Oxidized Cellulose Research Articles

Fractionation of Winemaking Grape Stalks by Subcritical Water Extraction to Obtain Added-Value Products

Grape stalks (GSs) from winemaking were submitted to a green process to valorise its lignocellulosic biomass that applied subcritical water extraction (SWE) at 170 °C and 180 °C to obtain active extracts and cellulose-enriched fractions. The sum of the total phenolic content of the soluble extract and the solid residue fractions from the SWE exceeded that of the GS, which suggests the generation of compounds with antioxidant properties through SWE. All SWE fractions showed high antioxidant power. The increased temperature promoted the extraction of polyphenolic compounds, enhancing the antioxidant power of both extracts and solid residues. These solid residue fractions were bleached with alkaline hydrogen peroxide solutions (4 and 8% v/v) to purify cellulose. After two bleaching cycles, no notable delignification progress was observed, as the bleaching yield or whiteness index did not significantly change in the further cycles. The first bleaching cycle led to a significant reduction in the lignin content at both SWE temperatures. The cellulose purity was higher in the samples obtained at 170 °C and bleached with 4% alkaline hydrogen peroxide. SWE at 180 °C led to greater cellulose oxidation during the bleaching step regardless of the hydrogen peroxide concentration.

Optimizing addition of NaClO in TEMPO-mediated oxidation of cellulose for less nanofiber degradation

Optimizing addition of NaClO in TEMPO-mediated oxidation of cellulose for less nanofiber degradation

Novel carboxymethyl cellulose-based hydrogel embedded with metal organic framework for efficient cationic dye removal from water

The rGO/CMC/β-CD (RCβ) hydrogel was synthesized from reduced graphene oxide (rGO), β-cyclodextrin (β-CD) and sodium carboxymethyl cellulose (CMC) by radical polymerization. A novel hydrogel adsorbent was created by growing the metal-organic framework (Cu-BTC) in-situ on RCβ hydrogel, which has excellent adsorption capacities for cationic dyes in wastewater. The adsorption parameters such as the amount of adsorbent, pH of solution and adsorption time were optimized through batch adsorption experiments. Under the optimal conditions of pH 6.0, adsorbent dosage of 0.01 g and experimental temperature of 25 °C, Langmuir isothermal model was used to fit the maximum adsorption capacities of methylene blue (MB), crystal violet (CV) and malachite green (MG), which were 892.66, 842.75 and 633.77 mg g−1, respectively. The fitting results of adsorption kinetics revealed that the pseudo-second-order model can describe the adsorption process better. Based on proposed studies, the dye molecules were adsorbed onto RCβ@Cu-BTC hydrogel mainly through electrostatic interaction, hydrogen bonding and π–π interactions. After five cycles, the adsorption efficiency of the RCβ@Cu-BTC hydrogel for MB, CV and MG can still reach 80 %, 77 % and 72 %, which shows that the adsorbent has good adsorption performance. Various adsorption experiments shows that RCβ@Cu-BTC hydrogel has great potential in treating dye wastewater.

Dicarboxylate cellulose nanofibrils-supported silver nanoparticles as a novel, green, efficient and recyclable catalyst for 4-nitrophenol and dyes reduction

This study reports dicarboxylate cellulose nanofibrils (DCNF) as a novel reducing and supporting agent for producing silver nanoparticles (AgNPs) with high efficiency (63.82 % reduction) and loading (6.88 %) using UV light. Unlike previous research, AgNPs formation with DCNF doesn't involve cellulose oxidation. Instead, it appears to involve a loss of carboxyl groups from DCNF. In comparative studies, pristine CNF (PCNF) and TEMPO-oxidized CNF (TOCNF) were also examined for AgNPs production. The resulting AgNPs from DCNF exhibited a significantly smaller average size (3.9 ± 0.7 nm) compared to those from PCNF (26.9 ± 10.9 nm) and TOCNF (13.5 ± 4.5 nm). Catalytic activity evaluation by the 4-nitrophenol (4-NP) reduction reaction revealed a high rate constant of 8.47× 10−3 s−1 by AgNPs/DCNF, which surpassed AgNPs/TOCNF (1.79 × 10−3 s−1) and AgNPs/PCNF (0.63 × 10−3 s−1) by 4.7 and 13.4 times, respectively. Besides 4-NP, AgNPs/DCNF aerogels were also applied for methyl orange and Rhodamine B dyes reduction. The aerogels showed excellent reusability, maintaining over 95 % conversion even after five cycles and also effective in treating real samples and mixed dye solutions. This study opens the door for future research exploring DCNF as a support material for various metal, metal oxide, and carbon nanoparticles.

Dynamic nuclear polarization solid-state NMR spectroscopy as a tool to rapidly determine degree of modification in dialcohol cellulose

AbstractDialcohol cellulose can be prepared by periodate-mediated oxidation of cellulose followed by reduction with borohydride. The two-step reaction creates a modified cellulose polymer which is ring-opened between the C2 and C3 carbons in the glucose unit. This material has attracted both scientific and commercial interest, due to its potential role in the transition towards a fossil-fuel-free society. In order to become a reliable component in the materials of tomorrow, chemical properties such as degree of modification must be accurately quantified. In this work we describe how solid-state NMR spectroscopy, enhanced by dynamic nuclear polarization (DNP), can be used for this purpose. Our results illustrate that it is possible to obtain high sensitivity enhancements in dialcohol cellulose with the DNP enhanced solid-state NMR technique. Enhancements above a factor of fifty, on a 400 MHz/263 GHz DNP system in the presence of 12 mM AMUPol radical were achieved. This allows us to quantify the degree of modification in dialcohol cellulose samples in time spans as short as 20 min using DNP enhanced multiple-contact cross polarization experiments. We also exemplify how DNP enhanced, 13C-13C dipolar recoupling experiments can be used for the same purpose and for studying chemical shift correlations in dialcohol cellulose. Graphical abstract

Animal neuropathic pain aroused by conglutinating oxidative regenerative cellulose on dorsal root ganglion.

Neuropathic pain arises as a consequence of injury or disease in the peripheral or central nervous system. Clinical cases have shown that spine postoperative chronic neuropathic pain remains a troublesome issue in medical treatment due to the presence of various degrees of peridural fibrosis and different inflammatory factors after spinal surgery. To address this issue, we developed a new neuropathic mice model that successfully simulates the real clinical situation by applying oxidative regenerative cellulose to L5 DRG (dorsal root ganglion). Behavior tests were done by von Fray and thermal stimuli. ELISA and real-time PCR were employed to detect the expression of genes involved in neuropathic pain. This model not only successfully induces chronic pain but also causes membrane thickening, non-neuronal cell recruitment, and a local increase of TNFα and interleukin-6. Additionally, this model did not cause neuron loss in the affected DRG, which mimics the characteristics of sticky tissue-induced neuropathic pain after clinic surgery. Based on this model, we administrated a TNF inhibitor to mice and successfully reduced mechanical allodynia after DRG surgery. In this study, the developed animal model may be a novel platform for delivering neuropathic pain treatments, such as target-based drug discovery or personalized diagnostic approaches.

Enhancing the selective catalytic oxidation of lignocellulosic biomass to formic acid using hydrogen peroxide and a reusable MgAl hydrotalcite-derived as a catalyst in a green solvent

Biofuels or liquid fuels derived from natural matter, are one of the most intriguing yet divisive alternatives for petroleum-based fuels. The most common approach to produce biofuels is to transform plant sugars and other carbohydrates into oxygen-deficient chemicals. A growing relevance has been devoted in the direct synthesis of platform molecules from biomass resources, using one-pot or cascade techniques via adequate catalytic system tuning and improvement of the reaction conditions which have merged as a beneficial strategy from an economic and ecological standpoint. In a similar vein, the major objective of this contribution was to investigate and enhance the conditions for a selective oxidation of lignocellulosic biomass-derived cellulose to yield formic acid (FA), the latter is one of the most coveted liquid hydrogen carriers and among the key compounds used in the pharmaceutical, cosmetic, and leather industries. Both oxidizing aqueous hydrogen peroxide and calcined heterogeneous hydrotalcite catalyst have been employed at an atmospheric pressure for this purpose. The effect of reaction time, temperature, amount of catalyst and oxidant on the product's yield and selectivity have been investigated. The oxidation of a plant-derived cellulosic fiber at 70 °C using an H2O2 excess (7 mmol) provided an impressive result with a high yield and TON of 61.0 %, 12.30 respectively, the latter was confirmed to be relatively close to the one from the oxidation of pure cellulose. Furthermore, the reusability of the catalyst has also been studied which was demonstrated to result in the same yields for one reuse and 3 recycles.

Sorption properties of a new modified flax fibre sorbent

The purpose of this study is to develop a modified sorbent of flax waste and investigate its sorption properties towards Cu (II) ions. The authors conducted the modification in two steps. The first step was oxidation of flax fibre cellulose with sodium metaperiodate to dialdehyde cellulose, the second one was the addition of taurine to increase the sorption characteristics of the modified sorbent. The paper presents the conditions for the periodate oxidation reaction of flax fibre and the treatment of the resulting dialdehyde cellulose with taurine. We determined the sorption characteristics of the modified sorbent in comparison with the original flax fibre. Kinetic studies allowed us to establish the time of reaching sorption equilibrium in the heterophase system ‘aqueous solution of metal salt-sorbent’ and determine the reaction order using pseudo first and pseudo-second order kinetics models. The authors processed the sorption isotherms obtained during the experiments using the Langmuir model. The maximum sorption capacity increased by 3 times compared to the original flax fibre. IR spectroscopy confirmed the improvement of equilibrium and kinetic characteristics of flax fibre occuring as a result of the appearance of new sorption centres in its structure.

Reducing drought vulnerability of forest soils using Xanthan gum-based soil conditioners

Climate change increases the frequency and severity of droughts in many parts of Europe, thereby affecting the availability of water resources. Therefore, preserving the soil water content is essential for maintaining forest diversity and plant vitality. To improve soil hydraulic properties and reduce drought vulnerability, three xanthan-gum-based soil conditioners (SC_R, SC_CG, and SC_ZZC) were developed under the European ONEforest project. These soil conditioners (SCs), including oxide ash and cellulose fibres of different lengths, differ in their filler properties. This study evaluated the performance of these soil conditioners in forest soils in Slovenia (S1), Spain (S2), and Germany (S3). Water absorption, water retention, hydraulic conductivity, seed germination, and plant growth in the untreated soils and mixtures were analysed.The results showed a 53% to 100% increase in water absorption with high dosage of SCs (1.7% of dry SC per dry soil mass). The addition of SCs also significantly improved the water retention capacity of the treated soils within a suction range of 0-100 kPa, which is advantageous for maintaining adequate water availability for plant growth. The effect of SCs on unsaturated hydraulic conductivity varies depending on the soil type. For example, at a similar suction, the unsaturated hydraulic conductivity of mixtures with soils S2 and S3 can be more than an order of magnitude lower than that of untreated soils S2 and S3. In contrast, mixtures with soil S1 showed unsaturated hydraulic conductivity similar to that of the untreated soil. In the seeding experiment, plants in treated soils survived for up to 8 d without watering compared to those in untreated soils, with survival linked to the initial water content of the mixtures. These findings suggest that soil conditioners reduce drought vulnerability by improving water retention and regulating water loss. However, the optimal dosage should be adjusted according to different soil types and local environmental conditions.

Environmentally Benign High‐Performance Composites‐Based Hybrid Microcrystalline Cellulose/Graphene Oxide

ABSTRACTA novel silane functionalization prepared by a solution mixing approach of epoxy composites filled with eco‐friendly reinforcement filler, that is, graphene oxide (GO) and microcrystalline cellulose (MCC). The developed composites were subjected to comprehensive analysis using various characterization techniques, encompassing mechanical testing, water absorption analysis, thermal stability assessment, and scanning electron microscopy (SEM). The tensile strength and Young's Modulus of the epoxy composite filled with 1.0 wt.% of GO (EGO1.0) demonstrated the highest value viz. 29.83 MPa and 1991.71 MPa, respectively, when compared to neat epoxy composite (E0). Meanwhile, the thermal gravimetry analysis (TGA) studies, particularly char yield, highlight improvements in the thermal stability of the EGO2.5 composite, that is, 23.39% representing a 33.73% increment compared to the E0 composite. The synergistic effect of hybrid filler, achieved by a combination of micro and nanoparticle fillers within an epoxy matrix, was investigated as a virtuous alternative to the conventional epoxy nanocomposites. A uniform dispersion of GO on the MCC surface leads to significant improvements in the mechanical properties and thermal stability of the epoxy‐reinforced composite. The maximum tensile strength, Young's Modulus, and break strain of 39.77 MPa, 2591.27 MPa, and 2.90%, respectively, were observed for the modified EGO1.0MCC1.5 composite. The synergistic effect of hybrid eco‐friendly reinforcement fillers (GO/MCC) and a strong interfacial adhesion between the matrix and filler reduces the formation of defects, thereby resulting in good stress transfer from matrix to fillers.

Multifunctional electrospun membranes incorporated with metal oxide nanoparticles, cellulose acetate, and polyvinylpyrrolidone for wastewater treatment: Oil/water separation, dye adsorption, and dye degradation

Multifunctional membranes have gained considerable attention as useful materials for the treatment of complex wastewater that contains dye and oil substances. Electrospun nanofiber membranes (ENM) have substantial advantages and potential for complex wastewater remediation, owing to their unique properties. In this study, an environmentally compatible ENM is fabricated by incorporating photocatalytic metal oxide nanoparticles of zinc oxide (ZnO) or silver-zinc Oxide (Ag-ZnO) into cellulose acetate (CA)/polyvinylpyrrolidone (PVP) nanofibers using electrospinning. Composite membranes ZnO/CA/PVP, Ag-ZnO/CA/PVP, ZnO/DCA/PVP (DCA: deacetylated cellulose acetate), and Ag-ZnO/DCA/PVP (deacetylated) were employed for oil–water emulsion separation, owing to their superhydrophilic and underwater superoleophobic nature, photocatalytic dye degradation due to the presence of ZnO or Ag-ZnO, and dye adsorption resulting from their high surface area. The composite membranes showed more than 95% efficiency for oil/water separation, malachite green adsorption, and photocatalytic methylene blue degradation. These membranes displayed simultaneous oil–water and dye separation efficiency, as well as antibacterial properties. The membrane we present here provides a simple and effective platform for wastewater remediation with a low energy consumption.

Synthesis and characterization of a novel dual sensitive iron nanoparticles incorporated Schiff base composite hydrogel for diabetic wound healing therapy

Chronic wounds in diabetic patients deteriorate into multiple infections. A multifunctional transdermal material with high self-healing ability, remodeling capability, antibacterial and radicle scavenging activity, and an excellent multi-sensitive carrier was needed to promote wound healing. For that, Oxidized Cellulose (OC) and gelatin (GLN) are selected to construct a dual drug-loaded Schiff base hydrogel with iron nanoparticle (IONPS) incorporation for the controlled and sustained release of Insulin (INS) and Metfomin (MET), which synergistically promote wound repair. The INS/MET-IONPS-OC/GLN hydrogel drug payload was characterized using FT-IR, XRD, DLS, ZETA, TG, FE-SEM, TEM, and VSM analysis. The high drug loading and encapsulation efficiency were 93.20 % and 98.8 % for INS and 90.2 % and 95.1 % for MET, respectively. The temperature-sensitive drug release (92.0 % of INS and 90.0 % of MET) percentage is much better than the pH-sensitive drug release (83.5 % of INS and 80.2 % of MET). Above 90.0 % viability in MTT and apoptosis assay reveals the nontoxic nature of the INS/MET-IONPS-OC/GLN towards L929 normal cell lines. The zone of inhibition value of 12 and 15 mm in gram-negative bacteria reveals the anti-bacterial effect. The antioxidant activity of the carrier shields the cells against reactive oxygen species promotes healing rate ensures by DPPH assay.The cell proliferation and angiogenesis were confirmed by scratch assay on L929 cell lines in diabetic and non-diabetic conditions, showing the healing ability of the INS/MET-IONPS-OC/GLN hydrogel.

Preparation and characterization of polymeric cellulose wood adhesive with excellent bonding properties and water resistance

Developing the most abundant cellulose resources in nature as wood adhesives is a challenging but significant work. In this study, an oxidized cellulose-hexamethylene diamine-urea (OCHU) resin adhesive, of high bonding performance, and excellent water resistance has been prepared. The cellulose was firstly enzymatically hydrolyzed to increase its solubility and expose more hydroxyl groups, then oxidized by sodium periodate (NaIO4) to generate a biological compound being rich of aldehyde groups. The OCHU adhesive was prepared by crosslinking oxidized cellulose (OC) with a synthetic reactive polyurea (HU) polymer, which was formed through the deamidation reaction between hexamethylenediamine (H) and urea (U). This adhesive exhibited a 24 h cold water soaking strength of 1.61 MPa, 3 h hot water (63 °C) strength of 1.05 MPa and a dry strength of 1.71 MPa. Compared to oxidized cellulose-hexamethylenediamine (OCH) adhesive, a significant increase of 60 % in this adhesive's wet strength. The Schiff base and addition reactions in the preparation were confirmed by XPS, solid-state NMR, and FTIR. This cellulose-based wood adhesive has great market competitiveness for mass production and application in the plywood industry, due to its excellent bonding properties.

Structural Rheology in the Development and Study of Complex Polymer Materials.

The progress in polymer science and nanotechnology yields new colloidal and macromolecular objects and their combinations, which can be defined as complex polymer materials. The complexity may include a complicated composition and architecture of macromolecular chains, specific intermolecular interactions, an unusual phase behavior, and a structure of a multi-component polymer-containing material. Determination of a relation between the structure of a complex material, the structure and properties of its constituent elements, and the rheological properties of the material as a whole is the subject of structural rheology-a valuable tool for the development and study of novel materials. This work summarizes the author's structural-rheological studies of complex polymer materials for determining the conditions and rheo-manifestations of their micro- and nanostructuring. The complicated chemical composition of macromolecular chains and its role in polymer structuring via block segregation and cooperative hydrogen bonds in melt and solutions is considered using tri- and multiblock styrene/isoprene and vinyl acetate/vinyl alcohol copolymers. Specific molecular interactions are analyzed in solutions of cellulose; its acetate butyrate; a gelatin/carrageenan combination; and different acrylonitrile, oxadiazole, and benzimidazole copolymers. A homogeneous structuring may result from a conformational transition, a mesophase formation, or a macromolecular association caused by a complex chain composition or specific inter- and supramolecular interactions, which, however, may be masked by macromolecular entanglements when determining a rheological behavior. A heterogeneous structure formation implies a microscopic phase separation upon non-solvent addition, temperature change, or intense shear up to a macroscopic decomposition. Specific polymer/particle interactions have been examined using polyethylene oxide solutions, polyisobutylene melts, and cellulose gels containing solid particles of different nature, demonstrating the competition of macromolecular entanglements, interparticle interactions, and adsorption polymer/particle bonds in governing the rheological properties. Complex chain architecture has been considered using long-chain branched polybutylene-adipate-terephthalate and polyethylene melts, cross-linked sodium hyaluronate hydrogels, asphaltene solutions, and linear/highly-branched polydimethylsiloxane blends, showing that branching raises the viscosity and elasticity and can result in limited miscibility with linear isomonomer chains. Finally, some examples of composite adhesives, membranes, and greases as structured polymeric functional materials have been presented with the demonstration of the relation between their rheological and performance properties.

Photoelectrochemical valorization of cellulose over bismuth-based oxide modified titanium dioxide photoanodes

Valorizing biomass waste through photoelectrochemical (PEC) methodology provides an attractive strategy for generating H2 and value-added chemicals by enabling a carbon–neutral cycle. Herein, we present an investigation of a series of bismuth-based oxide-modified TiO2 as the photoanode for PEC valorization of cellulose in aqueous solution. The bismuth-based oxide was synthesized onto a TiO2 photoanode by a chemical bath deposition (CBD) method followed by heat treatments. The composition of the materials was adjusted by varying the concentration of the Cu2+ and Bi3+ precursors. The research shows that Bi2O3 effectively suppresses the water oxidation reaction over TiO2, a competitive side reaction in PEC cellulose oxidation, resulting in a Faradaic efficiency (FE) of 83.9 ± 4.9 % toward formate production. In contrast, unmodified TiO2 photoanode only exhibits a FE of 25.3 ± 3.7 %. On the other hand, the photoelectrode showed insufficient oxidative force for both water and cellulose oxidation by the surface modification of CuBi2O4.

Preparation and characterization of Baijiu Jiuzao cellulose nanofibers-kafirin composite bio-film with excellent physical properties

Jiuzao is the main solid by-products of Baijiu industry, which contain a high amount of underutilized cellulose and proteins. In recent years, cellulose nanofibers mixed with proteins to prepare biodegradable bio-based film materials have received widespread attention. In this study, we propose a novel method to simultaneously extract kafirin and cellulose from strong-flavor type of Jiuzao, and modify cellulose to prepare cellulose nanofibers by the TEMPO (2,2,6,6-tetramethylpiperidine-1-oxide) oxidation-pressure homogenization technique, and finally mix kafirin with cellulose nanofibers to prepare a new biodegradable bio-based composite film. Based on the analysis of one-way and response surface experiments, the highest purity of cellulose was 82.04 %. During cellulose oxidation, when NaClO was added at 25 mmol/g, cellulose nanofibers have a particle size of 80–120 nm, a crystallinity of 65.8°. Finally, kafirin and cellulose nanofibers were mixed to prepare films. The results showed that when cellulose nanofibers were added at 1 %, the film surface was smooth, the light transmittance was 60.8 %, and the tensile strength was 9.17 MPa at maximum, which was 104 % higher than pure protein film. The contact angle was 34.3°. This paper provides new ideas and theoretical basis for preparing biodegradable bio-based composite film materials, and improves the added value of Jiuzao.

Kinetic, gas emission, reaction pathway and interaction mechanism analysis during oxidative pyrolysis of aluminium electrolysis waste with beech wood

The oxidative pyrolysis kinetic, gas emission, reaction pathway and interaction mechanism during oxidative pyrolysis of spent cathode carbon block (SCCB) and beech wood (BW) were investigated via the thermogravimetry combined with Fourier transform infrared spectrometer (TG-FTIR) analysis. The hemicellulose, cellulose, and lignin in BW and the carbon materials and fluoride in SCCB were determined as the main five components based on thermogravimetric experiment. Compared with pure SCCB, the addition of BW increased the comprehensive oxidative pyrolysis index. Furthermore, the total of 44 kinetic parameters were obtained by the Shuffled Complex Evolution (SCE) method, which were used to further forecast the mass loss of the above five main components. The evolved gases were detected by FTIR, and the results indicated that the main gases for BW/SCCB oxidative pyrolysis were CO2, which corresponded to the oxidation of cellulose, lignin and carbon materials. Small amounts of phenols, alcohols, ethers, ketones, aldehydes, carboxylic acids, CO, aromatics, alkene were attributed to the thermal decomposition of hemicellulose and cellulose. Pyrolysis of cellulose and lignin produced small quantities of hydrocarbons. HF was formed by the thermal decomposition of fluoride. Eventually, the reaction pathway was proposed and the possible interaction mechanism was analyzed during the oxidative pyrolysis of BW/SCCB blends.

Visualized and pH-responsive hydrogel antibacterial coating for ventilator-associated pneumonia

Ventilator-associated pneumonia (VAP) is a common healthcare-acquired infection often arising during artificial ventilation using endotracheal intubation (ETT), which offers a platform for bacterial colonization and biofilm development. In particular, the effects of prolonged COVID-19 on the respiratory system. Herein, we developed an antimicrobial coating (FK-MEM@CMCO-CS) capable of visualizing pH changes based on bacterial infection and releasing meropenem (MEM) and FK13-a1 in a controlled manner. Using a simple dip-coating process with controlled loading, chitosan was cross-linked with sodium carboxymethyl cellulose oxidation (CMCO) and coated onto PVC-based ETT to form a hydrogel coating. Subsequently, the coated segments were immersed in an indicator solution containing bromothymol blue (BTB), MEM, and FK13-a1 to fabricate the FK-MEM@CMCO-CS coating. In vitro studies have shown that MEM and FK13-a1 can be released from coatings in a pH-responsive manner. Moreover, anti-biofilm and antibacterial adhesion results showed that FK-MEM@CMCO-CS coating significantly inhibited biofilm formation and prevented their colonization of the coating surface. In the VAP rat model, the coating inhibited bacterial growth, reduced lung inflammation, and had good biocompatibility. The coating can be applied to the entire ETT and has the potential for industrial production.

Improving the Interfacial Adhesion of Long Carbon Fiber-Reinforced Polyamide 6 Composites by Electrochemical Oxidation and Polyethylenimine-Carboxymethyl Cellulose Grafting.

Carbon fiber (CF)-reinforced thermoplastic composites have notable ascents in various sectors and applications. For high-performance composites, strong interfacial adhesion between the polymer matrix and the CF is crucial. This is achieved by introducing functional groups on the CF surface. In this paper, a water-based surface treatment was applied to long carbon fibers to enhance the interfacial bonding with the polyamide 6 (PA6) matrix. For that, PEI and CMC were grafted onto the surface of carbon fibers after electrochemical oxidation. The PEI-CMC sizing reduced the carbon fiber/water contact angle to 26.42° from 111.69°. The clear improvement in wettability resulted in a 164.8% increase in the interfacial strength of 26.7 MPa after the application of PEI-CMC sizing on carbon fibers (CFs). The resultant tensile and flexural strength increased by 19.3 and 11.7% from 2009.6 and 378.3 MPa for desized CF/PA6 composites to 250.3 and 422.7 MPa for PEI-CMC-sized CF/PA6 composites, respectively. Moreover, the fractured surface morphologies were also investigated to confirm the enhancement of mechanical properties. The proposed one-step electrochemical oxidation and water-based sizing procedure is found to be promising for the production of high-performance long-fiber-reinforced thermoplastic composites.

TEMPO/CaBr2/Ca(OCl)2 oxidation of hardwood bleached kraft pulp in water at pH 10 with aqueous Ca(OH)2 solution

The conventional TEMPO/NaBr/NaOCl system for oxidation of cellulose to prepare nanocellulose materials has some shortcomings in terms of controlling side reactions and clogging in washing/filtration process. A new TEMPO/CaBr2/Ca(OCl)2 system was then developed to oxidize a hardwood bleached kraft pulp (HBKP) in water at pH 10 (TEMPO = 2,2,6,6-tetramethylpiperidine-1-oxyl radical). An aqueous Ca(OH)2 solution was used to continuously control the reaction mixture at pH 10. After oxidation, the reaction mixture containing the oxidized products and chemicals was directly filtered on a 40-μm-mesh nylon filter and the water-insoluble oxidized products on the filter were washed with water without any clogging. The carboxy content increased to 1.5 mmol/g and the mass recovery ratio decreased to 87.7% as the amount of Ca(OCl)2 was increased to 10.0 mmol/g-HBKP. The oxidized products contained calcium ions but almost no chloride ions, indicating that they comprised almost pure –(COO)2Ca groups. The ready filtration and washing of the oxidized products was probably owing to the low degree of dissociation of the –(COO)2Ca groups in water. The X-ray powder diffraction (XRD) and solid-state carbon 13 nuclear magnetic resonance (13C-NMR) analyses revealed that the crystallinities and crystal widths of the original cellulose I structure were mostly retained in the oxidized products. However, size-exclusion chromatography and viscosity analyses revealed that substantial depolymerization occurred on the cellulose and oxidized cellulose molecules in the products, as in TEMPO/NaBr/NaOCl-oxidized products.Graphical