Increase In Crosslink Density Research Articles

Effect of Peptide-Polymer Host-Guest Electrostatic Interactions on Self-Assembling Peptide Hydrogels Structural and Mechanical Properties and Polymer Diffusivity.

Peptide-based supramolecular hydrogels are an attractive class of soft materials for biomedical applications when biocompatibility is a key requirement as they exploit the physical self-assembly of short self-assembling peptides avoiding the need for chemical cross-linking. Based on the knowledge developed through our previous work, we designed two novel peptides, E(FKFE)2 and K(FEFK)2, that form transparent hydrogels at pH 7. We characterized the phase behavior of these peptides and showed the clear link that exists between the charge carried by the peptides and the physical state of the samples. We subsequently demonstrate the cytocompatibility of the hydrogel and its suitability for 3D cell culture using 3T3 fibroblasts and human mesenchymal stem cells. We then loaded the hydrogels with two polymers, poly-l-lysine and dextran. When polymer and peptide fibers carry opposite charges, the size of the elemental fibril formed decreases, while the overall level of fiber aggregation and fiber bundle formation increases. This overall network topology change, and increase in cross-link stability and density, leads to an overall increase in the hydrogel mechanical properties and stability, i.e., resistance to swelling when placed in excess media. Finally, we investigate the diffusion of the polymers out of the hydrogels and show how electrostatic interactions can be used to control the release of large molecules. The work clearly shows how polymers can be used to tailor the properties of peptide hydrogels through guided intermolecular interactions and demonstrates the potential of these new soft hydrogels for use in the biomedical field in particular for delivery or large molecular payloads and cells as well as scaffolds for 3D cell culture.

Castor oil-based polyurethane Vitrimer modified asphalts regulated by dual dynamic reversible reactions and crosslinking density: Preparation, basic assessment and self-healing behavior

Thermosetting polymers, commonly used to improve asphalt properties, bring excellent pavement performance, but also pose significant challenges to the healing and recyclability of their modified asphalts after long-term service. An effective approach involves introducing dynamic bonds into the crosslinking networks to synthesize Vitrimer-modified asphalts with self-healing response. Due to the splendid mechanical properties, high elasticity, flexibility and easily controllable cross-linked structure of polyurethane, a novel castor oil-based polyurethane Vitrimer modified asphalt with disulfide bonds and Diels-Alder reactions was developed. Based on the prepared castor oil-based polyurethane Vitrimer (C-PUV, composed of components A and B) and its modified asphalts (C-PUVAs), a comprehensive study was conducted on the crosslinking density, mechanical properties, thermal stability, viscosity, compatibility, rheological properties, and self-healing behavior. The results indicated that C-PUVAs (C-PUVA1/C-PUVA2/C-PUVA3/C-PUVA4) exhibited sufficient retention times for viscosity, uniform phase distribution, and good high-temperature performance. The damaged C-PUVAs achieved a mechanical strength recovery rate more than 75 % after the first cycle of self-healing at 80 ℃ and 0.3 MPa. Furthermore, the crosslinking density of C-PUV was regulated by the segment length of component B. As the crosslinking density increased, C-PUV and C-PUVAs obtained higher mechanical strength while sacrificing part of self-healing efficiency. The mechanism is that increased crosslinking density altered the gel point distributions of the reversible crosslinked networks, resulting in a longer relaxation time and higher activation energy. In conclusion, the above findings provided valuable insights for developing bio-based polyurethane Vitrimer modified asphalts, and endosing thermosetting polymer modified asphalts with self-healing and recyclable properties.

Accelerating effect of metal ionic liquids for epoxy-anhydride copolymerization

One of the main drawbacks of high-performance epoxy-anhydride thermosets is slow cross-link kinetics requiring high temperature and long curing cycle. Herein, the accelerating effect of imidazolium metal-based ionic liquids (MILs) bearing (FeCl4)-, (ZnCl4)2-, and (CoCl4)2- anions on epoxy-anhydride copolymerization was investigated. It was observed that MILs accelerated bisphenol diglycidyl ether (DGEBA) − methylhexahydrophthalic anhydride (MHHPA) cross-linking, better than the reference catalysts (1-methylimidazole and 1-butyl-3-methylimidazolium chloride), especially at low temperatures through their ability to activate a rapid anhydride ring opening and formation of carboxyl groups, which initiates polyesterification. A detailed investigation of the polymerization mechanism revealed the formation of alternating epoxy-anhydride copolymers although several MILs-induced initiation mechanisms were detected. Despite the multiple-initiation consisting of imidazole, counter anion, and polyesterification pathways, the cross-linking kinetics was successfully fitted up to vitrification by the Kamal-Sourour model. Finally, MILs-induced cross-linking leads to homogeneous network build-up enabling to produce thermosetting materials with an increased cross-link density, a glass transition temperature above 150 °C, and excellent thermal stability.

The Role of Reduced Graphene Oxide in Enhancing the Mechanical and Thermal Properties of a Rubber Cover Joint.

The development of high-performance rubber composites has always been a research hotspot in the field of conveyor belt manufacturing. In this work, a rubber cover joint composite made of reduced graphene oxide (rGO) was prepared using latex mixing and mechanical blending methods, with a steel wire rope conveyor belt as the research object, and the influence of the rGO content on the properties of the rubber composite is discussed. The structure and morphology characterization of the rGO/NR rubber show that the addition of rGO does not change its crystal structure, and 1.2 phr rGO is uniformly dispersed throughout the rubber composite. As more rGO is added, the mechanical properties of the rGO rubber cover joint first improve and then worsen. With the addition of 1.2 phr, the cross-linking density increases by 80.6%, the tensile strength of the rubber composites increases by 49.7%, the elongation at break increases by 23.6%, and the adhesion strength increases by 12.4%. The tensile strength of the rGO rubber cover joint can still maintain 72.5% of its pre-thermal aging value. The wear resistance and thermal conductivity increase as more phr is added. When 3.0 phr is added, the wear resistance of the rubber composites increases by 32.9%, the thermal conductivity increases by 118.8%, and the temperature difference at the completion of vulcanization decreases from 4.5 °C to 1.8 °C. The results show that when 1.2 phr of rGO is added, the rubber conveyor belt joint obtains the best comprehensive performance. These enhanced comprehensive properties allow for the practical application of rGO nanomaterials to conveyor belt rubber.

Biological and Mechanical Performance of Dual-Setting Brushite-Silica Gel Cements.

Bone defects resulting from trauma, diseases, or surgical procedures pose significant challenges in the field of oral and maxillofacial surgery. The development of effective bone substitute materials that promote bone healing and regeneration is crucial for successful clinical outcomes. Calcium phosphate cements (CPCs) have emerged as promising candidates for bone replacement due to their biocompatibility, bioactivity, and ability to integrate with host tissues. However, there is a continuous demand for further improvements in the mechanical properties, biodegradability, and bioactivity of these materials. Dual setting of cements is one way to improve the performance of CPCs. Therefore, silicate matrices can be incorporated in these cements. Silicate-based materials have shown great potential in various biomedical applications, including tissue engineering and drug delivery systems. In the context of bone regeneration, silicate matrices offer unique advantages such as improved mechanical stability, controlled release of bioactive ions, and enhanced cellular responses. Comprehensive assessments of both the material properties and biological responses of our samples were conducted. Cytocompatibility was assessed through in vitro testing using osteoblastic (MG-63) and osteoclastic (RAW 264.7) cell lines. Cell activity on the surfaces was quantified, and scanning electron microscopy (SEM) was employed to capture images of the RAW cells. In our study, incorporation of tetraethyl orthosilicate (TEOS) in dual-curing cements significantly enhanced physical properties, attributed to increased crosslinking density and reduced pore size. Higher alkoxysilyl group concentration improved biocompatibility by facilitating greater crosslinking. Additionally, our findings suggest citrate's potential as an alternative retarder due to its positive interaction with the silicate matrix, offering insights for future dental material research. This paper aims to provide an overview of the importance of silicate matrices as modifiers for calcium phosphate cements, focusing on their impact on the mechanical properties, setting behaviour, and biocompatibility of the resulting composites.

Organic-inorganic hybrid epoxy resin coating with high thermal stability and hydrophobicity for corrosion protection prepared by (3-aminopropyl) triethoxysilane as a bridging agent

The corrosion protection application of epoxy resin (EP) in high-temperature environments is greatly restricted due to thermal stability limit and inherent hydrophilicity. In this study, a hybrid epoxy resin was synthesized by grafting hexadecyltrimethoxysilane (HDTMS), 1 H,1 H,2 H,2 H-perfluorodecyltrimethoxysilane (PFDTMS), and tetraethyl orthosilicate (TEOS) onto the molecule of epoxy resin, using (3-aminopropyl) triethoxysilane (APTES) as a bridging agent. Fourier transform infrared spectroscopy (FTIR) and X-ray photoelectron spectroscopy (XPS) analyses revealed the presence of C-N bonds and Si-O-Si bonds in the hybrid epoxy resin, confirming the success of the hybridization. Compared to pure epoxy resin, the hybrid epoxy resin coating effectively enhances the thermal stability while maintaining both corrosion resistance and hydrophobicity. Thermal gravimetric analysis (TGA) indicated that the initial decomposition temperature (T5%) of the hybrid epoxy resin coating increased from 327°C to 372°C. This enhancement is attributed to the introduction of Si-O-Si bonds and an increase in cross-linking density in the hybrid epoxy resin. Water contact angle measurements showed that with the introduction of C-F bonds and long carbon chains, the contact angle increased from 71° to 106°. The hydrophobic hybrid epoxy resin coating maintained a contact angle of 100° at 300°C for 300 hours. The transition from hydrophilicity to hydrophobicity improves the corrosion resistance of the coating.

Advancing flame retardancy, mechanical properties, and hydrophobicity of epoxy resins through bio-based cinnamaldehyde derivative

Developing flame retardants based on biomass materials to improve the flame retardancy and multifunctionality of epoxy resin (EP) is crucial. Herein, we synthesized a novel derivative, PPABCA, combining cinnamaldehyde and 9,10-dihydro-9-oxa-10-phosphaphenanthrene-10-oxide to serve as flame retardants for EP. Incorporating 5 wt% PPABCA into EP (EP/PPABCA-5) demonstrated remarkable flame retardancy, with a limiting oxygen index of 33.7% and a V-0 rating in UL-94 test. It also reduced the peak heat release rate, total heat release, and peak CO2 production by 32.9%, 29.9%, and 42.8%, respectively. The enhanced flame retardancy was facilitated by the capture of phosphorus-containing free radicals coupled with dilution of combustible gas characterized by the blow-out phenomenon and formation of a dense char layer enriched with triazine and phosphorus. Furthermore, EP/PPABCA-5 exhibited enhanced flexural and tensile strengths by 20.5% and 16.5% compared to EP, attributed to the increased cross-linking density and π-π conjugation from the high rigidity of PPABCA, along with its good compatibility with EP. Additionally, the improved hydrophobic properties of PPABCA, confirmed by electrostatic potential analysis, further enhanced the hydrophobicity of EP composites. Overall, this work underscored a strategic development of multifunctional, bio-based flame retardant, showcasing efficient flame retardancy, enhanced mechanical properties, and boosted hydrophobicity in EP.

Biomass carboxylic acid modified hydrotalcites for improving the mechanical strength and recyclability of 100 % biobased carbon content epoxy soybean oil based vitrimers

To realize the demand of sustainable development in materials industry, vitrimers deriving from epoxidized soybean oil (ESO) have received considerable attention because of their environmentally friendly and renewable. However, they suffer from poor mechanical strength and non-reprocessability, which confine their application. Herein, a facile design of 100 % bio-based carbon contents vitrimers incorporating ESO and citric acid modified layered double hydroxides (CA-LDHs) was proposed, which showing good mechanical properties and accelerated stress relaxation. Optimal performances of vitrimers with best tensile strength, curing and repairing efficiency were obtained at 20 wt% CA-LDHs loading. The tensile strength of 20EC-CLE increased by 233 % compared with pure EC-E due to the reinforcing effect of CA-LDHs and the increased cross-linking density. Benefit from the abundant Al3+ catalytic sites and large contact areas of the CA-LDHs lamella, the vitrimers showed an excellent curing and 82 % reprocessing efficiency. Interestingly, the precursor of the vitrimers was used as an adhesive layer for polyvinyl chloride (PVC) leather and provided 3.4 ± 0.4 N/cm peel strength and bonding reproducibility.

Role of crosslinkers on the properties of bio‐based wood adhesives

AbstractAs people became more conscious of the risks associated with pollution in the early 21st century, eco‐friendly adhesives made from plant oil began to be used. Bio‐based adhesives are widely used due to their low price, easy accessibility, and high biodegradability; however, their low adhesive strength is an issue. This work incorporates three natural crosslinkers: tannic acid (TA), sorbitol (SR), and cellulose (CL) to address the drawbacks of bio‐based adhesives, such as low adhesive strength, inferior output in humidity and longer curing time that result from excess water. Methylene diphenyl diisocyanate (MDI) was used to react with soybean oil‐based polyol (SOP) plus the crosslinkers to make bio‐based polyurethane adhesives. The maximum bonding strength of the soybean‐based adhesive containing 10 wt.% of SR (SR‐10%) was measured at 6.19 MPa which is about 44% higher than the sample without SR. The higher strength is due to the crosslinking ability of SR. The effect of crosslinking is also observed in the study of polar protic and polar aprotic solvents used to dissolve the adhesive. As compared with the polar aprotic solvent tetrahydrofuran, TA‐containing adhesive samples showed a maximum tensile strength of 3.69 MPa in methanol; a polar protic solvent that can participate in further hydrogen bonding to form a higher crosslinked complex. The glass transition temperature (Tg) increases with the increase in crosslinker amount. The observed increase in Tg may be attributable to an increase in crosslinking density, which reduces polymer chain flexibility and causes a stronger material.Highlights Bio‐adhesives based on soybean oil and diisocyanate were synthesized. Natural crosslinking agents such as tannic acid, sorbitol, and cellulose were used. The effect of crosslinking using polar protic and aprotic solvents was studied. The glass transition temperature increases with the increase in crosslinker amount.

Preparation of strong, UV-blocking and sustainable glucose-cross-linked cellulose plastics via hydroxyl-yne click reaction

The construction of functional cellulose plastics possessing strong UV-blocking, hydrophilicity, and biodegradability is challenging. Therefore, we provide a novel strategy to successfully prepare sustainable and hydrophilic glucose-cross-linked cellulose (GC) plastics showing effective UV-blocking and excellent mechanical properties via hydroxyl-yne click reaction at room temperature. The results demonstrated that hydroxyl-yne click chemistry enabled efficient crosslinking of cellulose with glucose using 4-dimethylamino pyridine (DMAP) as a catalyst. Moreover, the DMAP residue imparted good UV-shielding properties to GC films exhibiting nearly 100 % UVC (200–275 nm) and 100 % UVB (320–275 nm) shielding ratios. The introduction of glucose imparted superior hydrophilicity (water contact angle of 40.3–43.2°) and improved water adsorption. Additionally, the mechanical properties of the GC films increased with the increasing crosslinking density, and the highest tensile stress was 94 MPa. The water-induced breaking and hydrogen bond reforming strategy led to a stress of 127 MPa and a strain of 25.6 % for the final GC2 film, which were excellent compared to those of the most reported cellulose films. Additionally, GC films were biosafe, exhibited improved oxygen barrier, and good biodegradability. Hence, this study provides a promising and efficient approach for preparing high-performance cellulose plastics.

Organic radicals stabilization in natural rubber: Discerning the influence of thermo-oxidation using chemically modified or unmodified lignin as antioxidant

We have implemented a lignin compatibilization strategy through silylation and elaborated NR compounds with lignin and silylated lignin. Then, the lignin’s contribution to the preservation of physico-mechanical properties and stability of the materials obtained against thermo-oxidation was studied. Thus, our work considered the indirect study of the antioxidant activity on NR compounds by determining the physico-mechanical properties before and after accelerated thermo-oxidative aging, which allowed us to determine that the increase in crosslinking density during the initial hours of accelerated aging was the main observed cause associated with a higher tensile strength retention rate (TSRR: 13.4 %) in NR compound with 5 phr of lignin (CL5) versus a TSRR: 4.7 % for the compound with 5 phr of silylated lignin (CL5Si1). On the other hand, the direct study of the antioxidant capacity by thermogravimetric analysis (TGA) and differential scanning calorimetry (DSC) using oxygen atmosphere indicated greater thermal stability in NR compounds when lignin is not silylated. The maximum degradation temperature for the CL5 compound was 341.6 °C, while for the CL5Si1 compound it was 328.6 °C. The oxidation induction temperature (OITtemp) in the CL5 compound was 190.9 °C with a peak at 221.0 °C, while for CL5Si1 it was 170.3 °C with a peak at 194.1 °C, indicating again that unsilylated lignin is more suitable as an antioxidant. Finally, through Electron Paramagnetic Resonance (EPR), we determined that the radical quenching effect due to the presence of lignin was significant as the lignin content increases, with a reduction in radical presence close to 50 % compared to a reference compound without lignin.

Novel multifunctional highly crosslinked bio-based waterborne polyurethane networks modified via long fatty hydrophobic side chains

The mechanical properties and water resistance of castor oil-based waterborne polyurethane are mutually limited due to the presence of a hydrophilic chain extender. Herein, Arbutin (AT) was used as a crosslinking agent, and benzimidazole (CR-455) was utilized as an ultraviolet absorber, sustainable long fatty hydrophobic chain extenders, sorbitan monooleate (SP), glycerol laurate (GML), glycerin monostearate (GMS), and trimethylolpropane monooleate (TPM), were introduced into castor oil-based waterborne polyurethane (CWPU) backbones through molecular structure design respectively. Subsequently, the amount of SP was changed to prepare a series of waterborne polyurethane dispersions, and their emulsion and film properties were thoroughly investigated. The finding showed that the incorporation of long fatty hydrophobic chain extenders led to an increase in crosslinking density, thereby endowing CWPU films with good mechanical properties, water resistance, and anti-corrosion efficacy. Moreover, the bio-based content in the CWPU film had reached an impressive 90.9 %. The addition of SP content resulted in a gradual improvement in the mechanical properties, water resistance, and corrosion resistance of CWPU-SP films. When the SP content was 40 %, due to the high strength of hydrogen bonds and the density of crosslinking in systems, the tensile strength, toughness, water absorption rate, and corrosion protection efficiency of the CWPU-SP40 film reached 18.1 MPa, 20 MJ/m3,7.7 %, and 98.47 %, respectively. Particularly, the prepared transparent CWPU films exhibited complete UV shielding. This work would pave the way for the application of bio-based waterborne polyurethanes in high-performance coatings, such as anti-corrosion and sunscreen.

The Facile Synthesis and Application of Mesoporous Silica Nanoparticles with a Vinyl Functional Group for Plastic Recycling.

Due to growing concerns about environmental pollution from plastic waste, plastic recycling research is gaining momentum. Traditional methods, such as incorporating inorganic particles, increasing cross-linking density with peroxides, and blending with silicone monomers, often improve mechanical properties but reduce flexibility for specific performance requirements. This study focuses on synthesizing silica nanoparticles with vinyl functional groups and evaluating their mechanical performance when used in recycled plastics. Silica precursors, namely sodium silicate and vinyltrimethoxysilane (VTMS), combined with a surfactant, were employed to create pores, increasing silica's surface area. The early-stage introduction of vinyl functional groups prevented the typical post-synthesis reduction in surface area. Porous silica was produced in varying quantities of VTMS, and the synthesized porous silica nanomaterials were incorporated into recycled polyethylene to induce cross-linking. Despite a decrease in surface area with increasing VTMS content, a significant surface area of 883 m2/g was achieved. In conclusion, porous silica with the right amount of vinyl content exhibited improved mechanical performance, including increased tensile strength, compared to conventional porous silica. This study shows that synthesized porous silica with integrated vinyl functional groups effectively enhances the performance of recycled plastics.

Mechanically resilient hybrid aerogels containing fibers of dual-scale sizes and knotty networks for tissue regeneration.

The structure and design flexibility of aerogels make them promising for soft tissue engineering, though they tend to come with brittleness and low elasticity. While increasing crosslinking density may improve mechanics, it also imparts brittleness. In soft tissue engineering, resilience against mechanical loads from mobile tissues is paramount. We report a hybrid aerogel that consists of self-reinforcing networks of micro- and nanofibers. Nanofiber segments physically entangle microfiber pillars, allowing efficient stress distribution through the intertwined fiber networks. We show that optimized hybrid aerogels have high specific tensile moduli (~1961.3 MPa cm3 g-1) and fracture energies (~7448.8 J m-2), while exhibiting super-elastic properties with rapid shape recovery (~1.8 s). We demonstrate that these aerogels induce rapid tissue ingrowth, extracellular matrix deposition, and neovascularization after subcutaneous implants in rats. Furthermore, we can apply them for engineering soft tissues via minimally invasive procedures, and hybrid aerogels can extend their versatility to become magnetically responsive or electrically conductive, enabling pressure sensing and actuation.

Bouligand-like structured CNT film with tunable impact performance through pitch angle and intertube interaction

The Bouligand structure, characterized by a helicoidal arrangement of fibers, is prevalent in arthropods. Leveraging the exceptional impact resistance inherent in this structure, mantis shrimp could effortlessly crack the shells of shellfish using their dactyl club. Drawing inspiration from this natural phenomenon, we propose a novel Bouligand-like structured carbon nanotube film (BCNF) that combines the Bouligand structure with super-strong one-dimensional carbon nanotubes (CNTs). Through systematic investigation via molecular dynamics simulations, we explore the impact resistance and energy dissipation properties of BCNF. Our results reveal that the impact behaviors under different velocities can be tuned by adjusting the pitch angle of BCNFs. At an impact velocity of 1 km/s, the projectile exhibits three typical phenomena after impact, including embedding in the film, bouncing back, and penetration. At an impact velocity of 2 km/s, all films are penetrated. Furthermore, to enhance the impact resistance of BCNF, we introduce intertube crosslinking bonds, forming a crosslinked Bouligand-like structured CNT film (CBCNF). The study demonstrates that crosslinking effectively modulates the energy dissipation mode of the film. With increasing crosslinking density, the predominant energy dissipation mode shifts from interface sliding and bending of the CNTs to the fracture and collapse of CNTs. This research provides valuable insights into the microstructure design of CNT-based films and offers theoretical guidance for their applications in impact protection.

Effect of cross-link density on the performance of polyimine/epoxy vitrimers

Vitrimers are polymers rich in dynamic covalent bonds in cross-link networks. When the dynamic covalent bonds are not activated, the vitrimers show the performance stability of the traditional thermosetting polymer. When the dynamic covalent bonds are activated, the vitrimers can show some novel and unique properties, such as stress relaxation, self-healing and reprocessing. This new type of polymer has attracted wide attention because of its unique properties. As thermoset materials, the degree of cross-link and cross-link density of the materials are very important for the performance of vitrimers. In order to find out the effects of cross-link density on the properties of vitrimers, a series of dynamic polyimine/epoxy cross-link networks with different cross-link densities were designed and prepared, and their properties were characterized. The materials with higher cross-link density show higher thermal properties, mechanical properties and shape fixation ratio. However, due to the increase of cross-link density, the mobility of molecular chain and the exchange of dynamic bonds are limited, so the healing efficiency, shape recovery ratio and shape recovery rate will decrease to a certain extent. This study provides important insights into a deeper understanding of this new type of polymer.

Robust anti-impact, energy absorption and thermal properties of polyurethane nanocomposites modified by phenol-amine chemistry

It is still a considerable challenge for polyurethane elastomers (PUE) to possess outstanding mechanical and thermal performance simultaneously against harsh dynamic impact environment due to their heat accumulation, thermal stress softening and mechanical failure. Thus, this article innovatively prepared binary nanofibers composed of carbon nanofiber (CNFs) and aramid nanofibers (ANFs) to reinforce PUE, where catechol (CC) and polyethyleneimine (PEI) were served as interfacial modifier between nanofibers and polymer matrix. PUE with 1.5 wt% binary nanofibers achieve 31.62 % increase in crosslinking density, 146.8 °C improvement in thermal decomposition temperature compared to Neat PUE. Besides, the absorption energy and dynamic compression strength of composites were increased by 40.36 % and 38.26 %, respectively. Because reinforced nanofibers with crosslinking network structures improve the interface interaction between fillers and matrix, facilitate stress transfer and increase the energy threshold of thermal decomposition. The paper supplements the impact resistance analysis of PUE-based protective materials under impact loads, providing a systematic and scientific reference for the design and manufacture of impact resistant materials.

Advanced corrosion Protection: Development of MnO2@rGO/EP-GTA nanocoating

This study investigates the potential of utilizing reduced graphene nanosheets to enhance the anticorrosion properties of MnO2 coatings. Specifically, the study focuses on the incorporation of reduced graphene oxide (rGO) into MnO2 coatings to improve their anticorrosion performance. The MnO2-decorated graphene oxide nanocomposite (MnO2@rGO) was thoroughly characterized using various analytical techniques, including Fourier-transform infrared spectroscopy (FTIR), transmission electron microscopy (TEM), and scanning electron microscopy (SEM). These analyses elucidated the morphological and structural features of both rGO and MnO2, highlighting the chemical bonding between MnO2 and rGO. Furthermore, the MnO2@rGO nanocomposite underwent additional modification with glycidoxypropyltrimethoxysilane (GTA) before integration into the epoxy resin, resulting in the formation of the epoxy coating (MnO2@rGO/EP-GTA) on steel plates. Electrochemical and potentiometric measurements demonstrated that the inclusion of rGO significantly prolonged the cathodic protection duration of MnO2 within the coatings. This enhancement can be attributed to rGO acting as an impermeable barrier within the coating matrix, thereby enhancing electrical conductivity and facilitating efficient electrical connection between manganese oxide particles and the steel substrate. Additionally, the incorporation of MnO2@rGO and GTA modification led to improved performance of the MnO2@rGO/EP nanocoating, including enhanced resistance to UV aging and salt spraying, effective dispersion of the MnO2@rGO nanocomposite within the epoxy resin, and increased cross-linking density and adhesion strength of the epoxy coating.

Effects of Peroxide and Sulfur Curing Systems on Physical and Mechanical Properties of Nitrile Rubber Composites: A Comparative Study.

This study compares the effect of sulfur and dicumyl peroxide (DCP) vulcanizing systems on the physical and mechanical properties of rubber compounds based on acrylonitrile butadiene rubber (NBR). NBR compounds cured by different amounts of DCP and NBR vulcanizates filled with various concentrations of carbon black (CB) and a constant amount of sulfur or DCP were prepared. The vulcanizates were characterized by tensile testing, dynamic mechanical thermal analysis (DMTA), and cross-link density determination. The tensile strength and Young's modulus were found to increase with the rising amount of DCP and CB, while elongation at break decreased. The samples vulcanized by the sulfur system and filled with CB show a substantial increase in tensile strength from 13.1 to 21.2 MPa. Higher storage modulus and glass transition temperature were observed with the increase in the amount of peroxide and filler, and consequently, the increase in cross-link density, indicating rigidity increase and lower molecular mobility. The changes in the physical and mechanical properties of the NBR vulcanizates were in correlation with the changes in solvent uptake and cross-link density.

Enhancing corrosion resistance and toughness of solvent-free epoxy coatings with low-viscosity fluorine-containing hyperbranched polyether

In this study, a low-viscosity epoxy-terminated fluorine-containing hyperbranched polyether (FHBPE) was synthesized and incorporated in a solvent-free epoxy coating formulation to enhance coating toughness and corrosion resistance while minimizing the impact on coating viscosity. FHBPE was synthesized by a solvent-free one-pot method with hexafluorobisphenol A (A2 monomer) and trimethylolpropane triglycidyl ether (B3 monomer). Subsequently, FHBPE, E51 epoxy resin, and an alicyclic amine curing agent were blended to create the solvent-free epoxy coating, which was applied onto a steel substrate by a scraping coating method. This research demonstrates that addition of FHBPE did not show adverse effect on coating viscosity; instead, it reduced the viscosity at around 6 wt% loading. The epoxy-terminated FHBPE increased the cross-linking density of neat E51 coating by up to 20.7 %. Furthermore, the introduction of flexible segments enhanced the toughness, leading to a one-grade increase in the coating flexibility from 1 to 0.5 mm. Furthermore, FHBPE significantly improved the corrosion resistance of the coatings, attributed to increased cross-linking density and hydrophobic properties of the coating. Among FHBPE-modified coatings, the coating with 6 wt% loading demonstrated superior overall performance. Over a 60-day immersion period, its electrochemical impedance value remained stable, while the neat E51 coating experienced a two-orders-of-magnitude decrease. Furthermore, the 6 wt% FHBPE-modified coating passed the 750-h salt spray test without obvious rust, outperforming the neat E51 coating (200 h). This study presents a feasible and promising strategy for the formulation design and mass production of solvent-free epoxy coatings.