Various Morphologies of Graphitic Carbon Nitride (g-C3N4) and Their Effect on the Thermomechanical Properties of Thermoset Epoxy Resin Composites.

This research aims to highlight the importance of diverse forms of graphitic carbon nitride (g-C3N4) as strengthening elements in epoxy composites. It explores the influence of three different forms of g-C3N4 and their concentrations on the mechanical properties of the epoxy composites. Various characterization techniques, such as scanning electron microscopy (SEM), dynamic light scattering (DLS), thermogravimetric analysis (TGA), and Fourier-transform infrared spectroscopy (FTIR), were utilized to comprehend the effects of g-C3N4 morphology and particle size on the physical and chemical characteristics of epoxy resin. Mechanical properties, such as tensile strength, strain, modulus, and fracture toughness, were determined for the composite samples. SEM analysis was performed to examine crack morphology in samples with different reinforcements. Findings indicate that optimal mechanical properties were achieved with a 0.5 wt% bulk g-C3N4 filler, enhancing tensile strength by 14%. SEM micrographs of fracture surfaces revealed a transition from brittle to rough morphology, suggesting increased toughness in the composites. While the TGA results showed no significant impact on degradation temperature, dynamic mechanical analysis demonstrated a 17% increase in glass transition temperature. Furthermore, the improvement in thermal breakdown up to 600 °C was attributed to reinforced covalent bonds between carbon and nitrogen, supported by FTIR results.

Cellulose Functionalization Using N-Heterocyclic-Based Leaving Group Chemistry.

There has been continuous interest in developing novel activators that facilitate the functionalization of cellulosic materials. In this paper, we developed a strategy in which trisubstituted triazinium salts act as cellulose preactivators. As leaving groups, these triazinium salts utilize N-heterocycles (pyridine, imidazole, and nicotinic acid). Initially, we optimized the synthetic route for developing these novel cellulose preactivators (triazinium salts), whose structures were confirmed using NMR spectroscopy. The surface zeta potential of cellulose changed from a negative value to a positive one after preactivation due to the cationic nature of these preactivators. To enhance the scope of the study, we functionalized the cellulose-preactivated materials with a series of amine- or hydroxy-containing aliphatic and aromatic hydrocarbons, nucleophilic amino acids (cysteine), colorants (2-aminoanthraquinone and 2-amino-3-methyl-anthraquinone), and biopolymer (zein protein). The treated samples were analyzed using FTIR, time-gated Raman spectroscopy, and reflection spectroscopy, and the success of the functionalization process was validated. To widen the scope of such chemistries, we synthesized four reactive agents containing N-heterocyclic-based leaving groups (pyridine and nicotinic acid) and successfully functionalized cellulose with them in one step. The proposed single- and two-step functionalization approaches will provide opportunities for chemically linking various chemical compounds to cellulose for different applications.

Self-Healability of Poly(Ethylene-co-Methacrylic Acid): Effect of Ionic Content and Neutralization.

Self-healing polymers such as poly(ethylene-co-methacrylic acid) ionomers (PEMAA) can heal themselves immediately after a projectile puncture which in turn lowers environmental pollution from replacement. In this study, the thermal-mechanical properties and self-healing response of a library of 15 PEMAA copolymers were studied to understand the effects of the ionic content (Li, Na, Zn, Mg) and neutralization percentage (13 to 78%) on the results. Differential scanning calorimetry (DSC), dynamic mechanical analysis (DMA), and tensile testing were used to study the thermo-mechanical properties of PEMAA copolymers while the self-healing response was studied using the projectile test. Puncture sites were observed using scanning electron microscopy (SEM) and the healing efficiency was quantitatively measured using the water leakage test. Five different self-healing responses were observed and correlated to ionic content and neutralization. At high neutralization, divalent neutralizing ions (Zn and Mg) that have stronger ionic interactions exhibited brittle responses during projectile testing. PEMAA samples neutralized with Mg and Li at low concentrations had a higher healing efficiency than PEMAA samples neutralized with Zn and Na at low neutralization. The PEMAA copolymers with higher tensile stress and two distinct peaks in the graph of loss factor versus temperature that indicate the presence of sufficient ionic aggregate clusters had improved healing efficiency. By increasing the neutralization percentage from 20% to 70%, the tensile strength and modulus of the samples increased and their self-healability generally increased. Among the investigated samples, the copolymer with ~50% neutralization by Li salt showed the highest healing efficiency (100%). Overall, the strength and elastic response required for successful self-healing responses in PEMAA copolymers are shown to be governed by the choice of ion and the amount of neutralization.

Mesoscopically ordered bone-mimetic nanocomposites.

A sustainable approach that highly mimics bone-material deposition is reported to produce mechanically stable, degradable composites with nanostructures resembling that of natural bone. Molecular self-assembly combining intermolecular crosslinking leads to resilient matrices possessing long-range ordered aqueous domains, inside which moderately aligned poorly crystalline apatite is converted from the transient amorphous calcium phosphate phase.

Epoxy resin monomers with reduced skin sensitizing potency.

Epoxy resin monomers (ERMs), especially diglycidyl ethers of bisphenol A and F (DGEBA and DGEBF), are extensively used as building blocks for thermosetting polymers. However, they are known to commonly cause skin allergy. This research describes a number of alternative ERMs, designed with the aim of reducing the skin sensitizing potency while maintaining the ability to form thermosetting polymers. The compounds were designed, synthesized, and assessed for sensitizing potency using the in vivo murine local lymph node assay (LLNA). All six epoxy resin monomers had decreased sensitizing potencies compared to those of DGEBA and DGEBF. With respect to the LLNA EC3 value, the best of the alternative monomers had a value approximately 2.5 times higher than those of DGEBA and DGEBF. The diepoxides were reacted with triethylenetetramine, and the polymers formed were tested for technical applicability using thermogravimetric analysis and differential scanning calorimetry. Four out of the six alternative ERMs gave polymers with a thermal stability comparable to that obtained with DGEBA and DGEBF. The use of improved epoxy resin monomers with less skin sensitizing effects is a direct way to tackle the problem of contact allergy to epoxy resin systems, particularly in occupational settings, resulting in a reduction in the incidence of allergic contact dermatitis.