Effect of the processing of injection-molded, carbon black-filled polymer composites on resistivity

Determination of Local Electrical Properties Using a Potential Field Measurement for Electrically Conductive Carbon Fiber Reinforced Plastics with Metal Contact Pins Joined via Injection Molding

Carbon fiber reinforced plastics (CFRP) bear a high potential in terms of electrical conductivity and its potential applications. A locally resolved electrical measurement method for these anisotropic materials is a key prerequisite for understanding the structural and manufacturing process-related interrelationships. The aim of this paper is to develop a measurement method that allows this to be achieved and also to investigate areas of overmolded metal contact pins in detail. CFRP samples with polyamide 6 and polycarbonate matrices were used, which were produced by using a custom-designed injection mold. In order to evaluate the measurement results and to correlate them to process related structural properties, reflected light microscopy and X-ray microtomography were used. Typical areas with significant fiber structures of assembly injection molded samples were electrically and structurally characterized to identify correlations. Among further results, the correlation of equipotential lines, acquired from the electrical analysis, with specific fiber orientations within the injection molded samples was demonstrated, fiber-poor areas were identified, and a beneficial influence of weld lines on contact resistances was determined.

Vascular Pressure-Flow Measurement Using CB-PDMS Flexible Strain Sensor

Regular monitoring of blood flow and pressure in vascular reconstructions or grafts would provide early warning of graft failure and improve salvage procedures. Based on biocompatible materials, we have developed a new type of thin, flexible pulsation sensor (FPS) which is wrapped around a graft to monitor blood pressure and flow. The FPS uses carbon black (CB) nanoparticles dispersed in polydimethylsiloxane (PDMS) as a piezoresistive sensor layer, which was encapsulated within structural PDMS layers and connected to stainless steel interconnect leads. Because the FPS is more flexible than natural arteries, veins, and synthetic vascular grafts, it can be wrapped around target conduits at the time of surgery and remain implanted for long-term monitoring. In this study, we analyze strain transduction from a blood vessel and characterize the electrical and mechanical response of CB-PDMS from 0-50% strain. An optimum concentration of 14% CB-PDMS was used to fabricate 300-μm thick FPS devices with elastic modulus under 500 kPa, strain range of over 50%, and gauge factor greater than 5. Sensors were tested in vitro on vascular grafts with flows of 0-1,100 mL/min. In vitro testing showed linear output to pulsatile flows and pressures. Cyclic testing demonstrated robust operation over hundreds of cardiac cycles, with ±2.6 mmHg variation in pressure readout. CB-PDMS composite material showed excellent potential in biologic strain sensing applications where a flexible sensor with large maximum strain range is needed.

Injection-molded lightweight and high electrical conductivity composites with microcellular structure and hybrid fillers

Polypropylene/carbon black (PP/CB) and PP/CB/multiwalled carbon nanotube (PP/CB/MWCNT) composites were fabricated by solid and foam injection molding, with the goal of enhancing the electrical conductivity of the composites while decreasing the cost of the final product. The foaming behavior and through-plane (T-P) electrical conductivity of the composites were characterized and analyzed. Cell growth increased the interconnection of the conductive fillers, changed the filler orientation, and enhanced the T-P electrical conductivity of the composites. Under appropriate processing conditions (200°C melt temperature, 70 cm3/s injection flow rate, and 5% void fraction), the T-P electrical conductivity of the foam PP/CB composites was 5 orders of magnitude higher than that of the solid composites (from 5.877 × 10−12 S/m to 1.010 × 10−7 S/m). Moreover, the T-P electrical conductivity values of the PP/CB and PP/CB/MWCNT were compared at the same conductive fillers content (15 wt%). The results showed that the T-P electrical conductivity of the PP/CB/MWCNT composites was far higher than that of the PP/CB composites by almost five orders of magnitude because the MWCNT acted as a bridge between CB particles, and a unique geometric shape was formed in the system. The T-P electrical conductivity of the foam PP/CB/MWCNT composites with 15 wt% carbon fillers was higher than that of the solid PP/CB composites with 20 wt% carbon fillers. This study reveals that the effect of foaming and the addition of hybrid fillers can improve the T-P electrical conductivity of plastic products, which is very important for the development of lightweight conductive plastics.

Strategy for the Improvement of the Mechanical Properties of Cellulose Nanofiber-Reinforced High-Density Polyethylene Nanocomposites Using Diblock Copolymer Dispersants

Cellulose nanofibers (CNFs) hold great potential as sustainable reinforcement fillers with excellent mechanical, thermal, and chemical properties. However, in polyolefin nanocomposite materials, the rational control of dispersion and the improvement of interfacial strength remain challenging. Herein we propose the tuning of the interface between CNF and high-density polyethylene by the design of polymer dispersants on the basis of surface free energy and the glass transition temperature. The former is related to the wettability against the polymer matrix and is therefore critical to the dispersion of CNF whereas the latter is related to the interfacial strength between CNF and HDPE. As a result of this investigation, we discovered a suitable dispersant for CNFs, poly(dicyclopentenyloxyethyl methacrylate)-block-poly(2-hydroxyethyl methacrylate), which played a pivotal role in achieving both a uniform dispersion of CNF and greatly improved mechanical properties, including a 4-fold increase of the Young's modulus over that of neat HDPE with 10 wt % CNF loading.