Cross-linking Compounds Research Articles

Formation and evolution of coke of pyrolytic volatiles of low-rank coal on the carbon-based catalysts

The catalytic upgrading of coal pyrolysis volatiles is an effective technique to achieve clean and efficient conversion of low-rank coal. However, a major problem in this process is catalyst deactivation caused by coke deposition. This study investigated the catalytic cracking effect of activated carbon and metal-modified activated carbon on coal pyrolysis volatiles. It also explained the physical and chemical properties of coke and its formation mechanism related to volatile cracking. The results indicate that phenolic oils, pitch, oxygen-containing compounds, and polycyclic aromatics are linearly related to the coke deposited on the surface of carbon-based catalysts. These compounds act as precursors and are easily transformed into coke via cracking, deoxidation, crosslinking, and polycondensation reactions when the cracking rate of volatiles does not match the hydrogen supply rate. The micro-morphology of coke is primarily composed of amorphous carbon, which is mainly found in pores ranging from 0.50 to 5.00 nm and on the outer surface of carbon-based catalysts. The chemical structure of coke primarily consists of large aromatic clusters containing at least six benzene rings and oxygen-containing cross-linking compounds with a high degree of graphitization and a low number of carbon structural defects. This results in an increase in radical concentration of carbon-based catalysts, as well as a decrease in combustion reactivity. The outcomes will aid in controlling coke deposition during catalytic cracking of pyrolytic volatiles of low-rank coal.

DETERMINATION ON NITROGEN CONTENT OF ANTIBACTERIAL COTTON FABRIC TREATED WITH CHITOSAN

The study aims to evaluate the nitrogen content on antibacterial cotton fabrics treated with chitosan using four different quantitative determination methods: field-emission scanning electron microscopy with energy dispersive X-ray spectroscopy (FESEM-EDX), dyeability of antibacterial treated samples based on color strength (K/S), elemental analyses via combustion tests, and antibacterial ability under dynamic contact conditions or the dynamic shake flask test. The nitrogen content was analyzed under the effects of molecular weight (MW) of chitosan (2.6 kDa and 187 kDa), crosslinkers including citric acid (CA) and dimethylol dihydroxyethyleneurea (DMDHE), and washing cycles. The findings from these measurements not only determined the nitrogen content of antibacterial cotton fabric but also elucidated the bonding mechanism between cellulose and chitosan in the presence of crosslinking compounds. Consequently, the antibacterial activity of cotton fabrics treated with chitosan could be indirectly assessed through the nitrogen content obtained from the amine groups of finishing compounds.

Evaluation of the stabilizing effect and ageing time indicator properties of poly(flavonoids) in a cyclic olefin copolymer

Few studies are concerned with the stabilization of polymers using natural polymeric polyphenols. There are no literature reports on the use of poly(flavonoids) produced by bio-chemical polymerization as stabilizers. The aim of the research was to analyse the stabilizing potential (anti-ageing UV) of poly(catechin) and poly(naringenin) in polymer compositions based on the thermoplastic elastomer of ethylene-norbornene copolymer (TOPAS Elastomer E-140). Poly(flavonoids) were obtained in a polymerization reaction with a cross-linking compound and then introduced into cyclic olefin copolymer TOPAS. For comparison, materials with monomeric catechin and naringenin were also prepared. The scope of research included the thermal analysis of the polymer compositions (Oxidation induction time OIT, Thermogravimetry TG), determination of carbonyl indices and ageing coefficients K (based on changes in mechanical properties) after UV ageing (400 h). In addition, the colour change after ageing of the samples was investigated. Samples containing polymeric forms of catechin and naringenin were more susceptible to degradation than samples with monomeric flavonoids. Inferior stabilizing properties of poly(flavonoids) were associated with steric hindrances and limited availability of hydroxyl groups to provide the antioxidant activity of the polymeric compounds. The work extends the literature data by providing an analysis of the stabilizing effect of synthetic poly(flavonoids) in polymer compositions.

Novel Biocomposite of Starch and Flax Fiber Modified with Tannic Acid with Biocidal Properties.

The purpose of this paper was to develop novel biocomposites with biocidal properties in microorganisms, with enhanced mechanical strength and hydrophobicity as well as with increased biodegradation rates. The main idea and the novelty of this work was to use cross-linking compounds and, at the same time, biocidal compounds-natural compounds of plant origin with biocidal properties. The authors assumed that the modification of flax fiber by natural plant compound will reduce the hydrophilicity of novel biocompositie. Biopolymer based on thermoplastic starch reinforced with flax fibres modified with tannic acid (TA) was prepared by extrusion and injection molding processes. The effects of TA modification on the mechanical and structural properties of biocomposites were analyzed through DMA, tensile tests, DSC, and TG. The biocidal and wettability properties of the biocomposites were investigated. The article also discusses the outcomes of research conducted on the structural characteristics and rates of the biodegradation of biocomposites.

Immobilization of Urease from Psophocarpus tetragonolobus L. DC. using Natrium Alginate Supporting Matrix

Urease is an enzyme that has the role to hydrolyzes urea into ammonia and carbon dioxide. Immobilization is one of the most efficient strategies to improve its activity recovery and properties of urease. This research started with the germination of winged beans for 8 days. The winged bean was extracted by grinding using a mortar and pestle and then added with phosphate buffer at pH 7. The solution was homogenized using a stirrer and then centrifuged in cold conditions so that an extract of urease was obtained. Urease extracts were immobilized using a chitosan-supporting matrix. Optimization of the immobilization process of urease extract includes the concentration of chitosan and sodium tripolyphosphate (TPP) and contact time. The obtained was free and immobilized urease activities then tested using the Nessler method and measured using a UV-Vis spectrophotometer with a wavelength of 500 nm. The obtained data were then statistically tested using ANOVA. Urease-chitosan beads were further tested in repeated use and analyzed with SEM-EDX (Scanning Electron Microscopy-Energy Dispersive X-ray). The results showed that the optimum conditions for making urease-chitosan beads were a concentration of 4% (w/v), 2.5% (w/v) TPP, and 60 minutes of contact time, resulting in an activity value of 15.076 U/mL, which can be used 5 times with 46% activity from the initial activity. The EDX analysis results after the addition of the enzyme showed atom composition changes leading to increasing carbon and nitrogen contents. The existence of phosphor showed that TPP was a chitosan cross-link compound.
 
 Keywords: Chitosan, immobilization, TPP, urease, winged bean

Comparative study on matrix resins in two low‐density polyethylene based cable insulation materials with different voltage grades

AbstractIn industry, crosslinked polyethylene (XLPE) cable insulation is usually produced from crosslinkable compounds consisting of low‐density polyethylene (LDPE) and additives, which known as “cable materials”. Considering that in addition to additives, the structure of matrix resin is a key factor in determining the property of XLPE, it is worthy to study the structure requirements of matrix resin for the development of cable materials with different voltage grades. In this work, the structure of matrix resins of a high voltage grade and an extra high voltage grade cable material were comparatively investigated. Interestingly, it was found that the matrix resins have no significant difference in chain structure parameters including molecular weight and its distribution and vinyl content between two samples, and their crystalline structure as well as the melt rheology and melting crystallization behavior are also very similar. These results suggest that these matrix resins may not substantially differ. Our work shows that cable materials with different voltage grades are not necessarily diverge in terms of matrix resin structure, and it could be possible to develop higher grade cable materials using the same matrix resin as lower grade counterparts.

Comparison of Aging Simulation to Real Aging of Silicone Self-adhesives Tapes

The paper presents a comparison of the aging of silicone self-adhesive tapes in real conditions and accelerated aging in laboratory conditions. In order to check the correlation between the tested tapes, the tapes were tested immediately 24 h after making and after aging to determine changes in values functional properties such as adhesion, cohesion and tack. The tapes were manufactured on the basis of a selected pressure-sensitive silicone adhesive, which were cross-linked after adding the cross-linker and different dye content. As a result of the compared simulation in the test chamber (accelerated aging) and 7 years aging test, values of useful properties (e.g. adhesion) were obtained similarly. In the presented work, the influence of the amount of dye on the properties of pressure-sensitive adhesives was also examined, which allowed to obtain samples with similar functional properties, easy to compare with each other. The samples together with the dye and the cross-linking compound were subjected to artificial conditions in the chamber (artificial aging) and stored for 7 years.

Recent Research on Lipase Immobilization with Multipoint Covalent Treatment by Glutaraldehyde

Abstract: Immobilized lipase has played an essential role in the chemical and biological sciences as a viable alternative to standard chemical catalysts. Glutaraldehyde is a low-cost crosslinking agent at risk of being superseded by developing crosslinking compounds with biocompatible, biodegradable, and non-toxic characteristics. The multipoint covalent treatment method using glutaraldehyde has both advantages and disadvantages. Immobilization techniques can be improved to improve the overall performance of immobilized lipase. The most recent update on lipase immobilization with multipoint covalent treatment by glutaraldehyde was summarized in this review. Covalent binding lipase on pre-activated support and aggregation-crosslinking lipase into crosslinked enzyme aggregates (CLEAs) or adsorptioncrosslinking lipase on support are the most common immobilization techniques. Based on the above technologies, the advancement trends in important domains, such as the advancement of supports, additives, reactors, and cross-linking agents, are summarized. In addition, the application of the improved immobilized lipase by glutaraldehyde in the production of fatty acids, glycerides, biodiesel, and drug precursors was reviewed. In view of this, we put forward further studies on multipoint covalent treatment in lipase immobilization with glutaraldehyde. Various analytical methods are required to provide additional information about the structure of glutaraldehyde and its crosslinked products for assisting the proper immobilization conditions. Applying the composite strategy can also bring new opportunities for improving the efficiency of biological catalysts.

Probing conformational changes during activation of ASIC1a by an optical tweezer and by methanethiosulfonate-based cross-linkers.

Acid-sensing ion channels (ASICs) are neuronal, proton-gated, Na+-selective ion channels. They are involved in various physiological and pathological processes such as neurodegeneration after stroke, pain sensation, fear behavior and learning. To obtain information on the activation mechanism of ASIC1a, we attempted in this study to impose distance constraints between paired residues in different channel domains by using cross-linkers reacting with engineered Cys residues, and we measured how this affected channel function. First, the optical tweezer 4′-Bis(maleimido)azobenzene (BMA) was used, whose conformation changes depending on the wavelength of applied light. After exposure of channel mutants to BMA, an activation of the channel by light was only observed with a mutant containing a Cys mutation in the extracellular pore entry, I428C. Western blot analysis indicated that BMA did not cross-link Cys428 residues. Extracellular application of methanethiosulfonate (MTS) cross-linkers of different lengths changed the properties of several Cys mutants, in many cases likely without cross-linking two Cys residues. Our observations suggest that intersubunit cross-linking occurred in the wrist mutant A425C and intrasubunit cross-linking in the acidic pocket mutant D237C/I312C. In these mutants, exposure to cross-linkers favored a non-conducting channel conformation and induced an acidic shift of the pH dependence and a decrease of the maximal current amplitude. Overall, the cross-linking approaches appeared to be inefficient, possibly due to the geometrical requirements for successful reactions of the two ends of the cross-linking compound.

Facile synthesis of a MOF-derived magnetic CoAl-LDH@chitosan composite for Pb (II) and Cr (VI) adsorption

A novel sorbent Co-Al-LDH@CS/Fe3O4 was synthesized in this learning for the elimination of Pb (II) and Cr (VI) from water using Co-Al layered double hydroxides (LDHs) as precursors, combined with cross-linked compounds of magnetically interspersed chitosan (CS) and cystamine. The successful synthesis of the adsorbent Co-Al-LDH@CS/Fe3O4 was demonstrated by SEM, FTIR, XRD and XPS characterization. The maximum adsorption capacities of Co-Al-LDH@CS/Fe3O4 at 25 °C were 558.84 and 710.79 mg/g for Pb (II) (pH = 6) and Cr (VI) (pH = 4), respectively. The sorption kinetics prove that the sorption is chemisorption and the rate-limiting step is exterior dispersion. The adsorption isotherms indicate that the sorption process is an irreversible process with positive synergistic effects at multiple sites. Thermodynamic studies show that Pb (II)/Cr (VI) sorption is spontaneous and irreversible in the process. Further, Co-Al-LDH@CS/Fe3O4 also possesses a good selectivity and reusability (5 cycles) for Pb (II) and Cr (VI). The DFT calculations revealed that -SH and –NH2 on the adsorbent surface have a stronger affinity for Pb (II) and Cr (VI).

Silicone pressure-sensitive adhesives with increased thermal resistance

The purpose of this work was to obtain single-sided tapes with different concentrations of kaolin and to check its impact on the self-adhesive properties of commercial adhesives. The most important self-adhesive properties were examined, such as tack, peel adhesion, shear strength, shrinkage, and thermal resistance. Tapes based on silicone PSAs with kaolin can be used in many branches of industry to bond elements operating at elevated temperatures, i.e., in aeronautics, aerospace including solar cells for satellites and space stations. There are few reports on one-sided adhesive tapes based on silicones with the addition of kaolin. However, taking into account the number of their potential applications, we did self-adhesive tests and explained how kaolin affects them. In addition, the reactivity of the crosslinking compound and silicone adhesive during the crosslinking process and the thermal effects of this process were also examined. In connection with the various applications of the obtained tapes, also the flammability and heat of combustion were tested, in accordance with applicable standards. As a result of the tests, one-sided self-adhesive tapes with new properties (increased temperature resistance, less shrinkage, and increased resistance to flammability) were obtained.

Microbial Transglutaminase Is a Very Frequently Used Food Additive and Is a Potential Inducer of Autoimmune/Neurodegenerative Diseases.

Microbial transglutaminase (mTG) is a heavily used food additive and its industrial transamidated complexes usage is rising rapidly. It was classified as a processing aid and was granted the GRAS (generally recognized as safe) definition, thus escaping full and thorough toxic and safety evaluations. Despite the manufacturers claims, mTG or its cross-linked compounds are immunogenic, pathogenic, proinflammatory, allergenic and toxic, and pose a risk to public health. The enzyme is a member of the transglutaminase family and imitates the posttranslational modification of gluten, by the tissue transglutaminase, which is the autoantigen of celiac disease. The deamidated and transamidated gliadin peptides lose their tolerance and induce the gluten enteropathy. Microbial transglutaminase and its complexes increase intestinal permeability, suppresses enteric protective pathways, enhances microbial growth and gliadin peptide’s epithelial uptake and can transcytose intra-enterocytically to face the sub-epithelial immune cells. The present review updates on the potentially detrimental side effects of mTG, aiming to interest the scientific community, induce food regulatory authorities’ debates on its safety, and protect the public from the mTG unwanted effects.

Novel Polymeric Biomaterial Based on Naringenin.

Biomaterials prepared based on raw plant materials are becoming more and more popular due to their specific properties and environmental friendliness. Naringenin is a flavonoid naturally occurring in citrus fruit with antioxidant and pharmacological activity. Polymeric materials based on flavonoids may have favorable properties in comparison to monomeric polyphenols, such as stronger antioxidant and antimicrobial properties. One of the methods of obtaining the polymeric form of flavonoids is polymerization with a cross-linking compound. This method has already been used to obtain poly(quercetin) and poly(rutin) from a flavonol group as well as poly(catechin) from the flavan-3-ol group of flavonoids. However, to date, no polymeric forms of flavanones have been prepared in a cross-linking reaction; the aim of this study was to obtain poly(naringenin) by reaction with a cross-linking compound using glycerol diglycide ether GDE. The degree of conversion of naringenin to poly(naringenin) determined by FTIR spectroscopy was 85%. In addition, the thermal, antioxidant and antimicrobial properties of poly(naringenin) were analyzed. Poly(naringenin) was characterized by greater resistance to oxidation and better thermal stability than monomeric naringenin. Moreover, polymeric naringenin also had a better ability to scavenge ABTS and DPPH free-radicals. In contrast to monomeric form, poly(naringenin) had antimicrobial activity against Candida albicans. Polymeric biomaterial based on naringenin could potentially be used as a natural stabilizer and antimicrobial additive for polymer compositions, as well as pro-ecological materials.

An efficient chitosan-based adsorption material containing phosphoric acid and amidoxime groups for the enrichment of Cu(II) and Ni(II) from water

A novel modified chitosan (CS) material, CS-g-AOPAM, was prepared by the amidoximation of the crosslinking compound of CS and a terpolymer of acrylamide, acrylonitrile and 3-dimethylaminoallyl phosphonic acid, which was applied to adsorb Cu(II) and Ni(II). The material CS-g-AOPAM was characterized by SEM, FTIR, XPS and TG, indicating porous structure and excellent thermal stability. In order to investigate the effects of coexisting ions, pH, initial concentration, adsorption time, and temperature on adsorption capacity of CS-g-AOPAM, batch adsorption experiments were carried out to obtain the corresponding adsorption behavior. According to the linear fitting of Langmuir model, the results proved that CS-g-AOPAM had excellent adsorption performance, exhibiting the maximum adsorption capacities of 215.5 mg·g−1 and 213.4 mg·g−1 for Cu(II) and Ni(II), respectively, which was higher than that of most similar CS adsorbents. The adsorption isotherms were in good agreement with Langmuir model, indicating a monolayer adsorption. Moreover, various adsorption kinetic and thermodynamic models were employed for analyzing adsorption behavior of CS-g-AOPAM, suggesting that the adsorption was a chemisorption as well as spontaneous endothermic process. Further, based on the analysis of FTIR and XPS, the adsorption sites and potential bonding modes of Cu(II) and Ni(II) were proposed. Overall, CS-g-AOPAM is a pretty promising novel adsorption material for the removal of heavy metal ions from wastewater.

The influence of physico-chemical methods on the process of ostrich fat warming

The work is devoted to the study of the influence of technological parameters and optimization of the duration of the process of fat extraction in the presence of electroactivated liquid. The introduction of innovative technologies that allow the rational use of animal fats. The proposed new technical solutions are aimed at obtaining fat with a controlled melting point, high yield and consumer properties, reducing water consumption, energy consumption and industrial waste, reducing the environmental load on the environment. The foregoing gave reason to consider the chosen area of research quite promising. A catholyte with desired properties, obtained by electrolysis of an aqueous solution of NaCL with a mass fraction of 4 g/ 100 cm3, was used as the aqueous phase in wet ejection. The main technological factors were chosen pH of the electroactivated medium, the temperature of the expulsion of raw fat and the duration of the process. It has been revealed that the use of an electrochemical activated medium in wet fat pushing of fat reduces the risks of the formation of free fatty acids and cross-linking compounds. Due to the complex effect of physical and chemical factors, the process of fat extraction without loss in yield of the final product has been intensified. Reducing the duration of heat treatment of raw materials helps to prevent deep hydrolysis of fat and improves the quality of melted fat.

Thermally Stable and Antimicrobial Active Poly(Catechin) Obtained by Reaction with a Cross-Linking Agent.

(+)-Catechin is a flavonoid with valuable antioxidant and antimicrobial properties, found in significant amounts in green tea leaves. Polymeric forms of catechin have been obtained by enzymatic reaction, photopolymerization, and polycondensation in designed processes. However, so far, poly(catechin) has not been received in the cross-linking reaction. Reactions with the cross-linking compound allowed for the preparation of antibacterial and antioxidant materials based on quercetin and rutin. The aim of the research was to obtain, for the first time, poly(catechin) by reaction with glycerol diglycide ether cross-linking compound. The polymeric form of (+)-catechin was confirmed using FTIR and UV-Vis spectroscopy. In addition, thermal analysis (TG and DSC) of the polymeric catechin was performed. The antioxidant and antibacterial activity of poly (flavonoid) was also analyzed. Poly(catechin) was characterized by greater resistance to oxidation, better thermal stability and the ability to reduce transition metal ions than (+)-catechin. In addition, the polymeric catechin had an antimicrobial activity against Staphylococcus aureus stronger than the monomer, and an antifungal activity against Aspergillus niger comparable to that of (+)-catechin. The material made on the basis of (+)-catechin can potentially be used as a pro-ecological stabilizer and functional additive, e.g., for polymeric materials as well as dressing materials in medicine.

New approaches of curing and degradation on epoxy/eggshell composites

Epoxy resin suitable for structural composite based on bisphenol A diglycidyl ether (DGEBA) was mixed with anhydride methyl tetrahydrophthalic (MTHPA) as curing agent. As catalyzer two systems were investigated, the synthetic 2,4,6-tris(dimethylaminomethyl)phenol (DEH 35), and the natural based on chicken eggshell (E) and chicken eggshell membrane (M). The influence of DEH 35, E and M on the thermal stability and curing behaviors were evaluated by thermogravimetry (TGA), differential scanning calorimetry (DSC), and Fourier transform infrared spectroscopy (FTIR). Increasing the heating rates “S” curing plots were displayed to higher temperatures, whereas under higher catalyzer content the curing started at lower temperatures. Based on FITR spectra, consuming and development of main chemical groups connected with epoxy curing were precisely followed, corroborating TG and DSC data. Proper curing rate, thermal stability and degradation rates were reached in epoxy upon EM and M addition suggesting improved cross-linked compounds. Summing up, this work presents the curing kinetics and degradation analyses of epoxy/eggshell composites, thermodynamics and kinetics parameters are reported as well as the main molecular groups involved with phase transitions, which can help to understand and control both mechanisms.

Tailoring the molecular structure of crosslinked polymers for pervaporation desalination

Polymer crosslinking imbues chemical stability to thin films at the expense of lower molecular transportation rates. Here in this work we deployed molecular dynamics simulations to optimise the selection of crosslinking compounds that overcome this trade-off relationship. We validated these simulations using a series of experiments and exploited this finding to underpin the development of a pervaporation (PV) desalination thin-film composite membrane with water fluxes reaching 234.9 ± 8.1 kg m−2 h−1 and salt rejection of 99.7 ± 0.2 %, outperforming existing membranes for pervaporation and membrane distillation. Key to achieving this state-of-the-art desalination performance is the spray coating of 0.73 μm thick crosslinked dense, hydrophilic polymers on to electrospun nanofiber mats. The desalination performances of our polymer nanocomposites are harnessed here in this work to produce freshwater from brackish water, seawater and brine solutions, addressing the key environmental issue of freshwater scarcity.

Dorada mešavine pamuk/PES kombinacijom reaktivne smole i hitozana

The tendency of textile materials to crease is reduced by the finishing process when cross-linked compounds are incorporated in the amorphous phase, which improve the recovery of material after the elimination of the pressure load. Because of adverse effects on human health conventional formaldehyde-based processing compounds are increasingly substituted by new compounds and by use of biopolymers. In the paper, examined is the possibility of using the biopolymer chitosan in combination with reactive resin to improve the physical properties of fabrics made of blended cotton/PES. The use of chitosan in combination with commercial reactant improves the physical characteristics of fabrics, because increasing the concentrations of biopolymer progressively increases recovery angle (a0), quality number (K) and the bursting strength of the treated fabric.

Synthesis of epoxy resins derivatives of naphthalene-2,7-diol and their cross-linked products

The aim of this study was the synthesis of three different epoxy compounds based on naphthalene-2,7-diol (2,7-NAF.EP, 2,7-NAF.WEP, 2,7-NAF.P.EP) and then their cross-linking by triethylenetetramine (TETA). All epoxides were prepared by the reaction of naphthalene-2,7-diol with epichlorohydrin but under different conditions and with other catalysts. The structures of the obtained compounds before and after the cross-linking reactions were confirmed by the attenuated total reflectance Fourier transform infrared spectroscopy (ATR/FT-IR). The ATR/FT-IR spectra of cross-linked compounds show disappearance of the C–O–C bands (about 915 cm−1) derived from the epoxy groups. DSC and TG/DTG measurements indicated that the obtained materials possess good thermal resistance; they are stable up to about 250 °C. The hardness of the cross-linked products was determined using the Shore D method. The highest value of hardness was obtained for the 2,7-NAF.EP-POL. Additionally, the UV–Vis absorption spectra of the obtained polymers were registered and evaluated.