Enhancement of Electromagnetic Interference Shielding Performance and Wear Resistance of the UHMWPE/PP Blend by Constructing a Segregated Hybrid Conductive Carbon Black-Polymer Network.

The low-percolation-threshold conductive networking structure is indispensable for the high performance and functionalization of conductive polymer composites (CPCs). In this work, conductive carbon black (CCB)-reinforced ultrahigh-molecular-weight polyethylene (UHMWPE)/polypropylene (PP) blend with tunable electrical conductivity and good mechanical properties was prepared using a high-speed mechanical mixing method and a compression-molded process. An interconnecting segregated hybrid CCB-polymer network is formed in electrically conductive UHMWPE/PP/CCB (UPC) composites. The UPC composites possess a dense conductive pathway at a low percolation threshold of 0.48 phr. The composite with 3 phr CCB gives an electrical conductivity value of 1.67 × 10-3 S/cm, 12 orders of magnitude higher than that of the polymeric matrix, suggesting that CCB improves both the electrical conductivity and electromagnetic interference shielding effectiveness (EMI SE) of the composite at the loading fraction over its percolation threshold. The composite with 15 phr CCB presents an absorption-dominated electromagnetic interference shielding effectiveness (EMI SE) as high as 27.29 dB at the X-band. The composite also presents higher tribological properties, mechanical properties, and thermal stability compared to the UP blend. This effort provides a simple and effective way for the mass fabrication of CPC materials with excellent performance.

Spatiotemporal spread pattern of the COVID-19 cases in China.

The COVID-19 pandemic is currently spreading widely around the world, causing huge threats to public safety and global society. This study analyzes the spatiotemporal pattern of the COVID-19 pandemic in China, reveals China's epicenters of the pandemic through spatial clustering, and delineates the substantial effect of distance to Wuhan on the pandemic spread. The results show that the daily new COVID-19 cases mostly occurred in and around Wuhan before March 6, and then moved to the Grand Bay Area (Shenzhen, Hong Kong and Macau). The total COVID-19 cases in China were mainly distributed in the east of the Huhuanyong Line, where the epicenters accounted for more than 60% of the country's total in/on 24 January and 7 February, half in/on 31 January, and more than 70% from 14 February. The total cases finally stabilized at approximately 84,000, and the inflection point for Wuhan was on 14 February, one week later than those of Hubei (outside Wuhan) and China (outside Hubei). The generalized additive model-based analysis shows that population density and distance to provincial cities were significantly associated with the total number of the cases, while distances to prefecture cities and intercity traffic stations, and population inflow from Wuhan after 24 January, had no strong relationships with the total number of cases. The results and findings should provide valuable insights for understanding the changes in the COVID-19 transmission as well as implications for controlling the global COVID-19 pandemic spread.

Largely enhanced thermal conductivity and thermal stability of ultra high molecular weight polyethylene composites via BN/CNT synergy.

In recent years, thermally conductive polymer-based composites have garnered significant attention due to their light weight and easy formation process. In this work, the thermal conductivity of ultra high molecular weight polyethylene (UPE) composites was improved through construction of a hybrid filler network of boron nitride sheets (BNs) and carbon nanotubes (CNTs) in the matrix via hot compression. The morphology, UPE aggregate structure, thermal conductivity, heat dissipation capacity and thermal stability of the UPE composites were investigated. The thermal conduction mechanism of the UPE composites was explored through simulations with Agari's semi-empirical formula. The results showed that the thermal conductivity of the UPE composite with 40 wt% BNs and 7 wt% CNTs was 2.38 W m-1 K-1, which was 495% higher than that of pure UPE, showing a synergistic effect between BNs and CNTs. The simulations with Agari's semi-empirical simulation suggested that increasing the CNT content contributed to synergistically assist BNs to form a better continuous and effective hybrid filler thermal network, thereby reducing phonon scattering and thermal resistance between BNs. In addition, UPE composites doped with BNs and CNTs presented better heat dissipation capacity and higher thermal stability as compared to that of pure UPE.