导热型芳纶纳米纸基绝缘材料的制备及性能

研究了氮化硼(BN)导热填料的种类、添加量及成形方式对导热型芳纶纳米(ANFs)纸基绝缘材料的绝缘、导热及力学性能的影响。研究结果表明,溶胶凝胶法(Sol-gel)使得ANFs之间形成的交织网络结构可改善BN填料在纸张中的分布均匀性,解决了纸张"两面差"问题,减小了填料聚集现象从而实现均匀传热,制备的20%BN@ANFs绝缘纸导热系数达到0.125 W/(m·K),比空白ANFs绝缘纸提高了3.7倍。当添加经过功能化改性的BN-OH时,可提高ANFs与BN之间的界面结合力从而降低界面热阻,绝缘纸的导热系数高达0.144 W/(m·K),比空白纸提高了4.2倍,同时具有优异的力学性能(拉伸强度145 MPa)与绝缘强度(耐压强度25.3 kV/mm),有望满足未来小型化、轻质化、集成化的电气绝缘设备对绝缘材料性能不断的升级要求。

Interaction between PCC Filler and Cellulosic Fiber in Fiber/Filler Co-refining System

Mineral fillers are important for conserving raw fiber materials and reducing production costs in the paper industry.However,the increase in filler content will inevitably result in strength reduction,which limits the adding amount of filler in paper production.In this study,we designed a cellulose fiber/filler co-refining approach to improve the strength and optical properties of paper;moreover,the synergistic interaction between fibers and precipitated calcium carbonate(PCC)fillers in the co-refining process was investigated.Results of fiber separation and PCC particle size analysis showed that,compared with conventional refining,the content of fines increased,whereas the PCC particle size decreased.More importantly,composites were formed between the PCC and fines,which promoted strength improvement of paper.Physical tests show that the tensile index of paper with 15%PCC content increased by 22%compared with that of the paper filled by conventional method,whereas the brightness and opacity of paper improved by fiber/filler co-refining for a specified filler content.These findings provide a basis for the further development of co-refining filling technology.

Highly Improved Microstructure and Properties of Poly(p-phenylene terephthalamide) Paper-based Materials via Hot Calendering Process

In this study,the effect of hot calendering process on the microstructure and properties of poly(p-phenylene terephthalamide)(PPTA) paper-based materials was investigated.The microstructures of the fracture surface,crystalline structure,and single fiber strength of the PPTA paperbased materials as well as the different bonding behaviors between the PPTA fibers and PPTA fibrids obtained before and after the hot calendering process were examined.The results indicated that a high linear pressure would result in a limited improvement of the strength owing to the unimproved paper structure.The optimal values of tensile index and dielectric strength of 56.6 N·m/g and 27.6 kV/mm,respectively,could only be achieved with a synergistic effects of hot calendering temperature and linear pressure(240℃ and 110 k N/m,respectively).This result suggested it was possible to achieve a significant reinforcement and improvement in the interfacial bonding of functional PPTA paper-based materials,and avoid the formation of unexpected pleats and cracks in PPTA paper-based materials during the hot calendering process.

Preparation of Highly Crystalline Microcrystalline Cellulose by Hydrolysis of Cellulose with Phosphotungstic Acid

Phosphotungstic acid(H_3PW_(12)O_(40), HPW), a kind of solid acid, is widely used for hydrolyzing cellulose to prepare microcrystalline cellulose(MCC). MCC is usually used in food, synthetic leather, chemical and pharmaceutical industries. The use of response surface methodology(RSM)can help avoid the random error caused by single factor experimental design,reduce test times and cost, and improve quality. The RSM was used in this study to determine the following optimal process conditions: H^+ molar quantity, 31 mmol/L; reaction temperature, 93℃; reaction time, 2 h; and solid to liquid ratio, 1∶38. Under these conditions, the crystallinity of MCC was77.4%. Thus, the use of RSM allows the preparation of MCC with higher performance and increased crystallinity.

Coaxing Polysaccharide Granules into Supramolecular Biocolloidal Additives for Papermaking

In light of developments in polysaccharide-based sustainable processes involving supramolecular interactions,we herein present our findings pertaining to coaxing polysaccharide granules into functional supramolecular biocolloids.Translucent biocolloidal dispersions containing various forms of starch are facilely designable,essentially built upon complexation between disassembled native cornstarch granules and amphiphilic ligands.Oily moieties of guest molecules are dynamically attractable into cavities of helical structures,with cationic groups pointing toward the bulk phase.This noncovalent attraction can generate core-shell biocolloidal particles.The significantly higher gelatinizability of freeze-dried biocolloids in contrast to native cornstarch granules is attributable to complex formation,and a homogenous dispersion is readily formable at room temperature.Our results also show biocolloids'ligand-related antibacterial activity.The use of biocolloids as wet-end additives for biofiber assemblies(cellulosic paper)can enhance mechanical strength,fines retention,and filler bondability.Supramolecular biocolloids with positively charged,translucent,easily gelatinizable,antibacterial,and polysaccharide-bondable functionalities would find tailorable use in the paper industry.

Foam Forming: An Effective Method to Prepare Polyimide Fiber-based Paper

Well-dispersed fiber suspension is the precondition of good paper formation. Compared with cellulosic fibers, synthetic fibers are prone to flocculate because of their long length and hydrophobic nature, resulting in poor paper formation. To solve this problem, dispersants and extremely low forming consistency are typically adopted during the traditional wet-forming process, which cause a large amount of water consumption and treatment cost. Therefore, increasing forming consistency without compromising paper formation remains a challenge for papermakers. In this work, foam forming was adopted to disperse polyimide fibers (PI) with high forming consistency. The results showed that the formation index of handsheets increased when the bubble size and distribution became small and narrow. Compared with traditional wet-forming process with the same consistency (0.4%), the formation index of handsheets by foam forming increased by approximately 100% when C8 alkyl glucoside (APG08) concentration reached 16 g/L. Notably, forming consistency could increase by eight times while keeping the same level of paper formation. Overall, foam forming exhibits great advantages in dispersing long fiber and reducing water consumption and environmental pressure, and has potential applications in specialty paper made of long fibers.