Highly Tough Yet Stiff, Transparent, and Recyclable PMMA Nanocomposites Incorporating TPU Nanofibril Networks with High Thermal Stability and Strong Interfacial Adhesion.

In this paper, we develop high aspect ratio nanofibrils from a polycaprolactone-based thermoplastic polyurethane (TPU) and evaluate their performance as a toughening agent. Poly(methyl methacrylate) (PMMA) was chosen as the matrix material because of its inherent brittleness and low resistance to sudden shocks and impact. We show that the addition of as little as 3 wt % of TPU nanofibrils with an average diameter of ∼98 nm and very high aspect ratio can significantly improve both the tensile toughness (∼212%) and impact strength (∼40%) of the chosen matrix (i.e., PMMA) without compromising its original strength, stiffness, and transparency. We compare the performance of TPU nanofibrils with TPU spherical particles─the form TPU typically manifests into when melt-mixed with an immiscible polymer. Our findings highlight that the structure of TPU plays a crucial role in determining the critical concentration of TPU needed for the brittle-ductile transition of the matrix. We also provide new and valuable insights into the unique interfacial interaction (i.e., formation of fibrillar bridges) observed between the PMMA matrix and TPU. We also show that the inclusion of 3 wt % of TPU nanofibrils can notably enhance resistance to creep deformation, even at temperatures close to the glass transition temperature of the matrix. Finally, we evaluate recyclability and demonstrate that the composite containing 3 wt % of TPU nanofibrils can be mechanically recycled without losing any properties. The proposed TPU nanofibrils can withstand repeated reprocessing at temperatures up to 190 °C due to their very high melting point and thermal stability. This presents the opportunity for them to be utilized not just with amorphous PMMA, but also with a range of other materials that can be processed at or below this temperature to remarkably improve their toughness without sacrificing strength and stiffness.

Enhancing Mechanical Performance of High-Density Polyethylene at Different Environmental Conditions with Outstanding Foamability through In-Situ Rubber Nanofibrillation: Exploring the Impact of Interface Modification.

In this study, we utilized in situ nanofibrillation of thermoplastic polyester ether elastomer (TPEE) within a high-density polyethylene (HDPE) matrix to enhance the rheological properties, foamability, and mechanical characteristics of the HDPE nanocomposite at both room and subzero temperatures. Due to the inherent polarity differences between these two components, TPEE is thermodynamically incompatible with the nonpolar HDPE. To address this compatibility issue, we employed a compatibilizer, styrene/ethylene-butylene/styrene copolymer-grafted maleic anhydride (SEBS-g-MA), to reduce the interfacial tension between the two blend components. In the initial step, we prepared a 10% masterbatch of HDPE/TPEE with and without the compatibilizer using a twin-screw extruder. Subsequently, we processed the 10% masterbatch further through spun bonding to create fiber-in-fiber composites. Scanning electron microscopy (SEM) analysis revealed a significant reduction in the spherical size of HDPE/TPEE particles following the inclusion of SEBS-g-MA, as well as a much smaller TPEE nanofiber size (approximately 60-70 nm for 5% TPEE). Moreover, extensional rheological testing revealed a notable enhancement in extensional rheological properties, with strain-hardening behavior being more pronounced in the compatibilized nanofibrillar composites compared to the noncompatibilized ones. SEM images of the foam structures depicted substantial improvement in the foamability of HDPE in terms of the cell size and density following the nanofibrillation process and the use of the compatibilizer. Ultimately, the in situ rubber fibrillation and enhancement of HDPE and TPEE interface using a compatibilizer led to increasing the HDPE ductility at room and subzero temperatures while maintaining its stiffness.

Comparative Effects of Hydrazine and Thermal Reduction Methods on Electromagnetic Interference Shielding Characteristics in Foamed Titanium Carbonitride MXene Films.

The urgent need for the development of micro-thin shields against electromagnetic interference (EMI) has sparked interest in MXene materials owing to their metallic electrical conductivity and ease of film processing. Meanwhile, postprocessing treatments can potentially exert profound impacts on their shielding effectiveness (SE). This work comprehensively compares two reduction methods, hydrazine versus thermal, to fabricate foamed titanium carbonitride (Ti3CNTx) MXene films for efficient EMI shielding. Upon treatment of ≈ 100 µm-thick MXene films, gaseous transformations of oxygen-containing surface groups induce highly porous structures (up to ≈ 74.0% porosity). The controlled application of hydrazine and heat allows precise regulation of the reduction processes, enabling tailored control over the morphology, thickness, chemistry, and electrical properties of the MXene films. Accordingly, the EMI SE values are theoretically and experimentally determined. The treated MXene films exhibit significantly enhanced SE values compared to the pristine MXene film (≈ 52.2 dB), with ≈ 38% and ≈ 83% maximum improvements for the hydrazine and heat-treated samples, respectively. Particularly, heat treatment is more effective in terms of this enhancement such that an SE of 118.4 dB is achieved at 14.3 GHz, unprecedented for synthetic materials. Overall, the findings of this work hold significant practical implications for advancing high-performance, non-metallic EMI shielding materials.