Yu Bao

Super-tough conducting carbon nanotube/ultrahigh-molecular-weight polyethylene composites with segregated and double-percolated structure

Super-tough conducting carbon nanotube (CNT)/ultrahigh-molecular-weight polyethylene (UHMWPE) composites were prepared by a facile method; a very small amount of high-density polyethylene (HDPE) was used as the percolated polymer phase to load the CNTs. A structural examination revealed the formation of unique conductive networks by combination of the typical segregated and double-percolated structure, in which the fully percolated CNT/carrier polymer layers were localized at the interfaces between UHMWPE granules. Owing to the synergistic effect of the segregated and double-percolated structures, only 0.3 wt% of CNTs can make the composite very conductive. More interestingly, after the addition of only 2.7 wt% of HDPE, the ultimate strain, tear strength, and impact strength reached 478%, 35.3 N and 58.1 kJ m−2, respectively; these corresponded to remarkable increases of 265%, 61.9%, and 167% in these properties compared with the conventional segregated materials. These results were ascribed to the intensified interfacial adhesion between UHMWPE granules, which resulted from the strong inter-diffusion and heat-sealing between the HDPE and UHMWPE molecules. A model was proposed to explain the outstanding ductility and toughness properties of the segregated and double-percolated CPC material.

Double-segregated carbon nanotube–polymer conductive composites as candidates for liquid sensing materials

Double-segregated conductive polymer composites were fabricated as candidates for liquid sensing materials; these composites exhibited ultralow percolation (∼0.09 vol%), good reproducibility, and a large liquid sensing capacity (∼8 × 104%) with a balanced electrical conductivity (∼1 S m−1).

Facile, green and affordable strategy for structuring natural graphite/polymer composite with efficient electromagnetic interference shielding

An electromagnetic interference (EMI) shielding composite based on natural, economical graphite and ultrahigh molecular weight polyethylene (UHMWPE) with a typical segregated structure was first fabricated by a facile and green method, i.e., mechanical mixing plus hot compaction, without the use of intensive dispersion and any organic solvents. Superior shielding effectiveness of 51.6 dB was achieved at a low graphite loading of only 7.05 vol%, which was comparable to or even superior to the expensive carbon nanofillers (e.g., carbon nanotube and graphene) based polymer composites owning to the successful creation of the segregated structure in which the graphite particles were selectively located at the interfaces of UHMWPE polyhedrons. Our work suggests a new way of effectively utilizing economical graphite in conductive polymer composites, especially for EMI shielding applications.

Segregated Conductive Ultrahigh-Molecular-Weight Polyethylene Composites Containing High-Density Polyethylene as Carrier Polymer of Graphene Nanosheets

This article reports a novel conductive ultrahigh-molecular-weight polyethylene (UHMWPE) composite with a segregated and double percolated structure, in which graphene nanosheets (GNSs) form prefect conductive pathways in the high-density polyethylene (HDPE) and the GNS/HDPE component forms continuous conductive layers at the interface between the UHMWPE granules. The combination of segregated and double-percolated GNS conductive network achieved an ultralow percolation of 0.05 vol. %. Structural observations and the determination of the critical exponent t-value obtained from the classical threshold mechanism indicate the formation of a two-dimensional GNS network in GNS/HDPE/UHMWPE composites. Comparison of the electrical performance of GNS and CNT-filled segregated composites indicated that the geometry of the conductive nanoparticles can greatly affect the dimensionality of the segregated conductive network.

Influence of the Compaction Temperature on the Electrical and Mechanical Properties of the Segregated Conductive Ultrahigh Molecular Weight Polyethylene/Carbon Nanotube Composite

The effect of the compaction temperature on the electrical and mechanical properties of the segregated conductive polymer (CPC)/carbon nanotube (CNT) composites was investigated. The conductive fillers were not uniformly dispersed in the composites but were dominantly localized on the granule boundaries, very efficiently forming conductive networks. The ultrahigh-molecular-weight polyethylene (UHMWPE) segregated CPCs were synthesized with two compaction temperature, one just above the melting temperature (145°C) and another higher than the melting temperature (200°C). UHMWPE/CNT exhibited the better electrical conductivity by comparing to high-density polyethylene (HDPE)/UHMWPE/CNT, while the HDPE/UHMWPE/CNT segregate CPCs displayed the higher values of the tensile mechanical properties than those of UHMWPE/CNT at the two compaction temperatures. The higher compaction temperature was in favor of the improvement on mechanical properties and degraded the electrical performance of UHMWPE/CNT. For HDPE/UHMWPE/CNT, the electrical and mechanical properties both reduced with decreasing the compaction temperature. These results can further determine the optimal preparation conditions of the segregated composites.

Tunable liquid sensing performance of conducting carbon nanotube–polyethylene composites with a porous segregated structure

An electrically conductive carbon nanotube–polyethylene composite with a porous segregated structure was fabricated using a combination of hot compaction and salt-leaching. The composite exhibited high electrical conductivity (∼8.5 S m−1), good reproducibility, and a tunable liquid sensing capacity over a large range of 220–1718%.

Temperature resistivity behaviour in carbon nanotube/ultrahigh molecular weight polyethylene composites with segregated and double percolated structure

Abstract A novel conductive polymer composite (CPC) based on carbon nanotube (CNT) and binary polymer blend of low density polyethylene (LDPE) and ultrahigh molecular weight polyethylene (UHMWPE) was successfully fabricated by high speed mechanical mixing and hot pressing. The conductive CNT/LDPE component was only dispersed on the surfaces of UHMWPE particles, manifesting combined segregated and double percolated structure. The temperature resistivity behaviour of the CPC was investigated in this paper. A typical double positive temperature coefficient (PTC) of resistivity was observed near the melting points of LDPE and UHMWPE followed by a negative temperature coefficient (NTC) of resistivity. The resistivity began to rise at the maximum crystallisation temperature during cooling, indicating that the conducting nanoparticles were expelled from the crystalline phase. This CPC also exhibited a relatively low PTC and NTC effect, which was determined by the combined segregated and double percolated conductive network as well as high viscosity of UHMWPE matrix. Moreover, with the assistance of in situ optical micrograph and transmission electron microscopy, we found that the subtle microstructural evolution of the conductive network via Brownian motion and crystallisation induced flow was responsible for the higher room temperature resistivity.

Towards efficient electromagnetic interference shielding performance for polyethylene composites by structuring segregated carbon black/graphite networks

An electromagnetic interference (EMI) shielding composite based on ultrahigh molecular weight polyethylene (UHMWPE) loaded with economical graphite-carbon black (CB) hybrid fillers was prepared via a green and facile methodology, i.e., high-speed mechanical mixing combined with hot compression thus avoiding the assistance of the intensive ultrasound dispersion in volatile organic solvents. In this composite, the graphite-CB hybrid fillers were selectively distributed in the interfacial regions of UHMWPE domains resulting a typical segregated structure. Thanks to the specific morphology of segregated conductive networks along with the synergetic effect of large-sized graphite flakes and small-sized CB nanoparticles, a low filler loading of 7.7 vol% (15 wt%) yielded the graphite-CB/UHMWPE composites with a satisfactory electrical conductivity of 33.9 S/m and a superior shielding effectiveness of 40.2 dB, manifesting the comparable value of the pricey large-aspect-ratio carbon nanofillers (e.g., carbon nanotubes and graphene nanosheets) based polymer composites. More interestingly, with the addition of 15 wt% graphite-CB (1/3, W/W) hybrid fillers, the tensile strength and elongation at break of the composite reached 25.3 MPa and 126%, respectively; with a remarkable increase of 58.1% and 2420% over the conventional segregated graphite/UHMWPE composites. The mechanical reinforcement could be attributed to the favor of the small-sized CB particles in the polymer molecular diffusion between UHMWPE domains which in turn provided a stronger interfacial adhesion. This work provides a facile, green and affordable strategy to obtain the polymer composites with high electrical conductivity, efficient EMI shielding, and balanced mechanical performance.

Influence of surface polarity of carbon nanotubes on electric field induced aligned conductive network formation in a polymer melt

Pristine carbon nanotubes (CNTs) and carboxyl carbon nanotubes (CNTs-COOH) were used to study the influence of CNT surface polarity on the electric field induced aligned conductive network formation in an ethylene-vinyl acetate (EVA) melt. The dynamic rheological measurements indicated that the molecular chain–nanotube interaction in CNT-COOH–EVA was stronger than that in CNT–EVA, because of the high affinity between carboxyl groups of CNTs-COOH and ester groups of EVA chains. The critical time for the CNT or CNT-COOH conductive network formation decreased with the elevated annealing temperature and CNT loadings, but the existence of surface polarity of CNTs-COOH lowered the efficiency of conductive network formation. This was well verified by the activation energy of conductive network formation, which was ∼79.4 kJ mol−1 for CNT–EVA, obviously less than that (∼92.7 kJ mol−1) for CNT-COOH–EVA. On the basis of the thermodynamic percolation model, the percolation threshold at the equilibrium state was about 0.25 vol% for CNT–EVA, while it rose to 0.38 vol% for CNT-COOH–EVA. Moreover, morphological observations showed that the CNTs exhibited a higher degree of alignment in CNT–EVA than that in CNT-COOH–EVA induced by an electric field. These results demonstrated that the aligned nanotube conductive network tended to build up easily in a polymer melt with the relatively weak molecular chain–nanotube interactions under the action of an electric field.