Content Of Polar Functional Groups Research Articles

Study on the mechanical properties and microstructure of high‐performance carbon fiber/epoxy composites

AbstractA high‐toughness epoxy has been prepared using carboxyl‐terminated butadiene acrylonitrile (CTBN) as a toughening agent to modify the AG‐80 epoxy resin. High‐performance carbon fiber/epoxy (CF/EP) composites are fabricated using the CTBN‐toughened epoxy resin as the matrix and two types of CF, namely, T800SC and T800HB, as reinforcement. The mechanical properties of the matrix, surface properties of the CFs, tensile properties, and fracture morphologies of the composites are systematically investigated to elucidate the key factors influencing interfacial bonding in high‐performance CF/EP composites. The results reveal that the most significant improvement in toughness is achieved when the CTBN content is 6.90 wt.% in the epoxy resin. Owing to the high content of polar functional groups and excellent surface wettability of T800SC, the T800SC/EP composite exhibits superior mechanical properties compared with the T800HB/EP composite.

The influence of structural properties on the adsorption capacities of microwave-assisted biochars for metazachlor removal from aqueous solutions

Biochars, carbonaceous materials prepared without the usage of chemical agents, are porous materials capable of adsorbing pollutants from ground- and surface waters. In this study, biochars prepared from various types of agricultural biomass were tested for the adsorptive removal of herbicide metazachlor from an aqueous environment. Banana wastes, red mombin seeds, corncob, cocoa pod husk, and coffee husk were used as precursors. Biochars were prepared with the aid of microwave treatment. The effect of precursor type on structure and adsorption was examined. Adsorption was controlled by a multistep mechanism, adsorption kinetics followed predominantly the pseudo-second-order model, adsorption isotherms suited to both Langmuir and Freundlich isotherms, depending on the particular biochar. Significant differences between the structural properties and adsorption capacities of the examined biochars were observed. The best adsorption properties for metazachlor uptake were observed for banana waste-based biochar, which had large, elongated pores, highest volume of micropores and one of the highest contents of polar functional groups. The maximum adsorption capacity, calculated from Langmuir isotherm, was 146.01 mg·g−1, The adsorption capacity at equilibrium, obtained by kinetic measurements, was 27.25 mg·g−1, the kinetic constant was 5.14·10−3 dm3·min−1 (both calculated from pseudo-second order model). Molecular modeling revealed that metazachlor molecules preferably entered two layer wide cavities containing one COOH group with their pyrazole rings.

Effect of surface functionalization on the surface and inter-facial properties of thermoplastic-coated carbon fibers

Hydroxyl- and amino- functionalized carbon fibers (CF―OH and CF―NH2) were prepared by surface oxidation with an acid mixture (H2SO4:HNO3 of 3:1 v/v) followed by grafting with ethylenediamine. The functionalized CFs were sized with a sulfonated poly (ether ether ketone) (SPEEK) sizing agent to prepare CF―OH―SPEEK and CF―NH2―SPEEK materials. The effect of surface functionalization on the surface properties of the CFs and their interfacial properties in PEEK matrix composites were investigated. Results showed that the content of polar functional groups and wettability of the CFs increased significantly after surface functionalization. Chemical reactions between the modified CFs and the sizing agent, improved the interfacial adhesion between them. The interfacial shear strengths of CF―OH―SPEEK and CF―NH2―SPEEK reinforced PEEK matrix composites were increased by 6.2% and 14.0%, respectively, compared with that of the composites reinforced with desized-SPEEK CFs. The surface functionalization helps improve the interfacial adhesion of thermoplastic-coated CF/PEEK composites.

Integrated structural and chemical analyses for HCl-supported hydrochar and their adsorption mechanisms for aqueous sulfachloropyridazine removal

In this study, various HCl-supported hydrochar made from root powder of long-root Eichhornia crassipes were applied to adsorb aqueous sulfachloropyridazine (SCP). Adsorption capacity (qe μg g−1) was positively correlated with combined severity-CS. With CS increasing, carbonization degree, hydrophobicity, porosity and isoelectric point of hydrochar increased, but content of polar functional groups decreased. Hydrophobic interaction was important for SCP adsorption. A 24 × 36 peak area table was generated from 24 FT-IR absorbance spectra computed by peak detection algorithm. Afterwards, correlation analysis between qe μg g−1 and FT-IR peak area were conducted, indicating that wavenumbers at 555.4, 1227.47, 1374.51, 1604.5, 2901.4/2919.2 and 3514.63 cm−1 were helpful for SCP adsorption. Further, multivariate linear regression analyses showed that aromatic skeleton and phenolic hydroxyl were the two biggest contributors. Electrostatic attraction did not exist during the SCP adsorption process. Under strong acid condition, protonated amino groups in cationic SCP acting as a hydrogen donator interacted with electron-rich functional groups onto hydrochar by Hydrogen interaction. Under weak acid condition, neutral SCP served as an π electron donor to bond with hydrochar by π-π electron donator-acceptor interaction. This work could guide the functional groups modification strategy of hydrochar to make better use of it in water purification field.

Polypropylene/Ethylene-And Polar-Monomer-Based Copolymers/Montmorillonite Nanocomposites: Morphology, Mechanical Properties, and Oxygen Permeability.

This research reports the influence of polar monomer contents in ethylene vinyl acetate copolymer (EVA) and ethylene vinyl alcohol copolymer (EVOH) on the morphology, mechanical and barrier properties of polypropylene/ethylene copolymer (PP) reinforced with organically modified montmorillonite (MMT). PP/EVA and PP/EVOH (75/25 wt %) blends were reinforced with 3 wt % MMT in an internal mixer system. Samples were compression-molded into films of 300. The structural characterization was made using X-ray diffraction (XRD), scanning electron microscopy (SEM) and transmission electron microscopy (TEM), the mechanical properties were obtained by tension tests and the barrier properties by oxygen transmission rate (OTR). XRD patterns showed a combination of intercalated/exfoliated morphologies for the MMT, with higher d-001 interplanar distance increments for the blends with higher content of polar functional groups. SEM and TEM micrographs complement the results of the XRD analysis and show differences in the morphologies depending on the miscibility of the polyolefin and the polar monomer copolymer. Mechanical properties and oxygen permeability of composites exhibited a higher improvement, by the addition of MMT, for higher intermolecular interactions and most miscible polymeric system of the EVA. These results show that the higher the number of interactions, given by the VA or OH polar functional groups, the morphology and the miscibility between polyolefin and copolymer imply dispersion improvements of the nanocomposites and, in consequence, a higher improvement on the mechanical and barrier properties of the composite material.

Effects of hydrophobicity-based fractions of Pony Lake fulvic acid on the colloidal stability and dissolution of oppositely charged surface-coated silver nanoparticles

Environmental contextThe fate of silver nanoparticles (AgNPs) in aqueous systems could be influenced by the hydrophobicity of natural organic matter. We observed that the aggregation and dissolution of oppositely charged AgNPs were controlled by the selectivity and dynamics of sorption processes involving the nanoparticle surface and hydrophobic groups on natural organic matter. These findings will be helpful to understand the fate and effects of coated AgNPs in natural systems. AbstractThe fate of silver nanoparticles (AgNPs) released into aquatic environments is significantly affected by natural organic matter (NOM). However, current studies are still insufficient to understand interactions between NOM and AgNPs because they do not explicitly consider the heterogeneity of NOM. We investigated how NOM components with different properties (hydrophobicity, molecular weight, aromaticity, and polarity of functional groups) interact with AgNPs coated with citrate (Cit) and branched polyethylenimine (BPEI) and influence their colloidal stability and dissolution. Pony Lake fulvic acid (PLFA) selected as a model NOM was fractionated into hydrophobic (HPO) and transphilic (TPI) fractions. Sorption of PLFA molecules with a high content of polar functional groups bound to the aromatic rings onto nanoparticles was more favourable in the case of the TPI fraction, which most likely resulted in higher aggregation for both AgNPs and stronger protection of BPEI-AgNPs against dissolution compared with the HPO fraction. Additionally, in contrast to the Cit-AgNPs, resorption of Ag+ ions released from BPEI-AgNPs and/or sorption of Ag+-PLFA complexes to the nanoparticles was most likely a dynamic process, as suggested by the time-dependent changes in the molecular weight of the PLFA fractions sorbed to the BPEI-AgNP surface. These observations suggest that the accessibility of the AgNP surface for the hydrophobicity-based fractions of NOM as well as their colloidal stability and dissolution are controlled by the type and charge of coating materials and by the molecular weight, aromaticity, and content of polar functional groups of NOM.

Mechanism of ultrasonic treatment under nickel salt solution and its effect on electroless nickel plating of carbon fibers

The carbon fibers were ultrasonically treated under nickel chloride solution, and nickel ions were attached to the surface of the carbon fibers, which replaces the nitric acid oxidation method used in the original electroless nickel plating. Electroless nickel plating was performed on the surface of the carbon fibers using a palladium-free technique successfully. Nickel-plated carbon fibers with a higher weight gain ratio than the original method was obtained. XPS was used to study the functional group changes on the surface of carbon fibers and the chemical valence of nickel element. The mechanism of ultrasonic treatment on the surface of carbon fibers was analyzed, and the effect of ultrasonic treatment on the weight gain rate of nickel-plated carbon fibers was discussed. The results show that the ultrasonic treatment under nickel chloride solution can significantly increase the content of polar functional groups on the surface of carbon fibers and can promote the bonding of the carboxyl group on the surface of the carbon fibers with the hydrated nickel ion to form CFCOONi. The formation of CFCOONi enhances the bonding strength between the nano-nickel particles and the carbon fibers, thereby increasing the bonding strength between the plating layer and the substrate. The concentration of nickel chloride solution and ultrasonic power during ultrasonic treatment has a great influence on the weight gain rate of carbon fibers after electroless plating. When the concentration is greater than 10 g/L, the higher the concentration, the smaller the weight gain rate. When the treatment concentration is less than 10 g/L, the concentration has little effect on the weight gain rate. The optimum treatment concentration obtained in the experiment was 7 g/L. As the ultrasonic power increases, the weight gain rate increases first and then decreases, and the optimal ultrasonic power is 80 W. Ultrasonic time does not have a large effect on the weight gain rate, but the too low ultrasonic time will cause a slight decrease in the weight gain rate.

Structure characteristics and adhesive property of humic substances extracted with different methods

The structure characteristics and adhesive property of humic substance (HS) extracted with different methods were mainly studied by terms of elementary analysis, visible spectrum, FT-IR spectroscopy, viscosity, adsorption and pelletizing experiments. The results show that HSs extracted with new method (HS-a) own higher degree of aromatization and polymerization, larger relative molecular mass and more polar functional groups than HS extracted with usual method (HS-b). The viscosity of HS-b is about 30–40 mPa·s lower than that of HS-a. The maximum adsorption amounts of HS-a and HS-b onto iron concentrates are 9.11 mg/g and 8.08 mg/g, respectively. Meanwhile, HS-a has a better performance than HS-b in the practical application for pelletizing of iron concentrates. The difference in agglomeration behaviors with iron concentrates lies in the differences of the structure characteristics of HSs. With higher content of polar functional groups, larger relative molecular mass and viscosity of HSs, the agglomeration behavior is improved.

Influence of Oxygen Plasma Treatment on Surface Properties of Armos Fiber

Armos fiber (F-12 aramid fiber in paper) was provided with broad application foreground as reinforcement material for advanced composites in aviation and spaceflight field, due to its outstanding properties, such as high modulus, high strength, high temperature resistance, erosion resistance and so on. However, the exertion of property was still limited by slippery surface, low surface energy and weak interfacial adhesion performance. In this study, the effects of oxygen plasma treatment time on polar functional groups introduced onto the fiber surface, surface free energy and surface topographic images were discussed by X-ray photoelectron spectroscopy (XPS) analysis, dynamic contact angle analysis system (DCA) and atomic force microscopy (AFM), respectively. It was found that the content of oxygen element and polar functional groups on fiber surface were all increased obviously after oxygen plasma treatment. The content of oxygen element on surface for untreated F-12 aramid fiber was 11.13%, while it increased to 15.20% after oxygen plasma treatment for 10 min; The content of polar functional groups on surface for untreated F-12 aramid fiber was 28.14%, while it increased to 38.11% after oxygen plasma treatment for 10 min. The polar component (γp) of fiber surface energy increased sharply from 6.82 mN/m to 36.68 mN/m after 10 min plasma treatment, the total surface free energy was increased from 46.26 mN/m to 64.66 mN/m.The results indicated that oxygen plasma treatment had introduced a large amount of reactive functional groups onto the fiber surface, and these groups can form together as covalent bonding to improve the surface wettability and increase the surface energy of fibers. At the same time, oxygen plasma treatment was able to generate a mass of bulges and grooves on F-12 aramid fiber surface, which had an active effect on increasing the chemical bond and mechanical function between fiber and resin and enhancing the interfacial adhesion performance of composite. The fiber surface grooves had been increased with the time prolonging before 10 min while decreased after 10 min, the results maybe relate to partial organic on fiber surface melting. It had an adverse effect on the interfacial adhesion properties of composite. Therefore, the optimum plasma treatment time was between 5 min and 10 min.

Purification of the used palm oil by adsorption

Purification of the used palm oil by adsorption The components of fresh vegetable oils are mainly non-polar. During frying of food, complex and multistage reactions occur in the oil, which produce various polar compounds. Active carbons are characterized by small contents of polar functional groups, which are responsible for adsorbing such polar compounds. Effective purification of the used frying oils must involve the removal of the polar substances. To improve the quality of the used palm oil, an active carbon oxidized by a hydrogen peroxide treatment was used. Such a carbonaceous adsorbent improves the quality of the oil used for frying food by purifying it from colour substances, lipid hydrolysis products, oxidation products and total polar compounds.