TOF-MS analysis, silver-related clusters are detected in the range of m/z 1000-4000. Inhibition of the production of silver cluster ions can be achieved by the use of a nonpolar matrix (e.g., PRN) or polar matrix (e.g., DHB) with copper salts.

Analysis of Toxic Metals in Aerosols from Devices Associated with Electronic Cigarette, or Vaping, Product Use Associated Lung Injury.

Research gaps exist in toxic metals characterization in e-cigarette, or vaping, products (EVPs) as these analytes typically have low concentrations and most standard aerosol trapping techniques have high metals background. An additional complication arises from differences in the EVP liquid formulations with nicotine products having polar properties and non-nicotine products often being non-polar. Differences in polar and non-polar matrices and the subsequent aerosol chemistries from various EVPs required modifications of our previously reported nicotine-based EVP aerosol method. Validation and application of the expanded method, suitable for both hydrophobic and hydrophilic aerosols, are reported here. The metals analyzed for this study were Al, Cr, Fe, Co, Ni, Cu, Cd, Sn, Ba, and Pb. The method limits of detection for the modified method ranged from 0.120 ng/10 puffs for Cd to 29.3 ng/10 puffs for Al and were higher than reported for the previous method. Results of the analyses for metals in aerosols obtained from 50 EVP products are reported. Cannabinoid based EVP aerosols were below reportable levels, except for one sample with 16.08 ng/10 puffs for Cu. Nicotine-based EVP results ranged from 6.72 ng/10 puffs for Pb to 203 ng/10 puffs for Sn. Results of the analyses for these metals showed that aerosols from only 5 of the 50 devices tested had detectable metal concentrations. Concentrations of toxic elements in the aerosols for nicotine-based EVP aerosol metal concentration ranges were consistent with previously published results of aerosol analyses from this class of devices.

Microwave Hydrophobized Lignin with Antioxidant Activity for Fused Filament Fabrication

The poor compatibility and aggregation propensity of lignin in nonpolar polymer matrices greatly limits its application in polymer blends and composites. We demonstrate an efficient, solvent-free, and catalyst-free microwave-assisted approach for hydrophobization of alkali lignin to enhance its compatibility with polylactide. Effective modification with up to 98% substitution of lignin’s hydroxyl groups was achieved under mild and catalyst-free reaction conditions. The modified acetylated and hexanoated lignins exhibited enhanced thermal stability and thermoplasticity, which were reflected by the good melt-extrusion and 3D printing properties of the corresponding polylactide/lignin blends. The tensile properties varied somewhat depending on the degree and type of substitution and the amount of hydrophobized lignin but in general the tensile properties were in the same range as those of polylactide. Blends consisting of up to 50 weight-% acetylated lignin were successfully extruded to filaments and 3D printed, demonstrating good processability and tensile properties regardless of the high lignin content, while it was not possible to extrude continuous filaments of polylactide and nonmodified alkali lignin even at low concentration (10 weight %). Additionally, the polylactide/acetylated lignin blends exhibited antioxidant activity as revealed by radical scavenging ability and improved thermo-oxidative stability with up to 40 °C increase in oxidation induction temperature compared to neat polylactide. The sustainable compatibilization strategy proposed herein paves the way for value-added utilization of lignin in fully biobased 3D printing filaments with improved oxidative stability.

Highly Hydrophobic Organosilane-Functionalized Cellulose: A Promising Filler for Thermoplastic Composites.

The aim of this work is to design and optimize the process of functionalization of cellulose fibers by organosilane functional groups using low-pressure microwave plasma discharge with hexamethyldisiloxane (HMDSO) precursor in order to prepare a compatible hydrophobic filler for composites with nonpolar thermoplastic matrices. Particular attention was paid to the study of agglomeration of cellulose fibers in the mixture with polypropylene. In our contribution, the dependence of the surface wettability on used process gas and treatment time was investigated. Scanning electron microscopy (SEM) and X-ray photoelectron spectroscopy (XPS) analyses were applied to characterize the surface morphology and chemical composition of the cellulose fibers. It was observed that the plasma treatment in oxygen process gas led to the functionalization of cellulose fibers by organosilane functional groups without degradation. In addition, the treated cellulose was highly hydrophobic with water contact angle up to 143°. The use of treated cellulose allowed to obtain a homogeneous mixture with polypropylene powder due to the significantly lower tendency of the functionalized cellulose fibers to agglomerate.

POLYMER BIOCOMPOSITES BASED ON AGRO WASTE: PART I. SOURCE, CLASSIFICATION, CHEMICAL COMPOSITION AND TREATMENT METHODS OF LIGNOCELLULOSIC NATURAL FIBERS

At present, the depletion of natural resources and environmental problems have generated great interest in finding a sustainable alternative to create new materials that are environmentally friendly. In recent years, many researchers have focused on investigations related to agricultural waste products to solve environmental problems associated with the disposal of agro waste. Thanks to their annual renewability and biodegradability, over the past two decades, agricultural waste has become an environmentally friendly alternative to synthetic fibers. In this regard, this review gives a general idea of new lignocellulosic polymer composite materials in which various natural fibers are used as fillers and reinforcing additives. The sources, classification and chemical composition of lignocellulosic natural fibers have been also given. Natural fibers include a hydroxyl functional group that makes the fibers hydrophilic. Hydrophilic natural fibers and hydrophobic polymer matrix lead to incompatibility and weak interfacial bonds between them. To resolve the problem of incompatibility of plant fibers with non-polar polymer matrices, various methods of surface treatment of natural fibers, including physical, chemical and biological processing, have been considered. From this perspective, in our opinion, the data presented in this article can be used as a database for further study of agricultural waste as fillers or reinforcing additives in polymer composites in order to accelerate the development and stimulate the commercial production of these new materials.

A rotating disk sorptive extraction based on hydrophilic deep eutectic solvent formation

An elegant preconcentration method assumed sorption of polar analytes from complex non-polar matrices on a rotating disk based on hydrophilic deep eutectic solvent formation is presented for the first time. The surface of poly(vinylidene fluoride-co-tetrafluoroethylene) rotating disk was coated with choline chloride acted as a precursor of deep eutectic solvent (hydrogen bond acceptor). The rotating disk was immersed in vegetable oil sample and phenolic compounds (hydrogen bond donors) were efficient separated on the disk during its rotation due to deep eutectic solvent formation. Ability of hydrophilic deep eutectic solvent decomposition in aqueous phase was used for fast analytes elution from the disk surface (2 min). Finally, the obtained aqueous solution of phenolic compounds and choline chloride was analyzed by high-performance liquid chromatography with fluorescence detection. Under optimal conditions, the limits of detection for gallic acid, protocatechuic acid, tyrosol, vanillic acid, p-coumarinic acid, syringaldehyde and thymol were in the range of 10–60 μg L−1. The developed approach allowed to significantly reduce sorption and elution time in comparison with previously reported rotating disk sorptive extraction approaches. The extraction mechanism based on deep eutectic solvent formation provided selective separation of target analytes with absolute extraction recovery in the range of 66–87%.

Improved Mechanical Properties of Jute Fiber/Polypropylene Composite with Interface Modified by Sodium Lignosulfonate

How to improve the interfacial compatibility between polar fibers and non-polar polymer matrices is still a challenge for the application of natural fiber/polymer composites. In this study, the jute fibers (JF) was firstly treated by coating sodium lignosulfonate (SL) layer, then the JF-SL/polypropylene (PP) composite was fabricated by injection molding technique. The morphology, surface chemical property, surface energy, mechanical properties of JF and JF-SL, as well as the mechanical properties of JF/PP and JF-SL/PP composites were systematically studied. The results showed that the SL coating layer successfully formed on the surface of JF, and the dipole bond and hydrogen bond interaction occurred between the SL and JF. Compared with JF/PP composite, the tensile modulus, tensile strength, flexural modulus and flexural strength of JF-SL/PP composite increased by 8.25%, 16.79%, 16.87% and 19.71%, respectively, due to the enhancement of the interfacial binding force between JF-SL and PP matrix. These results indicate that SL possesses great potential to be used as a compatibilizer to effectively improve the mechanical properties of JF-SL/PP composite. It could provide an reference basis for the feasibility of SL used as a compatibilizer for natural fiber/polymer composites.

Nonpolar Organic Dispersion of 2D Ti3C2Tx MXene Flakes via Simultaneous Interfacial Chemical Grafting and Phase Transfer Method.

Herein, we demonstrate a simple and versatile way for preparing stable Ti3C2Tx MXene dispersions in nonpolar organic solvents through a simultaneous interfacial chemical grafting reaction and phase transfer method. Alkylphosphonic acid ligands were chemically grafted on the hydroxyl terminal groups of Ti3C2Tx flakes at the liquid-liquid interface between water and water-immiscible organic medium to form a covalent Ti-O-P bond via interfacial nucleophilic addition and sequential condensation reaction at room temperature; the surface-functionalized Ti3C2Tx flakes concurrently migrated from the aqueous phase to the organic phase. Unlike conventional surface chemical modification methods that require many complex and tedious steps, this is a simple and easy process for fabricating a Ti3C2Tx organic dispersion in various organic solvents, from highly polar to nonpolar. The nonpolar Ti3C2Tx dispersion in chloroform also exhibits strong oxidation resistance and stable long-term storage. This approach provides an opportunity for preparing MXene nanocomposites with nonpolar polymeric matrices that are soluble in organic media for future applications such as stretchable electrode.

METHODS OF DESIGNING HARDWARE DECORATION OF PRODUCTIONS OF CARBON NANOTUBES AND BY-PRODUCTS ON THEIR BASIS

From the positions of system analysis and the theory of optimal design the approach to the development of hardware design of industrial production of carbon nanotubes and by-ptoducts on the basis of their functionalized forms is proposed. Functionalization is carried out by oxidation of nanotubes with concentrated nitric acid and their subsequent modification by titanium stearate. Functionalized by this method, carbon nanotubes have increased hydrophobic properties and are semi-products for use in composites based on non-polar matrices. Material flows of production of nanotubes and semi-products on their basis are analyzed. Interrelations between them are established. The cost of the product is used as a global economic criterion of optimality. A three-level decomposition of the technological scheme of nanotubes and their functionalized forms production on the principle of "production – stage of production – hardware design stage" is made. At the second level of decomposition, the following stages are identified: catalyst preparation; preparation of carbonaceous raw materials; synthesis of nanotubes; utilization of gaseous pyrolysis products; treatment of material after synthesis; oxidation of nanotubes; modification of oxidized nanotubes with titanium stearate. Economic optimality criteria are determined for them, taking into account the return of by-products from the stages of purification of carbon nanotubes and neutralization of gaseous pyrolysis products at the stage of catalyst production and preparation of the initial carbon-containing raw materials, respectively. The interrelation of information and coordinating signals of the first and second level of the task of designing a new production is established. The correlation of initial design data (qualitative composition of carbon-containing raw materials, production capacity, complex quality index of carbon nanotubes and their morphological characteristics) and the main design and operating parameters of the hardware design of industrial production of carbon nanotubes and semi-products based on them is shown. The task of designing a new production taking into account the combined production of catalyst-free and functionalized carbon nanotubes with the use of the same hardware design is formulated.

Polymeric Sorbent with Controlled Surface Polarity: An Alternate for Solid-Phase Extraction of Nerve Agents and Their Markers from Organic Matrix.

Extraction and identification of lethal nerve agents and their markers in complex organic background have a prime importance from the forensic and verification viewpoint of the Chemical Weapons Convention (CWC). Liquid-liquid extraction with acetonitrile and commercially available solid phase silica cartridges are extensively used for this purpose. Silica cartridges exhibit limited applicability for relatively polar analytes, and acetonitrile extraction shows limited efficacy toward relatively nonpolar analytes. The present study describes the synthesis of polymeric sorbents with tunable surface polarity, their application as a solid-phase extraction (SPE) material against nerve agents and their polar as well as nonpolar markers from nonpolar organic matrices. In comparison with the acetonitrile extraction and commercial silica cartridges, the new sorbent showed better extraction efficiency toward analytes of varying polarity. The extraction parameters were optimized for the proposed method, which included ethyl acetate as an extraction solvent and n-hexane as a washing solvent. Under optimized conditions, method linearity ranged from 0.10 to 10 μg mL-1 ( r2 = 0.9327-0.9988) for organophosphorus esters and 0.05-20 μg mL-1 ( r2 = 0.9976-0.9991) for nerve agents. Limits of detection (S:N = 3:1) in the SIM mode were found in the range of 0.03-0.075 μg mL-1 for organophosphorus esters and 0.015-0.025 μg mL-1 for nerve agents. Limits of quantification (S:N = 10:1) were found in the range of 0.100-0.25 μg mL-1 for organophosphorus esters and 0.05-0.100 μg mL-1 for nerve agents in the SIM mode. The recoveries of the nerve agents and their markers ranged from 90.0 to 98.0% and 75.0 to 95.0% respectively. The repeatability and reproducibility (with relative standard deviations (RSDs) %) for organophosphorus esters were found in the range of 1.35-8.61% and 2.30-9.25% respectively. For nerve agents, the repeatability range from 1.00 to 7.75% and reproducibility were found in the range of 2.17-6.90%.

Effect of graphene on polar and nonpolar rubber matrices

BackgroundSo far, the effect of graphene oxide (GO) and reduced graphene oxide (rGO) in rubber matrix has not been well established.MethodsThe effects of graphene oxide (GO) and reduced graphene oxide (rGO) on the physical properties of polar acrylonitrile-butadiene rubber (NBR) and non-polar Ethylene-propylene-diene terpolymer rubber (EPDM) matrix have been investigated and their properties compared. NBR vulcanizates exhibited higher cure rates compared to the EPDM systems.ResultsEffective dispersion of the nanosheets within the different matrices was observed to be a reason for the improvement in properties, but the effective nanosheets-matrix interactions played a key role in reinforcing action. This was noticeable in the various properties (crosslinking density, tensile properties, and dynamical mechanical analysis) evaluated. Typically, the polar NBR matrix was observed to show about 461 and 405% higher interactions parameter with GO and rGO fillers (loaded from 0.1~1phr) than composites of EPDM based on Kraus model.ConclusionsWhile this present work has confirmed the significance of considering the polarities of graphene sheets or derivative graphene (GSD) and their respective polymers matrices for effective property enhancement for specific applications, it has also demonstrated the future prospects of rubber-graphene nanocomposites for several applications which include structural, barrier, and dielectric energy storage materials.