Leszczyńska Agnieszka, Radzik Paulina, Szefer Ewa, Mičušík Matej, Omastová Mária, Pielichowski Krzysztof
Department of Chemistry and Technology of Polymers, Cracow University of Technology, ul. Warszawska 24, 31-155 Kraków, Poland.
Polymer Institute, Slovak Academy of Sciences, Dúbravská cesta 9, 845 41 Bratislava 45, Slovakia.
Polymers (Basel). 2019 May 13;11(5):866. doi: 10.3390/polym11050866.
The surface modification of cellulose nanocrystals (CNC) is a key intermediate step in the development of new functionalities and the tailoring of nanomaterial properties for specific applications. In the area of polymeric nanocomposites, apart from good interfacial adhesion, the high thermal stability of cellulose nanomaterial is vitally required for the stable processing and improvement of material properties. In this respect, the heterogeneous esterification of CNC with succinic anhydride was investigated in this work in order to obtain CNC with optimised surface and thermal properties. The influence of reaction parameters, such as time, temperature, and molar ratio of reagents, on the structure, morphology and thermal properties, were systematically studied over a wide range of values by DLS, FTIR, XPS, WAXD, SEM and TGA methods. It was found that the degree of surface substitution of CNC increased with the molar ratio of succinic anhydride to cellulose hydroxyl groups (SA:OH), as well as the reaction time, whilst the temperature of reaction showed a moderate effect on the degree of esterification in the range of 70-110 °C. The studies on the thermal stability of modified nanoparticles indicated that there is a critical extent of surface esterification below which only a slight decrease of the initial temperature of degradation was observed in pyrolytic and oxidative atmospheres. A significant reduction of CNC thermal stability was observed only for the longest reaction time (240 min) and the highest molar ratio of SA:OH. This illustrates the possibility of manufacturing thermally stable, succinylated, CNC by controlling the reaction conditions and the degree of esterification.
纤维素纳米晶体（CNC）的表面改性是开发新功能以及针对特定应用定制纳米材料性能的关键中间步骤。在聚合物纳米复合材料领域，除了良好的界面粘附性外，纤维素纳米材料的高热稳定性对于材料性能的稳定加工和改善至关重要。在这方面，本工作研究了CNC与琥珀酸酐的非均相酯化反应，以获得具有优化表面和热性能的CNC。通过动态光散射（DLS）、傅里叶变换红外光谱（FTIR）、X射线光电子能谱（XPS）、广角X射线衍射（WAXD）、扫描电子显微镜（SEM）和热重分析（TGA）方法，在很宽的值范围内系统地研究了反应参数（如时间、温度和试剂摩尔比）对结构、形态和热性能的影响。发现CNC的表面取代度随着琥珀酸酐与纤维素羟基的摩尔比（SA:OH）以及反应时间的增加而增加，而反应温度在70-110°C范围内对酯化度有中等程度的影响。对改性纳米颗粒热稳定性的研究表明，存在一个临界表面酯化程度，低于该程度时，在热解和氧化气氛中仅观察到降解初始温度略有下降。仅在最长反应时间（240分钟）和最高SA:OH摩尔比下观察到CNC热稳定性显著降低。这说明了通过控制反应条件和酯化程度来制造热稳定的琥珀酰化CNC的可能性。
