Abstract:

The large-scale preparation of nanocellulose-embedded cryogel microspheres can be realized by crystallization pore-forming and low-temperature polymerization in a multi-microtube reactor. In this process, the formation of hydroxyethyl methacrylate monomer solution embedded with nanocellulose through multi-microtube reactor is the primary condition. It is of great significance to study the dynamic characteristics of the forming process. Using high-speed imaging and computational fluid dynamics (CFD) simulation methods, the droplet formation process of hydroxyethyl methacrylate embedded with different proportions (1%, 3%, 5% of monomer mass) of nanocellulose at different inlet flow rates (6, 8, 10 mm·s^-1) was visualized. The effects of nanocellulose content on droplet formation, droplet diameter distribution, necking line length, droplet falling speed and other factors were investigated. The results show that the hydroxyethyl methacrylate droplets embedded with nanocellulose undergo stretching and compression processes after forming and dripping in a multi-microtube reactor, and finally stabilized into a spherical shape. The measured droplet diameter and necking line length were positively correlated with the cellulose concentration in the monomer solution. The increase of cellulose content increased the viscosity and surface tension coefficient of the monomer solution, thus increasing the droplet size and necking line length. The simulation results are basically consistent with the experimental results. The difference of droplet diameter is 2.1%—6.3%, and the difference of necking line length is 7.2%—11.9%. In the amplification simulation of droplet formation, the average droplet diameter is 3.98 mm and the average necking line length is 4.14 mm at the inlet velocity of 10 mm·s^-1. Finally, a multi-microtube reactor was used to successfully prepare nanocellulose chimeric crystalline microspheres. The effective porosity of the microspheres can reach more than 80%, and the absolute dry porosity is close to 90%. It is an ideal carrier for the field of biological separation and the adherent growth of microorganisms.

Key words: chimeric crystal glue microspheres, nanocellulose, multi-microtube reactor, droplet, kinetics, imaging, numerical simulation

摘要：

利用多微管反应器，采用结晶致孔与低温聚合方法可实现纳米纤维素嵌合型晶胶微球的规模化制备。该过程中内嵌纳米纤维素的甲基丙烯酸羟乙酯单体溶液经多微管反应器的成形是首要条件，研究其成形过程的动力学特性具有重要意义。利用高速成像和计算流体力学（CFD）模拟方法对不同入口流速（6、8、10 mm·s^-1）下内嵌不同比例（单体质量的1%、3%、5%）纳米纤维素的甲基丙烯酸羟乙酯液滴形成过程进行可视化研究，考察了纳米纤维素含量对液滴成形、液滴直径分布、颈缩线长度、液滴下落速度等因素的影响规律。结果表明，内嵌纳米纤维素的甲基丙烯酸羟乙酯液滴经多微管反应器的成形及滴落，会经历拉伸与压缩过程，最后稳定为球状，测得液滴直径和颈缩线长度与纤维素浓度呈正相关，纤维素含量的增加使得单体溶液黏度和表面张力系数增加，从而增大液滴尺寸和颈缩线长度，模拟得到的结果与实验基本一致，液滴直径差异为2.1%~6.3%，颈缩线长度差异为7.2%~11.9%；在对液滴成形的放大模拟中，10 mm·s^-1的入口流速下液滴平均直径为3.98 mm，平均颈缩线长为4.14 mm。最终，利用多微管反应器成功制备了纳米纤维素嵌合型晶胶微球，微球有效孔隙率可达80%以上，绝干孔隙率接近90%，是生物分离领域与微生物贴壁生长的理想载体。

关键词: 嵌合型晶胶微球, 纳米纤维素, 多微管反应器, 液滴, 动力学, 成像, 数值模拟