Preparation and characterization of the bacterial cellulose/polyurethane nanocomposites

New nanocomposites based on bacterial cellulose nanofibers (BCN) and polyurethane (PU) prepolymer were prepared and characterized by SEM, FT-IR, XRD, and TG/DTG analyses. An improvement of the interface reaction between the BCN and the PU prepolymer was obtained by a solvent exchange process. FT-IR results showed the main urethane band at 2,270 cm^?1 to PU prepolymer; however, in nanocomposites new bands appear as disubstituted urea at 1,650 and 1,550 cm^?1. In addition, the observed decrease in the intensity of the hydroxyl band (3,500 cm^?1) suggests an interaction between BCN hydroxyls and NCO-free groups. The nanocomposites presented a non-crystalline character, significant thermal stability (up to 230 °C) and low water absorption when compared to pristine BCN.     

Preparation of activated carbon from cotton stalk and its application in supercapacitor

High specific capacitance and low cost are the critical requirements for a practical supercapacitor. In this paper, a new activated carbon with high specific capacitance and low cost was prepared, employing cotton stalk as the raw material, by using the phosphoric acid (H₃PO₄) chemical activation method. The optimized conditions were as follows: the cotton stalk and activating agent with a mass ratio of 1:4 at an activation temperature of 800 °C for 2 h. The samples were characterized by nitrogen adsorption isotherms at 77 K. The specific surface area and pore volume of activated carbon were calculated by Brunauer–Emmett–Teller (BET) and t-plot methods. With these experimental conditions, an activated carbon with a BET surface area of 1,481 cm²?g^?1 and micropore volume of 0.0377 cm³?g^?1 was obtained. The capacitance of the prepared activated carbon was as high as 114 F?g^?1.The results indicate that cotton stalk can produce activated carbon electrode materials with low cost and high performance for electric double-layer capacitor.     

Tailoring microporosity and nitrogen content in carbons for achieving high uptake of CO2 at ambient conditions

A series of nitrogen-containing carbon spheres (CS) was prepared using the modified Stöber method. These CS were synthesized by using resorcinol and formaldehyde as carbon precursors, melamine as nitrogen precursor and ammonia as a polymerization reaction catalyst. Hydrothermal treatment followed by activation of these polymer spheres resulted in highly porous nitrogen-containing CS. Elemental analysis and N₂ adsorption showed that the aforementioned CS exhibited high surface area (reaching 1,610 m²/g) with large fraction of fine micropores (volume of micropores smaller than 1 nm was estimated to be 0.40 cm³/g) and comparatively high nitrogen content (about 4.0 at.%). Interestingly, high CO₂ adsorption capacities, 4.4 and 6.9 mmol/g, were obtained for these CS at 1 bar and two temperatures, 25 and 0 °C, respectively.     

Thermal Pretreatment of Harvest Residues and Their Use in Anaerobic Co-digestion with Dairy Cow Manure

Several batch experiments were conducted on the anaerobic co-digestion of dairy cow manure (DCM) with three harvest residues (HR) (soybean straw, sunflower stalks, and corn stover). The influence of thermal pretreatment of HR on biogas production was investigated, where the HR were thermally pretreated at two different temperatures: T = 121 °C and T = 175 °C, during t = 30 and t = 90 min, respectively. All anaerobic co-digestion batch experiments were performed simultaneously under thermophilic regime, at T = 55 °C. Biogas and methane yields were significantly improved in experiments performed with corn stover thermally pretreated at 175 °C for 30 min (491.37 cm³/g VS and 306.96 cm³/g VS, respectively), if compared to experiments performed with untreated corn stover. The highest VS and COD removal rates were also observed in the same group of experiments and were 34.5 and 50.1%, respectively. The highest biogas and methane yields with soybean straw (418.93 cm³/g VS and 261.44 cm³/g VS, respectively) were obtained when soybean straw pretreated at 121 °C during 90 min. The highest biogas and methane yields with sunflower stalk (393.28 cm³/g VS and 245.02 cm³/g VS, respectively) were obtained when sunflower stalk was pretreated at 121 °C during 90 min.     

Textile grade long natural cellulose fibers from bark of cotton stalks using steam explosion as a pretreatment

Textile grade long natural cellulose fibers with fineness of 27 dtex have been extracted from bark of cotton stalks by a combination of steam explosion, potassium hydroxide and peroxide treatments (explosion–KOH–H₂O₂). It was reported that natural cellulose fibers from bark of cotton stalks had significantly better mechanical properties than those from other lignocellulosic agricultural byproducts such as rice and wheat straws. Fibers from bark of cotton stalks were used to reinforce thermoplastic composites but could not be spun into yarns for textile applications due to their high fineness value (around 50 dtex) and/or low aspect ratio (around 660). In this research, barks of cotton stalks were treated using three methods, including steam explosion, a combination of steam explosion and potassium hydroxide treatments (explosion–KOH) and explosion–KOH–H₂O₂. The morphology, composition, carding yield, crystalline structures and tensile properties of three different cotton stalk fibers were analyzed. Results showed that cotton stalk fibers extracted by explosion–KOH–H₂O₂ had the lowest fineness value of 27 dtex and moderate aspect ratio of 1,150 in three kinds of fibers. The fibers also had most clean and smooth surfaces, highest carding yield of 68.6 %, and highest cellulose content of 82.1 wt% due to effective removal of non-cellulose impurities. Moreover, the fibers had tensile properties close to cotton fibers. Overall, the cotton stalk fibers presented a better potential to be used as textile fibers than those reported by previous researches. explosion–KOH–H₂O₂ could be an efficient method for exploring textile applications of bark of cotton stalks.     

Effect of Surface Passivation in Spinel Slurry Toward Hydrolysis: Neutron Scattering and Rheological Studies

Aqueous colloidal forming of magnesium aluminate (MgAl₂O₄) spinel offers much potential for various applications; however, these advantages are generally offset by the basic nature of the powder and its affinity for hydrolysis. Hydrolysis in the presence of water generally imparts surface chemical changes resulting in the degradation of colloidal stability. In the present study, spinel powders were subjected to thermally assisted surface passivation and evaluated for the effectiveness of preventing hydrolysis through quasielastic neutron scattering (QENS) technique and correlated with rheological measurements. In order to evaluate the extent of hydrolysis, spinel slurries prepared with (SP) and without surface passivation (WSP) were studied by rheological and QENS measurements at regular intervals of time. While WSP slurry exhibited a steep enhancement in viscosity from 1.02 to 19.4 Pa · s and fraction of the elastic intensity from 0.20 to 0.38 for 96 and 200 hours, respectively, a negligible change in viscosity for SP slurries from 0.313 to 0.345 Pa · s and fraction of the elastic intensity from 0.16 to 0.17 for the similar period confirmed the inhibition of hydrolysis, revealing change in surface chemistry due to hydrolysis. Microscopic details as obtained from neutron scattering data revealed that dynamical behavior of water molecules in both the slurries could be described very well by the Singwi–Sjolander model of jump diffusion. Further analysis showed lower diffusivity ～1.82 × 10^?5 cm²/sec and higher residence time ～6.39 ps for WSP slurry in comparison with 2.16 × 10^?5 cm²/sec and 5.80 ps, complimenting the inhibition of hydrolysis in case of SP slurry.     

Thermal decomposition of metal nitrates

The paper presents a study regarding the preparation of 40 %M^IIFe₂O₄/60 %SiO₂ nanocomposites (M = Ni, Zn, Cu) by thermal decomposition of metal nitrates—poly(vinyl alcohol)–tetraethyl orthosilicate gels. Thermal analysis and FT-IR spectroscopy have evidenced that a redox reaction takes place between PVA and NO ₃ ^? ions in the pores of the formed hybrid gels. The result of this redox reaction is the formation of carboxylate-type coordination compounds that have the role of a precursor of the ferrite nanoparticles. By thermal decomposition of these precursors inside the silica matrix, the corresponding MFe₂O₄/SiO₂ nanocomposites are obtained starting with 600 °C, as resulting from XRD analysis. Elemental maps of the corresponding involved elements M (Ni, Zn, Cu), Fe, and Si have confirmed the homogenous distribution of the ferrite nanoparticles within the silica matrix. TEM images have shown that the nanocomposites were obtained as fine nanoparticles, with diameter up to 20 nm. All nanocomposites 40 %M^IIFe₂O₄/60 %SiO₂ obtained at 1000 °C presented magnetic properties characteristic to this type of nanocomposite.     

Graphene oxide-modified polyaniline pigment for epoxy based anti-corrosion coatings

In the present work, a set of polyaniline–graphene oxide (PANI–GO) nanocomposites which exhibit superior properties in terms of shelf life, processability and conductivity due to the synergistic effect of GO and PANI, have been synthesized by varying the concentration of highly non-conducting GO with respect to aniline. The obtained materials were characterized by UV–Vis, FTIR, XRD, Raman, TGA as well as FESEM, TEM analysis. The results reveal that nanocomposites show better dispersibility, crystallinity, thermal stability, and conductivity. Further, the synthesized composites have been tested for their anti-corrosion properties. The potentiodynamic results reveal that PANI nanocomposites with 1% GO exhibited long-term anti-corrosion behavior with a corrosion rate of 6.5 × 10^?5 mm year^?1, which is much lower than its individual components and commercial-grade red oxide. Also, it possesses highest impedance modulus ~33 kΩ cm² and real impedance ~32 kΩ cm², maximum coating resistance ~14.81 × 10³ Ω cm² and minimum coating capacitance after 96 h of immersion in 3.5% mass NaCl than those exhibited by all other coated samples. Higher concentration of GO could not retard the corrosion rate confirming that hydrophilicity of GO play an important role in the redox mechanism of PANI.     

Development of nano-catalyzed membrane for PEM fuel cell applications

Nano-catalyzed membrane with different platinum (Pt) catalyst loadings (0.25 to 1 mg cm^?2) was investigated for proton exchange membrane fuel cell applications, and the Pt loading on the Nafion membrane was prepared by non-equilibrium impregnation reduction method. The prepared catalyzed membranes were subjected to various characterisations, namely, X-ray diffraction, high-resolution scanning electron microscopy (HRSEM) with energy-dispersive X-ray, cyclic voltammetry, polarisation and electrochemical impedance spectroscopy. The polycrystalline fcc cubic structure and the particle size of Pt catalyst were estimated by X-ray diffraction analysis. The membrane with 0.4 mg cm^?2 of Pt loading exhibits a favourable surface morphology which is confirmed by HRSEM image. Electrochemical investigations were clearly evident that the uniform distributions of Pt particles with fine pores on Nafion membrane facilitated the three-phase boundary which leads to a better cell performance. Electrochemical impedance spectroscopy demonstrated that the cell constructed using 0.4 mg cm^?2 of platinum-loaded membrane has lower resistance than the other Pt loading.     

Comparative Analysis of the Distribution of Copper in Green and Brown Brazilian Propolis Extracts

We proposed here a novel analytical procedure for copper speciation in green and brown propolis extracts using SEC—HPLC—GFAAS with 0.5% m v^?1 SDS in 2.5 m mol L^?1 Tris–HCl (pH 7.4) as the mobile phase buffer solution. Both basic (0.05 mol L^?1 NaOH) and acid (0.05 mol L^?1 HCl) conditions were evaluated for sample extraction. Depending on the extraction procedure, differences in copper distribution were identified. Copper was mainly associated with high-molecular-weight (HMW) fractions in green propolis extract when extracted with basic solution, whereas with acid extraction solution, only low-molecular-weight (LMW) fractions were obtained in both samples. Furthermore, combined analysis of results obtained using SEC-UV and GF AAS confirmed the association of copper with LMW and HMW species.     

Concurrent synthesis of SnO/SnO<Subscript>2</Subscript> nanocomposites and their enhanced photocatalytic activity

The SnO/SnO₂ nanocomposites were synthesized using semisolvothermal reaction technique. These nanocomposites were prepared using different combination of solvents viz., ethanol, water, and ethylene glycol at 180 °C for 24 h. The synthesized nanocomposites were analyzed with various characterization techniques. Structural analysis indicates the formation of tetragonal phase of SnO₂ for the sample prepared in ethanol, whereas for other solvent combinations, the mixture of SnO and SnO₂ having tetragonal crystal structures were observed. The optical study shows enhanced absorbance in the visible region for all the prepared SnO/SnO₂ nanocomposites. The observed band gap was found to be in the range of 3.0 to 3.25 eV. Microstructural determinations confirm the formation of nanostructures having spherical as well as rod-like morphology. The size of nanoparticles in ethanol-mediated solvent was found to be in the range of 5 to 7 nm. Thermogravimetric analysis indicate the weight gain around 1.3 wt% confirming the conversion of SnO to SnO₂ material. The photocatalytic activity of synthesized nanocomposites was evaluated by following the aqueous methylene blue (MB) degradation. The sample prepared in ethylene glycol-mediated solvent showed highest photoactivity having apparent rate constant (K_app) 0.62 × 10^?2 min^?1.     

Catalytic activity of novel thermoplastic/cellulose-Au nanocomposites prepared by cryomilling

Due to environmental concerns, increasing attention has been focused on the application and preparation of biobased polymers and their blends. In this study, cellulose, the most spread biopolymer on Earth, was used in the preparation of novel cotton/polypropylene-Au and cotton/polyethylene-Au nanocomposites via a green mechanochemical approach. First, mechanoradicals were generated by ball milling of the cotton and thermoplastics under cryo conditions, and then, these radicals were used in the reduction of Au ions to Au nanoparticles (Au NPs). Nanocomposites were characterized by scanning electron microscopy (SEM), X-ray diffraction (XRD), and X-ray photoelectron spectroscopy (XPS). The application of mechanochemistry in obtaining the cotton/thermoplastic blends allowed homogenous and fine blending of the samples and in addition, excluded the usage of toxic solvents. Since Au NPs exhibit a wide range of applications, e.g., in catalysis, cotton/thermoplastic-Au nanocomposites were used to catalyze the reduction reaction of 4-nitrophenol to
4-aminophenol, followed by UV-Vis spectroscopy. Finally, the hydrophobicity of the nanocomposites was alternated by tuning the blend composition. In the prepared nanocomposites, cotton and thermoplastics acted as very good supporting matrices for the Au NPs and provided satisfactory access to the NPs.     

Physicochemical characterization of sanguinarine-hydroxypropyl-β-cyclodextrin binary and ternary systems

Complexation of sanguinarine with hydroxy-propyl-β-cyclodextrin (HPβCD) in the presence and absence of hydrophilic polymer—polyvinylpyrrolidone K30 was studied. Respective binary and ternary systems were prepared using two techniques, physical mixture and lyophilization, and characterized by FT-infrared spectrometry, differential scanning calorimetry and X-ray diffractometry. The Fourier Transform Infrared spectra of the lyophilized binary and ternary systems showed significant shifts in the regions of 1240–1300 cm^?1, 1450–1525 cm^?1 and 1600–1650 cm^?1, where absorptions of –C–O–C– asymmetrical stretching of sanguinarine rings A and F and ν_C=C ring vibrations of sanguinarine benzo[c]phenanthridine system can be observed respectively. Moreover, in the case of ternary products ν_C=O amide band absorption of polyvinylpyrrolidone (1600–1750 cm^?1) shifted to the lower wavenumbers in both the physical mixture and the lyophilized product. These changes in the spectra of the studied systems proved the involvement of the respective molecular groups in complexation process. Differential scanning calorimetry and X-ray diffractometry indicated different states of drug amorphization and entrapment in HPβCD in the presence and without polyvinylpyrrolidone. The obtained results let us conclude that obtained binary and ternary systems represent sanguinarine-HPβCD molecular complexes, with different rate of inclusion in the presence and without polyvinylpyrrolidone.     

A facile method to prepare graphene-coat cotton and its application for lithium battery

The free-standing and binder-free electrode materials, cotton/graphene (CGN) composites were prepared via a simple “dipping and freeze-drying” process using raw cotton as the supporting body (platform) and graphene oxide (GO) as the suspension. Then the cotton/GO (CGO) composites were annealed at 1000 °C under an Ar flow conditions to obtain CGN composites. The results show that the CGN structure can protect the cotton framework and have better thermal stable property than the cotton alone. Galvanostatic charge–discharge tests demonstrated that the GO concentration had great effects on their electrochemical performances. The CGN (for the GO with 3 and 5 mg ml^?1) provide reversible discharge capacity of 160 mAh g^?1 after 100 cycles, which is about 1.5 times higher than that of the cotton alone (115 mAh g^?1 after 100 cycles). Excellent electrochemical properties of CGN can be ascribed to its controllable structure with more lithium ion storage sites, high electronic conductivity, and fast ion diffusion velocity. The results suggest that this work develops a simple, cheap, and suitable large-scale production method in the lithium-ion batteries.     

Gels dried under supercritical and ambient conditions: a comparative study and their subsequent conversion to silica–carbon composite aerogels

In present work, we have prepared gels with various compositions of methyltrimethoxysilane—3-(2,3-epoxypropoxy) propyltrimethoxysilane (MTMS-GPTMS) using a two-step acid base sol–gel process. To make a comparative study between the two common drying routes, we prepared gels under supercritical and also under ambient conditions. The density of the supercritically dried hybrid aerogels lies between 0.18 and 0.31 gcm^?3, while the density of the ambient dried ones ranges between 0.35 and 0.42 gcm^?3. The surface area of MTMS-0.25 GPTMS aerogel dried under supercritical conditions, has been found to be 464 m² g^?1 with a pore volume and average pore diameter of 1.24 cm³ g^?1 and 11 nm respectively. The same composition dried under ambient conditions is found to have similar properties i.e. a BET surface area of 439 m² g^?1, pore volume of 1.22 cm³ g^?1 and average pore diameter of 11 nm. The aerogels were later pyrolyzed yielding silica/carbon composite aerogels. The pyrolized aerogels possessed a surface area as high as 207 m² g^?1 with a total pore volume of 0.98 cm³ g^?1. The pyrolysed aerogels were also calcined to yield carbon free materials.     

Novel aqueous spongy foams made of three-dimensionally dispersed wood-fiber: entrapment and stabilization with NFC/MFC within capillary foams

This article describes the preparation of novel aqueous spongy foams that are composed of three-dimensionally distributed wood-fiber networks stabilized with nanofibrillate cellulose (NFC) and/or microfibrillated cellulose (MFC). The free standing aqueous spongy foams were prepared with the entrapment of NFC and/or MFC—stabilized air-in-water (A/W) capillary foams using “gel trapping technique”. The stability of spongy foams could be controlled by manipulating the volume fraction of NFC and/or MFC and a secondary liquid immiscible with the continuous phase of the NFC and/or MFC suspension. Possible morphology and mechanical distribution of NFC and/or MFC within spongy foams were verified with optical microscope, SEM, and functional load-bearing method. Owing to three-dimensionally dispersed wood-fiber structure, ultra-lightweight (0.01–0.06 g/cm³), high porosity (>90%), and microporous (10–80 μm), the NFC and/or MFC reinforced spongy foams, improved compressional strength-vertical direction obviously, from 0.0 to more than 13.78 kPa.     

Polyaniline/iron nanocomposites prepared by cryomilling

The polyaniline/iron nanocomposites with both conducting and magnetic properties have been prepared by cryomilling (high‐energy ball milling under cryogenic temperature), in which the average size of iron grains attains 20 nm. Enhanced coercivity of 206 Oe and decreased conductivity of 0.1 S cm^?1 at room temperature have been obtained for the nanocomposites containing 10% volume fraction of iron in polyaniline after cryomilling for 20 h. The high value of the coercivity could be considered due to the presence of a fraction of single‐domain particles in the nanocomposites. The low value of the conductivity could be considered due to the dedoping of conducting polyaniline with the cryomilling time. © 2006 Wiley Periodicals, Inc. J Polym Sci Part B: Polym Phys 44: 3157–3164, 2006     

Production of highly electro-conductive cellulosic paper via surface coating of carbon nanotube/graphene oxide nanocomposites using nanocrystalline cellulose as a binder

Electro-conductive cellulosic paper has attracted great attention as a promising alternative material in the emerging field of flexible and portable electronic devices. However, the environmentally friendly fabrication of electro-conductive cellulosic paper still remains challenging. Herein, green multi-walled carbon nanotube (MWCNT)/graphene oxide (GO) nanocomposites towards the sustainable development strategy were developed and subsequently used to impart electro-conductivity to cellulosic paper via surface coating process. GO exfoliated from graphite powder was used as a dispersant to improve the dispersion of MWCNTs in water media, and nanocrystalline cellulose (NCC) derived from cotton fibers was employed as a binder for the MWCNT/GO nanocomposites. Effect of NCC amount on the rheological behavior, particle size distribution, sedimentation stability and zeta potential of MWCNT/GO nanocomposites as well as the electro-conductivity and mechanical properties of coated paper was investigated. Results demonstrated that NCC enhanced the dispersion of MWCNT/GO nanocomposites in addition to serving as a binder. Surface coating application of MWCNT/GO nanocomposites was found to impart high electro-conductivity of up to 892 S m^?1 to the cellulosic paper while improving its mechanical properties.     

TG–MS analysis of thermal behavior and gaseous emissions during co-combustion of straw with municipal sewage sludge

The thermal behavior and gas product distribution during combustion of straw (wheat straw, corn stalks, and cotton stalks), municipal sewage sludge (MSS), and their blends were investigated by thermogravimetry–mass spectroscopy. The experiments were conducted with various blending ratios and temperatures ranging from 323 to 1,173 K. Addition of MSS decreased the combustion performance of the straw. The reactions between wheat straw and corn stalks with MSS proceeded more easily than that of cotton stalks. Significant interactions were observed between the straw and MSS at the char combustion stage. Gaseous species (CO₂, SO₂, NH₃, HCN, and NO) were mainly produced at temperatures of 523–873 K at which most of the mass loss occurred. Higher MSS proportions in the blends resulted in lower emissions peaks for CO₂, NH₃, HCN, and NO except for SO₂. To ensure combustion performance and mitigate problematic gaseous emissions, the proportion of MSS added to the blends should be <30 mass%.     

Mechanical and thermal investigation of thermoplastic nanocomposite films fabricated using micro- and nano-sized fillers from recycled cotton T-shirts

The thermal and mechanical performance of composites with nano-sized cotton fillers embedded in low-density polyethylene (LDPE) is investigated. Microfibrillated cotton was prepared by microgrinding mechanical treatment of pulverized cotton (pCot) derived from waste T-shirts, resulting in nano-sized fibrils of the cellulose that retain high crystallinity. Film composites of LDPE with pCot before and after microgrinding were fabricated through melt extrusion and the effect of filler size on mechanical, thermal and morphological properties of the composite was investigated. Compounding microfibrillated cotton with LDPE resulted in well-dispersed nanocomposites with no discoloration after 10 min of melt extrusion at 170 °C. At concentrations up to 10 % by weight, the composites showed increased modulus, increased tensile strength and a slight decrease in elongation to break. Further improvement in the dispersion and mechanical properties of the cotton-based fillers was realized by the use of LDPE powder instead of polymer pellets fed to the extruder. This research demonstrates the processing and applicability of the use of recycled cotton-based nano-sized fillers in melt-processing.