Critical transition of epoxy resin from brittleness to toughness by incorporating CO2-sourced cyclic carbonate

Preparation of Biobased Nonisocyanate Polyurethane/Epoxy Thermoset Materials Using Depolymerized Native Lignin

Polyurethane polymers are found in a wide range of material applications. However, the toxic nature of isocyanates used in their formulation is a major concern; hence, more environmentally friendly alternatives are of high interest in the search for new sustainable polymer materials. In this work, we present the preparation of isocyanate-free polyurethane/epoxy hybrid thermosets with a high biobased content (85-90 wt %). The isocyanate-free polyurethanes were based on polyhydroxyurethanes (PHUs) prepared from depolymerized native lignin, which we refer to as lignin hydrogenolysis oil (LHO). The LHO was functionalized with epichlorohydrin to yield the epoxidized structure (LHO-GE), which was in turn reacted with CO₂ to form the cyclocarbonated species (LHO-CC). Blends of the LHO-CC and glycerol diglycidyl ether (GDGE) were cured to produce hybrid PHU/epoxy (LHO-CC/GDGE) thermosets. Thermosetting materials with flexural moduli of 4.5 GPa and flexural strengths of 160 MPa were produced by optimizing the mass ratio of the two main components and the triamine hardener. These novel biobased hybrid materials outperformed the corresponding epoxy-only thermosets and comparable hybrid PHU/epoxy materials produced from petrochemicals.

Mechanical Performances of Phenolic Modified Epoxy Resins at Room and High Temperatures

Epoxy is an important resin matrix and has been widely applied in laminated composites as a coating or adhesive material. In this article, the phenolic was applied to modify the mechanical properties of epoxy resin. The phenolic modified epoxy resins with various phenolic content were prepared via a polytetrafluoroethylene mould, and the phenolic modified epoxy-based plain woven laminated composites (PWLCs) were manufactured via vacuum assisted resin transfer method for further study of phenolic modified epoxy resins’ mechanical properties. The compression tests were performed perpendicularly to thickness at 2 mm/min to investigate the mechanical performances of phenolic modified epoxy resins and epoxy-based PWLCs. The results showed that the addition of phenolic into epoxy could improve the mechanical performances of epoxy resins and epoxy-based composites at room temperature, and the phenolic influenced epoxy-based PWLC more than epoxy matrix at room temperature. However, at high temperatures, the addition of phenolic decreased the mechanical performances of epoxy resins and epoxy-based composites, and the adverse effect of phenolic became more serious with the increase of phenolic content at high temperature. In addition, the thermogravimetric analyses were also conducted from 30 °C to 800 °C on phenolic modified epoxy resins and the results showed that the phenolic modified epoxy resin had an earlier loss in weight than unmodified epoxy resin. The earlier loss in weight meant that the addition of phenolic into epoxy resin led to the formation of unstable molecules at high temperature.

Influence of Interfacial Bonding on the Mechanical and Impact Properties Ring-Opening Metathesis Polymer (ROMP) Silica Composites

Polymers formed by ring-opening metathesis polymerization (ROMP) such as poly(dicyclopentadiene) (pDCPD) exhibit a technologically desirable combination of high toughness, high glass transition temperature, and outstanding low-temperature performance. However, because of their nonpolar molecular structure, they tend to suffer from relatively low elastic moduli and poor adhesion to common fillers, fibers, and substrates, limiting their utility as adhesives and composite binders without specialized bonding agents. Here, we investigate the mechanical properties of a pDCPD-based copolymer filled with well-defined spherical microparticles having four distinct surface chemistries capable of strong, moderate, or weak bonding to the matrix with surfaces ranging from polar to nonpolar. Measurements in uniaxial tension, quasi-static fracture, and high-velocity impact are complemented by digital image correlation (DIC), scanning electron microscopy (SEM) fractography, and X-ray computed tomography (X-μCT) of subcritically loaded crack tips, yielding insight into the complex roles played by interfacial bonding in strength, stiffness, and toughening mechanisms of an already tough polymer. Analysis using quantitative fracture and impact mechanism models provided valuable guidelines for designing heterogeneous systems that combine structural and tough performance.