CaCO3 mineralization in polymer composites with cellulose nanocrystals providing a chiral nematic mesomorphic structure
CaCO3 mineralization in polymer composites with cellulose nanocrystals providing a chiral nematic mesomorphic structure
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聚合物复合材料中的 CaCO3 矿化与纤维素纳米晶体提供手性向列介晶结构
DOI：
10.1016/j.ijbiomac.2019.09.045
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发表时间：
2019
影响因子：
8.2
通讯作者：
Yoshiyuki NISHIO
中科院分区：
文献类型：
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作者：
Yukiko NAKAO;Kazuki SUGIMURA;Yoshiyuki NISHIO
CaCO₃矿化是用纤维素纳米晶体(CNC)/聚合物复合材料进行的，其中CNC组件的手性向列相结构通过前体水性CNC/乙烯基单体lyotropics （7-11 wt% CNC在进料中）的聚合过程预先固定。制备了CNC/聚甲基丙烯酸2-羟乙基酯（PHEMA）和CNC/聚甲基丙烯酸2-羟乙基酯-共丙烯酸(P （HEMA-co-AA), HEMA: AA= 95.5 - 70:30 (mol)）两个系列聚合物复合材料。通过在低碱性条件下（pH≤9）将复合膜浸泡在含有Ca 2 + HCO₃−的盐溶液中，可以实现矿化。用x射线衍射仪检测了CaCO3沉积在膜内的多态性，并将其作为浸泡时间（1-5天）和基质组成的函数。在CNC/PHEMA系列中，多晶形态从无定形碳酸钙（ACC）（浸泡1天）转变为亚稳结晶型水晶石（浸泡3天），然后转变为水晶石和文石的混合物（浸泡5天）。在CNC/P （HEMA-co-AA）系列成矿过程中，除少量水晶石外，稳定方解石的形成较为突出。推导出乙烯基聚合物中的介面填料CNC和AA单元都带有阴离子基（-SO₃−或coo−），有助于捕获Ca 2⁺，从而促进CaCO₃在膨胀膜基质中的沉积。预先投资的手性向列组织保持在任何矿化膜（干燥）中；然而，与矿化前相比，螺旋节距明显降低，这是由于CNCs周围的离子强度随着湿过程的增加而增加。热重分析结果表明，矿化作用明显改善了中晶有序CNC/聚合物复合材料的热性能（耐热性/阻燃性）。
CaCO₃ mineralization was carried out using cellulose nanocrystal (CNC)/polymer composites wherein a chiral nematic structure of CNC assembly was immobilized in advance via a polymerization process of the precursory aqueous CNC/vinyl monomer lyotropics (7–11 wt% CNC in feed). Two series of polymer composites were prepared: CNC/poly (2-hydroxyethyl methacrylate)(PHEMA) and CNC/poly (2-hydroxyethyl methacrylate-co-acrylic acid)(P (HEMA-co-AA), HEMA: AA= 95: 5–70: 30 in mol). The mineralization was allowed to proceed solely by soaking the composite films in a salt solution containing Ca²⁺ and HCO₃− under a low-basic condition (pH≤ 9). Polymorphism of CaCO3 deposited inside the films was examined by X-ray diffractometry as a function of the soaking time (1–5 day) and also of the matrix composition. In the CNC/PHEMA series, the polymorphic form changed from amorphous calcium carbonate (ACC)(1-day soaking) to metastable crystalline vaterite (3-day soaking) and then to a mixture of vaterite and aragonite (5-day soaking). In the mineralization of the CNC/P (HEMA-co-AA) series, the formation of stable calcite was prominent besides minor appearance of vaterite. It was deduced that the mesofiller CNC and the AA unit in the vinyl polymer, both bearing an anionic group (-SO₃− or-COO−), contributed to capturing Ca²⁺ to facilitate the CaCO₃ deposition in the swollen film matrix. The pre-invested chiral nematic organization was kept in any of the mineralized films (dried); however, the helical pitch was appreciably reduced relative to that observed before the mineralization, attributable to the increase of ionic strength in the CNCs' surroundings accompanied by the wet process. Thermogravimetry showed that the mineralization definitely improved the thermal performance (heat/flame resistance) of the mesomorphic order-retaining CNC/polymer composites.