Formation Of Crosslinked Structure Research Articles

Char formation during pyrolysis of torrefied cellulose: Role of potassium catalysis and torrefaction pretreatment

Torrefaction is an efficient pretreatment technology for large-scale and high-value utilization of biomass fuel. This study aims to enhance the understanding of the thermochemical conversion of torrefied biomass by delineating the role of potassium and torrefaction on primary/secondary charring reactions during pyrolysis of torrefied cellulose. Celluloses with varying potassium loading levels were torrefied at temperatures ranging from 200 to 320 °C and subsequently pyrolyzed at 1000 °C. Two contrasting pyrolysis conditions, i.e., limiting and enhancing transport resistance, were employed to tune the occurrence of secondary reactions, thereby determining the role of torrefaction and potassium on primary and secondary charring reactions. Potassium content, torrefaction severity, and pyrolysis conditions both profoundly affects char formation during pyrolysis of torrefied cellulose, resulting in a wide range of pyrolysis char yields from 1.95 wt% to 64.35 wt%. The structural changes induced by torrefaction, including the depolymerization of the carbohydrate structure and the formation of crosslinking structures, promote the char formation. Potassium enhances the char formation of torrefied cellulose in two ways: i) by catalyzing the transformation of the carbohydrate structure into the crosslinking structure during torrefaction, and ii) by catalyzing the charring reactions of both the carbohydrate and the crosslinking structures during pyrolysis. Raman spectral analysis of the char carbon structure indicates that increased potassium loading level and torrefaction severity enlarge the aromatic system of the char. The findings highlight the potential of optimizing biomass pyrolysis through controlled torrefaction and potassium, paving the way for more efficient biofuel production and high-quality biochar applications.

A sustainable rapeseed oil-based bio-additive designed for hard asphalt binders: Performance, environmental, and economic assessment

The inherent properties of hard asphalt binder give it both mechanical and economic benefits, rendering it a naturally advantageous material for preventing permanent deformation at higher temperatures. However, its poor resistance to thermal and fatigue cracking limits its application in the paving industry. This study aimed to improve the low-temperature and fatigue performance of hard asphalt binders by using the newly developed vegetable oil-based sub-epoxidized rapeseed oil (SERO). Two SEROs with epoxidation degree of 49.1% and 98.1% were synthesized through an oxidation reaction, respectively. Subsequently, the microstructural characteristics of SEROs were examined by Fourier transform infrared spectroscopy (FTIR) and Hydrogen nuclear magnetic resonance tests. The anti-oxidative aging properties of SERO modified hard asphalt binders were investigated through the utilization of mass loss and aging index. Additionally, the comprehensive rheological properties of SERO modified hard asphalt binders were explored via dynamic shear rheometer and bending beam rheometer tests. Furthermore, the modification mechanism of SERO on hard asphalt binders was confirmed through the quantitative analysis using the FTIR test. The findings suggested the improvement in anti-volatilization and anti-oxidative aging performance of bio-modified hard asphalt binders, which was positively related to the epoxidation degree of SERO. A notable softening effect of SERO on the hard asphalt binders was observed, which enhanced their resistance to thermal and fatigue cracking at lower and intermediate temperatures. The epoxy groups within SERO engaged in ring-opening reactions, forming a new oxygen bridge bond by combining with the unsaturated double bond presented in the asphalt. Consequently, this process resulted in the formation of cross-linked structures within bio-modified hard asphalt binders, thereby enhancing the elasticity. Notably, this phenomenon was most conspicuous in the SERO-H modified 50# binder. Finally, the environmental and economic assessment of SERO modified hard asphalt binders were conducted by the techno-economic method and the emission factors technique. The data revealed that the production of one ton of SERO modified hard asphalt binders could reduce the production costs by about 30%, energy consumption and CO2 emissions by around 20% in contrast to styrene–butadiene–styrene block copolymer modified asphalt binders. Hence, the substantial economic and environmental advantages make SERO an attractive bio-renewable additive for sustainable pavements.

In-situ construction of modified layer on the surface of anion exchange membrane to improve antifouling performance

A new strategy combining electrodeposition with co-deposition modification was proposed to in-situ construct a stable antifouling modified layer on the AEM surface without disassembling the membrane stack. Specifically, dopamine (DA) was introduced into the electrodeposition process of poly (sodium 4-styrene sulfonate) (PSS) to co-deposit onto the AEM surface, in which the polymerization reaction could promote by supporting electrolyte (NaCl). The formation of cross-linked structure and π-π stacking effect during in-situ modification could ensure the stability of the modified layer. The in-situ modified AEM had a negatively charged and more hydrophilic surface, significantly improving the antifouling performance against organic matter (sodium dodecylbenzene sulfonate) without affecting desalination performance. Moreover, it still had excellent antifouling properties after 96 h neutral rinsing. This work provided a novel approach for preventing organic fouling of AEM in ED process through surface modification.

Fabrication of rigid polyimide foams by adopting active crosslinking strategy

Rigid polyimide foams (PIFs) with excellent mechanical and thermal properties were fabricated by thermal foaming of active cross-linkable units terminated polyester ammonium salts (PEAS) precursor powders. The active cross-linking strategy was realized by breaking CC bonds in maleic anhydride under heating treatment. Results showed that the formation of cross-linked structure before complete imidization effectively resisted matrix shrinkage and endowed PIFs with outstanding mechanical properties. The room temperature compressive strength and modulus of PIFs with four repeating units reached as high as 2.34 and 56.1 MPa, respectively. Moreover, the PIFs exhibited excellent thermal properties with onset decomposition temperatures ranging from 490 to 550 °C and the glass transition temperatures exceeding 290 °C. The PIFs displayed better thermal insulation, and the values of thermal conductivity fell within a range of 0.056–0.090 W m−1 K−1, which demonstrates potential application as high temperature resistant structural materials in aerospace and energy sectors.

Advances in water-resistant modification of aqueous acrylic resins: modification methods, mechanism of action

Waterborne acrylic resin is widely available in architectural coatings, road adhesives, etc. Its non-toxicity, non-irritating odour, and low cost are characteristics that have received increasing attention in recent years. Concerning the water-resistance of the resin, this review introduces the effect of inorganic materials like silane coupling agents, fluorine silicone, and copolymers on the hydrophobic properties of aqueous acrylic resins, analyses and discusses the mechanism of action of various methods and their factors affecting hydrophobic properties, such as the formation of cross-linked structures and micro-convex structures on the surface, also points out the problems and challenges in the water-resistance modification of aqueous acrylic resins.

A novel waste-recycled chelating agent for the stabilization of lead in municipal solid waste incineration fly ash: Preparation, feasibility, and mechanism analysis

There are two key issues in the area of waste management: one is stabilizing heavy metal, lead (Pb), in municipal solid waste incineration fly ash (MSWI-FA), the other is enhancing nitrogen utilization efficiency from organic waste. However, the connection between both issues was limited. In this study, a novel organic chelating agent based on food waste, FW-CA, was produced for immobilizing Pb. A maximum 86.22% of polypeptide in hydrolysis liquid of FW was utilized for preparing FW-CA with a yield of 8.22 g/L. Results indicated that FW-CA-stabilized fly ash satisfied the criteria of GB 18598–2019 with a dosage of 4.6%, lower than the demand of pure chemicals and industrially applied chelating agents. After treating with FW-CA, the exchangeable and bound to carbonate fraction of Pb decreased by 5.08% and 18.57%, respectively, contributing to a low environmental risk class of the Pb assessment code. FW-CA effectively chelated Pb at a wider range of leaching pH (3.19–11.24), and the leachability was hardly affected by curing time, which were attributed to the presence of dithiocarbamate group and formation of cross-linked structure between Pb and sulfur. Overall, the unique waste-utilized chelating agent was a suitable alternative for Pb stabilization in MSWI-FA.

A Cathodic Electrochromic Material Based on Thick Perylene Bisimide Film with High Optical Contrast and High Stability

A Cathodic Electrochromic Material Based on Thick Perylene Bisimide Film with High Optical Contrast and High Stability

Processing bulk natural bamboo into a strong and flame-retardant composite material

We report a simple and effective approach to process natural bamboo directly into a high-performance composite material with light weight, high tensile strength, high modulus, and low flammability. Our process involves delignification of natural bamboo followed by surface treatment of highly aligned cellulose fibers in the delignified bamboo and finally infiltration of epoxy resin into the porous structure of the surface-treated delignified bamboo. Surface treatment of the highly aligned cellulose fibers by boric acid (BA) under alkaline conditions resulted in the formation of cross-linked structures between the hydroxyl groups of BA and the diol or carboxylic groups of the cellulose backbone. Because the aligned bamboo fibers were well-preserved, the BA-bamboo/epoxy composite showed increases of 234% and 177% in tensile strength and impact strength, respectively, compared to the pristine epoxy. The BA-bamboo/epoxy composite exhibited comparable mechanical properties but significantly improved flame retardancy compared to the delignified bamboo/epoxy composite. Specifically, the limiting oxygen index of the BA-delignified bamboo/epoxy composite was 26.5% larger and the peak heat release rate was 63% smaller than those of the pristine epoxy resin in cone calorimeter measurements. Thermogravimetric analysis indicated that BA promoted charring of the bamboo/epoxy composite, which was responsible for the significantly improved flame retardancy. The simultaneous enhancement of the mechanical properties and flame retardancy makes such bamboo-based composites highly suitable for use as structural materials.

Molecular docking explores heightened immunogenicity and structural dynamics of acetaldehyde human immunoglobulin G adduct.

Acetaldehyde is a metabolite of ethanol, an important constituent of tobacco pyrolysis and the aldehydic product of lipid peroxidation. Acetaldehyde induced toxicity is mainly due to its binding to cellular macromolecules resulting in the formation of stable adducts accompanied by oxidative stress. The aim of this study was to characterize structural and immunological alterations in human immunoglobulin G (IgG) modified with acetaldehyde in the presence of sodium borohydride, a reducing agent. The IgG modifications were studied by various physicochemical techniques such as fluorescence and CD spectroscopy, free amino group estimation, 2,2-azobis 2-amidinopropane (AAPH) induced red blood cell hemolysis as well as transmission electron microscopy. Molecular docking was also employed to predict the preferential binding of acetaldehyde to IgG. The immunogenicity of native and acetaldehyde-modified IgG was investigated by immunizing female New Zealand white rabbits using native and modified IgG as antigens. Binding specificity and cross reactivity of rabbit antibodies was screened by competitive inhibition ELISA and band shift assays. The modification of human IgG with acetaldehyde results in quenching of the fluorescence of tyrosine residues, decrease in free amino group content, a change in the antioxidant property as well as formation of cross-linked structures in human IgG. Molecular docking reveals strong binding of IgG to acetaldehyde. Moreover, acetaldehyde modified IgG induced high titer antibodies (>1:12800) in the experimental animals. The antibodies exhibited high specificity in competitive binding assay toward acetaldehyde modified human IgG. The results indicate that acetaldehyde induces alterations in secondary and tertiary structure of IgG molecule that leads to formation of neo-epitopes on IgG that enhances its immunogenicity.

Cross-linked highly sulfonated poly(arylene ether sulfone) membranes prepared by in-situ casting and thiol-ene click reaction for fuel cell application

End-group cross-linked sulfonated poly(arylene ether sulfone) (SPAES) membranes were prepared using thiol capped SPAES (SH-SPAES) with different amounts of vinyl polysulfone (VPSf) as a polymeric cross-linker. The cross-linked membranes showed remarkably improved physicochemical stabilities compared to the corresponding linear SPAES membrane. Although the proton conductivity of the SPAES membrane composed of SPAES with the degree of sulfonation (DS) as 70 mol% could not be measured due to its low physical stability under the measurement condition, those of the cross-linked membranes were repeatedly evaluated due to the enhanced stability through the formation of cross-linked structures. The obtained proton conductivity values from cross-linked membranes are larger than those of the linear SPAES membrane which composed of SPAES with DS of 50 mol% having the ion exchange capacity (IEC) similar to that of the cross-linked membranes, especially at relative low humidity conditions. Furthermore, the fuel cell performance of the membrane electrode assembly (MEA) prepared with the cross-linked membrane, showing the optimized physicochemical stabilities and proton conductivity exhibited a maximum power density of 692 mW cm−2, which was larger than that with Nafion 212 (603 mW cm−2) at 80 °C under fully humidified H2/Air condition.

Synthesis and characterization of silanized-SiO2/povidone nanocomposite as a gate insulator: The influence of Si semiconductor film type on the interface traps by deconvolution of Si2s

The polymer nanocomposite as a gate dielectric film was prepared via sol-gel method. The formation of cross-linked structure among nanofillers and polymer matrix was proved by Fourier transform infrared spectroscopy (FT-IR). Differential thermal analysis (DTA) results showed significant increase in the thermal stability of the nanocomposite with respect to that of pure polymer. The nanocomposite films deposited on the p- and n-type Si substrates formed very smooth surface with rms roughness of 0.045 and 0.058 nm respectively. Deconvoluted Si2s spectra revealed the domination of the SiOH hydrogen bonds and SiOSi covalence bonds in the structure of the nanocomposite film deposited on the p- and n-type Si semiconductor layers respectively. The fabricated n-channel field-effect-transistor (FET) showed the low threshold voltage and leakage currents because of the stronger connection between the nanocomposite and n-type Si substrate. Whereas, dominated hydroxyl groups in the nanocomposite dielectric film deposited on the p-type Si substrate increased trap states in the interface, led to the drop of FET operation.

Functionalization of Electrospun Poly(vinyl alcohol) (PVA) Nanofiber Membranes for Selective Chemical Capture

Electrospun poly(vinyl alcohol) (PVA) nanofiber membranes were functionalized by incorporating either poly(methyl vinyl ether-alt-maleic anhydride) (PMA) to create negative charges, or poly(hexadimethrine bromide) (PB) and chitosan (CS) to create positive charges on the fiber surface. The functionalized PVA nanofiber membranes were heat-treated at elevated temperatures to impart cross-linking and improve the water-resistance. The optimum heat-treatment temperatures for both PVA/PMA and PVA/PB/CS systems were screened by Fourier transformed infrared spectroscopy (FTIR), and scanning electron microscopy (SEM). Formation of cross-linked structure and increased crystallinity were triggered by the heat-treatment. A cationic dye, methylene blue (MB), and an anionic dye, acid red 1 (AR1), were used to represent charged moieties in solution. The surface-charged PVA nanofiber membranes were able to selectively capture counter-charged dye molecules from aqueous solutions. The capture processes obey the pseudo-secon...

Radiation-induced Grafting of Styrene onto Polyethylene Films for Preparation of Cation Exchange Membranes: Effect of Crosslinking+

Crosslinked cation exchange membranes bearing sulfonic acid groups (PE-g-PSSA/DVB) were prepared by radiationinduced grafting of styrene/divinylbenzene (DVB) mixtures onto low density polyethylene (PE) films followed by sulfonation reactions. The effect of addition of DVB (2 and 4%) on the grafting behavior and the physico-chemical properties of the membranes such as ion exchange capacity, swelling and ionic conductivity were evaluated incorrelation with grafting yield (Y%). The structural and thermal properties of the membranes were also studied using differential scanning calorimetry (DSC) and thermal gravimetric analysis (TGA), respectively. Crosslinking with DVB was found to considerably affect the properties of the membranes in a way that reduces the swelling properties and enhances the chemical stability. The ion conductivity of the crosslinked membranes recorded a level of 10–2 S/cm at sufficient grafting yield (28%) despite the reduction caused by the formation of crosslinking structure. The results of this work suggest that membranes prepared in this study are potential alternatives for various electrochemical applications.

Experimental and Statistical Optimization of the Tensile Strength of Carbon Fibers from Pitches with Different Composition

A factorial analysis was used to maximize the tensile strength of the carbon fibers obtained from pitch by means of a rational selection of variables and precursor properties. The combined influence of the fiber diameter, the soaking time at the optimum stabilization temperature, and the effect of the polycondensation degree of the pitch on the tensile strength of the carbonized fibers was assessed using a factorial design. For the first time, the strong influence of the degree of polycondensation of the parent pitch was evidenced, even though less polycondensed pitches were spun at a higher yield and favored the homogeneous fixation of oxygen during stabilization. Fibers prepared from the most polycondensed pitches exhibited the best values of tensile strength. However, very highly polycondensed pitch compositions may hinder oxygen diffusion and the formation of cross-linked structures during stabilization, leading to a poorer mechanical performance that can be overcome by increasing the stabilization time.

Enhancement of a magnetorheological PDMS elastomer with carbonyl iron particles

A magnetorheological elastomer based on silicone rubber with carbonyl iron micro-particles was developed. The influence of the different amount of iron particles was experimentally studied by means of XRD, SEM, FTIR, EDS, XPS, uniaxial tension and rheological and cyclic tests. Different contents of carbonyl iron particles (10–40 wt%) were used to obtain the ratio of magnetic particles/silicone rubber that could provide the best mechanical properties on the MRE material. It was found that the composite material can have an increase of about 95% in its tensile strength when adding 20% of carbonyl iron particles to the raw rubber material. SEM analysis indicates a good dispersion of the magnetic particles on the rubber matrix, and the FTIR and XPS techniques confirm, as expected, that there is no chemical interaction between the iron from the carbonyl iron particles and the silicone rubber matrix due to a proper coating of the particles with silicone oil used as coupling agent. The TGA results evidenced that the addition of coated carbonyl iron particles had an impact on the thermal stability of the MRE and on the formation of cross-linked structures. The viscoelastic behavior of the magnetorheological elastomer is described by running experimental test on a rheometer device. Furthermore, cyclic testing were performed on the material sample to characterize the Mullin's effect.

Poly(arlyene ether sulfone) based semi-interpenetrating polymer network membranes containing cross-linked poly(vinyl phosphonic acid) chains for fuel cell applications at high temperature and low humidity conditions

Semi-interpenetrating polymer network (semi-IPN) membranes are prepared by in-situ casting and thermal-initiated radical polymerization of vinyl phosphonic acid (VPA) and bis(2-(methacryloyloxy)ethyl) phosphate (BMAEP) in N,N-dimethylacetamide solutions of sulfonated poly(arylene ether sulfone) (SPAES). The incorporation of VPA units into the SPAES membranes improves proton conductivity especially at high temperature and low humidity conditions. In addition the cross-linker, BMAEP, prevents the decrease of the mechanical and chemical stabilities by the aliphatic linear poly(vinyl phosphonic acid) chains in the semi-IPN membranes, and furthermore the phosphonic acid group in BMAEP can prevent the decrease of the proton conductivity by the formation of cross-linked structures. Therefore, the resulting semi-IPN membranes show high proton conductivities up to 15 mS cm−1 at 120 °C and 40% RH. The fuel cell performance (187 mW cm−2 at 120 °C and 40% RH) of membrane-electrode assembly (MEA) from the semi-IPN membrane is found to be superior to that (145 mW cm−2 at 120 °C and 40% RH) of MEA from the SPAES membrane. The durability test result at the operating conditions indicates that the semi-IPN membrane is electrochemically very stable maintaining the low hydrogen cross-over and high power densities.

2-(2-methoxyethoxy)ethyl methacrylate hydrogels with gradient of cross-link density

Abstract Electron beam irradiation of 2-(2-methoxyethoxy)ethyl methacrylate and ethylene glycol dimethacrylate mixtures leads to the formation of cross-linked structures that exhibit a gradient of cross-link density, as demonstrated by gel fraction, swelling and Differential Scanning Calorimetry analysis. The reason for observed phase separation is formation of the high molecular weight clusters and its precipitation before gelation dose. This effect can be controlled/influenced by absorbed dose and cross-linker concentration.

Preparation and properties of waterborne bio-based polyurethane/siloxane cross-linked films by an in situ sol–gel process

Abstract Waterborne castor oil-based polyurethane-silica hybrid materials with chemically bonded polymer matrix and silica nanoparticles were designed and prepared. The formation of cross-linking structures in the waterborne polyurethane system was confirmed by Fourier transform infrared spectroscopy. Transmission electron microscopy images indicated that nano-silica was encapsulated by polyurethane and exhibited an apparent core–shell structure. The nano-silica in the polyurethane matrix was vital in improving both the hydrophobicity and thermal stability of the resulting hybrid polyurethane films. With increased silicone content, the roughness, hydrophobicity, and thermal stability of the films were enhanced, but the transparency of the films in the 300–800 nm region was decreased. These results can aid in the design of bio-based hydrophobic waterborne polyurethane films with favorable thermal stability and optical transmittance.

Crosslinking of Polyamide 6 by Reactive Processing

In order to check the feasibility of crosslinking engineering plastics through chemical coupling, reactive blending of polyamide 6 (PA6) was performed with various amounts of a multi-functional epoxide named as Joncryl ADR®4370s. The formation of cross-linked structure in ADR modified PA6 was clearly verified by utilizing dynamic rheological technique. The thermal properties of modified PA6 were compared with that of pristine nylon by combination of differential scanning calorimetry (DSC) and thermal gravimetric analysis (TGA). Mechanical tests were also carried out and the results showed that ADR had a positive effect on improving tensile properties of polyamide.

Direct arylation polycondensation for the synthesis of bithiophene-based alternating copolymers

Direct arylation polycondensation reactions using a simple catalytic system gave eight kinds of bithiophene-based alternating copolymers. The conditions for the reactions of 3,3′,4,4′-tetramethylbithiophene with dibromoarylenes were optimized to obtain high-molecular-weight polymers without formation of cross-linked structures. In the reaction of a dibromoarylene containing a reactive C–H bond, a short reaction time (1.5 h) was suitable for preventing side reactions. In contrast, a long reaction time (6 h) gave high-molecular-weight polymers from dibromoarylene monomers without a reactive C–H bond. This polycondensation reaction enables the synthesis of polymers containing dye structures such as diketopyrrolopyrrole and isoindigo, which are applicable as materials for polymer solar cells.