Enhancing Thermal Conductivity in Polymer Composites through Molding-Assisted Orientation of Boron Nitride.

Incrementing thermal conductivity in polymer composites through the incorporation of inorganic thermally conductive fillers is typically constrained by the requirement of high filler content. This necessity often complicates processing and adversely affects mechanical properties. This study presents the fabrication of a polystyrene (PS)/boron nitride (BN) composite exhibiting elevated thermal conductivity with a modest 10 wt% BN content, achieved through optimized compression molding. Adjustments to molding parameters, including molding-cycle numbers, temperature, and pressure, were explored. The molding process, conducted above the glass transition temperature of PS, facilitated orientational alignment of BN within the PS matrix predominantly in the in-plane direction. This orientation, achieved at low filler loading, resulted in a threefold enhancement of thermal conductivity following a single molding time. Furthermore, the in-plane alignment of BN within the PS matrix was found to intensify with increased molding time and pressure, markedly boosting the in-plane thermal conductivity of the PS/BN molded composites. Within the range of molding parameters examined, the highest thermal conductivity (1.6 W/m·K) was observed in PS/BN composites subjected to five molding cycles at 140 °C and 10 MPa, without compromising mechanical properties. This study suggests that compression molding, which allows low filler content and straightforward operation, offers a viable approach for the mass production of polymer composites with superior thermal conductivity.

Bidirectionally Oriented Carbon Fiber/Silicone Rubber Composites with a High Thermal Conductivity and Enhanced Electromagnetic Interference Shielding Effectiveness.

Effective thermal management and electromagnetic shielding have emerged as critical goals in contemporary electronic device development. However, effectively improving the thermal conductivity and electromagnetic shielding performance of polymer composites in multiple directions continues to pose significant challenges. In this work, inspired by the efficiency of interchange bridges in enabling vehicles to pass quickly in multiple directions, we employed a straightforward method to fabricate bidirectionally oriented carbon fiber (CF)/silicone rubber composites with an interchange-bridge-like structure. The high aspect ratio of CFs and their bidirectional orientation structure play a pivotal role in facilitating the formation of thermal and electrical pathways within the composites. Meanwhile, the bidirectionally oriented CF/silicone rubber composites showed a significant enhancement in tensile strength in both the vertical and horizontal directions, attributed to the cross-arrangement of CF arrays within the composites. At a filler content of 62.3 wt%, the bidirectionally oriented CF/silicone rubber composites had a high tensile strength of 6.18 MPa. The composites also exhibited an excellent thermal conductivity of 25.3 W/(m·K) and a remarkable electromagnetic interference shielding effectiveness of 61.6 dB. The bidirectionally oriented CF/silicone rubber composites show potential for addressing thermal management and electromagnetic shielding issues in electronic devices.

Bio-preparation of (R)-DMPM using whole cells of Pseudochrobactrum asaccharolyticum WZZ003 and its application on kilogram-scale synthesis of fungicide (R)-metalaxyl.

Methyl (R)-N-(2,6-dimethylphenyl)alaninate ((R)-DMPM) is a key chiral intermediate for the production of (R)-metalaxyl, which is one of the best-selling fungicides. A new strain, Pseudochrobactrum asaccharolyticum WZZ003, was identified as a biocatalyst for the enantioselective hydrolysis of (R,S)-DMPM. The key parameters including pH, temperature, rotation speed and substrate concentrations were optimized in the enantioselective hydrolysis of (R,S)-DMPM. After the 48 h hydrolysis of 256 mM (R,S)-DMPM under the optimized reaction conditions, the enantiomeric excess of product (e.e.p ) was up to 99% and the conversion was nearly 50%. Subsequently, the unhydrolyzed (S)-DMPM was converted to (R,S)-DMPM through the n-butanal-catalyzed racemization. Furthermore, stereoselective hydrolysis of (R,S)-DMPM catalyzed by whole cells of P. asaccharolyticum WZZ003 was scaled up to kilogram-scale, offering (R)-MAP-acid with 98.6% e.e.p and 48.0% yield. Moreover, (R)-metalaxyl was prepared at kilogram scale after subsequent esterification and coupling reactions. Therefore, a practical production process of (R)-DMPM and (R)-metalaxyl with the prospect of industrialization was developed in this study. © 2018 American Institute of Chemical Engineers Biotechnol. Prog., 34:921-928, 2018.