College of Materials and Energy, South China Agricultural University, Guangzhou 510642, PR China.
College of Materials and Energy, South China Agricultural University, Guangzhou 510642, PR China.
Int J Biol Macromol. 2020 Dec 1;164:1766-1775. doi: 10.1016/j.ijbiomac.2020.07.320. Epub 2020 Aug 5.
Cellulose nanofibrils (CNFs) with cellulose I and II allomorphs were efficiently prepared by sulfuric acid hydrolysis of eucalyptus cellulose under three different conditions followed by mechanical treatments: (i) classical sulfuric acid hydrolysis of cellulose I (CNF-I), (ii) sulfuric acid hydrolysis of mercerized cellulose II (MNF-II), and (iii) solubilization and hydrolysis of cellulose I by concentrated sulfuric acid and subsequent recrystallization in water (RNF-II). Crystal structure, surface chemistry, morphology and thermal properties of three CNFs were investigated and compared. Three CNFs of 2-10 wt% were mixed with PVA to prepare biodegradable composite films. CNF allomorph had significant impact on crystal structure, mechanical and thermal properties of the PVA composites. The maximum Young's modulus of CNF-I/PVA, RNF-II/PVA and MNF-II/PVA were increased by 62, 32 and 44%, respectively. Addition of CNFs raised onset degradation temperature (T) and thermal decomposition temperature (T) of PVA nanocomposite, while decreased the melting temperature (T). Temperature window (T - T) for the melt processing of nanocomposites (10 wt% CNF loading) were increased 2.8, 3.2 and 2.5 times for CNF-I/PVA, RNF-II/PVA and MNF-II/PVA, respectively. All composite films remained excellent transparency with addition of CNFs. This comparative study provided important knowledge of selecting CNF allomorph for fabrication of high-performance CNF/PVA composites.
纤维素纳米纤维（CNFs）具有纤维素 I 和 II 两种晶型，通过三种不同条件下的硫酸水解桉树木纤维素和机械处理来高效制备：（i）纤维素 I 的经典硫酸水解（CNF-I），（ii）丝光纤维素 II 的硫酸水解（MNF-II），以及（iii）浓酸溶解和水解纤维素 I 以及随后在水中重结晶（RNF-II）。对三种 CNF 的晶体结构、表面化学、形态和热性能进行了研究和比较。三种 CNF 浓度为 2-10wt%，与 PVA 混合制备可生物降解的复合材料薄膜。CNF 晶型对 PVA 复合材料的晶体结构、力学和热性能有显著影响。CNF-I/PVA、RNF-II/PVA 和 MNF-II/PVA 的最大杨氏模量分别提高了 62%、32%和 44%。CNFs 的添加提高了 PVA 纳米复合材料的起始降解温度（T）和热分解温度（T），而降低了熔融温度（T）。纳米复合材料（10wt% CNF 负载）的熔融加工温度窗口（T-T）分别增加了 2.8、3.2 和 2.5 倍，对于 CNF-I/PVA、RNF-II/PVA 和 MNF-II/PVA。所有复合薄膜在添加 CNFs 后仍保持优异的透明度。这项比较研究为制造高性能 CNF/PVA 复合材料选择 CNF 晶型提供了重要的知识。
