Thermal, Mechanical and Electrical Properties of Carbon Fiber Fabric and Graphene Reinforced Segmented Polyurethane Composites

Thermal conductive materials with reliable and high performances such as thermal interface materials are crucial for rapid heat transferring in thermal management. In this work, carbon fiber fabric and graphene reinforced segmented polyurethane composites (CFF-G/SPU) were proposed and prepared to obtain superior thermal, mechanical and electrical properties using the hot-pressing method. The composites exhibit excellent tensile strength and can withstand a tensile force of at least 350 N without breaking. The results show that, comparing with the SPU material, the thermal conductivity is increased by 28% for the CFF-G/SPU composite, while the in-plane electrical conductivity is increased by 8 orders of magnitude to 175 S·m−1. The application of CFF-G/SPU composite as a winding thermal interface material with electric-driven self-heating effect presents good performances of fluidity and interface wettability. The composite has great advantages in phase transition and filling the interfacial gap in the short time of few seconds under the condition of electrical field, with the interface temperature difference between two layers significantly reduced.

Polyhedral oligomeric silsesquioxane (POSS)-modified phenolic resin: Synthesis and anti-oxidation properties

In this work, octamercapto polyhedral oligomeric silsesquioxane (POSS-8SH) and octaphenol polyhedral oligomeric silsesquioxane (POSS-8Phenol) were successfully synthetized. POSS-8Phenol was added into the synthesis process of liquid thermoset phenolic resin (PR) to obtain POSS-modified phenolic resin (POSS-PR). Chemical structures of POSS-8SH, POSS-8Phenol, and POSS-PR were confirmed by FTIR and 1H-NMR. TG and DTG analysis under different atmosphere showed that char yield of POSS-PR at 1,000°C increased from 58.6% to 65.2% in N2, which in air increased from 2.3% to 26.9% at 700°C. The maximum pyrolysis temperature in air increased from 543°C to 680°C, which meant better anti-oxidation properties. XRD results confirmed both POSS-8Phenol and POSS-PR-generated crystalline SiO2 in air, which could explain the improvement of anti-oxidation properties. SEM showed that the POSS-PR had phase separation during curing process. Finally, carbon fiber fabric-reinforced POSS-PR (C-POSS-PR) was prepared to verify the anti-oxidation properties of POSS-PR.

Epoxy and epoxy novolac adhesive binders for structural reinforcement systems of building structures

Today, along with the conventional materials and technologies for reinforcement of building structures, structural reinforcement systems based on polymer composites are on the rise. A structural reinforcement system consists of reinforcing filler (normally, carbon fiber fabric or cloth) and adhesive binder. This paper investigated the modification of epoxy nobake adhesive binders to provide a higher thermal resistance and mechanical strength. The influence of epoxy novolac resins on the processing and physical mechanical properties of adhesives, thermal resistance is studied. It is found that the substitution of 20-40 % of epoxy resin for epoxy novolac resin in the binder increases tensile strength by 40-50 %, flexural modulus by 20 %, reduces tensile strain, and increases glass transition temperature. From the processing point of view, it is more reasonable to use liquid epoxy novolac resins with a functionality of f=2.5 than semisolid resins with a functionality of f=3.6.

Implementation of anisotropic soft pads in a surgical gripper for secure and gentle grip on vulnerable tissues

Current surgical grippers rely on friction grip, where normal loads (i.e. pinch forces) are translated into friction forces. Operating errors with surgical grippers are often force-related, including tissue slipping out of the gripper because of too low pinch forces and tissue damaging due to too high pinch forces. Here, we prototyped a modular surgical gripper with elastomeric soft pads reinforced in the shear direction with a carbon-fiber fabric. The elastomeric component provides low normal stiffness to maximize contact formation without the need of applying high normal loads (i.e. pinch forces), whereas the carbon-fiber fabric offers high shear stiffness to preserve the formed contact under the lateral loads (i.e. shear forces) that occur during tissue lifting. Additionally, we patterned the pads with a sub-surface micropattern, to further reduce the normal stiffness and increase shear stiffness. The body of the prototype gripper, including shaft, joints, and gripper tips, was fabricated in a single step using 3D printing, followed by manual attachment of the soft pads to the gripper. The gripping performance of the newly developed soft gripper on soft tissues was experimentally compared to reference grippers equipped with metal patterned pads. The soft-pad gripper generated similar gripping forces but significantly lower pinch forces than metal-pad grippers. We conclude that grippers with anisotropic-stiffness pads are promising for secure and gentle tissue grip.