Dehydration of bacterial cellulose and the water content effects on its viscoelastic and electrochemical properties

Figures & data

Figure 1. Storage (G′) and loss (G″) moduli of BC membranes holding 100, 80 and 50% water, measured as a function of strain (left) and frequency (right).

Notes: The red dots indicate the interceptions between G′ and G″.

Figure 2. Representative Nyquist plots of BC membranes with 100% (never-dried membrane), 80 and 50% water content.

Figure 3. Randles circuit used for fitting the experimental data.

Notes: The solid lines (─) represent the respective fittings.

Table 1. Average values of bulk resistance Rs, polarization resistance Rp, constant phase element CPE and N values of Randles circuit used to fit the experimental data of six never-dried BC membranes per BC water content (100, 80 and 50%).

BC water content (%)	Rs (kΩ)	Rp (kΩ)	CPE (μF)	N
100	3.3 ± 0.6	15.9 ± 0.8	6.2 ± 0.5	≈1
80	5.8 ± 3.0	371 ± 81	1.6 ± 0.6	≈1
50	3.9 ± 1.3	1400 ± 900	1.1 ± 0.8	≈1

Figure 4. Experimental weight-loss (solid square ■) and respective modelling (solid line ─) of BC membranes 8 mm thick and 8 mm of diameter (T8D8), 8 mm thick and 5 mm of diameter (T8D5), 2 mm thick and 8 mm of diameter (T2D8) and 2 mm thick and 5 mm of diameter (T2D5).

Notes: The weight-loss curves of each size/thickness correspond to an average of five samples and the error bars correspond to the respective standard deviations.

Table 2. Rate coefficients obtained from the model expressed in Equation (2(2) $$\begin{array}{cc}\frac{\text{d}}{\text{d}t}B\left(t\right)\hfill & =k_{2}F\left(t\right)-k_{1}B\left(t\right)\hfill \\ \text{and}\hfill & \\ \frac{\text{d}}{\text{d}t}F(t)\hfill & =-k_{1}B\left(t\right)+k_{2}F\left(t\right)-k_{3}F(t)\hfill \end{array}$$(2) ) that gives the best agreement with the experimental data. It is also related to surface area to volume ratio for each sample’s dimension.

	k 1 (hours^−1)	k 2 (hours^−1)	k 3 (hours^−1)	R ^2	Surface area/volume (SA/V) (mm^−1)
T8D8	0.56	11.8 × 10^−8	0.55	1.0	0.6
T8D5	0.68	1.0 × 10^−8	0.68	0.99	0.9
T2D8	0.70	65.6 × 10^−8	0.70	0.95	1.0
T2D5	1.02	20.5 × 10^−8	1.02	0.93	1.3

Table 3. Influence of changes to the values of the rate constants in the model.

k 1	k 2	k 3
=	↑	↑
=	↓	↓
↑	=	↓
↓	=	↑
↑	↑	=
↓	↓	=

Notes: = no change, ↑  increase, ↓  decrease.

Figure 5. Schematic of the molecular structure of bacterial cellulose and their bound and free water.