Effect of tow size and interface interaction on interfacial shear strength determined by Iosipescu (V-Notch) testing in epoxy resin

Testing methodologies to accurately quantify interfacial shear strength (IFSS) are essential in order to understand fiber-matrix adhesion. While testing methods at a microscale (single filament fragmentation test-SFFT) and macroscale (Short Beam Shear-SBS) are wide spread, each have their own shortcomings. The Iosipescu (V-notch) tow test offers a mesoscale bridge between the microscale and macroscale whilst providing simple, accurate results with minimal time investment. However, the lack of investigations exploring testing variables has limited the application of Iosipescu testing to only a handful of studies. This paper assesses the effect of carbon fiber tow size within the Iosipescu tow test for epoxy resin. Tow sizes of 3, 6, and 9 k are eminently suitable, while more caution must be shown when examining 12, and 15 k tows. In this work, tows at 18 and 24 k demonstrated failure modes not derived from interfacial failure, but poor fiber wetting. A catalogue of common fracture geometries is discussed as a function of performance for the benefit of future researchers. Finally, a comparison of commercial (T300), amine (T300-Amine), and ethyl ester (T300-Ester) surface modified carbon fibers was conducted. The outcomes of this study showed that the Iosipescu tow test is inherently less sensitive in distinguishing between similar IFSS but provides a more \u27real world\u27 image of the carbon fiber-epoxy interface in a composite material

Phosphorus-based α-amino acid mimetic for enhanced flame-retardant properties in an epoxy resin

This work demonstrates the introduction of a phosphonate moiety into a commonly used curing agent, 4,4′-diaminodiphenylmethane (DDM), via an α-aminophosphonate. This compound (DDMP) can be prepared and isolated in analytical purity in under 1 h and in good yield (71 %). Thermoset polymer (epoxy-derived) samples were prepared using a room-temperature standard cure (SC) and a post-cured (PC) protocol to encourage incorporation of the α-aminophosphonate into the polymer network, with improved flammability properties observed for the latter. Thermogravimetric analysis under a nitrogen atmosphere showed increased char yield at 600°C, and similar observations were made when analysis was conducted in air. Significant reductions in flammability are observed at very low phosphorus content (P% = 0.16-0.49 %), demonstrated by higher char yields (25.5 from 14.0 % in air), decreased burn time from ignition (60 to 24 s), and decreased mass loss after ignition (87.6 to 58.5 %). Limiting Oxygen Index for the neat polymer (P% = 0 %, 20.3 ± 0.8 %) increased with increasing α-aminophosphonate additive (P% = 0.16 %, 20.8 ± 0.6 %; P% = 0.32 %, 21.4 ± 0.4 %; P% = 0.49 %, 22.6 ± 0.8 %)

Using in situ polymerization to increase puncture resistance and induce reversible formability in silk membranes

Silk fibroin is an excellent biopolymer for application in a variety of areas, such as textiles, medicine, composites and as a novel material for additive manufacturing. In this work, silk membranes were surface modified by in situ polymerization of aqueous acrylic acid, initiated by the reduction of various aryldiazonium salts with vitamin C. Treatment times of 20 min gave membranes which possessed increased tensile strength, tensile modulus, and showed significant increased resistance to needle puncture (+131%), relative to \u27untreated\u27 standards. Most interestingly, the treated silk membranes were able to be reversibly formed into various shapes via the hydration and plasticizing of the surface bound poly(acrylic acid), by simply steaming the modified membranes. These membranes and their unique properties have potential applications in advanced textiles, and as medical materials

Insulating Composites Made from Sulfur, Canola Oil, and Wool

An insulating composite was made from the sustainable building blocks wool, sulfur, and canola oil. In the first stage of the synthesis, inverse vulcanization was used to make a polysulfide polymer from the canola oil triglyceride and sulfur. This polymerization benefits from complete atom economy. In the second stage, the powdered polymer is mixed with wool, coating the fibers through electrostatic attraction. The polymer and wool mixture is then compressed with mild heating to provoke S-S metathesis in the polymer, which locks the wool in the polymer matrix. The wool fibers impart tensile strength, insulating properties, and flame resistance to the composite. All building blocks are sustainable or derived from waste and the composite is a promising lead on next-generation insulation for energy conservation

Examining the Role of Aryldiazonium Salts in Surface Electroinitiated Polymerization

Historically, the irreversible reduction of aryldiazonium salts has provided a reliable method to modify surfaces, demonstrating a catalogue of suitable diazonium salts for targeted applications. This work expands the knowledge of diazonium salt chemistry to participate in surface electroinitiated emulsion polymerization (SEEP). The influence of concentration, electronic effects, and steric hindrance/regiochemistry of the diazonium salt initiator on the production of polymeric films is examined. The objective of this work is to determine if a polymer film can be tailored, controlling the thickness, density, and surface homogeneity using specific diazonium chemistry. The data presented herein demonstrate a significant difference in polymer films that can be achieved when selecting a variety of diazonium salts and vinylic monomers. A clear trend aligns with the electron-rich diazonium salt substitution providing the thickest films (up to 70.9 ± 17.8 nm) with increasing diazonium concentration and electron-withdrawing substitution achieving optimal homogeneity for the surface of the film at a 5 mM diazonium concentration.</p

Fiber with Butterfly Wings: Creating Colored Carbon Fibers with Increased Strength, Adhesion, and Reversible Malleability

International audienceColored and color-changing materials are central to perception and interaction in nature and have been exploited in an array of modern technologies such as sensors, visual displays and smart materials. Attempts to introduce color into carbon fiber materials have been limited by deleterious impacts on fiber properties, and the extension of colored fibers towards 'smart composites' remains in its infancy. We present carbon fibers incorporating structural color, similar to that observed on the surface of soap bubbles and various insects and birds, by modifying the fiber surface through in situ polymerization grafting. When dry, the treated fibers exhibit a striking blue color, but when exposed to a volatile solvent, a cascade of colors across the visible region is observed as the film first swells and then shrinks as the solvent evaporates. The treated fibers not only possess a unique color and color-changing ability, but can also be reversibly formed into complex shapes and bear significant loads even without being encased in a supporting polymer. The tensile strength of treated fibers shows a statistically significant increase (+12%) and evaluation of the fiber-to-matrix adhesion of these polymers to an epoxy resin shows more than 300% improvement over control fibers. This approach creates a new platform for the multifaceted advance of smart composites