Hard-Soft Thermoset Alloy with Enhanced Toughness, Impact-Resistance, Electric Conductivity via Interpenetrated Dynamic Crosslinked Interface

Polymer alloys are traditionally a mixture of two or more types of polymers to enhance the properties of the polymeric materials. However, thermosets with crosslinked structures are immiscible and could not be used for preparing polymer alloys. Herein, two immiscible covalent adaptable networks containing phenoxy carbamate bonds are explored as the typical polymeric materials to prepare the hard-soft thermoset alloy by the interpenetrated dynamic crosslinked interface to greatly enhance the toughness. Specifically, two types of polyurethane covalent adaptable networks with either high stiffness (thermoset) and high extensibility (elastomer) were prepared, respectively. The granules of thermoset and elastomer at the micrometer scale were mixed and hot-pressed to prepare the hard-soft thermoset alloy. The hard-soft thermoset alloy shows significantly improved mechanical properties with a toughness of 22.8 MJ m^-3 which is 14 times higher than that of hard thermoset. In addition, the hard-soft thermoset alloy shows excellent impact-resistance property with the similar puncture force after 1000 punctures. Moreover, the obtained hard-soft thermoset alloy via addition of carbon nanotubes in the hard-soft thermoset alloy can significantly decrease the electric resistance over 6 orders of magnitudes as compared to the blending method, which is due to the distribution of the carbon nanotubes at the interfaces of the two networks. This article is protected by copyright. All rights reserved.

Bioinspired Impact-Resistant and Self-Monitoring Nanofibrous Composites

Lightweight and impact-resistant materials with self-monitoring capability are highly desired for protective applications, but are challenging to be artificially fabricated. Herein, a scalable-manufactured aramid nanofiber (ANF)-based composite combining these key properties is presented. Inspired by the strengthening and toughening mechanisms relying on recoverable interfaces commonly existing in biological composites, mechanically weak but dense hydrogen bonds are introduced into the ANF interfaces to achieve simultaneously enhanced tensile strength (300 MPa), toughness (55 MJ m^-3 ), and impact resistance of the nanofibrous composite. The achieved mechanical property combination displays attractive advantages compared with that of most of previously reported nanocomposites. Additionally, the nanofibrous composite is designed with a capability for real-time self-monitoring of its structural safety during both quasi-static tensile and dynamic impact processes, based on the strain/damage-induced resistance variations of a conductive nanowire network inside it. These comprehensive properties enable the present nanofibrous composite with promising potential for protective applications.