Increase In Carboxyl Content Research Articles

Evolution of oxygen-containing functional groups on coal char surface during gasification in H2O/CO2

Gasification converts coal into syngas (CO and H2) for downstream utilization. The most important reaction in an autothermal gasifier is the char−H2O/CO2 reaction. The evolution of C(O) complexes on the coal char surface directly determines the pathways and rates of CO and H2 generation. This study mainly used a fixed bed reactor to prepare Zhundong coal char with different reaction levels in H2O and CO2, and its surface carboxyl, lactone, phenolic hydroxyl, and hydroxyl functional groups were systematically analyzed by using Boehm titration, FT-IR, and XPS. The results show that the contents of the four oxygen-containing groups in raw coal are in the order of carboxyl＞lactone＞phenol hydroxyl＞hydroxyl. In H2O gasification, the lactone groups were more susceptible to H2O resulting in a significant increase in carboxyl content at the early stage of the reaction. The hydroxyl, as a very active group in the reaction, and the amount of its generation and consumption was very obvious. The phenolic hydroxyl−the least thermally stable group among these four types of groups, was unable to participate in the inter-transformation between oxygen-containing functional groups during the gasification. During CO2 gasification, the hydroxyl was rapidly consumed at the initial stage of the reaction and then shown a slow growth trend, and the newly generated hydroxyl would continue to undergo dehydrogenation to form new functional groups. At the end of the reaction, the transformation of other oxygen-containing functional groups into more stable carbonyl groups leads to a sudden increase in the content of carboxyl and lactone. In this work, Boehm titration was introduced into the determination of oxygen-containing functional groups on the surface of char during gasification in H2O/CO2.

Tuning a green carboxymethyl cellulose-based pre-tanning agent via peroxide oxidation for high chrome exhaustion in leather industry

The low chrome uptake by collagen in the conventional tanning process leads to the pollution of the wastewater. Due to environmental concerns, leather scientists are already searching for innovative ways to produce pre-tanning agents as a high exhaustion chrome tanning auxiliary. Herein, a novel kind of pre-tanning agent is engineered by converting carboxymethyl cellulose (CMC) to oxidized carboxymethyl cellulose (OCMC) via the hydrogen peroxide process. FT-IR and carboxyl content analysis demonstrated the increase in carboxyl content after oxidation. After that, the obtained OCMC was utilized as a pre-tanning agent, resulting in a high exhaustion of chrome (92.76 %) which is 27.76 % more than conventional chrome tanning (65 %), and the amount of chrome in wastewater reduced to 7.24 %. The hydrothermal stability of wet-blue increased by increasing the uptake of chrome (Ts = 118 °C). The obtained crust leather represented excellent mechanical properties (Tensile strength: 305.68 kg/cm2; tear strength: 50 kg/cm) and desirable organoleptic properties. The environmental analysis signifies a significant step towards a cleaner and sustainable tanning process (COD = 1600, BOD5 = 560 mg/L) compared to the conventional chrome tanning process. Consequently, the obtained results offer a green pre-tanning agent to meet the requirements of the sustainable development of the leather industry.

Adjusting concrete resistance to corrosive ions by varying carboxyl contents in chemical additives

In this study, polycarboxylate ether-based superplasticizers (PCEs) with various carboxyl densities were synthesized as chemical additives to evaluate the effect of PCE carboxyl density on the resistance of concrete to chloride permeability and sulfate attack. The microstructures of concrete, the properties of PCEs, and the cement hydration processes were investigated to explore the improvement mechanism of PCE-doped concrete resistance to chloride permeability and sulfate attack. Results show that increase in carboxyl density of doped PCEs was advantageous for concrete resistance against chloride permeability and sulfate attack. As the carboxyl content increased, PCE molecules were adsorbed on the cement more efficiently, leading to delayed cement hydration and formation of less foams. Therefore, the number of microcracks and the total porosity of the concrete decreased with increase in carboxyl content of the doped PCE, producing concrete with better resistance against chloride permeability and sulfate attack. By improving concrete resistance to chloride and sulfate ions via doping higher-carboxyl content PCEs, this work can contribute to the development of essential infrastructure constructed with considerable longevity and reliability in tropical marine environments.

A yeast-malic acid crosslinker/polyacrylic acid hydrogel containing doxycycline for the treatment of periodontitis.

Doxycycline (DX) is a drug of choice for the treatment of periodontitis, with the limitation of requiring a high dose, which may be overcome by the preparation of a targeted controlled-release hydrogel containing a newly synthesized yeast-malic acid crosslinker (YMC). YMC was synthesized via thermochemical modification of yeast with malic acid at 100-140 °C and compared with glutaraldehyde-saturated toluene (GST). Swelling capacity, acid and carboxyl content, scanning electron microscopy (SEM) imaging, Brunauer-Emmett-Teller (BET) analysis, viscosity, cross-linking density, DX loading and release behavior at pH 6.5, mucoadhesion, and antimicrobial and periodontal efficacy of the glutaraldehyde hydrogel (HGG) and YMC hydrogel (HGY) were compared. Changes from C-O (1421 cm-1) to C[double bond, length as m-dash]OOR (1702 cm-1) in the infrared spectroscopy, along with changes in the degree of substitution from 0 to 0.39, degree of esterification from 0 to 40 ± 1.5 and COOH content from 129 ± 0.5 to 290 ± 0.5 (meq. per 100 g), were found between yeast to YMC, respectively. The results revealed 1.5 times more dynamic swelling, 0.25-fold decrease in acid content, 2.3-fold increase in carboxyl content, and 1.2- and 2.1-fold increases in cross-linking density and viscosity of HGY as compared to HGG, respectively. The SEM and BET results revealed that HGY had a 2 times greater porous surface than HGG. HGY/DX was 35 ± 2% more effective in controlling periodontitis bacteria, decreased periodontal depth from 4 to 3.2 mm, and gingival index from 3 to 1 as compared to HGG/DX in patients suffering from periodontitis. HGY/DX not only serves as a tool for the controlled release of DX in periodontal pockets but also contributes to the treatment of gingival periodontitis.

Analysis of causes for high hydration and low drainage rate of wheat straw chemi-thermo-mechanical pulp

The wheat straw chemi-mechanical pulp has the characteristics of high yield, good mechanical performance and low production cost. However, there are significant problems in the papermaking process by such as high pulp hydration, poor drainage, and large energy consumption during the paper drying-process. It was found that during the chemical mechanical pulping of wheat straw, due to the residual alkali and temperature, the hemicellulose in the pulp was continuously dissolved, some of it entered the water phase, and some of it migrated to the fiber surface. Which reflected in the raise in cation demand for anionic substances in the aqueous phase, the increase in carboxyl content on the surface of pulp fibers, and the aggravation in hydration degree. Further research found that the high valence metal ions can combine the carboxylate radical on the hemicellulose molecule in the aqueous phase with the carboxylate radical on the pulp surface to form a covalent bond, so that the hemicellulose entering the aqueous phase can be re-adsorbed to the fiber surface, thus further increasing the degree of pulp hydration. Carboxymethyl starch was used to simulate hemicellulose, and the hemicellulose re-adsorption phenomenon verification experiments were reproduced in a calcium ion environment. The above findings indicate that during the production of wheat straw chemi-mechanical pulp process, the hemicellulose dissolved and re-adsorption not only leads to the increase of pulp hydration, but also results in poor water filtration during paper formation. Therefore, this study can provide a theoretical basis for optimizing the production process of chemi-mechanical pulp of wheat straw and controlling the technology and method of pulp hydration.

Poly (arylene ether ketone) with carboxyl groups ultrafiltration membrane for enhanced permeability and anti-fouling performance

• 1. C-PAEK ultrafiltration membrane was prepared by NIPS method to form finger-like pores and provide a transport channel for water. • 2. The introduction of carboxyl monomer improves the hydrophilicity and permeability of ultrafiltration membrane. • 3. C-PAEK ultrafiltration membrane was used for filtration of pure water /BSA solution. • 4. C-PAEK ultrafiltration membrane has high stability and excellent reusability. In this study, a novel poly (arylene ether ketone) with carboxyl groups (C-PAEK) was synthesized by adjusting the ratio of 4-carboxylphenyl hydroquinone (4C-PH) with bisphenol A (BPA). Fourier transform infrared spectroscopy (FTIR) and 1 H Proton Nuclear Magnetic Resonance ( 1 H NMR) spectra demonstrated that C-PAEK polymer was successfully synthesized by the nucleophilic polycondensation reaction. A series of C-PAEK ultrafiltration membranes were prepared by nonsolvent-induced phase separation (NIPS) method. The effect of carboxyl content on the structure and properties of C-PAEK ultrafiltration membranes was studied by scanning electron microscope (SEM), thermogravimetric analysis, porosity, water contact angle (WCA), molecular weight cut-off (MWCO), ultrafiltration and antifouling experiments. C-PAEK membranes showed the typical asymmetric structure and finger-like channels. With the increase of carboxyl content in PAEK, the WCA of membranes decreased from 76.9 ± 1.8° (M0) to 57.3 ± 1.6° (M4). In addition, the weight loss temperature of 5% and the maximum weight loss rate temperature of C-PAEK are about 432 ℃ and 502 ℃, respectively. Among the prepared membranes, the porosity (ε) of M2 with 10 wt% carboxyl groups content increased from 82.3 ± 3.6% to 91.2 ± 1.2%, but the average pore sizes (r m ) of the membranes were similar. M2 showed the highest pure water flux (511.5 L/(m 2 h)), which was 1.7 times of M0. Rejection and flux recovery rate (FRR) of were 96.4 ± 2.5% and 63.4%, respectively. Meanwhile, in the cyclic filtration experiment of C-PAEK membrane, with the increase of carboxyl groups, the FRR of both cycles was higher than that of the PAEK membrane. All results indicated that the membrane had high permeability, anti-fouling stability and durability. In short, the novel C-PAEK ultrafiltration membrane functionalized with 4C-PH demonstrated great potential for pollutant removal in the fields of pharmaceutical industry, food industry and bioengineering.

Effect of Carboxyl Content on the Performance of Carboxylated Graphene/Chitosan Leather Finishing Agent

Graphene oxide was modified with bromoacetic acid, and then carboxylated graphene was prepared, and its basic structure was characterized by infrared spectroscopy; then chitosan was used as a matrix, carboxylated graphene was used as a filler, and the solution blending method was used to prepare carboxylated graphene/chitosan composite leather finishing agent. The results of this study indicate that the content of carboxyl groups increased with the increase in the amount of bromoacetic acid, so was their stability. The crosslinking degree of carboxylated graphene/chitosan also increased with the increase of carboxyl content. The increase of the carboxyl content also improved the hydrophilicity and solvent resistance of the composite; the carboxylated graphene/chitosan composite with the carboxyl content of 6.48 mmol/L had the best physical and mechanical properties. At the same time, abrasion resistance can be increased to level 4, dry rub resistance to level 5, and wet rub resistance to level 4-5.

Preparation of oxidized corn starch in dry method assisted by kneader

In this study, oxidized starch (OCS) with different carboxyl content was prepared by the dry method, with H2O2 as the oxidant and CuCl2 as the catalyst. The optimum conditions were obtained by an orthogonal experiment, under the carboxyl and carbonyl content of 0.6813 and 1.0416% respectively. Fourier transform infrared (FTIR) spectroscopy, X-ray diffraction and gel permeation chromatography characterized the structures of OCS, and the thermal, gelatinization, viscosity property and its viscosity stability were measured. The results demonstrated that the crystallinity decreased slightly and the A-type crystal remained unchanged after oxidation, and the molecular weight of OCS decreased greatly. The thermal decomposition temperature, apparent viscosity and setback viscosity also decreased. With the increase of carboxyl content in OCS, the cold-water solubility and paste transparency of OCS paste increased gradually, while the viscosity of OCS paste decreased, and the viscosity stability displayed a trend of first increasing and then reducing. The OCS obtained by a kneader had low solution viscosity and high viscosity stability, suitable for sizing high count warp yarns.

Structure and properties of polycarboxylic acid dispersants synthesized by RAFT method

Polycarboxylic acid dispersants (PCs) with comb‐like molecular structure have become the focus of dispersants. However, there are many contradictions in the study of molecular structure of polycarboxylic acids. In this article, a series of PCs with different molecular structures were prepared from acrylic acid (AA) and methyl allyl alcohol polyoxyethylene ether (TPEG) by reversible addition fragmentation chain transfer (RAFT) polymerization. The structural characteristics of PCs were characterized by flourier transform infrared spectrometer (FT‐IR), 1H nuclear magnetic resonance (NMR) spectroscopy and gel permeation chromatography (GPC). The dispersion performance of PCs to cement was measured by the fluidity and adsorbing capacity. The results show that the dispersion performance and adsorbing capacity of PCs are significantly related to its structure. The adsorption and dispersion properties increase with the increase of carboxyl content and molecular weight. However, this phenomenon is limited to a certain range that the acid ether ratio in this range is no greater than 5:1, and the molecular weight is no greater than PC‐4 (Mw = 82 125, Mn = 63 889).

Preparation and properties of microfibrillated cellulose with different carboxyethyl content

Carboxyethyl reaction was used as a pretreatment method before grinding and homogenization to prepare microfibrillated cellulose (MFC). The effect of carboxyethylation on the properties of cellulose materials and prepared MFC samples were investigated. Results showed that cellulose materials with different carboxyethyl content were obtained by controlling the chemical dosage. This reaction increased the water retention value, decreased the degree of polymerization and crystallinity, and changed the crystalline structure of cellulose. After pretreatment, the cellulose fibers were easier to be swelled and fibrillated, which greatly reduces the frequency of grinding. In addition, the diameter of the produced MFC decreased with the increase of carboxyl content. The charge density, suspension stability and transparency of MFC increased obviously due to the presence of carboxyethyl groups. This study provides a comprehensive understanding of carboxyethyl pretreatment for the preparation of MFC, which may help to enrich and promote the preparation and application of MFC.

Coupling effect of PVDF molar mass and carboxyl content in CNTs on microstructure and thermal properties of CNT/PVDF composites

Poly(vinylidene fluoride) (PVDF) membranes were blended with loading different kinds of carboxylated multi-walled carbon nanotubes (MWCNTs) by phase inversion method. PVDF with different molecular weight of 450 and 800 kDa was selected for our study, whereas four CNTs as pristine multi-walled carbon nanotubes, carboxylated multi-walled carbon nanotubes with different carboxyl content from 0.49, 2 to 3.86 wt.% were chosen for a comparison. The casting solution was set as 18 wt%. The effects of carboxyl content in MWCNTs and molecular weight of PVDF on membrane morphology, surface roughness, surface hydrophilicity, pore size and porosity were comprehensively investigated by field emission scanning electron microscope, atomic force microscopy, water contact angle measurements, the Brunauer–Emmett–Teller and the gravimetric method. The crystallinity, thermal and mechanical properties of different membranes were evaluated by x-ray diffractometer, differential scanning calorimetry and single-fiber electronic tensile tester. With the increase of carboxyl content in MWCNTs, the thermal stability of composite membranes was enhanced to some degree and the crystal transformation was slightly altered. The results indicated that the composite membranes containing carboxyl content of 0.49 wt.% in MWCNTs and higher molecular weight of PVDF possessed better mechanical properties, higher hydrophilicity and more preferable morphology, which have great significance in fundamental researches as well as the application of composite membranes.

Preparation of Paper Strengthening Agent by Esterification of Cellulosic Fines

Paper strengthening agents play an important role in the papermaking industry with the increase of secondary fiber applications. The objective of this study was to create a dry-strength agent by esterification. The fines from the pulp were collected and modified with trimesic acid and citric acid, respectively, to obtain the dry-strength agent. The influences of acid type and dosage on the enhancing effect were investigated. Compared with the control sample, the physical properties of paper sheet were improved after adding modified fines. The properties of recycled paper were also improved by the modified fines. When the dosage of citric acid agent was 7%, the effect on paper properties saw the greatest improvement. The tensile index, burst index, and folding endurance were increased by 60.3%, 18.3%, and 146.2%, respectively, compared with the control. The improvement of paper properties was due to the increase of carboxyl content in the modified fines. Based on the findings, it can be concluded that the esterification is an effective approach for producing paper dry-strengthening agent.

Preparation, functional characterization and hemostatic mechanism discussion for oxidized microcrystalline cellulose and its composites

Effective and affordable hemostatic materials are of great interests in the development of biomaterials. Lignocellulose, which is a raw material for microcrystalline cellulose, is one of the most economical and readily available polymers in the nature. The oxidized microcrystalline cellulose particles prepared in NO2/CCl4 oxidation system may be a type of affordable, effective and nontoxic hemostatic biomaterial. The FT-IR and 13C solid state NMR results showed that the hydroxyl groups on C6 of cellulose were highly selectively oxidized. The increase of carboxyl content and Zeta potential of OMCC were highly dependent on the oxidation time at the first 64 h. XRD spectra indicated that the crystallinity changed from 70.01 % (MCC) to 60.63 % (OMCC-96 h), and the particle size decreased to 80 µm (OMCC-96 h). To composite with oxidized regenerated cellulose gauze, the OMCC-64 h was optimal, based on the dramatically reduced DP value after 64 h oxidization. The results showed this novel composite with negative charge exhibited good hemostatic property and antibacterial activity. The composite was possessed of both the good biocompatibility for mouse endothelial cells in vitro and the superior biodegradation for rabbits in vivo. Moreover, the data of enzyme-linked immunosorbent assay and blood coagulation tests in vitro suggested that the composite could adsorb and activate the platelets, and then the platelet glycoprotein (GPIIb/IIIa) receptor became competent to bind soluble fibrinogen. The composite also greatly accelerated the activation of the blood coagulation factor XII, and promoted the generation of thrombin, so that the extrinsic route of blood coagulation was initiated.

Modification of poovan banana (Musa AAB) starch by γ‐irradiation: effect on in vitro digestibility, molecular structure and physico‐chemical properties

SummaryThis study focussed at evaluating the effect of gamma irradiation on the in vitro digestibility, molecular structure and physico‐chemical properties of poovan banana (Musa AAB) starch using γ‐rays from a 60Co source at different doses with a dose rate of 2 kGy h−1. Physico‐chemical properties varied significantly and exhibited strong dose‐dependent relationship. Escalating irradiation leads to decrease in amylose content, pH, swelling power of the starch granules and syneresis of the gelatinised starch, while the same led to an increase in carboxyl content, in vitro digestibility, solubility and water absorption capacity of the starch granules. The results revealed that peak, hold, final and setback viscosities were significantly reduced. X‐ray diffraction pattern remained the same upon irradiation but a decrease in relative crystallinity was observed with increasing irradiation dose. Gelatinisation temperature and enthalpy decreased significantly when the increasing the dose of gamma irradiation.

Characterization of Structure and Property of the Monocarboxyl Bamboo Pulp Fibers

The oxidized bamboo pulp fiber yarns were prepared by the HNO3 /H3PO4-NaNO2 oxidation system. The effects of the oxidation concentration and reaction time on the weight loss, the carboxyl content and the breaking strength of the bamboo pulp fiber yarns were studied and the aggregation structure was investigated by Fourier transform infrared, X-ray and scanning electron microscopy. The results revealed an increase in carboxyl content and a decrease in breaking strength of oxidized bamboo pulp fiber yarns with increasing concentration of oxidant and reaction time. The breaking strength of oxidized bamboo fiber yarns was damaged seriously once the reaction time was more than 120 min or the concentration of oxidant was greater than 1.0%. The crystallinity of bamboo pulp fibers increased slightly under low oxidation degree but decreased with higher oxidation degree.

Dissolution performance of coals in ionic liquid 1-butyl-3-methyl-imidazolium chloride

A series of coals with various ranks were extracted with ionic liquid (IL) 1-butyl-3-methyl-imidazolium chloride (BMIC), which was found to be a very effective solvent for the extraction of coals in a previous study. The relationship between the extract yield of coal with BMIC and the quantities of oxygen-containing functional groups in lignites was investigated. Also the mechanism of extraction of Xianfeng lignite (XL) with BMIC was investigated by the diffuse reflectance spectra (DRIFT) analysis. It was found that the extract yields of coals with BMIC varied with the ranks of coals. With the increase of the oxygen content and the decrease of carbon content, extract yield of coal with BMIC significantly increased. Extract yield of lignites with BMIC increases almost linearly with the increase of carboxyl content. The extraction with BMIC significantly changes the types and the distribution of hydrogen bonds in XL.

Influence of HNO3/H3PO4–NANO2 mediated oxidation on the structure and properties of cellulose fibers

The bamboo pulp cellulose fiber was oxidized with HNO3/H3PO4–NaNO2 mixture to obtain oxidized cellulose containing different levels of carboxyl content and with high yields. The effects of HNO3/H3PO4–NaNO2 mediated oxidation on structure and properties of the fiber were investigated. The results showed that an increase in carboxyl content and weight loss of oxidized fibers appeared with increasing oxidation time. Compared with the original cellulose, the oxidized fibers had lower crystallinity (29–40%) and thermal stability. The patterns of 13C NMR, X-ray diffraction and other testing methods revealed that the oxidation mostly occurred at C6 primary hydroxyl groups of cellulose. Moreover, an oxidized fiber with 94.14–98.59% of high yields and 1.13–3.56% of carboxyl content was obtained in the range of oxidation time from 15 to 60min, while its mechanical properties did not change significantly. This work presented some detailed information about structure–property correlations of oxidized bamboo pulp cellulose fibers and was useful in planning applications of these products.

Agar-encapsulated adsorbent based on leaf of platanus sp. to adsorb cadmium ion in water.

A low cost and environmentally friendly adsorbent was developed based on leaf of platanus sp. to adsorb cadmium ion in water. The adsorbent was modified with citric acid and then also encapsulated in agar for easy separation after the adsorption process. Parameters such as adsorbent dose, stirring time, solution pH and modification of the adsorbent with citric acid were investigated in a batch experiment in order to determine the optimum condition for Cd (II) adsorption. Based on the Langmuir isotherm adsorption model, the adsorption capacity of cadmium ion for raw adsorbent, modified adsorbent with citric acid and encapsulated adsorbent were 3.69, 15.31 and 6.89 mg/g, respectively. The high adsorption capacity after treatment with citric acid may be due to the increase in carboxylic content of the adsorbent surface and also the increase of surface area and pore volume of the adsorbent. With this high adsorption capacity for cadmium ion and an abundance of raw materials, this bio-adsorbent could be considered as a low cost adsorbent in the near future.

Preparation and Properties of Oxidized Corn Starches by Semi‐Dry Process

ABSTRACTOxidized corn starch prepared by a semi‐dry process using hydrogen peroxide as an oxidant was studied. The optimum oxidation conditions of corn starch were mole ratio of H2O2 and anhydroglucose unit (0.219); mole ratio of NaOH and anhydroglucose unit (0.144); moisture content of the reaction mixture (27.2%); and reaction temperature (65°C). Compared with oxidized corn starch produced by reacting starch with sodium hypochlorite in alkaline slurry, oxidized corn starches produced by a semi‐dry process apparently had different properties. Oxidation by a semi‐dry process for corn starch resulted in significant changes in the degree of crystallinity of starch and the changes increased with the increase of carboxyl content of starch. Peak viscosities of oxidized starches produced by a semi‐dry process were lower than those of commercial corn starch at similar carboxyl contents, while the final viscosities and setbacks of the former were much higher than the latter. There were apparent differences for texture properties among oxidized starches prepared by different processes. Onset temperature, peak temperature, and conclusion temperature of semi‐dry oxidation starches were higher than those of commercial oxidized starch, while the enthalpy of gelatinization of the former were lower than the latter.

Adsorption of zwitterionic drugs on oxidized cellulose from aqueous solutions

Adsorption of zwitterionic drugs (β-lactam antibiotics and amino acids) on samples of oxidized cellulose (OC) with various carboxyl contents and structure characteristics from aqueous solutions was investigated. It was established, that drug binding with OC occurs via proton transfer from carboxyl group of ion exchanger to the carboxylate ion of adsorbed zwitterion. The adsorption process can be described according to the theory of localized stoichiometric adsorption and represented by Langmuir-like isotherms. The constants of sorbate interfacial distribution with some exceptions increase with a growth of sorbate relative hydrophobicity. The drug uptake is shown to increase with an increase of carboxyl content in the OC phase. The degree of crystallinity of sorbent has no considerable effect on drug adsorption from aqueous solutions.