Abstract:

Films with tunable gas permeation are important for the development of the packaging and preservation field, while designing films with pH-responsive permeation and high mechanical properties remains a challenge. In this paper, a two-step substitution reaction of succinic anhydride esterification and diethylenetriamine amidation was designed to achieve functionalized modification of amine group (A-CNC) and carboxyl group (S-CNC) on the surface of cellulose nanocrystals, which was further composited with poly(butylene adipate-co-terephthalate) (PBAT) to prepare composite films with pH-responsive gas permeation. The results showed that the cellulose nanocrystals and their functionalisation were characterised by scanning electron microscopy (SEM), infrared spectroscopy (FTIR) and nuclear magnetic resonance ¹³C spectroscopy (¹³C NMR), confirming the success of the modification. Characterisation of the composite film properties: in terms of mechanical properties, the tensile strength of S-CNC/PBAT (3/97) and A-CNC/PBAT (5/95) composite films reached the highest, which was 40.44% and 50.56% higher than PBAT respectively, whereas the elongation at break decreased and the fracture mode shifted from ductile to brittle fracture. In terms of gas permeability, the composite films showed mutual inverse pH response permeability characteristics. The permeability of S-CNC/PBAT (5/95) composite films showed a positive response to the trend of change, with the increase of buffer pH (3—12), CO₂ and O₂ permeability increased by 67.98% and 48.34%, respectively, and the water vapour permeability varied from 2.467×10^-13 to 3.039×10^-13 g·cm/(cm²·s·Pa), and A-CNC/PBAT (5/95) composite film permeation appeared pH negative responsive phenomenon, CO₂ and O₂ permeability decreased by 63.00% and 54.61%, respectively, and the water vapour permeability changed from 2.747×10^-13 to 2.043×10^-13 g·cm/(cm²·s·Pa). This composite film with pH-responsive permeability has a broad prospect in the field of smart packaging.

Key words: cellulose nanocrystals, functionalized modification, composite material, mechanical properties, responsive permeation

摘要：

具有可调控气体渗透的薄膜对包装保鲜领域发展具有重要意义，而设计具有pH响应性渗透和高力学性能的薄膜仍然是一个挑战。设计琥珀酸酐酯化与二乙烯三胺酰胺化的两步取代反应，实现纤维素纳米晶表面胺基（A-CNC）与羧基（S-CNC）功能化修饰，进一步与聚对苯二甲酸-己二酸丁二醇酯（PBAT）复合，制备具有互反pH响应性气体渗透的复合薄膜。结果表明，通过扫描电镜（SEM）、红外光谱（FTIR）和核磁共振¹³C谱（¹³C NMR）对纤维素纳米晶及其功能化修饰进行表征，证实改性成功。对复合薄膜性能表征：在力学性能方面，S-CNC/PBAT（3/97）与A-CNC/PBAT（5/95）复合薄膜拉伸强度达到最高，比PBAT分别增加40.44%与50.56%，但断裂伸长率下降，断裂模式由韧性向脆性断裂转变。在气体渗透性方面，复合薄膜展现出互反pH响应渗透特征。S-CNC/PBAT（5/95）复合薄膜渗透性出现正响应变化趋势，随着缓冲液pH（3~12）升高，CO₂与O₂渗透性分别增加67.98%和48.34%，水蒸气渗透性从2.467×10^-13变化到3.039×10^-13 g·cm/（cm²·s·Pa）；而A-CNC/PBAT（5/95）复合薄膜渗透出现pH负响应性现象，CO₂与O₂渗透性分别降低63.00%与54.61%，水蒸气渗透性从2.747×10^-13变化到2.043×10^-13 g·cm/（cm²·s·Pa）。这种具有pH响应性渗透的复合薄膜在智能包装领域具有广阔的前景。

关键词: 纤维素纳米晶, 功能化修饰, 复合材料, 力学性能, 响应性渗透