Advanced isoconversional cure kinetic analysis of epoxy/poly(furfuryl alcohol) bio-resin system

Core-Shell Rubber Nanoparticle-Modified CFRP/Steel Ambient-Cured Adhesive Joints: Curing Kinetics and Mechanical Behavior

Externally bonded wet-layup carbon fiber-reinforced polymer (CFRP) strengthening systems are extensively used in concrete structures but have not found widespread use in deficient steel structures. To address the challenges of the adhesive bonding of wet-layup CFRP to steel substrates, this study investigated the effect of core-shell rubber (CSR) nanoparticles on the curing kinetics, glass transition temperature (Tg) and mechanical properties of ambient-cured epoxy/CSR blends. The effects of silane coupling agent and CSR on the adhesive bond properties of CFRP/steel joints were also investigated. The results indicate that CSR nanoparticles have a mild catalytic effect on the curing kinetics of epoxy under ambient conditions. The effect of CSR on the Tg of epoxy was negligible. Epoxy adhesives modified with 5 to 20%wt. of CSR nanoparticles were characterized with improved ductility over brittle neat epoxy; however, the addition of CSR nanoparticles reduced tensile strength and modulus of the adhesives. An up to 250% increase in the single-lap shear strength of CFRP/steel joints was accomplished in CSR-modified joints over neat epoxy adhesive joints.

Role of Surface Enhancement in the Enzymatic Cross-Linking of Lignosulfonate Using Alternative Downstream Techniques

Lignosulfonate (LS), one of the byproducts of the paper and pulp industry, was mainly used as an energy source in the last decade until the valorization of lignin through different functionalization methods grew in importance. Polymerization using multicopper oxidase laccase (from the Myceliophthora thermophila fungus) is one of such methods, which not only enhances properties such as hydrophobicity, flame retardancy, and bonding properties but can also be used for food and possesses pharmaceutical-like antimicrobial properties and aesthetic features of materials. Appropriate downstream processing methods are needed to produce solids that allow the preservation of particle morphology, a vital factor for the valorization process. In this work, an optimization of the enzymatic polymerization via spray-drying of LS was investigated. The response surface methodology was used to optimize the drying process, reduce the polymerization time, and maximize the dried mass yield. Particles formed showed a concave morphology and enhanced solubility while the temperature sensitivity of spray-drying protected the phenol functionalities beneficial for polymerization. Using the optimized parameters, a yield of 65% in a polymerization time of only 13 min was obtained. The experimental values were found to be in agreement with the predicted values of the factors (R ²: 95.2% and p-value: 0.0001), indicating the suitability of the model in predicting polymerization time and yield of the spray-drying process.