Effect of Drying Methods on Rehydration of Bacterial Cellulose
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摘要:
目的 探究干燥方式对细菌纤维素(Bacterial cellulose,BC)复水性能的影响。 方法 采用热风干燥、微波真空干燥和真空冷冻干燥3种干燥方式干燥BC,比较不同干燥方式对BC的溶胀率和复水量的影响,并对BC微观结构进行表征。 结果 不同干燥方式会影响BC结构,引起复水性能变化。与未干燥的BC相比,冷冻干燥的BC复水率达44.79%,复水性能较其他干燥方式好;热风干燥的BC的复水性能次之;微波真空干燥的BC的复水性能最差。电子扫描电镜结果分析表明,冷冻干燥的BC纤维丝排列疏松,较好地保持了BC的表面结构,热风干燥和微波真空干燥的BC纤维排列致密。从复水性能来看,冷冻干燥方法优于2种干燥方法,且在−80 ℃冷冻后进行冷冻干燥的细菌纤维素的复水性能最好。动力学分析表明,细菌纤维素复水过程遵循Fickian扩散定律,BC的网络结构保持的越完整,材料的扩散系数越高,对应的复水性能也越好。 结论 冷冻干燥的复水性能最好。 Abstract:Objective Effects of drying methods on rehydration property of bacterial cellulose (BC) were investigated. Method BC samples dried by means of hot air, microwave under vacuum, and freeze-drying were compared on the swelling and reconstitution rates upon rehydration. A scanning electron microscope (SEM) was used to observe and characterize the BC microstructure. Result The varied dehydration processes affected the microstructure and rehydration of the dried BC. Among the untreated control and treated samples, the freeze-dried BC displayed the highest rehydration rate of 44.79%. It was followed by the hot air and the microwave-vacuum dried specimens. The SEM images showed the freeze-drying rendered BC with a loose but well-defined fibrous network, while the other two methods produced a tight structure with clusters. Insofar as hygroscopic property is concerned, freeze-drying BC at −80 ℃ was superior to all other methods. The dynamics of the water adsorption and swelling of BC followed the Fickian diffusion law. A better maintained 3D structure would have greater diffusion coefficient, and therefore, more efficient water absorption for the dried BC when water was added. Conclusion The freeze-dried BC could be rehydrated most desirably among all tested samples. The processing technology was recommended for the dehydration. -
Key words:
- Bacterial cellulose /
- hot air drying /
- microwave-vacuum drying /
- freeze drying /
- rehydration
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图 1 不同烘干方式烘干后的细菌纤维素的外观形态
注:a:70 ℃热风干燥;b:50 ℃热风干燥;c:微波真空干燥;d:−20 ℃预冷真空冷冻干燥;e:−80 ℃预冷真空冷冻干燥。图2同。
Figure 1. Appearances of dried BC samples
Note: a: BC-DD70: BC dehydrated by 70 ℃ hot air drying; b: BC-DD50: BC dehydrated by 50 ℃ hot air drying; c: BC-MVD: BC dehydrated by microwave-vacuum drying; d: BC-FD20: BC dehydrated by −20 ℃ freeze-drying; e: BC-FD80: BC dehydrated by −80 ℃ freeze-drying. The same as Fig.2.
图 4 细菌纤维素吸水后表观效果
注:a:70 ℃热风干燥;b:50 ℃热风干燥;c:微波真空干燥;d:−20 ℃预冷真空冷冻干燥;e:−80 ℃预冷真空冷冻干燥;f:未干燥(对照)。
Figure 4. Morphology of rehydrated BC samples
Note: a: BC-DD70: BC dehydrated by 70 ℃ hot air drying; b: BC-DD50: BC dehydrated by 50 ℃ hot air drying; c: BC-MVD: BC dehydrated by microwave-vacuum drying; d: BC-FD20: BC dehydrated by −20 ℃ freeze-drying; e: BC-FD80: BC dehydrated by −80 ℃ freeze-drying; f: untreated (CK).
表 1 不同干燥方法的细菌纤维素的吸水性能
Table 1. Water absorption of dried BC samples
样品
Samples每克干细菌纤维素的复水量
Rehydration mass of
per gram of dry bacterial
cellulose/g溶胀率
Swelling ratio/%对照 Contrast 75.11±0.11 a 7411.54±11.00 a 70 ℃热风干燥
BC-DD7018.12±0.18 e 1711.93±18.07 e 50 ℃热风干燥
BC-DD5033.74±0.24 d 3274.10±24.10 d 微波真空干燥
BC-MVD8.05±0.15 f 704.49±15.23 f −20 ℃预冷真空冷冻干燥
BC-FD2042.63±0.13 c 4162.74±12.74 c −80 ℃预冷真空冷冻干燥
BC-FD8043.79±0.19 b 4279.34±19.34 b 注:表中同列数据后不同小写字母表示差异达显著水平(P<0.05)。Note: The same column of date in the table followed by lowercase letters are significantly different (P<0.05). 表 2 不同干燥方式细菌纤维素的吸水溶胀过程的溶胀特征指数
Table 2. Rehydration indices of BC samples dried by different methods
不同干燥方式
Different drying species70 ℃ 热风干燥
BC-DD7050 ℃ 热风干燥
BC-DD50微波真空干燥
BC-MVD−20 ℃ 预冷真空冷冻干燥
BC-FD20−80 ℃ 预冷真空冷冻干燥
BC-FD80溶胀特征指数 n 0.4400 0.4942 0.3173 0.3610 0.1245 表 3 不同干燥方式细菌纤维素的吸水溶胀过程的扩散系数
Table 3. Diffusion coefficients of dried BC samples upon rehydration
不同干燥方式
Different drying species70 ℃ 热风干燥
BC-DD7050 ℃ 热风干燥
BC-DD50微波真空干燥
BC-MVD−20 ℃ 预冷真空冷冻干燥
BC-FD20−80 ℃ 预冷真空冷冻干燥
BC-FD80扩散系数 D(m2.h−1) 0.0512 0.2977 0.0013 1.5490 0.5749 -
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